Grade 7 Q&A: Chapter 4: Nutrition in Living Organisms

Concept Questions

Q1: What is nutrition?

Answer: Nutrition is the process of taking in food and utilizing it for energy, growth, and repair of the body. It involves the intake of nutrients and their assimilation for various life processes.

Q2: Define autotrophic nutrition and give an example.

Answer: Autotrophic nutrition is a mode of nutrition where organisms produce their own food from simple inorganic substances like carbon dioxide and water, using light energy or chemical energy. Green plants are prime examples of autotrophs.

Q3: What is photosynthesis? Write its chemical equation.

Answer: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy (food) using carbon dioxide and water. The chemical equation is: $6CO_2 + 6H_2O + \text{Sunlight Energy} \xrightarrow{\text{Chlorophyll}} C_6H_{12}O_6 + 6O_2$.

Q4: List the raw materials required for photosynthesis.

Answer: The raw materials required for photosynthesis are carbon dioxide ($CO_2$), water ($H_2O$), sunlight, and chlorophyll.

Q5: What is the role of stomata in leaves?

Answer: Stomata are tiny pores mainly on the underside of leaves. Their role is to facilitate the exchange of gases (intake of $CO_2$ and release of $O_2$) and to regulate transpiration (loss of water vapor).

Q6: Differentiate between xylem and phloem.

Answer: Xylem is the plant tissue that transports water and minerals from the roots to the leaves. Phloem is the plant tissue that transports the food (glucose) prepared in the leaves to all other parts of the plant.

Q7: What is heterotrophic nutrition?

Answer: Heterotrophic nutrition is a mode of nutrition where organisms cannot synthesize their own food and depend on other organisms for their nutritional needs.

Q8: Explain saprophytic nutrition with an example.

Answer: Saprophytic nutrition is a mode where organisms obtain nutrients from dead and decaying organic matter. They secrete digestive juices onto the dead matter and absorb the digested nutrients. Examples include fungi like mushrooms, yeast, and bread mould, and some bacteria.

Q9: What is parasitic nutrition? Give an example of a parasitic plant.

Answer: Parasitic nutrition is a mode where organisms (parasites) obtain food from another living organism (host) without killing it, but often causing harm. An example of a parasitic plant is Cuscuta (Dodder plant).

Q10: Why are insectivorous plants considered unique? Give two examples.

Answer: Insectivorous plants are unique because they are green plants that perform photosynthesis, but they also trap and digest insects to obtain essential nutrients, primarily nitrogen, which they cannot get sufficiently from the soil. Examples include Pitcher plant and Venus flytrap.

Q11: What is symbiotic nutrition?

Answer: Symbiotic nutrition (or symbiosis) is a relationship between two different organisms where both organisms live together and benefit from each other.

Q12: Give an example of symbiotic nutrition involving a plant and bacteria.

Answer: An example of symbiotic nutrition is the relationship between Rhizobium bacteria and leguminous plants (e.g., peas, beans). The bacteria live in the root nodules and convert atmospheric nitrogen into a usable form for the plant, while the plant provides food and shelter to the bacteria.

Q13: What are the main products of photosynthesis?

Answer: The main products of photosynthesis are glucose (food for the plant) and oxygen (released into the atmosphere).

Q14: How do fungi obtain their food?

Answer: Fungi obtain their food through saprophytic nutrition. They secrete digestive enzymes onto dead and decaying organic matter, break it down externally, and then absorb the digested nutrients.

Q15: Why is chlorophyll essential for photosynthesis?

Answer: Chlorophyll is essential for photosynthesis because it is the green pigment responsible for absorbing sunlight energy, which is the primary energy source for the entire food-making process in plants.

Application-Based Questions

Q16: A gardener observes that a plant has yellow, thread-like structures growing all over it, and the host plant appears weak. What kind of nutrition is being exhibited by the yellow thread-like plant?

Answer: The yellow thread-like plant is exhibiting **parasitic nutrition**. This description matches Cuscuta (Dodder plant), which lacks chlorophyll and obtains nutrients by growing on and drawing food from a host plant, causing it to weaken.

Q17: If a plant is kept in a dark room, will it be able to perform photosynthesis? Explain why or why not.

Answer: No, a plant kept in a dark room will not be able to perform photosynthesis. Photosynthesis requires sunlight as an energy source. Without light, the chlorophyll cannot capture the necessary energy to convert carbon dioxide and water into glucose and oxygen.

Q18: You find a strange organism growing on a dead log in a forest. It has no leaves and doesn't appear to be green. What mode of nutrition is it likely to have, and why?

Answer: This organism is likely to have **saprophytic nutrition**. Since it's growing on a dead log and is not green (meaning no chlorophyll for photosynthesis), it must be obtaining its nutrients from the dead and decaying organic matter of the log. Fungi (like mushrooms) are common examples of such organisms.

Q19: Why is it important for plants to release oxygen during photosynthesis?

Answer: It is important for plants to release oxygen during photosynthesis because oxygen is vital for the survival of most living organisms on Earth, including humans and animals, who use it for respiration. This process replenishes the atmospheric oxygen that is consumed by living beings.

Q20: Explain the symbiotic relationship between Rhizobium bacteria and leguminous plants. How do both benefit?

Answer: This is a symbiotic relationship where both organisms benefit. Rhizobium bacteria live in the root nodules of leguminous plants. The bacteria convert atmospheric nitrogen into a usable form (nitrogen fixation) for the plant, which is crucial for plant growth. In return, the leguminous plant provides the bacteria with food (sugars produced during photosynthesis) and a protective habitat within the root nodules.

Q21: A plant lives in soil that is deficient in nitrogen. What special adaptation might this plant have developed to obtain nitrogen? Give an example.

Answer: If a plant lives in nitrogen-deficient soil, it might have developed an adaptation to become **insectivorous**. These plants trap and digest insects to supplement their nitrogen intake. An example is the Venus flytrap, which has modified leaves that snap shut to capture insects.

Q22: How does the transportation system (xylem and phloem) ensure the plant receives all necessary components for growth and distributes its food effectively?

Answer: The transportation system ensures efficiency: Xylem transports water and dissolved minerals upwards from the roots to all parts of the plant, including the leaves where photosynthesis occurs. Phloem then transports the food (glucose) produced in the leaves downwards and to other non-photosynthetic parts (like roots, fruits, growing tips) where it is needed for energy and storage. This two-way transport ensures all cells receive what they need.

Q23: Why do parasitic plants like Cuscuta not have chlorophyll?

Answer: Parasitic plants like Cuscuta do not have chlorophyll because they do not need to perform photosynthesis. Instead, they obtain all their ready-made food and nutrients directly from their host plant using specialized structures called haustoria that penetrate the host's tissues.

Q24: Imagine a world without decomposers (like saprophytes). What would be the major consequences for the environment?

Answer: Without decomposers, dead organic matter (dead plants, animals, waste) would accumulate indefinitely, leading to a massive buildup of waste. More critically, essential nutrients locked within this dead matter would not be recycled back into the soil, eventually depleting the soil of fertility and making it impossible for new plants to grow, thus collapsing ecosystems.

Q25: How does the process of nutrition differ fundamentally between a human and a green plant?

Answer: The fundamental difference lies in their mode of food acquisition: * Green plants (autotrophs): Produce their own food internally through photosynthesis, using inorganic raw materials ($CO_2$, $H_2O$) and sunlight. * Humans (heterotrophs): Cannot produce their own food. They obtain food by consuming other organisms (plants or animals) and then digest and assimilate the organic matter externally obtained.

Textbook Exercise Solutions

A. Fill in the blanks:

1. The process by which green plants make their own food is called photosynthesis.
2. Plants that obtain food from dead and decaying matter are called saprophytes.
3. A parasitic plant that lacks chlorophyll is Cuscuta.
4. The tiny pores on the underside of leaves are called stomata.
5. The symbiotic association between an alga and a fungus is called lichen.

B. Match the following:

Column A

1. Autotrophs
2. Saprophytes
3. Parasites
4. Insectivorous plants
5. Symbiosis

Column B

1. Mushroom
2. Cuscuta
3. Green plants
4. Pitcher plant
5. Rhizobium bacteria

Answers:

1. Autotrophs - Green plants
2. Saprophytes - Mushroom
3. Parasites - Cuscuta
4. Insectivorous plants - Pitcher plant
5. Symbiosis - Rhizobium bacteria

C. Answer the following questions:

Q1: What is nutrition? Why is it important for living organisms?

Answer: Nutrition is the process of taking in food and utilizing it for energy, growth, and repair of the body. It is important for living organisms because food provides the necessary energy to perform all life processes, helps in growth and development, and aids in repairing damaged tissues and cells.

Q2: Explain the process of photosynthesis in plants.

Answer: Photosynthesis is the process by which green plants make their own food. During photosynthesis, green plants use carbon dioxide from the air and water from the soil. They absorb sunlight energy with the help of chlorophyll (the green pigment in their leaves). This energy converts carbon dioxide and water into glucose (food) and oxygen. The oxygen is released into the atmosphere. The process can be summarized as: Carbon Dioxide + Water + Sunlight Energy $\xrightarrow{\text{Chlorophyll}}$ Glucose + Oxygen.

Q3: Differentiate between autotrophic and heterotrophic nutrition.

Answer:

• Autotrophic Nutrition: Organisms produce their own food from simple inorganic substances (like $CO_2$ and $H_2O$) using light or chemical energy. Examples: Green plants, algae.
• Heterotrophic Nutrition: Organisms cannot synthesize their own food and depend on other organisms for their nutritional needs. Examples: Animals, fungi, some bacteria.

Q4: Describe saprophytic nutrition with an example.

Answer: Saprophytic nutrition is a mode of nutrition where organisms obtain nutrients from dead and decaying organic matter. They secrete digestive juices onto the dead matter, which breaks it down externally, and then absorb the digested nutrients. An example is a mushroom, which grows on dead wood or decaying leaves.

Q5: What are insectivorous plants? Why do they eat insects?

Answer: Insectivorous plants are green plants that perform photosynthesis but also trap and digest insects. They eat insects primarily to fulfill their nitrogen requirements. These plants usually grow in soil that is deficient in nitrogen, and by consuming insects, they obtain the necessary nitrogen compounds for their growth.

D. Give reasons:

Q1: Fungi are called decomposers.

Answer: Fungi are called decomposers because they obtain their nutrition by breaking down dead and decaying organic matter. They secrete enzymes that digest complex organic substances into simpler forms, which they then absorb. This process helps in recycling nutrients back into the environment, making them available for other organisms.

Q2: Cuscuta is a parasitic plant.

Answer: Cuscuta is a parasitic plant because it lacks chlorophyll and therefore cannot perform photosynthesis to make its own food. Instead, it grows on other living plants (hosts) and derives all its nutrients directly from the host plant, weakening it in the process.

Q3: Lichens show a symbiotic relationship.

Answer: Lichens show a symbiotic relationship because they are formed by the mutual association of two different organisms: an alga and a fungus. The alga, being photosynthetic, prepares food for both. The fungus, in return, provides shelter, absorbs water and minerals from the environment, and protects the alga from harsh conditions. Both organisms benefit from this association.

Q4: Insectivorous plants are green, yet they trap insects.

Answer: Insectivorous plants are green and can perform photosynthesis to make their own food (glucose). However, they typically grow in nitrogen-deficient soils. To compensate for this lack of nitrogen, they have evolved specialized mechanisms to trap and digest insects, from which they obtain the necessary nitrogen compounds for their growth and survival.

Q5: Oxygen is essential for all living organisms.

Answer: Oxygen is essential for most living organisms because it is required for cellular respiration. During respiration, organisms use oxygen to break down food (glucose) to release energy, which is vital for performing all life processes. Without oxygen, most organisms cannot efficiently release energy from their food and would not be able to survive.

References

1. Maharashtra State Board 7th Standard Science Syllabus (Based on current curriculum for nutrition in living organisms)
2. Screenshot_2025_0527_230219.jpg (Provided content and exercise questions)