AQA additional science - cells

Most human cells like most other animal cells have the following 

parts: 

− a NUCLEUS which controls the activities of the cell 

− CYTOPLASM in which most of the chemical reactions take place 

− a CELL MEMBRANE which controls the passage of substances in  

and out of the cell 

− MITOCHONDRIA, which is where most energy is released in 

respiration  

− RIBOSOMES, which is where protein synthesis occurs.  

• Plant cells also have a CELL WALL which strengthens the cell. Plant 

cells often have:  

− CHOLOROPLASTS which absorb light energy to make food 

− a PERMANENT VACUOULE filled with cell sap.  

• The chemical reactions inside cells are controlled by enzymes.  

Not all cells have the same function. Cells are different shapes, sizes and materials to aid them in their function

The head contains a nucleus and enzymes to help break through the egg. It has a tail to help it travel. The middle section is where the mitochondria is stored. It's general streamlined shape helps it to get through fluids with more ease. 

This is just one example. Your paper 1 exam will likely give you a cell and ask you how the cell is adapted to its function. Key things to look for when analyzing a cell can be found on the next card.

THE SHAPE: The shape is generally a good indicator. It won't always give information and is often best ignored if the shape is a simple circle but if it has an unusual shape like a sperm cell or a root cell try to see a use.

THE DISTRIBUTION: How much cytoplasm is there? How much mitochondria is there? Where are these organelles? This questions will usually indicate some sort of way the cell is adapted.

USUAL CHARACTERISTICS: Most cells have a unique unusual characteristic that separate them from other cells. These characteristics almost always indicate adaption to function. Did you know a fat cell has two membranes? Did you know a blood cell has no nucleus? These all have a purpose behind them. You just have to try and find it.

• Dissolved substances can move into and out of cells by diffusion 

and osmosis. 

• Diffusion is the spreading of the particles of a gas, or of any 

substance in solution, resulting in a net movement from a region 

where they are of a higher concentration. The greater the 

difference in concentration, the faster the rate of diffusion.  

Oxygen required for respiration passes through cell membranes by 

diffusion.  

• Water often moves across boundaries by OSMOSIS.  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. 

• Differences in the concentrations of the solutions inside and 

outside a cell cause water to move into or out of the cell by 

osmosis. 

Diffusion: The random movements of particles from a high concentration to a low concentration.

Turgid: Swollen and distended; congested

Osmosis: Diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane.

Permeable: Something that can be permeated or penetrated.

Permeate:  To pass through the openings of.

Organelle: Parts of a cell. e.g. A nucleus, a membrane exc.