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BIOLOGY GCSE EDEXCEL > Topic 6 - Plants > Flashcards

Topic 6 - Plants Flashcards

1
Q

What is photosynthesis

A

When plants and algae trap energy (transferred by sunlight) and produce glucose

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2
Q

Photosynthesis equation

A

carbon dioxide + water -> glucose + oxygen

6CO2 + 6H2O -> C6H12O6 + 6O2

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3
Q

Where does photosynthesis occur

A

Chloroplasts containing chlorophyll (green pigment which traps energy transferred by light)

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4
Q

What type of reaction is photosynthesis

A

Endothermic - products have more energy than reactants as it takes energy from surroundings

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5
Q

What are factors affecting photosynthesis

A
  1. Temperature
  2. Carbon dioxide concentration
  3. Light intensity
  4. Distance from light
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6
Q

How does temperature affect photosynthesis

A

Increase in temp = increase in rate

Reactions in photosynthesis are catlaysed by enzymes which work better in warmer temps

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7
Q

How does carbon dixoide concentration affect photosynthesis

A

More CO2 = faster rate
It is a reactant for photosynthesis so reaction can occur faster

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8
Q

How does light intensity affect photosynthesis

A

More light = more rate (DIRECTLY PROPORTIONAL)

Light provides more energy for reaction

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9
Q

What is a limiting factor

A

A factor which at low levels prevents the rate of photosynthesis increasing

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10
Q

How does distance from light source affect photosynthesis

A

INVERSELY PROPORTIONAL - further the distance, less photosynthesis

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11
Q

How to find light intensity from distance

If lamp 2m away, intensity is?

A

Light intensity = 1/distance^2

intensity = 1/4

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12
Q

Finding new light intensity when distance changes

A

Lnew = Loriginal x Distance^2original / D^2 new

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13
Q

Root hair cell function

A

Absorbs water by osmosis and absorbs mineral ions by active transport. Found in tips of roots

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14
Q

Root hair cell adaptations

A
  1. ‘Hairs’ provide large surface area so water and mineral ions can be quickly absorbed
  2. ‘Hairs’ have thin walls so short diffusion distance and flow of water into cells isnt slowed down.
  3. Large vacuole so speed of osmosis is faster
  4. Lots of mitochondria to provide energy for active transport
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15
Q

Xylem function

A

For uptake of water anad mineral ions from roots to shoots

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16
Q

Xylem adaptations

A
  1. Cells are dead and their top and bottom cell walls disintegrate creating long empty vessels so water can move easily
  2. Xylem vessles are rigid (thick walls and cells are lignified) so water pressure doesn’t burst vessels
  3. Unidirectional (allows H2O to only travel up)
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17
Q

Phloem function

A

Carries products of photosynthesis (incl sucrose) to all parts of plants

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18
Q

Phloem adaptations

A
  1. Sieve cells have holes which sucrose solution can flow through to be translocated
  2. Companion cells have lots of mitochondria and cytoplasm (phloem doesn’t) to have lots of energy to pump sucrose in or out sieve cells
  3. Small pores between it and sieve cells (to pump sucrose)
  4. Bidirectional (sucrose travels up to growing shoots or down to storage organs)
19
Q

How does transpiration work?

A
  1. Plant opens stomata to let in carbon dioxide, water on spongy mesophyll and palisade mesophyll evaporates and diffuses out of the leaf to atmosphere.
  2. Water is drawn from xylem to replace lost water from leaves
  3. Water molecules inside the xylem cells are strongly attracted to other water molecules. There is strong cohesion between the molecules because of hydrogen bonding. So, a continuous column of water is pulled up the stem in the transpiration stream by evaporation from the leaves.
  4. As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots by osmosis.
20
Q

Transpiration function

A
  1. provides water for photosynthesis
  2. transports mineral ions
  3. cools leaf as water evaporates
  4. Provides water to keep cell turgid
21
Q

Adaptations of the guard cell

A
  1. It opens and closes the stomata
  2. Found in lower epidermis because lower surface is shaded and cooler so less water lost by transpiratiion
  3. Open during day so diffusion of co2 and o2 can occur
  4. Open when lots of water near (osmosis; h20 moves into guard cells so swells and opens)
  5. closes at night so photosynthesis cant cocur (reduces transpiration + water is conserved)
  6. closes when hot/losing water (becomes flaccid to reduce water loss)
  7. Thin outer wals for gas exchange
22
Q

Factors affecting transpiration

A
  1. Temperature
  2. Humidity
  3. Wind
  4. Light intensity
23
Q

How does temperature affect transpiration?

A

Increase in temp = increase in rate

Increases evaporation of water out of leaves

24
Q

How does humidity affect transpiration?

A

Decrease in humidity = increase in rate

Humidity creates low water concentration in environment
If less humidity, larger concentration gradient between inside + outside of stomata so water diffuses quicker

25
Q

How does wind affect transpiration?

A

More wind = increase in rate

wind moves water molecules away from stomata so larger concentration gradient

26
Q

how does light intensity affect transpiration?

A

More light = increase in rate

More photosynthesis makes stomata open so H2O can diffuse out of the leaf

27
Q

How does translocation work

A

It is movement of sucrose from source to sink via phloem. Movement is bidirectional and an active process.

  1. Sucrose is actively pumped into companion cells by active transport from source
  2. Sucrose moves down the concentration gradient by diffusion from companion cells into the sieve tube
  3. Sucrose moves out of sieve tubes by diffusion
  4. it travesl through pores (plasmodesmata) of sieve tubes to sinks
28
Q

What does source to sink mean

A

Source (leaf) is place where photosythensis first occurs to produce sucrose from glucose

Sink is where sucrose is stored as starch

29
Q

How is leaf adapted

A
  1. Large surface area so lots of light absorbed
  2. thin so short diffusion distance for co2 to travel to palisade mesophyll quickly (where photosynthesis occurs)
  3. lots of chlorooplast contaning chlorophyll which traps light energy used for photosynthesis producing glucose
  4. Chloroplasts move towards or away from light (protection from bright light damage)
  5. Spongy mesophyll
  6. Epidermis cells
  7. Waxy cuticle
  8. Veins
  9. guard cells
30
Q

How is spongy mesophyll adapted

A

They are irregularly shaped which creates air spaces so gases can diffuse easily inside leaf.

31
Q

How is epidermis adapted

A

Lower and upper epidermis are transparent so light can enter easily

32
Q

How is waxy cuticle adapted

A

Produced by epidermis cells.
Layer that is waterproof which prevents water loss

33
Q

How are veins adapted

A

Support leaf and transport water, mineral ions, sucrose

34
Q

How are leaves adapted for extreme weather conditions

A
  • In winter, deciduous plants lose leaves preventing water loss.
  • Conifers have needle shaped leaves with small SA + think cuticle creating less wind resistance (can survive winds)
  • Water vapour is trapped close to leaves reducing water loss as diffusion is decreased
35
Q

What is stimulus

A

Change in the environment that causes a response by an organism

36
Q

What is a tropism

A

Response to stimulus by growing towards/away from it

37
Q

How does phototropism work in plants

A
  • phototropism is tropism caused by light
  • plants SHOOTS are positively phototropic (towards light) so it gets more light for photosynthesis
  • plant ROOTS are negatively phototropic
  • It is caused by auxins
  • Auxins are produced in tips of shoots, if light is shone in one directioin, auxins move to shaded side, making cells on shaded side elongate, causing shoots to grow towards light
38
Q

What is gravitropism

A

Tropism caused by gravity

39
Q

how do plant shoots show gravitropism

A

Plant shoots show negative gravitropism (grow away from gravity). If shoots are horizontal, auxins move to lower side. Cells of shoot grow more on side with more auxins. So cell growth and cell elongation is stimulated on lower side, making shoot bend and grow upwards. Beneficial because more light is further away from the ground

40
Q

how do plant roots show gravitropism

A

Plant roots show positive gravitropism (grow towards gravity). If root is horizontal, auxin moves to the lower side. Cells of roots grow on side with less auxin so inhibits cell elongation and stimulates cells to grow on upper side, making root bends and grow down. Beneficial because more water and nutrients are lower down, and provides stability for plant.

41
Q

How are auxins used in commerical uses

A
  1. As weed killers as artificial auxins are synthesised to only affect weeds. Increased auxin makes plant grow uncontrollably and die.
  2. As rooting powders. Auxins cause plant cuttings to develop roots fast. Many identical plants can be produced fast.
42
Q

How are giberellings used in commercial uses

A
  1. Allows seed germination by breaking seed dormancy so fruits can grow larger and flowering plants flower faster.
  2. Giberelling cause plants to produce plants without being pollinated. Pollination causes seeds, so seedless fruits can be produced.
43
Q

How is ethene used in commercial uses

A

used to ripen fruits that were picked unriped as it stimulates enzymes that ripen fruit. Reduces wastage.

BIOLOGY GCSE EDEXCEL (7 decks)

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