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aqa biology a level > Energy transfer in and between organisms > Flashcards

Energy transfer in and between organisms Flashcards

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AP® Biology flashcards
1
Q

What are the adaptations of leaves in order to carry out photosynthesis most effectively?

A
  • Large surface area to absorb sunlight
  • Leaf arrangements to stop overlapping of leaves and shadowing of each other
  • Thin for a short diffusion distance
  • Transport cuticle/epidermis to let light through to the mesophyll layer
  • Long upper mesophyll cells with many chloroplasts for sunlight
  • Many stomata for gas exchange/short diffusion path
  • Stomata responds to differences in light intensity (open/close)
  • Air spaces in lower mesophyll layer for rapid diffusion
  • Xylem + Phloem network to bring water/carry sugars produced
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2
Q

What is the balanced symbol equation for photosynthesis?

A

6CO2 + 6H20 -> C6H12O6 + 6O2

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3
Q

What is the word equation for photosynthesis?

A

Carbon Dioxide + Water -> Glucose + Oxygen

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4
Q

What are the 3 stages of photosynthesis?

A
  1. Capturing light energy -> by chloroplast pigments (e.g chlorophyll)
  2. Light Dependent Reaction -> light energy is conserved in chemical bonds, an electron flow is created by effect of light on chloroplast pigments. Products are reduced NADP, ATP and Oxygen
  3. Light Independent Reaction -> Protons are used to produce sugars and organic molecules
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5
Q

What is the structure of chloroplasts?

A

Disc shaped + 2-10 micrometres long + double membrane
Grana (stacks of thylakoids) where LDR happens
Sroma (fluid filled matrix) where LIR happens

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6
Q

What is the light dependent reaction of photosynthesis?

A

Chlorophyll absorbs light energy causing the photoionisation of chlorophyll

Some energy from the electrons released during photoionisation is conserved in the production of ATP and reduced NADP

ATP production involves electrons moving down an electron transfer chain and the movement of protons across chloroplast membrane down a concentration gradietn and this is catalysed by ATP synthase - Chemiosmotic Theory

The photolysis of water produces protons, electrons and oxygen

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7
Q

What is the equation for the photolysis of water?

A

H20 -> 2H+ + 2e- + 1/2O2

Water -> Protons + Electrons + Oxygen

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8
Q

What are the products of the LDR?

A

ATP and NADPH

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9
Q

How do protons cross the phospholipid bilayer between thylakoids and stroma?

A

Protons are pumped via proton carriers from stroma
Electrons transfer energy from photolysis of water and proteins increase their concentration
Concentration gradient between thylakoids and stroma of proteins is maintained (high -> thylakoid, low -> stroma)
Protons can only cross membrane through ATP synthase channel proteins (rest of membranes is hydrophobic so protons are repelled)
As protons pass through ATP synthase channel, enzyme structure is changed causing the catalysis of ADP + Pi to lower activation energy to form ATP.
Protons pass out of thylakoids through ATP synthase channels, NADPH is formed from NADP - electron carrier - taking up protons

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10
Q

What is the Light independent reaction?

A

Uses NADPH from LDR to form a simple sugar, hydrolysis of ATP provides additional energy

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11
Q

What occurs in the light independent reaction? (Calvin Cycle)

A
  1. CO2 diffuses into the stroma
  2. Co2 reacts with RuBP and this reaction is catalysed by Rubisco which produces two molecules of 3 carbon GP
  3. NADPH is used to reduce GP to Triose Phosphate using energy from ATP
  4. NADP is reformed and goes back
  5. Some triose phosphate is used to regenerate RuBP in calvin cycle
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12
Q

What are the products of the Light Independent Reaction?

A

RuBP and Oxygen

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13
Q

What is the site of the independent reaction?

A

Takes place in the stroma of the chloroplasts

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14
Q

What are the limiting factors of photosynthesis?

A
  1. Light Intensity
  2. CO2
  3. Temperature
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15
Q

Why is Light Intensity a limiting factor of photosynthesis?+ describe the shape of the graph

A

Curve that has a steep gradient at first but eventually levels off

Steep gradient -> more light therefore more photons hitting photosystems thus more photoionisation, more electrons excited and more ATP available for the LIR and more reduced NADP. More photolysis releases more O2

Levels off-> Limited amount of ADP/NADP available, if they run out there is nothing to accept electrons so LDR gets blocked

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16
Q

Why is Carbon Dioxide a limiting factor of photosynthesis?+ describe the shape of the graph

A

Straight line that has a steep gradient at first that levels off

Steep gradient-> more CO2 can be fixed by joining to Rubisco

Levels off-> Carbon fixation is limiting factor due to all RuBP being in use and it cannot be regenerated any faster

17
Q

Why is Temperature a limiting factor of photosynthesis?+ describe the shape of the graph

A

Mountain like curve with peak at the centre of the graph

Peak-> optimum temperature
Decrease in photosynthesis if temperature is too high//low-> enzymes such as ATP synthase and Rubisco denatured

For every increase of 10 degrees the rate doubles as particles have more kinetic energy

18
Q

What is the equation for respiration?

A

Glucose + Oxygen -> CO2 + H2O + 32-38 ATP

19
Q

What are the two different equations for anaerobic respiration?

A

Glucose -> Lactic Acid + 2ATP (animal cells)

Glucose -> Ethanol + CO2 (yeast/plants)

20
Q

What are the 4 stages of aerobic respiration?

A
  1. Glycolysis
  2. Link Reaction
  3. Krebs cycle
  4. Oxidative Phosphorylation
21
Q

What happens in glycolysis and where does it occur?

A

Occurs in the cytoplasm of all living cells
Where a hexose sugar (glucose) is split into two (3 carbon) molecules of Pyruvate

  1. Glucose is phosphorylated to glucose phosphate by the addition of two phosphates (these come from the hydrolysis of two ATP).
  2. Glucose is split into two 3 carbon molecules of TP
  3. Triose phosphate is oxidated by the removal of hydrogen + is transferred to a hydrogen-carrier molecuels called NAD to form NADH
  4. Enzyme reactions convert each triose phosphate into 3 carbon Pyruvate. 2 molecules of ATP are regenerated
22
Q

What are the energy yields of glycolysis?

A

One glucose…

  • 2 molecules of ATP (4 are produced in total but 2 are used for the phosphorylation of glucose)
  • 2 molecules of reduced NAD
  • 2 molecules of pyruvate
23
Q

What happens in the link reaction?

A
  • Pyruvate molecules are transported to matrix of mitochondria through active transport
    1. Pyruvate is oxidised to acetate: Pyruvate loses a CO2 molecule + 2 hydrogens (hydrogens are used to reduce NAD to produce ATP later)
    2. Acetate (2 carbon) combines with Coenzyme A to produce Acetyl-coenzyme A
24
Q

What is the equation for the link reaction?

A

Pyruvate + NAD + Coenzyme A -> Acetyl-Coenzyme A + reduced NAD + CO2

25
Q

What happens in the Krebs Cycle?

A

Series of oxidation reduction reactions

  1. 2 C Acetyl-coenzyme A combines with a 4 carbon molecule to produce a 6 carbon molecule
  2. 6 Carbon loses CO2 and H to give a 4 carbon molecule and 1 ATP
  3. 4 Carbon molecule combines with a new molecule of acetyl-coenzyme A to begin cycle again

2 molecules of pyruvate are produced for each glucose

26
Q

What does each molecule of pyruvate produce in the krebs cycle?

A
  • reduced coenzymes NAD and FAD to provide energy for ATP production in oxidative phosphorylation
  • one ATP
  • 3 Co2
27
Q

What are the different coenzymes?

A

NAD (respiration)
FAD (krebs cycle)
NADP (photosynthesis)

They are molecules enzymes require to function

28
Q

What happens in Oxidative Phosphorylation? + where does it take place?

A

Takes place in the mitochondria
Energy of electrons in hydrogen is conserved in form of ATP

  1. H ions combine with coenzymes NAD and FAD
  2. reduced NAD/FAD donate electrons from hydrogen atoms to first molecule in chain
  3. Electrons pass along chain in oxidation-reduction reaction which releases energy which allows the active transport of protons to inter-membrane space
  4. Protons accumulate in the space and diffuse into matrix through ATP synthase channels
  5. At the end of the chain, electrons combine with protons and oxygen to form water - oxygen is final acceptor
29
Q

Why are there more mitochondria in metabolically active cells? + which cells are these

A

Muscles, liver + epithelial which carryout active transport

More cristae gives a large surface area for enzymes/proteins in oxidative phosphorylation

30
Q

Why is energy released slowly?

A

More can be harvested as large amounts of energy released causes more to be released as heat so less energy is available thus less electrons are passed along transfer molecules

31
Q

Why do electrons move down an energy gradient?

A

Each transfer molecule has a slightly lower energy level

aqa biology a level (13 decks)

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