LDR

Question 1

What are the 2 different stages of photosynthesis?

Answer 1

• Light dependent reaction.
• Light independent reaction.

Question 2

Where do the light independent/ dependent reactions of photosynthesis occur?

Answer 2

• Light dependent: in thylakoid/ chloroplast membrane.
• Light independent reaction: in the stroma.

Question 3

What are the 4 stages of the light-dependent reaction?

Answer 3

1.) Photoionisation.
2.) Electron transfer.
3.) Production of ATP/ reduced NADP ie. NADPH.
4.) Photolysis

Question 4

How else can “reduced NADP” be written?

Answer 4

• NADPH.
• The H represents the protons/ electrons NADP gains in order to become reduced.

Question 5

What are the 2 main products formed in the light-dependent reaction?

Answer 5

• NADPH ie. reduced NADP.
• ATP.

Question 6

Describe the first 3 stages of the light-dependent reaction?

up till movement of electrons!

Answer 6

1.) Photoionisation. Chlorophyll absorbs light, excites/ moves electrons in chlorophyll.
2.) Electrons are lost, chlorophyll-a becomes positively charged.
3.) Excited electrons are raised to higher energy level/ move along electron carrier proteins in electron transfer chain.

Question 7

Where are the electrons, that are excited by light absorption, found?

Answer 7

• Found in ‘chlorophyll –a’, within photosystem membrane proteins in the thyalkoid membrane.

Question 8

What different proteins do we find within the thyalkoid membrane?

Answer 8

• Electron carrier proteins.
• Photosystems proteins containing ‘chlorophyll-a’ and electrons within ‘the chlorophyll-a’
• ATP synthase.

Question 9

Describe what happens after electrons move in the electron-transfer chain in the LDR.

Give 3 steps/ stages!

Answer 9

1.) Transfer of electrons leads to release of energy used to transport protons ie. H+ across thylakoid/ chloroplast membrane - from stroma into thyalkoid lumen.
2.) Creates proton concentration gradient/ movement of protons via facilitated diffusion through ATP synthase from thyalkoid lumen into stroma.
3.) Release of energy, caused by proton movement, is used by ATP synthase to join ADP and Pi to form ATP.

Question 10

True or False

Photosystem membrane proteins only contain ‘chlorophyll-a’

Answer 10

• False!
• Photosystems also contain other pigments!

Question 11

What are on the different sides of the thyalkoid membrane?

Answer 11

• Stroma: this is where NADPH/ ATP are produced.
• Thyalkoid lumen: this is where H+ ions/ protons are moved into from stroma!

Question 12

How do we represent protons?

Answer 12

H+

Question 13

Describe what happens in the LDR after ADP and Pi join together to form ATP.

give 2 stages

Answer 13

1.) The co-enzyme is reduced by H+ ie. gains protons and electrons to form reduced NADP (NADPH.)
2.) The photolysis of water produces protons, electrons and oxygen.

Question 14

The co-enzyme NADP gains protons and electrons to form NADPH, where does it gain protons from? HB electrons?

Answer 14

• Protons: from H+ that moves from thylakoid lumen into stroma across thyalkoid/ chloroplast membrane, catalysed by ATP synthase.
• Electrons: from electron carrier proteins in the electron-transfer chain.

Question 15

What is photolysis? What is benefit of photolysis in LDR of photosynthesis?

Answer 15

• Use of light to split water into protons, electrons and oxygen.
• Benefit: provides positively charged ‘chlorophyll-a’ with electrons, that will then be excited by light and begin to move in electron-transfer chain.

Question 16

What is the “chemiosomotic theory?”

Answer 16

• Production of ATP involves:
• Transfer of electrons down electron-transfer chain.
• Passage of protons through thyalkoid/ chloroplast membrane, catalysed by ATP synthase

Question 17

What 2 different processes release energy in the LDR?

Answer 17

• Movement of protons ie. H+ across thyalkoid membrane through ATP synthase protein.
• Movement of electrons in electron-transfer chain.

Question 18

What is meant when we say:
“some of the energy from electrons released during photoionisation is conserved in production of ATP and reduced NADP.”

Answer 18

• Without photoionisation, you would not get the production of reduced NADP and ATP.

Question 19

Exam Q 2016-2021 PMT “Photosynthesis”

Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.

When treated with Atrazine, weeds have been shown to give off small
amounts of heat.

Suggest an explanation for this observation.

Answer 19

• Energy released from excited electrons (that were lost from chlorophyll and didn’t move down ETC.)

() - extra info for clarification.