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Chapter 1

Transport in Plants

Class 8 - Concise Biology Selina


Multiple Choice Questions

Question 1

Diffusion occurs when molecules move:

  1. from lower concentration to higher concentration.
  2. from higher concentration to lower concentration through a membrane.
  3. from higher concentration to lower concentration.
  4. when energy is used.

Answer

from higher concentration to lower concentration.

Reason — The movement of molecules (gas, liquid or solid) from higher concentration to lower concentration is called diffusion.

Question 2

Ascent of sap in plants takes place through.

  1. Cortex
  2. Epidermis
  3. Xylem
  4. Phloem

Answer

Xylem

Reason — Xylem the vascular tissue is responsible for the transport of water and minerals.

Question 3

If the xylem vessels of a plant are plugged:

  1. The leaves will turn yellow
  2. No food will be made
  3. The plant will wilt (shrivel)
  4. The plant will continue to grow

Answer

The plant will wilt (shrivel)

Reason — The xylem vessel of the plant is responsible for the conduction of the water and mineral salt in the plant body. So if the xylem vessels of the plant are plugged then the conduction of water will be stopped and then the plant will wilt.

Question 4

Force responsible for the ascent of sap is:

  1. Capillary force
  2. Root pressure
  3. Transpirational pull
  4. All the three

Answer

All the three

Reason — Ascent of sap takes place through xylem. Forces like capillary force, root pressure, transpirational pull helps in this unidirectional movement of water.

Question 5

Raisins swell when put in:

  1. Rain water
  2. Saline water
  3. Mustard oil
  4. Saturated sugar solution

Answer

Rain water

Reason — When raisins are placed in rain water, they absorb water through Osmosis as rain water serves as a dilute solution in comparison to the contents of raisins. In case of saline water and saturated sugar solution, they are more concentrated than the raisins hence Osmosis doesn't take place. As Mustard oil is not water, so it is not absorbed by the raisins.

Question 6

The root hairs are suited for absorbing water from the soil because:

  1. They have a large surface area
  2. They have a semi-permeable membrane
  3. They contain a solution of higher concentration than the surrounding water.
  4. All the three.

Answer

All the three

Reason — Root hairs are long and thin so they can penetrate between soil particles and they have a large surface area for absorption of water which in return, increases the speed at which water and nutrients can be absorbed. The cell sap in the root hair cell is said to be of a high concentration as it contains more solutes compared to the surrounding soil water. This promotes water absorption.

Question 7

Transpiration is defined as:

  1. the rise of water up to the stem of a plant.
  2. the elimination of water with dissolved water products.
  3. the loss of water as water vapour from the aerial parts of a plant.
  4. the loss of water as water vapour from the roots as well as the leaves of the plant.

Answer

the loss of water as water vapour from the aerial parts of a plant.

Reason — Transpiration is the loss of water in the form of water vapour from the aerial parts of a plant.

Question 8

Which one of the following favours the fastest transpiration rate?

  1. A cool, humid, windy day,
  2. A hot, humid, windy day,
  3. A hot, humid, still day,
  4. A hot, dry, windy day.

Answer

A hot, dry, windy day.

Reason — Transpiration is mainly affected by the temperature, humidity, and wind speed. On a hot, dry, windy day transpiration increases.

Short Answer Questions

Question 1

An experiment was set up as shown in the figure below. After some time, the water level in test tube A fell down but not in test tube B.

An experiment was set up as shown in the figure below. After some time, the water level in test tube A fell down but not in test tube B. Why was there a fall in the water level of test tube A and not in that of test-tube B? Transport in Plants, Concise Biology Solutions ICSE Class 8.

Why was there a fall in the water level of test tube A and not in that of test-tube B?

Answer

Test tube A contains plant, therefore, the water level in test tube A falls because the water is absorbed by the plant through the roots dipped in the water. Since the test tube contains oil, no water loss occurred due to evaporation because oil prevents water molecules from evaporating. In test-tube B the water level remains the same because there is no plant present as well as oil refrains the water to evaporate.

Question 2

How are roots useful to the plants? Give any two points.

Answer

Roots are useful to the plants in the following ways:

  1. Roots absorb water and minerals from the soil.
  2. Roots fix the plant firmly in the ground.

Question 3

What do xylem vessels carry?

Answer

Xylem vessels carry water and mineral salts from the roots to the aerial parts of the plant.

Question 4

Name the plant tissue which helps in carrying the food to different parts of a plant.

Answer

Phloem carries the food to different parts of the plant.

Question 5

Define the terms:

(a) semi-permeable membrane

(b) osmosis

Answer

(a) Semi-permeable membrane — A semi-permeable membrane is a membrane which allows the passage of molecules selectively. It allows a solvent such as water molecules to pass through it freely but prevents the passage of the solute (sugar or salt molecules in solution).

(b) Osmosis — Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi permeable membrane.

Question 6

Under what conditions do plant transpire (a) more quickly and (b) most slowly?

Answer

(a) Plants transpire more quickly on hot, dry, windy days as Sunlight, higher temperatures, fast winds and low humidity increase the rate of transpiration.

(b) Transpiration is most slow on cool, humid, still days as lower temperatures, still winds and high humidity decrease the rate of transpiration.

Question 7

Given alongside is an enlarged diagram of a part of the root. Draw arrows on the diagram to show the movement of water passing through different parts.

Given alongside is an enlarged diagram of a part of the root. Draw arrows on the diagram to show the movement of water passing through different parts. Transport in Plants, Concise Biology Solutions ICSE Class 8.

Answer

Movement of water passing through different parts of the root is shown with arrows in the below diagram:

Movement of water passing through different parts of the root shown with arrows. Transport in Plants, Concise Biology Solutions ICSE Class 8.

Question 8

Why is the structure of a root hair considered suitable for absorbing water from the soil?

Answer

The root hair is suitable for absorbing water from the soil in the following three ways:

  1. The numerous root hairs provide a large surface area. More the surface area, greater is the absorption.
  2. Root hairs contain cell sap which is of a higher concentration than the surrounding soil water.
  3. The cell wall is freely permeable, i.e., permits movements of all types of substances. But the cell membrane is semi-permeable. It allows only some substances to pass through it.

Question 9

Briefly explain, how transpiration helps in the upward conduction of water in plants?

Answer

As a result of transpiration, a suction force is created in the xylem vessel. This force causes the water to be pulled up from the xylem in the roots to the stem and then to the leaves. This pulling force is called transpirational pull.

Question 10

How does temperature, light intensity and wind affect transpiration?

Answer

  1. Temperature — Higher temperatures increase the rate of transpiration due to faster evaporation of water.
  2. Light intensity — With Sunlight the rate of transpiration is faster as stomata are open to allow inward diffusion of carbon dioxide for photosynthesis. During night time, the stomata remain closed and hence transpiration hardly occurs.
  3. Wind — Transpiration is more when the wind is blowing faster as water vapour moves away faster from the surface of leaves.

Question 11

The set up shown alongside was kept in sunlight for an hour. It was observed that drops of water appeared on the inside surface of the polythene bag.

The set up shown alongside was kept in sunlight for an hour. It was observed that drops of water appeared on the inside surface of the polythene bag. Name the process which is being demonstrated. Why was the pot with its soil left uncovered by the polythene bag? Why was the pot left in sunlight? Suppose that the pot in this experiment was placed inside a dark room instead of placing it in sunlight for some time. What difference would be noticed? Transport in Plants, Concise Biology Solutions ICSE Class 8.

(a) Name the process which is being demonstrated.

(b) Why was the pot with its soil left uncovered by the polythene bag?

(c) Why was the pot left in sunlight?

(d) Suppose that the pot in this experiment was placed inside a dark room instead of placing it in sunlight for some time. What difference would be noticed?

Answer

(a) Transpiration is being demonstrated here.

(b) The pot and its soil were left uncovered by the polythene bag because in the experiment we need to observe the loss of water occurred by plants. If the pot is covered, the water from the soil may also get evaporated and we will not get accurate results.

(c) In sunlight, the rate of transpiration is faster as the stomata are open to allow inward diffusion of carbon dioxide for photosynthesis. Hence, the plant was left in sunlight.

(d) If the pot was placed inside a dark room, transpiration will hardly occur as the stomata of the plant are closed. Hence, negligible water droplets will get condensed on the inner side of polythene bag.

Question 12

State whether the following statements are True or False. Rewrite the false statements correctly.

(a) Water absorption mainly occurs through the root-hair.

(b) Water enters the root-hair by osmosis.

(c) Water absorbed by the roots reaches the leaves and is used in producing food for the entire plant.

(d) A semi-permeable membrane allows larger molecules to pass through but prevents the smaller ones.

(e) Transpiration is the loss of water from the roots of the plant.

(f) Transpiration cools the plant when it is hot outside.

Answer

(a) True

(b) True

(c) True

(d) False
Corrected statement — A semi-permeable membrane allows smaller molecules to pass through but prevents the larger ones.

(e) False
Corrected statement — Transpiration is the loss of water from the aerial parts of the plant.

(f) True

Question 13

Fill in the blanks with suitable terms given below: (fast, leaves, conducting, ascent, humid)

(i) Transportation in plants is carried out by a ............... system.

(ii) The upward movement of sap that contains water and minerals is called ............... of the sap.

(iii) Transpiration is more when the wind is blowing ...............

(iv) Most water gets evaporated from the plant from its ...............

(v) Transpiration is reduced if the air is ...............

Answer

(i) Transportation in plants is carried out by a conducting system.

(ii) The upward movement of sap that contains water and minerals is called ascent of the sap.

(iii) Transpiration is more when the wind is blowing fast.

(iv) Most water gets evaporated from the plant from its leaves.

(v) Transpiration is reduced if the air is humid.

Long Answer Questions

Question 1

Draw a magnified view of the root-hair, and describe how it helps in the absorption of water from the soil?

Answer

Given below is the magnified view of a root-hair. It is a long protuberance of an epidermal cell of the root. This cell contains a fluid sap which is more concentrated than the surrounding soil water. It has a outer cell wall and an inner cell membrane. Cell wall is freely permeable whereas cell membrane is semi-permeable. The cell membrane allows the water molecules to pass through it but prevents the other larger molecules. So, the water from the soil passes into the root hairs by Osmosis.

Draw a magnified view of the root-hair, and describe how it helps in the absorption of water from the soil? Transport in Plants, Concise Biology Solutions ICSE Class 8.

Question 2

How does transpiration help the roots absorb water and minerals from the soil?

Answer

As a result of transpiration, a suction force is created in the xylem vessel. This force causes the water to be pulled up from the xylem in the roots to the stem and then to the leaves. This pulling force is called transpirational pull. Xylem tissues are in the form of capillary tubes. Whenever the xylem vessels lie empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force. As more water and minerals are drawn upwards through the stem, this causes the roots to absorb more water and minerals from the soil.

Question 3

Define the three processes by which plants absorb water and minerals from the soil.

Answer

The three processes by which plants absorb water and minerals from the soil are:

  1. Osmosis — Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi permeable membrane.
  2. Diffusion — The movement of molecules (gas, liquid or solid) from higher concentration to lower concentration is called diffusion.
  3. Active transport — The movement of molecules from their lower concentration to a higher concentration by using energy is called Active transport.

Question 4

How the water absorbed by the roots is important for the plants?

Answer

The water absorbed by the roots is important for the plant in the following three ways:

  1. Transportation — The water in the plant body, both in xylem and phloem, transports substances in a solution form from one part to another.
  2. Food production — Water is required for photosynthesis. It combines with carbon dioxide from the air in the presence of sunlight and chlorophyll to produce glucose and oxygen.
  3. Cooling — The heat utilized when water is transpired from the surface of leaves in the form of water vapour induces a cooling effect.

Question 5

Name the factors that affect the rate of transpiration. State their role in each case.

Answer

The following main factors affect the rate of transpiration —

  1. Sunlight — During daytime, the rate of transpiration is faster. This is because the stomata remain open to allow the inward diffusion of carbon dioxide for photosynthesis. During night time, the stomata are closed, and hence transpiration hardly occurs.
  2. Temperature — Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises.
  3. Humidity — Transpiration is reduced if the air is humid. Air cannot hold any water molecules when it is already laden with moisture (humidity).
  4. Wind — Transpiration is more when the wind is blowing faster as water vapour moves away faster from the surface of leaves.

Question 6

Mention the two ways in which transpiration helps the plants.

Answer

Transpiration helps the plants in the following two ways —

  1. Cooling the plant — The heat utilized when water is transpired from the surface of leaves in the form of water vapour induces a cooling effect.
  2. Transpiration helps in maintaining the concentration of the sap inside the plant body — The roots continue to absorb water from the soil. If excess water is not evaporated out, the sap would then become dilute, preventing further absorption of water along with the minerals required by the plant.

Question 7

Describe an experiment to show that the plant loses water through its leaves.

Answer

Take a small-sized, well-watered potted plant with a few branches. Place a polythene bag over its one branch as shown in (A) and tie it with a rubber band.
Remove all the leaves from another branch (B) of the same plant, cover this too with a polythene bag and tie it with a rubber band.
Place the plant in sunlight, and observe it after 4-6 hours. We will notice that tiny water droplets have appeared on the inner surface of the polythene bag over branch A, while no water drops appear on branch B.
Conclusion — This experiment proves that plant loses water through its leaves.

Describe an experiment to show that the plant loses water through its leaves. Transport in Plants, Concise Biology Solutions ICSE Class 8.

Question 8

Name any three minerals whose deficiency causes diseases in plants. Give the symptoms of each deficiency.

Answer

The table below lists the three minerals along with the symptoms of deficiency of each:

MineralMajor Deficiency Symptoms
Nitrogen (N)Yellowing of leaves, wrinkling of cereal grains.
Phosphorus (P)Purple and red spots on leaves, delay in seed germination.
Potassium (K)Poor growth with reduced rate of transpiration.

Question 9

List out the differences between xylem and phloem.

Answer

Differences between xylem and phloem are:

XylemPhloem
Conducts water and mineral salts from the roots to the aerial parts of the plant.Translocates food from the leaves to the storage organs and growing parts of the plant.
Made up of tracheids, vessels, xylem parenchyma and xylem fibres.Made up of sieve tubes, companion cells, phloem parenchyma and phloem fibres.
Conducting cells (vessels and tracheids) are dead.Conducting cells (sieve tubes) are living.
Conduction is unidirectional.Conduction is bidirectional.
Conduction does not require any expenditure of energy.Conduction requires expenditure of energy.
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