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Biology Revision

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Biodiversity is the measure of the number and variety of species in a certain area.

Biodiversity is highest nearer the equator and lower nearer the poles.

Global biodiversity is the total number of species on the planet, for which values are only

estimates because not all species have been…

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Increase in human population puts strain on resources and space to live, leading to

industrialisation, destroying habitats and food sources, for example by deforestation.

Pollution causes a decrease in biodiversity.

Over-harvesting of food sources such as fish decreases biodiversity, for example cod

has become endangered from over-harvesting.

A reduction in…

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Ex situ conservation is when a species is protected by moving it from its natural habitat,

for example relocating them to a safer area, breeding schemes in captivity,

development of botanic gardens, and creating seed banks (freezing seeds of plants).

Ex situ conservation allows control of the environment, but it's…

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Being adapted to an environment means an organism has features that increase its

chances of survival and reproduction, and because the desirable genes are passed on,

the chances of the offspring reproducing successfully are also increased.

Behavioural adaptations are ways organisms act that increase the chance of their survival…

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Darwin explained these observations by saying individuals within a population show

variation in their phenotypes (characteristics), predation, disease and competition create

a struggle for survival, better adaptations are more likely to survive, reproduce and pass

on their advantageous adaptations to their offspring, so over time the number of

individuals with…

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DNA evidence can be used to show evolution, as evolution is the gradual change in the

base sequences of an organisms DNA, and because species are more closely related the

more recently they diverged, organisms that diverged more recently should have more

similar DNA, for example humans and chimps diverged…

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Classification groups similar organisms together to make them easier to identify and


Taxonomy is the study of classification.

There are seven taxonomical groups; kingdom, phylum, class, order, family, genus.

Organisms in the same genus are often very similar but are different species because

they can't breed together to…

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Respiratory system
The lungs are found in the thorax, and are specialised for gas exchange.

Gas exchange is the absorption of oxygen into the blood, and carbon dioxide out of the

blood into the lungs.

Gas exchange takes place in the alveoli, which have a squamous epithelium layer one cell…

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The bronchi have smaller pieces of cartilage, smooth muscle, elastic fibres, goblet cells

and a ciliated epithelium.

The bronchioles have no cartilage and the alveoli have no cartilage, no smooth muscle, no

goblet cells, elastic fibres and a squamous epithelium.

Pleural fluid is found between the lungs and the lining…


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