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Bio Yr 13: Energy Transfers In + Between Organisms > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

What is the function of chloroplasts?

A
  • site of photosynthesis in plant cells which takes place in the form of light dependent + light independent reactions
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2
Q

What is the structure of chloroplasts?

A
  • surrounded by double phospholipid membrane
  • contains stroma (fluid): site of light independent stage
    • contains ribosomes, circular chloroplast DNA + starch grains
  • thylakoid membranes (fluid filled sacs that stack to form grana): site of light dependent stage + contains pigments, enzymes + e- carriers
  • grana are connected by lamellae (membranes): creates large SA to inc. NO° of light dependent reactions
    • membranes contain many pigment molecules arranged in photosystems = inc light absorption
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3
Q

What is the equation for photosynthesis?

A
  • carbon dioxide + water —-> oxygen + glucose
  • 6CO2 + 6H2O —-> C6H12O6 + 6O2
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4
Q

How are (dicotyledonous) plant leaves adapted to carry out photosynthesis?

A
  • waxy cuticle: prevents water loss
  • transparent upper epidermis: so light can reach palisade cells
  • palisade mesophyll layer: tightly packed, elongated cells w many chloroplast to absorb light
  • air spaces in spongy mesophyll layer: creates larger SA to inc rate of gas exchange
  • stomata on bottom of leaf: guard cells control diffusion of gases into + out of leaf
  • thin leaves: inc light absorption + has a shorter diffusion distance so inc rate of gas exchange
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5
Q

What are the 2 stages of photosynthesis?

A

1st stage: light dependent reaction
2nd stage: light independent reaction (Calvin cycle)

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6
Q

Where does the light dependent stage of photosynthesis occur?

A
  • thylakoid membranes + thylakoid spaces which contain pigments, enzymes + e- carriers
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7
Q

What are the diff stages of the light dependent reaction (LDR)?

A
  • photolysis of water
  • photoionisation of chlorophyll
  • chemiosmosis + photophosphorylation
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8
Q

Describe the process of photolysis of water in the light dependent reaction.

A
  • light energy, absorbed by chlorophyll, splits water in the thylakoid lumen, into oxygen, H+ and e- = H+ gradient bc of a high conc of H+
  • H+ moves down conc gradient into stroma
  • e- pass along ETC within thylakoid membrane
  • oxygen (waste product) is used for respiration or diffuses out of leaf via stomata
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9
Q

Describe the process of photoionisation of chlorophyll in the light dependent reaction.

A
  • light energy, absorbed by chlorophyll in thylakoid membrane, causes e- to become excited to a higher energy lvl + are released from chlorophyll (ionised)
  • they then pass along ETC within the thylakoid membrane + are replaced by e-s from photolysis of water
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10
Q

Describe the process of chemiosmosis + photophosphorylation in the light dependent reaction.

A
  • as excited e- pass along ETC, it produces energy to move H+ ions from stroma to thylakoid lumen, creating a conc gradient
  • H+ move down conc gradient, by facilitated diffusion, through ATP synthase back into stroma
  • produces energy for phosphorylation of ADP into ATP by ATP synthesis
  • NADP (coenzyme) combines w e- at end of ETC + H+ passed through ATP synthase to produce reduced NADP/NADPH (used in LIR)
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11
Q

What products are formed from the light dependent reaction?

A
  • ATP
  • NADPH
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12
Q

What do pigments do?

A
  • absorb diff. wavelengths of light
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13
Q

What are the 2 groups of pigments called?

A
  • chlorophylls (primary pigments): absorb wavelengths in blue-violet + red regions of light spectrum = reflect green light, so appears green
  • carotenoids (accessory pigments): absorbs wavelength in blue-violet region of spectrum
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14
Q

Describe the method for investigating photosynthetic pigments in leafs by chromatography.

A
  • draw a pencil line (origin line) approx. 1cm above bottom of chromatography paper
  • extract pigment from leaf by crushing leaf in a solvent (e.g. acetone) using a pestle + mortar
  • add drop of pigment to centre of origin line using a capillary tube
  • allow to dry + repeat until pigment dot is 3-5mm in diameter
  • suspend paper vertically straight in solvent below the pencil line
  • remove paper using forceps + draw a pencil line to mark where solvent moved up to
  • calculate Rf values to identify pigments present in leaf
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15
Q

What is the equation for the Rf value?

A

Rf value = distance moved by pigment / distance moved by solvent

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16
Q

What does the Rf value indicate?

A
  • how far a dissolved pigment travels
  • larger Rf value = pigment more soluble
17
Q

What are the approx. Rf values of the diff. pigments present in chloroplasts?

A
  • chlorophyll A: 0.65
  • chlorophyll B: 0.45
  • carotene: 0.95
  • xanthophyll: 0.71
18
Q

Why must the origin line be drawn in pencil + not pen?

A
  • bc the ink would dissolve in solvent + run
19
Q

Why should you draw a line where the solvent reaches immediately?

A
  • bc the solvent evaporates rapidly
20
Q

Why should you measure the Rf value from the middle of the pigment mark?

A
  • bc it standardises the measurements to allow for comparisons
21
Q

Why should the chromatography paper be vertical + straight?

A
  • so pigments move straight up paper + not runoff the side
22
Q

Where does the light independent stage (Calvin cycle) of photosynthesis occur?

A
  • stroma
23
Q

What are the 3 main steps in the light independent stage (Calvin cycle)?

A
  • carbon fixation
  • reduction of GP
  • regeneration of RuBP
24
Q

Describe carbon fixation in the light independent stage (Calvin cycle).

A
  • CO2 reacts w RuBP (5C) [ribulose bisphosphate] to form 2 GP (3C) [glycerate 3-phosphate] molecules which is catalysed by the enzyme rubisco (found in stroma)
25
Q

Describe reduction of GP in the light independent stage (Calvin cycle).

A
  • each GP molecule is reduced to TP (3C) [triose phosphate] using energy from ATP + by accepting a H+ from NADPH
  • 1 carbon from 1 TP leaves the cycle each turn to be converted into useful organic substances
  • e.g. starch/cellulose, glycerol so can combine w fatty acids to make lipids for cell membranes or it can be used in the production of AA for protein synthesis
26
Q

Describe regeneration of RuBP in the light independent stage (Calvin cycle).

A
  • the rest of the TP molecules (5C) is used to regenerate RuBP using energy from ATP
27
Q

What are the main limiting factors of photosynthesis?

A
  • light intensity
  • CO2 concentration
  • T°C
28
Q

How does light intensity affect the rate of photosynthesis?

A
  • greater light intensity = greater rate of photosynthesis bc more energy supplied to plant = faster light dependent stage occurs
  • this produces more ATP + NADPH for light independent stage/Calvin cycle allowing it to occur at a faster rate
  • when light intensity inc. past a certain point it is no longer a limiting factor (T°C or CO2 conc is the limiting factor)
29
Q

How does CO2 concentration affect the rate of photosynthesis?

A
  • greater CO2 conc = greater rate of photosynthesis bc faster carbon fixation in LIR/Calvin cycle occurs (since CO2 combines w RuBP during this step)
  • when CO2 conc inc. past a certain point it is no longer a limiting factor (T°C or light intensity is the limiting factor)
30
Q

How does T°C affect the rate of photosynthesis?

A
  • greater T°C = greater rate of photosynthesis (as long as there’s enough light to produce ATP + NADPH) bc light independent reactions are controlled by enzymes
  • but if T°C inc. above a certain T°C, enzymes begin to denature + ROR dec
31
Q

How do agricultural practices remove limiting factors to maximise photosynthesis?

A
  • growing plants under artificial lighting to maximise light intensity + so plants continue to grow at night
  • irrigation systems supply water + may contain fertilisers to aid plant growth
  • burning fuel (e.g. paraffin burners) to release more CO2 for plants to absorb

Bio Yr 13: Energy Transfers In + Between Organisms (4 decks)

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