AQA Biology B2 Revision

Most ANIMAL CELLS contain a NUCLEUS, CYTOPLASM, CELL MAEMBRANE, MITOCHONDRIA and RIBOSOMES.

PLANT CELLS contain ALL THE ABOVE as well as a CELL WALL and in MANY CASES, CHLOROPLASTS and a PERMANENT VACUOLE filled with SAP.

ENZYMES CONTROL the CHEMICAL REACTIONS INSIDE CELLS.

CELLS MAY BE SPECIALISED to carry out a PARTICULAR FUNCTION.

Examples of specialised cells are FAT CELLS, CONE CELLS, ROOT HAIR CELLS AND SPERM CELLS.

DISSOLVED SUNSTANCES move IN AND OUT OF CELLS by DIFFUSION, OSMOSIS and ACTIVE TRANSPORT.

DIFFUSION is the NET MOVEMENT of PARTICLES from an area where they are at a HIGH CONCENTRATION to an area where they are at a LOW CONCENTRATION.

OSMOSIS is a SPECIAL CASE OF DIFFUSION.

Osmosis is the DIFFUSION OF WATER from a HIGH WATER CONCENTRATION (DILUTE SOLUTION) to a LOW WATER CONCENTRATION (CONCENTRATED SOLUTION) through a PARTIALLY PERMEABLE MAEMBRANE that allows the PASSAGE OF WATER MOLECULES.

PHOTOSYNTHESIS can be summed up by the equation;

CARBON DIOXIDE (CO2) + WATER (H2O) [+ light energy] = GLUCOSE (C6H12O6) + OXYGEN (O2).

During photosynthesis, LIGHT ENERGY is ABSORBED by the CHLOROPHYLL in the CHLOROPLASTS. It is used to CONVERT CO2 AND WATER into GLUCOSE. Oxygen is released as a by product

Leaves are WELL ADAPTED to allow the MAXIMUM PHOTOSYNTHESIS to take place.