3.2 Photosynthesis Flashcards
What are the two stages of photosynthesis?
The light dependent stage and the light independent stage
Give a brief explanation of what occurs in the light dependent stage:
The light dependent stage converts light energy to chemical energy. The light energy gives the energy for the photolysis of water (H20 molecule) which releases protons and electrons. Energy carried by the electrons causes a proton gradient across the thylakoid membrane. The energy is used to phosphorylate ADP which produces ATP, in phosphorylation. The protons and electrons reduce NADP to NADPH.
Give a brief explanation of what occurs in the light independent stage:
In the light independent stage the ATP and NADPH reduce carbon dioxide and produce energy-containing glucose.
What is the overall equation of photosynthesis?
6CO2 + 6H20 ——> C6H12O6 + 6O2
What does the term photophosphorylation mean?
An endergonic reaction bonding a phosphate ion to a molecule of ADP using energy from light, making ATP.
How is the light independent stage dependent on the light dependent stage?
As the products of the light dependent stage (ATP and reduced NADP) are needed for the light independent stage to work.
Discuss the structure of the chloroplast:
Chloroplasts are surrounded by a double membrane. The inner membrane folds inwards to make thylakoid lamellae. These combine in stacks of up to 100 disc shaped flattened sacks forming granums. This is where the photosynthesis pigments like chlorophyll a are found, it is also where the reactions of the light-dependent stage of photosynthesis take place. Then there is the rest of the fluid filled space of the chloroplast called the stroma, this is where the light independent stage occurs.
Where are the chloroplasts found on the plant and why?
The chloroplast needs light and so are only found on the parts of plants most exposed to light - the leaf and the stem.
Why are chloroplasts found on leafs?
-Leaves have a large surface area thus capturing as much light as possible.
-Thin this light penetrates through the leaf.
- Air spaces in the spongy mesophyll allows carbon dioxide to diffuse to the photosynthesising cells.
- Spaces between the palisade cells for the same reason above.
How are chloroplasts adapted for photosynthesis?
- Large S.F for maximum absorption of light.
- They move within the spaces of palisade layers so they can move to the top of the cells on dull days for more light, and bottom of the cells on high light intensity days to avoid bleaching of pigments.
- Chloropasts rotate within palisade cells for thylakoids to maximise light absorption.
- more chloroplasts in palisade cells than spongy mesophyll as palisade cells are at the top of the leaf more exposed to light.
How are chloroplasts transducers?
Chloroplasts are transducers as they turn energy in the photons of light into chemical energy, made available through ATP and incorporated into molecules such as glucose.
What is a pigment?
A molecule that absorbs different wavelengths of light.
What is the antenna complex?
An array of protein and pigment molecules in the thylakoid membranes that transfer energy from light of a range of wavelengths (that they uniquely can absorb) to the primary pigment that is chlorophyll a (at the reaction centre).
What are the accessory pigments in the antenna complex?
They are different pigments that absorb different wavelengths of light known as chlorophyll b and carotenoids like b-carotene.
What happens when the energy reaches chlorophyll a?
Once the energy reached chlorophyll a it excited the electrons within chlorophyll a and thus raised a lone pair to a higher energy level.
What is a photosystem?
A collection of accessory pigments that absorb light at a variety of wavelengths and then transfers the energy to the primary pigment at the reaction centre.
What is cyclic photophosphorylation?
ATP can be produced by electrons that take a cyclic pathway and are recycled back into the chlorophyll a in photosystem 1. Basically just making more and more ATP from ADP.
What is non-cyclic photophosphorylation?
ATP can be produced by electrons that are excited by light photons, move through PS1 and PS2 and takes a linear pathway from water to NADP, which the electrons reduce with the photons from the photolysis of water.
What is the Z scheme?
The pathway taken by electrons in non-cyclic photophosphorylation - DRAW IT NOW ON UR WHITEBOARD
What is photolysis?
The spitting of water molecules by light producing hydrogen ions (protons that reduce stuff), electrons and oxygen.
Write the photolysis of water equation and state where the products go:
H20–> 2H+ + 2e- + 1/2 02
The electrons produced replace those lost from PS2, the protons from water (H+) reduce NADP along with electrons from PS1, the oxygen diffuses out of the chloroplast and cell, out through the stomata as a waste product.
What is the passage of protons and phosphorylation?
As electrons pass through a proton pump in the thylakoid membrane, they provide energy to pump protons from the stroma into the thylakoid space. The protons join the H+ ions form the photolysis of water and accumulate. This generates large electrochemical gradient, since there are more inside the thylakoid than in the stroma. This gradient is a source of potential energy . This is where things get tekky. Chemiosmosis occurs where the H+ ions diffuse down the electrochemical gradient through the ATP synthetase wedged in the thylakoid membrane that leads to the stroma. This forces the energy into one place making it available, so this is the site of phosphorylation where ADP is made into ATP using this now available energy. And then once the H+ ions have made it through the ATP synthetase and into the stroma they are used to reduce NADP into reduced NADP.
What are the three factors maintaining the proton gradient between the thylakoid space and the stroma?
- The proton pump that initially pumps the H+ ions into the thylakoid space using the energy from electrons that passed through it from getting excited by photons.
- The photolysis of water in the thylakoid space.
- The removal of protons from the stroma as they are used in reducing NADP.
What is the first stage of the Calvin cycle?
A five carbon acceptor molecule, ribulose biphowphate, combines with carbon dioxide, catalysed by the enzyme ribulose bisphosphate carboxylase, abbreviated to rubisco. It is the most abundant protein in the biosphere. This forms an unstable 6-carbon compound is formed.
