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Biology > Transport In Plants > Flashcards

Transport In Plants Flashcards

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1
Q

What are the 3 main reasons a plant needs a transport system?

A

1- Metabolic demands
2- Size
3- SA:V ratio

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2
Q

What is a dicot plant?

A

Make seeds that contain 2 cotyledons - organs that acts as food stores for the developing embryo and form the first leaves when the seed first germinates

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3
Q

In the stem of a herbaceous dicot, where are the vascular bundles?

A

Around the edge for strength and support

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4
Q

What is a vascular bundle?

A

The xylem and phloem grouped together

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5
Q

In a herbaceous dicot root, where is the vascular bundle found?

A

In the middle to help the plant withstand the tugging strain from wind

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6
Q

In a herbaceous dicot leaf, where are the vascular bundles found?

A

In midrib which also helps to structure the leaf

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7
Q

What is a midrib?

A

The main vein in a leaf that carries the vascular bundle

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8
Q

What are the 2 main functions of the xylem?

A
  • Transport water / mineral ions

- Support

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9
Q

What are xylem vessels?

A
  • The main structures in the xylem

- They are long, hollow structures of dead cells fused end to end

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10
Q

How is lignin relevant to the xylem?

A
  • Lines the walls of xylem vessels in ring, spiral or tube form
  • Contain many bordered pits (unlignified areas) to allow water to leave
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11
Q

What is the phloem?

A

Living tissue that transports organic solutes around the plant

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12
Q

In what direction can organic solutes in the phloem travel?

A

Both up and down the plant

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13
Q

What are sieve tube elements?

A

Unlignified hollow structures that are the main transport vessels of the phloem

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14
Q

What are sieve plates?

A

Thin pores between sieve tube cells to allow phloem contents out

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15
Q

How are companion cells linked to the sieve tube elements?

A

Via many plasmodesmata

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16
Q

What are plasmodesmata?

A

Microscopic channels through cell wall linking the cytoplasm of adjacent cells

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17
Q

What do companion cells do?

A
  • Supports sieve tube elements

- Provides ATP (sieve tube cells have no mitochondria)

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18
Q

What are root hair cells?

A

Exchange surface in plants where water is taken in from the soil

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19
Q

How are root hair cells adapted to perform their function?

A
  • Microscopic size to easily penetrate the soil
  • Large SA:V ratio
  • Thin surface layer allows for a short diffusion and osmosis pathway
  • High water potential gradient between cell and soil water
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20
Q

What are the 2 possible pathways water can take through a root hair cell?

A

Apoplast and symplast

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21
Q

Describe the symplast pathway

A
  • Water moves across plasma membrane by osmosis

- Moves between cytoplasm of one cell to the next via plasmodesmata

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22
Q

Describe the apoplast pathway

A
  • Water and minerals move through the cell walls
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23
Q

What is the endodermis?

A

The layer of cells surrounding the vascular tissue in the roots

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24
Q

What is the Casparian Strip?

A

A band of waxy suberin that runs around each of the endodermal cells forming a waterproof layer

25
Q

What is the function of the Casparian Strip?

A
  • Impermeable to water so forces water from apoplast pathway through the cell membrane (symplast pathway)
  • Membrane repels charged particles
26
Q

Why do xylem cells have a much lower water potential than the endodermal cells?

A

Solute concentration in endodermal cells is relatively dilute

27
Q

Once inside the vascular bundle, water takes which pathway up the xylem?

A

Apoplast

28
Q

What helps to give water a push up the xylem?

A

Root pressure

29
Q

How is root pressure generated?

A

The pumping of minerals into the xylem producing movement of water by osmosis

30
Q

What is some evidence for the role of active transport in root pressure?

A
  • Adding cyanide to root cells
  • Active transport requires energy released by ATP and cyanide affects mitochondria, where ATP is held. When cyanide is added to root cells, root pressure stops
  • Root pressure rises with temperature increases and falls with a fall in temperature
  • This suggests chemical reactions are involved, i.e the breaking of the phosphates in ATP
  • If oxygen levels fall, root pressure falls
  • Oxygen is needed for respiration to release energy
31
Q

Why is water required in a leaf?

A

A leaf is the site of photosynthesis and water is required for photosynthesis

32
Q

Why is carbon dioxide required in a leaf?

A

A leaf is the site of photosynthesis and carbon dioxide is required for photosynthesis

33
Q

What is transpiration?

A

The loss of water vapour from the leaves and stems of plants via stomata

34
Q

What are 3 adaptations of the leaf to aid transpiration?

A

1- Large SA - captures sunlight to carry out PHS
2- Waxy cuticle - makes leaf waterproof preventing too much water loss by evaporation
3- Stomata - can be opened or closed by guard cells to allow gases to diffuse in or out

35
Q

How does water move in the transpiration stream?

A

By mass flow

36
Q

What is mass flow?

A

All water molecules move together as one body, helped by cohesion and tension

37
Q

What is capillary action?

A
  • Water molecules attached to lignin in xylem walls

- Adhesion and cohesion move water upwards

38
Q

What is the benefit of narrow vessel diameter in terms of capillary action?

A

Prevents the formation of air bubbles

39
Q

Describe the process of transpiration

A
  • Water molecules evaporate from the surface of mesophyll cells into the air spaces in the leaf and then out via stomata to the surrounding air by diffusion
  • This lowers the water potential of the mesophyll cell, so water moves into this cell by osmosis
  • This is repeated across the leaf to the xylem
  • Capillary action occurs in the xylem as water moves up to replace the water lost in the leaf
40
Q

What is the cohesion-tension theory?

A
  • Transpiration of water through stomata
  • Creates low pressure at top of xylem
  • Water is pulled up, creating tension
  • Water molecules stick to each other (cohesion)
  • Water molecules are sucked up to the leaves (like a straw)
41
Q

What is the evidence to support cohesion-tension theory?

A
  • Changes in the Diameter of Trees
  • When transpiration is at its highest during the day, xylem tension is at its highest so the diameter shrinks
  • When transpiration is at its lowest, the tension in the xylem is at its lowest and the tree diameter increases
  • Breaking a Xylem Vessel
  • Breaking a xylem vessel causes air to be drawn into the xylem and this stops the continuous flow of water molecules
42
Q

Why may high light intensity be an issue for the transpiration of plants?

A
  • High light intensity means photosynthesis will be occuring at a rapid rate
  • Therefore a lot of gaseous exchange will be occuring and the stomata will be open frequently
  • This could mean that the plant loses too much water via the stomata
43
Q

What piece of equipment measures transpiration?

A

Potometer

44
Q

Why may measuring transpiration not be 100% accurate?

A

Measuring water loss is difficult so water uptake is measured and we make the assumption that water uptake = water loss

45
Q

Draw and label a potometer

A

-

46
Q

Why is the stem of the leaf used in a potometer cut at an angle?

A

To increase its surface area

47
Q

What factors affect transpiration?

A
  • Light - more light increases rate (as it opens stomata)
  • Temperature - higher temperature increases rate (as increases KE)
  • Humidity - less humidity increases rate(as increases water vapour gradient)
  • Wind - more wind increases rate (as increases water vapour gradient)
48
Q

What is translocation?

A

The process of transporting organic solutes from source to sink (requires energy)

49
Q

In translocation, what are the products of photosynthesis to be transported called?

A

Assimilates

50
Q

What is the main assimilate transported in translocation?

A

Sucrose

51
Q

Explain the process of translocation of assimilates from source to sink
(Mass flow hypothesis)

A

Source:

  • High conc of solutes, e.g. sucrose
  • Active transport of solute from companion cell into sieve tube element
  • Decreases water potential
  • Water moves in by osmosis from companion cell and xylem
  • Creates high hydrostatic pressure in phloem

Sink:

  • Uses, breaks down or converts the solute into something else
  • Creates a low concentration of solute (e.g. sucrose into starch)
  • Increases water potential
  • Water moves out by osmosis
  • Decreases pressure in phloem
52
Q

Explain the process of active loading into companion cells

A
  • Active transport of H+
  • Out of companion cells
  • Creates H ion concentration gradient
  • Facilitated diffusion if H+ back into companion cells
  • Assimilates (sucrose) move in with H+
  • By co-transport
53
Q

What is the evidence to support translocation?

A
  1. Radioactive labelling
    - Use radioactive C14 label
    - Grow plants in C14 atmosphere
    - Measure C14 as it moves down stem
  2. Ringing experiments
    - Remove bark in a ring from the tree trunk (contains phloem but not xylem)
    - Solutes can’t move up or down
    - Bulge forms about the ring
    - Fluid above the ring has more solutes, e.g. sugars than below
    - Evidence the solutes are moving down
54
Q

What are xerophytes?

A

Plants that are adapted to living in dry environments

55
Q

What are the adaptations of xerophytes?

A
  • Curled leaves
  • Stomata sunken in pits
  • Hairs on epidermis
    (Water vapour builds up and decreases water vapour gradient)
  • Thick waxy cuticle (reduces evaporation)
  • Fewer stomata (less opportunities for the water vapour to come out)
56
Q

What are hydrophytes?

A

Plants that are adapted to living in/on water

E.g. water lilies

57
Q

What are the adaptations of hydrophytes?

A
  • Air spaces in leaves (leaves float on surface of water so more light for PHS)
  • Long, flexible leaf stalks (leaves don’t break off in current so don’t need to support any weight)
  • Stomata on upper surface (allows gas exchange and prevents air spaces filling with water)
  • Large, thin leaves (increase SA for gas exchange)
58
Q

Name the 7 structures of a leaf in order from top to bottom

A 
1- Waxy cuticle
2- Upper epidermis
3- Palisade cells
4- Spongy mesophyll
5- Lower epidermis
6- Guard cells
7- Stomata

Biology (19 decks)

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