Transport in Plants

Question 1

xylem

Answer 1

transport of water and mineral ions, it also supports the plant

Question 2

phloem

Answer 2

transport of sucrose and amino
acids

Question 3

structure of xylem vessels

Answer 3

• many dead cells
• empty lumen with no cytoplasm - cells joined end to end with no cross walls to form a long continuous tube
• thick walls with lignin: a hard substance that prevents collapse of the vessel
• no cell contents

Question 4

structure of phloem

Answer 4

• consists mainly of long tubes called sieve tubes
• sieve plates allow rapid flow of manufactured food substances through the sieve tubes

Question 5

root hair cell and its adaptations

Answer 5

root hair cell absorbs mineral ions from the soil solution by active transport.

• it is long and narrow, which increases the surface area to volume ratio. this increases the rate of absorption of water and mineral ions
• the cell membrane is partially permeable. it encloses a cell sap which is more concentrated than the soil solution. hence, it can absorb water by osmosis
• the root hair cell has many mitochondria to release energy for active transport

Question 6

the path of water through the root

Answer 6

root hair cells, root cortex cells, xylem, mesophyll cells

Question 7

transpiration

Answer 7

the loss of water vapour from leaves
water evaporates from the surfaces of the mesophyll cells into the air spaces and then
diffuses out of the leaves through the stomata as
water vapour

Question 8

transpiration pull

Answer 8

a transpiration pull, a suction force that draws up a column of water molecules, held together by forces of attraction between water molecules

Question 9

movement of water inside a leaf

Answer 9

water evaporates from a thin film of moisture and moves into the large internal surface area provided by the interconnecting air spaces between mesophyll cells.

water vapour then diffuses through the stomata to the drier air outside the leaf. this is transpiration. an increase in the size and number of stomata, increases the rate of transpiration

Question 10

importance of transpiration

Answer 10

• draws water and mineral ions
• removes latent heat of vaporisation, cooling the plant and prevents it from being scorched by the sun
• water can be used for photosynthesis, to keep cells turgid which keeps the leaves spread out widely

Question 11

factors affecting transpiration

Answer 11

speed, temperature, light, humidity

Question 12

speed

Answer 12

wind blows the water vapour that accumulates outside the stomata. this maintains the water vapour concentration gradient between the leaf and the atmosphere. the stronger the wind, higher transpiration.

in still air, water vapour that diffuses out makes air around leaf more humid, so lower rate of transpiration

Question 13

temperature

Answer 13

higher temperature, higher rate of evaporation of water from cell surface, so higher transpiration

Question 14

light

Answer 14

affects size of stomata. in sunlight, stomata opens wide - high transpiration. in darkness, stomata closes - less water is lost, low transpiration

Question 15

humidity

Answer 15

high humidity, low transpiration & vice versa. when air is drier, conc gradient of water vapour is steeper - high transpiration

Question 16

wilting

Answer 16

the turgor pressure in the mesophyll cells of the leaf helps it to support the leaf and keep it firm. when the rate of transpiration exceeds the rate of absorption by water by the roots, the cells lose their turgor. they become flaccid and plant wilts

Question 17

advantages of wilting

Answer 17

rate of transpiration will reduce as stomata will close when guard cells become flaccid

Question 18

disadvantages of wilting

Answer 18

reduces rate of photosynthesis

Question 19

translocation

Answer 19

the movement of sucrose and amino acids in phloem from sources to sinks

Question 20

sources

Answer 20

the parts of plants that release sucrose or amino acids

Question 21

sinks

Answer 21

the parts of plants that use or store sucrose or amino acids

Question 21

sinks

Answer 21

the parts of plants that use or store sucrose or amino acids