Biology Unit 2 topic 4

HideShow resource information
  • Created by: Scarlett
  • Created on: 28-05-13 12:37


The variety of life in a given place. 

Gene Pool - All the alleles of all the genes in a population.

Population - Interbreeding individuals of the same species in the area.

Community - The various populations make up a community.

Niche- How an organism exploits its environment.

Co- adaption - Becoming dependant on something and adapting closely together.

1 of 15


Behavioural - Actions of an organism that help it survive or reproduce. E.g - Ground nesting birds may use a broken-wing display to attract any predators away from the nest.

Physiological - Internal workings of an organism that help it survive or reproduce. E.g - Many animals that live by the sea but cannot take in salt, excrete it by ion pumps.

Anatomical - The bodily structure of an organism and how its adapted to survive or reproduce. E.g - Bees have tongues that are the right length for the type of flower they feed off.

The ability to adapt depends on-

  • Strength of selection pressure
  • Size of gene pool
  • Reproduction rate
2 of 15

Natural Selection

Proposed by Darwin and Wallace. As a population increases, more of the individuals will die or fail to reproduce. Leads to evolution - a change in allele frequency in a population over time. This has led to headlice becoming resistant to headlice shampoos. 

Survival of the Fittest - The individual with the most desirable trait or advanatge is more likely to survive and reproduce. An allele can be selectively neutral (no advantage or disadvantage) but can suddenly become desirable due to a change in environment.

Classification - The Binomial system is a way of naming an organism using a genus and it`s species both in latin. 

Identification - Dichotomous Key were used to identify organisms. However now Computer Assisted Taxonomy (CAT) is used as its quicker and easier. 

3 of 15

Taxonomic Hierarchy

4 of 15


Animalia - Mutlicellular eukaryotes. (Animals)

Plantae - Multicellular aukaryotes that make their own organic molecules by photosynthesis. (Plants)

Fungi - Multicellular eukaryotes which absorb nutrients from decaying matter. (Fungi)

Protoista - Eukayotes that photosynthesise or feed on organic matter. (Algae or Amoeba)

Prokaryote - Prokaryotes. (Bacteria)

5 of 15

Diversion of Kingdoms

6 of 15

Genetic Variation

Each individual of a species if different from the other, the helps keep the population diverse. 

Cause of genetic variation - A mutation in DNA is made. Independent assortment in meiosis is random and crossing over results in new combinations that are unlikely to be exactly replicated. There are already differences between each individual meaning multiple different parents and multiple different offspring. Random fertilisation, different combinations of alleles will come together depending on which sperm and egg fertilise. 

7 of 15

Plant Cells

Differs from animal cells - Has rigid cell walls and contains chloroplasts and a vacuole. 

8 of 15


Made of B glucose chains in 1-4glycosidic bonds. Hydrogen bonds form between neighbouring cellulose chains forming bundles of microfibrils which help produce a strong stucture.

Pectins hold together the microfibrils. They bind to each other and the cellulose.

9 of 15

Plant tissue

 The vascular tissue forms in bundles in young dicotyledons and merge to form rings as it ages. 

10 of 15

Xylem and Phloem

Xylem vessels transport water and inorgnic ions. Phloem sieve tubes transport products of photosynthesis.

11 of 15


Xylem are made of large cells with thick walls that form a column. The plant produces lignin which binds with the wall to make it waterproof. Tonoplast breaks down and the organelles, cytoplasm and cell surface membrane are broken down in autolysis leaving an empty tube. 

Water evaporates from the surface of the plant, diffuses out through the stomata and down a diffusion gradient (Transpiration) The transpirated water is then replaced by water from the roots. The water column doesnt break as its been sucked up due to cohesive forces between water molecules (Cohesion-tension theory).

Plants need inorganic materials to make amino acids. The nirtrogen from the nitrate ions is combined with organic molecules from photosynthesis to make all 20 amino acids.  Without nitrogen, the plants would not be able to grow effectively. If it lacks magnesium it cannot make chlorophyll and the leaves become yellow. Lack of calcuim cuases stunted groth due to its role in th cell wall. 

12 of 15

Xylem and Sclerenchyma

Lignin also helps with support in the cell and often forms spirals or rings. The sclerenchyma fibres also get lignin desposits, die and leave hollow fibres. 


It is hard to extract these fibres where there is more lignin present, so this is done using caustic alkali which breaks down the surronding tissue.

13 of 15

Seed Banks

Seeds are collected, dried and kept in a dark, cool room as this prevents germinaion and impoves seed life span. Samples are taken every 10 years and germinated to make sure the seeds are still viable. If germination falls below 75% then the seeds are grown and new samples are taken. 

14 of 15

Drug Trials

A drug has to been proven to be effective, safe and capable of making a profit. It can take a long time and cost a LOT of money. 

Pre-clinical Testing - Animal/Lab studes on isolated cells. Can take several years.

Clincal Trials-Phase 1 - Volunteers are given different doses. Determines whether  it can be absorbed, distributed and meabolised the way predicted.

Phase 2 - Volunteer patients with the disease are testedto look at effectiveness.

Phase 3 - A lage group of patients are selected and radomly divided into 2 groups. One given placeb or existing treatment. Double blind - Niether patients or doctors know who has which. 

15 of 15


No comments have yet been made

Similar Biology resources:

See all Biology resources »