B6 Transpiration Flashcards

1
Q

Describe how water is moved through a plant by cohesion tension theory

A

Water evaporated from the mesophyll cells
Reduces the water potential in cells
Water is drawn out of xylem vessels by osmosis
Creates tension between water molecules held together by hydrogen bonds
Water is pulled up the xylem vessels

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2
Q

The diameter of a tree is less during the day than it is at night. Explain how this supports cohesion tension theory

A

Water evaporates from surface of mesophyll cells and diffuses through stomata
Creates tension in the column of water in xylem vessels

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3
Q

Give 4 adaptations shown by xerophytes

A

Stomata in pits
Rolled leaves
Thick waxy cuticle
Hairs on surrounding stomata
Reduced number of stomata
Spines/fewer leaves

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4
Q

Why do some leaves have hairs on them?

A

Trap layer of water vapour around leaf (boundary layer)
Increases water potential around leaf
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of the leaf

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5
Q

Why do some leaves have stomata in pits?

A

Traps water vapour around the stomata
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of leaf

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6
Q

Why do some leaves have a thick waxy cuticle?

A

Hydrophobic waxy substances impede movement of polar water molecules
Increases diffusion distance
Decreases diffusion/transpiration of water molecules

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7
Q

Why do some leaves have rolled leaves?

A

Traps water vapour around the stomata
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of leaf

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8
Q

Why do some plants have spines or fewer leaves

A

Reduced surface area
Reduced water loss by diffusion/transpiration

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9
Q

Why might the rate of water uptake by a plant NOT be the same as the rate of transpiration?

A

Water used for turgidity
Water used in photosynthesis
Water used in hydrolysis
Water produced by condensation reactions
Water produced by respiration

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10
Q

Name the piece of apparatus that can be used to measure water uptake by a shoot

A

Potometer

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11
Q

List 4 environmental factors that increase the rate of transpiration

A

Increased temperature
Increased wind/air movement
Increased light intensity
Decreased humidity

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12
Q

Explain how an increase in temperature increases the rate of transpiration

A

Increased rate of evaporation
Increased rate of diffusion due to increased KE of water molecules out of leaf

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13
Q

Explain how an increase in wind increases the rate of transpiration

A

Air movement removes water molecules that have left the leaf
Maintains a steep diffusion gradient between internal and external surface of the leaf.
More water moves by diffusion through the stomata

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14
Q

Explain how an increase in light intensity increase the rate of transpiration

A

Stomata open to allow carbon dioxide to enter the leaf for photosynthesis
Increases number of water molecules moving through stomata and out of the leaf

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15
Q

Explain how an increase in humidity decreases the rate of transpiration

A

Increased number of water molecules in external atmosphere.
Reduces the water potential gradient between the internal and external environment
Decreases diffusion of water out of the leaf

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16
Q

How would you calculate the surface area of a leaf?

A

Draw round leaf on a piece of graph paper.
Count the number of squares inside the outline
Multiple by 2 (top and bottom surface of leaf)

17
Q

A potometer can be used to calculate the rate of water uptake by a shoot . List 3 measurements needed to calculate the rate of water uptake

A

Distance travelled by the air bubble
Time taken
Diameter/radius of the capillary tube lumen

18
Q

Name the tissue used to transport water in the stem and leaves of a plant

A

Xylem

19
Q

Why is a mass transport system needed for the movement of water in a plant

A

Maintains the diffusion gradient needed to bring water to and from the cell membrane of individual cells
Surface area to volume ratio too low to deliver the water required by every cell directly from the environment