Science Chapter 1 - Nutrition in Plants - Class 7 | Long Answer Type Questions

 

Science Chapter 1 - Nutrition in Plants

Class- 7

NCERT Important Questions

Long Answer Type Questions

Question 1: Sun is called the ultimate source of energy for all living organisms. Comments.

Answer: The solar energy is very important to carry out the process of photosynthesis.  it is captured by the leaves and stored in the plant in the form of food. And this in turn use by other organism to get food to obtain energy.  Thus, we say that sun is the ultimate source of energy for all living organisms.

 

Question 2. What is Symbiosis? What is Symbiotic relationship?

Answer:

Symbiosis: It is the type of nutrition in which two different kinds of depend on each other for their nutrition. In this both the organisms are benefited by each other

Symbiotic Relationship: Some organisms live together and share shelter and nutrients. This type of relationship is called symbiotic relationship.

 

Question 3. Define mode of nutrition .

Answer.

Autotrophs or Autotrophic: - In this mode of nutrition organisms make their food themselves from simple substances. All green plants are Autotrophs (Auto means self and trophs means nourishment)

Heterotrophs or heterotrophic. - Heterotrophic organisms are those who obtain food from other organisms. Since these organisms depend on other organisms for their food, they are called consumers. All animals and non-green plants like fungi come under this category.

 

Question 4. What are stomata? Explain their function.

Answer:

* Stomata are tiny pores on the underside of the leaf surface that are surrounded by guard cells.

* Their functions are to exchange gases by diffusion for photosynthesis and respiration and to cause transpiration by evaporation of water from the leaf surface.

 

Question 5. How is sunlight used by the plant for photosynthesis?

Answer:

* Sunlight is the energy source for photosynthesis. It is trapped by the green pigment chlorophyll that is present in the leaves and all green parts of the plants.

* The chlorophyll is present in organelles called chloroplasts. Most of the chlorophyll is present in the leaves and therefore leaves are the major site for trapping sunlight to convert it to chemical energy.

 

Question 6. Explain how photosynthesis occurs in plants.

Answer:

* Photosynthesis is the process by which solar energy is converted to chemical energy by the green plants.

* In this process simple inorganic molecules like carbon dioxide and water are used to synthesise organic food like starch.

* The reaction requires energy from sunlight. Sunlight is trapped by the pigment chlorophyll present in the leaves.

* The raw materials for photosynthesis are carbon dioxide and water. Carbon dioxide is absorbed from the atmosphere whereas water is absorbed from the soil. The energy from sunlight converts carbon dioxide and water to starch and oxygen.

* Starch is used as food by plants and other animals whereas the oxygen is released into the atmosphere. The overall reaction of photosynthesis can be represented as follows:

 

Question 7. How do plants obtain nutrients other than carbohydrates?

Answer:

* Plants synthesise carbohydrates using energy from sunlight to convert carbon dioxide and water to starch.

* The other nutrients are however obtained directly from soil. Nitrogen is absorbed as soluble nitrogen compounds from the soil. The nitrogen compounds are present in the soil due to the action of nitrogen fixing bacteria like Rhizobium that live in symbiotic association with roots of leguminous plants.

* Nitrogen compounds can be replenished by the addition of fertilizers and manure to the soil.

* Some plants like the pitcher plant and Venus flytrap fulfil their nitrogen requirements  by insectivore. In this case the insects are trapped and digested by plant parts and the nutrients are released into the plant body.

 

Question 8. What is the mode of nutrition in fungi?

Answer:

* The mode of nutrition in fungi is heterotrophic. They cannot synthesize their own food and are dependent on other ‘organisms’ for their carbon source.

* They perform extracellular digestion by releasing enzymes into their environment and obtain organic and inorganic nutrients through absorption.

There are three main ways of obtaining nutrition:

(i)   Saprotrophic: Decomposition of ‘dead organic matter’.

(ii)   Parasitic: Feeding from a living host.

(iii) Mutualism: Living in a mutually beneficial interaction with another organism. Example: lichen is a mutualism between fungi and algae.

 

Question 9. How can we demonstrate that chlorophyll is necessary for photosynthesis?

 Answer:

 Importance of chlorophyll can be demonstrated by using a variegated leaf.

* The outline of the leaf is traced on a paper and the green areas are marked before the start of the experiment

* The leaf is placed in sunlight for few hours to allow photosynthesis. The leaf is then decolourized by boiling in alcohol.

* To this iodine solution is added. It can be observed that the green areas of the leaf turn blue-black in response to iodine solution indicating the presence of starch.

* Thus it can be seen that photosynthesis occurs in the green areas of the variegated leaf showing that chlorophyll is important for photosynthesis.

 

Question 10 - Why do organisms need to take food?

Answer: Food is required by all living organisms mainly for four reasons or purposes:

* Food helps a living organism to grow. If enough food is not given or if, the food given is not of right kind, the organism will not have proper growth.

* Another important function of food is to provide energy which is required for any living organism for movements and other activities.

* Food is also needed by living organisms for replacement and repairing of their damaged parts.

* Food provide us the power to fight against infections and diseases.

 

Question 11 -  Distinguish between a parasite and a saprotroph.

Answer:

Parasite

* A parasite takes ready- made food from the organism on which it feeds.

* They feed on a living organism.

* The organism on which it feeds is called host

* It deprives the host of valuable nutrients.

Saprotroph

* They secrete the digestive juices on the matter

* They live and convert it into a solution and then absorb it.

* They feed on dead and decaying organism.

* They do not feed on a living organism.

* There is no host at all.

 

Question 12: Give a brief description of the process of synthesis of food in green plants.

Answer:

* Carbon dioxide from air is taken through stomata. Water and minerals are absorbed by roots and transported to leaves.

* Leaves have a green pigment called chlorophyll. In presence of sunlight, they use carbon dioxide and water to synthesize carbohydrate.

* During this process oxygen is released. The carbohydrates ultimately get converted into starch.

 

Question 13 - Whether food is made in all parts of a plant or only in certain parts?

Answer:

* Only certain part plant like leaves having green pigment chlorophyll. So Leaves are called the food factories of plants.

* Besides leaves, photosynthesis also takes place in other green parts of the plant — in green stems and green branches. The desert plants have scaleor spine-like leaves to reduce loss of water by transpiration. These plants have green stems which carry out photosynthesis.

 

Question 14-  Why are leaves called the food factories of plants? Explain.

Answer: Leaves are called the food factories of plants due to following functions:

1. Green leaves have all the raw materials necessary to carry the process of photosynthesis.

2. They have chlorophyll (green pigment) which captures the energy of sunlight.

3. Leaves consist of tiny pores called stomata on their surface.

4. Carbon dioxide from air is taken in through stomata.

5. Water and minerals are absorbed by the roots from the soil and transported to the leaves by vessels.

 

Question 15-  How would you test the presence of starch in leaves?

Answer:

* Take a potted plant which has been exposed to sunlight and pluck a leave from the plant.

* Then boil it in water for 5 min to soften it and then place the leave in a test tube containing alcohol

* Place the test tube in a beaker containing water gently heat the beaker till the alcohol dissolves in the chlorophyll and the leaves loses its green colour.

* Now wash the leaf with water and then place it on a plate and add a few drops of iodine solution the parts that turn blue black show the presence of starch

 

Question 16 - How humans and animals are directly or indirectly dependent on plants?

Answer:

* All living organisms require food. Plants can make their food themselves by organic substances but animals including humans cannot make their food themselves. They get it from plants or animals that eat plants. Thus, humans and animals are directly or indirectly dependent on plants.

 

Question 17: Whether food is made in all parts of a plant or only in certain parts? Explain.

Answer:

* Only certain parts of plant like leaves have green pigment called chlorophyll. So Leaves are called the food factories of plants.

* Besides leaves, photosynthesis also takes place in other green parts of the plant like in green stems and green branches.

* The desert plants have scale or spine like leaves to reduce loss of water by transpiration. These plants have green stems which carry out the process of photosynthesis.

 

Question 18:  What Is cell?

Answer: The body of living organisms are made of tiny units called cells, therefore Cell

are called the building blocks of living organism. Cells can be seen only under the

microscope. Some organisms are made of single cell they are called Unicellular. Ex.

Amoeba, Paramecium etc. While others are made of multicells and are called

multicellular. Ex. man, tree etc.

 

Question 19:  What is saprotrophic mode of nutrition?

Answer: This mode of nutrition in which organisms take in nutrients in solution form

from dead and decaying matter is called saprotrophic nutrition. Plants which use

Saprotrophic modes of nutrition are called saprotrophs. Example Fungi that secrete

Digestive juices on the dead and decaying matter and convert it into a solution. Then

they absorb the nutrients from it.

 

Question 20: How nutrients are replenished in soil?

Answer:

Nutrients are replenished in soil by following ways:

* By spreading manure or fertilizers that contain nutrients such as nitrogen in the fields. 

* By the bacterium Rhizobium that is commonly present in rot nodules of leguminous plant that can take atmospheric nitrogen and convert it into a soluble form like nitrates.

 

Question 21: What do you mean by Symbiosis?

Answer: Symbiosis is the type of nutrition in which two different kinds of organisms depend on each other for their nutrition. In this both the organisms are benefited by each other

 e.g, lichen is a symbiotic association between algae and fungi. In this one alga and one fungus live together and remain in symbiotic relationship.

 

Question 22: What is the role of leguminous plants in replenishing soil fertility?

Answer:

* Rhizobium is a type of bacteria that cannot make its own food and lives in the roots of gram, peas, moong , beans and other legumes.

* It converts atmospheric nitrogen into usable form which increases the fertility of soil, and legumes provide food and shelter to the bacteria.

 

Question 23: What do you mean by parasitic nutrition?

Answer:

* The mode  by which parasitic organism get and synthesize their food is called parasitic nutrition. Example: Cuscuta.

* it does not have chlorophyll; it takes readymade food from the plant on which it is climbing. The plant on which it climbs is called a host.

* In a parasitic nutrition only one of the partners is benefited and other is not.

 

Question 24. How would you test the presence of starch in leaves?

Answer:

* lodine solution is used to test leaves for the presence of starch

Test –

* Remove chlorophyll by boiling it in alcohol and then add 2 drops of iodine solution. If the color changes to blue, indicates the presence of starch in the leaves.

 

Question 25. How do plants obtain the raw materials from the surroundings?

Answer:

* Water and minerals present in the soul 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.

 

Question 26. Explain the mode of nutrition in fungi

Answer:

* They secrete digestive juices on the dead and decaying matter and convert it into a solution.

* Then they absorb the nutrients from it. This mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutation.

 

Question 27. If the pitcher plant is green and carries out photosynthesis, then why does it feed on insects?

Answer:

* These plants grow in soil that is deficient in nitrogen.

* All living things must have nitrogen. These plants (e.g. pitcher plant) are green and carry out photosynthesis to obtain a part of the food required by them. So, they feed on insects to obtain the nitrogen needed for their growth.

 

Question 28 . How farmer is benefited from symbiotic relationship between rhizobium bacteria and legumes?

Answer:

This association is of great significance for the farmers. The bacterium called Rhizobium present in leguminous plant can take atmospheric nitrogen and convert it into a soluble form. So, they do not need to add nitrogen fertiliser to the soil in which leguminous plants are grown.

 

Question 29. How do plants transport raw materials to the food factories of the plants?

Answer:

Water and minerals are transported to the leaves by the vessels which run like pipes throughout the root, the stem, the branches and the leaves. They form a continuous path or passage for the nutrients to reach the leaf. The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight.

 

Question 30. From where do the plants obtain nitrogen?

Answer:

* Nitrogen is present in abundance in gaseous form in the air.  However, plants cannot absorb nitrogen in this form.

* Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil. These soluble forms are absorbed by the plants along with water. Farmers add fertilisers rich in nitrogen to the soil.

 

Question 31. Can we say that the insectivorous plants are partial heterotrophs?

Answer:

These plants grow in soil that is deficient in nitrogen. All living things must have nitrogen. These plants are green and carry out photosynthesis to obtain a part of the food required by them. They feed on insects to obtain the nitrogen needed for their growth. So, we can say that the insectivorous plants are partial heterotrophs.

 

Question 32. Explain symbiotic relationship in rhizobium and leguminous plants.

Answer:

* The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form. 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, the plants provide food and shelter to the bacteria. They, thus, have a symbiotic relationship.

 

Question 33. Give a brief description of the process of synthesis of food in green plants?

Answer:

The synthesis of food in plants occurs in leaves. Therefore, all the raw materials must reach there.

* 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 stomata present on the surface of the leaves.

* Chlorophyll helps leaves to capture the energy of the sunlight. This energy is used to synthesis (prepare) food from carbon dioxide and water.

 

Question 34. Explain symbiotic relationship with the help of example.

Answer:

* Some organisms live together and share shelter and nutrients. This is called symbiotic relationship.

For example, 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 35. Define cells, cell membrane, nucleus and cytoplasm.

Answer:

Cells - the bodies of living organisms are made of tiny units called cells.

Cell membrane - The cell is enclosed by a thin outer boundary, called the cell membrane.

Nucleus - Most cells have a distinct, centrally located spherical structure called the nucleus.

Cytoplasm - The nucleus is surrounded by a jelly-like substance called cytoplasm.

 

Question 36. Can we imagine life on earth in the absence of photosynthesis?

Answer:

No, we cannot imagine life on earth in the absence of photosynthesis. In the absence of photosynthesis there would not be any food. The survival of almost all living organisms directly or indirectly depends upon the food made by the plants.

Besides, oxygen which is essential for the survival of all living organisms is produced during photosynthesis. In the absence of photosynthesis, life would be impossible on the earth.

 

Question 37. Write a note on pitcher plant?

Answer:

* The pitcher-like structure is the modified part of the leaf. The apex of the leaf forms a lid which can open and close the mouth of the pitcher.

* 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.

 

Question 38. How nutrients are replenished in the soil?

Answer:

* Plants absorb mineral nutrients from the soil. So, their amounts in the soil keep on declining. Fertilisers and manures contain plant nutrients such as nitrogen, potassium, phosphorous, etc.

* These nutrients need to be added from time to time to enrich the soil. The bacterium called Rhizobium present in the roots of legumes plants can take atmospheric nitrogen and convert it into a soluble form. This way Rhizobium bacterium also helps to replenish nitrogen in the soil.