Chapter 17 - Energy for Biological Processes

Question 1

Where does photosynthesis take place ?

Answer 1

Chloroplast
where chlorophyll traps light and uses carbon diozide and water to generate glucose and water

Question 2

What is the structure of the Chloroplast ?

Answer 2

Question 3

What are the functions of the structure of chloroplasts ?

Answer 3

Stroma - contain enzymes that catalyse the reactions of the light independent stage
Grana - Increases surface area of thylakoid which maximises absorption of light
DNA - codes for some of the protiens and enzymes used in photosynthesis
Starch grain - Stores the products of photosynthesis

Question 4

What is the function of Chlorophylls ?

Answer 4

• Pigment that absorbs specific wavelengths of light and reflects others

Question 5

What is the primary pigment ?
What are the accessory pigments ?
Where are they located ?

Answer 5

Primary - Chlorophyll a (centre of photosystems)
Accessory -
Chlorophyll b
Xanthophylls
Carotenoids (embedded in photosystems and form the harvesting system)

Question 6

What are the 2 stages of photosynthesis ?

Answer 6

1 - Light dependent stage
2 - Light independent stage

Question 7

What are the features of the light dependent stage ?

Answer 7

• Takes place on thylakoid membrane
• Energy from the sun os absorbed and used to form ATP
• First stage of photosynthesis
• Hydrogen from water is used to reduce NADP coenzyme

Question 8

What are the features of the light independent stage ?

Answer 8

• Takes place in the stroma
• Hydrogen from NADPH and CO2 is used to build glucose

Question 9

What are the two photosystems involved in photosynthesis ?

Answer 9

Photosystem II (P680)
Photosystem I (P680)

Question 10

What is a harvesting system ?

Answer 10

• System of accessory pigments and one one primary pigment
• Used to collect wavelenths of sunlight to excite electrons

Question 11

What is the equation for Rf value ?

Answer 11

Distance moved by solvent

Question 12

What stages does the light dependent stage of photosynthesis occur in ?

Answer 12

1) Non-cyclic photophosphorylation
2) Cyclic photophosphorylation

Question 13

How does non-cyclic photophosphorylation occur ?

Answer 13

1) Energy is absorbed from the sun via accessory pigments, this energy is then transferred to the reaction centre
2) This energy will then excite 2 electrons in the primary pigment which will enter an ETC
3) This is where chemiosmosis occurs, the energy given by the electrons to the ETC causes the movement of H+ ions to move into thylakoid lumen from stroma
4) Electron enters PS I which will also be excited and leaves the PS
5) As they pass the ETC they will oxidise proteins and pass down
6) Elecrons will combine with hydrogen ions and NADP to form NADPH

Question 14

Where do the hydrogen ions that the electrons from non cyclic phosphorylation come from ?

Answer 14

Photolysis
- Occurs in the Granum
- The splitting of water molecules into 2electrons, 2 hydrogen ions 0.5O2
- Replenishes PSII lack of electrons

Question 15

How does cyclic photophosphorylation occur ?

Answer 15

1) Energy from the sun is absorbed by accessory pigments and passed to reaction centre
2) Electron in primary pigment is excited and leaves PS I
3) Electron passes through ETC in doing so provide energy to Hydrogen pump to transport H+from stroma to thylakoid membrane and is captured by an electron acceptor and passes back into PS I
4) Build up H+ in Thylakoid lumen drives synthesis of ATP from ADP and Pi by the process of chemiosomosis

Question 16

Where does the light independent stage of photosynthesis take place ?
Why is it reliant on the light dependent stage of photosynthesis ?

Answer 16

• Stroma
• Uses the CO2, ATP, and NADPH produced from the light dependent stages of photosynthesis

Question 17

Explain the light independent stages of photosynthesis

Answer 17

1) CO2 enters intercellular space within spongy mesophyll of leaves via diffusion from stomata
2) CO2 combines with RuBP (RuBISCO enzyme catalyses this reaction)
3) Unstable intermediate is formed
4) Unstable intermediate breaks to form 2 GP
5) Each GP is converted to TP via the addition of a phophate group and hydrogen
6) One TP is used to regenerate RuP and the other makes : lipids, amino acids, glucose
7) ATP is reduced to ADP and Pi is used to phosphorylate RuP to RuBP

Question 18

What are the 3 simple steps of the Calvin cycle ?

Answer 18

1) Carbon fixation
2) Reduction
3) Regeneration

Question 19

What are the 3 limiting factors of CO2 ?
How can you control these ?

Answer 19

1) Light intensity :
- Light is needed as an energy source
- As light intensity increases so will ATP and NADPH
- Can be controlled via lamps
2) CO2 Conc.
- CO2 is needed as a source of Carbon
- Controlled via the controlled burning of propane
3) Temperature
- Affects the rate of enzyme controlled reactions
- As temp increases rate of enzyme controlled reactions increases until proteins are denatured or something else limits

Question 20

Why isnt water stress considered a limiting factor ?

Answer 20

• When water potential decreases cells are plasmolysed
• This means Absetsic acid is released
• This acid is translocated to the leaves
• This causes the stomata to close therefore CO2 becomes the limiting factor
• When water potential increases
• Oxygen form the roots is limited
• no respiration can occur
• No ATP is produced hence no active transport can occur and no mineral ions are absorbed

Question 21

What does the law of limiting factors state ?

Answer 21

• States that the rate of a physiological process will be limited by the factor which is in the shortest supply