AQA Biology Unit 2 (B2)

Animal cells
- Cell membrane = controls movement of substances in and out of cell 
- Cytoplasm = gel like substance where chemical reactions take place
- Mitochondria = site of aerobic respiration 
- Ribosomes = site of proteinsynthesis (chain of amino acids)
- Nucleus = controls protein production and contains genetic material 

Plant cells
(have everything animal cells have but MORE)
- Cell wall = made of cellulose fibres that supports and strengthens cell
- Chloroplasts = contain chlorophyll for photosynthesis
- Vacuole = cell sap (sugary substances)  

(OTHER CELLS - yeast cell, bacteria cell etc.) 

Diffusion - the net movement of particles from an area of high concentration to an area of low concentration (usually through the cell membrane)

Cells > Tissues > Organs > Organ system 
Epithelial cell > Epithelial Tissue > Stomach > Digestive system  

Photosynthesis equation 
CARBON DIOXIDE + WATER ---> GLUCOSE + OXYGEN (+energy)  

Limiting factors
Temperature, Light intensity, Carbon dioxide 

Uses of glucose
Respiration > converts glucose to other useful substances
Cell wall > glucose makes cellulose thats useful for cell walls (strengthens)
Proteins > glucose + nitrate ions = amino acids to make proteins
Seeds > glucose makes lipids stored in seeds
Starch > glucose can be stored as starch (in roots, stems and leaves) its insoluble.

Greenhouses | Ideal conditions
Parafin heaters = release c02 as well as heat
Artificial lighting
Ventilators = cools down house
Blinds = to reduce light intensity if too much  

Distribution of organisms depend on several environmental factors:

• temperature
• availability of water
• availability of oxygen + CO2
• availability of nutrients
• amount of light

 Collecting data

- Quadrats = square frames enclosing known area to measure how COMMON (to meaure     the mean = total/no. of quadrats
- Transects =  measuring the DISTRIBUTION of organisms along a area

Reliablity relies on sample size, random samples to improve reproducibility 

Validity relies on control variable and whether it supports the question (hypothesis maybe)

Enzymes are biological catalysts. They are not used up or changed in the reaction! 
Its important to have the right temperature and pH to avoid DENATURATION  

Enzyme + substrate --> enzyme substrate complex (active site) ---> enzyme + product 

Digestive enzymes (all located in the SMALL INTESTINE and PANCREAS)

• Amylase - starch to glucose (alkaline)
• Protease - proteins to amino acids (acid and alkaline) 
• Lipase - lipids to glycerol and fatty acids (alkaline) 

Bile is extremely alkaline that is located in the liver to neutralise the stomach acid 

Enzyme uses

Industry - protease = pre-digest protein in baby food, isomerase = convert glucose into fructorse, carbohydrase = starch into sugar syrup

Home - biological detergents

Aerobic respiration - glucose + oxygen --> carbon dioxide + water + energy 

Anaerobic respiration - glucose --> lactic acid + energy 

Changes during exercise 
Increase in heart rate = more oxygen and glucose travel to the muscles therefore releasing more energy from glucose (aerobic respiration) AND carbon dioxide and lactic acid are removed from the muscles meaning the prevention of oxygen debt. 

Cell division 
Mitosis - when a cell reproduces itself by splitting to form two identical offspring
Meisosis - produces cells that have half the normal number of chromosomes 

Differentiated cells
Embryonic stem cells - turn into ANY type of celll
Can cure many DISEASES e.g. blood diseases treated by bone marrow transplants

Mendel's work
1) characteristics in pea plants are determined by heriditary units
2) heriditary units are passes on from both parents
3) heriditary units can be dominant or recessive

Genetic disorders
Polydactaly - dominant
Cystic fibrosis - recessive 

Fossil evidence

-Gradual replacement
-Casts and impressions
-Preservation 

Causes of extinction

-Environmental changes
-New predators
-New disease
-Competition for food
-Catastrophic event e.g. volcano
-New species 

Speciation (development of new species)

*4, 5, 6 (explanation of natural selection)

1. similar organisms reproduce to give fertile offspring
2. physical barrier/ geological barrier e.g. mountains
3. causes isolation
4. each area show variation due to a wide range of alleles
5. selective advantage (survival of the fittest)
6. best alleles passed onto new generation
7. unable to interbreed and give fertile offspring