Photosynthesis

Question 1

What does the stroma contain and what is the function of each?

Answer 1

70s ribosomes, a loop of DNA and starch grains.
The loop of DNA codes for some of the chloroplasts proteins.
The ribosomes produce proteins.
Sugars formed during photosynthesis are stored as starch grains

Question 2

Function of membrane found in the stroma

Answer 2

1) Site of the light dependant reactions. It contains the pigments, enzymes and electron carriers required for the reactions.
2) The membranes of the grana create a large surface area to increase the number of light-dependant reactions that can occur

Question 3

Where does the light dependant stage and independent light stage occur in the chloroplasts?

Answer 3

Light dependant stage occurs in the thylakoids and the light independent stage occurs in the stroma

Question 4

Summary of the light dependant stage

Answer 4

1) Reduced NADP is produced when hydrogen ions combine with the carrier molecule NADP using electrons from the photolysis of water
2) ATP is produced during phosphorylation (uses the proton gradient generated by the photolysis of water)
3) Energy from ATP and hydrogen from reduced NADP are passed from the light independent stage of photosynthesis

Question 5

Summary of the light independent stage

Answer 5

1) Energy and hydrogen are used
2) Calvin cycle occurs
3) Complex organic molecules are produced (starch, sucrose and cellulose)

Question 6

What are the two types of pigment and the different types in them?

Answer 6

Chlorophylls - chlorophyll a and chlorophyll b
Carotenoids - carotene and xanthophyll

Question 7

In what region does chlorophyll absorb wavelengths?

Answer 7

In the blue-violet and red regions

Question 8

In what region do the carotenoids absorb wavelengths?

Answer 8

In the blue-violet region

Question 9

In what regions is photosynthesis highest?

Answer 9

In the blue-violet(400nm) and red regions(650nm) of the light spectrum as these are the wavelengths of lights that plants can absorb. Graphs have a trough in the green-yellow region

Question 10

Rf formula

Answer 10

Rf = distance travelled by component/distance travelled by solvent

Question 11

What does a smaller Rf value indicate?

Answer 11

The pigment is less soluble and larger in size

Question 12

The general Rf values of the pigments

Answer 12

Carotenoids have the highest Rf values. Chlorophyll B has a much lower Rf value. Chlorophyll A has an Rf value between the two

Question 13

When do cyclic and non cyclic photophosphorylation occur?

Answer 13

During the light dependent stage of photosynthesis

Question 14

What photosystem does cyclic photophosphorylation involve?

Answer 14

Photosystem I

Question 15

What photosystem does non cyclic photophosphorylation involve?

Answer 15

Photosystem I and II

Question 16

Describe cyclic photophosphorylation

Answer 16

1) Light is absorbed by photosystem I and passed to photosystem I primary agent
2) An electron in the primary molecule is excited to a higher energy level and is emitted from the chlorophyll molecule in photoactivation. This excited electron is captured by an electron acceptor, transported via a chain of electron carriers before being passed back to photosystem I
3) As electrons pass through the electron transport chain they provide energy to transport protons from the stroma to the thylakoid via a proton pump
4) A build up of protons in the thylakoid can be used to drive the synthesis of ADP to ATP from ADP and Pi

Question 17

Describe non cyclic photophosphorylation (photosystem II)

Answer 17

1) Light is absorbed by photosystem II and passed to photosystem II primary pigment.
2) An electron in the primary pigment molecule is excited to a higher energy level and is emitted from the chlorophyll molecule.
3) This excited electron is passed down a chain of electron carriers before being passed down to photosystem I. During this process ATP is synthesised from ADP and Pi
4) Photosystem II contains oxygen evolving complex which catalyses the breakdown of water by light. As the excited electron leave the primary pigment of photosystem II and are passed on to photosystem I, they are replaced from the electrons from the photolysis of water

Question 18

Describe non cyclic photophosphorylation (photosystem I)

Answer 18

1) Electrons in photosystem I also undergo photoactivation. The excited electrons from photosystem I also pass along an electron transport chain
2) These electrons combine with H ions and NADP to give reduced NADP
3) The reduced NADP, then passes to the light-independent reactions

Question 19

Describe where energy is obtained from during photophosphorylation

Answer 19

The energetic electrons release energy as they pass through the electron transport chain. The released energy is used to actively transport protons across the thylakoid membrane using a proton pump. This creates a proton gradient with a high concentration in the thylakoid lumen and a low concentration in the stroma. Protons the return to the stroma by facilitated diffusion through ATP synthase enzymes. This process provides the enrgy needed to synthesise ATP

Question 20

What are the 3 stages of the Calvin Cycle?

Answer 20

1) Carbon fixation
2) Reduction of glycerate 3-phosphate
3) Regeneration of ribulose biphosphate

Question 21

Carbon fixation

Answer 21

CO2 combines with a 5 carbon compound, ribulose biphosphate. Rubisco (enzyme) catalyses this reaction.
The resulting six carbon compound is unstable and splits in two. This gives two molecules of glycerate 3-phosphate (not carbohydrate)

Question 22

Reduction of glycerate 3-phosphate

Answer 22

Energy from ATP and hydrogen from reduced NADP are used to reduce glycerate 3-phosphate to a phosphorylated 3 carbon sugar known as triose phosphate

Question 23

Regeneration of ribulose biphosphate

Answer 23

Triose phosphate molecules are used to regenerate ribulose biphosphate. Requires ATP

Question 24

What intermediates are used to produce other molecules?

Answer 24

Glycerate 3-phosphate is used to produce some amino acids.
Trisose phosphate is used to produce amino acids, lipids and carbohydrates