Edexcel AS Biology
There are three units:
Unit 1: Lifestyle, Transport, Genes and Health (40% AS 20% GCE)
Exam: Jan 2013
Unit 2: Development, Plants and the Environment (40% AS 20%
GCE)
Exam: June 2013
Unit 3: Practical Biology and Research Skills (20% AS 10% GCE)
1500 - 2000 words report on into a biological topic – June
2013
Edexcel A2 Biology
There are three units:
Unit 4: The Natural Environment and Species Survival (40% A2
20% GCE) Exam: Jan 2013
Unit 5: Energy, Exercise and Coordination (40% A2 20% GCE)
Exam: June 2013
Unit 6: Practical Biology and Research Skills (20% A2 10% GCE)
Students will complete a written report of an experimental
investigation
What is involved.....
Skills: practical skills, fact learning, application
of knowledge, mathematical skills, independent
investigations- planning, implementing and
writing up scientific reports, research papers.
Topics: human biology, environmental biology,
plant biology, immunology, genetics.
Requirements: you need to be prepared to do
lots of independent research and self study.
Membranes
Why do cells need membranes?
• Control entry and exit of substances
• Keep things in!
Contain the cell contents and organelles;
compartmentalise individual cell processes
• Communication with external environment
• Site of chemical reactions
• Allows cell to change shape
• Transport and packaging within a cell
What are cell membranes made of?
 Mostly LIPIDS
...... And so is impenetrable to water soluble
substances
 Some PROTEINS .
These allow water-soluble substances and
other molecules to pass across.
Membrane Structure
3 main types of lipid
- Phospholipids – most abundant
- Cholesterol - helps to stabilise the membrane by
partial immobilising of the fatty acid chains
- Glycolipids - involved in cell to cell recognition and
communication
Phospholipids
Lipids formed when 2 fatty acids, a phosphate group and
glycerol are joined together.
Hydro – water
Phillic – loves
Due to the negative
charges on the
phosphate group
Hydro – water
Phobic – hates
The long hydrocarbon
chains do not have any
charged groups
Phosphate head
- Likes water so turned
towards water
Fatty acid tails
- Hates water
In water phospholipids tend to form into
a double layer with the phosphate ‘heads’
in the water and the fatty acid ‘tails’
away from it.
This is the basic
structure that forms all
cell membranes.
The fluid mosaic model of the plasma membrane:
The proteins and phospholipids can move in the layer. Small
molecules can move in and out of the membrane.
The fluid mosaic model of the plasma membrane:
Temperature affects
the fluidity of the
membrane.
HOW?
To be investigated......
Findings…
As the temperature increases the % absorbency
increases as more pigments are released from
the vacuole into the surrounding water. The
more pigment, the greater the light absorbed.