Complete summary notes according to official A Level ORC exam specification for photosynthesis component (5.2.1) of Communication, Homeostasis & Energy topic.
Photosynthesis
Photosynthesis occurs in autotrophic organisms such as plants,
algae and cyanobacteria.
Chloroplast Structure
Chloroplasts are roughly 2 - 10 μm in diameter (larger than
mitochondria).
Chloroplasts are filled with a fluid known as the stroma that
contains CO2, sugars, enzymes and other molecules.
The stroma contains smaller 70S ribosomes a loop of DNA and
starch granules.
The starch granules are used to store the starch, formed through
photosynthesis.
Chloroplast proteins are coded for in the DNA loop and produced
with the 70S ribosomes.
Chloroplasts contain thylakoids (small fluid filled sacks)
arranged in stacks called grana with lamella connecting separate
grana .
Chloroplasts are a double membrane structure with an outer
membrane permeable to a range of ions and small molecules and
Photosynthesis 1
, the inner membrane containing transport proteins only allowing
certain molecules or ions to pass though.
The thylakoid membranes have a large surface area and contain:
pigments, enzymes and electron carriers.
These pigment molecules are arranged into photosystems.
A photosystem is a funnel-like structure in the thylakoid
membrane, they work by each pigment transferring energy down to
the next pigment molecule until the energy reaches the primary
pigment reaction centre at the bottom of the photosystem.
Photosynthesis 2
, Photosynthetic Pigments
Pigment Name Colour Type of pigment
Different pigments
are found inside
Chlorophyll A Yellow-Green Chlorophyll
photosystems
Chlorophyll B Blue-Green Chlorophyll within the
β Carotene Orange Carotenoid thylakoid membrane
Xanthophyll Yellow Carotenoid (two types of
pigments are
Chlorophylls and
Carotenoids).
Chlorophylls absorb
light with wavelengths
in the blue/violet and
red regions of the
spectrum.
Carotenoids absorb
light with wavelengths
in only the
blue/violet religion
of the spectrum.
⬆ Credit: SaveMyExams.com
Photosystems
Photosystem 1 / PS1 / P700 Photosystem 2 / PS2 / P680
(alternate names) (alternate names)
The chlorophyll A in this The chlorophyll A in this
system has a maximum system has a maximum
absorption of light at absorption of light at
700nm wavelength. 680nm wavelength.
Middle of the electron This photosystem is at the
transport chain. beginning of the electron
transport chain.
Photosynthesis 3
, Light-Dependant Reaction
Takes place in the thylakoids and produces ATP and Reduced NADP
(NADPH).
Photolysis - light energy is used to break down water molecules
in the thylakoid into electrons, hydrogen ions (protons) and
oxygen.
Reduced NADP (NADPH) is produced when protons from the stroma
combine with the carrier molecule, NADP, and electrons from non-
cyclic photophosphorylation.
Photosynthesis 4
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