Biology (AQA) Cells

B2 Unit 1

  • Animal and Plant Cells
  • Specialised Cells
  • How do substances get in and out of cells
  • Osmosis
  • (Cell issues)

5 Features of animal cells and their functions

Cell Membrane: Controls what goes in and out of the cell.

Nucleus: Controls activitiesof the cell. Contains the DNA.

Cytoplasm: Chemical reactions occur here. Contains lots of enzymes, organelles and ribosomes. Jelly consistency.

(Note: Organelles are to Cells what Organs are to the body, e.g. ribosomes, mitochondria, chloroplasts)

Ribosomes: Involved in protein synthesis

Mitochondria: Aerobic respiration - energy from oxygen and glucose.

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Additional features found in plant cells

Cell Wall: Prevents cell from bursting. Made of cellulose.

Chloroplasts: Contain chlorophyll (which makes them green). They absorb light to make food by photosynthesis.

Sap Vacuole: Stored molecules and pigments. Helps control water potential of cell.

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However, diffusion doesn't applt to solutions inside cells because they are separated from those outside by the cell membrane which does not allow all types of particles through. This is called a partially permeable membrane.

Osmosis is the diffusion of WATER from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules. - got that? Basically

Water + Diffusion + Partially permeable membrane = Osmosis.

The movement is still HIGH > LOW however, remember that a dilute cup of ribena is actually a high concentration of water, there is a lot more water than ribena.

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Diagram of animal Cell


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( is the diffusion of water from a dilure to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules.

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Diagram of a plant cell


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Chemical Reactions in cells

Respiration: Most of the enzymes are in the mitochondria.

Photosynthesis: Most of the enzymes are in the chloroplasts

Protein synthesis: Most of the enzymes are on the surface of the ribosomes

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Examples of specialised cells

Cells may be specialised to carry out a particular function.
- Long Tail means they can swim
- Middle section contains tons of mitochondria to provide energy for the tail.
- Acrosome stores digestive enzymes to break down the outer layers of the egg..
- Large nucleus contains genetic information to be passed on.

( Hair
- Finger like means they have a large SA to take in water

Fat Cell
- Not much cytoplasmso loadsa room for fat,
- Then they can expand some more! (up to 1000X the original size)
- Not many mitochondria because they don't need much energy.

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Getting Around

There are three ways that dissolved substances can move into and out of your cells (across the cell membrane):

1. Diffusion


2. Osmosis


3. Active transport.


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Learn this:

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.


They all end up being a pretty even mixture, just remember that it goes from


Diffusion occurs in gases and particles in solution.

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Rates of diffusion

The rate of diffusion increases when there is a big difference between the two areas (a steep concentration gradient) or the temperature is increased (because the random movement of particles is decreased)

Net movement = particles moving in - particles moving out.

Eventually there will be no net movement and there will be equilibrium. Particles will still be moving though, but the same amount in each direction.

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Diffusion in living organisms

Diffusion is used in the transportation of:

  • Water
  • Simple sugars (e.g. glucose and amino acids)
  • Oxygen (from the air into your lungs)

Cells can be adapted to make diffusion easier and more rapid.

Increasing the surface area means there is more space for diffusion to take place. Often the SA is increased by having a folded membrane (of a cell) or tissue lining (of an organ).

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