Topic 5 Flashcards
Where does the Light dependent reaction (LDR) take place?
thylakoid membranes in chloroplasts
What products are formed in the LDR?
light enerfy and water used to create ATP and reduced NADP for use in LIR
Describe and explain what occurs in the first stage of the LDR (photolysis of water) in photosynthesis
- Photolysis of water
- light energy absorbed by chlorophyll which splits water into oxygen, H+ and e-
- H+ picked up by NADP to form reduced NADP for LIR
- e- passed along electron transfer chain
- O2 used for respiration/diffused out of leaf through stomata- O2 is a waste product
Describe and explain the second stage of the LDR in photosynthesis (Photoionisation of chlorophyll)
- Photoionisation of chlorophyll
- light energy absorbed by chlorophyll and energy results in electrons becoming excited and raise up an energy level to leave chlorophyll- Chlorophyll is ionised by light and an electron is lost
- some energy from released electrons used to make ATP and reduced NADP in chemiosmosis
Describe and explain the third stage of the LDR (chemiosmosis) in photosynthesis
- electrons that gained energy and left chlorophyll move along electron transfer chain (proteins embedded in thylakoid membrane)
- as they move, energy released used to pump protons across chloroplast membranes into intermembrane space of thylakoid
- electrochemical gradient created (more H+ ions in intermembrane space and few in chloroplast stroma) so H+ ions pass through ATP synthase via facilitated diffusion, which results in ATP production
- As H+ ions move through ATP synthase, protein changes shape, providing energy to catalyse reaction of ADP+Pi to make ATP
- protons combine with coenzyme NADP to become reduced NADP
Where does the LIR occur?
In Stroma of Chloroplasts
What is the product formed in the LIR?
A Hexose sugar
Why is the LIR temperature sensitive?
Involves enzymes (RuBisCo)
Describe the process of the LIR
- Carbon dioxide reacts with Ribulose bisphosphate (RuBP) to form 2 x glycerate 3phosphate (GP) (3C), catalysed by RuBisCO
- GP reduced to triose phosphate (TP) using energy from ATP (ATP hydrolysed) and by accepting a H from reduced NADP
- One carbon from TP leaves cycle each turn to be converted into useful organic susbstances (after 6 turns, 6 carbons removed so hexose sugar created)
- rest of TP molecule used to regenerate RuBP with energy from ATP
What can glucose be used for once it is created in the LIR?
- glucose is a monosaccharide that can join to form disaccharides e.g. sucrose and polysaccharides e.g. cellulose and starch
- glucose can be converted to glycerol and combine with fatty acids to make lipids for plant
What are the limiting factors of photosynthesis?
- light intensity
- carbondioxide concentration
- temperature
How does light intesnsity limit photosynthesis?
- Light required in LDR for photolysis and photoionisation
- as light intesnsity increases, rate of photosynthesis increases.
- when there is enough light, the rate no longer increases, so either temperature or carbon dioxide concentration must be the limiting factor
How does carbon dioxide limit photosynthesis?
- Carbon dioxide impacts LIR as is one of reactants in calvin cycle
- as carbon dioxide concentration increases, rate of photosynthesis increases
- past a certain point, there is enough carbon dioxide so increasing its concentration does not increase the rate of photosynthesis
- either light intensity or temperature must be the limiting factor
How does temperature limit photosynthesis?
- impacts LIR as controlled by enzymes
- As temperature increases, rate increases
- only up to a certain point,as when temperature too high, the active sites of enzymes change shape so substrate molecules no longer fit and the enzyme denatures.
- rate then decreases and photosynthesis stops
What agricultural practices are incorporated by famers to remove limiting factors?
- used to maximise photosynthesis and therefore plant growth
- growing plants under artificial lighting to maximise light intensity
- heating a greenhouse to increase temperature
- burning fuel e.g. paraffin burners to release more carbon dioxide
- extent that each used considered in terms of profit. If extra growth from photosynthesis minimal, then will not be cost effective to pay for heating/lighting/fuel
Where does the first stage of aerobic and anaerobic respiration (Glycolysis) take place?
cytoplasm
What are the products of Glycolysis?
2 Pyruvate
Net gain 2 ATP
2 NADH
Describe the process of Glycolysis
- glucose phosphorylated to glucose phosphate by hydrolysing 2 ATP molecules to release phosphate groups to add to glucose
- production of 2 triose phosphate (TP)- highly reactive glucose (has energy transferred from ATP) phosphate splits into 2 TP molecules
- oxidation of TP to produce pyruvate. )Coenzyme NAD picks up hydrogen from TP f to form reduced NAD). 2 ATP released in process.
- pyruvate and NADH actively transported from cytoplasm into the mitochondrial matrix for next stages
Describe the process of the Link reaction in aerobic respiration
- pyruvate made in glycolysis oxidised to acetate and one carbon atom is lost. NAD picks up hydrogen lost from pyruvate and becomes reduced NAD.
- acetate combines with coenzyme A to produce acetylcoenzyme A
What products are produced in the link reaction?
occurs x2 for every glucose molecule, so for one round of link reaction only 1 of every molecule made
1. 2 x Acetyl CoA
2. 2 x CO2 released
3. 2 x reduced NAD
Describe the process of the krebs cycle in aerobic respiration
- Acetyl-CoA reacts with a 4 carbon molecule releasing coenzyme A and producing a 6 carbon molecule that enters krebs cyle. Coenzyme A released to be reused in link reaction
- in a series of redox reaction krebs cycle generates reduced coenzymes and ATP by substrate level phosphorylation and CO2 is lost
What products are formed from the krebs cycle?
- 2 CO2 lost so 6 carbon molecule forms a 4 carbon molecule
- ATP made from ADP and Pi
- reduced FAD and reduced NAD made from FAD and NAD (6C molecule is oxidised)
Where does Oxidative Phosphorylation in aerobic respiration take place?
mitochondrial inner membrane-cristae
Describe the process of oxidative phosphorylation
- reduced coenzymes in mitochondrial matrix carry hydrogen to inner mitochondrial membrane
- hydrogen split into protons and electrons for reduced coenzymes
- electrons passed along electron transfer chain and everytime electron moves to next protein it releases energy to transport proton to intermembrane space via active transport
- electrochemical gradient created
- protons moved down concentration gradient by facilitated diffusion through ATP synthase (inner mitochondrial membrane impermeable to H+ ions). ATP catalyses condensation reaction of ADP and Pi to make ATP (phosphorylation of ADP).
