transport in plants

Question 1

what is the function of xylem cells ?

Answer 1

• transporting water and dissolved minerals from the roots to the photosynthetic part of the plant
• movement of water is always upwards

Question 2

xylem structure

Answer 2

• thick side walls and rings of lignin form rigid tubes
• tiny pores
• dead cells
• the lack of walls between the cells means that water flow is not slowed down

Question 3

what is the effect on the xylem to have rigid tubes ?

Answer 3

it will not burst or collapse and provides support

Question 4

the cells walls being lignified on the xylem …

Answer 4

stops the xylem tube collapsing in due to the pressure + allow the stem to be flexible and not break

Question 5

what do the tiny pores on the xylem allow ?

Answer 5

water and mineral ions to enter and leave the xylem

Question 6

the dead cells on the xylem have no cytoplasm so …

Answer 6

forms an empty tube for water to flow through

Question 7

movement of water up the xylem

Answer 7

1. water vapor evaporated out of the stomata on leaved - creates low pressure
2. when the water is lost by transpiration more water is pulled up the xylem to replace it
3. due to the hydrogen bonds between water molecules, they are cohesive - creates a column of water within the xylem
4. water molecules also adhere to the walls of the xylem - helps pull upwards
5. creates tension - pulling the xylem to become narrower

Question 8

what is the function of phloem ?

Answer 8

• main tissue transporting dissolved solutes around the plant
• up and down

Question 9

phloem struture

Answer 9

• holes in the ends of the cell walls
• pores to communicate with the companion cell
• mitochondria
• companion and sieve cell

Question 10

why do phloem have holes in the ends of the cell walls ?

Answer 10

allow liquids to flow from one sieve cell to the next

Question 11

why doe phloem have a very small amount of cytoplasm ?

Answer 11

so there is more room for the center channel

Question 12

sieve cells - function

Answer 12

• contain very little cytoplasm and no nucleus
• lined end to end to form a tube to transport sugars

Question 13

companion cells - function

Answer 13

• found in between sieve cells
• large nucleus and dense cytoplasm
• carry metabolic processes needed to support the sieve tube - metabolic energy, ATP and active transport of sucrose
• gaps in cells walls allowing communication and flow of minerals between the cells

Question 14

role of endodermis

Answer 14

in getting water into the xylem vessels

Question 15

structure of endodermis

Answer 15

• inside the endodermis is a layer of meristem cells called the pericycle
  – the vascular bundle is found at the center of the young root
• phloem is found in between the arms of the xylem

Question 16

where are vascular bundles found ?

Answer 16

near the outer edge of the stem

Question 17

what is cambium ?

Answer 17

a layer of the meristem cells that divide to produce new xylem and phloem

Question 18

Describe how insecticide would be transported from the soil into root hair cells and then to the leaves

Answer 18

• absorbed by diffusion - high conc in soil
• transported through apoplast - transported through symplastic pathway
• transported in xylem by transpiration

Question 19

apoplast pathway - mass flow

Answer 19

water travels across fully permeable spaces and structures whichever route the water is taken, once it reaches the casparian strip it enters the cytoplasm of the cells temporarily, the cell can then control the volume of water and minerals moving into the xylem

Question 20

symplast pathway- diffusion

Answer 20

water and sucrose moves by diffusion/osmosis through the interconnected cytoplasm in the plasmodesmata connecting cell in a plant

Question 21

vacuolar pathway - osmosis

Answer 21

• driven by the gradient of water potential
• limited pathway for the movement of large quantities of water
• root hair cells take up water from soil in this way as their contents have a much ore negative water potential than the vey dilute solution of ions found in soil water

Question 22

transpiration

Answer 22

the loss of water vapour from the surface of the plant that has evaporated from the surface of the spongy mesophyll cells mainly within the leaves

Question 23

how does transpiration occur ?

Answer 23

1. once the water reaches the leaves, it moves from the xylem in the veins of the leaves into the spongy mesophyll cells by osmosis
   2.ater then evapourates from the cellulose walls of the spongy mesophyll ells into the air spaces
2. it moves through the open stomata into the external air

Question 24

explain the transpiration stream and the cohesion - tension theory ?

Answer 24

• water is loss from the leaves through transpiration, as it moves by osmosis across the leaf from cell to cell from the xylem
• this creates a tension in the column of water in the xylem, which is transmitted all the way down into the roots, due to cohesion of water molecules (their polar nature and the hydrogen bonds between them, the water molecules ‘stick’ and there is tensile strength between them)
• more water is then pulled up the xylem to replace what is lost through transpiration

Question 25

what are the four factors affecting transpiration ?

Answer 25

light
temperature
air movement
air humidity

Question 26

explain how light affects the rate of transpiration

Answer 26

light causes stomata to open for photosynthetic gas exchange and so allow more water out, therefore transpiration increases with light intensity until all the stomata are open

Question 27

explain how temperature affects the rate of transpiration

Answer 27

at a given light intensity, as temp rises, water molecules have more kinetic energy, increasing evaporation and transpiration. this is until another factor becomes limiting

Question 28

explain how air movement affects the rate of transpiration

Answer 28

increased air movement moves the still air from near the leaf, increasing the diffusion gradient between the outside and inside of the leaf, increasing the rate of transpiration

Question 29

explain how air humidity affects the rate of transpiration

Answer 29

humidity is the concentration of water vapour in the air. as it increases there is a reduced concentration gradient between the outside and inside of the leaf and therefore there is less water lost through transpiration. very dry air has increased transpiration