AQA GCSE Biology unit 2 revision guide

A detailed revision guide of unit 2, with helpful pictures and diagrams.

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  • Created on: 26-05-09 00:05
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Fifth Form
Revision Guide
Unit Title
12.1 Animal and Plant Cells
12.2 Diffusion and Osmosis
12.3 Plant Requirements
12.4 Food Chains and Energy Flow
12.5 Decay and the Carbon Cycle
12.6 Enzymes
12.7 Homeostasis
12.8 Genetics and Inheritance
12.1 Animal and Plant Cells
Common Features
- Nucleus ­ `brain' of
the cell, controls the
activities of the cell,
contains the genetic
- Cytoplasm ­ medium in
which most chemical
reactions take place
- Cell membrane ­
semi-permeable membrane which controls the passage of
substances in and out of the cell

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Page 2

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Mitochondria ­ where energy is released in respiration, `power
stations' of the cell (see enzymes in respiration (12.…read more

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Specialised Cells
For each of the following cells, briefly describe how their
structure is related to their function (job):
Sperm Long tails with muscle like
Cell proteins for swimming
High numbers of mitochodria to
provide energy
Acrosome ­ containing digestive
enzymes to break through jelly
layer of the egg
Nucleus contains 23
chromosomes, so chromosome no.…read more

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Organ Systems
Whole Body
12.2 Diffusion and Osmosis
Cells need to take in substances as well as getting rid of waste
Substances move in and out of cells across the cell membrane
This can occur by diffusion, osmosis or active transport
Diffusion is:
- particles of a substance in solution spreading out
- the net movement of particles from high to low concentration
Go to:…read more

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Some cells make diffusion more rapid by increasing surface
area where diffusion can occur. Folds of the cell membrane
(villi) greatly increase the s.a.…read more

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- Cell membranes are partially permeable and allow water to
move across them
Osmosis is the movement of water across a partially
permeable membrane
- Water will move from a high water concentration (ie dilute
solution) to a low water concentration (concentrated solution).
- The amount of solutes (salts and sugars) in a liquid determine
how concentrated it is.
- Concentrations inside cells need to stay the same so chemical
reactions can occur.…read more

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Plant Requirements
- Animals = heterotrophs ­ get their energy from eating other
living things
Plants = autotrophs - make their own food
They do this through Photosynthesis (p/s)
Carbon Dioxide + Water Glucose + Oxygen
6CO2 + 6H2O C6H12O6 + 6O2
- Light energy absorbed by chlorophyll in chloroplasts used to
convert carbon dioxide and water into glucose
- Oxygen is produced as a by-product
Most p/s takes place in the leaves which are adapted for p/s:
- broad, large s.a.…read more

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- 0.4% surrounding concentration decreases throughout the
day ­ so in sunny weather CO2 normally the limiting factor
* Can control all these factors by growing in glasshouses
Using Glucose
- Respiration ­ all living cells respire, break down glucose to get
energy (waste products ­ CO2 and water ­ can be used in p/s)
(- Energy released is used to build up molecules, eg.…read more

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Disadv ­ expensive way to farm, uses lots of resources…read more

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Food Chains and Biomass
- Energy of all living things comes from the sun
- Some of the sun's radiated energy is trapped by p/s
- But a lot of the sun's energy doesn't hit plants or is reflected
back off the Earth's surface
The energy that is absorbed by plants is used for:
- Respiration
- Building new cell material ­ ie.…read more


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