5.1 and 5.2 Flashcards
What are the stages of photosynthesis and where do they take place?
Light dependent, thylakoid membrane of chloroplast
Light independed (also known as calvin cycle), stroma of chloroplast
Describe photoionisation in the LDR:
Chlorophyll absorbs light energy which excites its electrons
So electrons are released from chlorophyll
Describe what happens after photoionisation in the LDR:
Electrons move along electro transfer chain, releasing energy
This energy is used to actively pump protons from stroma into thylakoid
Protons move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase
Energy used to join ADP and Pi to form ATP (photophosphorylation)
NaDP accepts a proton and an electron to become reduced NADP
Describe photolysis of water in the LDR:
Water absorbs light and splits to produce protons, electrons and oxygen
- electrons replace those lost from chlorophyll
Describe the LIR:
CO2 reacts with ribulose bisphosphate, catalysed by enzyme rubisco
Forms 2 glycerate 3-phosphate molecules
GP reduced to triose phosphate using reduced NADP and energy from ATP (products of LDR)
Some triose phosphate converted to useful organic substances (e.g glucose)
Some triose phosphate used to regenerate RuBP in calvin cycle (using energy from ATP)
How does temperature affect rate of photosynthesis?
As temp increases, rate increases
- enzymes (e.g rubisco) gain kinetic energy so more E-S complexes form
Above optimum temp, rate decreases
- enzymes denature so fewer E-S complexes form
Describe and explain how light intensity affects rate of photosynthesis:
As light intensity increases, rate increases
- Light-dependent reaction increases so more ATP and NADPH produced
- So LIR increases as more GP converted to triose phosphate and more triose phosphate regenerates RuBP
Above a certain light intensity, rate stops increasing
- Another factor is limiting (e.g temp/ [CO2])
Describe and explain how CO2 conc. affects the rate of photosynthesis
As CO2 conc. increases, rate increases
- LIR increases
- More CO2 combines with RuBP to form GP
- So more GP reduced to triose phosphate, and more triose phosphate convereted to inorganic substances and more RuBP regenerated
Above a certain conc. rate stops increasing
- another factor is limiting (e.g light intensity or temp)
Explain the key considerations when evaluating data relating to agricultural practices used to overcome the effect of limiting factors:
Agricultural practice should increase rate of photosynthesis to increase yield
- as more glucose produced for faster respiration
- so more ATP to release energy for growth
But profit from extra yield should be greater than costs
Why is respiration important?
Respiration produces ATP
For active transport, protein synthesis etc
Summarise the stages of aerobic and anaerobic respiration:
Aerobic:
1. Glycolysis (cytoplasm)
2. Link reaction (matrix)
3. Krebs cycle (matrix)
4. Oxidative phosphorylation (inner mitochondrial membrane)
Anaerobic:
1. Glycolysis (cytoplasm)
2. NAD regeneration (cytoplasm)
Describe glycolysis:
Glucose phosphorylated to glucose phosphate
- using inorganic phosphates from 2ATP
Hydrolysed to 2x triose phosphate
Oxidised to 2 pyruvate
- 2 NAD reduced
- 4 ATP regenerated so net gain of 2
What happens after glycolysis if respiration is anaerobic?
Pyruvate converted to lactate (animals/bacteria) or ethanol (plants/yeast)
So glycolysis can continue, allowing continued production of ATP
Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration:
Only glycolysis involved which produces little ATP
No oxidative phosphorylation which produces majority of ATP
What happeens to pyruvate after glycolysis if aerobic respiration?
Pyruvate is actively transported into mitochondrial matrix
Describe the link reaction:
Pyruvate oxidised and decarboxylated to acetate
- CO2 produced
- Reduced NAD produced
Acetate combines with coenzyme A, forming acetyl coenzyme A
Describe the Kreb’s cycle?
Acetyl coenzyme A reacts with a 4C molecule
- releasing coenzyme A
- producing a 6C molecule that enters Krebs cycle
In a series of oxidation reduction reactions, the 4C molecule is regenerated:
- 2 CO2 lost
- Coenzymes NAD and FAD reduced
- Substrate level phosphorylation so ATP produced
What are the products per glucose of the Link reaction?
2x acetyl coenzyme A
2x CO2
2x reduced NAD
What are the products per glucose molecule of the Krebs cycle?
6x reduced NAD
2x reduced FAD
2x ATP
4x CO2
Describe the process of oxidative phosphorylation:
Reduced NAD/FAD oxidised to release H atoms, which split into protons and electrons
Electrons transferred down electron transfer chain by redox reactions
Energy released by electrons used in the production of ATP from ADP+Pi (chemiosmosis)
- Energy used by electron carriers to pump protons from matrix to intermembrane space
- Protons diffuse into matrix down an eletrochemical gradient via ATP synthase
- Releasing energy to synthesise ATP from ADP+Pi
In matrix at end of ETC, oxygen is fiinal electron acceptor, so protons, electrons and oxygen combine to form water
Give examples of other respiratory substrates:
Fatty acids from hydrolysis of lipids converted to acetyl coenzyme A
Amino acids from hydrolysis of proteins converted to intermediates in Krebs cycle
