Photosynthesis Flashcards
Suggest why plant leaves contain a mixture of pigments
- pigments absorb a wider spectrum of light
- more light energy absorbed for photosynthesis
Describe the effect of changing temperature on the rate of oxygen production in photosynthesis
- minimal since photolysis does not use enzymes
- may increase respiration rate (controlled by enzymes)
- respiration uses oxygen
Describe the purpose of the light dependent reaction of photosynthesis
- capture light energy
- for electron transfer chain to provide energy for synthesis of ATP
- for photolysis of water
Describe the stages of the light dependent reaction of photosynthesis
- photoionisation of photosystem II
- photon absorbed by chlorophyll molecules causing e- to be excited to a higher energy level
- (e- replaced by photolysis of water)
- taken up by e- carriers forming e- transfer chain
- passed by series of oxidation reduction reactions
- energy released drives proton pumps which move H+ from stroma into thylakoid interior
- photolysis of water further increases [H+]
- chemiosmosis of H+ down electrochemical gradient through ATP synthase into stroma
- ATP synthase changes shape to produce ATP
Suggest what is meant by the electron transfer chain
- e- passed along e- carriers down energy gradient
- each e- carrier is a slightly lower energy level than previous
- energy lost at each stage
- series of oxidation-reduction reactions
Suggest role of electrons released from photolysis of water
- replace lost electrons from chlorophyll
- due to photoionisation + e- transport chain
Suggest adaptations of chloroplast for light dependent reaction
- thylakoid membrane has a large surface area for attachment of chlorophyll, e- carriers + ATP synthase
- selectively permeable membrane allows protons to cross only through ATP synthase
- DNA + ribosomes to synthesis carrier proteins
Suggest what happens to H+ and electron produced from photolysis of water in light dependent reaction
- H+ accumulate into thylakoid space + moves by chemiosmosis to stroma via ATP synthase
- electrons replaced lost electrons from chlorophyll in PSII
- (passed along e- transport chain and NADP forms reduced NADP by accepting H+ and electron)
Non Cyclic Phosphorylation
- involves both PSI and PSII
- e-s travel between e- carriers along e- transport chain
- e-s accepted by NADP+
- photolysis occurs
- ATP, NADPH + O2 produced
Cyclic Phosphorylation
- involves only PSI
- e-s travel to cytochrome complex then back to PSI
- do not form NADPH or O2
- photolysis absent
- e-s lose some energy which pumps H+ across thylakoid membrane driving the production of ATP by ATP synthase
Suggest the purpose of cyclic phosphorylation
- produce ATP when no NADP is available
Suggest products of light dependent reaction
- ATP
- NADPH
Describe the stages of the light independent reaction of photosynthesis
- carbon fixation occurs when RuBP (5c) combines with CO2 catalysed by Rubisco
- forms two molecules of glycerate-3- phosphate (3c)
- energy from ATP (x2) and NADPH (x2) is used to reduce GP to triose-3-phosphate (3c)
- energy from ATP (X1) converts most of TP to RuBP
- one carbon per cycle used to produce organic products
Suggest adaptations of chloroplast for light independent reaction
- stroma has DNA + ribosome to synthesise enzymes
- stromal fluid is membrane bound to maintain a high concentration of enzymes and substrates
- stromal fluid surrounds grana so products can readily diffuse into stroma
Suggest why a flat sided flask is used to measure stages of the Calvin cycle
- most light energy absorbed/ less reflected
Suggest why hot methanol is used to measure stages of the Calvin cycle
- stops chemical reactions instantly
- enzymes denature
Describe how to carry out an experiment to measure stages of the Calvin cycle
- algae placed in flat sided flask and supplied with CO2 labelled with radioisotope 14C
- immediately after light is turned on samples are taken at 5 second intervals
- using a fast action valve and fixed by hot methanol
- double way chromatography and autoradiography used to identify carbon intermediates containing 14C
Suggest limiting factors of photosynthesis
- carbon dioxide concentration
- light intensity
- temperature
Give a reason a certain factor is limiting photosynthesis
- directly proportional
- as factor increases so does rate of photosynthesis
Give reasons why not all the light falling on leaves is used in photosynthesis
- most reflected
- wrong wavelength
- misses chloroplasts
- another factor may be limiting
Suggest ways to measure rate of photosynthesis
- volume of oxygen produced per unit time
- change in mass of plant
Explain how the use of radioactive CO2 allows biochemical changes in photosynthesis to be followed
- radioactive CO2 incorporated
- organic intermediates labelled
Suggest why a fast action valve is used to measure stages of the Calvin cycle
- allows samples to be taken at short intervals
- reactions occur quickly in photosynthesis
Suggest why the level of radioactivity in organic intermediates in light dependent reaction remain constant after a period of time
- maximum amount of radioisotope incorporated in cycle
- organic intermediates used and reformed
Explain what causes the amount of radioactively labelled glucose to decrease after the light is turned off
- used in respiration
- stored as starch
Describe the role of products of light dependent reaction of photosynthesis
- used in light dependent reactions
- H+ from NADPH reduces GP to TP
- ATP supplies energy for reduction of GP
Limiting factor
limits rate when lower than optimal level (give example to explain)
