Photosynthesis

Question 1

What is photosynthesis?

Answer 1

Photosynthesis involves the harvesting of light energy to the production of glucose; these products can then be used by plant cells in aerobic respiration.

Question 2

What happens to extra sugars made from photosynthesis ?

Answer 2

Stored as starch, or used to make cellulose, lipids or amino acids.

Question 3

What is the compensation point?

Answer 3

When the volume of oxygen produced by photosynthesis is equal to that used in aerobic respiration.

Question 4

What is the equation for photosynthesis?

Answer 4

6CO2 + 6H2O -> C6H12O6 + 6O2

Question 5

What is stroma?

Answer 5

A liquid containing enzymes for the light independent stage of photosynthesis.

Question 6

What is a granum?

Answer 6

A stack of thylakoids

Question 7

What is the thylakoid membrane?

Answer 7

Site of the photosystem and electron transport chain.

Question 8

What is the function of the inner membrane?

Answer 8

Less permeable than outer membrane, folded into thin plates (lamellae) and flattened sacs (thylakoids) in stacks (grana)

Question 9

Where does the light dependent stage take place?

Answer 9

Thylakoid membrane

Question 10

Where does the light independent stage take place?

Answer 10

Stroma

Question 11

What are photosystems?

Answer 11

Sometimes called antennae complexes, photosystems are funnel-shapes , light harvesting clusters of photosynthetic pigments held in place by protein complexes in the thylakoid membrane.

Question 12

What are photosynthetic pigments?

Answer 12

Molecules that absorb light energy. Each pigment absorbs certain wavelengths of light and reflects others.

Question 13

What is chlorophyll a?

Answer 13

There are 2 forms, P680 and P700 (numbers refer to absorption peaks).
Both appear green-yellow
Absorbing light excites electrons previously associated with magnesium.

Question 14

What is chlorophyll b?

Answer 14

It is an accessory pigment
It has absorption peaks at 500nm and 640nm.
It appears blue-green.

Question 15

What are carotenoids?

Answer 15

Include carotene and xanthophyll which are accesssory pigments.
They appear orange-yellow.

Question 16

How do you calculate the Rf value of a pigment?

Answer 16

Distance moved by the compound / distance moved by the solvent.

Question 17

What happens in the light dependent stage?

Answer 17

The LDS takes place across the thylakoid membranes of the chloroplast. Two photosystems (PSIand PSII) harvest light energy, converting it into a flow of electrons which ultimately drives the production of ATP and reduced NADP.

Question 18

What happens in cyclic photophosphorylation?

Answer 18

This involves only PSI.
Excited electrons pass through a chain of electron acceptors back to the chlorophyll molecule from which they were lost.
NADP is not reduced but small amounts of ATP are made. Photolysis of water do not occur.

The small amounts of ATP made quickly in cyclic photophosphorylation, as well as being used in the LIS, can be used to establish a water potential gradient between guard cells and the surrounding tissues, which leads to the opening of the stomata.

Question 19

What happens in non-cyclic photophosphorylation?

Answer 19

Energy is released as electrons pass between photosystems (PSI and PSII); some of that which is used to pump protons into the thylakoid.

The movement of electrons from a low to high energy state and back again is referred to as the Z-scheme.

Electrons from PSI and protons (having passed through ATP synthase) are used by NADP reductase to reduce NADP.

In cyclic photophosphorylation, electrons cycle back through the electron transport chain, returining to PSI rather than being used to reduce NADP.

Question 20

What are ATP and reduced NADP from the LDS used for?

Answer 20

They are used directly in the light-independent stage to fix carbon dioxide, which can be used in the building of complex organic molecules.

Question 21

What happens in the Calvin cycle?

Answer 21

The enzyme RuBisCO combines a 5 carbon molecule (RuBP) with CO2 to make an unstable 6 carbon intermediate.
This breaks down to two 3-carbon molecules which can be used to synthesise sugars, amino acids and lipids.
The LIS uses ATP and reduce NADP from the LDS and CO2, and it occurs in the stroma of the chloroplast.

Question 22

What is triose phosphate (TP) used in the synthesis of?

Answer 22

Carbohydrates
Lipids
Amino acids
It is also recycled to regenerate RuBP.

Question 23

What is Glycerate 3-phosphate (GP) used to synthesise?

Answer 23

Amino and fatty acids

Question 24

What is RuBisCO?

Answer 24

RuBisCO is the most abundant enzyme on the planet. It evolved during a time when CO2 concentrations were much higher and O2 levels were a lot lower. O2 also fits the active site of RuBisCO and, above 25°C, photorespiration rather than photosynthesis starts to occur, creating toxic waste products that require ATP to be broken down.

Question 25

What are the limiting factors of photosynthesis?

Answer 25

Light intensity, CO2 conc, temperature

Question 26

What are limiting factors?

Answer 26

Factors that are present at the least or lowest favourable value for a reaction to proceed.