Acquisition Of Water And Minerals

Question 1

State the need of transportation system in plants

Answer 1

As land plants evolved and increased in number, competition for light, water and nutrients also increased.
As a result, the size and complexity of plant body increased.
Therefore the simple ways of transportation of water and material became inadequate leading to the evolution of vascular tissues, consisting of xylem and phloem to carryout long distance transport in plants.
e.g. the xylem transports water and minerals from roots to shoots.
the phloem transports products of photosynthesis from where they are made or stored to where they are needed.

Question 2

State 2 methods of water and solute transportation in plants with examples

Answer 2

Both active and passive transport mechanisms occur in plants

Active transport
 Passive transport
Examples 
• Diffusion
• Osmosis
• Imbibitions
• Facilitated diffusion
• Bulk flow

Question 3

State the difference between active transport and passive transport

Answer 3

Passive transport occurs spontaneously,
and it does not require metabolic energy (ATP). It occurs along the concentration or water potential gradient
Movement of some materials across membranes takes place using ATP and that process is called an active transport. These process occurs against concentration or water potential gradient

Question 4

State some examples for short distance transport and long distance transport

Answer 4

Short distance transport 
• Diffusion
• Osmosis
• Imbibitions
• Facilitated diffusion

Long distance transport
• Bulk flow

Question 5

State the reason for the diffusion in particles

Answer 5

Molecules have an energy called thermal energy, due to their constant motion. One result of this motion is diffusion.

Question 6

Define diffusion

Answer 6

In the absence of other forces, the movement of molecules of a substance from a place where it is more concentrated to place where it is less concentrated, due to random motion of molecules is called diffusion.

Question 7

Features of diffusion

Answer 7

Diffusion takes place according to a concentration gradient
spontaneously
Do not using metabolic energy (ATP).
Diffusion takes place across the membrane if the membrane is permeable to those molecules.
The motion of a molecule is random, but movement of a population of molecules by diffusion is directional.

Question 8

Examples for diffusion

Answer 8

Water and soluble materials can diffuse through the cellulose cell wall
O2 and CO2 can diffuse through the plasma membrane

Question 9

Define osmosis

Answer 9

Osmosis is a special type of diffusion. The diffusion of free water molecules across a selectively permeable membrane is called osmosis.

Question 10

Define Imbibition and give examples

Answer 10

The physical adsorption of water molecules by hydrophilic materials is called imbibition.

e.g. adsorption of water molecules by the cellulose cell walls.

Question 11

Define facilitated diffusion

Answer 11

Movement of water and hydrophilic solutes across the membranes passively with the help of transport protein that span the membrane is called facilitated diffusion.

Question 12

Define bulk flow

Answer 12

Bulk flow is the movement of liquid and the materials (entire solution) in response to pressure gradient.

Question 13

Features of bulk flow

Answer 13

Always the bulk flow transports materials from higher pressure to lower pressure region.
It is a long-distance transport method.
This flow does not occur through the membranes occurs at much greater speed than diffusion.
This method of transport is independent of solute concentration gradient.
It is passive transportation

Question 14

Examples for bulk flow

Answer 14

Transportation of water in the xylem

Question 15

Define water potential

Answer 15

The physical property that predicts the direction in which water will flow governed by solute concentration and applied pressure is called water potential.

Question 16

What are the special adaptations seen in the root tips for an efficient water absorption

Answer 16

epidermal cells are to water

and many are differentiated to root hairs.

Question 17

State how absorption of water occur in plants

Answer 17

The root hairs absorb the soil solution, which consists of water molecules and dissolved mineral ions that are not bound tightly to soil particles.
This absorption takes place across the plasma membrane.
Water can enter root hair by osmosis, a passive movement along the concentration gradient.

Question 18

State hoe minerals are absorbed in plants

Answer 18

Mineral ions are absorbed by the plant roots mainly from the soil solution.

But in the root hairs concentration of mineral ions is greater than that of soil solution.
K+ concentration in the root hair is hundreds of time greater than in the soil solution.
Therefore, mineral ions transport occurs against concentration gradient, by an active transport.

Question 19

Define radial transport

Answer 19

Transport of water and minerals entered from soil to root cortex into the xylem of the root is known as radial transport.

Question 20

State the Last check point for radial transportation

Answer 20

Endodermis

Question 21

State Three routes are used in the radial transport

Answer 21

1. apoplastic route
2. symplasticroute
3. transmembraneroute

Question 22

State the structures included in the apoplastic

Answer 22

The apoplastic route consists of everything external to the plasma membrane of living cells and includes cell walls, extracellular spaces and the interior of dead cells such as vessel elements and tracheids.

Question 23

Define apoplastic route

Answer 23

Water and solutes move along continuum of the cell walls and extracellular spaces and it is known as apoplastic route.

Question 24

How does the endodermis blocks the cortical apoplast from vascular apoplast and prevent direct entry of soil solution transported through the apoplastic route

Answer 24

Endodermis blocks apoplastic route by a barrier located in the transverse and radial walls of endodermal cells, called the casparian strips.
It is a belt made of suberin which is impervious to water and mineral salts. Thus water and minerals cannot cross the endodermis and enter the vascular cylinder via apoplast.
Therefore, water and minerals cross the selectively permeable plasma membrane before entering the vascular tissue and keep unneeded and toxic materials out.

Question 25

Uses of endodermis

Answer 25

Keep unneeded and toxic materials out of the vascular cylinder

The endodermis also prevents solutes that have accumulated in the xylem from leaking back into the soil solution.

Question 26

What does the symplastic route contain

Answer 26

The symplast consists of the entire mass of cytosol of all living cells in a plant, as well as plasmodesmata, the cytoplasmic channels that interconnect them.

Question 27

Define symplastic route

Answer 27

In the symplastic route, water and solutes move along the continuum of cytosol.

This route requires substance to cross a plasma membrane once, when they first enter the plant. After entering one cell, substances can move from cell to cell via plasmodesmata.

Question 28

Define the transmembrane route

Answer 28

The transmembrane route requires repeated crossing of plasma membranes as water and solutes exit one cell and enter the next.

Question 29

Process involved in Ascent of xylem sap according to cohesion tension hypothesis in a tall plant

Answer 29

To explain the process involved in the ascent of xylem sap, cohesion-tension hypothesis is put forward.
According to this hypothesis, transpiration provides pull for the ascent of xylem sap and cohesion of water molecules transmits this pull along the entire length of xylem from shoots to roots.

Hence xylem sap is normally under tension (negative pressure).
The negative pressure potential helps water to move up through xylem and water moves according to the water potential gradient.

Adhesion and cohesion facilitate transport water by bulk flow.
Due to high adhesion water molecules are attracted to cellulose molecules in the xylem walls.
Cohesion of water molecules is unusually high due to hydrogen bonds among water molecules.
Therefore, a continuous water column is formed within xylem vessels and tracheids.
Transpiration pull can extend down to the root only through an unbroken chain of water.

As water evaporates from the mesophyll cells, water potential of mesophyll reduces, and water moves from cells of petioles to the mesophyll cells.
It reduces the water potential of cells of petioles. then water pulls upward due to this transpiration pull.
The xylem sap is driven by difference in pressure potential.
Therefore, the water potential gradient within xylem is essentially a pressure gradient.

The tensile force on xylem sap is transmitted all the way from the leaves to the root tips and even into the soil.
Therefore, water potential gradient between the soil solution and atmosphere through the plant body also help ascent of xylem sap, against the gravity.
The plants do not need energy to lift the xylem sap.

Question 30

Mechanism of Phloem translocation

Answer 30

Sinks usually receive sugar from the nearest sugar sources. For each sieve tube, the direction of transport depends on the locations of the sugar source and sugar sink that are connected by that tube.
Therefore, neighbouring sieve tubes may carry sap in opposite directions if they originate and end in different locations.

The first step in translocation of sugar is to transport or load into sieve tube elements.
In some species, it moves from mesophyll cells to sieve tube elements via symplast, passing through plasmodesmata.
In many plants, sugar movements into phloem requires active transport because sucrose is more concentrated in sieve tube element and companion cells than mesophyll cells.

Sucrose is unloaded at the sink end of the sieve tube.
The process varies by species and organ. However, the concentration of free sugar in sink is always lower than in the sieve tube because the unloaded sugar is consumed during growth and metabolism of cells of sinks or converted to insoluble polymers such as starch.
As a result of concentration gradient, sugar molecules diffuse from phloem into the sink and water follows by osmosis.

Question 31

Phloem translocation of angiosperms according to the pressure flow hypothesis

Answer 31

1. Loading of sugar into the sieve tube reduces water potential inside the sieve tube elements at the source
2. This causes the sieve tube to take up water from the xylem by osmosis.
3. This uptake of water generates a positive pressure that forces the sap to flow along the tube
4. The pressure is reduced by unloading of sugar and consequent loss of water from phloem to the xylem at the sink