Biology notes that will help you get an A*
Notes have been made to cater to the AQA Biology Mark Scheme
Contains everything on the spec for Energy Transfers:
- Photosynthesis
- Respiration
- Ecosystems
- Farming
- Nutrient Cycles
- Eutrophication
Photosynthesis
Plants convert sunlight energy into chemical energy in the form of organic molecules
GCOzHeO CHOs"60 .
It has 2 stages: Key words:
-
Light dependent stage in the thylakoid Metabolic pathway - series of small reactions
membrane uses light energy to produce controlled by enzymes (photosynthesis & respiration)
reduced NADP + ATP Photophosphorylation - adding phosphate to a
-
Light independent reaction occurs in molecule of light
the stroma of chloroplasts and Photolysis - splitting of a molecule using light energy
-
produces organic products using Photoionisation - when light energy ‘excites’
·
Calvin cycle electrons in an atom or molecule, giving them
more energy and causing them to be released.
Coenzymes: This makes the atom a positively-changed ion.
-
A coenzyme is a molecule that aids the function of an enzyme
-
They transfer a chemical group from one molecule to another
-
Coenzyme used in photosynthesis is NADP which transfers hydrogen so it reduces or oxidises a molecule
Chloroplast:
Thylakoids are stacked up into structures called grana
.
-
Grana are linked by bits of thylakoid membrane called lamellae
-
Chloroplasts contain photosynthetic pigments Thylakoid membrane
which are coloured substances that absorb DNA Ribosomes - produce proteins for
photosynthesis quickly
light. Pigments are found in the thylakoid Chloroplast envelope
·
membranes - they're attached to proteins.
Starch
Protein and pigment is called a photosystem. Grana
-
2 photosystems are used by plants to capture light
energy. Photosystem I absorbs light best at a
Stroma
wavelength of 700nm and photosystem II absorbs Lamellae
light best at 680nm.
-
Stroma is gel-like substance which contains enzymes, sugars and organic acids
i
Carbohydrates produced that are not used straight away are stored as starch grains in the stroma
, Light Dependent Reaction
·
Energy from photoionisation of chlorophyll is used for:
Photophosphorylation: making ATP from ADP + Pi
Making reduced NADP from NADP
Photolysis: splitting water into protons, electrons and oxygen
Non-cyclic photophosphorylation:
-
Photosystems are linked by electron carriers
·
Electron carriers are proteins that transfer electrons
·
Photosystems and electron carriers form an electron transport chain
↑
Electron transport chain is a chain of proteins through which excited electrons flow
Photoionisation: .Photolysis of water:
2
· Light energy is absorbed by PSII which excites electron Light energy splits water into protons,
-
in chlorophyll electrons and oxygen
-
Electrons move to a higher energy level HeO 2H" + @
· These electrons leave chlorophyll and move down electron The electrons formed replace those that
↑
transport chain to PSI leave PSII
= Oxygen is waste product that diffuses from
stomata - water is oxidised into oxygen gas
3 Excited electrons lose energy as they move down ETC
This energy is used to transport hydrogen ions from
stroma into the thylakoid
=
H ,0
↑
This forms a proton gradient across thylakoid 202
2H" +
membrane L
Light energy is absorbed by PSI which
-
Protons diffuse back into the stroma, down their excites electrons again to an even higher
concentration gradient, through the enzyme ATP energy level
synthase that is embedded in the membrane -
Electrons and a proton are transferred
The energy from this movement combines ADP and Pi to NADP to form reduced NADP
·
to form ATP
" =>
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