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OCR Biology A level 5.2.1 Photosynthesis summary notes
Summary notes for topic 5.2.1 Photosynthesis of OCR Biology A level Module 5. Detailed electronic notes with diagrams.
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Usually amylase production are switched on by naturally occurring gibberellins Adding can speed up process
Sugar production
Spraying on sugar cane can stimulate growth between nodes, making stems elongate
Sugar cane stores sugar in the cells of the internodes, making more sugar available from each plant
Plant breeding
Induces seed formation in young trees
o (Conifer plants take a particularly long time to breed as spend a long time as juveniles
before becoming reproductively active)
Harvesting seeds from biennial plants (only flower in second year of life)
o Induces seed production in first year
Spraying with gibberellin synthesis inhibitors can keep flowers short and stocky
o Ensures internodes of crop plants stay short
o Prevents lodging
Happens in wet summers where stem bends over because of the weight of water
collected on the ripened seed heads
Makes crop difficult to harvest
Cytokinins
Delay leaf senescence
Used to tissue culture to mass produce plants
o Promote bud and shoot growth from small pieces of tissue taken from a parent plant
o Produces a short shoot with a lot of side branches
o This can easily be split into lots of small plants
Ethene
Speeding up fruit ripening in citrus fruits, apples, tomatoes
Promoting fruit drop in cotton, cherry, walnut
Promoting female sex expression in cucumbers, reducing chance of self pollination (pollination
makes cucumbers bitter) and increasing yield
Promoting lateral growth in some plants - yield compact flowering stems
Can also restrict ethene
Store fruit in a low temperature with little oxygen and high carbon dioxide concentration
Prevents ethene synthesis
Therefore prevents fruit ripening
Means fruits can be stored for longer
5.2.1 Photosynthesis
Photosynthesis is the process whereby light energy from the Sun is transformed into chemical energy and used to
synthesise large organic molecules from inorganic substances.
Photosynthesis forms the basis of most food chains.
Autotroph:
Produce complex organic molecules
From simple inorganic molecules using energy from light (photosynthesis)
Or inorganic chemical reactions (chemosynthesis)
Heterotroph:
Organism that cannot manufacture its own food
, Ingest and digest complex organic molecules
All animals, protozoans, fungi and most bacteria are heterotrophs
In plants photosynthesis is a two- stage process taking place in chloroplasts;
a. Light Dependant Reactions (on the thylakoid membrane)
Photophosphorylation
Photolysis of water
Oxygen produced
ATP & reduced NADP produced and passed onto the . . . .
b. Light Independent Reactions (in the stroma)
Carbon fixation
Reduction
Regeneration
How the structure of chloroplasts enables them to carry out their functions;
Biconvex shape of chloroplast gives a large
surface area to absorb CO2;
Grana/thylakoid membranes
a. Large surface area to absorb light
energy;
b. Site of the light dependent reactions;
(photophosphorylation);
c. Electron carriers are located in
thylakoid membrane;
d. Proton pumps present to move
hydrogen ions;
i. into thylakoid space;
e. ATP synthase in the membrane
involved in ATP production;
Photosynthetic pigments
a. Arranged into light harvesting clusters
called photosystems
b. Found in the thylakoid membrane;
Photosynthetic pigments
a. Absorb light energy and lose excited electrons;
b. Chlorophyll a molecule at reaction centre of
photosystem;
Other photosynthetic pigments known as accessory
pigments; e.g. carotenoids
a. Accessory pigments ‘funnel’ electrons to reaction centre of photosystem
Different pigments absorb different wavelengths of light;
Wavelengths absorbed best by chlorophyll (blue + red or 450 + 680 nm);
Stroma
a. Enzymes needed for the light independent stage are found in the in stroma; e.g. rubisco;
b. DNA/ribosomes in stroma to making proteins; e.g. rubisco;
c. NADP present;
d. Surrounds grana; products of L dependent R can directly pass into stroma for L independent R
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