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Biology Year 13 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What do autotrophic organisms do?

A

Make complex organic compounds from simple compounds in their environment

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2
Q

What is photosynthesis?

A

The process by which living organisms, particularly plants and algae, capture the energy of the sun using chlorophyll and use it to convert carbon dioxide and water into simple sugars

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3
Q

What stores energy in organic molecules such as glucose and starch?

A

Their chemical bonds

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4
Q

How do heterotrophic organisms obtain complex organic molecules?

A

By feeding on other living organisms or their dead remains

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5
Q

What is the ultimate source of energy for the chemical reactions in almost all organisms?

A

The sun

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6
Q

What is the equation for photosynthesis?

A

Carbon dioxide + water (light energy, chlorophyll) -> glucose + oxygen

6CO2 + 6H2O -> (light energy + chlorophyll) -> C6H12O6 + 6O2

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7
Q

How is the energy from the sun used in photosynthesis?

A

To split the strong O-H bonds in the water molecules. The hydrogen released is combined with CO2 to form a fuel for the cells (glucose). Oxygen is released into the atmosphere as a waste product

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8
Q

What is the structure and features of chloroplasts?

A
  • they are relatively large organelles found in the cells of green parts of plants
  • each chloroplast is surrounded by an outer and inner membrane with a space between the teo onown as the chloroplast envelope
  • inside the chloroplast there is a system of membranes that are arranged in stacks called grana
  • A single granum is made up of stacks of membrane discs known as thylakoids
  • the green pigment chlorophyll is found on the thylaloids
  • the grana are joined together by lamellae, extensions of the thylakoud membranes which connect two or more grana
  • the lamellae act as a skeleton within the chloroplast maintaining a working distance between the grana so that they get the maximum light
  • the membrane stacks are surrounded by a matrix called the stroma. The stroma contains all the enzymes to complete the process of photosynthesis and produce glucose
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9
Q

What is the envelope of a chloroplast?

A

The outer and inner membranes along with the intermembrane space

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10
Q

What are grana?

A

Stacks of thykaloid membranes within a chloroplast

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11
Q

What are lamellae?

A

Extensions of the thykaloid membranes which connect two or more grana, acting as a supporting skeleton in the chloroplast, maintaining a working distance between the grana so that they get the maximum light and function as efficiently as possible

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12
Q

What is the stroma?

A

The matrix which sureounds the grana and contains all the enzymes needed to complete the process of photosynthesis and produce glucose

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13
Q

What is chlorophyll a?

A

A blue-green photosynthetic pigment found in all green plants

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14
Q

What is chlorophyll b?

A

A yellow green photosynthetic pigment

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15
Q

Whar are carotenoids?

A

Photosynthetic pigments made up of orange carotene and yellow xanthophyll

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16
Q

What is phaeophytin?

A

A grey pigment which is a breakdown product of the other photosynthetic pigments

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17
Q

What is chlorophyll a mixture of?

A

Closely related pigments

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18
Q

Which chlorophyll pigment is found in all photosynthesising plants?

A

Chlorophyll a

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19
Q

How do the chlorophyll pigments differ apart from in colour?

A

Each pigment absorbs and captures light from particular areas of the spectrum

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20
Q

What is the absorption spectrum?

A

A graph of the amount of light absobed by a pigment against the wavelength of light

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21
Q

How are the absorption spectra of different photosynthetic pigments found?

A

By measuring the absoprtion of light of different wavelengths

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22
Q

What is an action spectrum?

A

A graph showing the rate of photosynthesis against the wavelength of light

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23
Q

How did T.W Engelmann compare the rate of photosynthesis with the wavength of light?

A

By using bacteria that move towards oxygen to show where most of the oxygen was given off which is directly related to the amount of photosynthesis taking place. In this way he achieved an action spectrum

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24
Q

What do modern action spectra use to measure the rate of photosynthesis at different wavelengths of light?

A

Electronic data logging rather than bacterial movement

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25
Q

What does the action spectra show us?

A

That the rate of photosynthesis is vey closely related to the combined absorption of all the photosynthetic pigments in a plant. Which demonstrates that the range of photosynthetic pigments makes a much bigger portion of the wavelength of light available to plants

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26
Q

What can you use to tell the chlorophyll pigments apart? And what do you do after this?

A

Chromotography. Once you have carried out the chromatography work out the pigments Rf values and compare them to the Rf values of known pigments in the same solvent.

27
Q

How do you work out the Rf value?

A

Distance travelled by solute (photosynthetic pigment)/ distance travelled by solvent

28
Q

What is Photosystem I (PSI)

A

A combination of chlorophyll pigments which absorbs light of wavelength 700nm and is involved in cyclic and non-cyclic photophosphorylatipn

29
Q

What is Photosystem II (PSII)

A

A combination of chlorophyll pigments which absorbs light at wavelength 680nm and is involved only in non-cyclic photophosphorylation

30
Q

What are photosystems?

A

Chlorophyll complexes

31
Q

Where in the chloroplasts are PSI mainly found?

A

The intergranal lamellae

32
Q

Where in the chloroplasts are PSII particles often found?

A

On the grana themselves

33
Q

What are the two stages in photosynthesis?

A

Light dependent reactions and light independent reactions

34
Q

What are light dependent reactions?

A

Reactions that take place in the light on the thykaloid membranes of the chloroplasts. They produce ATP and split water molecules in a photochemical reaction, providing hydrogwn ions to reduce carbon dioxide and produce carbohydrates

35
Q

What are light independent reactions?

A

Reactions that use the reduced NADP and ATP produced by the light dependent stage of photosynthesis in a pathway known as the calvin cycle which takes place in the stroma of the chloroplast and result in the reduction of carbon dioxide from the air to bring about the synthesis of carbohydrates

36
Q

What is a photochemical reaction?

A

A reaction initiated by light

37
Q

What are the two functions of the light dependent stage of photosynthesis?

A
  • to split water molecules providing hydrogen ions to later reduce the carbon dioxide and make carbohydrates
  • to produce ATP which is needed to supply the energy to produce the carbohydrates
38
Q

What is the smallest unit of light?

A

A photon

39
Q

What happens when a photon of light hits a chlorophyll molecule?

A

The energy is transferred to the electrons of that molecule. The electrons are excited and are raised to higher energy levels. If an electron is raised to a sufficiently high energy level it will leave the chlorophyll molecule completely. The excited electron can be picked up by an electron acceptor (carrier molecule) and result in the synthesis of either cyclic or non-cyclic photophosphorylation.

40
Q

What is cyclic phosphorylation?

A

A process that drives the production of ATP. Light excited electrons from PSI are taken up by an electeon acceptor and passed directly along an electron transport chain to produce ATP, with the electron returning to PSI

41
Q

What is non-cyclic photophosphorylation?

A

A process involving both PSI and PSII in which water molecules are split using light energy to provide reducing power to make carbohydrates and at the same time produce more ATP

42
Q

What happens in non-cyclic phosphorylation?

A
  • Under light condutuons photons are constantly hitting chlorophyll molecules in both PSI and PSII, exciting the electrons to a high enough level for them to be lost and picked up by electron acceptors.
  • An excited electron from PSII is picked up by another electron acceptor and is passed along an electron transport chain to PSI, driving the synthesis of one molecule of ATP.
  • PSI recieves an electron to replace one that was lost to light-independent reactions.
  • Now the chlorophyll molecule in PSII is short of an electron and unstable. It’s original electron cannot be returned as it has been transferred to PSI. Therefore an electeon comes from the splitting of water to replace the original one: photolysis. Water dissociates spontaneously into (H+) ions and hydroxide (OH-) ions resulting in plenty of these ions being present in the cell including in the chloroplasts and also replacing the lost electrons. Once PSII’s chlorophyll molecule had recieved an electron it is restored to it’s original state
  • at the same time electrons in PSI are also being excited by light and lost to an electron acceptor
  • electrons are carried down an electron transport chain and taken up by the electron acceptor (NADP). The NADP also takes up a hydrogen ion from the dissociated water at the same time to form reduced NADP
  • The reduced NADP and ATP produced during non-cyclic phosphorylation can be used as a source of reducing power and energy in the light independent reactions
  • the hydroxide ions that are left behind react together to form oxygen and water, losing four electrons whilst doing this which are transferred to the chlorophyll
43
Q

What is photolysis?

A

The splitting of a molecule using light

44
Q

What is the calvin cycle?

A

A series of enzyme-controlled reactions that take place in the stroma of chloroplasts and result in the reduction of carbon dioxide from the air to bring about the synthesis of a carbohydrate

45
Q

What happens in the calvin cycle?

A
  • in the first step carbon dioxide from the air combines with the 5-carbon compound ribulose biphosphate (RuBP) in the chloroplasts. This is carbon fixation. The enzyme ribulose bisphosphate carboxylase/oxygenase (RUBISCO) is necessary for this. RUBISCO is the rate limiting enzyme in photosynthesis
  • the result of the reaction between carbon dioxide and RuBP is in theory a C-6 compound. It has never been able to be isolated. It immedietly splits to give two molecules of glycerate 3-phosphate (GP), a 3-carbon compound.
  • GP is then reduced to form glyceraldehyde 3-phosphate (GALP) a 3-C sugar. The hydrogen comes from reduced NADP and the energy comes from ATP
  • a lot of the 3-phosphate GALP passes through a series of steps to replace the RuBP. However some of it is synthesised into glucose of passed directly into the glycosis pathway where it may be used for synthesis of othwr molecules needed by the plant
  • the reactions of the Calvin cycle can take place in both the light and dark. The reactions only stop in the dark when the products of the light reaction run out
46
Q

What is Ribulise biphosphate (RuBP)

A

A five carbon compound that joins with carbon dioxide from the air in the Calvin cycle to fix the carbon dioxide and form a 6-C compound

47
Q

What is Ribulose biphosphate carboxylase/oxygenase (RUBISCO)?

A

A key rate controlling enzyme that catalyses the reaction between carbon dioxide and ribulose biphosphate

48
Q

What us glyceraldehyde 3-phosphate (GALP)?

A

A 3-C sugar produced from the calvin cycle. It is the key product of photosynthesis.

49
Q

What is GALP used for?

A
  • Some is used directly in glycosis so fed on to the Krebs cycle
  • some is used to produce glucose in a process called glyconeogenesis. This glucose may then be converted into disaccharides such as sucrose for transport or polysaccharides such as starch for energy storage and cellulose for structural support
  • to replace the RuBP at the beginning of the calvin cycle
50
Q

How is the GALP that feeds into the glycosis and Krebs cycle pathway used?

A

As a fuel to provide energy in the torm of ATP for the function of the cell

51
Q

If GALP continues around the Calvin cycle what can it be used for?

A

The production of nucleic acids with the addition of phosphates from the soil

52
Q

What is some of the GALP taken into the glycosis pathway converted to and what is this used for?

A

It is converted to acetyl coenzyme A, which in turn can be used to synthesise fatty acids needed for the production of phospholipids for membranes and lipids needed for storage and other functions within the plant

53
Q

What are C3 plants?

A

Plants that use the photosynthetic pathway where the carbon dioxide is fixed directly into 3 carbon compounds

54
Q

What are C4 plants?

A

Plants that produce a compound containing four carbon atoms and use this to raise the carbon dioxide levels inside the cells at all times. This in turn minimises photorespiration making photosynthesis more efficient

55
Q

What are CAM plants?

A

A groups of plants that have evolved a way of fixing carbon dioxide in the dark and releasing it during the day. They have evolved in hot, dry ecosystems. This adaptation enables them to keep their stomata closed during the day reducing water loss and still have plenty of carbon dioxide for efficient photosynthesis

56
Q

How can light act as the limiting factor of photosynthesis?

A

The amount of light available affects the amount of chlorophyll which is excited and therefore the amount of reduced NADP and ATP produced in the light-dependent stage. If there is a low level of light insufficient NADP and ATP will be produced to allow the reactions of the light dependent stage to progress at their maximum rate

57
Q

How can carbon dioxide act as a limiting factor?

A

If there is not enough carbon dioxide available for fixing in the calvin cycle the reactions cannot proceed at their maximum rate

58
Q

How can temperature act as the limiting factor in photosynthesis?

A

All of the calvin cycle reactions and many of the light dependent reactions of photosynthesis are controlled by enzymes and are therefore sensitive to temperature. So if the temperature is wrong they may not work at their maximum capacity

59
Q

What is the way in which plants grow and the ecosystems that develop in the real world governed by?

A

Competition by plants for factors that can limit photosynthesis and growth such as:
•light
•warmth
•the nutrients that are needed to convert the carbohydrate into proteins and fats

60
Q

What are the ways in which plants are adapted to get as much light as possible so photosynthesis is not limited?

A
  • Growth in height
  • spreading of leaves into a mosaic pattern, •climbing
  • developing large leaves
  • seed dispersal to ensure that seedlings do not develop in the shade of their parents
61
Q

What is photorespiration?

A

The alternative reaction catalysed by RUBISCO in a low carbon dioxide environment which uses oxygen and releases carbon dioxide making photosynthesis less efficient

62
Q

What is glyconeogenesis?

A

The synthesis of glucose from non-carbohydrates

63
Q

What is a limiting factor?

A

The factor needed for a reaction such as photosynthesis to progress that is closest to its minimum value

Biology Year 13 (16 decks)

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