9: Transpiration

Question 1

Describe diffusion

Answer 1

The random movement of particles from an area of high concentration to an area of low concentration

Question 2

Describe osmosis

Answer 2

The movement of water from areas of high concentration to low concentration through a semi-permeable membrane

Question 3

How does osmosis relate to turgor pressure in plant cells?

Answer 3

Osmosis creates turgor pressure in plant cells

Question 4

Describe a flaccid cell

Answer 4

When the water pressure inside a cell vacuole is low the cell membrane does not push against the cell well

Question 5

Describe a turgid cell

Answer 5

When the water pressure inside a cell vacuole is high the cell membrane will push against the cell wall

Question 6

T or F: Plant cells contain up to 90% water and it is stored mostly in the vacuole

Answer 6

True

Question 7

Describe evapotranspiration

Answer 7

How water moves from the soil, through the plant, and into the air

Question 8

Which processes are involved in evapotranspiration?

Answer 8

Water vapour moves OUT of the plant through the open stomata by DIFFUSIONS

Water moves INTO the plant via the root tips by OSMOSIS

Question 9

T or F: a water molecule is non-polar?

Answer 9

FALSE. A water molecule is polar

Question 10

Describe cohesion

Answer 10

Water molecule to water molecule attraction

ex. Water molecules stick together to form a droplet

Question 11

Describe adhesion

Answer 11

Water molecules attracted to surfaces

ex. Water sticks to a leaf by adhesion

Question 12

Describe capillary flow

Answer 12

The movement of water against gravity

Question 13

T or F: Water movement by capillary action is limited

Answer 13

True

Question 14

How does capillary flow work in plants?

Answer 14

The xylem tracheids and vessels have very small diameters so cohesion and adhesion allow the water to move against gravity

Question 15

What process does water enter the roots of a plant?

Answer 15

Water enters the root hairs from the soil via OSMOSIS because there is more water in the soil than in the cytoplasm of a root hair (increasing osmotic pressure), forcing the water into the root

Water then moves from the epidermis and root hairs into the spaces between the cortex cells

Question 16

How does water move through plant cells?

Answer 16

• Movement of water from the soil into the root xylem is either through the interior of each cell or along the cell walls
• The endodermis has a filter (the Casparian strip of suberin) - if the endodermis cell walls are completely closed off with suberin, water will move into and through the endodermal cell first and then into the root vascular system
• Mesophyll cell walls are soaked with water at all times which makes the interior of the leaf almost 100% relative humidity
• Roots (osmosis into root hairs) → xylem (adhesion and cohesion) → leaf (evaporation from stomata)

Question 17

How does water move into leaves and evaporate?

Answer 17

1. Water moves up via the xylem in a continuous stream through the stem and into the petiole of a leaf
2. The water uses the veins of the leaf for distribution to all mesophyll cells
3. Water evaporates from the cell walls of the mesophyll cells to become vapour which then exits out the stomata

Question 18

What are two ways a plant can reduce excessive water loss?

Answer 18

1. Boundary Layer

2. Canopy layer

Question 19

What is the boundary layer and how does it aid in preventing excessive water loss?

Answer 19

A stagnant layer of air that surrounds each leaf to slow transpiration vapour movement away from the plant

Question 20

What is the canopy layer and how does it aid in preventing excessive water loss?

Answer 20

The air beneath a plant’s canopy (tallest leaves) that slows air movement down

Question 21

what are 4 environmental factors that affect the rate of water vapour exit (transpiration)?

Answer 21

1. Temperature
   - increased T = increase transpiration
2. Humidity
   - Increased humidity = decreased transpiration
3. Air movement
   - increased movement = increased transpiration
4. Leaf surface area
   - increased SA = increased transpiration

Question 22

What process does water vapour exit a plant?

Answer 22

Diffusion

Question 23

What triggers the stomata to open?

Answer 23

Light (daytime) when the water enters the guard cells to open the stoma

Question 24

What triggers the stomata to close?

Answer 24

• Darkness
• when water leaves the guard cells and closes the stoma
• extreme drought

Question 25

T or F: subtle changes in humidity, water availability, and/or temperature will affect the opening/closing of stomata

Answer 25

FALSE

Question 26

Which two salts are important in plant cells?

Answer 26

Potassium (K)
Chlorine (Cl)

to make KCl - Potassium Chloride

Question 27

How does salt attract water?

Answer 27

When a salt (or plant nutrient) is dissolved in water, K becomes positive, and Cl becomes negative, this will attract water because of H2Os polarity.

With the salt in it, the water contains less water than an equal volume of PURE water

Question 28

Describe plasmolysis

Answer 28

When the cell membrane and organelles have shrunk away from the cell wall. The cell will become flaccid and eventually, if it is not treated, plasmolysis will cause death.

Question 29

Describe the process of active transport of nutrients

Answer 29

Dissolved nutrients are pushed into the epidermal cells using energy (ATP) and will move up the transpiration stream to where they are needed

• the number and type of nutrients actively absorbed depends on the plant demand (more growth = more demand)

Question 30

Describe root pressure and when does it occur

Answer 30

This is caused when water enters the root (via osmosis) when the stomata is closed

• happens at night usually

Question 31

Describe guttation

Answer 31

When there is a loss of salted xylem water from the tips of leaves

You can see the droplets of water on the leaves

Question 32

When does guttation occur

Answer 32

• night time when stomata are closed
• in moist, warm, well fertilized soils
• when water and nutrients are plentiful in the xylem
• when there is high humidity and cool air around the leaves