3.5.1 photosynthesis Flashcards
where does photosynthesis occur
in the chloroplast
describe the chloroplast membrane
double membrane envelope
what are the grana and the stroma?
Grana are stacks of disc structures called thylakoids, LDR occurs here, lamella join adjacent grana
Stroma is a fluid filled matrix where LIR occurs these may contain starch grains
what are photosynthetic pigments
coloured substances that absorb light energy
what does the thylakoid membrane contain
pigments, enzymes and electron carriers for LDR
why do thylakoids have a large surface area?
to allow maximum light energy absorption
what is the function of a starch grain?
to store products of photosynthesis (sugar)
describe a photosystem
funnel-like structure found in the thylakoid membrane, made from accessory pigments that absorb light energy and transfer it to the primary pigment reaction centre.
what is the first step in the light dependent reaction
photolysis of water. light energy is absorbed by chlorophyll and splits H20 into O2, H+ and ELECTRONS in the thylakoid lumen. this forms a proton gradient in the thylakoid lumen
what does photolysis of water produce?
protons, electrons and oxygen
what is the equation for photolysis of water
H20 -> 1/2 O2 + 2e- + 2H+
what is the second stage of LDR?
photoionization of chlorophyll. light energy is absorbed by the chlorophyll which results in electrons becoming excited to a higher energy level and leave the chlorophyll molecule. energy from released e- is used to make ATP and reduced NADP in chemiosmosis.
what does ‘become excited’ mean
gains energy
what is PSII and PSI
photosystem II and photosystem I located in the electron transport chain
describe the first 3 steps of chemiosmosis
- the excited electrons that left the chlorophyll are passed along the ETC.
- as they move along each protein carrier, they release energy. this energy is used to actively transport the H+ protons from the stroma to the thylakoid lumen.
- this results in a proton gradient. high conc of H+ in the thylakoid lumen and low conc in the stroma. there is also H+ present in the stroma due to photolysis
why is the movement of electrons described as a redox reaction
The electron carriers are reduced (as they gain an electron) and then oxidised (lose the electron by passing it to next carrier)
describe the last four steps of chemiosmosis
- protons move down their conc gradient via ATP synthase.
- the energy from this movement combines ADP and an inorganic phosphate to form ATP. this is phosphorylation.
- light energy is absorbed by PS1 which excites e- to an even higher energy level.
- electrons and H+ are transferred to co enzyme NADP to form reduced NADP.
describe the way in which ATP and reduced NADP are produced in the light dependent reaction of photosynthesis (5)
ATP: light energy excites electrons to a higher energy level. energy is released as they move along carriers. this energy combines ADP+Pi.
NADP: excited electrons and H+ from photolysis
describe how the structure of a chloroplast is adapted to its function in photosynthesis (3)
membrane disc shape provides a large SA for efficient light absorption. membrane layers allows many pigment molecules. stroma contains enzymes for LIR
describe the role of water in the LDR (2)
splits water into electrons, H+ and oxygen. electrons are used to provide energy to form ATP and reduced NADP. H+ is used to form reduced NADP
describe how plants absorb light energy from the sun and use this energy to produce useful substances in the LDR (5)
light energy is absorbed by PS2 in chlorophyll. this energy excites electrons to higher energy level and leave the chlorophyll molecule. electrons are passed along ETC/carriers releasing energy each time. this energy is used to make ATP from ADP + Pi and to form reduced NADP using H+ from photolysis
DNP is a substance which allows electron transport to take place without production of ATP. when DNP is given to rats, their body temp rises. explain why (2)
energy is released as heat as it is not being used to produce ATP
whats the function of ATP
to supply energy
