Photosynthesis Flashcards
Describe features in the cross-section of a leaf
- lots of chloroplasts that can move, large vacuole so pushed to the edge & vertically arranged so light can reach all.
-epidermis= thin & transparent so light can travel
-thin waxy cuticle to prevent water loss without blocking light
-palisade layer at top to absorb more light and increase rate of photosynthesis
-spongy layer has air spaces to allow gases to diffuse
-palisade layer has many chloroplasts to absorb all available light
What structures do chloroplasts contain?
Outer membrane
Inner membrane
Stroma
Thylakoid
Grana/granum
Lamella
They also have DNA and ribosomes similar to prokaryotic cells and are semi-automonous as they can synthesis some of their own proteins
What is ATP composed of?
Adenine, ribose, and 3 inorganic phosphates joined via high energy bonds
Describe the LDR
-Light energy hits the chlorophyll in the thylakoid membrane and it absorbs it which excites and raises the energy levels of electrons in chlorophyll via photoionisation.
-electrons pass down the electron carriers in the electron transfer chain at decreasing energy levels
-. The electron and proton from chloroplasts then join with NADP reducing it to NADPH at the end of the electron transfer chain.
-Whilst electrons moved down energy levels, some energy was lost as heat and used for proton pumping.
-As chlorophyll lost electrons in photoionisation its unstable so spits out water to form oxygen while releasing electros and protons via photolysis. -These protons are pumped from the stroma to the inside of the thylakoid via the proton pump in the thylakoid membrane.
-Inside the thylakoid, a proton gradient builds up, its higher inside than out so they moved down the conc gradient to the stroma via ATP synthase and the process of chemiosmosis,
-releasing energy that is coupled to phosphorylation of ATP from ADP and Pi.
How is ATP made from the LDR (5 marks)
- Light energy excites and raises the energy levels of electrons in chlorophyll
- Electrons pass down the electron transfer chain
3.electrons reduce carriers
4.they pass down the electron transfer chain in the thylakoid membrane and energy releases as they move down the decreasing energy levels
5.the energy is coupled to ATP synthesis from ADP and Pi
Describe the process of the LIR
-CO2 (a 1c molecule) joins with RuBP (a 5c molecule) to form 2 GP (3c) molecules. This is carbon fixation and catalysed by the enzyme Rubisco
-the 2 GP molecules are further reduced to 2 triose phosphate (3c) molecules via the oxidation of NADPH to NADP (which donates its H and goes back to the LDR) and use of energy from ATP (which is released when ATP is hydrolysed to ADP + Pi).
-5/6ths of the triose phosphate molecules are used to regenerate the RuBP (5c) molecule and the other 1/6th is used to make useful organic substances like glucose. (For glucose the cycle happens 6 times)
Discuss factors affecting the rubisco enzyme in the LIR
Temperature, PH, substrate concentration, enzyme concentration, inhibitors and heat stress
Describe heat stress and how it affects photosynthesis
A condition that occurs in plants exposed to high temperatures for a prolonged period of time.
It’s a major factor in limiting photosynthesis rate as it leads to a decrease in the LIR as it needs NADPH and ATP which is produced from the LDR.
Describe the steps of the Calvin cycle
->experiment conducted by Melvin Calvin to identify reactants of LIR - lollipop experiment:
-> algae grown in radioactive hydrogen carbonate as a carbon source for photosynthesis meaning carbon-14 would be incorporated into the compounds produced via photosynthesis.
-Radioactivity can be detected by autoradiography so compounds revealed could show the steps of LIR.
-once the algae had been supplied with the radioactive carbon source and exposed to light they started photosynthesising and a sample was taken every 5 seconds and dropped into hot methanol to kill the algae and stop all chemical reactions.
-the compounds found in the dead algae could be separated by two-way chromatography, and those that were radioactive were detected by autoradiography.
-by comparing the radioactive compounds after different lengths of time, the order in which the compounds are generated is determined.
What are the factors affecting photosynthesis
Temp, CO2 conc, light intensity, and wavelength of light
Discuss temp as a limiting factor of photosynthesis
-the rate of photosynthesis steadily rises as temp increases, reaching an optimum and then dropping down.
-this could be due to the Rubisco enzyme which catalyses carbon fixation in the LIR, as temp gets high the proteins denature and H bonds are distorted changing the tertiary structure so its no longer complementary and can’t form e-s complexes. So rate decreases as it can’t be catalysed. But prior to the drop there’s more kinetic energy so more collisions between RuBP and CO2 .
Describe CO2 as a limiting factor of photosynthesis
-raising CO2 means there’s more availability to bind with the RuBP in an enzyme-substrate complex in carbon fixation to produce GPin the LIR, so rate of photosynthesis steadily rises until v-max is reached before it steadily plateaus . From v-max more cO2 wont have an affect as there’s a different limiting factpor
-raising CO2 means there’s more availability to bind with the RuBP in an enzyme-substrate complex in carbon fixation to produce GPin the LIR, so rate of photosynthesis steadily rises until v-max is reached before it steadily plateaus . From v-max more cO2 wont have an affect as there’s a different limiting factor
Describe light intensity as a limiting factor of photosynthesis
-as light intensity increases , so does the rate of photosynthesis, this happens qui9ckly to begin with before slowing down, reaching v-max and plateauing as a different factor becomes limiting. The initial increase may be more to more light energy hitting the chlorophyll so more photolysis and more o2 produced
Describe agricultural practices in greenhouses not overcome effects of limiting factors
-artificial lighting day and night
-heater/parafin heater
-glass traps heat
-ventilation
-automated watering systems
-biological control - predator prey..
Describe agricultural practices in open fields to overcome effects of limiting factors of photosynthesis
-weed killer to avoid shading and competition for minerals
-selective breeding e.g. drought tolerance
-global warming effect - increased temp may increase photosynthesis but it also increases respiration so its counterproductive.
