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Biology > Topic 8 - Cell respiration and photosynthesis > Flashcards

Topic 8 - Cell respiration and photosynthesis Flashcards

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1
Q

What is the difference between oxidation an reduction?

A

Oxidation involves the loss of electrons,

reduction involves a gain of electrons.

Oxidation often involves gaining oxygen or losing hydrogen,

reduction often involves losing oxygen or gaining hydrogen

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2
Q

What are the three main stages of respiration?

A
  1. Glycolysis
  2. Anaerobic respiration
  3. Aerobic respiration
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3
Q

Summarise the process of glycolysis

A

In the cytoplasm, one hexose sugar is converted to two three-carbon atom compounds (pyruvate) with a net gain of two ATP and two NADH + H+

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4
Q

Outline the three stages of glycolysis

A
  1. Two molecules of ATP are used to initiate glycolysis. Phosphates from the ATPs phosphorylate glucose to form fructose-1,6-biphosphate. Phosphorylation occurs here
  2. The 6-carbon phosphorylated fructose is split into two 3-carbon sugars called glyceraldehyde-3-phosphate (G3P). Lysis occurs here
  3. **Oxidation occurs here. **Oxidation phase involving ATP and NADH formation. Each G3P undergoes oxidation to form NADH. As NADH is being formed, released energy is used to add an inorganic phosphate to the remaining 3-carbon compound. This results in a compound with two phosphate groups. Enzymes remove the phosphate groups and add them to ADP to produce ATP. End result is four molecules of ATP, two molecules of NADH. and two molecules of pyruvate. (pyruvate is the ionised form of pyruvic acid)
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5
Q

Where does the rest of aerobic respiration occur?

A

In mitochondria

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6
Q

What is decarboxylation?

A

The removal of a carbon atom.

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7
Q

What are coenzymes and what do they usually act as?

A

A molecule that aids an enzyme in its action. Usually acts as electron donor or acceptor.

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8
Q

What is NADH?

A

The reduced form of NAD+

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9
Q

What happens in the link reaction?

A
  1. Each pyruvate is decarboxylated to form 2-carbon acetyl group
  2. Carbon is released as CO2.
  3. The acetyl group is oxidised with the formation of NADH.
  4. The acetyl group combines with coenzyme A (CoA) to form acetyl CoA.
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10
Q

What are the products of the Krebs cycle?

A
  1. Two ATP
  2. Six NADH
  3. Two FADH2
  4. Four CO2 (released)
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11
Q

Outline the steps in the Krebs cycle

A
  1. Acetyl Coa combines with 4-carbon compound, oxoloacetate → 6-carbon compound called citrate
  2. Citrate is oxidised to form 5C compound. CO2 is released. While the 6C compound is oxidised, NAD+ is reduced to NADH
  3. 5C is oxidised and decarboxylated to form a 4C compound. CO2 is released and another NAD+ is reduced to NADH
  4. The 4C compound undergoes various changes resulting in several products: NADH, FAD is reduced to FADH2, ADP is reduced to ATP. The result is the starting compound of the cycle, oxoloacetate.
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12
Q

How many time does the Krebs cycle have to run for each glucose molecule?

A

Twice because each glucose forms two pyruvates

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13
Q

Where does electron transport chain occur?

A

On the inner mitochondrial membrane and on the membranes of the cristae

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14
Q

What happens in the electron transport chain?

A
  • A series of electron carriers
  • NADH supplies two electrons to the first carrier in the chain
  • Electrons come from oxidaion reactions in earlier stages of cell respiration
  • The two electrons pass along the chain because they give up energy each time they pass from one carrier to the next
  • At three points along the chain enough energy is given up for ATP to be made by ATP synthase
  • ATP production relies on the energy released by oxidative phosphorylation
  • FADH2 also feeds electrons into the transport chain, but at a slightly later stage and at only two stages is sufficient energy for ATP production
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15
Q

What is the role of oxygen in the electron transport chain?

A
  • Oxygen accepts hydrogen ions to form water
  • If oxygen is not available, the chain stops and NADH + H+ cannot be reconverted to NAD+
  • Supplies of NAD+ will run out and the link reaction and Krebs cycle will cease
  • Anaerobic respiration occurs without oxygen
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16
Q

Describe the process of chemiosmosis

A
  • Energy released as electrons pass along the electron transport chain is used to pump protons across the membrane into the space between inner and outer membranes
  • A concentration gradient is formed (a store of potential energy)
  • ATP synthase sends the protons back, which releases energy
  • Synthase uses the energy released to produce ATP
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17
Q

What is oxidative phosphorylation in terms of chemiosmosis?

A

Chemiosmosis is the movement of protons (H+) to provide energy so that phosphorylation can occur (formation of ATP). When oxygen is used, it is called oxidative phosphorylation.

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18
Q

How does the structure of the mitochondrion enable its function?

A
  • Cristae form a large surface area for the electron transport chain
  • Small space between inner and outer membranes allow accumulation of protons
  • Fluid matrix contain enzymes for the Krebs cycle
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19
Q

What is the overall equation for cellular respiration?

A

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

20
Q

Draw a diagram of the structure of a chloroplast

A
21
Q

What does photosynthesis consist of?

A

Light-dependent and light-independent reactions

22
Q

Where does light-dependent reaction occur?

A

In the thylakoids (in grana) of the chloroplast

23
Q

What is photophosphorylation?

A

The production of ATP in photosynthesis

24
Q

What are the final products of light-dependent reaction?

A

NADPH and ATP

25
Q

What happens in during light absorption in light-dependent reaction?

A
  • Chlorophyll absorbs a photon
  • The photon excites an electron → chlorophyll is photoactivated
  • Excited electrons are passed from molecule to molecule until they reach chlorophyll a in the reaction centre
  • Chlorophyll a passes the electron to a chain of electron carriers
26
Q

What is a photosystem?

A

Hundreds of molecules of chlorophyll arranged in groups located in thylakoid membranes.

27
Q

In what order does light-dependent reaction occur?

A

Photosystem II → Photosystem I

28
Q

How is ATP produced in light-dependent reactions?

A
  • An excited electron from the reaction centre of PSII is passed along a chain of carriers in the thylakoid membrane
  • It gives up some energy each time it passes from one carrier to another
  • The coupling of electron transport to ATP synthesis is by chemiosmosis
  • Electron flow causes a proton to be pumped across the thylakoid membrane into the fuild space inside the thylakoid
  • A proton gradient is created
  • ATP synthase lets the protons across the membrane down the concentration gradient and uses the energy released to synthesise ATP
  • This process is called non-cyclic photophosphorylation
29
Q

How is NADP produced in light-dependent reactions?

A
  • The electron from PSII is accepted by PSI
  • Electron replaces one previously given electron
  • With electron replacement the PSI can be photoactivated by abrobing light and give away another excited electron
  • This high-energy electron passes along a short chain of carriers to NADP+ in the stroma
  • NADP+ accepts two high-energy electrons and one H+ ion from the stroma to form NADPH (reduced NADP+)
30
Q

How is oxygen produced in light-dependent reactions?

A
  • PSII needs to replace the excited electron it gives away
  • With the help of an enzyme, water is split and its molecules are given to chlorophyll
  • Oxygen and H+ ions are produced as by-products
  • Only happens in light so is called photolysis
31
Q

What is cyclic photophosphorylation?

A
  • Occurs when light is not the limiting factor
  • NADPH accumulates in the stroma and there is a shortage of NADP+
  • A way of producing ATP with the lack of NADP+
    1. PSI abosrbs light and is photoactivated
    2. Excited electrons pass from PSI to a carrier between PSI and PSII
    3. AS the electrons flow they cause pumping of protons across the thylakoid membrane
    4. A proton gradient is formed and this allows the production of ATP
32
Q

Where do light-independent reactions occur?

A

In the stroma

33
Q

What is the Calvin cycle?

A

A cycle which uses CO2 and produces glucose

34
Q

What is ribulose biphosphate (RuBP)?

A

A 5-carbon sugar that combines with CO2 to produce two molecules of glycerate 3-phosphate

35
Q

What is glycerate 3-phosphate and what happens to it in light-independent reactions?

A

It is an organic acid that is converted into a carbohydrate by a reduction reaction.

  • Glycerate 3-phosphate is reduced to a 3-carbon sugar, triose phosphate (TP)
  • Linking together two triose phosphates produces glucose phosphate
36
Q

What is ribulose biphosphate carboxylase (rubisco)?

A

An enzyme that catalyses the reaction in which RuBP is combined with CO2. Large amounts of rubisco are present in the stroma because it functions rather slowly

37
Q

What happens in the Calvin cycle after glucose has been formed?

A

RuBP is regenerated by using triose phosphate. Five molecules of triose phosphate is converted into three molecules of RuBP

38
Q

How does the structure of chloroplasts support its function?

A
  • Large surface area of thylakoids for light absorption
  • Small space inside tylakoids for accumulation of protons
  • The fluid stroma for the enzymes and the Calvin cycle
39
Q

Summarise the complete process of photosynthesis

A
40
Q

Compare light-dependent and light-independent reactions

A
  • LD occurs in the thylakoids, LID occurs in the stroma
  • LD uses light energy to form ATP and NADPH, LID uses ATP and NADPH to form triose phosphate
  • LD splits water in photolysis to provide replacement electrons and protons and to release oxygen to the atmosphere, LID returns ADP, inorganic phosphate and NADP to the LD reaction
  • LD includes two electron transport chains and photosystems I and II, LID involves the Calvin cycle
41
Q

What is the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green plants?

A

Similarities:

  • The greatest absorption is in the violet-blue range
  • Also a high level of absorption in the red range of the spectrum
  • There is least absorption in the yellow-green range

Differences:

  • Little light is absorbed in the green-yellow range but there is some photosynthesis (due to accessory pigments that absorb pigments chlorophyll can’t)
42
Q

What are the limiting factors in photosynthesis?

A
  1. Light intensity
  2. Temperature
  3. Carbon dioxide concentration
43
Q

What is the rate-limiting step?

A

The rate of whichever step is proceeding most slowly at a particular time.

44
Q

What is the effect of light intensity on the rate of photosynthesis?

A
  • At low intensities there is a shortage of the products of the light-dependent reactions (NADPH, ATP) → the rate-limiting step is the point where glycerate 3-phosphate is reduced
  • Unless heavily shaded, light intensity is not usually the limiting factor
45
Q

What is the effect of CO2 concentration on the rate of photosynthesis?

A
  • At low concentrations the rate-limiting step is the point where CO2 is fixed to produce glycerate 3-phosphate
  • Carbon dioxide concentration is often the limiting factor
46
Q

What is the effect of temperature on the rate of photosynthesis?

A
  • At low temperatures all of the enzymes that catalyse the Calvin cycle work slowly
  • At high temperatures RuBP carboxylase does not work effectively, rate-limiting step is where CO2 is fixed

Biology (13 decks)

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