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Biology Exams > Transport of water > Flashcards

Transport of water Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are the two main functions of the xylem?

A

The transport of water and mineral ions

Support for the plant

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2
Q

What is the direction of flow in the xylem?

A

From roots up to shoots and leaves

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3
Q

What is the xylem made up of?

A

Dead, hollow cells with no end cell walls. This forms one continuous tube when the xylem cells are stacked on top of each other and fused together

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4
Q

What are the two other types of tissues associated with the xylem?

A

Xylem parenchyma

Lignin

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5
Q

What is xylem parenchyma?

A

Xylem parenchyma packs around xylem vessels, and stores food and contains tannin deposits

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6
Q

What is tannin?

A

A bitter tasting chemical that protects plant tissues from attack by herbivores

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7
Q

What is the function of lignin in the xylem?

A

Lignin lines the walls of the xylem.
It is important in:
- Supporting and strengthening the xylem
- Impermeable so prevents incorrect water loss

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8
Q

Where does water leave the xylem?

A

Un-lignified bordered pits

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9
Q

How is lignin arranged in the xylem?

A

It can form rings, spirals or solid tubes

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10
Q

How does the structure of xylem cells allow for the fastest flow of water?

A

They have no cytoplasm, cell organelles, or end walls, so there is nothing to slow the flow of water.

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11
Q

What occurs at the unlignified bordered pits in the xylem?

A

Water and minerals can leave the xylem tube it’s currently in, either entering a new xylem tube, or entering cells

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12
Q

4 reasons why water is important in plants

A
  • Turgor pressure provides a hydrostatic skeleton
  • Turgor pressure drives root expansion
  • Mineral ions and products of photosynthesis are transported in water
  • Water is a raw material for photosynthesis
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13
Q

What cell is responsible for the uptake of water into the plant?

A

Root hair cells are the exchange surface in plants where water is taken into the plant from the soil

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14
Q

What do root hair cells have attached to them?

A

Root hairs

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15
Q

Why are root hairs well adapted exchange surfaces?

A
  • Small size can easily penetrate soil
  • Large SA:V ratio
  • Thin layer
  • High water potential gradient between the soil water and the cell
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16
Q

Why is there a high water potential gradient between soil water and root cells?

A

Soil water has a very low concentration of dissolved minerals so a high water potential.
The cytoplasm and cell sap of the root hair cells has many different solutes (e.g sugars, minerals), and so has a low water potential.
Therefore water moves into the root hair cells via osmosis

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17
Q

Once water has entered the root hair cell, how does it move across the root to the xylem?

A

The water can travel either through the symplast or apoplast pathway to reach the xylem

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18
Q

How does water move in the symplast pathway?

A

It moves through the continuous cytoplasm of living plant cells by diffusion and osmosis

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19
Q

What joins cytoplasms together in the symplast pathway?

A

Plasmodesmata is a fine strand of cytoplasm that act as a bridge linking adjacent cells

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20
Q

How does water move in the apoplast pathway?

A

It moves through the cell walls and the intercellular spaces. It does this through water tension

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21
Q

What is the endodermis?

A

The layer of cells that surround the vascular tissue

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22
Q

What is more common for water to move through, symplast or apoplast pathway?

A

Most water goes from the root cell to the xylem through the apoplast pathway

23
Q

What is the Casparian strip?

A

A band of waxy material called suberin, which runs around the endodermal cell walls, forming a waterproof barrier

24
Q

What happens in the apoplast pathway when the water reaches the Casparian strip?

A

It cannot pass through the Casparian strip, so must join the symplast pathway

25
Q

What is the significance of apoplast water joining the symplast pathway?

A

The water must pass through the selectively permeable cell surface membranes; this excludes any potentially-toxic solutes in the soil water

26
Q

What happens once the water enters the endodermal cells, just outside the xylem?

A

Endodermal cells actively transport mineral ions into the xylem

27
Q

What is the impact of the active pumping of minerals into the xylem?

A

It lowers the water potential in the xylem, causing water to enter the xylem via osmosis

28
Q

What is root pressure?

A

The movement of water up the xylem due to the active pumping of mineral ions. Root pressure is independent of transpiration

29
Q

What is evidence to suggest that active transport has a role in root pressure?

A
  • When ATP inhibiting poisons like cyanide are added to root cells, there is no energy so root pressure disappears
  • Root pressure increases with a rise in temperature and falls with a fall in temperature
30
Q

What is the definition of transpiration?

A

The loss of water vapour by evaporation through stomata

31
Q

What are the pros of transpiration?

A
  • Cools plants down (prevents heat damage)

- Causes the transpiration pull, which allows minerals and water to be delivered to cells

32
Q

What is the transpiration pull?

A

Water is continuously drawn up the xylem to replace the water lost by evaporation/transpiration

33
Q

What are the cons of transpiration?

A

Loss of water = loss of turgor pressure = plant wilting

34
Q

What is the cohesion of water molecules in plants?

A

Water molecules form H bonds with each other, so are able to stick together and pull each other

35
Q

What is the adhesion of water molecules in plants?

A

Water molecules form H bonds with the carbohydrates in the walls of the narrow xylem vessels

36
Q

What is the cohesion-tension theory?

A

The model of water moving from the soil in a continuous stream up the xylem and across the leaf due to the cohesive property of water

37
Q

What is capillary action, and what properties of water allow it to occur?

A

Capillary action is the process by which water can move up a narrow tubes against the force of gravity. This is made possible by the combined effects of the adhesion and cohesion of water moving up the xylem

38
Q

Why is it important that the xylem tubes are narrow enough?

A

So the water can flow in a continuous stream

39
Q

How does water leave the plant?

A

Water molecules evaporate from mesophyll cells into the air spaces of the leaf and move out of the stomata into the outside air by DIFFUSION

40
Q

What happens once the water evaporates from the mesophyll cell out of the plant?

A

The water potential of the mesophyll cell is lowered, causing water to move from an adjacent cell to replace the lost water by osmosis. This has a knock on effect, and this process repeats throughout the plant continuously (this is the transpiration pull).

41
Q

Evidence of the cohesion-tension theory

A

If a xylem vessel is broken, water can no longer move water up as the continuous stream of water held together by cohesive forces is broken

42
Q

Why must transpiration occur?

A

Transpiration is a consequence of photosynthesis, as stomata must open to allow CO2 to enter and oxygen to leave, which allows transpiration to occur

43
Q

Why does increasing the temperature increase transpiration rate?

A

Water molecules have more kinetic energy, so evaporate more quickly

44
Q

Why does a lower humidity increase transpiration rate?

A

There is a higher water vapour concentration gradient, so water vapour will diffuse out more quickly

45
Q

Why does a higher light intensity increase transpiration rate?

A

More stomata will open to allow more CO2 so the plant can photosynthesise more

46
Q

Why does higher air movement increase transpiration rate?

A

Stronger winds will more quickly get rid the moist water vapour air from around the lead, increasing the water vapour concentration gradient

47
Q

Why does a lower soil-water availability decrease transpiration rate?

A

The plant will be under water stress, so stomata will close and rate of transpiration will decrease

48
Q

What instrument can be used to estimate the rate of transpiration?

A

Potometer

49
Q

Why is using a potometer an estimation not a measure of transpiration?

A

Potometers measure the rate of water uptake by a plant, and not all water taken up by the plant will transpire; some will be used in photosynthesis or in maintaining turgor pressure. Therefore not all water taken up will transpire

50
Q

How do potometers work?

A

They measure the distance travelled by the air bubble, and use this to find the volume of the water taken up

51
Q

How do you convert the distance travelled by the bubble into volume of water taken up?

A

Distance travelled by the bubble x (pi x radius^2) = volume of water

52
Q

To undergo an accurate potometer practical, what steps must you take?

A
  • Cut leafy shoots underwater
  • Place the shoot into a tube with a bung for a tight seal; seal joints with waterproof jelly so any water loss is from the plant
  • Do not get water on the leaves, or if you do leave it to dry
53
Q

Issues with using a potometer

A

Rate of water uptake does not equal water transpired

It is a complex set up, in which leaks are common and hard to detect

Biology Exams (28 decks)

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