Effect of Environmental Conditions on Transpiration

Question 1

Temperature

Answer 1

Hot day- water evaporates quickly from the leaves of a plant as water molecules have more energy.
Therefore transpiration will increase.

Question 2

Humidity

Answer 2

Very humid air contains lots of water vapour-Smaller concentration gradient, so slower transpiration.
Dry air, no water vapour so diffusion from leaf to atmosphere will be very fast
Therefore, transpiration increases as humidity decreases.

Question 3

Wind speed

Answer 3

Windy day (moving air), water vapour is blown away as fast as it is diffused out so increased transpiration.
Still air, region around a leaf will become saturated with water vapour very quickly, so transpiration slows down.
Therefore Transpiration increases as wind speed increases.

Question 4

Light intensity

Answer 4

Light does NOT directly affect the evaporation
Daylight- stomata are more open to supply carbon dioxide for photosynthesis
This allows for more water to diffuse out of leaf into atmosphere

Question 5

Function of a root hair

Answer 5

To absorb water and minerals from the soil

Question 6

How do mineral ions enter the root hair cells?

Answer 6

Active transport

Question 7

How does water from the soil enter the root hair cells?

Answer 7

Osmosis

Question 8

Define osmosis

Answer 8

the net diffusion of free water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane.

Question 9

Stomata

Answer 9

Holes on the (mostly bottom) surface of the leaf
Two guard cells on either side (which can open and close)

Question 10

Xylem

Answer 10

transports water and mineral ions from roots to leaves
Cell wall contains lignin (waterproofing)
Made up of thick walled dead cells which contain no cytoplasm

Question 11

Nitrate ions

Answer 11

Required to make amino acids and proteins

Question 12

Magnesium ions

Answer 12

Required to make chlorophyll

Question 13

Phloem

Answer 13

Transports sucrose and amino acids from leaves to growing points and storage areas
Moving these around requires energy. Process- translocation
Consists of living cells arranged end to end (cell walls made of cellulose)

Question 14

Potometer

Answer 14

device used to estimate transpiration rates

Question 15

Measuring the rate of transpiration (using a potometer)

Answer 15

1.Potometer must be set up under water to prevent any air bubbles from entering system and blocking system
2.Cut the stem of a shoot
3. Put the shoot stem into a bung and grease joint with petroleum jelly to prevent water loss and air entry
4.Place bung into potometer
5.Make sure tap is closed and it is full of water. Then lift the potometer out of the water
6.Leave the end of the capillary tube out of the water until an air bubble forms then put the end into a beaker of water
7. transpiration rate: distance the bubble travels in five minutes
8. Take at least 3 readings and calculate a mean transpiration rate.

Question 16

Describe a practical for investigating the factors determining the rate of transpiration from a leafy shoot

Answer 16

Independent: varying the environmental conditions around the plant stem (wind speed, humidity, temperature, light intensity)
Dependent: Measure the distance bubble moves in 5 minutes
Set up a potometer
Wind Speed-Use a hair dryer to simulate a windy day
Light intensity-put the light in a dark room for 24 hours and then take readings whilst it is in the dark room
Humidity-cover the plant with a clear plastic bag so humidity increases
Also do a control to compare the data sets against normal conditions
Repeat each experiment at least 3 times, remove anomalies and then take an average