Transportation In Plants

Question 1

State the functions of xylem and phloem

Answer 1

• Xylem: eater and mineral ions from the roots up to the leaves
• Phloem: transport sucrose made in the leaves during photosynthesis and in storage organs to other parts of the plants

Question 2

State the pathway taken by water through root,

stem and leaf

Answer 2

• During water uptake, water passes down from high water potential in the soil to a lower water potential in the root hair cells by osmosis
• Water passes down from a high water potential in the roots to a lower in the cortex cells and to the lower in the xylem vessels and to the lowest in leaves.

Question 3

Relate the structure and functions of root
hairs to their surface area and to water and
ion uptake

Answer 3

Have long extensions -> larger surface area to absorb water and ions from soil

Question 4

Define transpiration

Answer 4

evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata

Question 5

Describe the effects of variation of temperature,

humidity and light intensity on transpiration rate

Answer 5

• Light causes the stomata to open => increases the rate
• Humidity decreases because the air contains a great many water molecules => concentration gradient isn’t steep
• Temperature increases rate because warm air can hold more water vapour

Question 6

Explain the mechanism of water uptake and

movement in terms of transpiration pull

Answer 6

• Cohesion: the affinity of the same type of molecules with each other. Water molecules attract each other, sticking together
• Adhesion: the affinity of one type of molecule with a different type of a molecule. Water molecules tend to stick to the inside of xylem vessel
=> continuous flow of water from roots to leaves

Question 7

Define translocation

Answer 7

• the movement of sucrose and amino acids in phloem;
  • from regions of production
  • to regions of storage OR to regions of
  utilisation in respiration or growth
• for example: from leaves to:
  • Roots may change sucrose -> starch & store it.
  • Flowers use sucrose to make fructose
  • When fruits are developing, large amounts of sucrose may be used to produce sweet, juicy fruit to attract animals

Question 8

Describe translocation throughout the plant
of applied chemicals, including systemic
pesticides

Answer 8

The pesticides are translocated in the phloem tubes. Any insect feeding from the plant will ingest the pesticide, after a while the pesticide will build up in the insect and reach critical level and kill it.

Question 9

Compare the role of transpiration and translocation in the transport of materials from sources to sinks within plants at different seasons

Answer 9

• Water is absorbed by roots to leaves, flowers and fruits. Xylem vessels are columns of dead empty cells => movement of water is passive since relies on evaporation of water.
• Translocation = active process. Leaves are the source of food. Phloems tubes are living cells that contain cytoplasm. Process = water enters the phloem to build up pressure that forces phloem sap to the sinks

Question 10

Discuss the adaptations of the leaf, stem
and root to three contrasting environments,
to include pond, and desert

Answer 10

• Desert plants (xerophytes):
  + Leaves are reduced to spines => reduces the surface area of leaf which water can be lost
  + Thick waxy cuticle to prevent trnaspiration
  + Shallow, spreading root system to absorb water and overnight condensation
• Pond (hydrophates)
  + Little or no cuticle since there’s no need to conserve water
  + Have extensive air spaces to store co2 and o2 which diffuse slowly out of water