11. photosynthesis

Question 1

Symbol equation for photosynthesis

Answer 1

6H20 + 6CO2 = C6H12O6 + 6O2

Question 2

what is an autotroph

Answer 2

photosynthetic plants that gain all its chemical energy on its own

Question 3

give 4 adaptations of leaves (for photosynthesis)

Answer 3

large SA
overlapping leaves
thin, shot diffusion pathway
transparent cuticle
stomata

Question 3

Describe the structure of chloroplasts

Answer 3

the grana, stacks of disc-like structures called thylakoids, the site of light dependant stage of photosynthesis.
stroma, fluid matrix where light independent stage takes place. starch is found here.

Question 4

What process provides energy for proton pumps? (light dependant)

Answer 4

energy from ‘exited electrons’ in transport proteins

Question 5

What are the three key stages the light dependant reaction?

Answer 5

• Photolysis
• Photoionisation of chlorophyll
• Chemiosmosis
• Production of ATP and reduced NADP

Question 6

How are thylakoid membranes adapted for photosynthesis

Answer 6

• large surface area
• precise arrangement of proteins
• chloroplasts have DNA + ribosomes so they can manufacture proteins involved in the light-dependant reaction.

Question 7

Summarise the light independent stage of photosynthesis (calvin cycle)

Answer 7

• Rubp (5c sugar) undergoes carbon fixation (introduction of C from CO2) catalysed by rubisco
• GP, 3c sugar is reduced by ATP and NADPH (=NADP + ADP)
• 1 TP goes to make glucose
• 5 TP are regnarated into Rubp, requiring ATP.

Question 8

where does light dependant stage take place?

Answer 8

stroma of chloroplasts

Question 9

What happens to triose phosphate after the calvin cycle?

Answer 9

• some used to regenerate RuBP
• some converted into organic substances

Question 10

What enzyme catalyses carbon-fixation of RuBp?

Answer 10

rubisco

Question 11

What is the site of light independent stage? (photosynthesis)

Answer 11

stroma of chlorolplasts

Question 12

What can be found in the stroma? (4)

Answer 12

• thylakoids/grana
• 70s ribosomes
• a loop of DNA
• starch grains/sugars

Question 13

Photolysis of water.

Answer 13

Light energy is absorbed by chlorophyll and splits water into H+ and e-

H20 = (1/2 O2) + 2e- + 2H+

Question 14

What happens to H+ ions produced in photolysis of water?

Answer 14

Reduces NADP into NADPH, used in LIR

Question 15

What happens to electrons produced in photolysis of water?

Answer 15

Passed along electron carrier leading to photoionisation.

Question 16

Photoionisation of the chlorophyll.

Answer 16

• Light energy is absorbed by chlorophyll,
• Energy ‘excites’ electrons in chlorophyll,
• Up an energy level, leaving chlorophyll
• Energy from released electrons used in chemiosmosis.

Question 17

Summarize chemiosmosis

Answer 17

• Electrons that moved up energy level move along series of proteins in thylakoid membrane
• … releasing energy as they move
• Energy is used to pump protons across chloroplast membranes into thylakoid lumen
• Electrochemical gradient is created, H+ ions diffuse back to stroma through ATP synthase, resulting in production of ATP.
• co-enzyme NADP becomes reduced by H+ ions

Question 18

During chemiosmosis, where proton pumps on the thylakoid membrane get energy from?

Answer 18

From ‘exited’ electrons as they move along series of proteins.

Question 19

Three key processes in the calvin cycle.

Answer 19

• Carbon fixation of RuBp ( catalysed by rubisco)
• Reduction of GP to TP (NADPH and ATP needed)
• Regeneration of TP into RuBp (ATP required)

Question 20

Give three limiting factors of photosynthesis.

Answer 20

light intensity
CO2 concentration
Temperature

Question 21

How might agricultural practises remove limiting factors?

Answer 21

artificial lighting
heating
burning fuels, releasing CO2