Ibhl/ibsl Light Independent Photosynthesis

Front 1

What are ATP and hydrogen (derived from the photolysis of water) used for in photosynthesis?

Back 1

to fix carbon dioxide into organic molecules. Note that NADPH from the light-dependent reactions is also used, although not specifically mentioned in this particular objective. (fix means to take an atom that was in an inorganic molecule and make it part of an organic molecule)

Front 2

What are 3 ways you can measure the rate of photosynthesis

Back 2

directly by the production of oxygen (measure oxygen volume produced over a fixed period of time OR collect bubbles of oxygen from a water plant...probably our lab would be accepted too), directly by the uptake of carbon dioxide (measure carbon dioxide uptake over a fixed period of time OR measure color change of a pH indicator over a fixed time...ask if you want to know why that works), indirectly by measuring increase in biomass (measure increase in biomass over a fixed period of time OR harvest replicate samples at time intervals for biomass determination. (Level 3 objective, so be able to explain in some detail)

Front 3

Sketch a graph of the effect of temperature on the rate of photosynthesis and explain why the graph has that shape

Back 3

temperature increases at first (enzymes for photosynthesis and their substrates run into each other more often as temp increases and thus reaction rates increase), an optimum is reached, then photosynthesis rate declines as high temps denature proteins/enzymes involved in photosynthesis. Please remember that is you use a graph to help you answer a free reponse question then you must annotate it with a written desctiption to get any points)

Front 4

Sketch a graph of the effect of light intensity on the rate of photosynthesis and explain why the graph has that shape

Back 4

as light intensity increases, rate of photosynthesis increases at first (because light is required for photosystems I and II to be active. However, a plateau is reacher after which additional increase in light has no further effect on the rate of photosynthesis. This corresponds to when all of the photosystems are working at their maximum possible rate.

Front 5

Sketch a graph of the effect of carbon dioxide concentration on the rate of photosynthesis and explain why the graph has that shape

Back 5

as carbon dioxide concentration increases, rate of photosynthesis increases at first (because carbon dioxide is required for the Calvin cycle). However, a plateau is reacher after which additional increase in carbon dioxide has no further effect on the rate of photosynthesis. This corresponds to when all of the Calvin cycle enzymes are working at their maximum possible rate (or some other factor becomes limiting).

Front 6

Where do the light-independent reactions for photosynthesis happen/where are the enzymes for the Calvin cycle?

Back 6

in the stroma of the chloroplasts

Front 7

Explain the light-independent reactions

Back 7

Calvin cycle: In the stroma, ribulose bisphosphate (RuBP, a 5 carbon sugar) combines with carbon dioxide (a one carbon sugar) to make two molecules of glycerate-3-phosphate (each G3P is 3 carbons). This reaction was catalyzed by ribulose bisphosphate carboxylase (RuBP carboxylase). Glycerate-3-phosphate is converted to triose phosphate (also 3 carbons) using ATP and NADPH as an energy source; H+ from the light-dependent reactions also becomes part of triose phosphate. Thus, NADPH was oxidized and glycerate-3-phosphate was reduced. Two triose phosphate (3 carbons each) can be combined to make one glucose (6 carbons). A group of triose phosphate molecules can also be converted back to RuBP, thus completing the cycle; this process requires ATP as an energy source. Remember, all of the ATP and NADPH used here was made in the light-dependent steps (noncyclic electron flow). Note: if you get an essay on the light-independent reactions generally most or all of the points are for the Calvin cycle. Try to get

Front 8

Under what environmental conditions are plants likely to use the CAM or C4 pathways?

Back 8

Places where they risk loosing too much water and need to close their stomata...hot, dry, windy, etc. Plants in these places are called xerophytes (xero=dry phyte=love)

Front 9

What is photorespiration?

Back 9

When water is at low levels in the plant, it closes its stomata. This has the side effect of stopping gas exchange, so oxygen concentration increases and carbon dioxide concentration decreases. Photorespiration refers to RuBP carboxylase combining oxygen gas (rather than carbon dixide) to RuBP, resulting in a molecule that breaks down. (A big waste of energy that had already been invested in RuBP). This is not good for the plant, especially if it happens a lot. Plants that live in environments were water is scarce are likely to do the CAM or C4 pathways to try to avoid photorespiration.

Front 10

Describe the behavioral and biochemical adaptations of CAM plants

Back 10

They close their stomata in the day (to reduce water loss when it's hot) and open them at night. They use the enzyme PEP carboxylase to join carbon dioxide and PEP to oxaloacetate and another 4 carbon molecule at night and is stored in the vacuole; The reaction is reversed in the daytime to release carbon dioxide

Front 11

Describe the structural and biochemical adaptations of C4 plants

Back 11

The C3 (Calvin cycle) and C4 cycles are separated into different parts of the plant. Carbon dioxide is fixed in the mesophyll cells using the C4 cycle, which converts it into 4 carbon PEP (using the enzyme PEP carboxylase) and other 4 carbon molecules. These molecules are transported into the bundle sheath cells, where they are broken down to release carbon dioxide. This has the effect of funneling CO2 from many mesophyll cells to one bundle sheath cell, so the CO2 concentration int eh bundle sheath cell is higher than in the rest of the leaf. Thus, the bundle sheath cell does Calvin cycle without doing photorespiration. C4 plants, like C3 plants , have stomata open in the day and closed at night

Front 12

Do C4 and CAM plants still do the Calvin cycle?

Back 12

yes

Front 13

Explain the concept of limiting factors

Back 13

A limiting factor is the one factor in a reaction that limits how much of a product that you can make. Changing the limiting factor will change the rate. Increase the limiting factor, and the rate will go up. Further decrease the limiting reactant, and the rate will go down. Changing non-limiting factors will have no effect on the rate (unless you decrease them so much that they become the limiting factor)

Front 14

Discuss what happens when light intensity is the limiting factor for photosynthesis

Back 14

If light is the limiting factor, the rate-limiting step is the conversion of GP to TP (because it is the first step that requires ATP and NADPH from the light dependent reactions

Front 15

Discuss what happens when temperature is the limiting factor for photosynthesis

Back 15

If low temperature is limiting, then ALL of the steps in the Calvin cycle are slow. NADPH accumulates. If high temperatures, the enzymes activity decreases. RuBP carboxylase is particularly sensitive to this, so the rate-limiting step is the fixation of carbon dioxide

Front 16

Discuss what happens when carbon dioxide concentration is the limiting factor for photosynthesis

Back 16

If carbon dioxide is the limiting factor, the rate-limiting step is the fixation of CO2 by RuBP carboxylase. NADPH and RuBP build up (remember, the NADPH build-up will cause a switch from non-cyclic to cyclic electron flow