transpiration

Question 1

what is the epidermis covered by and what does this mean?

Answer 1

• covered by a waxy cuticle
• impermeable to water

Question 2

what does most water pass out of the stomata as?

Answer 2

as water vapour

Question 3

how does water leave the plant?

Answer 3

• water leaves the cells of the mesophyll and evaporates into the air spaces between the spongy mesophyll
• the water vapour then diffuses out through the stomata

Question 4

what does loss of water mean for the cells?

Answer 4

the cells have a lower concentration of water molecules- so water moves into them via osmosis from the surrounding mesophyll cells
- water leaves the xylem to replace the water lost from nearby cells

Question 5

what is the loss of water vapour from the leaves called?

Answer 5

transpiration

Question 6

what is transpiration?

Answer 6

the evaporation of water from the surface of a plant

Question 7

how can evaporation occur rapidly when the stomata are open?

Answer 7

the many interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area

Question 8

what does transpiration cause?

Answer 8

causes water to be pulled up the xylem in the stem and the roots in a continuous flow known as the transpiration stream

Question 9

what are the 4 functions of transpiration?

Answer 9

• transporting mineral ions to the leaves for the synthesis of amino acids and chlorophyll
• providing water to keep cells turgid to support the structure of the plant
• providing water to leaf cells for photosynthesis
• keeping the leaves cool- conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspaces requires heat energy- the use of heat to convert water into water vapour helps to cool the plant down

Question 10

what 5 factors affect the rate of transpiration?

Answer 10

• temperature
• humidity
• wind speed
• light intensity
• water supply

Question 11

how does temperature affect the rate of transpiration?

Answer 11

• on a hot day, water will evaporate quickly from the leaves of a plant- the water molecules have more kinetic energy
• transpiration will increase if temperature increases

Question 12

how does humidity affect the rate of transpiration?

Answer 12

• very humid air contains lots of water vapour- smaller conc gradient- transpiration slows down
• in dry air- diffusion of water vapour from the leaf to the atmosphere will be rapid
• if humidity increases, transpiration decreases

Question 13

how does wind speed affect the rate of transpiration?

Answer 13

• in still air, the region around a transpiring leaf will become saturated with water vapour so that no more can escape from the leaf- transpiration slows down
• moving air- water vapour will be blown away from the leaf- speeds up transpiration
• transpiration increases as wind speed increases

Question 14

how does light intensity affect the rate of transpiration?

Answer 14

• in daylight the stomata are open to supply carbon dioxide for photosynthesis
• allows more water to diffuse out of the leaves and into the atmosphere

Question 15

how does water supply affect the rate of transpiration?

Answer 15

• if water is in short supply and the plant is losing water by transpiration faster than it is being taken up by the roots, the plant may wilt
• before this happens the guard cells become flaccid and stomata start to close- reducing transpiration