NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

These NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Nutrition in Plants NCERT Solutions for Class 7 Science Chapter 1

Class 7 Science Chapter 1 Nutrition in Plants Textbook Exercise Questions and Answers

Question 1.
Why do organisms take food?
Answer:
Food is essential for all living organisms to survive. It is necessary to perform life processes such as respiration, growth, repair and replacement of damaged body cells or tissues. All living organisms require a continuous supply of energy for various activities. The various components present in our food such as carbohydrates, proteins, fats, vitamins, and minerals provide energy to our body. Hence, all living organisms need to take food for their survival.

Question 2.
Distinguish between a parasite and a saprotroph.
Answer:

Parasite Saprotroph
1. The organism that grows on the body of another live organism and derives nutrients from it is known as a parasite. 1. The organism that obtains nutrients from the dead or decaying organic matter is called saprotroph.
2. Parasite develops special organs like suckers, hooks or haustoria to obtain nourishment from the host. 2. Saprotroph secretes digestive enzymes on the decaying matter to digest complex molecules of into simpler forms and then absorb them.
3. Examples of parasites are Cuscuta, orchids, etc. 3. Examples of saprotrophs are fungi, certain bacteria, etc.

Question 3.
How would you test the presence of starch in leaves?
Answer:
To test the presence of starch in leaves, perform the following experiment:
Method:

  • Take two potted plants of the same kind.
  • Keep one in the dark for 72 hours and the other in the sunlight.
  • Take one leaf from each of the plants.
  • Boil the two leaves in water for about 10 minutes.
  • Again boil the two leaves in alcohol using a water bath for about 10 minutes to decolourise them.
  • Now wash the leaves thoroughly under running water and keep them in two separate petri dishes.
  • Put few drops of iodine solution on each of the leaves.

Observation:
The leaf kept in the sunlight will turn blue-black due to the presence of starch. The leaf kept in the dark will not turn blue-black because of the absence of starch.

Conclusion:
Plants prepare starch in the presence of sunlight by the process of photosynthesis.
Hence, the leaf kept in sunlight indicated the presence of starch.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 4.
Give a brief description of the process of synthesis of food in green plants.
Answer:
The process of synthesis of food in green plants is called photosynthesis. This process takes place in the cells containing the green pigment chlorophyll. The raw materials for this process are water, carbon dioxide and sunlight. Water and minerals present in the soil are absorbed by the roots and transported to the leaves. Carbon dioxide from air is taken in through the stomata present on the leaf surface. During photosynthesis, chlorophyll containing cells of leaves, in the presence of sunlight, use carbon

dioxide and water to synthesise carbohydrates. The process can be represented as an equation given below:
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 1

Question 5.
Show with the help of a sketch that plants are the ultimate source of food.
Answer:
Plants are autotrophs since they make their own food. Animals including humans depend on them for all their nutrition needs directly or indirectly. Figure given below shows that how flesh eating animals ultimately depends on plants for their nutrition as they feed on other animals which eat plants.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 2

Question 6.
Fill in the blanks:
a. Green plants are called …………… since they synthesise their own food.
b. The food synthesised by the plants is stored as ……………
c. In photosynthesis solar energy is captured by the pigment called ……………
d. During photosynthesis plants take in …………… and release …………… gas.
Answer:
a. autotrophs
b. starch
c. chlorophyll
d. carbon dioxide, oxygen

Question 7.
Name the following:
a. A parasitic plant with yellow, slender and tubular stem.
b. A plant that is partially autotrophic.
c. The pores through which leaves exchange gases.
Answer:
a. Cuscuta
b. Pitcher plant
c. Stomata

Question 8.
Tick the correct answer:
a. Cuscuta is an example of
(i) autotroph
(ii) parasite
(iii) saprotroph
(iv) host
b. The plant which traps and feeds on insects is
(i) Cuscuta
(ii) china rose
(iii) pitcher plant
(iv) rose
Answer:
a. (ii) parasite
b. (iii) pitcher plant

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 9.
Match the items given in Column I with those in Column II:

Column I Column II
Chlorophyll Rhizobium
Nitrogen Heterotrophs
Cuscuta  Pitcher plant
Animals Leaf
Parasite

Answer:

Column I Column II
Chlorophyll Leaf
Nitrogen Rhizobium
Cuscuta Parasite
Animals Heterotrophs
Insects Pitcher plant

Question 10.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
a. Carbon dioxide is released during photosynthesis.
b. Plants which synthesise their food are called saprotrophs.
c. The product of photosynthesis is not a protein.
d. Solar energy is converted into chemical energy during photosynthesis.
Answer:
a. False
b. False
c. True
d. True

Question 11.
Choose the correct option from the following:
Which part of the plant takes in carbon dioxide from the air for photosynthesis?
(i) Root hair
(ii) Stomata
(iii) Leaf veins
(iv) Sepals
Answer:
(ii) Stomata

Question 12.
Choose the correct option from the following:
Plants take carbon dioxide from the atmosphere mainly through their:
(i) roots
(ii) stem
(iii) flowers
(iv) leaves
Answer:
(iv) leaves

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 13.
Why do farmers grow many fruits and vegetable crops inside large greenhouses? What are the advantages to the farmers?
Answer:
A greenhouse is a closed space for the cultivation of fruits and vegetables. It consists of a structure that supports a translucent outer shell of glass or plastic. It is a protected place where you can control environmental factors such as temperature for optimal plant growth.

The main advantages of the greenhouses to the farmers are:

  • It increases production.
  • Off-season production of vegetables and fruit crops becomes possible.
  • Disease-free and genetically superior crops can be produced continuously.
  • Water requirement of such crops is very limited and they are easy to control.
  • Production of good quality and quantity of crops is achieved.

NCERT Extended Learning Activities and Projects

Project 1.
Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in their centres. Cover a part of two leaves with these papers and secure them with paper clips. Keep the plant in the sunlight for 2-5 days. Observe the difference in the colour of the covered and the uncovered portions on the leaf. Perform iodine test on this leaf. Did the two parts show any difference in results? Now take second leaf. Remove the strip and expose the covered part to the sunlight for 2-3 days and do the iodine test again. Describe your observations.
Hint:
a. The covered part will turn pale whereas the uncovered part will be bright green in colour.
b. The covered part on testing with iodine solution does not turn blue-black, whereas the uncovered part turns blue-black on testing with iodine solution indicating the presence of starch.
c. If the strip is removed from the covered part and exposed to sunlight for 2 to 3 days and tested with iodine solution, it will turn blue-black indicating the presence of starch.

Project 2.
Visit a green house if there is one near your place. Observe how they raise plants. Find out how they regulate the amount of light, water and carbon dioxide to grow the plants.
Hint:
Greenhouses are made of glass. When sunlight enters this glass, it is reflected inside and is trapped which raises the temperature inside the greenhouse. Carbon dioxide is present inside the greenhouse and plants are watered regularly.

Project 3.
Try growing a sweet potato just in water. Describe your experiment and observations.
Hint:
Fill the glass or jar with water and place the tip of the potato plant in the water. Poke in four toothpicks evenly spaced around the middle of the sweet potato plant to prevent it from falling into the water. Place the glass in dimly lit area. The sweet potato plant will begin to sprout several stems in a week. Leaves will appear shortly after that.

Activity 1

Objective: To show experimentally that light is essential for photosynthesis.
Materials Required: A healthy potted plant, a petri dish, a beaker containing water, forceps, a water bath, a piece of wire gauze, a tripod stand, a burner, a box of matches, alcohol, a strip of black paper, iodine solution and paper clips.

Procedure:

  • Take a potted plant and keep it in a dark place for 2-3 days so that the leaves get destarched.
  • Cover a part of one of its leaves with the strip of black paper. Make sure that you cover both the sides of the leaf.
  • Now place this plant in sunlight for 3-4 hours.
  • Pluck the selected covered leaf and remove the black paper covering it.
  • Place this leaf in the beaker containing water and boil it for about 10 minutes.
  • Take out the leaf and now boil it in alcohol, using the water bath, for 10 minutes. This removes the chlorophyll.
  • Take out the leaf and wash it under running water.
  • Place this leaf in the petri dish and put a few drops of iodine solution on it. Now observe the change in colour.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 3
Observations: The leaf turns blue-black except in the covered region. As this covered region did not receive sunlight, photosynthesis did not occur. Hence no starch was formed there. The uncovered region received sunlight and starch was formed there due to photosynthesis.
Conclusion: This activity shows that is essential for Photosynth.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Activity 2

Objective: To show that chlorophyll is necessary for photosynthesis.
Materials Required: Croton leaves, alcohol, iodine solution, petri dish.

  • Pluck one or two leaves from croton (coloured plant) which was kept outside in sun.
  • Make an outline sketch of the leaf to mark green and non-green areas of the leaf.
  • Boil the leaf in alcohol till the chlorophyll gets extracted and the leaf becomes almost colourless.
  • Now, keep the leaf in a petri dish and add sufficient amount of iodine solution over the leaf.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 4
Observations: Only that part of leaf becomes blue-black which was green and part which was non-green does not turn blue-black.
Conclusion: Chlorophyll is necessary for photosynthesis.

Raw Materials for Photosynthesis

  • Light: Coming from the sun.
  • Chlorophyll: Present in the green leaves.
  • Carbon dioxide: Taken from the atmosphere through stomata present on the leaf surfaces.
  • Water: Absorbed from the soil through the root system of the plant and transported to the leaves via pipe -like structures (vessels) which run throughout the plant body.

Cell: The bodies of all living organisms are made up of tiny microscopic units called cells. Each cell has an outer boundary called cell membrane. There is a dark coloured spherical structure near the centre of each cell called the nucleus. The nucleus is surrounded by a jelly-like substance enclosed within the cell membrane which is called the cytoplasm.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 5

How do Plants obtain Carbon Dioxide?
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 6

  • There are a large number of tiny pores called stomata (singular: stoma) on the surface of the leaves of plants. There are more stomata on the lower surface of a leaf as compared to its upper surface.
  • The carbon dioxide gas enters the leaves of the plant through the stomata present on their surface.
  • Each stomatal pore is surrounded by a pair of bean-shaped guard cells. The opening and closing of stomatal pores is controlled by these guard cells.

How do Plants obtain Water for Photosynthesis?
i. The water required by the plants for photosynthesis is absorbed by the roots of the plants from the soil.
ii. The water absorbed by the roots of the plants is transported upward through the xylem vessels to the leaves where it reaches the photosynthetic cells.
iii. Plants also need other raw materials such as nitrogen, phosphorus, iron, magnesium, etc., for building their body. Nitrogen is an essential element used by the plants to make proteins and other compounds.
iv. The plants take these materials from the soil. These materials are dissolved in the water absorbed by the plant roots.

  • Photosynthesis can also occur in other green parts of the plants, besides leaves, such as green stems and green branches. In desert plans, the leaves are reduced into spines. In such plants, the green stem prepares food for the plant.
  • Leaves, other than green leaves, also contain chlorophyll and perform photosynthesis. The large amount of coloured pigments such as red, brown, etc., masks the green colour of chlorophyll in such leaves.
  • Algae are plant-like organisms that can be seen growing in water bodies as slimy green patches. They also contain chlorophyll and perform photosynthesis.

Other Modes of Nutrition in Plants:
i. Parasitic nutrition: Parasitic organisms live on/in and derive their food from other organisms. The parasitic organism is called the parasite and the organism it lives on is called the host. The parasites produce special structures called haustoria for absorbing food from the host. Parasites may be total (completely dependant on host) or partial (partially dependant on host). Dodder or Amarbel (Cuscuta) is a total parasite. Parasites affect the growth of the host by depriving it of essential nutrients.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 7

ii. Insectivorous nutrition: This mode of nutrition is observed in plants like pitcher plant and the Venus flytrap. These types of plants depend on insects and small animals for their nutrition.

Pitcher plants have leaves modified into a pitcher or jar-like structure with a lid. There are hair inside the pitcher which traps small insects who enter the pitcher. These insects are digested by the digestive juices secreted in the pitcher and the nutrients released are absorbed by the plant. Insectivorous plants grow in those soils which do not contain sufficient nitrogen mineral. These types of plants are green and carry out photosynthesis to obtain food and meet their nitrogen requirements from the insects. Hence, insectivorous plants are sometimes called partial heterotrophs.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 8

iii. Saprotrophic nutrition: Mode of nutrition in which organisms or plants obtain their nutrition from dead and decaying organic matter is called saprotrophic mode of nutrition. The plants which exhibit saprotrophic mode of nutrition are called as saprotrophs. Saprotrophs secrete digestive juices onto the dead and decaying matter to dissolve it and then absorb nutrients from it.

Examples of saprotrophs are moulds, mushrooms, yeasts and some bacteria. The white cottony mass seen growing on decaying bread pieces are called Fungi. They are saprophytic and grow in moist and humid conditions. They are also seen growing on pickles, leather, clothes etc., and spoil many articles in rainy season.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Activity 3

Objective: To prove that fungi grow on bread if it is left in hot weather for a long time. Materials Required: A piece of bread and magnifying glass.
Procedure:

  • Take a piece of bread and moisten it with water.
  • Leave it in a moist warm place for 2-3 days or until fluffy patches appear on them.
  • These patches may be white, green, brown or of any other colour.
  • Observe the patches under a microscope or a magnifying glass.

Observations: Most probably you will see cotton-like threads spread on the piece of bread. These are fungi called bread mould.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 9
Conclusion: This shows that fungi grow on bread. But not only on this, they also grow on pickles and other articles that are left in hot and humid weather for a long time.

Symbiotic relationship: Some organisms lives together and share shelter and nutrients. This type of relationship between organisms in which both the partners are benefitted by each other is called symbiotic relationship.

For example, lichens are a symbiotic association having a fungal partner and an algal partner. The fungal partner provides shelter, water and minerals to the alga. In return, the alga provides food which it prepares by photosynthesis.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 10

Replenishment of Nutrients in the Soil:
i. Plants continuously take nutrients from the soil in order to synthesise food. As a result of this, amount of nutrients in the soil decreases.
ii. Nutrients in the soil are replenished by adding fertilisers. Fertilisers contain essential plant nutrients and minerals like nitrogen, phosphorus and potassium.
iii. Nutrients can also be replenished by adding manure to the soil. Manure is the organic matter prepared by decaying plant and animal waste. It enriches the soil of organic matter and improves its fertility.
iv. Another way to replenish soil is to grow leguminous crops (for example gram, peas, pulses, etc.) in it. Plants need nitrogen to synthesise proteins and fats. However, they cannot use atmospheric gaseous nitrogen directly. The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form that can be used by the plant. But Rhizobium cannot make its own food. So it lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. In return, plants provide food and shelter to the bacteria. Thus plants and bacteria have a symbiotic relationship here.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 11

Class 7 Science Chapter 1 Nutrition in Plants Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are stomata?
Answer:
Tiny pores present on the surface of the leaves which help in exchange of gases are called stomata.

Question 2.
What are autotrophs?
Answer:
Organisms able to make food for themselves from simple substances are called autotrophs. Example, green plants.

Question 3.
What is heterotrophic nutrition?
Answer:
Heterotrophic nutrition is the mode of nutrition in which organisms depend upon other organisms for their food. For example, animals.

Question 4.
What are insectivorous plants?
Answer:
Insect-eating plants such as pitcher plant are called insectivorous plants.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 5.
What do you mean by nutrition?
Answer:
Nutrition is the mode of taking food by an organism and its utilisation by the body.

Question 6.
Why photosynthesis is named so?
Answer:
Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis (Photos: light; synthesis: to combine).

Question 7.
Name a parasitic plant with yellow, slender and tubular stem.
Answer:
Cuscuta.

Question 8.
Name one plant that traps and feeds on insects.
Answer:
Pitcher plant.

Question 9.
Name one plant that has both the autotrophic and the heterotrophic mode of nutrition.
Answer:
Venus flytrap.

Question 10.
What are fluffy umbrella-like patches growing on rotting wood during the rainy season called?
Answer:
These organisms are called fungi.

Question 11.
How can cells be seen?
Answer:
Most type of cells can be seen only under the microscope.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 12.
From where do plants get raw materials to prepare their food?
Answer:
Plants get raw materials to prepare their food from their surroundings, i.e., water from the soil and carbon dioxide from the atmosphere.

Question 13.
Where does the synthesis of food in a plant usually take place?
Answer:
The synthesis of food in plants occurs usually in leaves.

Question 14.
What is the ultimate source of energy for all living organisms?
Answer:
Sun is the ultimate source of energy for all living organisms.

Question 15.
Write an equation that represents the process of photosynthesis.
Answer:
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 12

Question 16.
What are the nutrients, other than carbohydrates, which are required by plants?
Answer:
Proteins and fats are the nutrients, other than carbohydrates, which are required by plants.

Question 17.
In which form do plants absorb nitrogen?
Answer:
Plants absorb soluble form of nitrogen.

Question 18.
Why do farmers add nitrogenous fertilisers to the soil?
Answer:
Farmers add nitrogenous fertilisers to the soil to fulfil the requirement of nitrogen of the plants. Nitrogen is necessary to synthesise proteins.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 19.
Which microorganism helps to provide nitrogen to the plants?
Answer:
A certain type of bacteria called Rhizohium help to provide nitrogen to the plants.

Question 20.
How do plants absorb nutrients other than carbohydrates from the soil?
Answer:
Other nutrients are available in the soil in the form of minerals. Plants absorb these minerals from the soil along with water.

Question 21.
What are the essential factors for the photosynthesis?
Answer:
Carbon dioxide, water, chlorophyll and sunlight are the essential factors for the photosynthesis to take place.

Question 22.
Why do leaves look green?
Answer:
Leaves look green because of the presence of chlorophyll which is a green pigment.

Question 23.
Why is Cuscuta is called a parasite?
Answer:
Cuscuta is called a parasite because it derives valuable nutrients from the host and deprives it of those nutrients.

Question 24.
Where do Rhizobium bacteria live?
Answer:
They live in the root nodules of legumes such as gram, peas and other pulses.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 25.
What is a cell membrane?
Answer:
The cell is enclosed by a thin outer boundary called the cells membrane.

Question 26.
Reena segregates the waste at home and put the bio degradable waste in a pot containing soil. She leaves it for 15 days and uses that soil for her plants in the garden. Why do you think she did so?
Answer:
She used that soil because of the presence of organic matter in the soil which increased its fertility, water retention capacity and made it porous. All these factors are good for the growth of plants.

Short Answer Type Questions

Question 1.
What are nutrients?
Answer:
Food is essential for all living organisms. Carbohydrates, proteins, fats, vitamins and minerals are the components of food. The chemical substances present in the components of food that are necessary for our body are called nutrients.

Question 2.
Where and in what conditions do fungi grow?
Answer:
Fungi grow on pickles, leather, clothes and other articles that are left in hot and humid weather for long time.

Question 3.
Why are algae green in colour?
Answer:
Algae contain chlorophyll which gives them the green colour. They can also prepare their own food by photosynthesis.

Question 4.
Do insectivorous plants perform photosynthesis?
Answer:
Insectivorous plants have got green leaves, therefore they can photosynthesis, which means that they can prepare their food in the presence of sunlight.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 5.
What are algae?
Answer:
We often see slimy, green patches in ponds or in other stagnant water bodies. These are generally formed by the growth of plant-like green coloured photosynthetic organisms called algae.

Question 6.
Some plants have deep red, violet or brown leaves. Do these leaves also carry out photosynthesis?
Answer:
The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments mask the green colour. Photosynthesis takes place in these leaves also.

Question 7.
How do plants obtain the raw materials from the surroundings?
Answer:
Water and minerals present in the soil are absorbed by the roots. Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight. In this way, plants obtain the various raw materials for photosynthesis.

Question 8.
Whether food is made in all parts of a plant or only in certain parts?
Answer:
Only certain plant parts, like leaves, having green pigment chlorophyll can make food. Hence, leaves are called the food factories of plants. Besides leaves, photosynthesis also takes place in other green parts of the plant such as in green stems and green branches. The desert plants have scale-like or spine¬like leaves to reduce loss of water by transpiration. These plants have green stems which carry out photosynthesis.

Question 9.
How are the raw materials transported to the food factories of the plants?
Answer:
Plants have pipe-like vessels to transport water and nutrients from the soil.
These vessels are made of special cells, forming the vascular tissue. The vascular tissue for the transport of water and minerals in the plant is called the xylem. The vascular tissue for the transport of food and nutrients in the plant is called the phloem. Thus, xylem and phloem transport substances in plants.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 10.
What is a cell?
Answer:
The bodies of all living organism are made of tiny units called cells. Therefore, cells are called the building blocks of living organisms. Cells can be seen only under the microscope. Some organisms are made of only one cell. They are called unicellular. Examples: Amoeba, Paramecium, etc. Living organism made up of many cells are called multicellular, for example, man, tree, etc.

Question 11.
Differentiate between autotrophic and heterotrophic mode of nutrition.
Answer:

Autotrophic Nutrition Heterotrophic Nutrition
1. The mode of nutrition in which organisms make their own food using inorganic substances are called autotrophs, e.g., most green plants. 1. The mode of nutrition in which organisms cannot make their own food and depend directly or indirectly on autotrophs for their survival are called heterotrophs e.g., animals and fungi.
2. The raw materials required for preparation of food are carbon dioxide and water. 2. They do nor require any raw materials as they do not make their food.
3. Chlorophyll and sunlight are essential for photosynthesis and thus autotrophic nutrition to occur. 3. Chlorophyll and sunlight are not required for this nutrition.

Question 12.
How does the fungus get its nutrition?
Answer:
Fungus is a saprotroph. Its mode of nutrition is called saprotrophic mode of nutrition. It takes its food from dead and decaying matter. The digestive juice of fungus converts the dead materials into solution. Then, it absorbs nutrients from the decaying matter.

Question 13.
Write the importance of Rhizobium bacteria for the farmers.
Answer:
Rhizobium bacteria lives in the root nodules of the leguminous plants. It converts the atmospheric nitrogen into soluble forms such as nitrates and nitrites so that plants can take them up from the soil. Thus it enriches the soil and makes it fertile, thereby helping the farmers.

Question 14.
Is ‘nutrition’ a necessity for an organism? Discuss.
Answer:
Yes, food is a necessity for all living organisms. Food is required for the following purposes:

  • It provides energy for the various metabolic processes in the body.
  • It is essential for the growth of new cells and repair or replace worn out cells.
  • It is needed to develop resistance against various diseases.
  • It is necessary to carry out various life processes.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 15.
In the absence of green plants life is impossible on the earth. Explain.
Answer:
In the absence of green plants, there would be no photosynthesis. Without photosynthesis, there will be no food from the plants. The survival of almost all living organisms directly or indirectly depends upon the food made by the plants. If all green plants disappear from the earth, all the herbivores will die due to starvation and so will the carnivores. Besides, oxygen which is essential for the survival of all living organisms is produced during photosynthesis. Thus, we can say that life would be impossible on the earth in the absence of photosynthesis.

Question 16.
Why fertilisers and manures are required to be added to the soil periodically?
Answer:
Plants absorb the minerals and other nutrients from the soil. So the amount of these substances is decreased in the soil. Fertilisers contain nutrients like nitrogen, phosphorous and potassium while manure contains organic matter. Therefore, to overcome the deficit of these nutrients in the soil, we need to add these fertilisers and manures from time to time.

Question 17.
Explain parasitic mode of nutrition. Also give few examples.
Answer:
Parasitic nutrition is that nutrition in which an organism derives its food from the body of another living organism without killing it. The organism which obtains the food is called a parasite and the organism from whose body the food is obtained is called the host. A parasite usually harms the host. The host may be a plant or an animal. Parasitic mode of nutrition is seen in several fungi, bacteria, a few plants like Cuscuta and animals like plasmodium.

Long Answer Type Questions

Question 1.
Explain the process of photosynthesis.
Answer:
Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis. Green parts of a plant have green coloured bodies called chloroplasts. These chloroplasts have green pigment in them known as chlorophyll. Chlorophyll pigment traps light energy and uses to make food.

Plants receive light energy from the sun, carbon dioxide from the atmosphere and water from the soil. As a result of photosynthesis, plants synthesis carbohydrate and give out oxygen. Thus, the green plants convert these raw materials into food with the help of light energy.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 13
Here, the carbohydrate ultimately gets converted into starch and is stored in the plant.

Question 2.
Why are leaves called the food factories of plants? Explain.
Answer:
Leaves are called the food factories of plants due to following functions:

  • Green leaves have all the raw materials necessary to carry the process of photosynthesis.
  • They have chlorophyll (green pigment) which captures the energy of sunlight.
  • Leaves consist of tiny pores stomata on their surface. Carbon dioxide from air is taken in through these stomata.
  • Water and minerals are absorbed by the roots from the soil and transported to the leaves by vessels.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 3.
‘All animals depend upon the plants for their food’. Justify the statement.
Answer:
Animals cannot produce or make their own food. The plants on the other hand can make food by fixing solar energy in the form of chemical energy by the process of photosynthesis. This chemical energy is locked in the food molecules which are taken up by the animals. This food gives energy to the animals to do work and to grow. Thus, heterotrophic organisms such as animals are dependent on plants directly or indirectly.

Question 4.
What are the two important modes of nutrition? Explain them.
Answer:
Following are the two modes of nutrition:

  • Autotrophic mode of nutrition: The mode of nutrition in which organisms make their own food themselves from simple substances is called autotrophic mode of nutrition. For example: green plants.
  • Heterotrophic mode of nutrition: The mode of nutrition in which the organisms cannot make their own food but depend on plants and other organisms for their food is called heterotrophic mode of nutrition. For example: humans and other animals.

Question 5.
What do you understand by symbiotic relationship between organisms?
Answer:
Some organisms live together and share shelter and nutrients. This is called symbiotic relationship. For example, certain fungi live in the roots of trees. The tree provides nutrients to the fungus and in return, receives help from it to take up water and nutrients from the soil. This association is very important for the tree. In organisms called lichens, a chlorophyll containing partner, which is an alga and a fungus live together. The fungus provides shelter, water and minerals to the alga and in return, the alga provides food which it prepares by photosynthesis.

Question 6.
Explain the mechanism of eating insects by a pitcher plant.
Answer:
The leaves of the pitcher plants are modified into a pitcher-like structure. The apex of the leaves forms a lid which can open and close the mouth of the pitcher like-structure of the leaves. Inside the pitcher, there are hair which are directed downwards. When an insect lands in the pitcher, the lid closes and the trapped insect gets entangled into the hair. The insect is digested by the digestive juices secreted in the pitcher. Such insect-eating plants are called insectivorous plants. Such plants do not get all the required nutrients from the soil. So, they are called partial heterotrophs.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 14

Picture-Based Questions

Question 1.
a. Identify the following picture and label the parts marked as A and B.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 15
b. Which position of stomata-open or closed is shown in the figure?
Answer:
a. The figure represents the stomata of leaf. A is guard cell and B is the stomatal pore.
b. It shows the open position of stomata.

NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Question 2.
a. Draw a diagram of a pitcher plant to show the following parts:
i. Pitcher ii. Lid
b. What is the mode of nutrition of this plant?
c. Is it an autotroph or a partial heterotroph?
Answer:
a.
NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants 16
b. The mode of nutrition of the pitcher plant is insectivorous.
c. It is a partial heterotroph.

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