Photosynthesis

Question 1

Photosynthesis

Answer 1

A complex metabolic pathway that consists of three main stages:

1. Capturing of light energy
2. Light-dependent reaction
3. Light-independent reaction.

Overall, in the presence of light:

Question 2

Equation for photosynthesis

Answer 2

6CO₂ ​+6H₂​O​ ⟶C​H​₁₂O​₆ ​​+ 6O₂​

Question 3

Site of photosynthesis

Answer 3

Chloroplasts

Question 4

The 10 adaptations of a leaf:

Name at least 5

Answer 4

• Large surface area
• Arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of one leaf by another
• Thin so this keeps diffusion short
• Transparent cuticle
• Numerous stomata for gases exchange
• Long and narrow upper mesophyll cells packed with chloroplasts that collect sunlight
• Stomata open and close in response to changes in light intensity
• Many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of co2 and o2
• A network of xylem that brings water to the leaf cells and phloem that carries away the sugars produced during photosynthesis

Question 5

Light-dependent reaction

Answer 5

​The 2nd stage of photosynthesis that uses light energy to produce ATP, reduced NADP and oxygen (by-product).

takes place in the thylakoids of the chloroplast.

Question 6

Light-independent reaction (Calvin cycle)

Answer 6

The third stage of photosynthesis, in which the products of the light-dependent stage and carbon dioxide are used to form a simple sugar.

This stage does not require light energy and takes place in the stroma of the chloroplast.

Question 7

Limiting Factor

Answer 7

​A variable that limits the rate of a particular reaction.

Question 8

What is the 3 thing included in the structure of chloroplasts

Answer 8

Grana
Thylakoid
Stroma

Question 9

Where does light independent &light dependant reactions take place in plants.

Answer 9

Light-in dependant: Stroma of chloroplasts

Light dependant: in the thylakoids

Question 10

Raw material involved in photosynthesis

Answer 10

Water

Carbon dioxide

Question 11

Products of light-dependent reaction

Answer 11

Reduced NADP, ATP, Oxygen

Question 12

Products of a light-independent reaction

Answer 12

Sugars and others organic molecules

Question 13

Explain the role of light in photoionisation

Answer 13

Chlorophyll molecules absorbs energy from photons of light.

This ‘excites’ 2 electrons (raises them to a higher energy level), causing them to be released from the chlorophyll.

Question 14

Name the 2 main stages involved in ATP production in light-dependant reaction

Answer 14

1. Electron transfer chain

2. Chemiosmosis

Question 15

What happens in the electron transfer chain (ETC)?

Answer 15

Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reactions, which releases energy

Question 16

Oxidation

Answer 16

Loss of electrons of hydrogen or gain of oxygen

Question 17

Reduction

Answer 17

Gain of electrons or gain of hydrogen or loss oxygen

Question 18

How is a proton concentration gradient established during chemiosmosis?

Answer 18

Some energy released from the ETC is coupled to the active transport of H+ ions (protons) from the stroma into thylakoid space.

Question 19

How does chemiosmosis produce ATP in light-dependant stage?

Answer 19

H+ ions (protons) move down their concentration gradient from the thylakoid space into the stroma via the channel protein ATP synthase.

Question 20

Explain the role of light in photolysis

Answer 20

Light energy splits molecules of water

2H₂O → 4H⁺ + 4e⁻ + O₂

Question 21

What happens to the products of photolysis of water?

Answer 21

• H ⁺ ions: move out of thylakoid space via ATP synthase & are used to reduce the coenzyme NADP.
• e⁻ : Replaces electrons lost from chlorophyll.
• O₂: used for respiration or diffuses out of leaf waste gas.

Question 22

How and where is reduced NADP produced in the light-dependant reaction?

Answer 22

• NADP + 2H ⁺ + e⁻ → reduced NADP.
• Catalysed by dehydrogenase enzymes.
• Stroma of chloroplasts

Question 23

Where do the H ions and electrons used to reduce NADP come from?

Answer 23

• H ions: photolysis of water

- Electrons: NADP acts as the final electron acceptor of the electron transfer chain.

Question 24

Name the 3 main stages of the Calvin cycle.

Answer 24

1. Carbon fixation
2. Reduction
3. Regeneration

Question 25

What happens during carbon fixation?

Answer 25

- Reaction between CO₂ & ribulose bisphosphate (RuBP) catalysed by rubisco - Forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)

Question 26

What happes during reduction (in the calvin cycle)?

Answer 26

- 2 X GP are reduced to 2 x triose phosphate (TP) - Required 2 x reduced NADP & 2 x ATP - Forms 2 x NADP & 2 x ADP

Question 27

How does the light-independant reaction result in the production of useful organic substances?

Answer 27

1C leaves the cycle (i.e. some of the TP is converted into useful organic molecules).

Question 28

What happens during regeneration (in the calvin cycle)? after

Answer 28

- After 1C leaves the cyle, 5C compound RuP forms - RuBP is regenerated from RuP using 1x ATP - Form 1 x ADP

Question 29

Outline the seqeuence of events in the light-independant reaction (Calvin cycle).

Answer 29

Refer to PMT

Question 30

State the roles of ATP & (reduced) NADP in the light-indepent reaction Reduction transports

Answer 30

ATP: reduction of GP to TP & provides phosphate group to convert RuP into RuBP. - (Reduced) NADP: Coenzyme transports electrons needed for reduction of GP to TP.

Question 31

State the number of Carbon atoms in RuBP, GP & TP.

Answer 31

RuBP: 5 GP : 3 TP : 3

Question 32

Describe the structure of a chloroplast. 5 Flattened Intergranal Fluid F

Answer 32

- Usually disc-shaped - Doubled membrane (envelope) - Thylakoids: flattend discs stack to form grana - Intergranal lamellae: tubular extensions attach thylakoids in adjacent grana. - Stroma: fluid-filled matrix.

Question 33

How does the structure of the chloroplast maximise the rate of the light-dependent reaction?

Answer 33

- ATP synthase channels within granal membrane. - Large SA of thylakoid membrane for ETC. - photosystems postion chlorophyll to enable maximum absorption of light.

Question 34

How does the structure of the chloroplasts maximise the rate the light-independent reaction?

Answer 34

- Own DNA & ribosomes for synthesis of enzymes e.g. rubisco. | - Concentration of enzymes & substrates in stroma is high.

Question 35

Name 4 enviromentl factors that can limit the rate of photosynthesis.

Answer 35

- Light intensity (Light-dependent stage). - Co₂ levels (light-independent stage). - Temperature (enzyme-controlled steps). - Mineral/magnesium levels (maintain normal functioning of chlorophyll).