transport in plants

Question 1

state the functions of xylem and phloem

Answer 1

xylem – transport of water and mineral ions,
and support
phloem – transport of sucrose and amino
acids

Question 2

Relate the structure of xylem vessels to their
function

Answer 2

Thick walls of lignin
* helps keep plants upright
* lignin = very strong. helps support heavy trees

No cell contents
* more space for water to be transported

Cells joined end to end with no cross walls to form a long continuous tube
* no cross walls = easier to transport water up long continuous tube all the way from roots to leaves.

Question 3

Root hair cell function

Answer 3

• large surface area of root hairs increases uptake of water by osmosis and mineral ions by active transport
• root cap protects root as it grows though soil

Question 4

pathway taken by water through root stem leaf

Answer 4

root hair cells = root cortex cells = xylem = mesophyll cells

Question 5

define transpiration

Answer 5

loss of water vapour from leaves

Question 6

Outline the process of transpiration

Answer 6

• Water evaporates from surface of mesophyll cells
• Interconnecting air spaces between mesophyll cells creates a large surface area for evaporation
• Water vapour enters air spaces
• Water vapour diffuses out of leaf through stomata
• Down concentration gradient
• Diffusion occurs rapidly when stomata are open
• Many stomata = greater rate of diffusion of water vapour

*

Question 7

Explain the mechanism by which water moves upwards in the xylem

Answer 7

Loss of water vapour causes transpiration pull
- Column of water drawn up xylem
- Water molecules held together by cohesive forces of attraction (hydrogen bonds)

Question 8

What is the transpiration stream?

Answer 8

• Continuous column of water
• Moving up xylem from roots to leaves

Question 9

Describe the transport of water in a plant

Answer 9

Enters root hair cell by osmosis
- Water molecules are attracted to each other
- Transpiration stream in xylem
- Evaporation from mesophyll cells
- Diffusion of water vapour out of the stomata

Question 10

What is the role of the transpiration stream?

Answer 10

• Transports mineral ions
• Keeps plant cells turgid
• Cools the plant
• Supplies water for the leaves for photosynthesis

Question 11

Describe and explain how rates of transpiration may be increased

Answer 11

• Hot - water evaporates faster; water particles have more kinetic energy
• Dry - increases the concentration gradient between the leaf and the surrounding air
• Windy - water vapour is blown off the leaf increasing concentration gradient

Question 12

Describe and explain how rates of transpiration may be decreased

Answer 12

• Cold - water evaporates slower
• Humid - small concentration gradient between the leaf and the surrounding air
• Still air - water vapour is not removed from the surface of the leaf

Question 13

i love this chapter so much! hahahahaha

how does wilting ocurr

Answer 13

• no water in soil - plant wilts - cells become flaccid - they lose water
• inelastic cell wall keeps things in position

Question 14

what are sources

Answer 14

parts of plants that release
sucrose or amino acids

Question 14

define translocation

Answer 14

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

Question 15

what are sinks

Answer 15

parts of plants that use or store
sucrose or amino acids

Question 16

Explain why some parts of a plant may act as a source and a sink at different times

Answer 16

Spring
- Growth period for most plants
- Roots and storage organs act as source
- Starch converted into glucose
- Growing areas act as sinks
- Sucrose and amino acid needed for growth

Summer
- Most plants finished growing
- Leaves act as source
- Produce large quantities of sugars through photosynthesis
- Roots/tubers act as sink
- Store sucrose as starch until it is needed

Winter
- Many plants have no leaves
- Storage organs act as source
- Sucrose and amino acids transported from the storage organs (e.g. tubers, roots)
- To other parts of the plant for respiration