Photosynthesis Flashcards
Limiting factor
- factor which controls the rate
- increasing this factor increases the rate of photosynthesis
- factor not at optimum
Two environmental conditions that need to be controlled when investigating photosynthesis
- temperature, use a water bath
- CO2, add sodium hydrogen carbonate
- pH, use a buffer
- wavelength of light, use filter
How determine rate of photosynthesis
- equilibrate before timing
- remove bubbles from capillary tube at start
- use syringe to move O2 bubble into capillary tube
- measure bubble
- determine volume of O2
- rate calculation
- repeats to give reliable results
How ATP is made available by reactions in the chloroplast
- light is absorbed (harvested)
- by chlorophyll pigments (a and b)
- electrons excited to higher energy level
- electrons passed to electron transport chain (electron carriers)
- energy is lost from electrons
- energy released is used for ATP production
- photophosphorylation
- photolysis (splitting of water) provides electron source
Two products of photosynthesis that require phosphate ions
- rNAD
- ATP
Describe one method you could use to estimate the abundance of an organism at intervals along a transect line
- place quadrat at intervals
- calculate percentage cover or count the number of vegetation present
- belt transect
- systematic sampling
Abiotic factor that could determine the distribution of plants
- pH
- water
- minerals and nurtients
Describe the process of non-cyclic phosphorylation
- takes place on the thylakoid membrane
- function is to produce ATP need for synthesis of carbohydrates and for photolysis and produce rNADP
- light energy absorbed by PSII
- light energy excites electrons in chlorophyll (photosystem) to a higher energy level
- electrons from PSII pass along electron carriers to PSI
- PSI absorbs light, electrons are boosted to a higher energy level and pass down electron carriers
- electrons lose energy which is used to synthesise ATP
- energy is used to transport H+ into the thylakoid - forming proton gradient. H+ moves in the stroma via ATPase, which combings ADP + Pi to form ATP
- lost electrons from PSII need to be replaced, photolysis of water to produce 2e- and 2H+ and O2
- electrons excited from PSI combine with H+ from photolysis of water and are used to reduce an NADP
Describe what happens to the products of non-cyclic phosphorylation
- oxygen produced diffuse out of leaf or used in respiration
- ATP and rNADP enters the calvin cycle (light independent stage)
- used to synthesise carbohydrates
Describe the process of the light independent reaction
- takes place in the stroma
- function to reduce CO2 to form carbohydrates
- CO2 enters leaf through stomata and diffuses to stroma
- CO2 combines with 5C RuBP, catalysed by RuBISCO, forming a 6C compound
- 6C compound is unstable and breaks down in two 3C GP
- 3C GP is reduced to 3C GALP, using ATP and rNADP from light dependent reaction (forming ADP + Pi and NADP)
- cycle has to turn six times to produce one molecule of glucose
- 2/12 GALP are used to from 6C sugar
- 10/12 GALP are used to regenerate 5C RuBP using ATP from light dependent reaction
What can GALP and GP be used to synthesise
- amino acids
- nucleic acids
- carbohydrates
- lipids
Structure of a chloroplast
- stroma
- starch grain
- thylakoid (membrane) / chlorophyll
- granum
Where is oxygen produced in the chloroplast
- thylakoid (O2 formed from photolysis of water)
Explain how oxygen is produced in chloroplasts during photosynthesis
- photolysis of water (splitting of water using light energy)
- release of electrons to chlorophyll (to PSII) to replace lost electrons
- release of H+ ions
- release of oxygen
Describe and explain the effect of high concentrations of oxygen on the rate of carbohydrate production in a chloroplast
- a high oxygen concentration reduces production of carbohydrates
- more oxygen, less CO2 in atmosphere
- less carbon available for reduction to carbohydrate
- less CO2 is fixed
- RuBP is required to combine with CO2
- calvin cycle cannot occur
- enzyme RuBISCO cannot function
Environmental conditions which could increase the rate of oxygen production by plants
- high light intensity (for photolysis of water)
- change in wavelength
- high temperature, humidity
- high CO2 concentration
Why is it necessary to use a quadrat to estimate percentage cover
- fixed constant area
- valid comparison possible
- easy so can be repeated
- sampling method
Why might a transect be more appropriate than random sampling
- sampling along changing conditions
- systematic sampling/random sampling does not show distribution
Photolysis
- splitting of water using light
- water —> 2H+ + O + 2e-
Describe the role of the electrons in the light dependent reaction of photosynthesis
- light energy promotes electrons to a high energy level (excited)
- electrons pass along electron carriers, losing energy in redox reactions
- energy used to synthesis ATP
- electrons from photolysis used to replace lost electrons from PSII
- electrons from PSI combine with H+ to reduce NADP
Describe and explain how the products of the light dependent reaction are involved in the production of GALP
- CO2 combines with 5C RuBP, catalysed by enzyme RuBISCO
- 6C compound breaks down to into two 2C GP
- GP is reduced using H from rNADP
- using ATP produced in the light dependent reaction as a source of energy
GALP does not accumulate in a chloroplast during photosynthesis. Explain how GALP is used following its production
- 10/12 GALP used to regenerate RuBP
- 2/12 GALP used to form glucose
- or starch, amino acids, nucleic acids, lipids, carbohydrates
Describe the structures in a chloroplast that are involved in the light-dependent reaction
- thylakoid membranes are interconnected flattened fluid-filled sacs
- photosynthetic pigment (chlorophyll) and electron carriers are embedded in the membranes
- a granum is made up of stacks of thylakoid
Describe the structures in a chloroplast that are involved in the light-indepent reaction
- stroma, fluid surrounding the thylakoid membrane
- contains enzymes needed to carry out light-independent reactions
Suggest advantages of growing crops in glasshouses with artificial lighting rather than growing them in open fields
- crops can be grown all year
- plants photosynthesise 24 hours a day
- less physical damage from weather
- pest control easier
- can control temperature, humidity, water supply
Explain how a quadrat would be used to obtain the mean density of the two species of periwinkle in each area
- more than two readings
- use random quadrat positions
- number of individuals in each quadrat counted
- mean density calculated using total count dived by total area
