Biology

Niche - the way an organism exploits its environment

Adaptations - features which enable organisms to survive

Survival of the Fittest:
Individuals posessing characteristics that gives them an advantage over others and are well adapted are more likely to survive and breed and pass on useful alleles that help them survive in their environment.

Gene pool - all alleles of all genes present in a population

Species richness - number of species in a given habitat

Species evenness - number of organisms from a particular species in a habitat  

Gives plants their strength
it is a polysaccharide

Microfibrils are bundles of cellulose molecules:
- cellulose molecules remain straight chained
- H bonds form between OH groups in neighbouring chains
- held together by hemicelluloses and pectins

H bonds weak compared to glycosidic bonds but together form strong structure 

Cellulose structure:

Plasmodesmata - narrow fluid filled channels in cell walls

2 types of specialised cell to provide plants with support and to allow water and minerals to pass from roots to leaves:

- xylem vessels - form tubes for transport, stiffened cell wall help support plant
- sclerenchyma - columns of these cells with stiffened walls also provide support

Dermal tissue (epidermis)
Vascular tissue
Ground tissue

Lignin - produced to waterproof cell walls so water can be transported. Also stiffens and gives dreater tensile strength
Adhesion - H bonds formed between water and other molecules
Cohesion - H bonds formed between water molecules 

Modern Process
Human Cell testing
- test different concentrations of drug on different body cells
- says how well works against disease and how safe it is

Animal Testing
- if passes human cells, tested on animals
- makes sure works on whole organisms

Clinical Testing
- if passes animal tests, can be tested on people
- gives more information on effectiveness and safety

William Worthing's Process 
Treatment from tea
- woman showed signs of disease but drinking 'special' tea it cured

Investigation on plants

Human Testing - few people became healthy from doses of drug