Photosynthesis Flashcards
How does photosynthesis supply energy to heterotrophs
Photosynthesis is the process used by autotrophs that utilises sunlight energy, converting it to chemical energy that makes it available to heterotrophs.
Compensation point
rate of O2 production from photosynthesis = rate of O2 uptake from respiration
What came first photosynthesis or respiration
There was no free oxygen in the atmosphere on Earth until about 2 billion years ago, after oxygenic photosynthesis had evolved – oxygenic photosynthesis used water as a raw material and broke it down, releasing free oxygen
How is the chloroplast specialized to carry out photosynthesis
Many grana consisting of many thylakoid membranes gives large surface area for pigments,
electron carriers and ATP synthase enzymes for light-dependent stage.
Stroma has enzymes for light-independent stage. Stroma close to grana so products of first stage can pass to stroma for second stage.
Oil droplets in stroma as source of lipids to make membranes.
Ribosomes for protein synthesis of enzymes/electron carriers/anchoring proteins.
DNA – genes coding for some chloroplast proteins.
The role of water in photosynthesis
Electron donor; source of protons/hydrogen ions; source of by-product, oxygen; keeps cells turgid so they can function (all metabolic reactions need to be in solution)
DCPIP
Accepts electrons from photosystems/ chlorophyll in illuminated chloroplasts
How can a lack of nitrate ions in the soil affect the levels of RubisCo
RuBisCO is an enzyme and therefore a protein, for which nitrogen is needed, obtainable by plant from nitrate ions in soil
Why does illumination of chloroplasts lead to optimum conditions for the enzyme RuBisCo
As protons are pumped into the thylakoid space, out of the stroma, the pH of the stroma rises to 8, optimum for RuBisCO. The light-dependent stage produces ATP and this activates RuBisCO. Concentration of Mg2+ increases in the stroma and this acts as (metallic ion) cofactor and activates RuBisCO. Reduced ferredoxin (reduced by accepting electrons lost from illuminated PSI) activates enzymes that catalyse steps in the Calvin cycle.
Why do levels of LI stage fall when light intensity falls below a certain level
Insufficient light intensity stops the light-dependent stage. This stops the flow of NADP and ATP so the light independent stage cannot run. Without ATP and reduced NADP, TP cannot be made from GP. GP accumulates. TP drops. RuBP cannot be regenerated from TP so RuBP drops.
How do plants respond to water stress and how does this affect their ability to photosynthesize
Leaves lose more water by transpiration than can be replaced by uptake at roots. Cells lose water/become plasmolysed. Tissues become flaccid. Leaves wilt. Roots are unable to take in water and secrete abscisic acid, which travels in xylem to leaves causing stomata to close to prevent further water vapour loss. Closed stomata reduce gaseous exchange so not enough carbon dioxide for photosynthesis. Plasmolysed cells cannot function as enzymes cannot work. Reduced water availability for photosynthesis – as source of electrons and protons.
Why do the leaves float (experiment)
Accumulation of oxygen in the air spaces of the spongy mesophyll reduces their density.
What would happen to the leaf discs if they were illuminated with a) red light b) blue light c) green light
Float up quickest with red light as that wavelength absorbed in greater amounts by chlorophyll; then blue light as chlorophyll has another peak of absorption in blue light; slow if at all with green light – chlorophyll does not absorb green light, some accessory pigments absorb a little
How does air move out of the leaf
Air spaces in spongy mesophyll, out via open stomata
Outline how a student could carry out a chromatography experiment to determine the pigments present in the leaves of one type of plant
1) Extract some of the plant’s leaves by grinding up the leaves and adding e.g. anhydrous sodium sulfate, a few drops of propane, and then some petroleum ether
2) Take some of the liquid pigment extracts and build up a concentrated spot/point of origin on a thin layer chromatography plate
3) Put a lid on the beaker and leave it to develop
4) When the solvent has almost reached the top of the plate, remove the plate and mark the solvent front
5) Calculate the Rf values of the separated pigments in order to identify them
Explain safety precautions the student should take in a chromatography experiment when investigating the different pigments present in leaves
Wear gloves/ glasses as some of the chemicals involved are toxic
