Photosynthesis

Question 1

What is an autotroph? Therefore what can we call plants?

Answer 1

Auto troph is an organism that makes its own molecules, a plant is therefore a photo autotrophs

Question 2

Where does photosynthesis occur?

Answer 2

Chloroplasts

Question 3

Describe the internal structures of a chloroplast

Answer 3

Outer membrane
Inner membrane
Thylakoids which are the individual disk like sections, and granum which are stacks of thylakoids
Grana are connected by an intergranal lamallea

Question 4

What is a plants compensation point?

Answer 4

Where the plant respires at the same rate as it photosynthesises.
There is no net gain or loss of carbohydrates

Question 5

Give up to six adaptations of the plant to increase photosynthesis

Answer 5

Large surface area of the thylakoids= more electron carrier
Leaves are thin which reduces diffusion distance
Leaf arrangement prevents areas shading each other
Transparent, allows light to reach the mesophyll
Many stroma to help gaseous exchange
Opening and closing of stroma

Question 6

The light has two roles within the light dependant reaction give the end results of both of these roles.

Answer 6

Adds Pi, to ADP

Photolysis

Question 7

What is the role of an accessory pigment?

Answer 7

Cause energy to be directed towards a reaction centre, i.e. The chlorophyll

Question 8

What is a photosynthetic pigmemt?

Answer 8

A pigment that absorbs specific wavelength of light energy

Question 9

What inorganic ion is present within the chlorophyll?

Answer 9

Mg2+ (prophyrin group)

Question 10

Describe the light dependant reaction role on the chlorphyll to form ATP

Answer 10

Light energy excites an electron within A chlorophyll molecule
Electron leaves chlorophyll (hence chlorophyll is oxidised)
Electron carrier accepts the electrons
Redox reactions occur, down a electron transport chain, energy is lost at each stage
Energy used to pump hydrogen ions across the thylakoids membrane.
Only way hydrogen ions can diffuse back through is through ATP synthase channel proteins, which catayse ATP synthesis.

Question 11

Other than being pumped through ATP synthase molecules where else may a proton move to during photosynthesis?

Answer 11

NADP may accept the proton = NADPH

Question 12

Show the equation for photolysis

Answer 12

2H2O —> 4H+ + 4e- + O2

Question 13

State where the three products of photolysis go to (photosyntheis)

Answer 13

Oxygen- used in respiration
Protons - add to H+ gradient
Electrons- replace the lost electron in the chlorophyll

Question 14

Where does the light independent stage take place?

Answer 14

Stroma

Question 15

Give three adaptations that help the light independent reaction

Answer 15

Heavily abundant enzymes

Short diffusion pathway between the grana and stroma

Question 16

Why, despite its name, wont the light independent reaction occur in dark conditions?

Answer 16

It uses the products; ATP and NADPH which come from the light dependant reaction.

ATP also activates RuBisCo
Proton pumoing changes pH which is more optimum for RuBisCo

Question 17

Describe the light independent stage.

Answer 17

Co2 diffuses through the stomata into the stroma of the chloroplast
RuBisCo catalyses the carbon fixation onto ribulose bisphosphate
Product is unstable and breaks down to glycerate three phosphate

NADPH reduces glycerate 3 phosphate to triose phosphate, ATP supplies energy

Some triose phosphate molecules go back to be Ribulose bisphosphate where as others are converted

Question 18

What are the limiting factors of respiration?

Answer 18

CO2
H2O
Light intensity 
Enzyme availability 
Number of ATP synthase molecules

Question 19

Describe how light intensity will act as a limiting factor?

Answer 19

Powers the light dependant reaction
Therefore has an effect on the amount of NADPH and ATP
Less of these products leads to a disruption in the calvin cycle
Triose phosphate will not be produced from the reduction of glycerate-3-phosphate
Ribulose bisphosphate wont be regenerated

Also is a stimulant to the opening of stomata
Leads to other changes within other limiting factors

Question 20

Describe how [CO2] is a limiting factor

Answer 20

CO2 is needed to bind to ribulose bisphosphate
Accumulation of RuBP
Decline in triose phosphate and glycerate bisphosphate

Question 21

Describe how temperature is a limiting factor to photosynthesis.

Answer 21

Lower temperatures photosynthesis slower due to kinetic theory
Where tempertures are above 30 oxygen reacting woth RuBisCo is favoured over carbon
Where tempertures rise of 45 degrees denaturing may occur e.g. RuBisCo

Question 22

Give two ways in which water stress leads to the reduction in photosynthesis

Answer 22

Lack of water = plasmolysis = longer diffusion pathway
Abscisic acid is released (a hormone) closes the stomata, whilst successfully preventing water loss also prevents CO2 entering hence stops carbon fixing in light dependant

Question 23

What limitations are there to using oxygen production as a measurement for photosynthetic rate?

Answer 23

Some oxygen is used in respiration

Meausring gas production, not all gas is oxygen i.e. Some nitrogen

Question 24

Describe the roles of the following within a photosynthometer

• water bath
• Potassium hydrogencarbonate
• syringe

Answer 24

Water bath maintains a constant temperature
Potassium hydrogen carbonates concentration can be adjusted to change/ control carbon dioxide conc
Syringe allows for the movement of the air bubble within the tube

Question 25

What experiment was used to prove Calvins cycle

Answer 25

Lollipop experiment

Question 26

What is the basic idea of calvins ‘lollipop experiment’?

Answer 26

Add radioactive Carbon 14 to a flask with algae in it.
Drop samples at intervals into hot alcoholic solution (stops synthesis)
Split the chemicals by chromatography
See at which points which chemicals were radioactive i.e. How lomg alage had been left in flask