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Physiology - Photosynthesis

	What pigment captures the light which is transformed to chemical energy?
	chlorophyll

	Where does it have to be in order to achieve this transformation?
	in a photosystem in a granum of a chloroplast

	What process in these reactions is similar to a process in respiratory energy metabolism?
	an electron transport system

	Why would it be difficult for plants to survive with cyclic photophosphorylation alone?
	It only generates ATP and NADPH is required to make sugar.

	What are the inputs and outputs for non-cyclic photophosphorylation?
	light, water, NADP, ADP and phosphate in oxygen, NADPH, and ATP out

	Are the reactions of the Calvin cycle "dark reactions"
	Not really, they need the ATP and NADPH from the light reactions.

	What three uses does the plant have for the chemical energy from the light reactions?
	reduction of carbon, nitrogen and sulfur

	Where does the Calvin cycle occur?
	in the stroma (liquid phase) of the chloroplast

	What is the key enzyme in this pathway, what are its substrates and products?
	Ribulose 1,5-bisphosphate carboxylase (rubisco) Ribulose 1,5-bisphosphate (RuBP) and CO2 to phosphoglycerate (PGA)

	What happens to the products?
	PGA is reduced by NADPH to 3-carbon sugar and this goes through various sugar intermediates to return to RuBP and make some hexose (glucose).

	What are two problems with this pathway?
	Rubisco operates best at higher CO2 than present in the air and it also works with oxygen to break down RuBP in photorespiration.

	What are two ways that plants have overcome these problems?
	They concentrate CO2 by combining it with a three-carbon acid (similar to pyruvate) to make a four-carbon acid (usually malate). C4 plants do this in the mesophyll, CAM plants at night. The CO2 is released for fixation in the Calvin cycle in the bundle sheath in C4 plants and in the day in CAM plants.

	In the early light reactions of photosynthesis in most organisms oxygen is released from: chlorophyll carbon dioxide water
	No, light displaces an electron from chlorophyll   This is what most people thought at first - it seems logical if we think of photosynthesis as carbon reduction and the opposite of respiration, but it is not so.   Yes, light displaces electrons from chlorophyll whch are somehow extracted from water to release H+ ions and O2

	After light excitation electrons pass to: NADP oxygen ATP
	No, light displaces an electron from chlorophyll   This is what most people thought at first - it seems logical if we think of photosynthesis as carbon reduction and the opposite of respiration, but it is not so.   Yes, light displaces electrons from chlorophyll whch are somehow extracted from water to release H+ ions and O2

	After light excitation electrons pass to: NADP oxygen ATP
	Yes, electrons move in the opposite direction to the respiratory chain, from water to reduced nucleotide.   The respiratory electron transport chain moves electrons from NADH to oxygen. In essence the photosynthetic chain works in the opposite direction.   ATP is made as electrons move along the chain but that is not the end point.

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