Module 5: Energy for biological processes (Photosynthesis) Flashcards
Compensation Point:
The volume of oxygen produced is equal to the volume used for aerobic respiration.
What is meant by photosynthesis and aerobic respiration being complementary reactions?
Products of photosynthesis are the reactants of aerobic respiration vice versa.
Producers:
Photoautotrophs use photosynthesis and cell respiration. Source of biomass for food web
Consumers:
Heterotrophs, undertake cell respiration and ingest/absorb photosynthetic products.
Photosynthesis: Type of process
Anabolic process
Cell respiration: type of process
Catabolic process
Photosynthesis: Summary
Water is broken down into oxygen to release electrons for an electron transport chain. Electrons from the transport chain are taken up by hydrogen carriers. ATP is synthesised through chemiosmosis. Uses Calvin cycle to synthesise glucose.
What is the name of the cycle used to synthesise glucose:
Calvin Cycle
Is photosynthesis endothermic or exothermic?
Endothermic
Is cell respiration endothermic or exothermic?
endo -Use of Krebs of cycle to break down glucose
endo - Hydrogen carriers to release electrons for an electron transport chain
exo -Electrons from transport chain taken up by oxygen to form water.
exo -Hydrolysis of ATP
(overall exothermic)
Similarity between Respiration and photosynthesis:
ATP PRODUCTION
Both produce ATP - In photosynthesis ATP is produced via transducing light energy (photophosphorylation) and used to make organic molecules.
Similarity between Respiration and photosynthesis:
Electron transport chain
Production of ATP involves an electron transport chain and chemiosmosis in both.
- photosynthesis- electrons are donated by chlorophyll and protons accumulate in the thylakoid lumen
- Cell Respiration - electrons are donated by hydrogen carriers and protons accumulate in the intermembrane space
What is the stroma?
The central cavity that contains appropriate enzymes and suitable pH for the Calvin cycle to occur
What is a thylakoid?:
Flattened discs that have a small internal volume to maximise hydrogen gradient upon proton accumulation. ETC and ATP synthase for phosphorylation. Location of the light dependent phase of photosynthesis.
What is the grana:
Thylakoids are arranged into stacks to increase SA;Vol ratio of the thylakoid membrane.
What are photosystems:
Pigments organised into photosystems in the thylakoid membrane to maximise light absorption.
What are the lamellae
Connects and separates thylakoid stacks, maximising photosynthetic efficiency.
What is located in the stroma?
Starch, lipid, ribosomes, chloroplast DNA.
Where are chlorophyll pigments located?
They are sandwiched within lipids and proteins in thylakoid membranes.
What molecules are with the pigments:
Enzymes and electron-carrier molecules.
Which pigment is a primary pigment:
Chlorophyll a
What do antennae pigments do?
Funnel energy to primary pigments to excite electrons.
Absorption Spectrum:
Wavelengths absorped by each pigment
Action spectrum:
Overall rate of photosynthesis at each wavelength.
What is a pigment made up of?
Chlorin ring and hydrocarbon tail.
Chlorin ring:
light reacting component (magnesium centre) of chlorophyll
Purpose of hydrocarbon tail in pigment?
Anchors chlorophyll molecule to thylakoid centre.
Photosystem:
Light harvesting system that absorbs and funnels energy to a primary pigment to excite a delocalised electron which is transferred to an electron acceptor molecule.
Role of chlorophyll a:
Excite and release an delocalised electron
What do electron acceptors do in a photosystem?
Synthesise ATP
How can photosystems be differentiated?
By the wavelength of light absorbed at the photosystem’s primary pigment.
What is chemiosmosis?
The movement of ions across a partially permeable membrane down their electrochemical gradient.
What is the purpose of proton pumps in chemiosmosis?
To create an electrochemical gradient through the active transport of protons across the thylakoid membrane.
What is the purpose of accessory pigments?
To form a light harvesting system which absorbs light energy which is funnelled to the primary pigment, releasing high energy electrons.
What are the components of a light harvesting system?
The light harvesting system and the reaction centre
What is the effect of proton pumps on the location of protons in chemiosmosis?
There are more protons inside the thylakoid than the stroma, creating an electrochemical gradient.
Why is the electrochemical gradient important in chemiosmosis? (photosynthesis)
Allows the protons to diffuse out of the thylakoid space into the stroma through ATP synthase embedded in the thylakoid membrane.
Where is the light dependent stage of photosynthesis located?
The thylakoid membranes.
What is the purpose of a photosystem in photosynthesis?
To excite an electron and pass it through an electron transport chain to synthesise ATP through chemiosmosis.
What is meant by ATP releasing energy in a coupled reaction?
Energy is initially released through the hydrolysis of ATP by ATPase and then energy is used during phosphorylation.
How do electrons get excited?
Electrons absorb light energy, released when chemical bonds are broken, pass into electron transport chain to form a proton gradient.
Electron Transport Chain: Waterfall Model
Electrons pass from carrier to carrier have a progressively lower energy level.
Energy released.
Pump protons gradient
Maintained by an impermeability to H+
Protons must move through hydrophilic membrane channels linked to ATP synthase.
Providing energy to resynthesise ATP from ADP and Pi.
Photophosphorylation via Chemiosmosis:
The use of light energy from photosynthesis is used to establish a proton gradient to phosphorylate ADP into ATP.
What are the two hydrogen carrier macromolecules:
NAD and NADP
What do NAD and NADP carry?
Hydride ions
What are hydrogen carriers?
Organic macromolecules that transport hydrogen atoms from one place to another for use in metabolic processes.
What type of photophosphorylation only uses photosystem 1?
Cyclic- photophosphorylation
What type of photophosphorylation uses both photosystems 1&2:
Noncyclic- photophosphorylation
What is the main function of the light dependent phase?
To use light and photosynthetic pigments to release ATP and reduce NADP to supply the Calvin cycle.
What is the light dependent phase:
The use of photosynthetic pigments to convert light energy into chemical energy.
What are the key stages of the light dependent stage?
Excitation of photosystems by light energy
Production of ATP by chemiosmosis
Reduction of NADP
Where does photolysis take place:
An enzyme bound to photosystem 2
What are the products of photolysis and what are they used for?
2H+ Reduces NADP into NADPH
e- Replace electrons lost by PS2
1/2 O2 By-product
What is the name of the system excited electrons travel through in the thylakoid membrane from PS2 to PS1 across proton pumps?
An electron transport chain
What is photophosphorylation?
The production of ATP using light as the initial energy source.
Where do electrons released by PS2 go once they are deenergised after an electron transport chain?
PS1
What are the 3 factors affecting the rate of photosynthesis?
Temperature, CO2 concentration and light intensity.
How does light intensity affect the rate of photosynthesis?
Light is utilised in the photolysis of water to allow for chemiosmosis through non-cyclic photophosphorylation. Light is also used for the excitation of electrons in photosystems.
Why is light intensity a necessary factor?
Light is required to produce ATP and NADPH which is required for the reduction of GP and regeneration of RuBP.
What is the effect of light intensity being limited?
Less light dependent reaction -> less ATP and NADPH -> less reduction of GP and regeneration of RuBP -> build up of GP
How does CO2 concentration affect the rate of photosynthesis?
The CO2 provides a source of carbon for fixation in the Calvin Cycle.
Why is CO2 a necessary factor?
Carbon fixation is dependent on CO2 and-so is required for TP synthesis.
What is the effect of CO2 concentration being limited?
Reduced carbon fixation -> less GP -> Less TP -> Less glucose produced
Reduced Carbon fixation -> buildup of RuBP
How does temperature affect the rate of photosynthesis?
The temperature affects enzyme controlled reactions e.g carbon fixation and photolysis.
Photorespiration occurs at higher temperature due to build-up of O2 in leaves -> reduces photosynthetic efficiency.
Why is temperature a necessary factor?
- Achieving the activation energy for reaction
- Freq. of successful collisions.
- Enzyme Action -> increases rate significantly
- Photorespiration -> reduces photosynthetic efficiency.
What is the effect of temperature being limiting?
Either:
Less kinetic energy -> fewer successful collisions.
Too high kinetic energy -> denaturing of enzymes -> change in shape of active site -> prevents reaction.
+-> Photorespiration
How many CO2 molecules are required to form 1/2 a glucose molecule?
3 molecules
How many carbons are in GP?
3 carbons
How many GP molecules are required to form 1/2 a glucose molecule?
6 molecules
How many carbons are within a TP molecule?
3 carbons
How many molecules of TP leave the cycle to form 1/2 glucose?
1 molecule
Which parts of the Calvin Cycle require ATP?
The reduction of GP into TP, using 6ATP and 6NADPH#
The regeneration of RuBP using 3 ATP
How many TP molecules are used to regenerate 3 RuBP molecules?
5
How many carbons are within RuBP?
5
What is a limiting factor?
A required factor in short supply.
What molecule competitively inhibits Rubisco?
O2
Photorespiration (IN DEPTH):
Occurs at high and dry temperatures -> stomata close. CO2 conc. decreases + O2 conc. increases
O2 competitively inhibits rubisco and produces products that can’t produce sugars. -> decreases efficiency of Calvin cycle and reduces the energy yield.
What is the enzyme that catalyses the fixation of CO2 to RuBP?
Rubisco
What are the two direct methods of measuring photosynthesis?
Measure uptake of carbon dioxide in a unit time
Measure production of oxygen in a unit time
What is an indirect method of measuring photosynthesis?
Change in biomass in a unit time - dry mass per year
What is the hydrogen carrier in photosynthesis?
NADP
What is NADP reduced into?
NADPH
