Module 3 : Section 3 - Transpiration

Question 1

what is transpiration

Answer 1

• the evaporation of water from a plant’s surface, especially in the leaves
• happens as result of gas exchange

Question 2

what is meant by ‘transpiration is a consequence of gas exchange

Answer 2

• a plant needs to open its stomata to let in CO₂, so that it can produce glucose (by photosynthesis)
• this lets water out, there is a higher concentration of water inside the leaf than in the air outside. so this moves water out of the leaf down the water potential gradient when the stomata open

Question 3

what factors affect transpiration rate

Answer 3

• light intensity
• temperature
• humidity
• wind

Question 4

how does light intensity affect transpiration rate

Answer 4

• the higher the light intensity the faster the transpiration rate
• this is because the stomata open when it gets light, so CO₂ can diffuse into the leaf for photosynthesis
• when its dark the stomata are usually closed, so there’s little transpiration

Question 5

how does water move

Answer 5

from areas of higher water potential to area of lower water potential - it moves down the water potential gradient

Question 6

how does temperature affect transpiration rate

Answer 6

• the higher the temperature the faster the transpiration rate
• warmer water molecules have more kinetic energy so they evaporate from the cells inside the leaf faster
  -this increases the water potential gradient between inside and outside the leaf making water diffuse out of the leaf faster

Question 7

how does humidity affect transpiration rate

Answer 7

• the lower the humidity the faster the transpiration rate
• if the air around the plant is dry, the water potential gradient between the leaf and air is increased which increases transpiration

Question 8

how does the wind affect transpiration rates

Answer 8

• the windier it is, the faster the transpiration rate
• lots of air movement blows away water molecules from around the stomata
• this increases the water potential gradient which increases the rate of transpiration

Question 9

what factors alter the water potential gradient

Answer 9

wind
temperature
humidity

Question 10

what are xerophytic plants

Answer 10

• plants that are adapted to reduce water loss
• adapted to live in dry conditions
• their adaptations prevent them losing water by transpiration

Question 11

give examples of xerophytes

Answer 11

cacti
marram grass

Question 12

how is marram grass adapted to reduce water loss

Answer 12

• has stomata which are sunk in pits, so they are sheltered from wind. this slows down transpiration
• has a layer of hairs on the epidermis, traps moist air round the stomata which reduces water potential gradient therefore slowing transpiration down
• in hot or windy conditions marram grass plants roll their leaves, traps moist air slowing down transpiration. it also reduces exposed surface area for losing water and protects the stomata from wind
• thick waxy layer on the epidermis, reduces water loss by evaporation because the layer is waterproof

Question 13

how is cacti adapted to reduce water loss

Answer 13

• thick waxy layer on the epidermis, reduces water loss by evaporation because the layer is waterproof
  -cacti have spines instead of leaves, reduces surface area for water loss
• cacti close their stomata at the hottest times of the day when transpiration rates are the highest

Question 14

what are hydrophytes

Answer 14

plants such as water lilies, which live in aquatic habitats

Question 15

what do hydrophytes need adaptations for

Answer 15

• they don’t need adaptations for reducing water loss
• they need adaptations to help them cope with a low oxygen level

Question 16

what are the adaptation that hydrophytes have to cope with the low level of oxygen

Answer 16

• air spaces in tissue to help the plants float and can act as a store of oxygen for use in respiration, allows leaves the float on the surface of the water, increasing the amount of light they receive. the air spaces in the roots and stems allow oxygen to move from the floating leaves down to the parts of the plant that are underwater
  -stomata are usually only present only present on the upper surface of floating leaves. this maximises gas exchange]
• hydrophytes have flexible leaves and stems, these plants are supported by the water around them so they don’t need rigid stems for support. flexibility helps prevent damage