Biology B2 1

Key Points
1. Animal and plant cells have structures that enable them to do their jobs
2. Plant cells have some structures which animal cells don't have.

Animal and plant cells have some structures in common; they have:
- a nucleus to control the cell's activities
- cytoplasm where many chemical reactions take place
- a cell membrane that controls the movement of materials
- mitochondria where energy is released during aerobic respiration
- ribosomes where proteins are made (synthesised).

Plant cells also have:
- a rigid cell wall for support
- chloroplasts that contain chlorophyll for photosynthesis
- a permanent vacuole containing cell sap.

Check Yourself
1. Name three structures common to both plant and animal cells.
2. Where does aerobic respiration take place?
3. name two materials that move across the cell membrane.

Key Points
1. As organisms develop, some of their cells become specialised to carry out particular jobs. This is called 'differentiation'.
2. Differentiaion happens much earlier in the development of animals than it does in plants.

- When an egg is fertilised it begins to grow and develop.
-At first there is a growing ball of cells. Then as the organism gets bigger some of the cells change and become specialised.
- there are many different specialised cells for example: some cells in plants may become xylem or root hair cells; some cells in animals will develop into nerve or sperm cells.

A root hair cell has adapted to be suitable to carry out its job. Some of the ways it has adapted are:
- the hairs increase the surface area for water to move into the cell.
- a large permanent vacuole increases the amount of water moving into the cell from the soil
- their position close to the xylem tissue ensures efficient movement of water up the plant

A sperm cell has also adapted to be suitable to carry out its jobs. Some of the ways it has adapted are:
- long tails with muscle-like proteins to swim towards the egg
- lots of mitochondria which provides enough energy for the tail to work
- the acrosome stores digestive enzymes which break down the outer laters of the egg
- a large nucleus stores all the genetic information to be passed on

Check Yourself
1. Can you give two examples of specialised animal cells not mentioned here?
2. How is the structure of a nerve cell related to its function?
3. What do we call the process that results in some cells becoming specialised?

Key Poins
1. Diffusion is the result of random movement. It does not require any energy from the cell.

- Molecules move randomly because of the energy they have.
- Diffusion is the random movement of particles form a high concentration of particles to a low concentration of particles.
- The larger the difference in concentration, the faster the rate of diffusion.

Examples are:
- the diffusion of oxygen into the cells of the body from the blood stream as the cells are respiring (and using up oxygen)
- the diffusion of carbon dioxide into actively photosynthesising plant cells
- the diffusion of simple sugars and amino acids from the gut through cell membranes

Check Yourself
1. Why do particles move randomly?
2. Can you think of another example of diffusion in living cells?
3. Why is diffusion important?

Key Points
1. Osmosis is a special case of diffusion involving a partially (or semi-) permiable membrane.

- Osmosis is the movement of water.
- Just like diffusion, the movement of molecules is random and requires no energy from the cell.
- Osmosis is the diffusion of water across a partially permiable membrane from a dilute solution of water to a more concentrated solution of water.
- No solute molecules can move accross the membrane. The cell membrane is partially permeable.
- Water is needed to support cells and because chemical reactions take place in solution.

Check Yourself
1. How is osmosis like diffusion?
2. What do you think 'partially permeable' means?
3. Why do cells need water?