Transport In Plants

Question 1

Transpiration

Answer 1

The loss of water vapour from the stems and leaves of a plant as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through the stomata

Question 2

Cohesion tension theory

Answer 2

Water moving from the soil in a continuous stream up the xylem and across the leaf

Question 3

Adhesion

Answer 3

Water molecules form hydrogen bonds with carbohydrates in the walls of the narrow xylem vessels

Question 4

Cohesion

Answer 4

Water molecules form hydrogen bonds with eachother so stick together

Question 5

Water exhibiting capillary action

Answer 5

When water can rise up a narrow tube against the force of gravity

Question 6

Why does water exhibiting capillary action occur

Answer 6

Due to the combined effects of adhesion and cohesion

Question 7

Transpiration pull

Answer 7

When water is drawn up the xylem in a continuous stream to replace water lost by evaporation

Question 8

What does the transpiration pull result in?

Answer 8

Tension in the xylem vessel which helps to move water across the roots from the soil

Question 9

Evidence for cohesion tension theory

Answer 9

• changes in tree diameter
• when a xylem vessel is broken air is drawn into xylem instead of water leaking out
• when a xylem vessel is broken, air gets pulled in so water can no longer be moved up the stem so the continuous stream of water molecules is broken

Question 10

Why do plants need transport systems

Answer 10

• metabolic demands
• size
• sa:vol ratio

Question 11

Xylem

Answer 11

Non living tissue that has two main functions in a plant

Question 12

Function of the xylem

Answer 12

• transport of water and mineral ions
• support

Question 13

Xylem structure

Answer 13

• long hollow structures made by several columns of cells fusing together end to end
• made up of several cells that are mostly dead

Question 14

Xylem parenchyma

Answer 14

• thick walled
• packs around the xylem vessels storing food
• contains tannin deposits

Question 15

Tannin

Answer 15

A bitter, astringent tasting chemical that protects plant tissues from attack by herbivores

Question 16

Xylem fibres

Answer 16

• long cells
• lignified secondary walls that provide extra mechanical strength but don’t transport water

Question 17

Lignin

Answer 17

• can form rings, spirals or relatively solid tubes with many small unlignified areas called bordered pits

Question 18

Bordered pits

Answer 18

Where water leaves the xylem and moves into other cells of the plant

Question 19

Vascular system

Answer 19

A series of transport vessels running through the stems, toots and leaves in dicots
- made up of the xylem and phloem which are arranged in a vascular bundle

Question 20

Metabolic demands

Answer 20

• glucose and oxygen must be transported to parts of the plant that don’t photosynthesise
• waste products must be removed
• hormones and mineral ions must be transported to cells

Question 21

Size

Answer 21

-plants continue to grow throughout their lives
- need effective transport systems so substances can be moved up and down the plant

Question 22

SA:VOL ratio

Answer 22

• plants have a small SA:V ratio
• can’t rely on diffusion alone to supply cells with everything they need

Question 23

Factors affecting rate of transpiration

Answer 23

• light intensity
• relative humidity
• temperature
• soil-water availability
• air movement

Question 24

Light intensity

Answer 24

• if light intensity is high, more stomata will be open, increasing the rate of water vapour diffusing out
• increasing the evaporation from the surfaces of the leaf

Question 25

Relative Humidity

Answer 25

• high relative humidity will lowers the rate of transpiration due to the reduced water vapour potential gradient between the inside of the leaf and the outside air
• very dry air increases the rate of transpiration

Question 26

Temperature

Answer 26

• an increase in temp increases kinetic energy of molecules therefore increasing the rate of evaporation
• an increase in temp increases conc of water vapour that the external air can hold before it becomes saturated

Question 27

Soil-water availability

Answer 27

• the amount of water available in the soil can affect transpiration rate. If it is very dry the plant will be under water stress and will reduce the rate of transpiration