Chapter 2 - Cells: Structure & Function 1 Cells: ‘Structure & Function’ Chapter 2 Pages 22-50.

Chapter 2 - Cells: Structure & Function

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Cells: ‘Structure & Function’

Chapter 2Pages 22-50


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Looking at Cells Examination of cells using microscopes

reveals much about their internal organisation.

Each living cell is a small compartment with an outer boundary known as the cell membrane or plasma membrane.

Inside each cell is a fluid known as cytosol, that contains fluid and many vital substances for the cell.


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Looking at Cells Living cells can be divided into 2 distinct groups

according to the organisation of their internal structures.

Prokaryotic Cells – Lack of a nucleus or clear structure to house their DNA. (ie bacteria)

Eukaryotic Cells - Contain structures called organelles and the DNA is enclosed inside a membrane bound nucleus. (ie plants, animals, fungi & protists)


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The Cell Membrane The boundary of all living cells is the cell membrane. It

controls entry of dissolved substances into and out of the cell.

The cell membrane is ultra thin (thickness <0.01 micrometers).

A cell membrane contains both lipids and protein.

It consists of a double layer of lipids, in which proteins are embedded, forming a channel to allow certain substances into and out of the cell.


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The Cell MembraneFig 2.4 – Fluid Mosaic Model p25

Activity Sheet – Structure of Membranes


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Movement In and Out of Cells In order to survive, cells need to

take in and expel substances.

Cells generally let in particular dissolved substance. It is therefore said to be partially permeable. Fig 2.5 p25

Dissolved substances that pass across the cell membrane, does so by two processes – Diffusion & Active Transport.


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Free Passage - Diffusion Diffusion is the net movement of a substance

(solution), from a region of high concentration to a region of low concentration.

Diffusion does not require energy.

Fig 2.7 – Diffusion in action p27


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Free Passage - Diffusion One special case of diffusion is known as

osmosis. The process of osmosis is the net movement of water particles by diffusion in or out of a cell.

Osmosis – A Special Diffusion Case p28


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Free Passage - Diffusion Substances that dissolve in water are hydrophilic ‘water

loving’.

Substances that don’t dissolve are called lipophilic or hydrophobic.

Alcohol is a lipophilic substance.

Lipophilic substances enter the cell by absorbing through the lipid layer of the membrane.

This is known as lipid diffusion. The body absorbs alcohol using this method.


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Free Passage - Diffusion Solid particles (ie molecules) and those that cannot enter

via the lipid layer, enter the cell through a specific carrier protein in the membrane. This is known as facilitated diffusion.

Fig 2.9a – Facilitated diffusion

Facilitated diffusion travels from an area of high concentration to an area of low concentration.


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Active Transport Active transport is the net movement of dissolved

substances into or out of the cell against a concentration gradient (opposite to facilitated diffusion).

Active transport requires energy to perform.

Active transport enables cells to maintain stable internal conditions in spite of extreme external surroundings.


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Diffusion & Active Transport

Fig 2.9b – Active Transport


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Bulk Transport When bulk material is

taken into a cell as a solid, the process is termed ‘Phagocytosis’.

When bulk fluid is taken into a cell as fluid, the process is termed ‘Pinocytosis’.


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Bulk Transport - Endocytosis Unicellular protists (Amoeba) obtain their energy

in the form of relatively large food particles that they engulf.

The food gathers at the lipid layer of the membrane and is drawn in and enclosed within a sac where the food is digested.

This process of bulk material into a cell is known as endocytosis.


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Bulk Transport - Endocytosis

Fig 2.11a – Example of Endocytosis


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Bulk Transport - Endocytosis

Fig 2.11b – Example of Endocytosis


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Bulk Transport - Exocytosis Bulk transport out of cells (export or

waste material) is called exocytosis.

In exocytosis, vesicles formed within a cell fuse with the plasma membrane before the contents of the vesicles are released from the cell.


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Bulk Transport - Exocytosis

Fig 2.13 – Exocytosis

Activity Sheet – Exocytosis & Endocytosis p101


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Cell Walls The cell membrane forms the exterior of

animal cells.

However, in plants, fungi and bacteria, a rigid cell wall lies outside the cell membrane.

The cell wall varies in composition between plants, fungi and bacteria.


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Cell Walls

Quick Check Questions 1-3 p31


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Cell Organelles“The nucleus – control centre”

The control centre of the cells of animals, plants, algae and fungi is the nucleus.

The nucleus forms a distinct spherical structure that is enclosed within a double membrane known as the nuclear envelope.

Cells that have a membrane bound nucleus are called eukaryote cells.


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Cell Organelles“The nucleus – control centre” Cells that lack a nuclear envelope or nucleus are called

prokaryote cells.

Cells of organisms such as bacteria, contain genetic material (DNA) that is not enclosed within a distinct nucleus.

The nucleus contains many granules that are made of the genetic material Deoxyribonulceic Acid (DNA).

During cell reproduction, the DNA granules arrange themselves into rod-shaped granules called chromosomes.


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Cell Organelles“The nucleus – control centre”

The nucleus also contains one or more large inclusions known an nucleoli which are composed of ribonucleic acid (RNA).


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Organelles Mitochondrion “Energy Factories” Living cells require energy all the time.

The useable energy supply for cells is ATP (adenosine triphosphate).

ATP is produced in cells during a process called cellular respiration.

In eukaryote cells, energy is synthesised in mitochondrion, which are found in the cytoplasm.

Prokaryote cells do not have mitochondrion.


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Organelles Mitochondrion “Energy Factories”


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OrganellesRibosomes “Protein Factories” Cells must produce proteins in order to perform

specialised functions.

Haemoglobin-oxygen transport Insulin-blood sugar conversion

Ribosomes are the organelles where protein production occurs.

Ribosomes are part of the cytoplasm and can only be seen through a TEM.


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Organelles“Endoplasmic Reticulum”

Protein molecules produced by ribosomes need a transport system to exit the cell and reach its target cell/destination.

Transport of substances within a cell occurs through a system of channels known as the endoplasmic reticulum (ER).

The channel walls are formed by membranes.


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Organelles“Endoplasmic Reticulum”


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Organelles“Golgi Complex”

The golgi complex is prominent in cells as it allows proteins to exit the ribosome and enter the endoplasmic reticulum.

The golgi complex packages protein into membrane bound bags or vesicles for export.

The vesicles then carry the material out of the cell.


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Organelles“Golgi Complex”

Quick Check Questions 4-8 p35


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OrganellesLysosomes “Controlled Destruction” Lysosomes are membrane bound sacs containing

dissolved digestive enzymes.

Lysosomes can digest material brought into their sacs.

Lysosomes play a role in organised cell death.

The process of programmed cell death is known as apoptosis.

Example – Embryo Fingers p36


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OrganellesChloroplasts “Sunlight Trappers” Chloroplasts are relatively large organelles found in

photosynthetic cells of plants and algae.

Chloroplasts have an external membrane and layers of folded internal membranes.

Chlorophylls are located inside chloroplasts.

Chloroplasts trap energy from sunlight and convert it to chemical energy in sugars. This is called photosynthesis.


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OrganellesChloroplasts “Sunlight Trappers”


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OrganellesFlagella “Whipping Around” Some bacterial cells and other single celled

organisms have a whip like structure that is attached to the plasma membrane and protrudes through the cell wall.

This structure is known as a flagellum.

Vibration and rotation of the flagellum results in the cell being able to move around.


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OrganellesFlagella “Whipping Around”


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Putting It All Together


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Animal Cells


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Plant Cells


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Cells Activities Quick Check Questions 9-14 p42

Manual Activity – Cell Structures & Organelles p80-81

Manual Activity – Animal Cells p85

Manual Activity – Plant Cells p84


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Levels of Organisation Unicellular organisms must carry out all the

metabolic processes necessary for life.

In contrast, multicellular organisms have millions of specialised cells that depend on each other for survival.

Specialised cells in multicellular organisms are

organised into different levels so they can perform their specific fucntions.


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Tissues When cells that are specialised in an identical

way aggregate to perform a specific function, they are called a tissue.

Different kinds of tissue serve different functions in an organism.

For example, cardiac muscle is a particular type of muscle tissue comprised solely of cardiac cells and only found in the heart.


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Tissues


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Surface Area to Volume Ratio (SA:V) Both materials that enter a cell and wastes must enter

and exit the cell via the plasma membrane.

The larger the cell – the bigger the surface area for this exchange – the more materials that can enter or exit.

But when you increase surface area – you must also increase the volume in the cell even more.

Exchange of materials between tissues and their environments has the potential to be far more efficient if the tissue is made up of many small cells rather than fewer larger cells.


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Surface Area to Volume Ratio (SA:V)

Activity Sheet – Limitations to Cell Size p98-99


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Organs In multicellular organisms, groups of different

tissues often work together to ensure a particular function is successfully performed.

A collection of such tissues is called an organ.

Your stomach is an organ. It is comprised of tissues such as epithelium (lining), smooth muscle cells and blood.


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Organs


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Organ Systems Activity Sheet –

Levels of Organisation p108-109


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Chapter Review Bio-Challenge p47

Chapter Review Questions 1-9 p48

Chapter 2 - Cells: Structure & Function 1 Cells: ‘Structure & Function’ Chapter 2 Pages 22-50.

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