transport in plants

Question 1

what is the function of xylem and phloem

Answer 1

To transport substances from source, where they are taken in or made, to the sinks, where they are used

• xylem: water and mineral ions
• phloem: sucrose and amino acid

To support the stem

Question 2

xylem structure

Answer 2

• one way transport
• no end walls between cells
• thick lignified cells
• looks + shaped in cross section of a plant

Question 3

phloem structure

Answer 3

• two way flow
• end walls with perforations
• looks dot shaped in cross section of a plant

Question 4

function of root hair cell

Answer 4

Function: to absorb water and minerals from the soil

Question 5

adaptation of root hair cells

Answer 5

They have an elongated shape for more surface area which increases the rate of absorption of water by osmosis and ions by active transport

Question 6

describe the pathway of water in plants

Answer 6

Water enters root hair cell from moist soil via osmosis because water potential is higher in soil than in cytoplasm.

Water passes through the cortex cells by osmosis but mostly by “suction”.

Water and minerals are forced to cross the endodermis.

Water enters xylem then leaves when it gets to mesophyll cells

Question 7

what is transpiration

Answer 7

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

Water leaves mesophyll cells, into air spaces created by irregular shape of spongy mesophyll cells, then diffuses out of the stomata.

Question 8

what is wilting

Answer 8

occurs if water loss is greater than water uptake – cells become flaccid, tissues become limp and plant no longer supported

Question 9

describe water uptake

Answer 9

Caused by water loss in leaves which lowers its water potential

Water moves from xylem to leaf tissues via osmosis

Water moves up the stem in the xylem due to tension (because of cohesion of water molecules to each other) caused by water loss from the leaves

Ends with the gain of water through roots

This upward flow of water is called the transpiration stream

Question 10

factors affecting rate of transpiration

Answer 10

Temperature: higher temperatures increase water-holding capacity of air and increases transpiration rate

Humidity: low humidity increases water potential gradient between leaf and atmosphere ∴ increasing transpiration rate

Light intensity: high light intensity causes stomata to open (to allow more photosynthesis) which causes increase in transpiration

Question 11

what is translocation

Answer 11

Movement of sucrose and amino acids in phloem; from regions of production (sources) to regions of storage or to regions of utilization in respiration or growth (sinks).

Question 12

translocation in different seasons

Answer 12

Spring: sucrose transported from stores in roots to leaves

Summer & early autumn: sucrose goes from photosynthesizing leaves to root stores,

Question 13

advantages of plants wilting

Answer 13

stomata close ;
to prevent more water loss ;
water conserved for, other processes / other parts of plant ;
decrease surface area, exposed to the Sun / for absorption of heat ;