Unit 2.5 Flashcards
Explain the effect of light intensity and temperature on the rate of photosynthesis.
light: affects the light-dependent stage; at low intensities, insufficient ATP; and insufficient NADPH+H+ produced; this stops the Calvin cycle operating (at maximum rate);
temperature: affects light-independent stage / Calvin cycle; temperature affects enzyme activity; less active at low temperatures / maximum rate at high temperatures; but will then be denatured (as temperature rises further);
Explain how the rate of photosynthesis can be measured.
- CO2 + H2O –> (CH2O)n + O2/ suitable photosynthesis equation
- amount of CO2 absorbed (per unit time) can be measured
- increase in biomass (per unit time) can be measured
- O2 excretion (per unit time) can be measured
- volume of O2 (bubbles) produced per unit time can be measured
- dry mass can be measured
- increase in starch concentration in leaves (as measured by iodine)
- use of pH indicator can monitor CO2 uptake in water
- the rate of photosynthesis measured is relative because some of the CO2 is produced by the plant internally through respiration
- the rate of photosynthesis measured is relative because some of the carbohydrates are used internally by the plan for respiration
Explain the role of water in photosynthesis.
- water is a substrate / reactant / raw material / for photosynthesis / equation for photosynthesis
- water is a source of electrons
- to replace those lost by chlorophyll / photosystem II
- water is a source of H+ needed to produce NADPH + H
- photolysis / splitting / breaking of water
- water for non-cyclic photophosphorylation / ATP production
- water is transparent so photosynthesis can take place underwater / light can penetrate to chloroplasts
Photosynthesis and transpiration occur in leaves. Explain how temperature affects these processes.
- photosynthesis rate increases as temperature rises (up to an optimum temperature);
- (due to) increase in the rate of enzyme catalysed reactions/light independent
- reactions/the Calvin cycle;
- (steep) drop in rate of photosynthesis above the optimum;
- at high temperatures enzymes/Rubisco/RuBP carboxylase denature(s);
- graph with correctly labelled axes showing relationship between temperature and rate
- of photosynthesis;
- transpiration rate increases as temperature rises;
- (energy/heat leads to more) to more evaporation of water (in the leaf);
- faster diffusion of water vapour at higher temperatures;
- relative humidity falls as temperature rises / warmer air can hold more water vapour;
- stomata may close at very high temperatures reducing the transpiration rate;
- some plants open their stomata at very high temperatures to cool by transpiration;
photorespiration
Photorespiration is far less efficient at storing energy than photosynthesis. It produces only one molecule of G3P, along with a toxic phosphoglycolate molecule that the plant must expend energy to convert to a non-toxic substance.
since photorespiration binds oxygen instead. the CO2 is made which is just a waste for same amount of energy. you get only 1 G3P made per 6 cycles?? (1/2 the number of G3P made)
slows down calvin cycle
- higher photorespiration when there is high temp (that means that photorespiration still occurs at lower temperatures)
to test for photosystem II
to test for PSII, text the presence of oxygen in light
thylakoid membrane is punctured
less ATP is made, less sugar made
sun loving vs shady plant
a sun-loving plant will have more co2 uptake per light intensity than a shade loving plant but both graphs will be exponential and plateau out
high temperature
less water: photosynthesis will decrease even if the enzymes don’t denature at that point
- to conserve water, the stomata closes but CO2 doesn’t get in, there is less CO2 than there already is! The 1:4 ratio will shift to photorespiration and the graph will peak and then decrease are photorespiration occurs
light intensity
- the temperature: will plateau as the number of collisions at that temperature stabilizes the rate
- at higher light, other factors become limiting
- CO2: it plateaus since there isn’t enough substrate for the enzyme to bind (CO2 in environment is so low)
- everything limited: the enzyme concentration will limit the rate
- always positive as more light= more photosynthesis
- sometimes, some plants are adapted for different light intensities and can decrease is because
- too much light in chlorophyll can be damaged
photooxidation
damaging of the chlorophyll
other limiting factors
: chlorophyll concentration, water and pollution but water is RARELY limiting
calvin cycle
? light independent
primary electron acceptor
chlorophyll a
pigments
- during photosynthesis, chlorophyll a becomes oxidized and donates an electron to a primary electron acceptor
- carotenoids and chlorophyll b a re referred to as accessory pigments because after light absorption, they transfer this excitation energy to molecules of chlorophyll a
antenna complex
a cluster of light absorbing pigments embedded in the thylakoid membrane able to capture and transfer energy to special chlorophyll a molecules in the reaction center
reaction center
a complex of proteins and pigments that contains the primary electron acceptor
How are the Thylakoids important to photosynthesis?
The thylakoids are the site of the light dependent reactions of photosynthesis. The thylakoids themselves contain the chlorophyll, but the thylakoid membrane is where the light reactions take place. These reactions include light driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the Photosystems and cytochrome complex and ATP synthesis by the ATP synthase utilising the generated proton gradient.
adaptations for photosynthesis
- the top layer epidermis is so much compared to other plants so water doesn’t evaporate
- sunken stomates, thicker waxy cuticle, trichomes in the stomatal crypt
- there is also a very thick waxy cuticle on the surface of the leaf
- lower epidermis is collapsed in sunken pits. the guard cells care found inside the pits. when water evaporates out, it evaporates into the sunken pits. since wind increases the transpiration rate, the moist air is trapped which prevents further evaporation from taking place. the little hairs (tricones) prevent the wind from getting inside
- this won’t be able to survive as well in cold environment as the thick skin may stop the light from getting through as efficiently
what happens to a plant during dehydration:
- a decrease on chlorophyll causes lowered rate of light dependent reactions/less absorption of light energy
- decrease in CO2 take up causes lowered rate of light independent reactions/less CO2 fixation/Calvin cycle
- both stages reduced due to wilting/less surface of leaf/closure of stomata
c3 plants are best in
cool, wet environments where stomata can remain open and no adaptations for weather
c4 plants are best in
hot, sunny environments where there is separation of co2 between mesophyll and bundle sheath cells, stomata open during day
CAM plants are best in
very hot and dry environments. stomata remain open at night and there is a separation between day and night
light dependent reactions
- h20 splits to make o2
- h+ is a good source of electrons
- NADPH + H+ carries these h+ to the calvin cycle
z scheme
- there are two photosystems in the thylakoid membrane (PSII and PSI)
- first one is photosystem II since bacteria only have one photosystem the photosystems will be stimulated by slightly different wavelengths of red light but slightly different version of the reaction center chlorophylls and the ETC they are associated with
- reaction center contains actually two chlorophylls which is why two electrons are boosted to a higher energy level
locations of calvin cycle
stroma
