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Biology Paper 1 > Transport in Plants > Flashcards

Transport in Plants Flashcards

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1
Q

What is transpiration?

A

the evaporation of water from a plants surface.
this happens through the stomata

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2
Q

What is the function of the stomata?

A

they open to allow the entry of CO2 for photosynthesis

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3
Q

How is the rate of transpiration affected by light?

A
  • during daylight the stomata open to let CO2 enter
  • increases rate if transpiration as water evaporates from the mesophyll cells and diffuse out the kead
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4
Q

How dies temperature affect the rate of transpiration?

A
  • increase in temp increases rate of transpiration
  • water molecules are provided with more kinetic energy so the evaporate more rapidly m
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5
Q

How does humidity affect the rate of transpiration?

A
  • increase in humidity increases water potential in air
  • this decreases rate of transpiration
  • water potential gradient for diffusion of water decreases
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6
Q

Hoe does air movement affect the rate of transpiration?

A
  • Air movement removes water vapour from the leaf surface
  • This increases the water potential gradient and rate of transpiration
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7
Q

How does still air affect rate of transpiration?

A
  • in still water vapour will build up around the leaf
  • this decreases the water potential gradient thus rate if transpiration
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8
Q

What is a Xerophyte?

A

a plant that possesses a range of adaptations that limit water loss via transpiration

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9
Q

What is the purpose of the thick cuticle on a Xerphyte?

A
  • provides a long diffusion pathway
    this reduces the rate if transpiration
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10
Q

What is the function of the Hairs in Xerophyte leaves?

A
  • hairs on leaf surface trap layer of still air
  • this becomes saturated with water vapour which reduces the water potential gradient for water loss
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11
Q

What is the purpose of the rolling up if leaves in Xerophytes?

A
  • traps layer if still air which becomes saturated with water vapour
  • reduces water potential gradient for water loss
  • thus reducing transpiration rate
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12
Q

How does the position of stomata reduce water loss in Xerophytes?

A
  • they’re positioned in epidermal pits/grooves beneath leaf’s surface
  • this reduces exposure to air
  • this trapped air becomes saturated with water vapour
  • reduces water potential gradient for evaporation
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13
Q

Describe the structure of the Xylem

A
  • no cell contents
  • hollow tubes
  • cell wall strengthened by lignin which makes cell rigid and provides support
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14
Q

Describe the Cohesion-Tension theory.

A
  • water moves across leaf down water potential gradient
  • water is drawn from xylem, this creates tension in xylem
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15
Q

How is the water column in the xylem maintained?

A

by cohesive and adhesive forces

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16
Q

What is cohesion?

A

attention of water molecules to each other by hydrogen bonds

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17
Q

What is adhesion?

A

attraction of the water molecules to the xylem walls

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18
Q

How is water taken from the soil?

A
  • upward movement of water from the xylem in the roots maintain water potential gradient across root cells
  • water is taken from soil via osmosis
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19
Q

Describe the evidence for Cohesion-Tension theory.

A

rate if transpiration increases the diameter of a tree trunk decreases

  • evaporation from leaves draws water from xylem by osmosis
  • so water is pulled up xylem creating tension
  • the tension pulls in the walls of xylem vessels
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20
Q

What is a potometer?

A

measures rate of transpiration

21
Q

Why is the rate of water uptake not the same ad rate of transpiration?

A

some of the water taken up by plants is often used to maintain turgidity and a small % is used in photosynthesis

22
Q

What measurements do you need when calculating rate if transpiration in a potometer?

A
  • distance travelled by air buble
  • radius of lumen of the capillary tubing
  • time taken for air bubble to move
23
Q

What is the calculation for the volume of water taken up?

A

π x r^2 x d

pi x radius squared x distance moved

24
Q

What is needed for the potometer to work?

A
  • no air bubbles
  • rubber bung must have air tight seal
25
Q

Why should the shoot be cut underwater?

A

to prevent air entering

26
Q

How can mineral ions be traced?

A

radioactive isotopes can act as tracers to provide evidence that mineral ions travel in xylem

27
Q

Why are the xylem and phloem separated using a wax cylinder?

A

to prevent lateral (sideways) transport

28
Q

How is evidence for the movement of ions shown?

A
  • roots are supplied with potassium ions(radioactive)
  • plant is left for a few hours and amount of radioactivity in xylem and phloem tissues is measured and compared
29
Q

What does the change in radioactivity in xylem and phloem show?

A

radioactivity in xylem is higher which shows transport of the potassium ion

small amount of radioactivity in phloem is from lateral transport where the wax cylinder isn’t present

30
Q

What is translocation?

A

Transport of photosynthetic products
- occurs in phloem

31
Q

How are carbohydrates transported in the Phloem?

A

in the form of sucrose

32
Q

How are proteins transported in the phloem?

A

in the form if amino acids

33
Q

How are lipuds transported in the phloem?

A

as fatty acids and glycerol

34
Q

Where are photosynthetic products transported to?

A
  • there produced in keaves during photosynthesis and transported up and down stem of plant into the sinks
35
Q

What are the sinks if plants?

A
  • growing areas, young keaves and roots/shoot tips
  • roots
  • developing fruits and storage areas
36
Q

What are some properties of Sieve elements in the phloem?

A
  • joined end to end to form sieve tubes
  • end walls of sieve plates are sieve plates as the possess pores
  • no nucleus & cytoplasm only has few organelles
37
Q

Describe a companion cell

A
  • next to each sieve element
  • have dense cytoplasm and many mitochondria
38
Q

What is the method for translocation in the phloem?

A
  • mass flow of organic substances occurs down an hydrostatic pressure gradient
39
Q

How does sucrose enter phloem?

A

actively transported into sieve tubed by companion cell
- lowers WP of sieve tube so water enters from xylem creating high HS pressure

40
Q

What is the function of sugar in the sinks?

A

Sugars are being used in respiration for growth
Or they’re stored as insoluble starch

41
Q

What happens when sucrose is transported into the sink?

A
  • increases WP in sieve tubes and water moves back into xylem
  • so HS pressure is lower in sink
42
Q

What is the pathway products take in translocation?

A
  • actively transported into sieve tubes
  • low WP water enters from xylem
  • product transported to sink
  • this increases WP so water moves back to xylem
  • low HS pressure in sink
43
Q

How is evidence for transport in Phloem shown?

A

Ringing
- removing ring of phloem around a plant to prevent transport

44
Q

Why does swelling form after ringing?

A
  • due to the build up of photosynthetic products from the leaves which were prevented from being transported
45
Q

Describe an experiment where radioactive isotopes demonstrate translocation using ringing?

A
  • two plants of similar growth one ringed one not
  • leaf below ring supplied with isotope and left in the sun for abit
  • transport of radioactivity detected using autoradiography
46
Q

What does the plant not ringed show in autoradiography?

A
  • shows transport of photosynthesis products particularly in growing regions (young leaves root/shoot tips)
47
Q

How can some products get transported in a ringed plant?

A

via transport through the xylem (lateral transport)

48
Q

What is some evidence supporting the mass flow hypothesis?

A
  • cutting stem if plant results in phloem sap being released
    this indicates hydrostatic pressure in sieve tubes
  • lowering temperature reduces rate of translocation
    shows active transport is involved
49
Q

What is some evidence against the mass flow hypothesis?

A
  • specific structure of sieve tubes and plates is not required for mass flow
  • in young phloem tissue substances have been observed moving in the opposite direction in the same sieve tube

Biology Paper 1 (8 decks)

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