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A Level Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What does photosynthesis do?

A

It transfers energy from sunlight into the chemical potential energy of organic molecules.
Almost all of the energy in ATP molecules is derived from photosynthesis.

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2
Q

What are autotrophs?

What are the two types and how do they derive their energy?

A

an organism that can trap an inorganic carbon source (carbon dioxide) using energy from light or from chemicals

  1. Photoautotrophs: They derive their energy from light
  2. Chemoautotrophs: They derive their energy from oxidising (NH3) to nitrite (NO2-) or nitrate (NO3-)
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3
Q

What is photosynthesis?

A

It is the trapping of carbon dioxide and its subsequent reduction to carbohydrate using hydrogen and water.
it takes place inside the chloroplasts.

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4
Q

What is the general equation for photosynthesis?
What is the most common type of sugar formed?
What is the reaction in the case of the formation of this sugar?

A

nCO2 + nH2O –light energy–> (CH2O)n + nO2
Hexose sugars
6CO2 + 6H2O –light energy–> C6H12O6 + 6O2

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5
Q

What are the two stages of photosynthesis and how are they different?
Where do they take place in?

A
  1. Light dependant stage: Energy for photolysis where the H and O is removed from the water -the H is transferred to an ATP molecule
  2. Light independent stage: Energy is not needed as the H removed is just used to reduce the CO2 into a carbohydrate.

The Chloroplasts

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6
Q

What is the energy trapped by chlorophyll used for?

A
  1. To split apart the strong bonds in the water molecules
  2. To produce ATP
  3. To reduce a substance called NADP
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7
Q

What is NADP?

What is its function?

A

It is nicotinamide adenine dinucleotide phosphate
It is a coenzyme
It is used along with ATP in the transfer of H to carbon dioxide as it forms reduced NADP to produce complex organic molecules that will have energy.

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8
Q

How are the photosynthetic pigments divided?

A

Primary pigments: Chlorophyll
They are reaction centres.
Accessory pigments: a pigment that is not essential to
photosynthesis but which absorbs light of different
wavelengths and passes the energy to chlorophyll

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9
Q

What is a photosystem?

What are the types?

A
  • They are light-harvesting clusters

- PS I and PS II - each containing two different types of chlorophyll

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10
Q

What are the two types of photophosphorylation?

A
  1. Cyclic photophosphorylation

2. Non- cyclic photophosphorylation

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11
Q

What is the process of photophosphorylation?

A
  1. PS1 and PS2 absorb light energy and re raised to higher energy level.
  2. Excited electrons are released by chlorophyll and taken up by acceptors
  3. The electrons pass through a chain of electron carriers
  4. ATP is synthesized as electrons are passed along.
  5. The electrons are taken up by PS1
  6. At the end, they combine with NADP and H+ to form reduced NADP
  7. the hydrogen ions are produced from the photolysis of water. The electrons are resupplied after the photolysis of water
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12
Q

What is photolysis?
What are its products and the purpose of those products?
How is it done?
Where is it done?

A

It is the break down of water.

Products:

  1. H+: is used to reduce NADP to reduced NADP H
  2. O: combines to form molecular oxygen and diffuses out

Using an enzyme that is contained in PS II that is activated by light

in the PS II photosystem

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13
Q

What is the difference between the cyclic and non cyclic photophosphorylation?
What is the difference in products formed?

A

Cyclic: Electrons from PS I are passed straight back to the chain of electron carriers linking to those from PS II
Products: ATP but not NADP

Non-cyclic: follows the Z scheme where the electrons lost from PS I and PS II are not returned back to them.
Products: ATP and NADP

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14
Q

What is the Calvin cycle?
Where does it take place?
What is the enzyme involved?

A
  • It is the cyclical series of reactions in photosynthesis during which carbon dioxide is fixed into carbohydrate.
  • The Stroma
  • Ribulose biphosphate carboxylase - rubisco
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15
Q

What are the three stages of the calvin cycle?

A
  1. Carbon dioxide fixation
  2. Reduction of GP to TP
  3. Regeneration of RuBP
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16
Q

Describe carbon dioxide fixation

A
  • carbon dioxide diffuses into the chloroplast
  • combines with a 5C (rubulose biphosphate, RuBP)
  • two molecules of GP is formed - Glycerate 3-phosphate
  • catalysed by rubisco - ribulose biphosphate carboxylase
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17
Q

Describe the reduction of GP to TP in the Calvin cycle

A
  • glycerate 3-phosphate in the presence of ATP and reduced NADP becomes triose phosphate
  • It is the first carbohydrate produced in photosynthesis
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18
Q

Describe the regeneration of RuBP
What is the relationship of the products formed?
Therefore, what is the relationship between the Calvin cycle and the glucose?

A
  • Most of the triose phosphate is used to regenerate RuBP
  • 6 triose phosphate -> 5 RuBP + 1 photosynthesis product
  • 6 turns of the calvin cycle is required for 1 glucose
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19
Q

What is the triose phosphate used for?

How are the products produced?

A
  1. Pyruvate -> Actely coenzyme A -> Krebs cycle acids -> amino acids -> proteins
  2. Sugar phosphates
    - > glylcerol -> lipids (fatty acids from pyruvate)
    - > monosaccharides -> polysaccharides or disaccharides for
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20
Q

Describe the membrane structure available on the chloroplast?
what types of reactions take place?
what adaptations do they have?

A
  1. surrounded by 2 phospholipids membranes
  2. Membrane in the stroma -> light dependant reactions
    - Thylakoids (fluid filled sacs) -> grana
    - joined by membranes
    - holds pigments, enzymes and electron carriers
    - holds ATP synthase
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21
Q

Describe how pigments are arranged in the chloroplasts.

What do these pigment structures do/

A
  • Funnel like structure
  • Passes energy through it
  • Finally feeding it into chlorophyll a reaction centre
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22
Q

What is the stroma?

What structures does it contain?

A
  • site of light-independent reactions
  • 70S ribosomes
  • loop of DNA
  • lipid droplets
  • starch grains
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23
Q

What are the groups of pigments in a chloroplast?
What are the names of the pigments?
What is the colour of the pigments?

A
  1. Chlorophylls
    - chlorophyll a: blue green
    - chlorophyll b: yellow green
  2. carotenoids
    - beta carotene: orange
    - xanthophyll: yellow
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24
Q

what is the absorption peak of chlorophyll a and b?

A

a: 430 nm and 662 nm
b: 453 nm and 642 nm

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25
Q

what is the difference between a primary pigment and an accessory pigment?

A

primary pigment - chlorophyll a - are the ones that are most abundant
accessory pigment are chlorophyll b and the carotenoids: they absorb light of different wavelengths and transfer the energy to chlorophyll a.

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26
Q

what are carotenoids?

A

they are accessory pigments that protect the chlorphylls from oxygen free radicals - single oxygen atoms

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27
Q

What are the colours absorbed and reflected by chlorophylls and carotenoids?

A

Chlorophylls:
Absorbed: red and blue light
Reflects: green light

Carotenoids:
Absorbed: blue-violet lights

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28
Q

What is an absorption spectrum?

How does the range of wavelengths that can be absorbed by chlorpohyll increase?

A

It is a graph that shows the wavelengths of light absorbed by the photosynthetic pigments.
The absorption spectrum for chlorophylls and carotenoids is somewhat different.

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29
Q

what is an action spectrum?
How does an action spectrum relate to the absorption spectrum?
Why might there be a difference in the peaks of an action spectrum and absorption spectrum?

A
  • It is a graph that shows the rate of photosynthesis against the wavelength of light.
  • The shape of the action spectrum is similar to the absorption of the combined chloroplasts. It is these absorbed wavelengths provide the energy for photosynthesis.
  • Not all absorbed light is used in photosynthesis.
30
Q
  • Chromatography of photosynthetic pigments -
    What are the leaves ground up with?
    What is a a suitable solvent?
A
  • propanone

- 10% propanone 90% hexane

31
Q

What are the Rf values for the following pigments?

A
  • chlorophyll a: 0.60- 0.65
  • chlorophyll b: 0.50
  • beta carotene: 0.95
  • xanthophyll: 0.35
32
Q

How can ultraviolet light be used to show the energy used to drive photosynthesis?

A
  • Ultraviolet light is shined
  • the light is absorbed and the electrons are excited
  • when extracted pigments are used, there is no ETC, so the electrons return to an unexcited state
  • this causes them to release thermal energy - it is this energy that drives photosynthesis
33
Q

What are the main external factors that affect the rate of photosynthesis?
How do they affect the rate?

A
  1. Light intensity: light is needed as an energy source for the light dependant reactions.
  2. Temperature: enzyme catalysed reactions in the light independent reactions depend on collisions.
  3. Concentration of carbon dioxide: carbon dioxide needs to be fixed in the light independent reactions.
  4. Availability of water: required for light dependant reactions - it may also affect the closing of stomata so can affect it indirectly.
  5. Wavelength:
34
Q

How can we use the rate of photosynthesis to prove that the photochemical reaction happens at two different stages?

A
  • At a high light intensity, the rate of photosynthesis affect changes rapidly as the temperature is increased
  • However at lower light intensities, the rate of photosynthesis doesn’t change much as the temperature is increased.
35
Q

What is the limiting factor?

A

it is the factor that holds back the rate of reaction.

the one factor, of many affecting a process, that is nearest its lowest value and hence is rate-limiting

36
Q

What is the procedure for using an aquatic plant to investigate the rate of photosynthesis?

A
  1. A fresh piece of an aquatic plant is cut and placed upside down in the test tube of water
  2. Bubble of oxygen are collected in the flared end of the capillary tube
  3. After measured period of time the oxygen is drawn into the capillary tube using the syringe
  4. The length of gas bubble in the syringe is measured. The length of the gas bubble per unit time is a measure of the rate of photosynthesis.
37
Q

How are the following factors of rate of photosynthesis investigated using an aquatic plant.

  • light intensity
  • carbon dioxide
  • temperature
A
  • light intensity can be changed by changing the distance of a lamp from the plant
  • The concentration of hydrogen-carbonate ions can be changed by adding various amounts of sodium hydrogen carbonate to the water.
  • The test tube containing the aquatic plant is placed inside a beakers with a thermometer to the beaker and varying it over a range of temperatures.
38
Q

When investigating the rate of photosynthesis using a suspension of chloroplasts, how is the suspension made?

A

A suspension of chloroplasts can be isolated from leaves of a plant such as spinach by liquidising the leaves in ice-cold buffer solution , then filtering or centrifuging the mixture to remove unwanted cell debris.

39
Q

What is the basis of the hill reaction?

A

When chloroplasts are exposed to light they undergo photolysis and release H+ with a reducing power.
This reducing power can be used to reduce DCPIP which changes colour.

40
Q

What is the procedure to investigate the rate of photosynthesis using the Hill Reaction?

A
  1. A freshly made suspension of chloroplasts in the buffer is placed in a small cold tube and kept in the dark until used.
  2. DCPIP solution is added to the tube, the tube shaken and the time noted.
  3. The tube is placed at a fixed distance from a bright light from a bench lamp.
  4. At suitable intervals, the tube is placed in a colorimeter with a red filter and the absorbance of the contents recorded.
41
Q

What are the problems with C3 plants, requiring them to adapt and form C4 plants?

A
  • Stomata close on hot dry days, so less carbon dioxide moves in, and the rate of photosynthesis is lower.
  • At high temperatures and high light intensity, photorespiration occurs.
42
Q

Explain what is meant by photorespiration.
- Where does it occur?
- What are the conditions for it to occur?
- What is the product as a result of it
- What is the negative effect of such a reaction?
What kind of process is it?

A

The process occurring in chloroplasts at a high temperatures and high light intensity, where rubsico binds oxygen to RuBP in place of carbon dioxide; RuBP is broken down into carbon dioxide and water and less carbon dioxide is fixed and no ATP is produced
it is an oxidative process.

43
Q

How is carbon dioxide fixed in a C4 plant?

A
  1. In the mesophyll cells, CO2 is absorbed, which reacts with PEP to form the 4 carbon compound known as oxaloacetate
  2. It is then converted to malate and is then passed into the bundle sheath cells
  3. The CO2 is released from the malate to which then goes to the Calvin cycle by combining with RuBP (in the bundle sheath cells)
  4. In this way rubisco is kept away from oxygen
  5. Photorespiration is avoided
  6. Allows the calvin cycle to continue
44
Q

What are the full name of PEP?

A

PEP: phosphoenolpyruvate

45
Q

How does a C4 plant differ in its anatomy from a C3 plant?

A
  1. They have 2 types of photosynthetic cells called:
    i. bundle sheath cells - which keep the rubisco away from air to avoid photorespiration
    ii. mesophyll cells arranged in two rings around vascular bundles which absorb the CO2 and allow it to combine with RuBp
  2. High optimum temperature enzymes involved
46
Q

Examples of C4 plants.

A
  1. maize
  2. sugar cane
  3. sorghum
47
Q

What is the role of the bundle sheath cells?

How do they get CO2?

A

They carry out the calvin cycle but not the light dependant reactions
No air gets to these cells, and they get carbon dioxide from the mesophyll cells.

48
Q

What is the role of the ring of mesophyll cells?

What is the role of the structures inside it?

A

It excludes the air from the cells inside the ring
the cytoplasm fixes carbon dioxide
the chloroplasts capture light and carry out the light dependant reactions but not the Calvin cycle.

49
Q

Explain how the palisade mesophyll cells are adapted for photosynthesis. [12]

A
  1. Closely packed to absorb maximum incident light
  2. Vertical/ at right angles of the lead to reduce the number of cross walls (light absorbing walls)
  3. Large vacuole pushes chloroplasts to edge of cell
  4. Chloroplasts at edge short diffusion path for carbon dioxide
  5. Chloroplasts at the periphery - absorbs most light
  6. large number of chloroplasts to absorb maximum light
  7. Air spaces/ cylindrical cells to circulate the gases
  8. Moist cell surfaces for the diffusion of gases
  9. Cell walls thin for maximum light penetration
  10. Large surface area for diffusion of gases
  11. chloroplasts can move towards the light
  12. chloroplasts can move away from high light intensities
50
Q

What wavelengths of light does the 2 photosystems absorb?

A

PI - 700 nm

P II - 680 nm

51
Q

Explain the shape of an action spectrum in terms of the rate of photosynthesis for red and blue light.

A
  1. The peaks on the absorption correspond to a high rate of photosynthesis
  2. absorbed light is used for photosynthesis
  3. A higher rate of photosynthesis in red and blue light
52
Q

Why does increasing the concentration of carbon dioxide increase the rate of production of carbohydrates at high light intensities. [10]

A
  1. light is not limiting
  2. much ATP/ reduced NADP available
  3. CO2 is a limiting factor
  4. because low concentration of CO2
  5. more CO2 combines with RuBp
  6. Rubisco
  7. Calvin cycle
  8. GP to TP
  9. More hexose is produced
    10 . fate of hexose
53
Q

Describe the structure of a chloroplast [15]

A
  1. Biconcave disc
  2. 3-10 um
  3. double membrane
  4. internal membrane system
  5. Flattened/ fluid filled sacs
  6. arranged in stacks of Grana
  7. holds pigments
  8. clusters of pigments
  9. ATP synthase
  10. intergranal lamellae
  11. Stroma
  12. Contains enzymes of the Calvin cycle
  13. lipids/ starch grains
  14. Stroma contains ribosomes
54
Q

How can a chloroplast be determined from its micrograph?

A
  1. Starch grain
  2. Grana
  3. Having a typical chloroplast shape
55
Q

What are the functions of the water stored in the vacuoles of plant cells?

A
  1. (raw material) for photosynthesis
  2. maintains turgidity
  3. Pushes chloroplasts to the edge of the cell
  4. Used in hydrolysis reactions
  5. Solvent for ions and pigments
56
Q

What are the ways that commercial growers of crop plants increase their yield? [9]

A
  1. Optimum temperature
  2. Heaters/ ventilation
  3. Optimum CO2 concentration
  4. Burners pump in CO2
  5. High light intensity
  6. Irrigation
  7. Fertilisers
  8. Pest/ disease control
  9. Artificial pollination
57
Q

What is the name of the cell covering most of the undersurface of a dicotyledonous leaf?

A

Epidermal cells

58
Q

What is the role of the stomata?

A
  1. Allows carbon dioxide in the leaf as most of the leaf is covered with a waxy cuticle
  2. Allows oxygen out
  3. Control of loss of water vapour
  4. ^ down their concentration gradients
59
Q

What are the adaptations of the guard cells in plant tissue that allows them to open and close?

A
  1. Sausage shaped
  2. Joint on on the ends
  3. Unevenly thickened walls
  4. Vacuoles
60
Q

Explain how the products of phosphorylation are used in the Calvin cycle [3]

A
  1. ATP along with NADP will reduce GP to TP
  2. ATP is used as an energy source
  3. Used in the regeneration of RuBP
61
Q

What are the structural differences between guard cells and other lower epidermal cells

A
  • They have chloroplasts
  • There is a varying thickness in cell walls
  • No plasmodesmata
62
Q

Explain how having a large surface area and being thin are beneficial for photosynthesis,

A

SA:

  • Allows more light/carbon dioxide.
  • Allows better gas exchange to occur

Thinness:

  • shorter diffusion distance for gases
  • faster diffusion of gases
63
Q

How does the loss of potassium ions from a guard cell lead to the closure of the stomata?

A
  • Water potential of the guard cells increases
  • water leaves the cell(s)
  • by osmosis down a water potential gradient
  • (guard cell) becomes flaccid and less turgid
64
Q

Where is the enzyme rubisco found in a chloroplast?

A

Stroma

65
Q

Where in the chloroplast are RuBP and GP found?

A

Stroma

66
Q

Does temperature affect photolysis?

A
  • No

- Photolysis is only activated by light

67
Q

What is the role of reduced NADP in the light-independent stage of photosynthesis?

A
  • Reduces/ donates hydrogen

- to turn GP to TP

68
Q

describe how photophosphorylation differs from oxidative phosphorylation

A 
light involved
occurs in chlorplast/chlorophyll
on thylakoid membranes
cyclic and non-cyclic 
photolysis of water
light is not involved
oxygen is the final acceptor
69
Q

Explain the role of the thylakoid membrane in photosynthesis

A
  1. Photosystems - Light dependant stage
  2. Maintains carriers in position -> site of ETC
  3. Proton pumping
  4. Large surface area
  5. ATP Synthase
  6. Produces reduced NADP
70
Q

Describe the photoactivation of chlorophyll.

A
  1. Chlorophyll absorbs mainly red and blue light
  2. Light is absorbed by an antenna complex
  3. Energy is transferred to the reaction centres
  4. Light energy excites the electrons/ Passes them to a higher energy level
  5. It is then lost from the chlorophyll.
71
Q

Explain how photolysis of water occurs.

A 
Water is split into H+ and OH-
Electron is removed from OH-
to replace the electron lost from the photosystem
OH- breaks into O2 and water
H+ used to form NADPH

A Level Biology (6 decks)

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