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Biology > 5.7 Photosynthesis > Flashcards

5.7 Photosynthesis Flashcards

1
Q

What is the equation for photosynthesis? and what is needed?

A

6CO2 + 6H2O ~> (1) C6H12O6 + 6O2
Needed = light energy

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2
Q

What are the two stages of photosynthesis?

A
  1. The light dependent reaction (LDR)
  2. The light independent reaction (LIR)
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3
Q

Describe the structure of the chloroplast.

A
  • Double membrane bound
  • Inner and outer membrane that make up envelope
  • thylakoids and thylakoid membranes
  • grana (stacks of thylakoids)
  • lamella that join grana
  • Starch grains
  • ribosomes
  • storma (like cytoplasm)
  • circular DNA
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4
Q

Where does the light dependent reaction occur?

A

In the Thylakoid membrane of grana (in the photosystems)

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5
Q

Where does the light independent reaction occur?

A

in the stroma

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6
Q

Describe and explain photosynthetic pigments and what they do

A

photosynthetic pigments make up the light harvesting system and are embedded in thylakoid membrane and make up a photosystem.

They absorb light energy of specific wavelengths.

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7
Q

What are the types of photosynthetic pigment?

A
  • Chlorophyll a (primary)
  • Chlorophyll b
  • Xanthophyll
  • Carotenoids
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8
Q

Describe the two types of photosystems.

A

Photosystem 1 (PS1) harvests light at max wavelengths of 700nm whereas Photosystem 2 (PS11) harvests light at max wavelengths of 680nm.

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9
Q

What roles do the accessory pigments have? Give some examples

A
  1. They protect the primary pigment from over exposure
  2. Make up the light harvesting system/ cluster
  • Carotenoids eg xanthophyll
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10
Q

What reaction comes first and why?

A

The Light dependent reaction (LDR) as the NADred and ATP are generated which is needed in the calvin cycle.

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11
Q

Describe the process of the Light dependent reaction

A
  1. Light energy excites the electrons (photo-excitation) in Photosystem 2 (PS11) into a higher energy level
  2. The electrons then move along the electron transport chain via electron carrier proteins. This generates energy that’s lost be electrons as they pass down the chain to pump H ions across the thylakoid membrane into the lumen in the thylakoid creating a concentration gradient
  3. The H ions move back across the concentration gradient (chemiosmosis) through ATP synthase and this provides energy for photophosphorylation of ADP + Pi to make ATP
  4. Photolysis occurs next to photosystem 2 to replace the missing electrons and this splits water into 1/2 O2 + 2e- + 2H ions
  5. The electrons from the etc get dumped at Photosystem 1 (PS1) and then get further excited again. They then combine with NADP and the H ions from photolysis to make NADPred which is needed for Calvin cycle
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12
Q

Describe the Light independent reaction (LIR)

A
  1. CO2 (1c) combines with RUBP (5c) this is carbon fixation and makes a 6c compound. The enzyme RuBisCO aids this.
  2. 6c gets split into 2 x GP (3c)
  3. GP undergoes reduction and NADPred returns to NADP also ADP gets produces and GP gets phosphorylated to make 2 x TP
  4. TP looses 1c to make a hexose and the other 5c make RUP
  5. RUP gets phosphorylated into RUBP and this is the regeneration of RUBP
  • After 6 turns a hexose is made
  • hexose could be starch or cellulose
  • Also lipids are made from glycerols and fatty acids.
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13
Q

What are the uses of TP?

A
  • to regenerate RUBP
  • 1/6 each turn goes towards a carb makes a hexose after 6 turns
  • also makes glycerols for lipids
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14
Q

What are the limiting factors for photosynthesis and there optimums?

A
  1. Light intensity (certain wavelength)
  2. Temperature (around 25°c)
  3. CO2 conc (0.4%) in atmosphere
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15
Q

What are the differences between cyclic and non cyclic photophosphorylation?

A

Cyclic : Only PS1, Only makes ATP, NO photolysis

Non cyclic: PS1 + PS11 used, makes ATP and O2 and NADPred, Has photolysis

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16
Q

Draw out the calvin cycle.

A
17
Q

What are the optimum conditions for photosynthesis?

A

UK plants:
- High light intensity of a certain wavelength.
- Temperatures around 25°c
- Carbon dioxide levels at 0.4%

18
Q

What are the limiting factors of photosynthesis?

A

Light intensity, Temperature, Carbon dioxide concentration.

19
Q

What is a photosystem? And where are they located?

A

A cluster of photosynthetic pigments located in the thyroid membranes of chloroplast. They are involved in the light dependent stage.

20
Q

What pigment is found at the reaction centre of photosystems?

A

Chlorophyll a

21
Q

What is the compensation point?

A

A particular level of light intensity where the rate of photosynthesis exactly matches the rate of respiration.

22
Q

Describe non cyclic photophosphorylation in stages.

A
  1. Light energy absorbed by PS11 and this excites the electrons into a higher energy level. The electrons then move along the electron transport chain to PS1 (photo-excitation)
  2. Photolysis of water replaces electrons lost so the light energy splits water into H ions electrons and 1/2 an O2
  3. Excited electrons loose energy as the pass along the etc so this energy is used to pump H+ ions into the thylakoid through electron carrier proteins. Makes a higher concentration of H+ in the thylakoid and lower in the stroma creating a proton gradient. The H+ ions then move back down the concentration gradient into the stroma via ATP synthase and this allows ATP to be made from ADP + Pi (photophosphorylation)
  4. The electrons are then further excited into an even higher energy level and then the e are transferred to NADP with a H+ ion to form NADP red
23
Q

What does non cyclic photophosphorylation produce ?

A

ATP, NADP red , O2

24
Q

What is the difference between cyclic and non cyclic photophosphorylation?

A

Cyclic only produces ATP but non cyclic produces ATP and NADPr and O2

Cyclic only uses PS11 but non cyclic uses PS11 and PS1

Cyclic has no Photolysis

25
Q

Describe the stages in Cyclic photophosphorylation.

A
  1. Electrons are excited from PS11 by light energy.
  2. BUT they are passed back to the photosystem 11 by electron carrier proteins.
  3. Still makes ATP as electrons still move down ETC and loose energy driving the conc gradient and so the move back through ATP.
26
Q

What is the primary pigment?

A

Chlorophyll A

27
Q

What is a limiting factor?

A

something that limits the rate of photosynthesis.

Biology (25 decks)

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