3.2 photosynthesis Flashcards

1
Q

How are angiosperm leaves adapted for photosynthesis?

A

Large surface area for maximum light absorption
Thin for maximum light penetration
Transparent upper epidermal cells
Palisade cells packed with chloroplasts, which orientate themselves towards the light

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2
Q

How are chloroplasts adapted for photosynthesis?

A

Range of photosynthetic pigments to maximise wavelengths of light absorbed
Large surface area of thylakoids

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3
Q

What do the photosynthesis action spectra show?

A

The rate of photosynthesis at different wavelengths of light

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3
Q

Name the photosynthetic pigments present in the antenna complex of the photosystems.

A

Xanthophylls
Beta carotene
Chlorophylls a and b

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3
Q

Why are chloroplasts said to be transducers?

A

They convert energy from one form to another - light energy to chemical energy of ATP

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3
Q

What do absorption spectra of photosynthetic pigments show?

A

The light absorbed by the each pigment at different wavelengths of light

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4
Q

What is the role of a photosystem?

A

To harvest light energy

Photons of light are absorbed and the energy is channelled via photosynthetic pigments down to the reaction centre

Each chlorophyll molecule loses one excited electron

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4
Q

What deductions can be made when studying the absorption and action spectra?

A

There is a close correlation between the two, suggesting that the light absorbed by the different pigments is used for photosynthesis

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5
Q

What are the components of a photosystem?

A

The antenna complex comprising a range of photosynthetic pigments
The reaction centre containing 2 chlorophyll a molecules

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5
Q

Describe non-cyclic photophosphorylation

A

Light is absorbed by both PSII and PSI
Excited electrons emitted by the chlorophyll a molecules in PSII are passed via the ETC to PSI
The electrons are replaced through the photolysis of water
Excited electrons from chlorophyll a molecules in PSI are passed to NADP
ATP and NADPH are produced

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6
Q

Describe how ATP is produced in a chloroplast

A

Electron transfer via carriers in the ETC (within the thylakoid membrane) releases energy
This powers the pumping of protons from the stroma into the thylakoid space (using 1 proton pump)
Protons build up, lowering the pH
Protons flow down their gradient through ATP synthetase, releasing energy to form ATP

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6
Q

Describe cyclic photophosphorylation

A

Light is absorbed by PSI
Excited electrons emitted by the chlorophyll a molecules are taken up by an electron acceptor and passed back to the ETC via a proton pump
The electrons travel back to PSI
ATP is produced

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7
Q

What is photolysis?

A

The splitting of water using light energy
Electrons produced replace those lost by the chlorophyll a molecules in PSII
Oxygen is produced as a by-product (2 protons and 2 electrons combine with NADP to form NADPH)

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8
Q

Which products of the light dependent stage are used by the light independent stage

A

ATP and NADPH

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8
Q

Where does the light independent stage of photosynthesis take place?

A

The stroma

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9
Q

Where does the light dependent stage of photosynthesis take place?

A

The thylakoids

10
Q

How is the TP used that drops out of the Calvin cycle?

A

To manufacture glucose (actually fructose bisphosphate), lipids and amino acids
Other products include starch and cellulose

10
Q

How many turns of the Calvin cycle are required to produce one molecule of glucose?

A

6
(3 turns will result in the availability of 1 TP for the production of glucose; 5 TP will be recycled)

10
Q

What is the name of the enzyme which catalyses the fixation of carbon dioxide by ribulose bisphosphate?

11
Q

What does carbon fixation mean?

A

The incorporation of inorganic carbon into an organic compound

12
Q

What is produced first in the Calvin Cycle, following the fixation of carbon dioxide?

A

2 molecules of Glycerate-3-phosphate (G3P)

12
Q

How are NADPH and ATP used in the Calvin Cycle?

A

Both NADPH and ATP are used to reduce Glycerate-3-phosphate (G3P) to Triose phosphate (TP)
ATP also used to reform ribulose bisphosphate from ribulose phosphate

13
Q

What is the compensation point?

A

The point at which the rate of respiration equals the rate of photosynthesis

13
Q

What is a limiting factor in photosynthesis?

A

The factor that limits the rate of photosynthesis as it is in the shortest supply

14
Q

Why is magnesium needed in a plant?

A

To synthesise chlorophyll

14
Q

How do you calculate the retention factor (Rf) of a pigment in a chromatogram?

A

Dstance travelled by pigment / distance travelled by solvent

14
Q

What are the main limiting factors in photosynthesis?

A

Carbon dioxide concentration
Light intensity
Temperature
(Also Magnesium and Nitrogen)

15
Q

Why is nitrogen needed by a plant?

A

To synthesise nucleic acids, amino acids and chlorophylls

15
Q

What is Net Primary Productivity (NPP)?

A

The rate at which light energy is converted to chemical energy in biomass (crop yield)

NPP = GPP - R

Measured in kJ/m2/yr

16
Q

Why is photosynthetic efficiency never 100%?

A

Some light passes through the leaf without striking a chloroplast
Some light is not of a suitable wavelength
Some light is reflected from the surface of the leaf

17
Q

What is GPP (Gross Primary Productivity)?

A

The rate at which light energy is converted to chemical energy in organic compounds during photosynthesis

Measured in kJ/m2/yr

18
Q

What is the definition of photosynthetic efficiency?

A

The percentage of available light energy that is converted to chemical energy during photosynthesis

19
Q

What is the term used to describe the yellowing of plant leaves, due to lack of chlorophyll?