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Biology > Topic 6 - Plants and Photosynthesis > Flashcards

Topic 6 - Plants and Photosynthesis Flashcards

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1
Q

What is photosynthesis?

A

An endothermic reaction that uses light energy to convert carbon dioxide and water into glucose and water

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2
Q

What is glucose used for in plants

A
  • It is used as a ‘food source’ in plants
  • it is used in respiration to release energy
  • it is used to make larger, more complex molecules such as cellulose which makes up the cell wall
  • excess glucose is converted into starch for storage
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3
Q

Where does photosynthesis happen?

A

-It takes place in the chloroplasts of plant cells
- the chloroplasts contain chlorophyll which absorbs the light energy
- it happens in the leaves of all green plants

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4
Q

Why are plants so important for the ecosystem

A
  • they are photosynthetic organisms that are the main producers of biomass and therefore food
  • they store energy which is transferred to organisms that eat it and works its way up the food chain
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5
Q

Equation for photosynthesis

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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6
Q

How does sunlight exposure affect photosynthesis

A
  • Plants exposed to more sunlight can photosynthesise longer
  • This means they produce more glucose because glucose is a product of photosynthesis
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7
Q

What is a limiting factor

A
  • A factor that stops photosynthesis from happening faster
  • If a factor is too high or low it will become the limiting factor
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8
Q

What are the 3 limiting factors?

A
  • Light intensity
  • carbon dioxide concentration
  • temperature
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9
Q

Effect of light intensity

A
  • up to a certain point, as light intensity increase the rate of reaction increases as well
  • this is because light provides the energy needed for photosynthesis
  • after a certain point, the graph will start to plateau and increasing L.I won’t make a difference
  • now another factor is limiting factor
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10
Q

effect of carbon dioxide concentration

A
  • up to a certain point, as CO2 intensity increases the rate of reaction increases as well
  • this is because CO2 is a reactant needed for photosynthesis
  • after a certain point, the graph will start to plateau and increasing CO2 concentration won’t make a difference
  • now another factor is a limiting factor
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11
Q

effect of temperature

A
  • up to a certain point, as temp increases the rate of reaction increases as well
    -enzymes work more quickly and the molecules move faster due to more kinetic energy
  • at the optimum temperature, something else is the limiting factor
  • after the optimum temperature, the rate of reaction decreases as the enzyme begins to denature
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12
Q

How do you test a leaf for starch

A
  • place leaf in beaker with boiling water to melt waxy cuticle
  • put leaf in boiling tube and put ethanol, to remove the chlorophyll from the leaf: this decolourises it
    -put leaf back in boiling water to soften it
    -lay leaf on tile and flood with iodine, to see where the starch is
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13
Q

test for starch

A

iodine changes colour from brown- orange to blue-black

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14
Q

inverse square law

A

1/ distance²

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15
Q

translocation

A

movement of organic solutes ( e.g : sucrose ) from a source to a sink
through the phloem

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16
Q

what is the organic molecules used for

A

1) used for respiration instantly to release energy
2) make larger molecules ( e.g : starch) for storage

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17
Q

Phloem

A
  • transports food substances ( e.g : sucrose ) made in the leaf
  • transports it up AND down the plant ( it goes from leaves to roots and vice versa)
  • columns of elongated living cells with small pores in end walls
  • requires energy from respiration
  • translocation
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18
Q

transpiration

A

the loss of water from a plant’s surface

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19
Q

How plant loses water

A
  • evaporation of water from inside the leaf
  • followed by diffusion of water vapour from the stomata
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20
Q

Xylem

A
  • carry water and mineral ions
  • only transports it UP the plant
    -from roots to the stem and leaves
  • made of dead cells joined together with NO end walls
  • strengthened by lignin
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21
Q

Transpiration stream

A

movement of water and mineral ions through a plant from the roots to the leaves to obtain more water for photosynthesis

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22
Q

Process of transpiration

A
  • water evaporates from cells into air spaces within the leaf
    -water then diffuses out of the leaf through stomata
    -this creates a shortage of water in the leaf
  • more water is drawn up from the rest of the plant through the xylem vessels to replace it
  • this means more water is drawn up from roots, so there is a constant transpiration stream
23
Q

Root hair cells

A
  • cells on the surface of plant roots that grow into hairs which stick out into the soil
  • this increases the surface area for absorbing water and mineral ions
24
Q

What 3 factors affect transpiration rate

A
  • light intensity
  • temperature
    -air flow
25
Q

how does light intensity affect transpiration

A
  • the greater the light intensity, the greater the transpiration rate
  • as it gets darker the stomata closes, as the plant can no longer photosynthesise
  • this means that when the stomata are closed water can’t escape
26
Q

how does temperature affect transpiration

A
  • the warmer it is the faster the rate of transpiration
  • water particles have more kinetic energy and so diffuse out of the stomata faster
27
Q

how does air flow affect transpiration

A
  • the better the air flow, the faster the rate of transpiration
  • if it is windy, the water vapour is swept away from the leaf
  • this means there is al ow concentration of water outside the leaf compared to outside it
  • this maintains a high concentration gradient, which increase the rate of diffusion of water out of the leaf
28
Q

what do you use to measure rate of transpiration

A

potometer

29
Q

what are guard cells

A

two guard cells surround each stoma to help open and close them

30
Q

what happens to the guard cells when the plant has lots of water

A
  • guard cells fill with water and become turgid
  • this opens the stomata so gases can be exchanged for photosynthesis
31
Q

what happens to the guard cells when the plant is short of water

A
  • water moves out of the guard cells and they become flaccid
  • this closes the stomata so gases can be exchanged for photosynthesis
32
Q

how does the guard cells respond to lack of light

A

it closes to save on water without losing out on photosyntheis

33
Q

how is the upper part of the leaf adapted for photosynthesis

A

upper epidermis covered with a thick waxy cuticle layer, to reduce water loss by evaporation
- upper epidermis cells are transparent to allow light to pass through to the palisade layer

34
Q

how is the palisade part of the leaf adapted for photosynthesis

A
  • cells in palisade mesophyll contain lots of chloroplasts. contain lots of chlorophyll to absorb light energy needed
  • xylem and phloem form a network of vascular bundles, which also supports the structureh
35
Q

how is the lower part of the leaf adapted for photosynthesis

A
  • lower epidermis is full of holes called stomata which let CO2 and water diffuse directly in and out of the leaf
  • air spaces in spongy mesophyll increase the rate of diffusion of gases through the leaf due to increased S.A
  • leaves are broad, so there is a large S.A exposed to light
36
Q

how are plants in dry extreme habitats adapted for photosynthesis

A
  • they have small leaves or spines to reduce S.A for water loss by evaporation
  • thicker waxy cuticle to further reduce water loss by evaporation
  • curled leaves reduce air flow close to leave which reduces rate of transpiration
  • stems of some plants are thick and fleshy to help store more water
  • stomata sunk in pits to reduce air flow in same way as curled leaves/hairs
37
Q

what do plants need to do?

A

plants need to detect and respond to stimuli in order to survive

38
Q

What is auxin?

A

a plant hormone that controls growth near the tips of roots and shoots

39
Q

phototropism

A

plant growth in response to light

40
Q

gravitropism

A

plant growth in response to gravity

41
Q

shoots

A
  • auxins stimulate growth in shoots
  • positively phototropic
  • negatively gravitropic
42
Q

roots

A
  • auxins inhibit growth in shoots
  • negatively phototropic
  • positively gravitropic
43
Q

how do shoots respond to light?

A
  • due to the light stimulus detected, auxins will diffuse down the concentration gradient from the tip
  • diffuse unevenly and accumulate more of shady side
  • this cause the shoot to bend away from the shady side, closer to light
44
Q

how do shoots respond to gravity?

A
  • due to the gravity stimulus detected, auxins will diffuse down the concentration gradient from the tip
  • diffuse unevenly and accumulate more on lower side
  • this cause the shoot to bend away from the lower side, upwards and away from gravity
45
Q

how do roots respond to light?

A
  • due to the light stimulus detected, auxins will diffuse down the concentration gradient from the tip
  • diffuse unevenly and accumulate more of shady side
  • this cause the shoot to bend towards the shady side, away from light
46
Q

how do roots respond to gravity?

A
  • due to the gravity stimulus detected, auxins will diffuse down the concentration gradient from the tip
  • diffuse unevenly and accumulate more on lower side
  • this cause the shoot to towards the lower side, therefore towards gravity
47
Q

Auxins - use for selective weedkillers

A

-spraying high concentrations of auxins disrupts plants’ normal growth patterns.
- because weeds have broader leaves than grass they have a greater S.A and so weeds take up more auxins and are killed, but the grass survives

48
Q

Auxins - rooting powder

A
  • rooting powder can be added to cuttings to stimulate them to grow roots
  • they contain auxins which controls the roots growth
  • they will start growing rapidly as new plants
  • this enables people to produce lots of clones of desirable plants
49
Q

What are gibberellins?

A

a plant hormone that stimulates seed germination ( growth of seed -> plant) and flowering

50
Q

Gibberellins - controlling seed germination

A
  • most seeds won’t germinate until certain conditions are met ( e.g : warmth)
  • they only germinate at certain times of the year
  • exposure to gibberellins can cause the seed to germinate at times of the year they normally wouldn’t
  • it makes sure seeds in a batch all germinate at the same time
51
Q

Gibberellins - flower formation

A
  • gibberellins can be used to make plants flower earlier than they would
    or under conditions that they usually wouldn’t
  • can be used to reduce flower formation
  • improves fruit quality
52
Q

gibberellins - seedless fruit

A
  • fruit normally grows on flowering plants that have been pollinated, which also makes the seed grow
  • if gibberellin is added, the fruit will grow but the seeds won’t
53
Q

What is ethene?

A

a plant hormone produced by aging parts of the plant that causes the fruit to ripen

54
Q

ethene - Commercial use

A
  • used to speed up the ripening of fruits
  • they can be picked while its still unripe which make it firmer and less easily damaged when transported
  • ethene gas is added on the way to the supermarket so it’s perfect just as it reaches the supermarket

Biology (9 decks)

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