AQA Biology Unit 2 (B2) - Cells, Transport, Plants, Food Chains & Energy Flow

Notes on cell structure, specialized cells, diffusion, active transport, photosynthesis, limiting factors, plants and minerals, biomass, energy flow and pyramids of biomass/number.

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Additional Biology (AQA
Structure of Cells

The two main types of cells you need to know for this exam are animal cells and plant cells and
their structure. The following are features that both plant and animal cells share:

A nucleus which controls cell activity and holds genetic…

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There are a few cells that are specialized for a certain function. These cells normally have
adaptations which help them carry out their specialized function effectively. Examples include:

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Table from BBC Bitesize.

Transport of Substances in and out of Cells

There are two different ways (for additional biology) in which substances travel in and out of cells.
These are diffusion and osmosis.

Diffusion is defined as the net movement of particles from an area of high concentration to…

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example when the smell of cooking travels through the house. Diffusion is down a concentration
gradient, meaning that it will only occur when there is an area of lower concentration to diffuse to.

The diagram shows that eventually there will be a near enough equal amount of particles on either…

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Plants are adapted for photosynthesis in a number of ways:

The leaves are broad, creating a large surface area for light to be absorbed
Leaves are thin, so carbon dioxide does not have to go far to reach the cells of the leaf
A complex root system brings water into…

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it burns. Doing this ensures the maximum yield for their crops, as photosynthesis can occur at an
optimum rate.

Plants and Minerals

A number of different elements are required by plants so they can stay alive, which include carbon,
hydrogen and oxygen. Carbon and oxygen can be acquired from carbon…

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Diagram from GCSE Revision 101

In a pyramid of numbers, the size of each trophic level (stage of the pyramid going up) reflects,
generally, how many of the certain type of organisms are involved on this part of the food chain. As
you can see, there is only one oak…


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