transpiration

Question 1

what is transpiration

Answer 1

the evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from the plant leaves, through the stomata

Question 2

transpiration stream:

Answer 2

• the loss of water from the mesophyll cells sets up a water potential gradient
• this ‘draws’ water by osmosis from the surrounding mesophyll cells
• xylem vessels supply mesophyll tissues with water
• water enters root hair cell via osmosis

Question 3

functions of the transpiration stream

Answer 3

• transporting mineral ions
• providing water to keep cells turgid to support the plant
• providing water to leaf cells for photosynthesis
• keep the leaves cool by evaporation
• providing water for the cytoplasm

Question 4

what is the function of root hair cells?

Answer 4

absorb minerals and water from the soil

Question 5

why do root hair cells contain no chloroplasts?

Answer 5

no photosynthesis is needed

Question 6

why do root hair cells have a semi-permeable membrane

Answer 6

it will allow water and mineral ions into the cell

Question 7

what’s the ‘finger-like’ projection for

Answer 7

increases surface area for absorption of water and mineral ions

Question 8

list and explain 4 adaptations of root hair cells:

Answer 8

• finger-like extensions
  -> increases SA:vol
  -> to absorb water + mineral salts at a faster rate
• low water potential/concentration
  -> allows osmosis and diffusion of nitrates to take place
• large vacuole
  -> to absorb as much water as it can hold
• is a living cell
  -> carries out respiration
  -> this provides energy for active transport to take place when the concentration gradient is reversed

Question 9

role of roots in transpiration:

Answer 9

• water moves into the root hair cells by osmosis
  -> high to low water potential
  -> root hair cells have a large surface area to maximise water absorption
  -> thin walls, decreases the distance of the pathway
• water moves into the root cortex cells by osmosis
• water then moves into the xylem by osmosis

Question 10

how do the transpiration stream help keep the water potential low?

Answer 10

the water is constantly moving from the root hair cells to the xylem. also, the high concentration of solute keeps the water potential low in the cell

Question 11

why do plants need a transport system

Answer 11

to move nutrients and water within the plant

Question 12

what does the xylem transport

Answer 12

water and dissolved minerals from the roots to other parts of the plant

Question 13

what does the phloem transport

Answer 13

sucrose and amino acids between the leaves and other parts of the plant

Question 14

the xylem contains……..

Answer 14

dead cells arranged end-to-end forming continuous vessels

Question 15

what does the xylem begin life as?

Answer 15

living cells

Question 16

as the xylem cells develop:

Answer 16

• become elongated
• original cell walls become impregnated with lignin (made by the cytoplasm)

Question 17

what happens when xylem cells mature?

Answer 17

they contain no cytoplasm - instead they have a hollow central space (lumen) for water to pass through

Question 18

what does the xylem transport and where does it transport it to?

Answer 18

• water and mineral salts
• from the roots up the shoot to the leaves in the transpiration stream

Question 19

what are two roles of lignin?

Answer 19

• to transport liquids throughout the plant
• reinforces the cell walls and keeps them from collapsing

Question 20

what is adhesion of water molecules

Answer 20

attraction to the cell wall

Question 21

what is cohesion of water molecules

Answer 21

attraction to each other

Question 22

what is a potometer

Answer 22

a simple piece of apparatus, which measures the rate of transpiration or the rate of water uptake by the plant

Question 23

potometer practical method:

Answer 23

1. apparatus is placed in sink of water
2. cut stem of plant underwater
3. stem is pushed into rubber tubing under water to stop any air entering
4. vaseline is used to seal any joints
5. if the water moves quickly, faster rate of transpiration

Question 24

does high temp increase or decrease rate of transpiration and why

Answer 24

• increase
• increased kinetic energy of water molecules -> molecules move faster
• evaporation/diffusion faster

Question 25

does high humidity increase or decrease rate of transpiration and why

Answer 25

- decrease - air around plant is already saturated with water - decrease gradient

Question 26

does high light intensity increase or decrease rate of transpiration and why

Answer 26

- increase - stomata open to all carbon dioxide to enter for photosynthesis

Question 27

does wind speed increase or decrease rate of transpiration and why

Answer 27

- increase - removes water vapour from leaf