CBSE Class 7 Science Nutrition in Plants and Animals Assignment

I. Label the diagram of a human digestive system.
Answer:
1. Mouth / Buccal cavity
2. Salivary gland
3. Liver
4. Gall bladder
5. Small intestine
6. Anus
7. Oesophagus (Food pipe)
8. Stomach
9. Pancreas
10. Large intestine
11. Rectum
12. Appendices / Appendix
13. Cecum
In simple words: The human digestive system breaks down food into simpler substances that the body can absorb, passing through the mouth, food pipe, stomach, and intestines.
Exam Tip: Learn the correct sequence of organs from the mouth to the anus and identify the digestive glands (salivary glands, liver, and pancreas).

II. Reasoning based questions:

Question i. What would happen if plants do not possess chlorophyll?
Answer: Chlorophyll is the green pigment responsible for trapping sunlight required to prepare food through photosynthesis. If plants did not possess chlorophyll, they would not be able to synthesize their own food and would eventually die unless they adopted a parasitic or heterotrophic mode of nutrition.
In simple words: Without chlorophyll, plants cannot capture sunlight to make food and will fail to survive.

Exam Tip: Always mention the role of chlorophyll in trapping solar energy during photosynthesis.

Question ii. Herbivores have well developed incisors. Why?
Answer: Herbivores feed primarily on plant materials such as leaves, grass, shoots, and twigs. Well-developed, sharp incisors in the front are required to bite off and cut vegetation efficiently.
In simple words: Incisors help herbivores cut and crop grass and plant leaves easily.

Exam Tip: Relate the type of teeth in animals directly to their feeding habits and diet.

Question iii. Why does a plant shed its leaves if kept inside a closed room for too long?
Answer: Inside a closed room, a plant may not receive adequate sunlight, fresh air, or carbon dioxide required for photosynthesis and respiration. To conserve water and energy when food production drops, the plant sheds its leaves.
In simple words: Lack of proper sunlight and fresh air forces the plant to drop its leaves to reduce stress and conserve energy.

Exam Tip: Focus on environmental factors like sunlight and gas exchange when explaining plant responses.

Question iv. Consider a farmhouse where there are only animals and no plants. Will there be a change in the level of carbondioxide level in the atmosphere in 24 hrs. Explain why?
Answer: Yes, the level of carbon dioxide in the atmosphere will increase over 24 hours. Animals constantly release carbon dioxide through respiration day and night. In the absence of plants, there are no photosynthetic organisms to absorb carbon dioxide and release oxygen, leading to a net accumulation of carbon dioxide.
In simple words: Animals breathe out carbon dioxide, and without plants to absorb it, the level of carbon dioxide in the air will go up.

Exam Tip: Balance between respiration (releases carbon dioxide) and photosynthesis (consumes carbon dioxide) is key to such ecological questions.

III. Differentiate between:

Question i. Stomata and chlorophyll
Answer:
- Stomata: These are tiny pores present on the surface of leaves that help in the exchange of gases (\(\text{CO}_2\) and \(\text{O}_2\)) and transpiration.
- Chlorophyll: This is a green pigment found inside chloroplasts of plant cells that traps solar energy for photosynthesis.
In simple words: Stomata are tiny breathing pores on leaves, while chlorophyll is the green pigment that absorbs sunlight.

Exam Tip: Distinguish clearly based on structure/location and function.

Question ii. Herbivores and omnivores
Answer:
- Herbivores: Animals that eat only plants and plant products (e.g., cow, goat, rabbit).
- Omnivores: Animals that eat both plants and other animals (e.g., human, bear, crow).
In simple words: Herbivores eat only plants, whereas omnivores eat both plants and meat.

Exam Tip: Always provide suitable examples along with definitions for differentiation questions.

Question IV. Design an activity to show the movement of water in plants.
Answer:
Aim: To demonstrate that water moves upward through the stem in plants.
Materials Required: A tender stem of a plant (like balsam or celery), a beaker, water, red or blue ink, and a blade.
Procedure:
1. Fill one-third of the beaker with water.
2. Add a few drops of red or blue ink to the water to make it colored.
3. Cut the base of the tender stem cleanly and place it upright inside the beaker.
4. Leave the setup undisturbed in bright sunlight for a few hours.
Observation: After some time, you will observe colored streaks appearing on the stem and veins of the leaves turning the color of the ink.
Conclusion: This activity proves that water travels upward from the roots through the stem to reach the leaves and other aerial parts of the plant.
In simple words: Putting a plant stem in colored water shows how water travels up through the stem to the leaves.

Exam Tip: Structure your activity scientifically under headings: Aim, Materials, Procedure, Observation, and Conclusion.

V. Write short notes on:

Question i. Photosynthesis
Answer: Photosynthesis is the process by which green plants containing chlorophyll prepare their own food (glucose) using carbon dioxide and water in the presence of sunlight. Oxygen is released as a byproduct during this process. The chemical word equation is represented as:
\(\text{Carbon dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Carbohydrate (Glucose)} + \text{Oxygen}\)
In simple words: Photosynthesis is how plants make their food using sunlight, water, and carbon dioxide.

Exam Tip: Always write the word equation or chemical equation when asked about photosynthesis.

Question ii. Types of teeth
Answer: Human beings have four different types of teeth in each jaw, each serving a specific function:
1. Incisors: Chisel-shaped front teeth used for biting and cutting food.
2. Canines: Sharp, pointed teeth used for piercing and tearing flesh.
3. Premolars: Broad teeth with flat surfaces used for grinding and chewing food.
4. Molars: Larger back teeth with flat surfaces specialized for fine grinding and crushing food.
In simple words: Humans have four types of teeth: incisors for cutting, canines for tearing, and premolars and molars for grinding.

Exam Tip: Mention both the shape/location and the function of each tooth type for full marks.

Question VI. Complete the given column:
Answer:

Exam Tip: Ensure concise and accurate scientific terms are filled in table completions.