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A-level Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What is a photoautotrope?

A

Plants which carry out photosynthesis (producers)

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2
Q

What is a photon?

A

Particle of light that contains a set amount of energy

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3
Q

What is the equation for photosynthesis?

A

6CO2 + 6H2O (+ energy from photons )——> C6H12O6 + 6O2

Endothermic process and hence needs energy from light

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4
Q

What is the purpose of respiration and photosynthesis in relation to CO2?

A

Responsible for the recycling of CO2 in the atmosphere

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5
Q

What happens during photosynthesis?

A

Light energy is converted into chemical energy where CO2 and Water are used to produce large organic molecules to be used within the plant.

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6
Q

What is the compensation point for respiration and photosynthesis?

A

When photosynthesis and respiration occur at the same time so there is no net loss or gain of carbohydrates

Respiration -carbohydrates used up

Photosynthesis- carbohydrates replenished

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7
Q

What is the structure of a chloroplast?

A

Outer membrane
Inner membrane
Thylakoids (stack is called a granum)
Stroma

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8
Q

What are the purpose of the thylakoids?

A

Where the light dependent stage of photosynthesis takes place

Have a large surface area for photosynthesis to occur on as well as containing lots of electron carriers and ATPsynthase proteins

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9
Q

What is the purpose of the stroma?

A

Where the light independent stage of photosynthesis takes place.

Fluid filled matrix containing proteins, starch grains, oil droplets and small ribosomes.

Also contains a chloroplasts own DNA

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10
Q

What are accessory pigments?

Give some examples

A

Light absorbing compounds that work along side chlorophyll A. Each pigment absorbs a different wavelength of light.

Chlorophyll A
Chlorophyll B
Carotenoids
Xanthophyll

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11
Q

How is light absorbed by chlorophyll in a photosystem?

A

Light (photons) pass through the photosystem by accessory pigments where it hits the reaction centre of chlorophyll A which absorbs the photons

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12
Q

What is the structure of chlorophyll A?

A

Porphyria group with an Mg2+ ions and 4 hydrocarbon chains.

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13
Q

What are the types of photosystem?

A 
Photosystem II (P680):
Peak absorption of light of wavelength 680nm
Photosystem I (P700):
Peak absorption of light of wavelength 700nm
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14
Q

What is the purpose of the light dependent reaction of photosynthesis?

A

To capture light energy which is used for the production of ATP and to produce H+ ions from the photolysis of water.

Also produces NADPH for the light independent stage of photosynthesis.

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15
Q

What happens during the light dependent stage of photosynthesis?

A
  1. Light absorbed by chlorophyll excites 2 electrons in PSII. (These electrons are replaced by photolysis of water)
  2. The excited electrons are accepted by an electron acceptor (containing Fe^3+ ion which becomes reduced to Fe^2+)
  3. The electrons are passed down the electron carriers via a series of redox reactions ( reduction and oxidation of iron ions). Each redox reaction releases a small amount of energy. (Goes to chemiosmotic theory for cyclic phosphorylation)
  4. Eventually the electron reaches photosystem II where is is excited again by photons.
  5. The electrons are accepted by ferredoxin (electron acceptor) which enables NADP to accept the electrons to form reduced NADPH in the stroma (2e- + 2H+ + NADP —> NADPH)
  6. NADPH is then available to be used in the light independent stage of photosynthesis.
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16
Q

What is the chemiosmotic theory?

A
  1. The energy released from the redox reactions down the ETC in the thylakoids membrane is used to pump H+ ions into the thylakoid lumen from the stroma.
  2. H+ ions accumulate in the thylakoid lumen and create a chemiosmotic gradient.
  3. H+ ions diffuse through ATPsynthase proteins which catalyses a reaction of ADP + Pi ——> ATP
  4. ATP is generated which is then used in the light independent reaction
17
Q

What are the products of the light dependent stage of photosynthesis?

A

ATP
Red. NADPH
O2 (inhibitor)

18
Q

What is the photolysis of water?

And why is it useful?

A

Light energy splits water molecules into protons electrons and oxygen.

2H2O ——> 4H+ + 4e- + O2

The electrons replace those lost in PSII and the H+ ions are used to reduce NADP to form NADPH and help create the chemiosmotic gradient.

19
Q

What is photoionisation?

A

Where electrons in the reaction centre of a chlorophyll molecule are excited by light energy (photons) and leave the chlorophyll molecule.

20
Q

What is the difference between cyclic and non cyclic photosynthesis?

A

Cyclic photosynthesis:
The ETC produces energy to pump H+ ions across membrane to produce ATP (no O2 or NADPH is produced)

Non cyclic photosynthesis:
Electrons pass down the ETC From PSII to PSI and produce ATP (via chemiosmosis) as well as NADPH and O2 from photolysis.

21
Q

What is photo phosphorylation?

A

Using light energy to produce ATP from ADP + Pi

22
Q

Briefly explain the passage of electrons in the light dependent reaction of photosynthesis

A 
Electrons are photoionised from PSII
Travel down ETC to PSI
Photoionised from PSI
Accepted by ferredoxin
Released to reduce NADP to NADPH (using NADP reductase)
23
Q

Briefly explain what the energy released from the ETC is used for?

A 
To pump H+ ions into thylakoid 
Build up a H+ ions gradient in thylakoids
H+ ions diffuse into stroma
Via ATPsynthase
Produces ATP
24
Q

How is NADP reduced?

A

The electrons are passed from ferredoxin into the stroma. Here to combine with H+ ions produces by the photolysis of water, to combine with NADP and with the help of NADP Reductase from NADPH.

25
Q

Where does the light independent reaction take place?

A

In the stroma of a chloroplast

26
Q

Where does the light dependent reaction take place?

A

Takes place on the thylakoid membrane and inside the thylakoid lumen.

27
Q

What is the purpose of the light independent reaction of photosynthesis?

A

To synthesis organic compounds such as glucose

And generate more RuBP to keep the cycle continuing.

28
Q

How does CO2 get into the stroma?

A

CO2 from the atmosphere Diffuses through stomata where it then dissolves in water around the mesophyll layer. Then diffuses through the cell membranes and cytoplasm to reach the stroma

29
Q

What happens in the light independent reaction?

Calvin cycle

A
  1. In the stroma RuBP reacts with CO2 to produce an unstable 6 carbon molecule with the enzyme RUBISCO
  2. This is then split into 2x 3 carbon molecules called glycerate 3 phosphate (3-PGA)
  3. Using energy from the hydrolysis of ATP(from light dependent reaction) and NADPH is used to reduce 3-PGA (itself oxidised) to form a triose phosphate (Glyceraldehyde 3 phosphate /G3P / TP)
  4. NADP is deformed and goes back to the light dependent reaction to be reduced again
  5. Some G3P is used to synthesis organic substances that the plants require (such as glucose or amino acids)
  6. Some G3P is used to regenerate RuBP using energy from hydrolysis of ATP (from LDR) which can then be used again in the Calvin cycle.
30
Q

How is the chloroplast adapted to carry out the light independent reaction?

A

Stroma fluid contains enzymes to carry out light independent reaction.

Stroma fluid surrounds grana and hence allows products of LDR to rapidly diffuse into stroma for light independent reaction.

Contains own DNA and ribosomes to synthesis any proteins required for the light independent reaction.

31
Q

What factors affect the rate of photosynthesis?

A 
Light intensity
CO2 concentration
Temperature
pH
Enzyme/substrate concentration
32
Q

How does light intensity affect rate of photosynthesis?

A

As light internist increases the rate of photosynthesis increases as more photons are being absorbed by the photosynthetic pigments. Once the maximum number of photons has been absorbed the rate of photosynthesis becomes to plateau and light intensity is no longer the limiting factor.

33
Q

How does CO2 concentration affect the rate of photosynthesis?

A

As CO2 concentration increases the rate of photosynthesis increases as there is more CO2 available to be used in the photosynthetic pathway. However eventually CO2 concentration will react a point where any additional CO2 has no effect on the rate of photosynthesis and and there is a plateau as CO2 concentration is no longer the limiting factor.

34
Q

How does temperature affect the rate of photosynthesis?

A

As the temperature increases the rate of photosynthesis increases as enzymes and substrates have more kinetic energy. His means there will be more successful collisions forming ESC’s and increase the rate of photosynthesis.
At optimum temperature the rate of diffusion is also highest so CO2 can diffuse quickly and less likely to limit the rate of photosynthesis.
Above optimum temperature and the hydrogen bonds of the R groups of the amino acids are broken changing the tertiary structure of and active site shape on enzymes (RUBISCO). This means fewer ESC’s are formed and the rate of photosynthesis decreases.

35
Q

How does pH affect the rate of photosynthesis?

A

Above and below optimum pH enzymes are denatured (R groups ionic bonds disrupted and hence enzymes cannot form ESC’s with substrates so rare of photosynthesis is slower.
At optimum pH enzymes can work efficiently and bind with substrates forming ESC’s to increase the rate of photosynthesis.

36
Q

How does enzyme substrate concentration affect the rate of photosynthesis?

A

As the E/S concentration increases so does the rate of photosynthesis as more E/S can bind together forming ESC’s to carry out photosynthesis. As the E/S reach a point where they are not equal to each other and one exceeds the other the rate of photosynthesis plateaus as either the enzyme or substrate concentration becomes the limiting factor.

37
Q

How does oxygen act as an inhibitor of photosynthesis?

A

Oxygen is a competitive inhibitor or photosynthesis so as the O2 concentration increase the rate of photosynthesis decreases.

This means that an increased O2 concentration would lead to an increased number of molecules binding to enzymes active sites in place of the substrate and therefore preventing ESC’s from being formed and the rate of photosynthesis decreases.

A-level Biology (23 decks)

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