TOPIC 5 - CH 11

Question 1

What is the equation for photosynthesis?

Answer 1

6CO₂ + 6H₂O + light energy -> C₆H₁₂O₆ + 6O₂

Question 2

What are the 3 main stages of photosynthesis?

Answer 2

1. Capturing of light energy by pigments/ photosystems such as chlorophyll
2. Light-dependent reaction, where light energy is converted into chemical energy
3. Light-independent reaction, where sugars and other organic molecules are produced

Question 3

What is the site of photosynthesis?

Answer 3

Chloroplasts

Question 4

What is the role of ATP in organisms?

Answer 4

molecule that temporarily stores
and quickly releases energy
for various cellular processes

Question 5

What is the relationship between respiration and photosynthesis?

Answer 5

Products of photosynthesis, glucose and oxygen, can be used as reactants in respiration to synthesise ATP

Products of respiration, carbon dioxide and water, can then be used as reactants in photosynthesis

Question 6

How are plant leaves adapted for photosynthesis (7)?

Answer 6

• large surface area - to absorb sunlight
• minimal overlapping - avoid shadowing
• thin - short diffusion distance
• transparent cuticle and epidermis - allow light to enter leaves
• chloroplast-packed mesophyll cells - carry out photosynthesis
• stomata - gas exchange
  -xylem and phloem - transport reactant and products of photosynthesis between the leaves and the rest of the plant

Question 7

Why do leaves have a transparent cuticle and epidermis?

Answer 7

to let light through to the photosynthetic mesophyll cells underneath

Question 8

Which cells of a leaf carry out photosynthesis?

Answer 8

mesophyll cells
(which are packed with chloroplasts)

Question 9

What is the role of photosynthetic pigments?

Answer 9

absorb energy from certain wavelengths of light

Question 10

What is the stroma?

Answer 10

fluid-filled matrix in a chloroplast
where light-independent stage of photosynthesis takes place

Question 11

What are grana, thylakoids and lamellae?

Answer 11

grana are stacks of flattened sacs called thylakoids
some thylakoids are joined by membranous extensions called lamellae
thylakoids membranes contain complex pigments that absorb light for photosynthesis
which is where light-dependent reactions occur

Question 12

How many membranes do chloroplasts have?

Answer 12

2

Question 13

What is the main function of chloroplasts and where are they usually found?

Answer 13

Chloroplasts are the site of photosynthesis
found in some algae and plant cells - mesophyll tissues in leaves

Question 14

What is the main pigment in photosynthesis?

Answer 14

chlorophyll

Question 15

What is the site of light-dependent reaction, and how is this region adapted for this function (3)?

Answer 15

thylakoids

• large surface area for chlorophyll and electron carriers in the electron transport chain
• contain ATP synthase channels
• selectively permeable, allowing a proton gradient to be established for ATP production

Question 16

What are oxidation and reduction?

Answer 16

Oxidation is when a substance loses electrons or gains oxygen

Reduction is when a substance gains electrons or loses oxygen

Question 17

What are the main reactants of the light-dependent reaction?

Answer 17

water and light energy

Question 18

What are the products of the light-dependent reaction? (non-cyclic photophosphorylation)

Answer 18

ATP, reduced NADP, and oxygen

Question 19

What are the products of the cyclic photophosphorylation light-dependent reaction?

Answer 19

ATP

Question 20

What are the key stages of the light-dependent reaction (6)?

Answer 20

1. absorption of light by pigments
2. release of electrons from pigments
3. electron transfer along the electron transport chain
4. photolysis of water to provide protons (H+) and electrons (e-, to replace those lost)
5. chemiosmosis
6. production of ATP and reduced NADP

Question 21

What is the role of chemiosmosis in photosynthesis?

Answer 21

the diffusion of protons across the partially permeable thylakoid membrane
down their electrochemical gradient
through ATP synthase channels
movement of protons releases energy
that is used to synthesis ATP

Question 22

What is the role of the electron transport chain in the light-dependent reaction?

Answer 22

transfers excited electrons from photosynthetic pigments to electron carriers
this transfer releases energy
used to pump protons across thylakoid membrane
creating a proton gradient that drives ATP synthesise

Question 23

What is the equation for the photolysis of water?

Answer 23

2H2O → 4H+ + 4e- + O2
or
H2O → 2H+ + 2e- + ½O2

Question 24

How is photolysis useful in photosynthesis(4)?

Answer 24

produces electrons to replace those lost by pigments
produces protons that help set up the proton gradient that drives ATP synthesis
electrons are protons also used to reduce NADP
produces oxygen as a by-product

Question 25

How is NADP reduced?

Answer 25

when is takes up protons in stroma produced during photolysis carrying the electrons into the light-independent reaction

Question 26

How is ATP produced in the light-dependent reaction?

Answer 26

ATP synthase catalyses the production of ATP from ADP and Pi this uses energy from the flow of protons down their concentration gradient from the thylakoid space into the stroma through ATP synthase channels

Question 27

Where does the light-independent stage of photosynthesis take place?

Answer 27

Stroma of chloroplasts

Question 28

What are the reactants and products for the light-independent stage of photosynthesis?

Answer 28

Reactants: carbon dioxide, ATP, reduced NADP Products: glucose and other organic molecules

Question 29

What are the light-independent reactions?

Answer 29

series of reactions where carbon is fixed and glucose is produced

Question 30

What enzyme catalyses the reaction between carbon dioxide and RuBP?

Answer 30

Rubisco

Question 31

What is the first step in the light-independent stage of photosynthesis?

Answer 31

Reaction of CO2 with a 5-carbon RuBP to form an unstable 6-carbon intermediate the 6C breaks down forming two 3-carbon glycerate-3 phosphate (GP) molecules (cabon dioxide is fixed)

Question 32

What is the second step in the light-independent stage of photosynthesis?

Answer 32

energy from ATP and protons and electrons from reduced NADP used to reduce GP to 3C triose phospohate (TP)

Question 33

What is the role of triose phosphate in th light-independent stage of photosynthesis?

Answer 33

some regenerate RuBP using ATP from light-dependent reaction the rest is used to produce otrher organic molecules needed by the plant

Question 34

What are the 3 key steps in the light-independent reactions?

Answer 34

1. Fixation - carbon dioxide is fixed to form 2 glycerate-3-phosphate (GP) 2. Reduction - GP is reduced to triose phosphate (TP) using protons and electrons from reduced NADP and energy from ATP 3. Regeneration - RuBP is regenerated from TP and energy from ATP

Question 35

What happens to NADP after the light-independent reaction?

Answer 35

NADP is reformeed and goes back to the light-dependent reaction to be reduced again

Question 36

What are some of the organic molecules that triose phosphate can be converted to?

Answer 36

- starch - glucose - cellulose - lipids - amino acids - nucleotides - sucrose

Question 37

What are the 5 factors required for photosynthesis to occur?

Answer 37

- presence of photosynthetic pigments - supply of carbon dioxide - supply of water - light energy - suitable temperature

Question 38

What are the 3 main factors that affect the rate of photosynthesis?

Answer 38

- light intensity - carbon dioxide concentration - temperature

Question 39

What is a limiting factor?

Answer 39

a requirement for a physiological process that is in the shortest supply and increasing this factor allows the rate of this process to increase

Question 40

Describe and Explain how temperature affects the rate of photosynthesis

Answer 40

When temp is limiting factor, rate of photosynthesis initially increases as temp is increased until an optimum enzyme and substrate have more kinetic energy, increasing reaction rates and GP,TP and RuBP concentrations as higher temps, rate decreases as enzymes denature, preventing the light-independent stage from proceeding

Question 41

Describe and Explain how light intensity affects the rate of photosynthesis?

Answer 41

When light is limiting, rate of photosynthesis increases as light intensity increases increased rate of light-dependent stage, producing mor ATP and reduced NADP leads to mor GP being converted to TP and increased RuBP regeneration at higher light intensities, rate of photosynthesis reaches a plateau and another factor becomes limiting

Question 42

Explain how carbon dioxide concentration affects the light-independent stage, and thus the rate of photosynthesis overall.

Answer 42

low COs concs reduce the amount of GP and TP due to less carbon dioxide being fixed reduces rate of photosynthesis

Question 43

What is the light compensation point in photosynthesis?

Answer 43

when the vol of oxygen produced and carbon dioxide absorbed in photosynthesis is balanced by the oxygen absorbed and carbon dioxide produced by respiration