Topic 8: Metabolism, cell respiration, photosynthesis Flashcards
Explain photophosphorylation in chloroplasts. [8]
- Energy from light provides energy
- Photoactivation produces an excited electron
- Absorption of light in PSII gives electron to a chain of carriers
- Photolysis
- H+ pumped across thylakoid membrane
- Protons pass through ATP synthase to produce ATP
- Chemiosmosis
- PSI absorbs light
- Non-cyclic: photolysis of water produces H+
- Cyclic: electron returns to photosystem I
Outline photoactivation of photosystem II in the light-dependent reaction of photosynthesis. [2]
- Light absorbed by pigment molecules in chlorophyll
- Electrons passed to chlorophyll in the reaction center
- Electrons become excited
- Electron passed along chain of carrier molecules in PSII
Explain the effect of inhibitors on the activity of enzymes. [8]
Both reduce enzyme activity/rate of reaction
Competitive: similar shape to substrate, binds to active site, prevents substrate binding, e.g. succinate dehydrogenase by malonate, increase in substrate conc returns normal rate
Non-Competitive: different shape to substrate, attaches to allosteric site, changes active site shape, e.g. respiratory enzymes by cyanide, increase in substrate conc. does not return normal rate
Explain the process of aerobic cell respiration after glycolysis has occurred. [8]
- Pyruvate produced by glycolysis
- Pyruvate enters mitochondria
- Loses CO2 in link reaction
- Formation of acetyl CoA
- Takes part in Krebs cycle
- each pyruvate molecule produces: 2 CO2, one ATP from ADP + Pi, three NADH, 1 FADH2
- NADH provides electrons circulating in electron transport chain on the inner mitochondrial membrane
- H+ accumulates in the inner membrane space
- Come back into matrix via ATP synthase to produce by chemiosmosis
- O2 is the last electron acceptor
Explain how chemiosmosis assists in ATP production during oxidative phosphorylation. [9]
- Aerobic respiration
- Oxidative phosphorylation occurs in the electron transport chain
- Electrons passed between carriers
- Releases energy
- Joins with O2 to form H2O
- Occurs in cristae
- Chemiosmosis is the movement of protons
- Along a conc. gradient
- Into the space between two membranes
- Protons flow back to the matrix
- Through ATP synthase
- Energy released to produce more ATP
Outline the importance of enzymes to metabolic processes. [4]
- increase rate of reaction
- lowers activation energy
- specific enzyme for each substrate
- metabolic process blocked if enzyme is inhibited
- end-product inhibition controls metabolic pathways
Explain the processes by which light energy is converted into chemical energy. [8]
- plants convert light to chemical energy via photosynthesis
- chlorophyll absorb light
- electrons excited
- pass along chain of electron carriers
- energy from electrons pump protons across thylakoid membrane
- chemiosmosis used to make ATP
- ATP synthase generates ATP
- electrons from PSII flow to PSI
- electrons from PSI reduce NADP
- ATP and reduced NADP used in Calvin cycle (light independent)
- glucose containing energy produced
Explain how chemical energy for use in the cell is generated by electron transport and chemiosmosis. [8]
- NAD reduced by gaining 2 hydrogen
- reduced NAD produced in glycolysis
- delivers electrons to ETC
- in inner membrane
- electrons release energy as carried from carrier to carrier
- electrons carriers act as proton pumps
- protons pumped into intermembrane space
- energy released as protons travel down the gradient
- ATP synthase converts ADP to ATP + Pi
Describe photolysis in photosynthesis. [3]
- water is split
- using energy from light
- electrons pass through PSI
- oxygen is a waste product
- hydrogen ions produced
Explain chemiosmosis in photophosphorylation. [8]
- phosphorylation is production of ATP
- light absorbed by chlorophyll
- photolysis
- electrons transport chain moves electrons through a series of carriers
- occurs in thylakoid membrane
- proton gradient builds up in thylakoid space
- hydrogen ions move by diffusion through ATP synthase
- ADP + Pi forms ATP
- movement of hydrogen ions generates ATP
The light-dependent reactions in photosynthesis take place on the thylakoid membranes. Explain the light-dependent reactions. [8]
- Chlorophyll in PSII absorbs light
- photoactivation produces excited electron
- electron passed from carrier to carrier in ETC
- protons pumped across thylakoid membrane
- ATP produced
- ATP production by chemiosmosis by ATP synthase
- electrons from PSII passed to PSI
- photoactivation of electrons in PSI
- reduces NADP
- electrons from photolysis needed for PSII
- oxygen from photolysis is a waste product
- cyclic photophosphorylation: electrons from PSI return to it
Outline two factors that affect the rate of photosynthesis. [5]
1) Increase in light intensity increases rate
- until another factor is limiting
- light is needed for light dependent reactions
2) Increase in temperature increases rate
- to an optimum temperature above which the rate drops
- temperature affects enzyme activity
3) Increase in CO2 conc. increases rate
- until another factor is limiting
- CO2 is needed for light-independent reactions
Explain the light-independent reactions of photosynthesis. [9]
- Calvin cycle
- take place in chloroplast stroma
- produce carbohydrates
- CO2 fixed to RuBP by rubisco
- forms unstable 6 carbon compound
- splits into two molecules of G3P
- ATP and NADPH produced in light-dependent reaction
- ATP provides energy
- NADPH provides hydrogen
- GP reduced to triose phosphate
- some three carbon sugars form hexose sugars
- some make more RuBP
Outline the process of glycolysis. [5]
- occurs in cytoplasm
- hexose phosphorylated using ATP
- hexose phosphate separated into 2 triose phosphates
- reduction of NAD to NADH
- net gain of 2 ATP
- 2 pyruvates formed
Explain the relationship between the structure of the mitochondria and its function. [3]
- enzymes in the matrix for Krebs cycle
- cristae provides surface area for oxidative phosphorylation
- inner membrane contains ETC and ATP synthase
- small intermembrane space for higher conc. of protons
