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Biology > Unit 5A: Photosynthesis > Flashcards

Unit 5A: Photosynthesis Flashcards

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1
Q

Adaptations of a leaf

A
  • broad and thin for larger SA
  • waxy cuticle and upper epidermis transparent for sunlight
  • palisade mesophyll are tightly packed for more chlorophyll
  • spongy mesophyll have air spaces for gas exchange
  • stoma on bottom of leaf to minimise water loss
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2
Q

How do stomata open and close

A
  • turgor pressure makes guard cells expand, forcing the tough inner walls to be convex, opening the stoma.
  • close during day and open during night to maximise gas exchange and minimise water loss
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3
Q

Features of chloroplasts

A
  • double membrane
  • 70S ribosomes
  • lipid droplets
  • starch granules
  • stroma
  • integral lamella
  • thylakoids (grana)
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4
Q

Permeability of double membrane

A
  • outer membrane permeable to small molecules, e.g water, co2
  • inner membrane regulates passage of large substances through channel proteins
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5
Q

What does stroma contain

A
  • enzymes, starch granules, proteins, chloroplast DNA and ribosomes
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6
Q

What are thylakoids

A

Disk shaped, fluid filled sacs, hollow, containing photosynthetic pigments.

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7
Q

What is a photosynthetic pigment

A

Coloured biological compound present in chloroplasts and photosynthetic bacteria, capturing light energy for photosynthesis

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8
Q

Why do we need pigments?

A

To capture the frequencies of all of the waves, allowing us to see them as visible light

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9
Q

What happens to light after it strikes a leaf

A

12% is reflected
83% is absorbed
4% is used in photosynthesis
5% of light is transmitted

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10
Q

Photosystem notes

A
  • Pigment + protein = photosystem
  • PS1 and PS2 contain a chlorophyll molecule which absorbs red light
  • PS1 found in lamellae, absorbs 700nm
  • PS2 found in thylakoid, absorbs 680nm
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11
Q

Two types of photosynthetic pigments

A
  • chlorophylls (primary)
  • carotenoids (accessory)
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12
Q

What is chromatography

A

A method used to separate molecules in mixtures

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13
Q

How does chromatography work

A

Molecules are dissolved and move through the mobile stage (liquid solvent) and get fixed to a stationary phase: different molecules spend different amounts of time in the mobile phase, separating them.

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14
Q

The longer the compounds spend in mobile phase depends on:

A

1) solubility - the more soluble the pigment the further it will travel
2) affinity to stationary phase - molecules which interact more strongly with the plate will not travel as far
3) mass - the smaller the molecule the further it will travel

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15
Q

Why should you use a non-polar solvent in chromatography

A

A polar solvent does not compete well, making the compounds remain in the stationary phase, therefore they would not move as far as they would with a non-polar solvent.

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16
Q

Where does light dependent reaction happen, and why

A

Thylakoids, because light energy is absorbed by chlorophyll in photosystems

17
Q

How is light converted into energy

A
  • Light energy excites the electrons in the chlorophyll, giving them more energy.
  • electrons are released from chlorophyll, making it positively charged
18
Q

What are coenzymes

A
  • aids the function of an enzyme
  • transfer a chemical group from one molecule to another
19
Q

NADP notes

A
  • coenzyme used in photosynthesis
  • transfers hydrogen from one molecule to another
  • reduces a molecule by giving it a hydrogen atom
  • or oxidise another molecule, by reducing itself to NADPH
20
Q

What is the light independent reaction

A
  • calvin cycle
  • doesnt use light directly
  • can take place in the dark but not for long, as it uses products from light-dependent reaction
  • happens in the stroma
  • ATP and NADPH supply energy
21
Q

Stages of non-cyclic photophosphorylation

A

1) photoionisation of chlorophyll in PS2
2) photolysis of water
3) electron transport chain
4) photophosphorylation (chemiosmosis)
5) photoionisation of chlorophyll in PS1
6) reduction of NADP to NADPH

22
Q

What us photoionisation of chlorophyll in PS2

A

Chlorophyll absorbs light energy and causes excitation of an electron. The electron is lost from the chlorophyll, and captured by an electron acceptor, moving along the electron transport chain. Chlorophyll is then oxidised and positively charged

23
Q

What is photolysis of water

A

Photoionisation of chlorophyll results in photolysis (splitting of water using light energy) into oxygen, hydrogen ions and electrons. Electron lost from chlorophyll molecule can be replaced and chlorophyll is reduced.

24
Q

What is electron transport chain

A

Electron is passed from carrier to carrier along ETC in a series of rapid redox reactions, energy is released at each stage. Energy is used to move hydrogen ions from the stroma into thylakoid space against conc. gradient, creating an electrochemical gradient.

25
Q

What is photophosphorylation (chemiosmosis)

A

Hydrogen ions pumped into thylakoid space move through enzyme ATP synthase, embedded in thylakoid memrbane. Energy from their movement catalyses ADP + Pi = ATP

26
Q

What is the photoionisation of chlorophyll in PS1

A

Light energy excites electrons that have gone through the ETC to PS1, moving them to a higher chemical level. Excited electron is captured by an electron acceptor electron lost from chlorophyll in PS1 is replaced by electron from ETC.

27
Q

What is reduction of NADP to NADPH

A

Excited electron from PS1 is passed along a series of electron carriers to final acceptor molecule NADP
Hydrogen ions from photolysis of water also combine with NADP to form NADPH:
2H+ + 2e- + NADP = NADPH

28
Q

Cyclic photophosphorylation notes

A
  • only PSI involved
  • oxygen not involved
  • electrons recycled
  • ATP synthesised
  • last electron acceptor is PSI
  • photophosphorylation in PSI only
  • no photolysis of water
  • does not require external electrons
29
Q

How is cyclic flow stimulated

A
  • during light-independent reaction, more ATP is consumed than NADPH.
  • when ATP runs low, NADPH accumulates because calvin cycle slows down.
  • rise in NADPH levels stimulates a shift to cyclic flow
30
Q

Calvin cycle process

A

1) CO2 reacts with ribulose biphosphate, a 5C compound, in a reaction catalysed by rubisco.
2) resulting 6C compound is unstable and immediately breaks down into two molecules of a 3C compound called glycerate-3-phosphate.
3) the 2GP is reduced to two molecules of triose phosphate, a 3C compound, using hydrogen ions / electrons from reduced NADP and energy from ATP.
4) one C molecule of triose phosphate is converted to complex organic molecules
5) triose phosphate molecules are used to regenerate RuBP in a series of enzyme catalysed reactions, one of which requires energy from ATP

31
Q

How many cycles of calvin needed for glucose and why

A

Six cycles, as one C atom is released each time.

32
Q

Limiting factors of photosynthesis

A
  • light intensity
  • carbon dioxide concentration
  • water availability
  • chlorophyll availability

Biology (8 decks)

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