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Biology 5 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What are the 2 groups of reactions of photosynthesis called?

A

Light-dependent and light-independent reactions

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2
Q

What happens to chlorophyll when it absorbs light?

A

It becomes photoionised and the energy of electrons is increased, producing ATP and reduced NADP.

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3
Q

Where is chlorophyll found?

A

On the internal membranes of chloroplasts.

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4
Q

Write a definition of chemiosmosis.

A

The diffusion of hydrogen ions (protons) through a partially permeable membrane, which is linked to the generation of ATP.

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5
Q

How is carbon dioxide taken into the cell biochemistry?

A

It reacts with ribulose bisphosphate (RuBP) - a simple sugar; this is catalysed by the enzyme rubisco.

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6
Q

What is the role of the Calvin cycle in photosynthesis?

A

To fix carbon dioxide and make it into useful organic compounds (simple sugars).

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7
Q

What are the sources of energy for the Calvin cycle?

A

ATP and reduced NADP from the light-dependent reaction.

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8
Q

What is the product of carbon dioxide reacting with RuBP?

A

2 molecules of glycerate 3-phosphate (GP).

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9
Q

What is triose phosphate used for?

A

Regeneration of RuBP and making useful organic molecules within the plant.

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10
Q

What are the types of useful organic compounds produced by photosynthesis?

A

Glucose, cellulose, starch, disaccharides, lipids, and amino acids.

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11
Q

What happens to water during photosynthesis?

A

Photolysis - during the light-dependent reactions, it is split to produce oxygen, 2 electrons, and 2 protons to reduce NADP.

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12
Q

What is the likely limiting factor in a greenhouse, heated with a paraffin heater and sufficient watering?

A

Light intensity.

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13
Q

How can chlorophylls be separated experimentally?

A

A thin layer or paper chromatography.

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14
Q

What is the role of dehydrogenase enzyme?

A

Catalyses the reaction where electrons are accepted by NADP in chloroplasts.

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15
Q

In the Calvin cycle, what is glycerate 3-phosphate (GP) reduced to?

A

Triose phosphate.

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16
Q

In which reactions of photosynthesis is carbon dioxide is present in?

A

Light-independent

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17
Q

The light-dependent reactions.

A

Where the light is absorbed by chlorophyll and a water molecule is split.

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18
Q

Where does the light-dependent reaction take place?

A

The thylakoid membrane.

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19
Q

The light-independent reactions.

A

Where carbon dioxide is synthesised into useful organic compounds.

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20
Q

Location of light-independent reactions.

A

Stroma.

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21
Q

Site of photosynthesis.

A

Leaves.

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22
Q

Adaptations of leaves.

A

A large surface area absorbs as much sunlight as possible.
An arrangement of leaves on the plant minimised overlapping and so avoids the shadowing of one leaf by another.
Thin, as most light is absorbed in the first few micrometres of the leaf, and the diffusion distance for gases is kept short.
A transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath.
Long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight.
Numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion pathway from one.
Stomata that open and close in response to changes in light intensity.
Many air spaces in the lower mesophyll layer allow rapid diffusion in the gas phase of carbon dioxide and oxygen.
A network of xylem that brings water to the leaf cells, and phloem that carries away the sugars produced during photosynthesis.

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23
Q

3 main stages of photosynthesis.

A

Capturing of light energy, light-dependent reaction and light-independent reaction.

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24
Q

Chloroplast.

A

Site of photosynthesis.
Surrounded by a double-membrane envelope.
Filled with a fluid - stroma.

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25
Q

Stroma.

A

Site of light-independent reaction.
Contains 70S ribosomes, a loop of DNA and starch grains.
Loop of DNA codes for some of chloroplast proteins and the proteins coded for by this loop of chloroplast DNA are produced at the 70S ribosomes.
Sugars formed during photosynthesis are stored as starch inside starch grains.

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26
Q

Grana.

A

Thylakoids stacked up to form grana.
Grana are connected by membranous channels called stroma lamellae, which ensures the stacks of sacs are connected but distanced from each other.
Membranes of grana create large surface area to increase number of light-dependent reactions to occur.
Membrane system provides a large number of pigment molecules in an arrangement ensuring much light is absorbed.

27
Q

Photosystems.

A

Collection of photosynthetic pigments that absorb light energy.

28
Q

In a photosystem, the different pigment molecules are arranged in…

A

Funnel-like structures.
Each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre.

29
Q

Photosystem 2.

A

Primary pigment that absorbs light at a wavelength of 680nm and therefore called P680.
At the beginning of the electron transport chain and is where photolysis of water takes place.

30
Q

Photosystem 1.

A

Primary pigment that absorbs light at a wavelength of 700nm and therefore called P700.
In the middle of the electron transport chain.

31
Q

Photoionisation.

A

When a chlorophyll pigment becomes positively charged as a result of losing 2 electrons when it absorbs light energy.
2 electrons are lost because they are excited by the light energy and move to a higher energy level.

32
Q

What causes the photoionisation of chlorophyll?

A

When the light energy absorbed by the pigments is absorbed is passed to the primary pigment.

33
Q

Triose phosphate

A

A 3C sugar used to make the end products of photosynthesis including -

  • glucose, used in cellular respiration
  • cellulose, used as a structural component of cell walls
  • starch, stored as granules as energy reserves
  • disaccharides, including useful sugars.
34
Q

The light-dependent reaction of photosynthesis involves the capture of light whose energy is used for 2 purposes:

A
  • To add an inorganic phosphate molecule to ADP, thereby making ATP
  • To split water into H+ ions and OH- ions.
35
Q

Oxygen from photolysis.

A

Used in respiration or diffuses out of the leaf as a waste product.

36
Q

Adaptations of site for light-dependent reaction - thylakoid membrane

A

Provides a large surface area for the attachment of chlorophyll, electron carriers, and enzymes that carry out the reaction.

37
Q

Adaptations of site for light-dependent reaction - network of proteins in grana

A

Holds the chlorophyll in a very precise manner that allows maximum absorption of light.

38
Q

Adaptations of site for light-dependent reaction - granal membranes

A

Have ATP synthase channels within them, which catalyse the production of ATP; also selectively permeable allowing establishment of a proton gradient.

39
Q

Adaptations of site for light-dependent reaction - DNA and ribosomes in chloroplast

A

They can quickly and easily manufacture some of the proteins involved in the reaction.

40
Q

Process of light-dependent reaction.

A
  1. Light is absorbed by both photosystems. The light is passed to the primary pigment of each photosystem.
  2. Photoactivation - electrons in the primary pigment molecule of each photosystem are excited to a higher energy level.
  3. Excited electrons from photosystem 2 are passed to photosystem 1 via an electron transport chain, releasing sufficient energy to synthesise ATP.
  4. Electrons from the photolysis of water replace those lost from photosystem 2.
  5. Excited electrons from photosystem 1 and hydrogen ions from the photolysis of water both combine with NADP to form reduced NADP.
41
Q

During the light-dependent reaction, reduced NADP…

A

Is produced when hydrogen ions combine with carrier molecule of NADP using electrons from the photolysis of water.

42
Q

During the light-dependent reaction, ATP…

A

Is produced.

43
Q

During the light-dependent reaction, photophosphorylation uses the…

A

Proton (H+) gradient generated by the photolysis of water.

44
Q

The energy and hydrogen are used during the light-independent reactions…

A

To produce complex organic molecules.

45
Q

Main steps in Calvin Cycle.

A

Rubisco catalyses the fixation of CO2 by combination with a molecule of ribulose bisphosphate (RuBP) to yield 2 molecules of glycerate 3-phosphate (GP).
GP is reduced to triose phosphate (TP) in a reaction involving reduced NADP and ATP.
RuBP is regenerated from TP in reactions that use ATP.

46
Q

The Calvin Cycle.

A

CO2 reacts with ribulose bisphosphate (RuBP), a simple sugar.
The catalyst for this reaction is the enzyme rubisco. This forms 2 molecules of glycerate 3-phosphate (GP).
GP is reduced to triose phosphate using ATP and reduced NADP from the light-dependent reaction.
Some triose phosphate is used to regenerate RuBP, the rest is used to make useful organic compounds within the plant.

47
Q

How many times are the Calvin Cycle repeated to generate glucose?

A

6

48
Q

Glycerate 3-phosphate (GP) is used to produce…

A

Some amino acids.

49
Q

Triose phosphate (TP) is used to produce:

A

Hexose phosphates (6C) - starch, sucrose, cellulose.
Lipids for cell membranes.
Amino acids for protein synthesis.

50
Q

Carbon fixation.

A

CO2 combines with 5C sugar; an enzyme called rubisco catalyses the reaction. The resulting 6C is unstable and splits into 2 - 2GP.
The carbon dioxide has been fixed - it has been removed from the external environment and has become part of the plant cell.

51
Q

What are used to reduce glycerate 3-phosphate (GP)?

A

Energy from ATP and hydrogen from reduced NADP.

52
Q

Plants need:

A

Presence of photosynthetic pigments, supply of CO2 and water, light energy, suitable temperature.

53
Q

External factors affecting photosynthesis:

A

Light intensity, carbon dioxide concentration and temperature.

54
Q

As light intensity increases…

A

rate of photosynthesis increases.
The greater the light intensity, the more energy is supplied to the plant and therefore the faster the light-dependent stage of photosynthesis can occur.
Produces more ATP and reduced NADP for the Calvin cycle - at a greater rate.

55
Q

As carbon dioxide concentration increases…

A

rate of photosynthesis increases.
Carbon dioxide is one of the raw materials required for photosynthesis.
Required for the light-independent stage of photosynthesis, when CO2 is combined with the five-carbon compound ribulose bisphosphate (RuBP) during carbon fixation.
Means the more carbon dioxide that is present, the faster this step of the Calvin cycle can occur and the faster the overall rate of photosynthesis.
The natural level of CO2 in the atmosphere is 0.04%, it is therefore not advisable to increase the CO2 concentration much higher than this as it can become toxic.

56
Q

As temperature increases…

A

rate of photosynthesis increases as the reaction is controlled by enzymes.
As the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases.
Metabolic reaction - temp = large effect.
Temp has no significant effect on light-dependent reactions.

57
Q

Although the rate of enzymatic reactions is the main component affected by temperature, other components of the process can also be affected:

A

Increasing temperature causes stomata on the leaf to close in order to reduce water loss, when the stomata are closed CO2 cannot enter the leaves – therefore, a balance must be met here.
Light-dependent reaction relies on a proton gradient forming across the thylakoid membrane – it is important that a too high or too low temperature does not affect the permeability of the membrane which may lead to a dissipation of the proton gradient.

58
Q

Photosynthetic pigments.

A

Photosynthetic pigments = chlorophyll, and carotenoids.
2 chlorophyll molecules - chlorophyll a (yellow-green colour); chlorophyll b (blue-green colour).
Each chlorophyll absorbs different wavelengths of light.
Paper or thin layer chromatography can be used to separate the pigments.
The chlorophyll from plants growing in light versus shady conditions can be compared.

59
Q

At low concentration of CO2, the reaction of RuBP to GP…

A

Slows down and causes levels of RuBP to increase and levels of GP and TP to decrease.

60
Q

At low light intensity…

A

The supply of ATP and reduced NADP will decrease, slowing the rate of light-independent reactions.

61
Q

At low temperatures…

A

Enzymes are inactive.

62
Q

At high temperatures…

A

Enzymes are denatured.

Proteins may be denatured and reduce the rate of photosynthesis.

63
Q

Light-dependent reactions.

A

Occur in the thylakoid membrane of the chloroplast.
When light strikes an electron in the chlorophyll, it becomes excited.
Requires light and water.
Oxygen released.
Produces ATP and NADPH to fuel Calvin Cycle.

64
Q

Light-independent reactions.

A

Occur in stroma of chloroplast.
CO2 is pulled from atmosphere and used to build sugars - carbon fixation.
Requires ATP, NADPH and CO2.
Produces GP, TP, RuBP.
Calvin Cycle uses energy from ATP and NADPH to transform CO2 and sugars into glucose.

Biology 5 (3 decks)

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