Unit 5: Photosynthesis Flashcards
What are the properties of ATP?
- released in small amounts
- released in a single step reaction
- quickly broken down and resynthesised
- energy is released immediately
- soluble in water
- Pi released during ATP hydrolysis can be uses to phosphorylate other compounds making them more reactive
What is phosphorylation?
the addition of an inorganic phosphate group
What is the function of ATP?
immediate energy source for biological processes
- when ATP is hydrolysed ADP and phosphate are produced and energy is released
What is the equation for the hydrolysis of ATP?
ATP > ADP + PI
(energy released)
What is the equation for the synthesis/phosphorylation of ATP?
ADP + Pi > ATP
(energy from respiration)
What are the functions of ATP?
- active transport
- synthesis reactions
- muscle contraction
- cell division
- light independent reactions
- first stage of glycolysis
What are chloroplasts
where photosynthesis takes place
describe chloroplasts
flattened biconvex discs surrounded by an envelope consisting of two membranes
What are thylakoids?
flattened membrane sacs
form stacks grana
- provide large surface area for chlorophyll and electron transfer chain of the light dependent reactions
What is the stroma?
contain enzymes sugars and starch granules
- site of the light independent reactions
What is photosynthesis
the production of organic compounds (such as carbohydrates and lipids) from the inorganic compounds CO2 and H2O using light energy
- CO2 is reduced
What is the equation for photosynthesis?
light energy
6H2O + 6CO2 > C6H12O6 + 6O2
chlorophyll
What conditions are required for photosynthesis?
- water
- carbon dioxide
- water
- light
- chlorophyll
- a suitable temp for enzymes
How is carbon dioxide reduced in photosynthesis?
using hydrogen obtained from the light induced photolysis
How is ATP produced during photosynthesis
by the conversion of light energy during photophosphorylation
What are the two stages of photosynthesis?
light dependent reaction
light independent reaction
Where does the light dependent reaction occur and what does it produce
thylakoids
produces: ATP, reduced NAPD, O2
where does the light independent reaction occur and what does it produce?
stroma
uses ATP and reduced NAPD to produce organic compounds
Outline the light dependent reaction
- light energy is absorbed by chlorophyll causing photo ionisation
- electrons gain energy and leave chlorophyll
- Water is split (photolysis) and releases electrons, protons (H+), and O2
- electrons replace those lost by photo ionisation
- electrons are passed from one carrier to another in the electron transport chain, releasing energy
- electrons are transferred to 2nd chlorophyll
- light energy is absorbed by this chlorophyll causing photo ionisation
8.electrons are accepted by NAPD - NAPD also accepts protons (H+) from photolysis and its now reduced
What is oxidation
the loss of hydrogen
What is reduction?
gaining hydrogen
Outline chemiosmotic theory of ATP production in the light dependent reaction
- as electrons wre tranferred in the ETC energy is released
- energy is used to pump protons from the stroma into the thylakoids
- proton gradient is established
- protons diffuse down the conc gradient into the stroma vis ATP synthase
- energy transferred by the movement of protons is used to phosphorylate ADP into ATP
Outline the light independent reaction (Calvin Cycle)
- CO2 diffuses into a leaf thru the stomata then into mesophyll cells then dissolve into the stroma
- CO2 is then fixed in the plant by combining with CO2 acceptor ribulose bisphosphate (RuBP)
- Reaction is catalysed by the enzyme Rubisco and forms 2 glycerate-3-phosphate (GP)
- GP molecules are then reduced using reduced NADP to produce triose phosphate and the hydrolysis of ATP supplies additional energy for this reaction
- Both NADP and the ATP come from the light independent stage
What is the equation for the formation of glycerate-3-phosphate
Rubisco
RuBP + CO2 > 2GP
What is the equation for the reduction of GP into Triose phosphate?
Reduced NAPD > Oxidsed NAPD
2GP —————> 2Triose phosphate
ATP > ADP+Pi
What is a photochemical process
a process thats dependent on light
What are the main limiting factors on the rate of photosynthesis?
- CO2
- light
- a suitable temp for enzymes
What are the uses of Triose phosphate?
- form all photosynthetic products (e.g glucose, fatty acids etc)
- regenerate the CO2 acceptors (RuBP) in the Calvin cycle
How does water stress limit photosynthesis?
leads to stomatal closure limiting photosynthesis due to a reduction in CO2 entering leaves
What is evidence that something is a limiting factor?
as this factor increases so does the rate of process (photosynthesis)
when the rate levels off its no longer limited by said factor
What are two explanations of the rate of photosynthesis levelling off on a graph
- the rate of photosynthesis is at maximum and no change in any factor will increase the rate
- the rate of photosynthesis is limited by some other limiting factor
What is the most important limiting factor?
Carbon dioxide
What are commercial glasshouses?
used to grow plants (crops) on a large scale
In order to increase the yield of crops commercial growers aim to provide conditions where photosynthesis occurs at the maximum rate possible
What is the carbon dioxide concentration needed for maximum rate of photosynthesis
0.1%
Why must temperature be kept at an optimum for photosynthesis
to maximise the rate of photosynthesis
- If it is any higher it causes denaturation of the enzymes involved
- higher temp also increases the rate of respiration which decreases crop yield
