Edexcel A2 Biology Notes

  • Subject: Biology
  • Level: A2
  • Exam board: Edexcel
  • Author: Henna
  • Year created: 2013

Edexcel A2 Biology

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Photosynthesis & Chloroplasts
6CO + 6HO CHO + 6O
Heterotroph ­ something which gets its food from other organisms
Autotroph ­ creates its own food
Photoautotroph ­ uses light & energy to create its own food
ATP - Adenosine Triphosphate (3 phosphate groups)
Universal energy source.
Powers cellular processes by building and breaking bonds
When we need energy, the third bond is broken by a hydrolysis reaction using
ATPase enzyme.
ATP ADP + Pi + energy
The Electron Transport Chain
ATP is made as a result of what is used in the electron transport chain. As
electrons move along the chain, they lose energy which can be used to drive
the synthesis of ATP to ADP & inorganic phosphate.
Hydrogen molecules removed from compounds are picked up by other
compounds and become reduced. ­ OILRIG (oxidation is loss, reduction is gain)

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Page 2

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Starch Grain Organelle which contains starch
Lamellae Extension of the Thylakoids (contain
PSI)
Thylakoids Organelle which contains chlorophyll
(and PSI & PSII) found in the Stroma in
stacks called Grana. Increase surface
area for light capture and allows
capture of photons with a wider
range of wavelengths. Light
Dependant Reactions occur in the
Thylakoid Membrane.
Grana (granum) Stack of Thylakoid discs
Stroma The space in a chloroplast surrounding
the Thylakoids.

Page 3

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Also contains starch
grains and lipid droplets.
Ribosomes Organelle for synthesis of
Polypeptides
Outer Membrane Permeable to most ions and
(double membrane) metabolites.

Page 4

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Xanthophyll
Phaeophytin
All parts of the plant do not need to carry out photosynthesis and therefore do not have
chloroplasts. The most abundant type of chlorophyll is `chlorophyll a' which is found in
most places. The benefit of having different types is that it is most efficient as each of
the pigments absorbs and captures light from particular areas, more energy from the
light can be used and photosynthesis is maximised.

Page 5

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Takes place on the thylakoid membranes of the chloroplasts. It has 2 main
functions:
1. To produce ATP, supplying energy for the synthesis of carbohydrates
2. Split water molecules in a photochemical reaction providing hydrogen
ions to reduce CO2 & produce carbohydrates
The smallest unit of light energy is a photon. When a photon of light hits a
chlorophyll molecule, the energy is transferred to the electrons of that
molecule.

Page 6

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PSI. PSI then receives an electron to replace the one that was lost to the light
independent reactions.
As the chlorophyll molecule in PSII is short of an electron and unstable, an
electron has to be found from somewhere to restore the chlorophyll to its
original state. The electron comes from the splitting of water ­ PHOTOLYSIS.
LIGHT INDEPENDENT REACTIONS
Carbon dioxide is converted to carbohydrates. These reactions
occur in the Stroma of the chloroplasts, surrounding the grana.

Page 7

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The Calvin Cycle
Intermediates of the Calvin Cycle:
RuBP (Ribulose Biphosphate)
Rubisco (Ribulose Biphophate Carboxylase/Oxygenase enzyme)
GP (Glycerate 3 ­ phosphate)
TP (Triose phosphate) = GALP (Glyceraldehyde 3 phosphate)

Page 8

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The enzyme Ribisco combines RuBP with CO to form a 6 carbon molecule
(unstable) which then splits into 2 GP molecules which are 3 carbons each.
These molecules are reduced using ATP energy & H+ from NADPH (from the
light dependent reactions) to form 2 GALP molecules (3 carbons each).
1 carbon goes off to make complex molecules; glucose, lipids and amino acids
& the other 5 start the process again converting back into RuBP.

Page 9

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Abiotic factors ­ non-living elements of the habitat of an organism e.g.
sunlight, temperature, soil, ph.
Biotic factors ­ living elements of a habitat which affect the ability of a group
of organisms to survive there e.g. the presence of suitable prey will affect the
number of predators in the habitat
BIOMES
Major ecosystems devised from the biosphere, distinguished by their
similar climates and plant communities.
Tropical Rainforest ­ high humidity, warm and plenty of sunlight, rain all year.

Page 10

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Secondary colonisers more adapted to the new environment will then
colonise the land
Larger trees block the growth of smaller plants, due to competition for
sunlight & species diversity drops.
Climax community is self-sustaining & reached where the
biodiversity is constant. Not many further changes occur.
Secondary Succession ­
Occurs as rivers shift their courses after fires & floods and disturbances
cause by humans.

Comments

Feeba

Wed 12th June, 2013 @ 17:20

thanks this is really gud

welldone:)

naruto qatar

Thu 27th June, 2013 @ 11:43

Awesome thank u so much :D

s

Tue 1st October, 2013 @ 15:11

Amazing thankyou!!

molly

Fri 25th October, 2013 @ 10:17


thankyou,so helpful

melissa

Wed 16th April, 2014 @ 12:09

hi i was just wondering if this covered both unit 4 and 5? thank you!

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