biologyteacherorg.files.wordpress.com · Web viewKey word list; Absorbed: When a substance is taken in by something or moved across a barrier such as a cell membrane, it is said

AQA Biology GCSEOrganisation and Digestion

Name: ______________________

Week Homework Task SCAN CODE Due1 Task 1: Watch the ‘Stem Cells & Their Uses’ video, complete the quick quiz

and answer the worksheet questions (this can be in your book or on the sheet if you print it) – submit a picture of this on MS Teams.

Task 2: Complete any unanswered exam questions from L1 in your booklet2 Task1: Watch the ‘Villi’ video, complete the quick quiz and answer the

worksheet questions (this can be in your book or on the sheet if you print it) – submit a picture of this on MS Teams.

Task 2: Complete any unanswered exam questions from L2 and 3 in your booklet

3 Task1: Watch the ‘Bile’ video, complete the quick quiz and answer the worksheet questions (this can be in your book or on the sheet if you print it) – submit a picture of this on MS Teams.

Task 2: Complete any unanswered exam questions from L4 and 5 in your booklet

4 Task1: Watch the ‘Enzymes and Food Groups’ video, complete the quick quiz and answer the worksheet questions (this can be in your book or on the sheet if you print it) – submit a picture of this on MS Teams.

Task 2: Complete any unanswered exam questions from L6 in your booklet

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Key word listAbsorbed: When a substance is taken in by something or moved across a barrier such as a cell membrane, it is said to have been absorbed.Acid: Corrosive substance which has a pH lower than 7. Acidity is caused by a high concentration of hydrogen ions.Active site: The part of the enzyme to which a specific substrate can attach or fit on to.Active transport: The transport of molecules against their concentration gradient from a region of low concentration to a region of high concentration.Adult stem cell: A type of stem cell found in specific locations in adults. Adult stem cells can only differentiate into a limited number of related cell types.Alkali: A base which is soluble in water.Amino acid: The building blocks that make up a protein molecule.Amylase: An enzyme that can break down starch into simple sugars.Bile: A substance produced in the liver. It emulsifies fats to prepare them for digestion.Brain: The organ of the central nervous system of mammals where vital functions are coordinatedBuffer solution: A solution that is used to produce a particular pH, and will maintain this pH if acids or alkalis are added.Carbohydrase: Enzyme that breaks down carbohydrates.Carbohydrate: Food belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis.Catalyst: A substance that changes the rate of a chemical reaction without being changed by the reaction itself.Cell: The basic building block of all living organismsCell membrane: A selectively permeable membrane surrounding the cell and controlling the entry and exit of materials.Cellulose: A carbohydrate. It forms the cell wall in plant cells.Compound: A substance formed by the chemical union of two or more elements.Control: A part of the experiment in which all the variables except the dependent variable are kept the same. A control lets you observe the effect (if any) of changing the independent variable.Denature: To change the shape of an enzyme's active site, for example because of high temperatures or extremes of pH. Denatured enzymes no longer work.Differentiation: When cells express specific genes that characterise a certain type of cell we say that a cell has become differentiated.Diffusion: The movement of molecules from an area of higher concentration to an area of lower concentration.Digestion: The breakdown of large insoluble food molecules to smaller soluble ones.Digestive system: Organ system involved in breaking food down so that it can be absorbed into the bloodstream.Egestion: The process of passing out the remains of food that has not been digested, as faeces, through the anus.Embryonic stem cell: A type of stem cell found in the embryo, capable of dividing into almost any cell type.Emulsify: To mix water with fats and oils to produce a cloudy mixture called an emulsion.Enzyme: A protein which catalyses or speeds up a chemical reaction.Ester: A type of organic compound formed in the reaction between an alcohol and a carboxylic acid.Fats: Naturally occurring compounds of carbon, hydrogen and oxygen. They are esters made from fatty acids and glycerol.Fatty acids: Carboxylic acids with a long chain of carbon atoms. Fatty acids react with glycerol to produce lipids (fats and oils).

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Gall bladder: Stores bile before releasing it into the duodenum.Glucose: A simple sugar used by cells for respiration.Glycerol: Propane-1,2,3-triol. It reacts with fatty acids to form esters, found in nature as fats and oils.Glycogen: Animals store glucose as glycogen in their liver and muscle tissues.Inverse: The reciprocal. Iodine solution: A solution of iodine in potassium iodide solution, also referred to as potassium triiodide solution.Ion: Electrically charged particle, formed when an atom or molecule gains or loses electrons.Large intestine: The lower part of the alimentary canal (gut) where absorption of water and production of faeces happens.Lymph: The liquid which circulates within a mammal's body transporting the products of fat digestion from the lacteals.Lipase: Enzyme that breaks down lipids (fats and oils).Lipid: Fat or oils, composed of fatty acids and glycerol.Liver: The large organ, beside the stomach, which has many functions, including processing substances absorbed by the digestive system and a role in the storage of the body's carbohydrate.Lock and key hypothesis: Model which compares the specificity of enzymes with a key and its lock.Maltase: An enzyme that converts maltose (a disaccharide) into glucose (a monosaccharide).Maltose: A disaccharide made from two glucose molecules joined together.Metabolism: All the chemical reactions in the cells of an organism, including respiration.Microorganism: Microscopic living things such as archaea, bacteria and some species of eukaryotes.Microvilli: Projections from the surface of an epithelial cell of the small intestine wall.Molecular movement: The movement of molecules resulting from their kinetic energy.Molecule: A collection of two or more atoms held together by chemical bonds.Multicellular: Having more than one cell.Neuron: Another term for a nerve cell that is specialised to transmit electrical impulses.Neutralise: To be made neutral by removing any acidic or alkaline nature.Nucleus: The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei.Oesophagus: The gullet, the tube that leads from the mouth to the stomach.Optimum: The best or most appropriate - for instance, the conditions under which an enzyme works best (eg temperature and pH).Organ: A structure made up of groups of different tissues, working together to perform specific functionsOrganelle: A specialised unit within a cell which performs a specific functionOrganism: Living entity, eg animals, plants or microorganisms.Organ system: A group of organs with related functions, working together to perform certain functions within the bodyPancreas: Large gland located in the abdomen near the stomach which produces digestive enzymes and the hormone insulin.Peristalsis: Wave-like muscular contractions in the smooth wall of the gut which move food through the alimentary canal.pH: Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline.Specialised: A cell that has become differentiated to carry out a particular function, eg red blood cell.Starch: A type of carbohydrate. Plants can turn the glucose produced in photosynthesis into starch for storage and turn it back into glucose when it is needed for respiration.Stem cells: cells that have not undergone differentiation. A cell which has not yet become specialised is called undifferentiatedStomach: Muscular organ in the digestive system that produces hydrochloric acid and protease enzymes.

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Tissue: A group of cells working together to perform a shared function, and often with similar structureVilli (villus singular): Finger-like projections in the small intestine that provide a large surface area for the absorption of food.

Paper 1 – Organisation and Digestion Fact Sheet

1.2.3.4.5.

6. Define 'differentiation'. The process where a cell becomes specialised/adapted to perform specific functions

7. What is a specialised cell? Specialised cells have adapted to form a specific function/role.

8. Define 'stem cell'. Undifferentiated cell with the potential to become specialised

9. Define 'adult stem cells'. Stem cells that can only differentiate into a specific type of cell

10. Where do you get adult stem cells in animals? Bone marrow

11. Where does differentiation occur in plants? Meristem/Root tip/Shoot tip

12. Define 'embryonic stem cells'. Stem cells from an early embryo that can differentiate into all cell types

13. Where do you get stem cells in plants? Meristem/Root tip/Shoot tip

14. What is the function of the nerve cell? Nerve cells transmit electrical signals around the body.

15. How is a nerve cell adapted to carry out its function?

They are long, to can carry messages up and down the body over large distances. The nerve cells have branched connections at each end, allowing them to make many connections with other nerve cells to pass messages.

16. Why are embryonic stem cells more useful? Stem cells from embryos can become more types of cell

17. State the function of the salivary glands. Produce digestive enzymes (eg. Amylase)

18. Name the tube that carries food from the mouth to the stomach.

Oesophagus

19. State the function of the stomach. Releases digestive enzymes to digest food

20. What is the function of hydrochloric acid in the stomach?

Creates optimum pH for enzymes and kills pathogens in food

21. State the function of the liver in the digestive system.

Produces bile for lipid digestion

22. State the function of the small intestine. Digest food and absorb nutrients from digested food

23. How are the nutrients carried away from the gut?

Absorbed into bloodstream through small intestine

24. What are villi? Finger like projections in the walls of the small intestine.

To revise these facts, fold this sheet in half and try to write the answers down from memory. Repeat!

Fold page here

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25. How is the small intestine adapted for absorption of nutrients?

Villi and microvilli give a large surface area, each villi has a good blood supply as it is surrounded by capillaries and they have thin walls to reduce diffusion distance. Mitochondria for energy for active transport of glucose.

26. State the function of the large intestine. Absorb water from digested food

27. State the function of the pancreas. Produces/Releases digestive enzymes

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28. State the function of the gall bladder. Store bile before release into small intestine

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29. What are carbohydrates made up of? Simple sugars

30. State the chemical formula of glucose. C6 H12 O6

31. Name a complex carbohydrate that is made up of glucose.

Starch/Cellulose/Glycogen

32. State the importance of having carbohydrates in our diet.

Energy source - Break down glucose in respiration to release energy for metabolic reactions

33. What are lipids made up of? 1 glycerol + 3 fatty acids

34. State the importance of having lipids in our diet. Energy store/Make up cell membranes/Steroid hormones

35. What are proteins made up of? Amino acids

36. State the importance of having proteins in our diet.

Structural components/Hormones/Antibodies/Enzymes

37. Name the reagent used to test for starch. Iodine

38. What is a positive result for starch test? Starch turns iodine from brown-red to blue-black

39. Name the reagent used to test for sugars. Benedict's solution

40. What is the positive result for sugars? Benedict's solution turn from clear blue to brick-red (precipitate)

41. What is the reagent used to test for proteins? Biuret solution

42. What is the positive result for proteins? Biuret turns from blue to purple

43. What is the reagent used to test for lipids? Ethanol (+water)

44. What is the positive test for lipids? White milky layer

45. State a risk of doing food tests. Ethanol is flammable/Biuret is corrosive

46. Define 'catalyst'. A substance that speeds up chemical reactions but don't get used up

47. Define 'enzyme'. Biological catalysts that speed up chemical reactions

48. What kind of molecule are enzymes - carbohdyrates, lipids or proteins?

Proteins

49. Define 'active site'. The site on an enzyme where the substrate binds

50. Briefly describe the lock- and-key model. Substrate fits into the active site to form enzyme-substrate complex --> Reaction occurs --> Enzyme releases products and binds to another substrate

51. Define 'denaturation'. Loss of active site

52. Define ' digestion'. Breakdown of large insoluble molecules into smaller soluble substances

53. Name the type of enzyme that digests carbohydrates.

Carbohydrases

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54. Name the enzyme that digests starch. Amylase

55. Name the product of the breakdown of starch. Simple sugars

56. Name the type of enzyme that digests proteins. Proteases

57. Name the product of the breakdown of proteins.

Amino acids

58. Name the type of enzyme that digests lipids. Lipases

59. Name the products of the breakdown of lipids. Glycerol and fatty acids

60. Which organs produce amylase? Salivary glands and pancreas

61. Which organs produce proteases? Stomach, pancreas, small intestine

62. Which organs produce lipases? Pancreas and small intestine

63. State the two functions of bile. Emulsifies fats + Neutralises food from stomach (HCl)

64. What is emulsification? Physically breaking down large oil drops into smaller droplets, increasing surface area for lipases to work on

65. Bile is an enzyme. True or false? FALSE

66. How does temperature affect enzymes' rate of reaction?

As temp increases, RoR increases until after optimum

67. Why do enzymes stop working past their optimum temperature?

Denatured (substrate can no longer bind to active site)

68. Why do enzymes not work well at lower temperatures?

Inactive (not enough KE to collide and bind to active site)

69. How does a change in pH affect enzyme structure?

pH change affects forces holding enzyme structure together, causing it to denature

Lesson Exam Question Marks

Lesson 1 – Organisation

Lesson 2 – Differentiation and Stem Cells

Lesson 3 – Digestive System /22

Lesson 4 – Food Tests /12

Lesson 5 – Enzymes

Lesson 6 – Factors that Affect Enzymes

Lesson 7 – Measuring Rate of Reaction of Enzymes

Lesson 1 Title: Levels of Organisation

Do Now: Instruction: Answer the following questions in your exercise book

1. Convert 0.35cm into mm2. Define diffusion

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3. State the three factors which affect the rate of diffusion

Lesson Checklist – tick these off as you complete them!

Watch the video (Scan the code above with your phone to watch the video on this topic)

Read the notes

Answer all recall questions

Answer all exam questions

Notes: Instruction: Read the notes below.

Part 1 - Define the terms cell, tissue, organ, and organ system.

The fundamental unit of all matter is atoms. However, in biology the building blocks of life are cells. These are the smallest ‘living’ unit. Many animals and plants are multicellular – in order to be multicellular cells have to work together to carry out specific roles in the organism.

When similar cells work together to carry out a particular function they form a tissue. Examples of tissues include muscle tissue (which contracts), epithelial tissue (which covers the outside of the body or around organs) and glandular tissue (which secrete mucus or hormones).

Groups of tissues working together make up an organ. An example of an organ is the stomach. The stomach is made up of muscular tissue, glandular tissue and epithelial tissue. Other examples of organs include heart, brain, skin, pancreas, and kidney.

A whole multi-cellular organism is made up of a range of organ systems. These organ systems are made up of many organs. An example of an organ system is the digestive system and it is made up of organs such as the mouth, stomach, small intestine and large intestine to name a few. Other examples of organ systems include the reproductive system, circulatory system and respiratory system.

An organism is made up of all its organ systems working together to keep it alive. Plants have organs too including the leaves, roots and stem. Each is made of tissues which help it to carry out functions like absorbing light for photosynthesis, absorbing nutrients from the soil

Part 2 - Identify each level of organisation in order and give examples in animals and plants.

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The organs of plants can be seen in the diagram on the left. You can see the leaf is made up of tissues that each carry out a role in the organ.

Recall Questions

Instruction: Answer these questions in your exercise book. Use the notes above to help you (like a comprehension)

1. What is the building block of all living things?2. What is a tissue?3. What is an organ?4. What is an organ system?5. Put the following in the correct order smallest to largest: organ, cell, tissue, organ system, organism.

Exam QuestionsInstruction: Answer these questions on this sheet – you can use the notes to help you but try and do them

from memory first!

Q1. The human body is organised to carry out many different functions.

(a) Use words from the box to complete Figure 1 by putting the parts of the body in order of size from smallest to largest.

The smallest one has been done for you.

(2)

Q2. In a living organism, the cells are organised into organs, systems and tissues.

(a) Use words from the box to complete the list of these structures in order of size.

organs organ systems tissues

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The smallest structure is at the top of the list and the largest is at the bottom.

1 cells

2 _________________

3 _________________

4 _________________

5 organism

(1)

Q1. Animals and plants contain organs and tissues.

Figure 1 shows some organs in the human thorax.

(a) Which organ system is the heart part of?

Tick one box.

Breathing system

Circulatory system

Digestive system

Excretory system

(1)

(b) A leaf is made of tissues.

What is a tissue?

___________________________________________________________________

___________________________________________________________________ (1)

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Q3. Leaves are made from layers of cells.

The diagram shows a section through part of a leaf.

(a) (i) Which word in the table describes layer A?

Tick ( ) one box.

Layer A Tick( )

Tissue

Organ

Cell

(1)

(ii) Which word describes a whole leaf?

Draw a ring around one answer.

organ tissue organism

(1)

(b) (i) Which two layers of cells, A, B, C and D, can photosynthesise?

Use information from the diagram to help you.Tick ( ) two boxes.

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Layer A

Layer B

Layer C

Layer D

(2)

(ii) Give one reason for your answer.

______________________________________________________________

______________________________________________________________ (1)

Q5. The diagram below shows the parts of the body that digest and absorb food.

(a) Complete the table to show whether each structure is an organ, an organ system or a tissue. For each structure, tick ( ) one box.

Structure Organ Organsystem Tissue

Stomach

Cells lining the stomach

Mouth, oesophagus, stomach, liver,pancreas, small and large intestine

Lesson 2 Title: Stem cells and differentiation

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1. Put the following in the correct order smallest to largest: organ, cell, organ system, organism, tissue. 2. Define osmosis.3. What is the main difference between a prokaryotic cell and a eukaryotic cell?



Read the notes




Part 1 - Define what a stem cell is

The basic animal and plant cells you have learnt about have the general structure but cells have to be specialised for specific roles to allow an organism to function correctly.

When a cell specialises it adapts to carry out it’s function. This process is called differentiation. The sub-cellular structures (organelles) like the nucleus, mitochondria and ribosomes can change and the shape and size of the cell can change too.

A good example is a nerve cell. It looks very different from the basic animal cell because it has become differentiated to carry out its function: to transmit electrical signals around the body.

Nerve cells are very long, to can carry messages up and down the body over large distances, and they have lots of branched connections at each end, allowing them to communicate with other nerves and cells.

Stem cells are cells that have not undergone differentiation. A cell which has not yet become specialised is called undifferentiated. They can multiply and become many types of specialised cell.

Part 2 - Describe the two types of stem cells giving examples in animal and plant cells.

Stem cells in humans

An embryo develops from a fertilised egg. Cells at the early stages in the development of the embryo are stem cells. Embryonic stem cells can differentiate into any cell type. This is important as it is what allows embryos to form all the different cells needed to form an adult human.

Differentiation

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Some stem cells remain in the bodies of adults, so these are called adult stem cells. Adult stem cells are found only in specific parts of the body, but the main source is in the bone marrow.

Adult stem cells can only differentiate into some cell types not all. For example, bone marrow cells can differentiate into red blood cells and white blood cells but not other cell types e.g skin cells.

Stem cells in plants

Cell division in plants occurs in growth regions called meristems.

Plant stem cells can be found in the meristems which are at the tips of shoots and roots.

Plant stem cells are different to animal stem cells as they can differentiate to produce all types of plant cells at any time during the life of the plant.

In a growing shoot, new cells are being produced continuously near the tip. As the cells become older, further away from the tip, they become differentiated – they enlarge and develop vacuoles.

Part 3 - Explain why it is important that some cells become specialised and some don’t.

Stem cells are important because in animals and plants they can constantly make new cells to repair or replace others, like red blood cells which only last around 115 days.

Stem cells have the ability to divide and produce different types of specialised cell, this is why they can also be used to treat diseases in humans. If a certain type of cell is damaged e.g brain cells, then stem cells can be used to make more brain cells which can be put back into the patient. Adult and Embryonic stem cells can be used for this. Embryonic stem cell are more useful than adult stem cells however, as they are able to differentiate into more types of cell, so they can be used to treat more disease.

Recall Questions


1. What is the function of the nerve cell?2. How is a nerve cell adapted to carry out its function?3. Define 'differentiation'.4. What is a specialised cell?5. Define 'stem cell'.6. Define 'adult stem cells'.7. Where do you get adult stem cells in animals?8. Where does differentiation occur in plants?9. Define 'embryonic stem cells'.10. Where do you get stem cells in plants?

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11. Why are embryonic stem cells more useful in medicine than adult stem cells?

Exam QuestionsInstruction: Answer these questions on this sheet – you can use the notes to help you but try and do them

from memory first!

Q1.

Q2.

The diagram shows a group of muscle cells from the wall of the intestine.

(a) On the diagram, use words from the box to name the structures labelled A, B and C.

cell membrane cell wall chloroplast cytoplasm nucleus

(3)

(b) How are these muscle cells adapted to release a lot of energy?

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________(2)

Q3. Diagrams A, B and C show cells from different parts of the human body, all drawn to the same scale.

A B C

(a) Which cell, A, B or C, appears to be best adapted to increase diffusion into or

out of the cell?

Give one reason for your choice.

___________________________________________________________________

___________________________________________________________________(1)

Q4. Human stem cells can develop into many different types of human cell.

Use the correct answer from the box to complete the sentence.

embryos hair nerve cells

Human stem cells may come from

______________________________________________________________(1)

Q5. Cells in the human body are specialised to carry out their particular function.

(b) Stem cells from human embryos are used to treat some diseases in humans.

Explain why.

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (2)

Q6. Stem cells can be taken from human embryos.

In therapeutic cloning, an embryo is produced that has the same genes as the patient.

(i) Name one source of human stem cells, other than human embryos.

______________________________________________________________(1)

Q7. This question is about stem cells.

(a) Give one place in a plant where stem cells are found.

___________________________________________________________________

___________________________________________________________________ (1)

Q8. Stem cells are undifferentiated cells.

Which statement about stem cells is correct?

Tick one box.

Animal stem cells are found in meristems

Animal stem cells divide by meiosis

Meristem cells in plants can differentiate throughout the life of the plant

Meristem cells in plants can only differentiate into one type of cell

(1)

Q9. Scientists are trying to develop a treatment for CADASIL using stem cells.

Specially treated stem cells would be injected into the damaged part of the brain.

(i) Why do the scientists use stem cells?

______________________________________________________________

______________________________________________________________

______________________________________________________________

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______________________________________________________________ (2)

Q10. The diagram shows how cells from human embryos can be used to grow ‘replacement body parts’ for humans.

(d) Stem cells become specialised in the process labelled H in the diagram.

What is the process labelled H?

Tick one box.

Differentiation

Evolution

Genetic modification

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Selective breeding

(1)

(f) Why might stem cells from human embryos be more useful than stem cells from adults?

___________________________________________________________________

___________________________________________________________________ (1)

Lesson 3 The Digestive system


1. What is diffusion2. What three features do all exchange surfaces have to speed up diffusion?3. Define cell differentiation.


Watch the videos (Scan the code above with your phone to watch the videos on this topic)

Read the notes




Part 1 - Identify and label all of the organs in the digestive system and describe the function of each

Your digestive system is between 6 and 9 m long. The food you take in and eat is made up of large insoluble molecules. Your body cannot absorb and use these molecules. They need to be broken down or digested to form smaller, soluble molecules that can be absorbed and used by your cells. This process of digestion takes place in your digestive system – one of the major organ systems of the body.The digestive system is a muscular tube that squeezes your food

The adaptation of the small intestine

The Digestive System

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through it. It starts at one end with your mouth, and finishes at the other with your anus. The digestive system contains many different organs.

There are glands such as the pancreas and salivary glands. These glands make and release digestive juices containing enzymes which help to break down your food.

The function of the digestive system is digestion and absorption. Digestion is the breakdown of food from large insoluble molecules into small molecules which can be absorbed into the blood stream and used by your body. The absorption of food happens in the small intestine.

Part 2 - Describe how the small intestine is adapted to carry out its function

The small intestine is covered in folds – these folds are covered in finger-like projections known as villi. The folds and finger-like villi increase the surface area of the walls of the small intestine. The cells that make up the villi have more folds called micro-villi which increase the surface area of each cell. Like all exchange surfaces the small intestine has some common adaptations such as a good blood supply to maintain a concentration gradient, thin walls to provide a short diffusion distance and lots of villi and microvilli to increase surface area. All these adaptations speed up the diffusion of digested food.

Glucose is an example of a molecule that has to be absorbed through the small intestine wall into the blood. The glucose molecules in the lumen of the small intestine might be in a higher concentration than in the intestinal cells and blood – for instance, after a sugary meal. This means glucose can diffuse

lumen

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from high concentration in the intestine to a lower concentration in the blood. However, active transport also occurs in the small intestine because sometimes glucose concentration in the intestine might be lower than in the blood so diffusion can no longer occur. Glucose is an important molecule needed for respiration so the body tries to absorb as much as it can through active transport. The process requires energy produced by respiration. The cells that line the small intestine may have lots of mitochondria to provide the energy for active transport.

Recall Questions


1. State the function of the salivary glands.2. Name the tube that carries food from the mouth to the stomach.3. State the function of the stomach.4. What is the function of hydrochloric acid in the stomach?5. State the function of the liver in the digestive system.6. State the function of the small intestine.7. How are the nutrients carried away from the gut?8. State the function of the large intestine.9. State the function of the pancreas.10. State the function of the gall bladder. 11. What are villi?12. How is the small intestine adapted for absorption of nutrients?

Exam Questions:

Instruction: Answer these questions on this sheet – you can use the notes to help you but try and do them from memory first!

Q1. Figure 1 shows the human digestive system.

Figure 1

(a) Which organ in Figure 1 produces acid?

Tick one box. (1)

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(b) Which organ in Figure 1 produces bile?

Tick one box. (1)

A B C D E

(c) Where in Figure 1 are digested foods absorbed into the blood?Tick one box. (1)

A B C D E

(d) Food molecules such as proteins cannot be absorbed unless they are digested.

Give one reason why.

___________________________________________________________________

___________________________________________________________________(1)

Q2. The digestive system breaks down food into small molecules.

The small molecules can be absorbed into the blood. The diagram below shows the human digestive system.

(a) (i) Which letter, A, B, C, D, E or F, shows each of the following organs?

Write one letter in each box.

large intestine

small intestine

stomach

(3)

(ii) Draw one line from each function to the organ with that function. (3)

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A B C D E

(b) Glucose is absorbed into the blood in the small intestine. Most of the glucose is absorbed by diffusion.

How does the glucose concentration in the blood compare to the glucose concentration in the small intestine?

Tick (✔) one box.

The concentration in the blood is higher.

The concentration in the blood is lower.

The concentration in the blood is the same.

(1)

Q3. Villi are found in some parts of the digestive system. Diagram 1 shows two villi.

(a) Draw a ring around the correct answer to complete each sentence.

muscle.

(i) Structure A is a nerve.

capillary.

(1)

(1)

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dialysis.

(ii) The villi absorb the products of digestion by diffusion.

osmosis.

(b) Diagram 2 shows the digestive system.

(i) In which part of the digestive system, X, Y or Z, are most villi found?

(1)

(ii) There are about 2000 villi in each cm2 of this part of the digestive system.

Why is it helpful to have lots of villi?

______________________________________________________________

______________________________________________________________(1)

Q5. The villi of the small intestine absorb the products of digestion.

The diagram shows two villi. It also shows parts of some of the surface cells of a villus. Describe and explain how the villi are adapted to maximise the rate of absorptionof the products of digestion.

_____________________________________________

_____________________________________________

_____________________________________________

_____________________________________________

_____________________________________________

_____________________________________________

_____________________________________________

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_____________________________________________

_____________________________________________

_____________________________________________

_____________________________________________ (5)

Q4. Diagram 1 shows two villi in the small intestine of a healthy person.

(b) Diagram 2 shows two villi in the small intestine of a person with coeliac disease.

(i) How do the villi of the person with coeliac disease differ from those of a healthy person?

______________________________________________________________

______________________________________________________________ (1)

(ii) Suggest how this difference might affect how well the small intestine functions.

______________________________________________________________

______________________________________________________________ (1)Lesson 4 Food Tests


1. Name the tube which connects the mouth to the stomach.2. How is the small intestine adapted for absorption of nutrients?3. Why is digestion necessary?



Read the notes




Part 1 - Describe the structure of carbohydrates, lipids/fats and proteins

Carbohydrates, lipids and proteins

Food tests

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Carbohydrates, lipids and protein make up most parts of a cell. Therefore, it is important we have lots of them. This makes them the main parts of our diet.

Carbohydrates help provide us with energy. All carbohydrates contain carbon, oxygen and hydrogen. Glucose (C6H12O6) is a simple carbohydrate made of a single carbohydrate molecule. Sucrose is also a simple carbohydrate made up of two carbohydrate molecules joined together. Glucose molecules can be combined in long chains to form complex carbohydrates including cellulose in plants. Glucose can also be stored as starch (plants) and glycogen (animals) which act as energy stores that can be used for respiration. Carbohydrate rich foods include bread, pasta and potatoes.

Lipids are fats and oils. They are an energy store in our cells. When combined with other molecules they can be used to make cell membranes. Like carbohydrates they are made up of carbon, hydrogen and oxygen. They are insoluble in water. Each lipid molecule is made up of three molecules of fatty acids combined with a molecule of glycerol. Olive oil, vegetable oil, cheese, butter and margarine are all sources of lipids.

Proteins are polymers made up of amino acids joined together. There are twenty different amino acids which can be combined in different orders to make new proteins. Proteins are used to build our cells and our enzymes. Protein is made up of carbon, hydrogen, oxygen and nitrogen. Protein rich foods include meat, fish and cheese. Over time, a lack of protein can make you lose muscle mass, which in turn cuts your strength, makes it harder to keep your balance, and slows your metabolism. It reduces growth in younger people and slows down healing in adults. It can also lead to anaemia, when your cells don't get enough oxygen, which makes you tired.

Part 2 – Describe the use of key nutrients in the body and explain what might happen without them

NutrientAtoms that make up the molecule

Uses in living organisms Sources in our dietProblems due to deficiency

CarbohydrateCarbon, hydrogen and oxygen

Energy source – used in respiration, used to form cellulose cell wall in plants. Glucose stored as starch in plants.

Bread, pasta and potatoes

Lack of energy due to lack of respiration. Reduce amount of cell growth in plants as no new cell walls

Lipids (Fats)Carbon, hydrogen and oxygen

Energy store, insulation, part of cell membranes

Olive oil, vegetable oil, cheese, butter

Lack of insulation and energy

Proteincarbon, hydrogen, oxygen and nitrogen

Proteins are used to build cells and make enzymes.

Meat, fish, diaryLack of growth and repair of cells. Anaemia as less haemoglobin (protein)

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Part 3 - Describe the methods and positive results for testing each food type

Food tests

There are some clever ways to identify what type of food molecules a sample of food contains. For each of the tests, you need to prepare a food sample. It’s the same each time – here is what you would do:

1- Break up food pieces using a pestle and mortar.2- Transfer the ground foo to a beaker and add some distilled water. 3- Give the mixture a good stir with a glass rod to dissolve some of the food.4- Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food. 5- Now this solution can be used to test for the presence of carbohydrates (starch/sugar), lipids and

proteins.

Nutrients tested Reagents used Positive results NegativeCarbohydrates – starch

Iodine Iodine turns blue/black Iodine remains brown-orange

Glucose/sugar Benedict’s solution Changes from blue to green, yellow or brick-red – it depends on how much sugar is in the food. Green = low levels, yellow = medium, brick-red = high

Remains blue

Lipids/fats Ethanol A milky-white emulsion forms if the test substance contains lipids.

No change

Proteins Biuret Colour changes from blue to purple Remains blueRecall Questions Instruction: Answer these questions in your exercise book. Use the notes above to help you (like a comprehension)

1. What are carbohydrates made up of?2. State the chemical formula of glucose.

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3. Name a complex carbohydrate that is made up of glucose.4. State the importance of having carbohydrates in our diet.5. What are lipids made up of?6. State the importance of having lipids in our diet.7. What are proteins made up of?8. State the importance of having proteins in our diet.9. Name the reagent used to test for starch.10. What is a positive result for starch test?11. Name the reagent used to test for sugars.12. What is the positive result for sugars?13. What is the reagent used to test for proteins?14. What is the positive result for proteins?15. What is the reagent used to test for lipids?16. What is the positive test for lipids?17. State a risk of doing food tests.

Exam Questions: Instruction: Answer these questions on this sheet – you can use the notes to help you but try and do them from memory first!

Q1. Some students tested a red cabbage leaf for starch.

This is the method used.

1. Boil the leaf in ethanol.

2. Rinse the leaf in water.

3. Add the reagent to test the leaf for starch.

(a) Give one safety precaution the students should take in this test.

___________________________________________________________________

___________________________________________________________________(1)

(b) Which reagent is used to test the boiled leaf for starch?

Tick one box.

Benedict’s solution

Biuret solution

Iodine solution

Sodium chloride solution

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(1)

(c) What colour will be seen if the test for starch is positive?

Tick one box.

Blue-black

Pale pink

Orange

Red

(1)Q2. An athlete decides to try a new type of protein drink after he exercises.

(a) The athlete tests the protein drink to check it contains protein.Which solution is used to test for protein in the drink? Tick one box.

Benedict’s

Biuret

Iodine

Universal indicator

(1)(b) What colour will the solution turn to if there is protein in the drink? Tick one box.

Blue-black

Purple

Red

Yellow

(1)(d) Why is a high protein diet useful to an athlete?

Tick one box.

Provides amino acids to make new muscle.

Provides fatty acids to produce urea.

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Provides glucose for energy.

Provides lactic acid for anaerobic respiration.

(1)

(e) Absorption happens in the small intestine. How is the small intestine in Figure 2 adapted to absorb the products of digestion quickly?

Tick two boxes.

It has a large surface area.

It has a long diffusion pathway.

It has a thin surface.

The concentration inside the small intestine is low.

Q3. Bread contains starch, protein and fat.

(a) Why do molecules of starch, protein and fat need to be digested?

______________________________________________________________

______________________________________________________________(2)

(b) In which part of the digestive system does the digestion of starch begin?Draw a ring around your answer.

large intestine mouth small intestine stomach(1)

Q4.(a) What product is formed when protein is broken down by the enzyme?

______________________________________________________________(1)

(b) Why is it necessary to break down proteins in the digestive system?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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(3)

Q5. A group of pupils investigated the digestion of fat by the enzyme lipase.

(a) What two substances are produced when fats are digested?

Tick ( ) two box.

Glucose

Fatty acids

Glycerol

Amino acids

Lesson 5 Enzymes


1. What are the products of lipid breakdown?2. What is the reagent used to test for proteins?3. What is the positive food result for starch?



Read the notes



Notes: Instruction: Read the notes below and fill in the table below:

Part 1 - Describe enzyme action and recall principal enzymes in digestion

Most of the food we eat is complex carbohydrates, proteins and lipids. These must be broken down to be absorbed into the body. The chemical reactions required to break them down would be too slow without enzymes.

Enzymes are biological catalysts– they speed up chemical reactions. Enzymes are required for most of the chemical reactions that occur in organisms. These reactions occur in the breakdown of chemical molecules, which we see in the digestive system. Enzymes are also involved in the building up of chemical molecules elsewhere in the body.

Enzymes are large protein molecules that have a complex 3D shape. The shape of an enzyme is vital for the enzyme to function. The long chains of amino acids are folded to produce a molecule with an active site that has a unique shape so it can only bind to a specific substrate molecule. The substrate – the molecule or

Enzymes are made up of chains of amino acids folded together to make large complex molecules, as you can see in this computer-generated image

Enzymes

Digestive enzymes

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molecules taking part in the chemical reaction – fits into the active site. Once bound to the active site, the chemical reaction takes place.

The lock and key theory The lock and key theory is a simple model of how enzymes work. The substrate of the reaction to be catalysed fits into the active site of the enzyme. You can think of it like a lock and key. Once it is in place, the enzyme and the substrate bind together. The reaction then takes place rapidly and the products are released from the surface of the enzyme. Remember that enzymes can join small molecules together as well as break up large ones. There are other, more complex models of how enzymes work but they are all based on the lock and key theory.

Digestive enzymes Most of your enzymes work inside the cells of your body, controlling the rate of the chemical reactions. Your digestive enzymes are different. They work outside your cells. They are produced by specialised cells in glands (such as your salivary glands and your pancreas), and in the lining of your digestive system. The enzymes then pass out of these cells into the digestive system itself, where they come into contact with food molecule.

Digesting carbohydrates

Enzymes that break down carbohydrates are called carbohydrases. Starch is one of the most common carbohydrates that you eat, it is broken down into glucose in your mouth and small intestine. This reaction is catalysed by an enzyme called amylase.

Amylase is produced in your salivary glands, so the digestion of starch starts in you mouth. Amylase is also made in the pancreas. No digestion takes place inside the pancreas. All the enzymes made there flow into your small intestine, where most of the starch you eat is digested.

Digesting protein

The breakdown of protein foods such as meat, fish and cheese into amino acids is catalysed by protease enzymes. Proteases are produced by your stomach, your pancreas and your small intestine. The breakdown of proteins into amino acids takes place in your stomach and small intestine.

Digesting lipids

The lipids (fats and oils) that you eat are broken down into fatty acids and glycerol in the small intestine. The reaction is catalysed by lipase enzymes, which are made in your pancreas and your small intestine. Again, the enzymes made in the pancreas are passed into the small intestine.

Once your food molecules have been completely digested into soluble glucose, amino acids, fatty acids and glycerol, they leave your small intestine. They pass into your bloodstream to be carried around the body to the cells that need them.

Task:

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Use the information above to fill in the details for each of the digestive enzymes.

Part 2 - Explain why enzymes stop working when they denature

If enzymes are exposed to extremes of pH or high temperatures the shape of their active site may change. If this happens then the substrate will no longer fit into the enzymes. This means the key will no longer fit the lock. We say that the enzyme has been denatured – denaturation is a permanent change.

Part 3 - Explain the role of bile in digestion

The liver does not secrete any enzymes, but it plays an important role in digestion, and then processing food molecules that have been absorbed.

The liver produces bile. This is stored in the gall bladder and released into the small intestine to assist the break down lipids. The two main functions of bile are:

1. Emulsifying lipids, breaking them up physically into tiny droplets. Tiny droplets have a much larger surface area, over which lipases can work, than larger pieces, or drops of lipid.

2. Bile neutralises stomach acid and produces the optimum pH for pancreatic enzymes in the small intestine.

Recall Questions


1. Define 'catalyst'.2. Define 'enzyme'.3. What kind of molecule are enzymes - carbohdyrates, lipids or proteins?4. Define 'active site'.5. Any substance can fit into the active site of an enzyme. True or false?6. Briefly describe the lock- and-key model.7. Define 'denaturation'.8. Define ' digestion'.

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Name of enzyme Nutrient it breaks down Site(s) of production Site(s) of action

Carbohydrase

Protease

Lipase

9. Name the type of enzyme that digests carbohydrates.10. Name the enzyme that digests starch.11. Name the product of the breakdown of starch.12. Name the type of enzyme that digests proteins.13. Name the product of the breakdown of proteins.14. Name the type of enzyme that digests lipids.15. Name the products of the breakdown of lipids.16. Which organs produce amylase?17. Which organs produce proteases?18. Which organs produce lipases?19. State the two functions of bile.20. What is emulsification?21. Bile is an enzyme. True or false?

Exam Style Questions

Q1. The diagram below shows the human digestive system.

(a) (i) What is Organ A?

Draw a ring around the correct answer.

gall bladder liver stomach(1)

(ii) What is Organ B?

Draw a ring around the correct answer.

large intestine pancreas small intestine(1)

(b) Digestive enzymes are made by different organs in the digestive system.

Complete the table below putting a tick (✓) or cross (✕) in the boxes.

The first row has been done for you.

Organ producing enzyme

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salivary glands stomach pancreas small

intestine

Enzyme

amylase ✓ ✕ ✓ ✓

lipase

protease

(2)

(c) The stomach also makes hydrochloric acid.

How does the acid help digestion?

___________________________________________________________________(1)

(d) Draw one line from each digestive enzyme to the correct breakdown product.

Digestive enzyme Breakdown products

amino acids.

Amylase breaks down starch into……

bases.

Lipase breaks down fats into…

fatty acids and glycerol.

Protease breaks down proteins into…

sugars.

(3)

Q2. Lipase is an enzyme that digests fat.

(a) (i) Complete the equation to show the digestion of fat.

Use the correct answer from the box.

glucose glycerol glycogen

fat fatty acids + ___________________(1)

(ii) Name one organ that makes lipase.

______________________________________________________________(1)

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(b) Some students investigated the effect of bile on the digestion of fat by lipase.

The students:1 mixed milk and bile in a beaker2 put the pH sensor of a pH meter into the beaker3 added lipase solution4 recorded the pH at 2-minute intervals5 repeated steps 1 to 4, but used water instead of bile.

Suggest two variables that the students should have controlled in this investigation.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

___________________________________________________________________ (2)

(c) The graph shows the students’ results.

(i) Why did the pH decrease in both investigations?

______________________________________________________________

______________________________________________________________(1)

(ii) Bile helps lipase to digest fat.

What evidence is there in the graph to support this conclusion?

______________________________________________________________

______________________________________________________________(1)

(iii) Suggest one reason why the contents of both beakers had the same pH at the end

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of the investigations.

______________________________________________________________

______________________________________________________________(1)

Q3.

(b) The egg white in each tube was 50 mm long at the start of the investigation. The table below shows the students’ results.

pH Length in mm of boiled egg white after 24 hours

1 38

2 20

3 34

4 45

5 50

6 50

7 50

(i) At which pH did the pepsin work best?

pH _________________(1)

(c) Pepsin is made by the stomach.

Name the acid made by the stomach which allows pepsin to work well.

___________________________________________________________________(1)

Q4. The diagram shows the digestive system. Complete the following sentences about digestive enzymes.

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(i) Amylase works in the _____________________ where it is involved in the

digestion of ________________________ to ________________________. (3)

(ii) Lipase works in the _____________________ where it is involved in the digestion

of ________________________ to ________________________. (3)

(b) Which gland produces:

(i) amylase;__________________________________(1)

(ii)

lipase;____________________________________(1)

Q5. Different parts of the human digestive system help to break down molecules of fat so that they can be absorbed into the body.

Describe how.

To gain full marks you should refer to:

• the enzyme and where the enzyme is produced

• the products of digestion

• any other chemicals involved.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(6)

Lesson 6 Factors that Affect Enzymes


1. Define ‘denaturation.’2. Define ‘active site.’3. What are the products of carbohydrate, lipid and protein digestion?



Read the notes




Part 1 - State the factors that can affect enzyme action

If enzymes are exposed to extremes of pH or high temperatures the shape of their active site may change. If this happens then the substrate will no longer fit into the enzymes. This means the key will no longer fit the lock. We say that the enzyme has been denatured. Denaturation is a permanent change.

Part 2 - Describe how conditions in the mouth and stomach allow enzymes to function optimally

Factors affecting enzyme activity

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Different areas of the digestive system have different pH levels which allow the enzymes in that region to work as effectively as possible. For example, the mouth and small intestine are slightly alkaline, while the stomach has a low, acidic pH value. The stomach provides an acidic condition by producing hydrochloric acid – this environment allows the enzymes in the stomach to work at its optimum (pH2).

Part 3 - Explain how pH and temperature would affect the action of enzymes in the body

How temperature affects enzyme activity.

The reactions that take place in cells happen at relatively low temperatures. As with other reactions, the rate of enzyme-controlled reactions increases as the temperature increases. As the temperature increases, the rate of reaction increases up to the optimum temperature.

However, for most organisms this is only true up to temperatures of about 40°C. After this, the protein structure of the enzyme is affected by the high temperature. The long amino acid chains begin to unravel, and as a result, the shape of the active site changes. The substrate will no longer fit in the active site – the enzyme is said to have been denatured. The active site loses its important shape and can no longer form enzyme-substrate complex, leading to a decrease in enzyme activity - it can no longer act as a catalyst. Most human enzymes work best at 37°C, which is human body temperature.

Without enzymes, none of the reactions in your body would happen fast enough to keep you alive. This is why it is dangerous if your temperature goes too high when you are ill. Once your body temperature reaches about 41°C, your enzymes start to be denatured, which will result in death.

Enzymes do not work well at lower temperatures as they will become inactive – they do not have enough kinetic energy (KE) to collide and bind to active site.

The rate of an enzyme-controlled reaction increases as the temperature rises-but only until the protein structure of the enzyme breaks down

These two digestive enzymes need very different pH levels to work at their maximum rate. Pepsin is found in the stomach, along with hydrochloric acid, while pancreatic amylase is in the first part of the small intestine along with alkaline bile.

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Not all enzymes work best at around 40°C. bacteria living in hot springs survive at temperatures up to 80°C and higher. On the other hand, some bacteria that live in the very cold, deep seas have enzymes that work effectively at 0°C and below.

Effect of pH on enzyme action

Different areas of the digestive system have different pH levels which allow the enzymes in that region to work as effectively as possible. For example, the mouth and small intestine are slightly alkaline, while the stomach has a low, acidic pH value.

The shape of the active site of an enzyme comes from forces between the different parts of the protein molecule. These forces hold the folded chains in place. Deviating from the optimum pH (too high or too low) causes the enzyme’s active site to become denatured and the active site loses its important shape. It can no longer form enzyme-substrate complexes, leading to a decrease in enzyme activity.

Substrate concentration

Enzymes will work best if there is plenty of substrate. As the concentration of the substrate increases, so does the rate of enzyme activity. However, the rate of enzyme activity does not increase forever. This is because a point will be reached when the enzymes become saturated and no more substrates can fit at any one time even though there is plenty of substrate available.

As the substrate concentration increases so does the rate of enzyme activity. An optimum rate is reached at the enzyme’s optimum substrate concentration. A continued increase in substrate concentration results in the same activity as there are not enough enzyme molecules available to break down the excess substrate molecules.

Recall Questions


1. What are the three factors that can affect how enzymes work2. How does temperature affect enzymes' rate of reaction?3. What is the function of hydrochloric acid in the stomach?4. Why do enzymes stop working past their optimum temperature?5. Why do enzymes not work well at lower temperatures?6. How does a change in pH affect enzyme structure?

Exam style Questions:

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Q1.Some students investigated the effect of pH on the digestion of boiled egg white by an enzyme called pepsin. Egg white contains protein.The students:

• put a glass tube containing boiled egg white into a test tube

• added a solution containing pepsin at pH 7

• set up six more tubes with solutions of pepsin at different pH values

At start 24 hours later

• left the test tubes for 24 hours at room temperature.

The image below shows one of the test tubes, at the start and at the end of the 24 hours.

(a) (i) Name the product of protein digestion.

______________________________________________________________(1)

(ii) What type of enzyme digests protein?

Tick ( ) one box.

Amylase

Lipase

Protease

(1)

(b) The egg white in each tube was 50 mm long at the start of the investigation. The table below shows the students’ results.

pH Length in mm of boiled egg white after 24 hours

1 38

2 20

3 34

4 45

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5 50

6 50

7 50

(i) At which pH did the pepsin work best? pH _________________(1)

(ii) The answer you gave in part (b)(i) may not be the exact pH at which pepsin works best.

What could the students do to find a more accurate value for this pH?

______________________________________________________________

______________________________________________________________(2)

(iii) There was no change in the length of the egg white from pH 5 to pH 7.

Explain why.

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

(c) Pepsin is made by the stomach.

Name the acid made by the stomach which allows pepsin to work well.

___________________________________________________________________(1)

Q2.(a) The graph shows the effect of pH on the activities of three enzymes, X, Y and Z.

These enzymes help to digest food in the human digestive system.Each enzyme is produced by a different part of the digestive system.

pH

(i) What is the optimum (best) pH for the action of enzyme Z? ______________(1)

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(ii) The stomach makes a substance that gives the correct pH for enzyme action in the human stomach.

Name this substance. ____________________________________________(1)

(iii) Which enzyme, X, Y or Z, will work best in the human stomach? ________ (1)(Total 3 marks)

Q3.A patient has a disease. The disease damages his pancreas.

A doctor prescribes a course of treatment for the patient:‘Take one capsule with each meal.’

Each capsule contains hundreds of small, dry beads.

The beads are made of enzymes. The pancreas normally produces these enzymes.

The outer coating of the capsule is made of lipid.

(a) One enzyme in the beads is lipase.

In a healthy person, lipase is made in the pancreas.

Name two other enzymes made in the pancreas of a healthy person.

1. _________________________________________________________________

2. _________________________________________________________________(2)

(b) The lipid coating on the capsule makes sure that the enzymes are not released until the capsule reaches the small intestine. Explain how.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(c) The lipase in the beads does not digest the lipid coating around the capsule. Suggest why

___________________________________________________________________

__________________________________________________________(1)

Q4. A group of students investigated the effect of temperature on the action of the enzyme lipase.

The students:

• put 1 cm3 of lipase solution into a test tube

• put 5 cm3 of lipid into a different test tube

• put both tubes in a water bath at 5 °C for 3 minutes

• mixed the lipid with the lipase solution.

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Every five minutes the students tested a sample of the mixture for lipid, until no lipid remained.The students repeated the experiment at different temperatures.

(a) To make their investigation fair the students needed to control some variables.

Give one variable the students controlled in their investigation.

___________________________________________________________________(1)

(b) The tubes of lipase solution and lipid were kept separately in the water bath for 3 minutes before mixing. Why?

Tick ( ) one box.

So that the lipase broke down the lipid quickly

So that the lipase and the lipid reached the right temperature

To give enough time for the lipase to break down the lipid

To give enough time for the water bath to heat up

(1)

The table shows the students’ results.

Temperaturein C

Time taken until no lipid remainedin minutes

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5 40

20 15

35 5

50 30

95 lipid still there after 120 minutes

(c) Describe the effect on the breakdown of the lipid of increasing the temperature from 5 °C to 50 °C.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(d) Suggest two ways in which the students could have improved their investigation.

Use information from the students’ method and the results table to help you.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

___________________________________________________________________ (2)

(e) (i) The lipase did not break down the lipid at 95 °C. Why?

______________________________________________________________(1)

(ii) At 35 °C the lipase broke down the lipid after 5 minutes.

What new substances will be in the tube? Draw a ring around one answer.

amino acids fatty acids and glycerol sugars

(1) (Total 8 marks)

Q5. Fresh milk is a mixture of compounds including lipid, protein and about 5% lactose sugar.

Lactose must be digested by the enzyme lactase, before the products can be absorbed. Lactase can be added to fresh milk to pre-digest the lactose. This makes ‘lactose-free’ milk, which is suitable for people who do not produce enough lactase of their own.

A student investigated the effect of changing pH and temperature on the digestion of lactose in milk.

The results are shown in Tables 1 and 2.

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Table 1Effect of pH Table 2

Effect of temperature

pHTime taken to

digest lactose in minutes

Temperaturein °C

Time taken todigest lactose in

minutes

4.0 20 25 20

5.0 18 30 14

6.0 13 35 11

7.0 7 40 6

8.0 5 45 29

9.0 6 50 No digestion

(a) The label on a carton of lactose-free milk states:

‘Lactase is normally produced in the stomach of mammals.’

The results in Table 1 suggest that this statement is not true.

Explain how.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(b) Explain, as fully as you can, the results shown in Table 2.

___________________________________________________________________

____________________________________________________________________ (3)(Total 5 marks)

Q6.(a) (i) What name is given to an enzyme which catalyses the breakdown of protein? ______________________________________________________________

(1) (ii) What product is formed when protein is broken down by the enzyme? ______________________________________________________________ (1)

The table shows the effect of pH on the activity of an enzyme which catalyses the breakdown of protein.

pH 1.0 2.0 3.0 4.0 5.0

Rate of formation of product in mmol per

10.5 23.0 10.5 2.5 0.0

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minute

(b) Draw a graph of the data in the table.

(3)

(c) The enzyme is produced by the human digestive system.

(i) At what pH does this enzyme work best? ____________________________(1)

(ii) Suggest which part of the digestive system produces this enzyme.

_____________________________________________________(1)

Lesson 7 Measuring the rate of Reaction


1. What are the 3 main factors what can affect how enzymes work?

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2. Why do enzymes stop working past their optimum temperature?3. Why do enzymes not work well at lower temperatures?4. What is the function of bile?



Read the notes




Part 1 - Describe a method for measuring the effect of temperature or pH on an enzyme

We will investigate the breakdown of starch by amylase at different pH. The different pH under investigation will be produced using buffer solutions. Buffer solutions produce a particular pH, and will maintain it if other substances are added. The amylase will break down the starch.

A control experiment must be set up – without the amylase – to make sure that the starch would not break down anyway. The result of the control experiment must be negative – the colour must remain blue-black – for results with the enzyme to be valid.

Variables

Independent variable – pH of the solution (buffer, amylase and starch)

RP Enzyme activity at different pH

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Dependent variable – the time taken for the disappearance of starch in secs

Control variable(s) – temperature and concentration of enzyme

Part 2 - Record data from an investigation into a factor on the rate of enzyme action

Part 3 - Interpret data from enzyme reactions and explain results

The enzyme amylase breaks down starch into glucose. If the enzyme is working effectively, this will happen quickly. At pH 7 it took the shortest time before the iodine no longer changed colour. This shows that the starch was broken down more quickly at this pH. The optimum pH for amylase is therefore pH 7.

The time taken for the disappearance of starch is not the rate of reaction.

It will give us an indication of the rate, but is the inverse of the rate – the shorter the time taken, the greater the rate of the reaction.

We can calculate the rate of the reaction by calculating 1/t, obtaining a measure of the rate of reaction by dividing one by the time taken for the reaction to occur.

So, from the results:

From the graph it is clear to see that this enzyme, amylase, works best at a pH of 7.

The effect of temperature on enzyme activity

A similar experiment can be carried out to investigate the effect of temperature on amylase activity.

You set up a series of test tubes in the same way and maintain these at different temperatures using a water bath – either electrical or a heated beaker of water.

Exam Questions

Basic:

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Q1.

Amylase is an enzyme that digests starch.

A student investigated the effect of pH on the activity of amylase.


1. Mix amylase solution and starch suspension in a boiling tube.

2. Put the boiling tube into a water bath at 25 °C.

3. Remove a drop of the mixture every 30 seconds and test it for the presence of starch.

4. Repeat the investigation at different pH values.

The table below shows the students’ results.

pH Time when no starch was detected in minutes

5.0 7.0

5.5 4.5

6.0 3.0

6.5 2.0

7.0 1.5

7.5 1.5

8.0 2.0

(a) The student concluded pH 7.25 was the optimum pH for the amylase enzyme.

This is not a valid conclusion. Suggest two reasons why.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

___________________________________________________________________(2)

(b) The student did another investigation.


1. Put amylase solution and starch suspension into a boiling tube.

2. Make the pH 7.25.

3. Put the boiling tube into a water bath at 25 °C.

4. Measure the amount of sugar produced every 30 seconds.

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The results are shown in the figure below.

Calculate the mean rate of sugar produced per minute during the first 5 minutes.

___________________________________________________________________

___________________________________________________________________

Mean rate = ________________ units per minute(2)

(c) Iodine solution is added to a sample taken from the boiling tube after 10 minutes and 60 minutes.

Suggest what you would see in these samples.

After 10 minutes _____________________________________________________

___________________________________________________________________

.After 60 minutes _____________________________________________________

___________________________________________________________________(2)

(d) The scientist repeated the investigation at 37 °C.

Draw a line on the figure above to show the predicted results.(2) (Total 8 marks)

Medium: Q2.Proteins are broken down by protease enzymes.

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(a) Which organs in the digestive system produce protease enzymes?

Tick one box.

Mouth and liver

Mouth and stomach

Pancreas and liver

Stomach and pancreas

(1)

A student used a colorimeter to investigate the rate of protein digestion of an insoluble protein.

A colorimeter measures the percentage of light that passes through a liquid.

The student measured the percentage of light passing through different concentrations of protein suspension. The student used the results to produce a concentration curve.

The table shows the results.

(b) Plot the data from the table on Figure 1. Draw a line of best fit.

Figure 1

(3)

(c) Explain the change in the percentage of light passing through the suspension.

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(d) Suggest how the student could improve their investigation to draw a more accurate concentration curve.

___________________________________________________________________

___________________________________________________________________(1)

The student then investigated the rate of protein digestion with protease obtained from two different organs.


1. Put 5 cm3 of protease from each organ into separate test tubes.

2. Put 10 cm3 of protein suspension into two other test tubes.

3. Put all four tubes into a water bath at 37 °C for 10 minutes.

4. Mix each 5 cm3 of protease into a tube of protein suspension.

5. Take a sample of each mixture every 2 minutes.

6. Measure the percentage of light passing through each sample using a colorimeter.

(e) Suggest why the protease and the protein suspension were put into a water bath before being mixed.

___________________________________________________________________

___________________________________________________________________(1)

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Figure 2 shows the student’s results.

Figure 2

(f) Determine the concentration of protein at the start of the reaction with protease from organ A.

Use Figure 2 and your graph in Figure 1.

___________________________________________________________________

___________________________________________________________________

Concentration = ____________________ g/dm3

(1)

(g) Calculate the rate of protein digestion with protease from organ A over the first 12 minutes.

Use Figure 2 and your graph in Figure 1.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Rate = ____________________ g/dm3 per minute(1)

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(h) Describe how the activity of protease from organ B is different from the activity of protease from organ A.

Suggest one reason for the difference.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(Total 13 marks)

Q3.Fresh milk is a mixture of compounds including lipid, protein and about 5% lactose sugar.

Lactose must be digested by the enzyme lactase, before the products can be absorbed.

Lactase can be added to fresh milk to pre-digest the lactose. This makes ‘lactose-free’ milk, which is suitable for people who do not produce enough lactase of their own.

A student investigated the effect of changing pH and temperature on the digestion of lactose in milk.

The results are shown in Tables 1 and 2.

Table 1Effect of pH Table 2

Effect of temperature

pHTime taken to

digest lactose in minutes

Temperaturein °C

Time taken todigest lactose in

minutes

4.0 20 25 20

5.0 18 30 14

6.0 13 35 11

7.0 7 40 6

8.0 5 45 29

9.0 6 50 No digestion

(a) The label on a carton of lactose-free milk states:

‘Lactase is normally produced in the stomach of mammals.’

The results in Table 1 suggest that this statement is not true.

Explain how.

___________________________________________________________________

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___________________________________________________________________(2)

(b) Explain, as fully as you can, the results shown in Table 2 .

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

____________________________________________________________________(3)

(c) Bile is produced in the liver and is released into the small intestine.

Bile helps the digestion of lipid in the milk.

Describe how.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(3) (Total 7 marks)

Hard: Q4.Starch is broken down into sugar by amylase. Amylase is produced in the salivary glands.

(a) Name two other organs in the digestive system which produce amylase.

____________________________ and ____________________________(2)

(b) A colorimeter measures colour intensity by measuring the percentage of light that passes through a solution.Graph 1 shows the percentage of light passing through sugar solutions of different concentrations to which a test reagent has been added.

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Students used a colorimeter to compare the starch-digesting ability of amylase enzymes obtained from two organs, P and Q.

• The students collected 5 cm3 samples of amylase from P and Q and placed them into a water-bath at 40 °C.

• Two test tubes containing 10 cm3 samples of starch solution were also placed into the water-bath.

• All the tubes were left in the water-bath for 10 minutes.

• Each amylase sample was added to one of the tubes containing the starch solution.

• The test tubes were placed back into the water-bath.

• Every minute, a few drops were taken from each tube, the test reagent was added and the percentage of light passing through this solution was measured in the colorimeter.

The tubes containing amylase samples and starch solution were left in the water-bath for ten minutes before the amylase was added to the starch.

Explain why.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(c) Graph 2 shows how the readings from the colorimeter changed over the next 20 minutes.

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(i) Use Graph 1 and Graph 2 to determine the concentration of sugar in the mixture from organ Q after 20 minutes.

______________________________________________________________

Answer _____________ mol per dm3

(1)

(ii) Use your answer to (c)(i) to calculate the rate at which sugar was produced in the mixture containing amylase from organ Q.

Show clearly how you work out your answer.

______________________________________________________________

______________________________________________________________

______________________________________________________________

Answer _______________________ mol per dm3 per minute(2)

(iii) Suggest why the amount of light passing through the mixture from organ P did not change after 16 minutes.

______________________________________________________________

______________________________________________________________

______________________________________________________________(1)

(iv) One of the students suggested that they could have completed their experiment more quickly if the temperature of the water-bath had been set at 80 °C.

This would not have been the case.

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Explain why.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

(Total 10 marks)

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Mark schemes

Q1.(a) any two from:

• same result at pH 7 and 7.5orcould be any pH between 7 and 7.5ornot tested at pH 7.25orneed to test at smaller pH intervals (between 7 and 7.5)

• accuracy of result only to nearest 0.5 minutes• no repeats• difficult to determine end point (colour)

2

(b) 2.7 / 51

0.54 (units per minute)allow 0.52 with no working shown for 2 marks

1

allow 1 mark for 0.52 or 0.56

(c) (after 10 minutes) solution goes black1

(after 60 minutes) solution stays the sameordoes not go blackorgoes slightly orange

1

(d) steeper curve1

levels off at 11.8 units and before 45 minutes1

[8]

Q2.(a) stomach and pancreas

1

(b) all points plotted correctlyallow 1 mark for 3 points correctly plotted

2

smooth curve drawn through all the points1

(c) as concentration of protein increases the percentage of light passing through decreases1

(because) mixture more cloudy

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allow idea of more particles in suspension1

(d) use protein concentrations between 2 and 10 g/dm3

1

(e) any one from:

• to allow them to reach 37 °Cto allow them to reach body temperature

• so they would be at the optimum temperatureallow so they would be at the same temperature

• so reaction temperature controlledallow temperature affects enzyme activity

1

(f) correctly read concentration at 57% from their graph 1

(g) their value given in part (f) – 0.5allow use of different values over straight line portion of graph

1

answer for their value given in

1

(h) (protease from organ B) is inactive or rate of digestion is zero and protease from organ A is active

allow only protease from organ B is inactive1

any one from:

• enzyme denatured by pH

• at the wrong pH

• enzyme not specific for this proteinallow active site damaged / changed by pH

1[13]

Q3.(a) stomach is acidic / has low pH

allow any pH below 7ignore stomach is not alkaline

1

lactase works best / well in alkali / high pH / neutral / non-acidic conditionsallow any pH of 7 and aboveaccept works slowly in acid conditions

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allow figures from table with a comparisonignore reference to temperature

1

(b) any three from:

• (below 40(°C)) increase in temperature increases rate / speed of reaction

• reference to molecules moving faster / colliding faster / harder / more collisions

• enzyme optimum / works best at 40°Callow value(s) in range 36 – 44ignore body temperature unless qualified

• high temperatures (above 40°C) / 45°C / 50°C enzyme denaturedallow synonyms for denaturation, but do not allow ‘killed’denaturation at high and low temperature does not gain this markignore references to time / pH

3

(c) any two from:

• acid neutralised or conditions made neutral / alkaliaccept bile is alkaline

• (allow) emulsification / greater surface area (of lipid / fat)allow description of emulsification eg fat broken down / broken up into dropletsdo not accept idea of chemical breakdown

• lipase / enzymes (in small intestine) work more effectively / betterallow better for enzymesignore reference to other named enzymes

2[7]

Q4.(a) pancreas

either order1

small intestine1

(b) any two from:

• to give them time to come to temperature of the water-bathaccept so (they / both) are at the same temperature

• at / near body temperature / best / optimum temperature

• otherwise reaction would take place at a series of different temperaturesor sensible statement about control / fair test

2

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(c) (i) 0.42allow in range 0.42 to 0.425

1

(ii) 0.021correct answer with or without workingallow ecf from (c)(i) ie (c)(i) ÷ 20 correctly calculated for 2 marksif answer incorrect 0.42 ÷ 20 or (c)(i) ÷ 20 gains 1 mark

2

(iii) (all) starch digested / gone / used up / turned to sugarallow the amount of sugar stays the same / maximum

1

(iv) any two fromallow reference to active site once only as alternative to first or second bullet point

• enzyme destroyed / denatured / damaged / shape changeddo not accept killed

• unable to fit (starch molecule)

• starch can’t be digestedenzymes don’t work is insufficient

2[10]

Q5.(a) digested / broken down / made soluble by protease enzyme

in stomach in small intestine / from stomach / from pancreasinto amino acidsamino acids / small molecules absorbed into blood

any four for 1 mark each4

(b) ideas thatlipase / enzyme works best in alkaline / neutral conditionsacid denatures or inactivates enzyme / inhibits enzyme activitybile emulsifies fat / bile produces larger surface area of fats / bile alkalinefor enzyme to work on / which increase activity of enzymes

any three for 1 mark each3

[7]

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biologyteacherorg.files.wordpress.com · Web viewKey word list; Absorbed: When a substance is taken in by something or moved across a barrier such as a cell membrane, it is said

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