unit 3, transpiration, cohesion and tension

Question 1

what is transpiration and where does it occur?

Answer 1

• the loss of water vapur from the stomata by evaporation
• occurs at the leaf due to the stomata being on the leaf

Question 2

what are the 4 conditions that effect transpiration?

Answer 2

-light intenstiy
-temperature
- humidity
-wind

Question 3

how does light intenstiy effect transpiration?

Answer 3

• positive correlation
  -more light means the stomata are open wider
• larger sufrace area for evaporation

Question 4

how does temperature effect transpiration?

Answer 4

• positive correlation
• more kinetic energy so more molecules moving
  -more evaporation

Question 5

how does humidity effect transpiration?

Answer 5

• negative correlation
  -more water vapour in the air compared to the leaf, so water potential more positive outside
• reducing water potential gradient

Question 6

how does wind effect transpiration?

Answer 6

• positive correlation
• more wind to blow away humidity
  -maintaining water potential gradient

Question 7

how does water move up the xylem, against gravity?

Answer 7

by: cohesion , adhesion and root pressure

Question 8

what is cohesion?

Answer 8

• water molecules sticking together
  -like molecules bonded together

Question 9

how does cohesion happen?

Answer 9

• due to water being dipolar, o2- and h+, so hydrogen bonds form between water molecules and stick together

Question 10

how does water move in the xylem?

Answer 10

a singular continuous column

Question 11

what is adhesion?

Answer 11

-when water sticks to the walls of the xylem
- molecules sticking to unlike molecules

Question 12

when is there bigger adhesion?

Answer 12

when the xylem is narrower

Question 13

what is root pressure?

Answer 13

• water moves into the root by osmosis increasing the volume of liquid inside the root
• pressure increases in root
• this forces water upwards

Question 14

what is capilarity?

Answer 14

upward motion against gravity

Question 15

what increases capilarity?

Answer 15

when the xylem is narrower

Question 16

what are features of the root hair cell?

Answer 16

• large surface area for maximal uptake of water
• creates a water potential gradient
• lots of mitochondira for active transport of minerals

Question 17

what are the features of the xylem?

Answer 17

-elongated dead cells that are impermeable to water
-lignin strengthened walls that are waterproof
-dead cells, no cytoplasm or membrane make the transpiration more efficient
-continous tube no end plates

Question 18

why is the strenghtneing of the xylem in spirals?

Answer 18

• to make the plant flexible so it doesnt snap
  -less lignin which reduces the mass of the plant
  -elongated

Question 19

what do thick lignin walls prevent?

Answer 19

the xylem walls collapsing

Question 20

describe the cohesion tension theory of water transport in the xylem

Answer 20

• water evaporates through leaf, creating a lower water potential in the mesophyll
• water is pulled up by cohesion, the water is a long continuous column due to the hydrogen bonds making them stick together
• there is adhesion of water to the walls of the xylem
• water is taken up through the roots

Question 21

Explain how xylem tissue is adapted for its function

Answer 21

-long cells / tubes with no end walls;
continuous water columns;
-no cytoplasm / no organelles / named, made of dead cells
to impede / obstruct flow / allows easier water flow;
-thickening / lignin;
support / withstand tension / waterproof / keeps water in cells;
-pits in walls;
allow lateral movement / get round blocked vessels;

Question 22

Describe and explain the effects of increasing light intensity on the tension in xylem vessels in leaves.

Answer 22

As light intensity is increased, tension in the xylem becomes greater.
> This causes the stomata to open more and increases the cohesion
> which increases the rate of transpiration
> Therefore the water potential of leaf cells become lower
> and more water moves out from xylem to surrounding cells down the water potential gradient.