D. Answer the following questions.

1. What is food? Why do living things need food?

Answer. Food is any substance consumed to provide nutritional support. Living things need food for energy, growth, repair, and overall health.

2. How is autotrophic nutrition different from heterotrophic nutrition?

Answer. Autotrophic nutrition involves organisms producing their own food through photosynthesis, while heterotrophic nutrition involves consuming other organisms for food.

3. What is photosynthesis? Describe the requirements for photosynthesis.

Answer. Photosynthesis is the process by which plants make food using sunlight, carbon dioxide, and water. It requires chlorophyll and light energy.

4. With the help of a labelled diagram, explain the process of photosynthesis in green plants.

Answer. Photosynthesis Process in Green Plants:

Photosynthesis is the process, by which green plants use sunlight to synthesize food from carbon dioxide and water. This process occurs in the chloroplasts of plant cells, which contain the pigment chlorophyll.

Steps of Photosynthesis:

1. Light Absorption: Chlorophyll absorbs light energy from the sun.
2. Water Splitting: The absorbed light energy splits water molecules (H2O) into oxygen (O2), protons (H+), and electrons (e-).
3. Oxygen Release: Oxygen is released as a byproduct into the atmosphere.
4. Carbon Dioxide Fixation: Carbon dioxide (CO2) from the air is absorbed through the stomata.
5. Glucose Formation: Using the energy from light, carbon dioxide and hydrogen ions are converted into glucose (C6H12O6), a form of sugar that provides energy and growth for the plant.

 Sunlight

              |

              v

  Chloroplasts in leaf cells

         /      |       \

      H2O   Chlorophyll  CO2

        |                   |

        v                   v

    O2 (released) Glucose (C6H12O6)

5. Give the word equation of photosynthesis

Answer. The word equation for photosynthesis is:

Carbon dioxide + Water + Sunlight → Glucose + Oxygen

6. What are xylem and phloem?

Answer. Xylem and phloem are types of vascular tissue in plants.

Xylem transports water and minerals from the roots to the rest of the plant.

Phloem carries sugars and nutrients produced by photosynthesis from the leaves to other parts of the plant.

7. Write a short note on each of the following. With one example each:

(i)Parasitic Plants. (ii) Symbiotic Plant (iii) Saprophytic Plants

Answer. (i) Parasitic Plants: Parasitic plants obtain nutrients and water by attaching themselves to a host plant. They have specialized structures called haustoria that penetrate the host’s tissues to access it’s resources. An example of a parasitic plant is mistletoe, which attaches to tree branches and absorbs water and nutrients from its host.

(ii) Symbiotic Plants: Symbiotic plants engage in mutually beneficial relationships with other organisms. They often form associations with fungi or bacteria that enhance their nutrient uptake. An example is legumes (such as beans and peas), which form symbiotic relationships with nitrogen-fixing bacteria in their root nodules, helping them obtain essential nitrogen from the soil.

(iii) Saprophytic Plants: Saprophytic plants feed on dead and decaying organic matter. They release enzymes to break down complex organic materials into simpler substances that they can absorb. An example of a saprophytic plant is the Indian pipe (Monotropa uniflora), which lacks chlorophyll and derives its nutrients from decomposing organic matter in the soil.

8. What are insectivorous plants? Give two examples

Answer. Insectivorous plants, also known as carnivorous plants, are plants that derive some or most of their nutrients by trapping and digesting insects and other small animals. They typically grow in environments with nutrient-poor soil, which necessitates obtaining nutrients from other sources.

Two examples of insectivorous plants are:

1. Venus Flytrap (Dionaea muscipula): This plant has modified leaves that snap shut when trigger hairs are touched, trapping insects inside.

2. Pitcher Plant (Nepenthes): These plants have deep, pitcher-shaped leaves filled with digestive enzymes. Insects are attracted to the pitcher, fall in, and are digested.

9. With the help of an example, explain how insectivorous plants trap insects.

Answer. Insectivorous plants trap insects using specialized structures to capture and digest them, supplementing their nutrient intake, especially in nutrient-poor soils. For example, the Venus Flytrap has modified leaves that act as traps. When an insect lands on the inner surface of the leaf and touches the tiny trigger hairs, the leaf snaps shut, trapping the insect inside. The plant then secretes digestive enzymes to break down the insect and absorb the nutrients. This process allows the Venus Flytrap to thrive in environments where essential nutrients like nitrogen are scarce.

10. Describe two ways in which nitrogen can be added back into soil.

Answer. Two ways in which nitrogen can be added back into the soil are:

1. Nitrogen-Fixing Plants: Certain plants, such as legumes, have symbiotic relationships with nitrogen-fixing bacteria like Rhizobium. These bacteria live in root nodules and convert atmospheric nitrogen into a form that plants can use, enriching the soil with nitrogen.

2. Organic Matter: Adding compost, manure, or other organic matter to the soil helps increase nitrogen content. As these materials decompose, they release nitrogen and other nutrients, which improve soil fertility and structure.

Both methods are natural and sustainable ways to maintain soil health and fertility.