Selina Concise Class 8 Biology Solution Chapter No. 1- ‘Transport In Plants’ For ICSE Board Students.
Multiple Choice questions:
1.) Put a tick mark against the correct alternative in the following statements:
a) Diffusion occurs when molecules move
i) from lower concentration to higher concentration.
ii) from higher concentration to lower concentration through a membrane.
iii) from higher concentration to lower concentration.
iv) when energy is used.
Ans. iii)
Explanation: The movement of molecules – gas, liquid or solid from higher concentration to lower concentration is called diffusion.
2.) Ascent of sap in plants takes place through
i) cortex
ii) Epidermis
iii) Xylem
iv) Phloem
Ans. iii)
Explanation: As in plants water is transported to the entire plant through xylem and Ascent of sap is the movement of minerals and water.
3.) If the xylem vessels of a plant are plugged:
i) The leaves will turn yellow
ii) No food will be made
iii) The plant will wilt(shrivel)
iv) The plant will continue to grow
Ans. iii)
Explanation: As xylem conducts water throughout the plants, and of the xylem vessels are plugged enough water would not be reached to the entire plant and the plant would wilt.
4.) Force responsible for the ascent of sap is:
i) Capillary force
ii) Root pressure
iii) Transpirational pull
iv) All the three
Ans. iv)
Explanation: All the three are responsible for ascent of sap as the sap has to travel throughout the plant.
5.) Raisins swell when put in:
i) Rain water
ii) Tap water
iii) Mustard oil
iv) Saturated sugar solution
Ans. i)
Explanation: Raisins swell in rain water due to endosmosis.
6.) The root hairs are suited for absorbing water from the soil because
i) They have a larger surface area
ii) They have a semi permeable membrane
iii) They contain a solution of higher concentration than the surrounding water.
iv) All the three
Ans. iv)
Explanation: The root hairs are suited for absorbing water as they have larger surface area, semi permeable membrane and contain a solution of higher concentration.
7) Transpiration is defined as:
i) the rise of water upto to the stem of a plant.
ii) the elimination of water with dissolved water products.
iii) the loss of water as water vapour from the aerial parts of a plant.
iv) the loss water as water vapour from the roots as well as the leaves of the plant.
Ans. iii)
Explanation: Transpiration is the loss of water in the form of water vapour from the aerial parts of the plant.
8) Which one of the following favours the fastest transpiration rate?
i) A cool, humid, windy dat\y
ii) A hot, humid, windy day
iii) A hot, humid, still day
iv) A hot, dry, windy day
Ans. iv)
Explanation: Transpiration is fastest on a hot, dry and windy day as sunlight, wind, temperature and humidity affect the rate of transpiration.
Short Answer Questions:
1.) An experiment was set up as shown in the figure below. After sometime, 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 nad not in that of test – tube B?
Ans. The water level in the test tube A falls down but not not in test tube B as test tube A has a rooted plant. Roots of the plant absorb the water as its function and hence the water level falls down. Due to the layer of oil on the surface of water in test tube B, the water level does not fall as there is no rooted plant in it. The major reason for no fall in the level of water is that the water didn’t even evaporate due to layer of oil.
2) How are the roots useful to plants? Give two points.
Ans. The roots are useful to plants in the following ways:
a) They absorb water and important minerals from the soil and help in transportation of it to the entire plant.
b) Roots anchor the plant to the soil firmly thus preventing soil erosion.
3) What do xylem vessels carry?
Ans. Xylem vessels carry water and minerals which are absorbed by the roots from the soil to the stem and leaves of the entire plant.
4) Name the plant tissue that helps in carrying the food to different parts.
Ans. Phloem carries the food to different parts of the plant.
5) Define the terms:
a) Semi- permeable: It a membrane that allows the passage of only solvent moleucles for example water molecules and prevents the entry of larger moleucles.
b) Osmosis: The movement of molecules from a dilute solution to a concentrated solution across a semi- permeable membrane is known as osmosis.
6) Under what conditions do plants transpire a) more quickly and b) most slowly?
Ans. a) Transpiration is faster when temperature is high, during daytime and when the wind is blowing faster.
b) Transpiration is reduced when air is humid. Air cannot hold any water molecules when it is already laden with moisture.( humidity)
7) Given here 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.
Ans. The water passes through the root hair to the xylem vessels.
8) Why is the structure of root hair considered suitable for absorbing water from the soil?
Ans.i) The cell of root hair is freely permeable which allows all the substances to pass through it.
ii) The cell membrane of the root hair is semi- permeable which facilitates the movement of water molecules from the soil into root cells.
iii) The cell sap in the root hair is said to be of higher concentration as it contains more solutes compared to the surroundings which promotes water absorption.
9) Briefly explain, how transpiration helps in the upward conduction of water in plants?
Ans. Transpiration results in the suction force which 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 the transpirational pull which helps in the upward conduction of water in plants.
10) How does temperature, light intensity and wind affect transpiration?
Ans.Transpiration is faster on hot summer days due to faster evaporation of water. During daytime, the rate of transpiration is faster as the stomata remain open to allow the inward diffusion of carbon dioxide for photosynthesis.During night time the transpiration hardly occurs. Transpiration is more when wind is blowing faster as water vapour moves away from the surface of the leaves.
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.
a) Name the process which is demonstrated?
Ans. The process demonstrated in the above picture is transpiration.
b) Why was the pot with its soil left uncovered by the polythene bag?
Ans. Soil and the pot also loses water wapour due to evaporation so those water droplets also would have got accumulated inside the poythene bag. Our experiment is conducted to find out that aerials parts of the plant transpire so the pot with the soil us left uncovered by the polythene bag.
c) Why was the pot left in sunlight?
Ans. During the daytime the rate of transpiration is fastest so the result would be achieved quicker.
d) Suppose that the pot in this experiment was placed inside a dark room instead of placing it in the sunlight for sometime? What difference would be noticed?
Ans. The process of transpiration hardly occurs when it is dark as the stomata remain closed.
12) State the following statements are True or False. Rewrite the false statements correctly.
a) Water absorption mainly occurs through root hairs.
Ans. True
b) Water enters the root hair by osmosis.
Ans. True
c) Water absorbed by the root hair reaches the leaves and is used in producing food for the entire plant.
Ans. True
d) A semi- permeable membrane allows larger moleucles to pass through, but prevents the smaller ones.
Ans. False. A semi permeable membrane allows only the smaller moleucles to pass through it preventing the larger ones.
e) Transpiration is the loss of water from the roots of the plant.
Ans. False, Transpiration occurs from the aerial parts of the plant in the form of water vapours.
f) Transpiration cools the plants when it is hot oustside.
Ans. True
13) Fill in the blanks with the suitable terms given below.
a) Transportation in plants is carroed by a conducting
b) The upward movement of sap that contains water and minerals is called ascent of sap.
c) Transpiration is more when the wind is blowing
d) Most water gets eveaporayed from the plant from its leaves.
e) Transpiartion is reduced when the air is
Long Answer Questions
1.) Draw a magnified view of the root hair, and describe how it helps in the absprption of water from the soil.
Ans.
The root hair has a cell wall which is freely permeable allowing all the substances to pass through it. The cell membrane is semi-permeable which allows only smaller molecules to pass through which facilitates the movement water molecules from soil into the roots cells.The cell sap in the root cell is of higher concentration as it contains more solutes compared to the surrounding soil water which promotes water absorption.
2.) How does transpiration helps the roots absorb water and minerals from the soil?
Ans. Transpiration results in creating a suction force 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 leaves.Thispulling force is called the transpirational pull which helps in conduction of water and minerals to be absorbed from the soil.
3.) Define the three processes by which the plants absorb and minerals from the soil.
Ans. The three processes are as follows:
a) Diffusion: The movement of molecules – solid, liquid or gas from higher concentartion to lower concentration is called diffusion.
Osmosis: The movement of water molecules from a dilute solution to a concencentration solution across a semi -permeable is known as osmosis.
Active transport: The movement of molecules from their lower concentration to a higher concentration requires energy is called active transport.
4.) How is water absorbed by the roots is important for the plants?
Ans.The water absorbed by the roots is important for plants in three main ways:
i) Transportation: The water in the plant body, both in xylem and phloem, transports substances in a solution form from one part to another.
ii) 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.
iii) Cooling: The heat utilized when water is transpired from the surface of leaves in the form of water vapour induces a cooling effect.
5.) Name the factors that affect the rate of transpiration. State the role in each case.
Ans.i) Sunlight: During daytime, the rate of transpiration is faster as the stomata remain open to allow the inward diffusion of carbon dioxide for photosynthesis.During night time the transpiration hardly occurs.
Temperature: Transpiration is faster on hot summer days due to faster evaporation of water.
Wind: Transpiration is more when the wind is blowing faster as water vapour moves away faster from the surface of leaves.
Humidity: Transpiration is reduced if the air is humid.Air cannot hold any water molecules when it is already laden with moisture.
6.) Mention the two ways in which transpiration helps the plants.
Ans.i) Cooling effect: In transpiration, water gets evaporated form the plant. The heat required for this evaporation is obtained form the plant itself and thus the plant is able to cool itself, when it is hot outside.
ii) Transpiration helps in maintaing the concentration of 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.
7.) Describe an experiment to show that plant loses its water through leaves.
Ans.
Take one small-sized, well – watered potted plant having a few branches.Place a polythene bag over its one branch and tie it with a rubber band. Remove all the leaves from another branch as in the other figure B of the same plant, cover this too with a polythene bag and tie it with a rubber band.
Place the plant in the sunlight,and observe it after 4- 6 hours.You will notice that drops have appeared on the inner surface of the polythene bag over branch A, while no water drop water appears on branch B.
Conclusion: This experiment indicates that most water gets evaporated from the plant through its leaves.
8.) Name any three minerals whose deficiency causes diseases in plants.Give the symptoms of each deficiency.
Ans. i) Nitrogen : Yellowing of leaves and wrinkling of cereal grains.
ii) Phosphorus: Purple and red spot on leaves, delay in seed germination.
iii) Potassium: Poor growth with reduced rate of transpiration.
9.) List out differences between xylem and phloem.
Ans.
Xylem |
Phloem |
1. Conducts water and mineral salts from the roots to the aerila parts of the plant. | 1. Translocates food from the leaves to the storage organs and growing parts of the plant. |
2.Made up of tracheids, vessels,xylem parenchyma and xylem fibres. | 2.Made up of sieve tubes,c ompanion cells,phloem parenchyma and phloem fibres. |
3.Conducting cells are dead. | 3. Conducting cells are living. |
4.Conduction is unidirectional. | 4.Conduction is bidirectional. |
5.Conduction does not require any expenditure of energy. | 5.Conduction requires expenditure of energy. |