lecture 5 Plant water requirement

Question 1

For every gram of organic matter produced, how much water is absorbed?

Answer 1

Water plays a critical role in the life of the plants. For every gram of organic matter produced by a plant, 500 g of water is absorbed by the roots and subsequently transpired through leaves.

Question 2

What happens if there is a slight imbalance in water flow?

Answer 2

A slight imbalance in water flow can cause water deficits and malfunctioning in cellular processes. Thus every plant must maintain balance in its uptake and loss of water

Question 3

What is important for nutrients uptake from soil?

Answer 3

The stream of water taken up by the roots is a step important for nutrients uptake from soil.

Question 4

What is the most limiting factor for agricultural productivity?

Answer 4

Of all the resources that plants need to grow and function, water is the most limiting factor for agricultural productivity.

Question 5

what does water availability limit?

Answer 5

Water availability limits the productivity of natural ecosystems. Therefore, a better understanding of the uptake and loss of water by plants is very important.

Question 6

The environmental condition when water deficits constraints agricultural production, is characterized as?

Answer 6

drought.

Question 7

What is the major difference between plant and animal cells that affects their relation with water?

Answer 7

is the existence of cell wall in plants.

Question 8

Cell wall allows plant cells to build up?

Answer 8

internal hydrostatic pressure, called turgor pressure which is essential for many physiological processes.

Question 9

The physiological processes include?

Answer 9

cell enlargement, gas exchange in the leaves, transport in the phloem, and across membranes.

Question 10

In growing plant tissues, water constitutes what % of mass?

Answer 10

water constitutes 80% - 95% of the mass.

Question 11

Many biochemical reactions of cell occur in the presence of?

Answer 11

water and it directly participates in many chemical processes.

Question 12

Why do plants evaporate water?

Answer 12

Plants continuously absorb and lose water. Plants evaporate water from the leaf to absorb CO2 needed for photosynthesis. Such water loss is called transpiration.

Question 13

What mechanisms are included in the transport of water from the soil to the plant body?

Answer 13

diffusion, bulk flow and osmosis.

Question 14

What happens in simple diffusion?

Answer 14

substances move down a concentration gradient

Question 15

What happens in pressure-driven bulk flow?

Answer 15

substances move down a pressure gradient

Question 16

What happens in osmosis?

Answer 16

both type of gradients influence transport.

Question 17

How is the direction and rate of water flow across a membrane dtermined?

Answer 17

not solely by the concentration gradient of water or by the pressure gradient, but by the sum of both driving forces.

Question 18

What are the major factors influencing the water potential in plants?

Answer 18

concentration, pressure, and gravity.

Question 19

What is strongly influenced by water potential and its components?

Answer 19

Cell growth, photosynthesis and crop productivity

Question 20

The plant water relations can be represented by a?

Answer 20

simple thermodynamic equation which relates to water potential.

Question 21

In which direction does water always move down its water potential gradient?

Answer 21

from areas of higher water potential to areas of lower water potential

Question 22

How is water potential typically measured?

Answer 22

Water potential is typically measured as the amount of pressure needed to stop the movement of water. The unit used to express this pressure is the megapascal (MPa).

Question 23

What happens when solutes are added to water?

Answer 23

the potential becomes negative

Question 24

What is main site for evaporative water loss (transpiration)?

Answer 24

Leaves are the main site of evaporative water loss (transpiration)

Question 25

Why do leaves show different degrees of structural adaptation?

Answer 25

to minimise water, loss, while allowing photosynthesis

Question 26

Adaptation can be extreme in?

Answer 26

hydrophytes and xerophytes

Question 27

A smaller range of features is shown in?

Answer 27

mesophytes

Question 28

What are hydrophytes?

Answer 28

aquatic plants (e.g. Water Lily)

Question 29

What are hygrophytes?

Answer 29

inhabit damp environments (e.g. ferns).

Question 30

What are Mesophytes?

Answer 30

go in well-aerated soils with good water availability but exposed to drying air (e.g. wheat)

Question 31

What are Xerophytes?

Answer 31

can tolerate dry conditions (e.g. Aloe)

Question 32

List the Abiotic or environmental stressess?

Answer 32

Water deficits or drought stress

Heat stress and heat shock

Chilling or freezing

Salinity stress

Nutrient deficiency

Heavy metal toxicity

Question 33

What is essential for yield stability and global food security?

Answer 33

The development of drought-tolerant and water use efficient crop varieties essential for yield stability and global food security

Question 34

What limits the efficiency of breeding drought tolerant plant types?

Answer 34

limited due to large scale seasonal variations in the magnitude of drought stress.

Question 35

What is essential to develop culivars suitable for water limited environments?

Answer 35

It is essential to identify underlying mechanisms related to drought tolerance in the breeding material aimed to develop cultivars suitable for water limited environments

Question 36

The ability of plants to endue drought can be characterized as?

Answer 36

drought escape, dehydration postponement and dehydration tolerance.

Question 37

Hygrophytes are found predominately in:

a) damp environments
b) aquatic environments
c) very dry conditions
d) drying environments but with access to soil water
e) none of these

Answer 37

a)damp environments

Question 38

Identify a physical property of water that is important to its role as the universal biological solvent:

a) high specific heat
b) low boiling point
c) minimum density at 4 degree
d) none of these

Answer 38

a)high specific heat

Question 39

What is the typical water content of a peanut seed (% of fresh weight)?

a) 94.3
b) 20.3
c) 50.6
d) 5.2
e) 0.3

Answer 39

d)5.2

Question 40

Which of the following properties is unique to water?

a) low specific heat
b) maximum density at 4 degrees Centigrade
c) low boiling point
d) poor solvent
e) none of these

Answer 40

b)maximum density at 4 degrees Centigrade

Question 41

Which of the following factors or changes causes an increase in transpiration:

a) decrease in radiation
b) increase in carbon dioxide
c) stomatal opening
d) reduction in wind speed
e) none of these

Answer 41

c)stomatal opening

Question 42

Identify the functional description that is most closely associated with the endodermis:

a) protects the plant from insect attack
b) controls water movement across the root
c) limits photosynthesis
d) facilitates penetration of the soil
e) none of these

Answer 42

b)controls water movement across the root

Question 43

Which of the following structures exerts a specific controlling influence over the movement of water through the

a) root hairs
b) root cortex
c) root endodermis
d) xylem vessels
ie) ntercellular spaces

Answer 43

c)root endodermis