Lecrure 11

Question 1

Why is water essential

Answer 1

• It carries nutrients in the soil to the roots
• Is the solvent for, and medium of, most biochemical reactions within plants
• Its loss from plants is an inevitable consequence of CO2 exchange with the atmosphere

Question 2

How do plants uptake nutrients

Answer 2

• Soil-water solution
• 98% obtained in soil-water solution
• 2% directly from soil

Question 3

How many bar at maximal water capacity

Answer 3

0 bar

Question 4

How many bar at field capacity

Answer 4

-0.33 bar

Question 5

How many bar at permanent wilting point

Answer 5

-15 bar

Question 6

What is water potential used to predict

Answer 6

which way water will move

Question 7

What is water potential measured in

Answer 7

units of pressure called megapascals (MPa)

Question 8

Potentials are a way to represent what

Answer 8

Free energy

Question 9

In terms of water potential what happens when a cell is placed in pure water

Answer 9

Water moves into the cell because the water potential of the cell is relatively negative

Question 10

In terms of water potential what happens when a cell is placed in a solution with different solute potential

Answer 10

water moves in the direction that eventually results in equilibrium – when both cell and solution have the same water potential

Question 11

Diffusion of water across a semi-permeable membrane is termed what

Answer 11

Osmosis

Question 12

If a plant cell is placed in a solution with high water potential (low osmotic
concentration) what will happen

Answer 12

-It will become swollen or turgid

Question 13

If a plant cell is placed in a solution with low water potential (high osmotic
concentration) what will happen

Answer 13

-It will exhibit shrinkage or plasmolysis

Question 14

Name the two ways water can enter plant roots

Answer 14

•Active Transport
•Passive Transport

Question 15

Write a short note on ACTIVE transport

Answer 15

•Water is absorbed due to activities going on in roots.
•Absorption of water occurs with the help of energy in the form of ATP. •Absorption takes place against concentration gradient - even when the concentration of cell sap is lower than that of soil water.

Question 16

Write a short note on PASSIVE transport

Answer 16

•Passive absorption is by osmosis. •Passive absorption takes place along the concentration gradient - when the concentration of cell sap is higher than that of soil water.
•Water is absorbed when transpiration rate is high or soil is dry.
•Due to high transpiration rate, water deficit is created in transpiring cells. •Rapid transpiration removes water and reduces turgor pressure in living cells of the root. The suction force developed is transmitted to root xylem. It pulls water from surrounding root cells to make up water deficit.

Question 17

Most of the water absorbed by plants comes in through what

Answer 17

The Root Hairs

Question 18

How is Root Hairs almost always turgid

Answer 18

their water potential is greater than that of soil

Question 19

What is required for ions to accumulate in root cells

Answer 19

•An expenditure of energy
•Once in the roots the ions are transported via the xylem throughout the plant

Question 20

How is surface area for water and mineral absorption further increased

Answer 20

•By Mycorrhizal Fungi
•Particularly helpful in PHOSPHORUS uptake

Question 21

Name the 3 transport routes that exist through cells

Answer 21

•Apoplast route
•Symplast route
•Transmembrane route

Question 22

Explain Apoplast route

Answer 22

Movement through the cell walls and the space between cells

Question 23

Explain Symplast route

Answer 23

A cytoplasm continuum between cells connected by plasmodesmata

Question 24

Explain Transmembrane route

Answer 24

Membrane transport between cells and across the membranes of vacuoles within cells

Question 25

What is Symplast and Transmembrane route summarised as since they are impossible to separate experimentally

Answer 25

Cell to cell component of transport

Question 26

Cortical cells have numerous interconnections via what two structures

Answer 26

•Cell walls
•Plasmodesmata

Question 27

What does the interconnections between cell wall and plasmodesmata in cortical cell link

Answer 27

The Protoplasm of each cells

Question 28

How can substances move in the cortical cell

Answer 28

•can move across the root, then, either via the cell walls (the apoplastic pathway) or via the cell contents (the symplastic pathway);
•these pathways are assumed to be important in the internal transport of water and nutrients.

Question 29

On their journey where do molecules reach

Answer 29

Endodermis

Question 30

Any further passage through the cells walls is blocked by what

Answer 30

The Casparian Strip

Question 31

What must molecules pass through of endless dermal cells to reach the xylem

Answer 31

must pass through the cell membranes and protoplasts of the endodermal cells

Question 32

Describe lateral transport of water in roots

Answer 32

•Uptake of soil solution by the hydrophilic walls of root hairs provides access to the apoplast. Water and minerals can then soak into the cortex along this matrix of walls.
•Minerals and water that cross the plasma membranes of root hairs enter the symplast.
•As soil solution moves along the apoplast, some water and minerals are transported into the protoplasts of cells of the epidermis and cortex and then move inward via the symplast.
•Within the transverse and radial walls of each endodermal cell is the Casparian strip, a belt of waxy material (purple band) that blocks the
passage of water and dissolved minerals.
•Only minerals already in the symplast or entering that pathway by crossing the plasma membrane of an endodermal cell can detour around the Casparian strip and pass into the vascular cylinder.

Question 33

What are Aquaporins

Answer 33

water channels that exist in vacuole and cell membranes

Question 34

What do Aquaporins speed up

Answer 34

speed up osmosis, without changing the direction of water movement

Question 35

Explain water movement in plant from root to stomata

Answer 35

Water first enters the roots and then moves to the xylem, the innermost vascular tissue. Water rises through the xylem because of a combination of factors.

Question 36

Name the two types of water movement for root to stomata

Answer 36

•Short-distance movement
•Long -distance movement

Question 37

Describe short-distance movement for water movement from roots to stomata

Answer 37

•Movement of water at the cellular level plays a major role in bulk water
transport.
•Water can diffuse through cell membranes.

Question 38

Describe long-distance movement for water movement from roots to stomata

Answer 38

•Water movement in most of the vascular plants from roots to leaves. •Sometimes more than 100 m

Question 39

Water moves from the soil into the roots only if the soil’s what is greater

Answer 39

Water Potential

Question 40

After water moves from soil into the roots what happens then

Answer 40

then moves along gradients of successively more negative water potentials in the stems, leaves and air

Question 41

Evaporation of water in a leaf creates what in the xylem

Answer 41

Negative pressure or tension

Question 42

What is the driving force for transpiration

Answer 42

the gradient in vapor pressure

Question 43

Name the 3 main forces of water movement through the xylem

Answer 43

• Transpiration Pull
• Cohesion Adhesion Forces (Cohesive Tension Theory)
• Root Pressure

Question 44

Explain transpiration pull

Answer 44

•It is the pulling force responsible for lifting the water column.
•As water is lost in form of water vapour to atmosphere from the mesophyll cells by transpiration,
•a negative hydrostatic pressure is created in the mesophyll cells which in turn draws water from veins of the leaves.

Question 45

What happens to the negative tension created during transpiration pull

Answer 45

•negative tension is then gradually transmitted downwards via xylem tissues of the leaf, stem and finally to the roots.
•As a result there is a continuous upward movement of water column in the plant.

Question 46

Explain cohesion adhesion forces (cohesive tension theory)

Answer 46

•The water molecules in the chain are held together by hydrogen bonds
which exist between neighboring water molecules. (cohesion)
•The chain of molecules is prevented from being pulled down because each water molecule in the chain is attracted to the walls of the xylem by hydrophilic attraction between water and the cellulose in the cell walls. (Adhesion)
•The water column which is held together by cohesion and prevented from lowering by adhesion is pulled up by the tension generated from above by transpiration.

Question 47

Explain root perssure

Answer 47

•Root pressure is caused by active transport of mineral nutrient ions into the root xylem.
•Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. •Water then diffuses from the soil into the root xylem due to osmosis.
•Root pressure is caused by this accumulation of water in the xylem pushing on the rigid cells.
•Root pressure provides a force, which pushes water up the stem, but it is not enough to account for the movement of water to leaves at the top of the tallest trees.

Question 48

Name the physical soil factors that affect water absorption in plants

Answer 48

Soil water contents Soil temperature Soil aeration Flooding
Texture and structure Speed of water movement Effective root zone

Question 49

Name the atmospheric factors that affect water absorption in plants

Answer 49

Temperature
Relative humidity
Vapour pressure deficit (VDP) Wind speed

Question 50

Name the biological factors that affect water absorption in plants

Answer 50

Plant species
Root length Root system Plant health
Biological stresses
Tolerance to stresses (Drought/Salinity) Plant genotype and phenotype
Growth rate
Plant hormones