3.1.3: transport in plants

Question 1

how do gases diffuse in and out of leaves?

Answer 1

via the stomata

Question 2

what does the xylem transport?

Answer 2

water and mineral ions

Question 3

what does the phloem transport?

Answer 3

sugars

Question 4

what is the transpiration stream?

Answer 4

the movement of water up a plant from the roots to the leaves

Question 5

how do mineral ions move into the root hair cells?

Answer 5

combination of facilitated diffusion and active transport

Question 6

how are root hair cells adapted for its function?

Answer 6

have a large surface area and have very thin walls

Question 7

what is the apoplastic pathway?

Answer 7

water moves from cell to cell through the cellulose walls

Question 8

what is the symplastic pathway?

Answer 8

water moves from cell to cell through the cytoplasm, then via connections from one cytoplasm to another

Question 9

what is the casparian strip and what does it do?

Answer 9

a waxy strip in the cell wall, which is waterproof, meaning no water can pass through so it slows down the flow of water and gives the plant control over which minerals pass

Question 10

what substances are in the xylem wall?

Answer 10

cellulose and lignin

Question 11

how is the xylem adapted for transporting water?

Answer 11

• has lignin in the walls, which is strong and waterproof
• tiny holes called pits which allow water to move sideways into neighbouring vessels if there are blockages

Question 12

what is the capillary affect?

Answer 12

more water molecules are in contact with the xylem walls because it is so narrow, increasing the adhesion forces

Question 13

how does transpiration occur?

Answer 13

• water from the xylem vessels enters the mesophyll cells
• making the spaces saturated with water vapour
• these air spaces are close to the stomata so the vapour evaporates out, by diffusion
• down a water potential gradient

Question 14

how have plants adapted to minimize water vapour losses during transpiration?

Answer 14

• a waxy cuticle
• stomata being on the underside of leaves
• stomatas being closed at night
• plants losing their leaves in winter

Question 15

where are the vascular bundles located in stems and why?

Answer 15

around the edges to support and strengthen

Question 16

where are the vascular bundles located in roots and why?

Answer 16

in the middle to help it withstand the tugging strains while in windy conditions

Question 17

where are the vascular bundles located in leaves and why?

Answer 17

in the midrib of a dicot leaf to support the structure of the leaf

Question 18

what does turgor pressure do?

Answer 18

provides a hydrostatic skeleton to support the stems and leaves

Question 19

what happens to the stomata during the day vs the night and why?

Answer 19

• day: mostly open, which allows free exchange of oxygen and carbon dioxide. water vapour is lost via diffusion
• night: mostly closed to prevent excessive loss of water vapour. the demand for carbon dioxide is low but oxygen is still required for respiration

Question 20

what are the 2 pieces of evidence for the cohesion tension theory and how?

Answer 20

1) changes in tree diameter -when transpiration is at its highest during the day, the tension in xylem vessels is at its highest too so the tree shrinks in diameter and vice versa
2) breaking a xylem vessel - air is pulled in to the xylem rather than water leaking out, meaning plant can no longer move water as a continuous stream

Question 21

what are the factors that affect transpiration?

Answer 21

1) light
2) humidity
3) temperature
4) air movement
5) soil-water availability

Question 22

how does light intensity affect transpiration?

Answer 22

increasing the light intensity gives an increasing number of open stomatas, meaning a higher rate of transpiration

Question 23

how does humidity affect transpiration?

Answer 23

very high relative humidity will lower the rate of transpiration because of a reduced water potential gradient

Question 24

how does temperature affect transpiration?

Answer 24

increased temperature also increases the kinetic energy of the water molecules, so it increases the rate of evaporation.

Question 25

how does air movement affect transpiration?

Answer 25

increased wind means when water is diffused out, the water potential concentration increases therefore increases transpiration

Question 26

how does soil-water availability affect transpiration?

Answer 26

if the plant is very dry, it will be under water stress and the rate of transpiration will be reduced

Question 27

what are xerophytes?

Answer 27

plants adapted to live in dry habitats, where there is little access to water

Question 28

how are xerophytes adapted and why?

Answer 28

• thick, waxy cuticle: minimise water loss
• sunken stomatas: reduces the water potential gradient
• reduced number of stomatas: reduce water loss
• reduced leaves: small surface area to volume ratio
• hairy leaves: creates a microclimate
• curled leaves: creates a microclimate
• leaf loss: prevents water loss
• long, tap roots: allow access to get a much from the soils as possible

Question 29

what are hydrophytes?

Answer 29

plants that live in water, partially submerged

Question 30

how are hydrophytes adapted and why?

Answer 30

• no waxy cuticle: no reason to conserve
• open stomatas on upper surface: maximise gas exchange and in contact with air
• reduced structure: water supports
• wide, flat leaves: capture sun light for photosynthesis
• small roots: can diffuse directly into stem and leaves
• air sacs: to float
• aerenchnyma: tissue to make it buoyant and low resistance internal pathways

Question 31

how is the xerophytes, cacti, adapted?

Answer 31

• thick, waxy cuticle to reduce water loss
• spines instead of leaves to reduce the surface area for water to be lost
• close their stomatas at the hottest times of day when transpiration rates are high to reduce water lost

Question 32

how is the xerophyte, marram grass, found and adapted?

Answer 32

• found in sand dunes
• sunk in pits so they are sheltered from wind, slowing down transpiration
• layers of hair on epidermis which traps moist air around the stomata and reducing the water potential gradient
• roll their leaves to reduce the exposed surface area for losing water and protects stomata from wind
• thick, waxy layer to reduce loss of water by evaporation

Question 33

how do hydrophytes transpire?

Answer 33

contain specialised structures at the tips of their leaves called hydathodes, which release water droplets which may evaporate from the surface

Question 34

what is translocation?

Answer 34

the movement of organic solutes, like sucrose, around a plant in the phloem, from source to sink

Question 35

what are the main sources of assimilates, and the main sinks, in plants?

Answer 35

sources:
- green leaves and green stems
- storage organs, like tubers and tap roots
- food stores in seeds
sinks:
- roots
- meristems
- developing seeds, fruits or storage organs

Question 36

how can you use a potometer to measure the factors effect on the rate of transpiration?

Answer 36

1) cut shoot underwater to prevent air from entering the xylem, and cute at a slant to increase the surface area available for water uptake
2) assemble the potometer in water and insert the shoot under water , so no air can enter
3) remove the apparatus from the water, but keep the end of the capillary tube submerged in a beaker of water
4) check that the apparatus is airtight and watertight
5) dry the leaves and allow time for the shoot to acclimatise and than shut the tap
6) remove the end of the capillary tube from the beaker of water until one air bubble has formed, then put the end of the tube back into the beaker
7) record the starting position of the air bubble
8) start the stopwatch and record the distance moved by the bubble per unit time - the rate of air bubble movement is an estimate of the transpiration rate
9) only change one variable but keep all the other conditions the same
- when using, don’t allow air bubble to move too far - enter xylem
- place open end in water - no new air bubbles
- keep shoot still

Question 37

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