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Biology Unit 3 > Photosynthesis (DONE) > Flashcards

Photosynthesis (DONE) Flashcards

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1
Q

How do chloroplasts arrange themselves in and why:
- Weak Light
- Strong Light

A
  • Arrange at the top of the cell to maximise absorption
  • Arrange in a column to minimise photodamage
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2
Q

What is the significance of having many different pigments?

A

Each pigment absorbs a specific wavelength of light, so numerous pigments collectively ensures a wide variety of absorption.

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3
Q

Give 4 examples of different plant pigments.

A
  • Chlorophylls a and b
  • Xanthophyll
  • Carotenoids
  • Anthocyanin
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4
Q

How can pigments be identified?
(3 marks)

A
  • Using thin-layer chromatography
  • Pigments move to different positions according to their solubility.More soluble the further they move
  • Rf values can be calculated and compared to known Rf values
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5
Q

Why are Rf values not absolute?

A

Depends on the solvent used. A solvent may not be able to seperate 2 pigments with the same solubility

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6
Q

What variables need to be controlled when comparing results of chromatography?
(2 marks)

A
  • Same solvent
  • Same temperature
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7
Q

What are the two spectrums used in photosynthesis and what do they show?

A
  • Absorption spectrum shows how much light is absorbed by a pigment at different wavelengths
  • Action spectrum shows the rate of photosynthesis of different wavelengths of light
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8
Q

What does overlapping the two spectrums suggest?

A

That the wavelengths of light absorbed by the pigments are actually used in photosynthesis due to the very close correlation shown when the graphs overlap.

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9
Q

Explain the results of the Thomas Englemann’s experiment with spirogyra.
(4 marks)

A
  • Oxygen is a product of photosynthesis
  • Most oxygen is produced at the wavelengths of light used most for photosynthesis
  • Aerobic bacteria need oxygen for respiration
  • Bacteria congregate at regions with high concentration of oxygen being evolved (red and blue regions)
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10
Q

What is light harvesting?
(7 marks)

A
  • Photosynthetic pigments are clustered together, which is known as an antenna complex
  • Chlorophyll a is a primary pigment
  • Other pigments are known as accessory pigments, which allow a range of wavelengths to be absorbed
  • Occurs within the thylakoid membrane
  • As light is absorbed, special proteins funnel light towards the primary pigment in the reaction centre
  • Each chlorophyll a (primary pigment) emits one electron
  • Each antenna complex is a photosystem
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11
Q

Briefly describe the light dependant stage that occurs in both cyclic and non-cyclic photophosphorylation.
(5 marks)

A
  • Occurs in the thylakoid membrane of the grana
  • Light energy/photon hits a photosystem/top of antenna complex and is passed through to the reaction centre. Proteins prevent light escaping the antenna complex.
  • Reaction centre contains two molecules of chlorophyll a, which will absorb light energy and emit high energy electrons
  • There are two photosystems found in the thylakoid membrane: PSI (P700) and PSII (P680)
  • Electrons are excited to a higher energy level as they are passed to the reaction centre, which are passed to electron acceptors (NADPH)
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12
Q

Describe the method of non-cyclic photophosphorylation also known as Z scheme.
(7 marks)

A
  • High energy electron is passed down a series of electron carriers (redox reactions) and release energy to power the proton pump.
  • Protons are pumped from the stroma to the thylakoid space (high H+ concentration)
  • Protons diffuse through the stalked particles to activate ATP synthase to produce ATP
    -Light strikes the two electrons in the reaction centre of PSI, exciting them to a higher energy level
  • Electrons are passed across the thylakoid membrane to the H+ where they reduce NADP to NADPH (requires 2 electrons)
  • PSII is unstable due to the loss of electrons, which are replaced by the photolysis of water
  • 2 Water > 4H+ and 4 Electrons
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13
Q

Describe the method of cyclic photophosphorylation.
(4 marks)

A
  • Light excites electrons in the reaction centre of PSI to raise them to a higher energy level
  • Electrons are passed down a series of electron carries through proton pumps and powering the production of ATP through chemiosmosis.
  • Electrons return to PSI to repeat the cycle.
  • This method generates more ATP, works in low light intensity and no NADPH is produced
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14
Q

How is the Rf value calculated?

A

Distance moved by pigment from origin DIVIDE BY the distance moved by solvent front from origin

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15
Q

What is photolysis?

A

The splitting of water by light, producing protons (Hydrogen ions), electrons and water

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16
Q

What is the light independent stage known as and what is its main purpose?

A
  • Calvin Cycle
  • Fixes CO2 into carbohydrates
17
Q

Describe the steps of the Calvin Cycle starting with the Five carbon compound.
(6 marks)

A
  • Ribulose bisphosphate (RUBP) (5C) is fixed with CO2 to form an unstable 6C compound
  • Two molecules of 3C glycerate-3-phosphate (GP). This reaction is catalysed by the enzyme rubisco
  • ATP and NADPH (from light dependent stage) reduce GP to 3C triose phosphate (TP)
  • TP can be converted into glucose, which is converted into starch by condensation reaction
  • Most of TP is converted into RUBP using ATP
  • Regeneration of RUBP allows Calvin cycle to continue
18
Q

How can lipids and proteins also be made from the Calvin Cycle?
(3 marks)

A
  • Acetyl coenzyme A can be synthesised from GP and converted into fatty acids
  • TP can be converted into glycerol which form triglycerides in a condensation reaction with fatty acids.
  • GP can be converted into amino acids for protein synthesis by adding Nitrogen from absorbed nitrate ions and ammonium by root hair cells by active transport
19
Q

What is a limiting factor for photosynthesis? What are the limiting factors?

A

A factor that control a process
- Light intensity > light is required for light dependant reactions. Light excites electrons in the photosystems.
- Temperature > Kinetic energy therefore rates of transport and enzyme activity affected (rubisco)
- COS concentrations > Carbon from CO2 fixed into carbohydrates in the Calvin Cycle.

20
Q

What are the two minerals needed for plants, why are they needed and what does deficiency cause?

A
  • Nitrogen (absorbed as NO3-) is needed for the synthesis of amino acids/nucleotides and ATP. Deficiency causes reduced growth of all organs and yellowing of leaves (chlorosis)
  • Magnesium (absorbed as Mg2+) is needed for chlorophyll production as it is the constituent of chlorophyll and ATPase. Deficiency causes chlorosis.

Biology Unit 3 (7 decks)

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