Photosynthesis In Plants

Question 1

What is the equation for photosynthesis? (Word + symbol)

Answer 1

Carbon dioxide + water = glucose + oxygen
6CO2 + 6H2O = C6H12O6 - 6O2
== light energy + chlorophyll

Question 2

What does the chloroplast contain?

Answer 2

-Outer and inner membrane (chloroplast envelope)
-Granum (a system of membranes arranged in stacks)
-Thylakoid (the membrane that stacks to make granum, where the green pigment is found)
-Lamellae (join the grana together, act as a skeleton within the chloroplast)
-Stroma (a matrix surrounding the membrane stacks, contains all enzymes needed to complete the process of photosynthesis)

Question 3

What pigments make up chlorophyll and what colour are they?

Answer 3

Chlorophyll A - blue green
Chlorophyll B - yellow green
Carotenoids - Orange carotene and yellow xanthophyll
Phaophytin - grey

Question 4

What is the absorption spectrum?

Answer 4

Describes the range of the amount of light of different wavelengths that a photosynthetic pigment absorbs, usually represented as a graph.
You can compare rate of photosynthesis with wavelength of light, first done by T.W Engelmann in the late 1800s. This resulted in the action spectrum.

Question 5

What is the action spectrum?

Answer 5

A way of demonstrating the rate of photosynthesis against the wavelength of light

Question 6

What is the Rf value and how do you calculate it?

Answer 6

The ratio of the distance travelled by the pigment to the distance travelled by the solvent alone
Rf value = distance travelled by solute (photosynthetic pigment) / distance travelled by solvent

Question 7

What is the difference between photosystem I and photosystem II?

Answer 7

They contain different pigments so absorb different wavelengths of light.

Question 8

Where does the light dependent reaction take place?

Answer 8

In the thylakoid membranes

Question 9

What are the two main functions of the light dependent reaction?

Answer 9

To split water molecules (photolysis) to provide hydrogen ions to reduce carbon dioxide and produce carbohydrates in the light independent stage
To produce ATP which is needed to supply the energy to produce those carbohydrates

Question 10

What is a photon?

Answer 10

A small unit of light

Question 11

What processes occur in the light dependent reaction and where does it occur?

Answer 11

Cyclic and non cyclic phosphorylation
Occurs in the thylakoid membrane

Question 12

What process occurs in the light independent reaction and where does it occur?

Answer 12

The Calvin cycle
Occurs in the stroma

Question 13

Cyclic phosphorylation

Answer 13

Photon hits a chlorophyll (PS1) and energy is transferred to elections making them excited. Leaves PS1 and is accepted by an electron acceptor and passed along the electron transport chain to produce ATP. It then returns to PS1 and starts again.

Question 14

Non cyclic phosphorylation

Answer 14

Photons hit the chlorophyll (PSII) and the electron gets excited meaning it leaves the chlorophyll and is picked up by an electron acceptor. It is then passed along the electron transport chain and goes to PS1 to replace the lost electrons from reduction of NADP for the light independent reaction. This leaves PSII unstable. PSII then gains an electron from photolysis.

Question 15

What is the light independent reaction

Answer 15

The Calvin cycle

Question 16

What is the Calvin cycle?

Answer 16

CO2 combines with ribulose biphosphate (RuBP) (5C), it then goes through the rate limiting enzyme RUBISCO resulting in a highly unstable 6C compound which immediately splits into 2 molecules of GP (3C compounds). This is then reduced (a hydrogen is added) forming 2 molecules of GALP (3C). The hydrogen comes from reduced NADP and the energy required comes from ATP. 1/6 reactions are synthesised into glucose and 5/6 replace RuBP and the cycle restarts.

Question 17

What is the product GALP used for

Answer 17

-Production of glucose (gluconeogenesis)
-Provides energy for cell functions
-Converted to acetyl coenzyme A to synthesise fatty acids

Question 18

What is a limiting factor?

Answer 18

A factor that affects the plants ability to photosynthesise

Question 19

What are the 3 main limiting factors of photosynthesis

Answer 19

-Light
-Carbon dioxide
-Temperature

Question 20

Light as a limiting factor

Answer 20

Amount of light available affects the amount of chlorophyll excited and therefore the amount of NADP and ATP produced. More NADP and ATP means reactions of the light independent stage can progress at their maximum rate.

Question 21

Carbon dioxide as a limiting factor

Answer 21

If there is not enough CO2 available for the Calvin cycle, the reactions can’t progress at their maximum rate.

Question 22

Temperature as a limiting factor

Answer 22

Many of the reactions are controlled by enzymes and therefore are sensitive to temperature.