Exercises: Nutrition in Plants | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

Objective type Questions

A. Fill in the blanks with the correct words.

Q.1. The mode of nutrition in which an organism makes its own food is called _________ (autotrophic/heterotrophic) nutrition.

The mode of nutrition in which an organism makes its own food is called autotrophic nutrition.

Autotrophic organisms are capable of synthesizing their own food using inorganic substances like carbon dioxide and water, and energy from sunlight or chemical reactions.

Q.2. The green pigment found in leaves is present in structures called ________ (chloroplasts/chlorophyll).

The green pigment found in leaves is present in structures called chloroplasts.

Chloroplasts are organelles found in plant cells that contain chlorophyll, the pigment that gives plants their green color. Chlorophyll is essential for photosynthesis, the process by which plants convert sunlight into energy.

Q.3. Water and other nutrients absorbed by the roots are transported from the roots to other parts of the plant through structures called the ________  (xylem/ phloem).

Water and other nutrients absorbed by the roots are transported from the roots to other parts of the plant through structures called the xylem. 
The xylem is a complex tissue system in plants that is responsible for transporting water, minerals, and other nutrients from the roots to the leaves and other parts of the plant. Xylem cells are hollow and dead at maturity, and they form a continuous network of tubes throughout the plant.

Q.4. The roots of saprophytic plants contain_____ (fungi/bacteria) that  convert dead and decaying matter into ______ ( nutrients/ oxygen).

The roots of saprophytic plants contain fungi that convert dead and decaying matter into nutrients. 

Saprophytic plants are organisms that obtain their nutrients from dead and decaying organic matter. The fungi present in their roots break down the organic matter and convert it into simpler compounds like carbon dioxide, water, and minerals, which can be used by the plant for growth and development.

Q.5. The _____ (symbiotic/parasitic) association between Rhizobium and leguminous plants replenishes the soil with ______ (oxygen/nitrogen).

The symbiotic association between Rhizobium and leguminous plants replenishes the soil with nitrogen. 
Rhizobium is a type of bacteria that forms a symbiotic relationship with leguminous plants like peas, beans, and clover. The bacteria live in the root nodules of the plants and convert atmospheric nitrogen into a form that can be used by the plant for growth. In return, the plant provides the bacteria with nutrients and a favorable environment to grow and reproduce.

B. Write T for the True and F for the False statements. 

Correct the false statements.

False
Some plants are heterotrophic in nature, such as the insectivorous plants that obtain nutrients by trapping and digesting insects or other small animals.

Q.2. Plants make food in the form of starch as a result of photosynthesis.

True
During photosynthesis, plants use sunlight, carbon dioxide, and water to synthesize glucose which is then converted into starch for storage.

Q.3. The leaf of the pitcher plant is modified into a tubular pitcher to trap insects.

True
The leaf of the pitcher plant has evolved into a tubular shape with a slippery interior to attract and trap insects, which are then digested by the plant.

Q.4. Lichens are a parasitic relationship between a fungus and a bacteria.

False
Lichens represent a symbiotic relationship between a fungus and an alga or a cyanobacterium, not a bacteria.

Q.5. Farmers grow leguminous plants alternately with other crops to restore potassium and phosphorus content of the soil.

True
Leguminous plants have the ability to fix atmospheric nitrogen into the soil, which helps to increase the nitrogen, potassium, and phosphorus content for other crops that are grown subsequently in the same soil.

C. Choose the correct option.

Very short answer type questions. Give two examples for the following.

Plants that have autotrophic mode of nutrition: Mango tree, Rice plant.

Q.2. Plants that have heterotrophic mode of nutrition 

Plants that have heterotrophic mode of nutrition: Venus flytrap, Indian pipe.

Q.3. Plants that grow in nitrogen-deficient soil 

Plants that grow in nitrogen-deficient soil: Peas, beans.

Q.4. Plants that harm their host plant

Plants that harm their host plant: Cuscuta, Dodder.

Q.5. Symbiotic plants

Symbiotic plants: Pea plant with Rhizobium bacteria, lichens.

Short Answer type Questions

Heterotrophic mode of nutrition refers to the mode of nutrition in which plants obtain their food from other living organisms. The four types of heterotrophic nutrition in plants are:
a) Parasitic plants 
b) Saprophytic plants
c) Insectivorous plants 
d) Symbiotic plants

Q.2. How do parasitic plants benefit from their host plants?

Parasitic plants attach themselves to the host plants and obtain their nutrients from them. They harm the host plant by taking away their nutrients and minerals, which can result in the death of the host plant in severe cases.

Q.3. What is the symbiotic association in lichens?

Lichens are a symbiotic association between fungi and algae. In this association, the fungus provides a protected environment for the algae to grow and the algae, in turn, provide food to the fungus through photosynthesis. This association benefits both organisms involved, and they cannot survive without each other.

Long answer type questions

Photosynthesis is the process by which autotrophs (plants) use the energy of light to convert water and carbon dioxide into sugar and oxygen. The process can be represented by the following chemical equation:

carbon dioxide + water (in the presence of light and chlorophyll) → sugar + oxygen

The conditions necessary for photosynthesis are:

(1) The presence of chlorophyll, a green pigment usually present in the leaves of plants.

(2) The availability of light energy, which is absorbed by the chlorophyll.

(3) The availability of carbon dioxide, obtained from the atmosphere through small openings called stomata.

(4) The availability of water, obtained from the soil through the root system of plants.

During photosynthesis, water reacts with carbon dioxide in the presence of light and chlorophyll to produce sugar and oxygen. The sugar produced is stored in the form of starch in various parts of the plant, while oxygen is released into the atmosphere.

A labelled diagram of photosynthesis in autotrophs is shown below:

Photosynthesis in Autotrophs

In this diagram, we can see that the chloroplast is the organelle responsible for photosynthesis. Within the chloroplast, there are stacks of thylakoid membranes, which contain chlorophyll molecules that absorb light energy. The thylakoid membranes are surrounded by stroma, a fluid containing enzymes that catalyze the various steps of photosynthesis.

During the light-dependent reactions of photosynthesis, light energy is absorbed by the chlorophyll molecules, which excite electrons that are passed along an electron transport chain. This process generates ATP (adenosine triphosphate), a molecule that stores energy, and NADPH (nicotinamide adenine dinucleotide phosphate), a molecule that carries electrons.

During the light-independent reactions of photosynthesis (also known as the Calvin cycle), ATP and NADPH are used to convert carbon dioxide into sugar. This process occurs in the stroma of the chloroplast, and requires the assistance of enzymes such as rubisco.

Overall, photosynthesis is a vital process that sustains life on Earth by producing the oxygen and food that support all living organisms.

Q.2. Describe how insectivorous plants trap and digest insects for nutrition. Support your answer with examples.

Insectivorous plants are those plants that derive their nutrients, especially nitrogen, from the digestion of insects. Insectivorous plants trap insects in various ways, such as:
Pitcher plants: These plants have a deep cavity filled with liquid, which attracts insects. The insects slip and fall into the cavity, where they are trapped and digested by the plant's enzymes. For example, the Nepenthes pitcher plant.
Sundews: These plants have sticky, glandular hairs on their leaves, which attract and trap insects. The plant then curls its leaves around the insect and secretes enzymes that digest it. For example, the Drosera sundew plant.
Venus flytrap: This plant has leaves that snap shut when triggered by an insect. The trapped insect is then digested by the plant's enzymes. For example, the Dionaea muscipula Venus flytrap plant.
After trapping the insect, the plant secretes digestive enzymes that break down the insect's proteins and other nutrients into simpler forms that the plant can absorb. The nutrients are then transported to the rest of the plant for growth and development.

Q.3. Discuss the different ways in which nutrients are replenished into the soil.

Nutrients are replenished into the soil in various ways, such as:
Decomposition: Dead plant and animal matter decompose and release nutrients back into the soil. This process is aided by microorganisms like bacteria and fungi.
Nitrogen fixation: Certain bacteria and cyanobacteria convert atmospheric nitrogen into a form that plants can use, such as ammonium or nitrate. This process is called nitrogen fixation and replenishes the soil's nitrogen content.
Weathering of rocks: Over time, rocks break down into smaller particles, releasing nutrients like potassium, calcium, and magnesium into the soil.
Fertilizers: Chemical fertilizers can be added to the soil to replenish its nutrient content. These fertilizers contain nutrients like nitrogen, phosphorus, and potassium in a form that plants can easily absorb.
Crop rotation: Growing different crops in the same field over time can replenish the soil's nutrient content. For example, legumes like beans and peas can fix nitrogen in the soil, while other crops can deplete the soil's nitrogen content. By rotating crops, the soil's nutrient content is balanced.
It is essential to replenish the soil's nutrient content to maintain its fertility and ensure healthy plant growth.