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Biology 🧬 > 5.1 Photosynthesis > Flashcards

5.1 Photosynthesis Flashcards

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1
Q

Where is the site of photosynthesis?

A

Chloroplasts

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2
Q

Equation for photosynthesis

A

Carbon dioxide + water –> glucose + oxygen

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3
Q

Balanced photosynthesis equation

A

6CO2 +6H2O –> C6H1206 + 6O2

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4
Q

Waxy cuticle adaptation

A

The transparent flattened cells of the epidermis and the transparent protective waxy cuticle readily allow light to pass through the leaf surface to the photosynthetic tissue

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5
Q

Blade of the leaf adaptation

A

The lamina has a large surface area to absorb light and is thin for rapid diffusion of gases

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6
Q

Palisade cells adaptation

A

The closely packed palisade cells with their numerous chloroplasts maximise light absorption for photosynthesis

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7
Q

Transport tissues adaptation

A

Numerous transport tissues permeate the leaf structure allowing water to be efficiently delivered to photosynthetic cells

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8
Q

Air spaces adaptation

A

The extensive network of air spaces in the spongy mesophyll for an easy passage for gases to and from the palisade cells and an efficient gas exchange system via the stomata

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9
Q

Stomata adaptation

A

Stomata are sites of gas exchange and their opening and closing is controlled by specialised epidermal cells called guard cells ; such regulation allows for efficient gas exchange while, at the same time, reducing water losses through transpiration

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10
Q

What are the three main stages to photosynthesis?

A
  1. Capturing of light energy
  2. Light-dependent reaction
  3. Light-independent reaction
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11
Q

Describe capturing of light energy

A

By chloroplast pigments such as chlorophyll

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12
Q

Describe the light-dependent reaction

A

Some of the light energy absorbed is conserved in chemical bonds. During the process an electron flow is created by the effect of light on chlorophyll, causing water to split (photolysis) into protons, electrons and oxygen. The products are reduced NADP, ATP, and oxygen

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13
Q

Describe the light-independent reaction

A

These protons (hydrogen ions) are used to produce sugars and other organic molecules

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14
Q

What are the two distinct regions inside a chloroplast?

A

Grana and Stroma

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15
Q

Describe the grana

A

The grana are stacks of disc-like structures called thylakoids where the light-dependent stage of photosynthesis takes place.

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16
Q

Describe the stroma

A

The stroma is a fluid-filled matrix where the light-independent stage of photosynthesis takes place. Within the stroma are a number of other structures

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17
Q

Where does the light-dependent reaction (LDR) take place?

A

In the thylakoids of chloroplasts

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18
Q

Describe photolysis

A

To split water into H+ ions and OH- ions, as the splitting is caused by light

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19
Q

Explain the role of light in photolysis

A

Light energy splits molecules of water
2H20 —> 4H+ + 4e- +O2

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20
Q

What happens to the products of the photolysis

A

H+ ions: move out of thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
e- : replace electrons lost from chlorophyll
O2 : used for respiration or diffuses out of leaf as waste gas

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20
Q
A
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21
Q

OILRIG

A

Oxidation is loss (of hydrogen), reduction is gain (of hydrogen). Oxidation results in energy being given in whereas reduction results in energy being taken in

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22
Q

Describe photoionisation

A

When a chlorophyll molecule absorbs light energy, it boosts the energy of a pair of electrons within this chlorophyll molecule, raising them to a higher energy level. These electrons are said to be in an excited state. The electrons become so energetic that they leave the chlorophyll molecule altogether, as a result the molecule becomes ionised

23
Q

Name the 2 main stages involved in ATP production in the LDR

A
  1. Electron transfer chain
  2. chemiosmosis
24
Q

What happens in the electron transfer chain?

A

The electrons released in photoionisation move down a series of carrier proteins embedded in the thyakoid membrane and undergo a series of redox reactions, which releases energy

25
Q

How is a proton concentration gradient established during chemiosmosis?

A

Some energy released from the electron transfer chain is coupled to the active transport of H+ ions (protons) from the thylakoid membrane into the thylakoid space

26
Q

How does chemiosmosis produce ATP in the LDR stage?

A

As electrons pass from one electron carrier to the next, energy is released which is used pump protons across the thylakoid membrane into the thylakoid space. This creates an electrochemical gradient across the thylakoid membrane. Protons flow back into the stroma through an enzyme which spans the membrane ; ATP synthase
ATP synthase catalyses ADP + Pi –> ATP

27
Q

How and where is reduced NADP produced in the light-dependent reaction?

A

NADP + 2H+ + 2e- —> reduced NADP. Catalysed by dehydrogenased enzymes.. thylakoid of chloroplasts

28
Q

Where do the H+ ions and electrons used to reduce NADP come from?

A

H+ ions : photolysis of water
electrons: NADP acts as the final electron acceptor of the electron transfer chain

29
Q

Equation of photolysis

A

2H20 —> 4H+ + 4e- + O2

30
Q

Why does photolysis occur?

A

The loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons. If the chlorophyll molecule is to continue absorbing light energy, these electrons must be replaced. The replacement electrons are provided from water molecules that are split up using light energy. This photolysis of water also produces protons

31
Q

What is the main product of the LDR stage?

A

Reduced NADP

32
Q

What is the oxygen produced is photolysis used for?

A

Either in respiration or diffuses out of the leaf as a waste product of photosynthesis

33
Q

How are chloroplasts adapted to their function of capturing sunlight and carrying out the light-dependent reaction:

A
  1. The thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light-dependent reaction
  2. A network of proteins in the grana hold the chlorophyll in a very precise manner that allows maximum absorption of light
  3. The granal membrane have ATP synthase channels within them, which catalyse the production of ATP. They are also selectively permeable which allows establishment of a proton gradient
  4. Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the LDR
34
Q

Where does the light-independent reaction occur?

A

Stroma

35
Q

Name the three main stages in the Calvin cycle

A
  1. Carbon fixation
  2. Reduction
  3. Regeneration
36
Q

What happens during carbon fixation?

A

Reaction between CO2 and ribulose bisphosphate (RuBP) cataylsed by rubisco
Forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)

37
Q

What happens during reduction?

A

2x GP are reduced to 2x triose phosphate (TP)
Requires 2x reduced NADP and 2x ATP
Forms 2x NADP and 2x ADP

38
Q

How does the light-independent reaction result in the production of useful organic substances?

A

1C leaves the cycle (some of the TP is converted into useful organic molecules)

39
Q

What happens during regeneration?

A

After 1C leaves the cycle, the 5C compound RuP forms
RuBP is regenerated from RuP using 1x ATP
Forms 1x ADP

40
Q

State the roles of ATP and reduced NADP in the light-independent reaction

A

ATP: reduction of GP to TP and provides phosphate group to convert RuP into RuBP
reduced NADP: coenzyme transports electrons needed for reduction of GP to TP

41
Q

State the number of carbon atoms in RuBP, GP and TP

A

RuBP: 5
GP: 3
TP: 3

42
Q

Describe the structure of a chloroplast

A
  • Usually disc-shaped
  • double membrane (envelope)
  • thylakoids: flattened discs stack to form grana
  • intergranal lamellae: tubular extensions attach thylakoids in adjacent grana
  • stroma: fluid-filled matrix
43
Q

How does the structure of the chloroplast maximise the rate of the LDR?

A
  • ATP synthase channels within granal membrane
  • large surface area of thylakoid membrane for electron transfer chain
  • photosystems position chlorophyll to enable maximum absorption of light
44
Q

How does the structure of the chloroplast maximise the rate of the light-independent reaction?

A
  • Own DNA and ribosomes for synthesis of enzymes, e.g. rubisco
  • concentration of enzymes and substrates in stroma is high
45
Q

How many turns of the calvin cycle are required to produce 1 molecule of glucose

A

6

46
Q

Define ‘limiting factor’

A

A factor that determines maximum rate of a reaction, even if other factors change to become more favourable

47
Q

Name 4 environmental factors that can limit the rate of photosynthesis

A
  • Light intensity (LDR)
  • carbon dioxide levels (light-independent stage)
  • temperature (enzyme-controlled steps)
  • mineral / magnesium levels (maintain normal functioning of chlorophyll)
48
Q

Outline some agricultural practices used to overcome the effect of limiting factors in photosynthesis

A
  • Artificial light, especially at night
  • artificial heating
  • addition of CO2 to greenhouse atmosphere
49
Q

Why do farmers try to overcome the effect of limiting factors?

A
  • To increase yield
  • additional cost must be balanced with yield to ensure maximum profit
50
Q

Suggest how a student could investigate the effect of a named variable on the rate of photosynthesis

A

Dependent variable: rate of O2 production / CO2 consumption
1. use a potometer
2. place balls of calcium alginate containing green algae in hydrogencarbonate indicator (colour change orange –> magenta as CO2 is consumed and pH increases)

51
Q

State the purpose and principal of paper chromatography

A

Molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (chromatography paper)

52
Q

Outline a method for extracting photosynthetic pigments

A

Use a pestle and mortar to grind a leaf with an extraction solvent e.g. propanone

53
Q

Outline how paper chromatography can be used to separate photosynthetic pigments

A
  1. Use a capillary tube to spot pigment extract onto pencil ‘start line’ 1 cm above bottom of paper
  2. place chromatography paper in solvent
  3. allow solvent to run until it almost touches the other end of the paper. pigments move different distances
54
Q

What are Rf values? How can they be calculated?

A
  • Ratios that allow comparison of how far molecules have moved in chromatograms
  • Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front

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