Diffusion—the spreading out of parcles The movement of parcles from an area of high concentraon to an area of low con- centraon. Down a concentraon gradient. The greater the difference in concentra- on in two cells the faster the rate of diffusion. (involves the movement of parcles, and therefore only takes place in liquids and gas- es) Plant Example Carbon dioxide diffuses into a leaf through the stomata. Minerals and water diffuse into the plant through the roots. Animal Example Food molecules diffuse into the blood stream in the small intesne. Water molecule diffuse into the blood stream in the large intesne. Oxygen molecules diffuse into the bloodstream in the lungs. Cells You need to be able to idenfy and know the funcons of the following parts of cells. nucleus – controls the acvies of the cell cytoplasm – where the chemical reacons take place cell membrane – controls the movement of substances into and out of the cell mitochondria – release energy (this is where aerobic respiraon occurs) ribosomes – where protein are made (protein synthesis) cell wall – strengthens the cell chloroplasts – absorb light energy to do photosynthesis. Chloroplasts contain chlo- rophyll which is a green substance. Cell Wall Cell Membrane Cytoplasm Nucleus DNA free in cell (no nucleus) Vacuole Bacterial Cell Yeast Cell Specialised Cells Some cells are specialised to carry out a parcular funcon. Root Hair Cell Large surface area to increase the uptake of water and nutrients Sperm Cell Have lots of mitochondria to release lots of energy so the sperm can swim towards the egg. Fat Cell Fat cells can expand to fill with fat. They have a small amount of cytoplasm to allow more space for fat.
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Diffusion—the spreading out of particles
The movement of particles from an area of high concentration to an area of low con-
centration. Down a concentration gradient. The greater the difference in concentra-
tion in two cells the faster the rate of diffusion.
(involves the movement of particles, and therefore only takes place in liquids and gas-
es)
Plant Example
Carbon dioxide diffuses into a leaf through the stomata.
Minerals and water diffuse into the plant through the roots.
Animal Example
Food molecules diffuse into the blood stream in the small intestine.
Water molecule diffuse into the blood stream in the large intestine.
Oxygen molecules diffuse into the bloodstream in the lungs.
Cells
You need to be able to identify and know
the functions of the following parts of
cells.
nucleus – controls the activities of the cell
cytoplasm – where the chemical reactions
take place
cell membrane – controls the movement
of substances into and out of the cell
mitochondria – release energy (this is
where aerobic respiration occurs)
ribosomes – where protein are made
(protein synthesis)
cell wall – strengthens the cell
chloroplasts – absorb light energy to do
photosynthesis. Chloroplasts contain chlo-
rophyll which is a green substance.
Cell Wall
Cell Membrane
Cytoplasm
Nucleus
DNA free in cell (no nucleus)
Vacuole
Bacterial Cell Yeast Cell
Specialised Cells
Some cells are specialised to carry out a particular function.
Root Hair Cell
Large surface area to increase the uptake
of water and nutrients
Sperm Cell
Have lots of mitochondria to release lots of
energy so the sperm can swim towards the egg.
Fat Cell
Fat cells can expand to fill with fat. They have a small
amount of cytoplasm to allow more space for fat.
Tissues, organs and organ systems
A group of cells that are specialised and come together for a spe-
cific function is known as tissue. Examples of tissues are:
Muscular tissue which can contract to bring about move-
ment. The cells have lots of mitochondria to release lots of
energy.
Glandular tissue, which can produce substances like en-
zymes and hormones
Epithelial tissue which covers some parts of the body
Organs are made up of different types of tissue. For example, the
stomach, (which is an organ) contains the following tissues:
Muscular tissue—to churn the contents of the stomach
Glandular tissue—to produce digestive juices
Epithelial tissue—to cover the outside and inside of the
stomach
Organs that work together to achieve a specific function is know as
an organ system. Examples of organ systems are:
The digestive system
The circulatory system
The respiratory system.
A group of organ systems working together form an organism.
Multicellular organisms have many different cells which are spe-
cialised for a particular function, an advantage over single-celled
organisms.
Some processes are easier for single-celled organisms, for example
oxygen can easily diffuse into a single cell.
Multicellular organisms need a transport system to bring oxygen to
every cell in their body. They also have specialised tissues that are
adapted for allowing things to move in and out of the body quickly.
Functions of the digestive system:
A system is a group of organs that
perform a particular function.
The function of the digestive system
is to break down the food you eat so
the food molecules can enter the
blood.
Each organ in the system has an im-
portant role to play to ensure that
this happens. See the diagram on the
left.
The digestive system includes:
Glands such as the pancreas
and salivary glands
The stomach and small
intestine where digestion occurs
The liver which produces bile
The small intestine where the
absorption of soluble food occurs
The large intestine, where
water is absorbed from the undigest-
ed food, producing faeces.
Enzymes
Enzymes are biological catalysts which speed up the rate of reactions. Enzymes are made from
PROTEINS.
Proteins: proteins are made up of AMINO ACIDS.
Factors Affecting Enzymes
1. Temperature— as the temperature increases the
rate of the reaction increases until an opti-
mum temperature is reached. If the tempera-
ture gets too hot the enzyme is DENATURED
which changes the SHAPE of the ACTIVE SITE.
This means the SUBSTRATE will no longer fit the enzyme and cannot be broken down.
2. pH—different enzymes work at different pH’s. The stomach produces HYDROCHLORIC
ACID to KILL BACTERIA in the food which makes the stomach acidic. Protease works
best in acidic conditions but lipase and amylase cannot work in acidic conditions. They
work best in alkaline conditions.
Enzymes in Digestion
Enzymes are released from glands.
They break down large molecules into smaller ones so that they can
be absorbed by the small intestine into the blood stream.
Bile
The LIVER produces bile which is then stored in the gall bladder. It is added to the food after
It leaves the stomach to neutralise the stomach acid. It is important to neutralise the acid so
that amylase and lipase can break down food in the small intestine.
Enzyme Enzyme made ….. Where it breaks food down…. What it breaks down…..
Amylase Salivary glands, pancreas, small
intestine
Mouth and small intestine Starch into sugars
Protease Stomach, pancreas, small intes-
tine
Stomach and small intestine Protein into amino acids
Lipase Pancreas and small intestine Small intestine Lipids into fatty acids and glycerol
Enzymes in the Home and Industry
Home:
Washing powder contains protease and lipase to break down fat and protein
stains on clothing.
Washing powders with enzymes in (biological detergents) are more effective
at lower temperatures and therefore you can save energy and money.
Industry:
Proteases are used to pre-digest proteins in baby foods.
Carbohydrases are used to convert starch into sugar syrup
Isomerase is used to convert glucose syrup into fructose syrup. Fructose is
sweeter and therefore less can be used in slimming products.
NEGATIVES: Enzymes cannot be used at high temperatures because they are
DENATURED. Enzymes are also COSTLY to produce.
Sampling 2 Areas to Compare Them
As scientists we may want to study the distribution of organisms in different areas.
Q. Describe how students could use a quadrat to estimate the numbers of different plants
growing on a field.
Place a quadrat on the field randomly. This avoids bias.
This could be done by throwing the quadrat or using a random number generator to
calculate coordinates.
Count the plants within the quadrat.
Repeat the process above
Then calculate a mean
If they wanted to compare two fields such as St Mark’s football field and HAM’s they would
do the same as above on each field and then compare the amount of plant being looked at.
The green dots show the randomly sampled areas to count. In
total this is 15 squares. The total area is 48.
To improve the estimate simply increase the sample size so in-
stead of counting 15 quadrats count 20 or 25 instead.
Only an estimate is being produced because the whole area/field
is not being counted.
Extra Info
If sampling the cover of 1 species only count a quadrat
is it is more than half full. Eg I would count quadrats
1, 2,4 and 5 but not count quadrat 3 and 6.
To improve the reproducibility and validity of the
estimates use a larger sample size eg more quadrats
or bigger quadrats.
Factors Affecting Organisms
Organisms (living things such as plants and animals) are affected by many physical factors:
Temperature
Availability of nutrients
Amount of light
Availability of water
Availability of oxygen and carbon dioxide
Without the things above, we could not survive. The more plants have of the things they
1 2 3
4 5 6
Sampling 1 Area Using a Line Transect
A line transect is simply a tape measure placed across an area.
Q. Describe how a line transect could be set up to estimate the numbers of different plants
growing at different places across a river.
Place a tape measure across the river to produce a transect
Place quadrats at regular intervals along the tape measure
Count the cover/percentage of plants in each quadrat
Repeat the process by placing the transect at different places along the stream. At
random or regular intervals
This
could be
done in
any en-
vironment such as a forest, a field or a pond.
Plants
Like all organisms, plants are made up of cells, which in turn form
tissues, which come together to form organs, then organ systems
and finally the complete organisms. The organs in a plant are made
up of tissues. Plant organs include stems, roots and leaves.
The whole plant is covered in a layer of epidermis tissue. The epi-
dermal tissue on the lower surface of the leaf has little holes called
stomata. These allow gases to diffuse in and out of the leaf.
Most of the cells in a leaf are mesophyll cells. This is where photo-
synthesis takes place.
Xylem and phloem tubes run through the entire plant. These are
tubes which make up the plant’s transport system: xylem carries
water from the roots to the leaves and sugars are transported
Photosynthesis
The word equation for photosynthesis is:
Energy from sunlight
Carbon dioxide + water glucose + oxygen.
The carbon dioxide comes from the air and diffuses into leaves
through the stomata. Water comes from the soil and enters by
diffusion into the roots. Glucose and oxygen are the products;
oxygen diffuses out of leaves as a by-product. Light energy is
absorbed by chlorophyll found in the chloroplasts of plant cells. Chlorophyll is green and is essential for pho-
tosynthesis.
Plants carry out photosynthesis to produce glucose for respiration. Plants carry out respiration just the same
as humans; they need energy for cell processes too. However, plants don’t use up all the glucose so they
store some of it as starch, which is insoluble. The glucose is also used:
To produce fats or oils as an energy store
To produce cellulose, which strengthens the cell walls
To produce proteins—but to make proteins, plants also need nitrates, which have to be absorbed
from the soil.
Limiting factors
This figure shows that as the light intensity increases , the rate of photosynthesis also increases. Between A and B, we say light is
a limiting factor for photosynthesis, as you can still increase the light intensity and see the rate of photosynthesis go up. However,
there comes a point where the rate of photosynthesis does not increase anymore, even when the plant is getting more light
(where the graph has levelled off). This is because something else is acting as a limiting factor, for instance, carbon dioxide concen-
tration.
Increasing the carbon dioxide concentration, then, will increase the rate of photosynthesis. However, eventually the graph levels off again, because some-
thing else (light intensity, or maybe temperature) is acting as a limiting factor.
Increasing the temperature tends to increase the rate of photosynthesis, but if it gets too hot, then enzymes denature and the rate drops again. See graph.
Growing crops in a greenhouse gives the grower a lot of control over the conditions in which plants live. A grower may be able to produce more tomatoes
quickly if they heat the greenhouse, but the cost of fuel might outweigh the increase in what they are paid for the tomatoes.