NCERT Solutions Class 7 Science Chapter 1 – Nutrition in Plants
NCERT Solutions for Class 7 Science Chapter 1: Nutrition in Plants
This chapter explains how plants make their own food through photosynthesis and explores different modes of nutrition in plants including autotrophic, parasitic, and insectivorous plants.
Exercise Questions and Answers
Q1. Why do organisms need to take food?
Answer: Organisms need to take food because:
- Food provides energy for various life processes like growth, movement, and repair
- Food provides nutrients needed for building and repairing body tissues
- Food helps in growth and development of the organism
- Food provides materials for protection against diseases
Q2. Distinguish between a parasite and a saprotroph.
| Parasite | Saprotroph |
|---|---|
| Lives on or inside a living organism (host) | Lives on dead and decaying matter |
| Takes nutrients from the living host | Takes nutrients from dead organic matter |
| Harms the host organism | Helps in decomposition, doesn’t harm |
| Examples: Cuscuta, lice, tapeworm | Examples: Mushrooms, bread mould |
Q3. How would you test the presence of starch in leaves?
Answer: Steps to test for starch in leaves:
- Pluck a green leaf from a plant kept in sunlight
- Boil the leaf in water to soften it
- Place the leaf in a test tube with alcohol and heat in a water bath to remove chlorophyll
- Wash the decolorized leaf with water
- Add a few drops of iodine solution to the leaf
- If the leaf turns blue-black, it confirms the presence of starch
Q4. Give a brief description of the process of synthesis of food in green plants.
Answer: The process of food synthesis in green plants is called photosynthesis:
Carbon dioxide + Water → (sunlight/chlorophyll) → Glucose + Oxygen
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- Plants absorb carbon dioxide through stomata in leaves
- Water is absorbed by roots and transported to leaves through xylem
- Chlorophyll (green pigment) in leaves captures sunlight energy
- This energy is used to convert CO₂ and H₂O into glucose (food)
- Oxygen is released as a byproduct through stomata
Q5. Show with the help of a sketch that plants are the ultimate source of food.
Answer: Food chain showing plants as ultimate food source:
Sun → Plants (Producers) → Herbivores (Deer, Rabbit) → Carnivores (Lion, Tiger) → Decomposers
Plants capture solar energy and make food. All other organisms directly or indirectly depend on plants for food. Even carnivores depend on herbivores that eat plants.
Q6. Fill in the blanks:
(a) Green plants are called _______ since they synthesise their own food.
(b) The food synthesised by plants is stored as _______.
(c) In photosynthesis solar energy is absorbed by the pigment called _______.
(d) During photosynthesis plants take in _______ and release _______.
Answer:
- (a) autotrophs
- (b) starch
- (c) chlorophyll
- (d) carbon dioxide and release oxygen
Key Takeaways
- Photosynthesis is the process by which plants make food using sunlight, CO₂, and water
- Chlorophyll is essential for capturing light energy
- Stomata are tiny pores on leaves for gas exchange
- Plants can be autotrophs, parasites, insectivorous, or saprotrophs
- Nitrogen-fixing bacteria help replenish soil nutrients
Key Concepts: Nutrition in Plants
Nutrition in Plants is a fundamental Chapter of Class 7 Science. It explains how plants prepare their own food through photosynthesis and how other plants and organisms get nutrients in different ways.
Modes of Nutrition
Living organisms obtain nutrition in different ways. The two main modes are:
- Autotrophic Nutrition: Organisms that make their own food using sunlight, water, and carbon dioxide. All green plants, algae, and some bacteria are autotrophs. The process is called photosynthesis.
- Heterotrophic Nutrition: Organisms that cannot make their own food and depend on other organisms. Animals, fungi, and most bacteria are heterotrophs.
Photosynthesis — The Food Factory of Plants
Photosynthesis is the process by which green plants make their own food (glucose) using:
- Sunlight — provides energy
- Carbon dioxide (CO₂) — from the air through stomata
- Water (H₂O) — absorbed by roots from soil
- Chlorophyll — the green pigment in leaves that captures sunlight
The equation for photosynthesis:
6CO₂ + 6H₂O + Sunlight → C₆H₁₂O₆ (Glucose) + 6O₂
Photosynthesis occurs in the chloroplasts (the organelles containing chlorophyll) in leaf cells. Oxygen is released as a by-product — this is why plants produce oxygen during the day.
Other Modes of Nutrition in Plants
- Parasitic Plants: Plants that grow on another plant (the host) and get nutrition from it. Example: Cuscuta (Dodder plant). The host plant is harmed.
- Insectivorous (Carnivorous) Plants: Plants that trap and digest insects to supplement their nitrogen intake. Example: Venus Flytrap, Pitcher Plant (Nepenthes). These plants usually grow in nitrogen-poor soil.
- Symbiotic Plants: Some plants live in a mutually beneficial relationship with other organisms. Example: Lichens (algae + fungi) and leguminous plants with Rhizobium bacteria in root nodules.
- Saprotrophic Plants: Some plants obtain nutrients from dead and decaying organic matter. Example: fungi (mushrooms, moulds).
Role of Nutrients in Plant Growth
Plants need several nutrients beyond what they get from photosynthesis:
- Nitrogen (N): For protein synthesis and leaf growth. Plants get it from soil. Legumes get it through root nodule bacteria.
- Phosphorus (P): For root development and energy transfer
- Potassium (K): For overall plant health and disease resistance
- Magnesium (Mg): Part of the chlorophyll molecule — essential for photosynthesis
Important Board Exam Questions
- What is photosynthesis? Write the equation.
- Name the raw materials required for photosynthesis.
- What is the role of chlorophyll in photosynthesis?
- Distinguish between autotrophic and heterotrophic nutrition with examples.
- What are parasitic plants? Give one example.
- What are insectivorous plants? Why do they trap insects?
- What is symbiosis? Give one example involving plants.
FAQs
Q: Why do plants appear green?
A: Plants appear green because their leaves contain chlorophyll, a pigment that absorbs red and blue light but reflects green light, which is what we see.
Q: Do plants respire?
A: Yes, plants respire all the time (24 hours). But during the day, photosynthesis produces more oxygen than respiration consumes, so plants appear to only release oxygen during the day.
Q: What is the difference between a parasite and a saprotroph?
A: A parasite feeds on a living host (e.g., Cuscuta on another plant). A saprotroph feeds on dead and decaying matter (e.g., fungi on dead wood).
