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A2 Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

Light-dependent reaction, light-independent reaction and the chloroplast

1
Q

What is oxidation?

A
  • loss of electrons or hydrogen

- gain of oxygen

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2
Q

What is reduction?

A
  • gain of electrons or hydrogen

- loss of oxygen

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3
Q

Where does photosynthesis take place?

A

Chloroplasts within leaves

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4
Q

Why are leaves adapted?

A

to bring together 3 raw materials of photosynthesis

- H2O, CO2 & light & remove O2 and C6H12O6

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5
Q

Adaptations of leaves for photosynthesis

A
  • large SA to absorb lots of light
  • arrangement of leaves on plant to minimize overlapping (avoids shadowing of 1 leaf by another)
  • Thin so DD for gases kept short
  • numerous stomata for gaseous exchange so all mesophyll cells only short DD from one
  • transparent cuticle & epidermis to let light through to photosynthetic mesophyll cells below
  • long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight
  • stomata that open & close in response to changes in light intensity
  • network of xylem that bring water to leaf cells & phloem that carries sugars away produced during photosynthesis
  • many air spaces in lower mesophyll level to allow rapid diffusion in the gas phase of O2 & CO2
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6
Q

Photosynthesis equation

A

6CO2 + 6H2O –>(light on arrow) C6H12O6 + 6O2

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7
Q

What is photosynthesis?

A
  • metabolic pathway with many intermediate reactions:
    (process of energy transferral where some of energy is conserved in form of chemical bonds
    1 capturing of light energy
    2 light-dependent reaction
    3 light-independent reaction
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8
Q

Shape of chloroplast (where photosynthesis takes place)

A
  • disc-shaped & 2-10 micrometers long & 1 micrometer in diameter
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9
Q

Structure of Chloroplast?

A
  • surrounded by double membrane

- inside are 2 distinct structures: grana & stroma

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10
Q

What is the grana?

A

stacks of thylakoids (disc-like structure) (where light dependent stage happens)
- within thylakoids is chlorophyll

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11
Q

What is intergranal lamellae ?

A

tubular extensions that join up with thylakoids in adjacent grana in some thylakoids

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12
Q

What is the stroma?

A

fluid filled matrix (where light-independent stage happens)

-within stoma are other structures e.g. starch grains

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13
Q

Uses of glucose

A
  • storage molecule (starch) stores chemical energy
  • used in respiration
  • cellulose
  • used to make lipids (glycerol)
  • used to make AAs
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14
Q

How does water enter plants?

A

Roots in transpiration

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15
Q

How does carbon dioxide come into plants?

A

Diffuses into leaves

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16
Q

The light-dependent reaction of photosynthesis involves what?

A
  • capture of light whose energy is used for 2 reasons:
  • add Pi molecule to ADP making ATP
  • split water into H+ ions (protons) & OH- ions, splitting caused by light (PHOTOLYSIS)
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17
Q

3 Equations involved in light-dependent reaction of photosynthesis

A

ADP + Pi -> ATP
NADP + H+ + 2e- –> NADPH (reduced NADP)
H20 –> 2H+ + 2e- + 1/2 O2

18
Q

Model Answer: Describe the events of the light-dependent reaction of photosynthesis

A

1 photon of light hits chlorophyll in photosystem 2 (PS2) causing photoexcitation - raises 2e- up an energy level, they leave PS2 (photoionisation) in an Electron transport chain (ETC)
2 they travel through electron carriers in a series of redox reactions releasing energy as they go
3 energy released from electron carriers in ETC is used as energy to move H+ ions against their conc gradient from stroma into thylakoid lumen, H+ ions move through ATP synthase down their conc gradient which catalyses ADP and Pi to form ATP (this is chemiosmosis)
ADP + Pi –> ATP
4 another photon of light hits chlorophyll in PS1 & re-excites electrons and they leave PS1 and ETC and join with NADP
H+ ions that moved down their conc gradient combine with NADP also to form reduced NADP in stroma
NADP + H+ + 2e- –> NADPH
5 Photolysis of water provides e- to reduce the chlorophyll in PS2 and replace the H+ used in the reduction of NADP.
H20 –> 2H+ + 2e- + 1/2O2

19
Q

What function is chloroplast adapted to?

A

capturing sunlight and carrying out light dependent reaction of photosynthesis

20
Q

Site of the light-dependent reaction

A

thylakoids of chloroplasts

- disc-like structures stacked together in groups (called grana)

21
Q

State 4 ways Chloroplast’s structure is adapted to its function

A

1 thylakoid membranes provide large SA for attachment of chlorophyll, electron carriers and enzymes that carry out LD reaction
2 chlorophyll arranged in photosystems to maximise absorption of light
3 granal membranes have ATP synthase channels within them (catalyses production of ATP), also selectively permeable which allows establishment of proton gradient
4 chloroplasts contain both DNA & ribosomes so they can quickly & easily manufacture some of the proteins involved in the light-dependent reaction

22
Q

Where does the Light-independent reaction of photosynthesis take place?

A

stroma of chloroplasts

23
Q

Another term for the light independent reaction?

A

The Calvin Cycle

24
Q

Model answer: Describe the process of the Calvin Cycle

A

1 RuBP (Ribulose Biphosphate) combines with CO2 to form a 6-carbon intermediate
2 catalysed by rubisco
3 6 carbon molecule breaks down into 2 x GP (glycerate-3-phosphate)
4 GP reduced to TP (triose phosphate) using reduced NADP - using energy from ATP & (both from light-dependent reaction)
5 some TP is used to manafacture organic substances/hexose sugars, some used to regenerate RuBP

note: organic substances produced from TP could be lipids, glucose, cellulose, amino acids, starch, nucleotides i.e. what the plant requires

25
Q

Why does when RuBP combines with CO2 it breaks down into 2 3-carbon molecules?

A

it’s an unstable intermediate molecule

26
Q

How is Glycerate-3-phospahte reduced to Triose phosphate?

A

reduced NADP from LD reaction is used to reduce GP to TP - using energy supplied by ATP

27
Q

State 2 uses of the triose phospahte produced

A

1 some of the triose phosphate is used to regenerate RuBP in the Calvin cycle
2 some of the triose phosphate is converted to useful organic substances

28
Q

How does the NADP go back into the LD reaction after its use in the calvin cycle?

A

NADP re-formed and goes back into light-dependent reaction to be reduced again by accepting more protons

29
Q

What are some of the useful organic substances TP (triose phosphate) is converted into?

A
  • starch
  • cellulose
  • lipids
  • AAs
  • nucleotides
30
Q

How is the chloroplast adapted to carrying out the light-independent reaction of photosynthesis?

A

1 fluid of stroma contains all enzymes needed for this reaction. Stromal fluid is membrane-bound in chloroplast so a chemical environment which has a high conc of enzymes and substrates can be maintained there - distinct from environment of cytoplasm
2 stromal fluid surrounds grana and so products of light-dependent reaction in the grana can readily diffuse into stroma
3 contains both DNA and ribosomes so it can quickly and easily manafacture some of the proteins involved in the light-independent reaction

31
Q

Identify environmental factors that limit the rate of photosynthesis

A

Light intensity
Temperature
CO2 concentration

32
Q

State the importance of sufficient water in photosynthesis

A

plants need a constant supply of water
too little - photosynthesis stops
too much - soil becomes waterlogged (reducing uptake of minerals)

33
Q

State all optimum conditions for photosynthesis

A
  • high light intensity of a certain wavelength
    (higher light intensity = more energy provided)
  • temp around 25 C
    (too low would make enzymes inactive, too high would denature them e.g. rubisco and ATP synthase)
  • Carbon dioxide at 0.4%
    (gives a higher rate of photosynthesis but higher and stomata start to close)
34
Q

How agricultural growers (farmers) counteract limiting factors that limit plant growth?

A

they create optimum conditions in glasshouses:
CO2 conc - CO2 added to air (by burning small amount of propane in CO2 generator)
Light - lights can get in through glass, lamps provide light at night
temp - glasshouses trap heat energy from sunlight, which warms air - heaters & cooling systems used to maintain optimum temp, air circulation makes sure temp is even throughout glasshouse

35
Q

What is the function of the light-dependent reaction?

A
  • to convert solar energy into chemical energy in the form of NADPH and ATP, which are used in calvin cycle and fuel assembly of sugar molecules
36
Q

What is the function of the calvin cycle?

A
  • making simple sugars from carbon dioxide and water
37
Q

state products of the light-dependent reaction

A

reduced NADP, ATP, Oxygen

38
Q

state products of the light-independent reaction

A

sugars and other organic molecules

39
Q

suggest why measuring the volume of gas produced by a plant (while investigating photosynthesis) may not be an accurate representation of rate of photosynthesis

A
  • vol of O2 produced will be less than that produced by photosynthesis as some of the O2 will be used in cellular respiration
40
Q

Do plants respire or just photosynthesize?

A
  • plants respire in the normal way i.e. using glycolysis, Krebs cycle, oxidative phosphorylation etc.
  • but respiration is masked by the fact that photosynthesis produces oxygen faster than respiration takes it up and photosynthesis uses carbon dioxide faster than respiration produces it
41
Q

The concentrations of Carbon dioxide in the air at different heights above the ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur [5 MARKS]

A
  1. High concentration of carbon dioxide linked with night/darkness;
  2. No photosynthesis in dark/night / light
    required for photosynthesis/light dependent reaction;
  3. (In dark) plants (and other organisms)
    respire;
  4. In light net uptake of carbon dioxide by
    plants/plants use more carbon dioxide than they produce/ rate of photosynthesis greater than
    rate of respiration;
  5. Decrease in carbon dioxide concentration with height;
  6. At ground level fewer leaves/less
    photosynthesising tissue/more animals/less light;
42
Q

microorganisms make the carbon in polymers in a dead worm available to cells in a leaf. Describe how [5 MARKS]

A
  1. Microorganisms are saprobionts
  2. Secrete enzymes (onto dead tissue) /
    extracellular digestion;
  3. Absorb products of digestion/smaller
    molecules
  4. Respiration (by microorganisms) produces carbon dioxide;
  5. Carbon dioxide taken into leaves;
  6. Through stomata;

A2 Biology (13 decks)

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