Nutrition in Plants Class 7 CBSE Science Notes – Complete Guide

Introduction to Nutrition in Plants

Understanding nutrition in plants is fundamental to comprehending how life sustains itself on Earth. All living organisms require food to perform essential life processes, and plants play a unique role in this ecosystem by producing their own nutrition. This comprehensive guide covers nutrition in plants for class 7 CBSE Science students, explaining key concepts, processes, and practical applications.

What is Nutrition?

Nutrition is the process of taking in food and its utilization by the body for growth, energy, and maintaining life processes. Food provides essential nutrients including carbohydrates, proteins, fats, vitamins, and minerals that are necessary for proper body functioning.

Plants require 17 essential elements (minerals) for normal growth and development:

• Carbon, Hydrogen, and Oxygen: Obtained from air and water
• Other Nutrients: Primarily absorbed from the soil

Classification of Plant Nutrients

Modes of Nutrition in Plants

Living organisms exhibit two main modes of nutrition based on their ability to produce food:

1. Autotrophic Nutrition

Definition: Autotrophic nutrition occurs when organisms can prepare their own food using simple inorganic substances.

Characteristics:

• Found in green plants
• Organisms called autotrophs or producers
• Uses the process of photosynthesis
• Requires chlorophyll (green pigment)
• Independent food production

Main Requirements:

• Chlorophyll pigment in leaves
• Carbon dioxide from atmosphere
• Water from soil
• Sunlight energy

2. Heterotrophic Nutrition

Definition: Heterotrophic nutrition occurs when organisms cannot manufacture their own food and must derive it from other sources.

Characteristics:

• Found in animals and non-green plants
• Organisms called heterotrophs or consumers
• Dependent on autotrophs directly or indirectly
• No chlorophyll present
• Sunlight not required

Types of Heterotrophs Based on Diet:

Comparison: Autotrophic vs. Heterotrophic Nutrition

Photosynthesis: The Food-Making Process

What is Photosynthesis?

Photosynthesis (photo = light; synthesis = to combine) is the process by which green plants prepare their own food using sunlight, carbon dioxide, and water. During this process, plants convert light energy into chemical energy stored in glucose molecules.

Essential Requirements for Photosynthesis

1. Chlorophyll

• Green pigment present in chloroplasts
• Located in leaves and young green stems
• Absorbs light energy for the photosynthetic process

2. Sunlight

• Provides energy for photosynthesis
• Absorbed by chlorophyll molecules
• Converted into chemical energy

3. Carbon Dioxide (CO₂)

• Absorbed from the atmosphere
• Enters through stomata (tiny pores on leaf surface)
• Used as a carbon source for glucose production

4. Water (H₂O)

• Absorbed from soil by roots
• Transported through vascular vessels (xylem)
• Provides hydrogen atoms for glucose formation

Site of Photosynthesis: Chloroplasts

Chloroplast Structure:

• Double membrane organelle
• Contains 10-100 chloroplasts per typical plant cell
• Composed of three main parts:
  1. Outer Membrane: Phospholipid bilayer providing protection
  2. Stroma: Aqueous fluid containing enzymes
  3. Thylakoids: Flattened disc-shaped structures stacked into grana

Thylakoid Function:

• Contains photosynthetic pigments
• Site where light reactions occur
• Houses photosystems for light absorption

The Two Stages of Photosynthesis

Stage 1: Light Reactions (Light-Dependent Reactions)

Location: Thylakoid membranes in grana

Process:

1. Chlorophyll absorbs sunlight energy
2. Water molecules split (photolysis)
3. Oxygen released as byproduct
4. Energy stored in ATP and NADPH molecules

Products:

• ATP (Adenosine Triphosphate) - Energy currency
• NADPH - Electron carrier
• O₂ (Oxygen) - Released through stomata

Stage 2: Dark Reactions (Light-Independent Reactions / Calvin Cycle)

Location: Stroma of chloroplast

Process:

1. Carbon dioxide fixed using ATP and NADPH
2. CO₂ combines with 5-carbon sugar (RuBP)
3. Forms 6-carbon intermediate
4. Breaks down into glucose and fructose
5. These combine to form sucrose (sugar)

Products:

• Glucose (C₆H₁₂O₆)
• Fructose
• Sucrose (stored energy)

Photosynthesis Formula Table

Role of Leaves in Photosynthesis

Leaf Adaptations for Photosynthesis

Leaves are perfectly designed for efficient photosynthesis:

1. Broad and Flat Surface: Maximizes sunlight absorption
2. Green Chlorophyll: Captures light energy effectively
3. Stomata: Tiny pores for gas exchange
4. Vascular System: Transports water and nutrients
5. Thin Structure: Allows easy diffusion of gases

Special Adaptations in Desert Plants

In desert plants facing water scarcity:

• Leaves modified into spines (reduced transpiration)
• Green, fleshy stems perform photosynthesis
• Stems contain chlorophyll for food production
• Minimizes water loss while maintaining nutrition

Stomata: The Gateway for Gas Exchange

What are Stomata?

Stomata (singular: stoma) are microscopic pores found on the surface of leaves that regulate gas exchange and transpiration.

Structure of Stomata

Components:

• Guard Cells: Two kidney-shaped cells surrounding the pore
• Stomatal Pore: Opening between guard cells
• Air Cavity: Space inside leaf connected to stomata

Mechanism of Stomatal Opening and Closing

Opening of Stomata (Daytime)

1. Light triggers guard cells to absorb water from surrounding cells
2. Guard cells become turgid (swollen)
3. Outer thin walls bulge outward
4. Inner thick walls pull apart
5. Stomatal pore widens and opens

Closing of Stomata (Nighttime)

1. Absence of light triggers water loss from guard cells
2. Guard cells become flaccid (deflated)
3. Inner thick walls straighten
4. Stomatal pore closes
5. Prevents water loss during non-photosynthetic periods

Factors Affecting Stomatal Movement

Functions of Stomata

1. Gas Exchange: Allow CO₂ entry for photosynthesis and O₂ exit
2. Transpiration: Regulate water vapor loss
3. Temperature Regulation: Control evaporative cooling
4. Moisture Control: Maintain plant water balance

Heterotrophic Nutrition in Plants

Not all plants are autotrophic. Some plants have evolved to obtain nutrition through alternative methods.

Types of Heterotrophic Plants

1. Parasitic Plants

Definition: Non-green plants that live on other living organisms (hosts) and derive food from them.

Mechanism:

• Develop special roots called haustoria
• Haustoria penetrate host tissue
• Reach vascular bundles to absorb nutrients

Types of Parasitic Plants:

a) Total Parasites

• Characteristics: Completely dependent on host for food
• Examples:
  • Cuscuta (Dodder/Amarbel): Yellow tubular structures wrapping around host stems
  • Apodanthes: Lacks chlorophyll entirely
• Adaptations:
  • No chlorophyll
  • Reduced or absent leaves
  • Specialized attachment structures

b) Partial Parasites

• Characteristics: Have green leaves, can photosynthesize partially
• Dependency: Require host for water and minerals only
• Example:Mistletoe - Grows on tree branches
• Advantage: Can survive better if separated from host

2. Saprophytic Plants

Definition: Plants that obtain nutrients from dead and decaying organic matter.

Mechanism:

• Secrete digestive enzymes onto dead matter
• Enzymes break down complex organic compounds
• Absorb simple nutrients through their surface

Examples:

• Mushrooms: Decompose forest litter
• Indian Pipe (Monotropa): White, waxy plant
• Other fungi: Molds, yeasts

Ecological Importance:

• Natural recyclers in ecosystems
• Return nutrients to soil
• Support nutrient cycling

3. Insectivorous (Carnivorous) Plants

Definition: Plants that trap and digest insects to supplement their nutrition.

Why They Trap Insects:

• Grow in nitrogen-deficient soils (bogs, marshes)
• Insects provide nitrogen and other minerals
• Still perform photosynthesis as autotrophs

Common Examples:

a) Pitcher Plant (Nepenthes)

Mechanism:

1. Leaf modified into pitcher-shaped structure
2. Contains digestive enzymes
3. Attracts insects with sweet nectar and bright colors
4. Slippery rim causes insects to fall inside
5. Digestive juices break down insect body
6. Nutrients absorbed by plant

b) Venus Flytrap (Dionaea)

Mechanism:

1. Leaves with two lobes having trigger hairs
2. Insect touches trigger hairs (2-3 times)
3. Lobes snap shut within milliseconds
4. Traps insect inside
5. Secretes digestive enzymes
6. Absorbs nutrients after digestion
7. Opens after 5-12 days

c) Sundew (Drosera)

Mechanism:

• Sticky, glandular hairs on leaves
• Insects get stuck on sticky droplets
• Leaf slowly curls around prey
• Digests and absorbs nutrients

Important Note: Despite eating insects, these plants are still autotrophs because they perform photosynthesis for carbohydrate production. Insects only supplement mineral nutrition, especially nitrogen.

4. Symbiotic Plants

Definition: Mutually beneficial relationship where both organisms derive advantages.

Example: Lichens

• Partnership: Fungus + Alga
• Fungal Contribution: Provides shelter, water, and minerals
• Algal Contribution: Performs photosynthesis and provides food
• Benefit: Both organisms survive better together

Example: Leguminous Plants

• Partnership: Plants (pea, beans) + Rhizobium bacteria
• Bacterial Contribution: Fix atmospheric nitrogen in root nodules
• Plant Contribution: Provides carbohydrates and shelter
• Benefit: Enhanced nitrogen availability for plant growth

Nutrition in Plants Class 7 Extra Questions with Answers

Very Short Answer Questions (1 Mark)

Q1. What is nutrition?

Answer: Nutrition is the process of taking in food and its utilization by the body for growth, energy, and maintaining life processes.

Q2. Name the green pigment present in leaves.

Answer: Chlorophyll is the green pigment present in leaves.

Q3. What are stomata?

Answer: Stomata are tiny pores present on the surface of leaves through which gas exchange occurs.

Q4. What is photosynthesis?

Answer: Photosynthesis is the process by which green plants prepare their own food using sunlight, carbon dioxide, and water.

Q5. Name two autotrophs.

Answer: Green plants and some bacteria are autotrophs.

Q6. Give one example of a parasite plant.

Answer: Cuscuta (Dodder/Amarbel) is a parasitic plant.

Q7. What is the full form of ATP?

Answer: ATP stands for Adenosine Triphosphate.

Q8. Name the organelle where photosynthesis occurs.

Answer: Chloroplast is the organelle where photosynthesis occurs.

Q9. What are heterotrophs?

Answer: Heterotrophs are organisms that cannot make their own food and depend on other organisms.

Q10. Name one insectivorous plant.

Answer: Pitcher plant or Venus flytrap.

Short Answer Questions (2-3 Marks)

Q11. Differentiate between autotrophic and heterotrophic nutrition.

Answer:

• Autotrophic Nutrition: Organisms prepare their own food using simple inorganic substances. Found in green plants with chlorophyll. Example: Green plants.
• Heterotrophic Nutrition: Organisms cannot prepare their own food and depend on others. Found in animals and non-green plants. Example: Animals, fungi.

Q12. Explain the role of guard cells in opening and closing of stomata.

Answer: Guard cells are kidney-shaped cells surrounding stomata. When guard cells absorb water, they become turgid and stomata open. When they lose water, they become flaccid and stomata close. This mechanism regulates gas exchange and prevents water loss.

Q13. What are the raw materials required for photosynthesis?

Answer: The raw materials required for photosynthesis are:

1. Carbon dioxide (from atmosphere through stomata)
2. Water (from soil through roots)
3. Sunlight (absorbed by chlorophyll)
4. Chlorophyll (green pigment in chloroplasts)

Q14. Why are some plants called insectivorous plants?

Answer: Some plants grow in nitrogen-deficient soils. To supplement their mineral nutrition, they trap and digest insects. These plants still perform photosynthesis but obtain nitrogen and minerals from insects. Examples include pitcher plants and Venus flytraps.

Q15. What is the significance of nitrogen for plants?

Answer: Nitrogen is essential for plants because it is a primary nutrient required in large amounts. It is a major component of proteins, chlorophyll, and nucleic acids. Nitrogen helps in plant growth, leaf development, and overall health. It is often supplemented as fertilizer.

Q16. Explain the term symbiosis with an example.

Answer: Symbiosis is a mutually beneficial relationship between two organisms. In lichens, fungi provide shelter, water, and minerals to algae, while algae perform photosynthesis and provide food to fungi. Both organisms benefit and survive better together.

Q17. What happens to oxygen produced during photosynthesis?

Answer: Oxygen produced during photosynthesis is a byproduct of the light reaction when water molecules split. Most oxygen is released into the atmosphere through stomata. Some oxygen is used by the plant for respiration.

Q18. Why do desert plants have spines instead of leaves?

Answer: Desert plants face extreme water scarcity. To reduce water loss through transpiration, their leaves are modified into spines. The green, fleshy stems contain chlorophyll and perform photosynthesis, allowing the plant to conserve water while still producing food.

Q19. What is the role of haustoria in parasitic plants?

Answer: Haustoria are special root-like structures developed by parasitic plants. They penetrate the host plant's tissue and reach the vascular bundles. Through haustoria, parasites absorb water, minerals, and nutrients from the host plant.

Q20. Name the three categories of plant nutrients based on requirement.

Answer: The three categories are:

1. Primary nutrients (Macronutrients): Nitrogen, Phosphorus, Potassium - required in large amounts
2. Secondary nutrients (Macronutrients): Calcium, Magnesium, Sulphur - required in large amounts
3. Micronutrients: Iron, Zinc, Manganese, etc. - required in small amounts

Long Answer Questions (5 Marks)

Q21. Describe the process of photosynthesis in detail.

Answer: Photosynthesis is the process by which green plants prepare their own food. It occurs in two stages:

Light Reactions (in thylakoids):

• Chlorophyll absorbs sunlight energy
• Water molecules split into hydrogen and oxygen
• Oxygen is released as a byproduct
• Energy is stored in ATP and NADPH molecules

Dark Reactions (in stroma):

• Carbon dioxide is fixed using ATP and NADPH
• CO₂ combines with a 5-carbon sugar (RuBP)
• Forms a 6-carbon intermediate
• Breaks down into glucose and fructose
• These combine to form sucrose

Overall Equation: 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂

The glucose produced is used for energy and growth, while oxygen is released into the atmosphere.

Q22. Explain how stomata open and close. List factors affecting stomatal movement.

Answer:Mechanism:

• Opening: During daytime, water enters guard cells from surrounding cells. Guard cells become turgid, outer walls bulge, inner walls pull apart, and stomatal pore opens.
• Closing: At night, water leaves guard cells. They become flaccid, inner walls straighten, and stomatal pore closes.

Factors Affecting Stomatal Movement:

1. Light: Opens in presence, closes in darkness
2. Temperature: Rise opens, fall closes stomata
3. Carbon Dioxide: Low CO₂ opens, high CO₂ closes
4. Water Availability: Water stress closes stomata through ABA hormone
5. Potassium Ions: K⁺ influx opens, efflux closes
6. Mechanical Shock: Causes closure
7. Hormones: Abscisic acid closes, Cytokinins open

Q23. Describe different types of heterotrophic nutrition in plants with examples.

Answer:

1. Parasitic Nutrition:

• Plants depend on living hosts for food
• Total Parasites: Cuscuta - completely dependent, no chlorophyll
• Partial Parasites: Mistletoe - has chlorophyll, needs only water and minerals

2. Saprophytic Nutrition:

• Obtain nutrients from dead organic matter
• Secrete digestive enzymes
• Examples: Mushrooms, fungi, molds

3. Insectivorous Nutrition:

• Trap and digest insects for minerals
• Grow in nitrogen-deficient soils
• Still perform photosynthesis
• Examples: Pitcher plant, Venus flytrap, Sundew

4. Symbiotic Nutrition:

• Mutually beneficial relationships
• Examples: Lichens (fungus + alga), Legumes (plant + Rhizobium bacteria)

Each type represents an adaptation to specific environmental conditions.

Q24. What is the role of leaves in photosynthesis? Explain the structure that makes them efficient.

Answer: Leaves are the primary organs of photosynthesis. Their structure is perfectly adapted for this function:

Structural Features:

1. Broad and Flat Surface: Maximizes sunlight absorption and CO₂ capture
2. Chlorophyll in Chloroplasts: Traps light energy efficiently
3. Stomata: Regulate gas exchange (CO₂ in, O₂ out)
4. Vascular Bundles: Transport water from roots and distribute glucose
5. Thin Lamina: Allows easy diffusion of gases to all cells

Functional Roles:

• Absorb sunlight through chlorophyll
• Take in carbon dioxide through stomata
• Receive water through xylem vessels
• Produce glucose through photosynthesis
• Release oxygen as byproduct
• Regulate transpiration to cool the plant

In desert plants, stems take over this function as leaves become spines to conserve water.

Q25. Explain the importance of photosynthesis for life on Earth.

Answer: Photosynthesis is crucial for life on Earth for multiple reasons:

1. Food Production:

• Plants are primary producers in food chains
• All organisms depend directly or indirectly on plants for food
• Provides carbohydrates, which are energy sources

2. Oxygen Production:

• Releases oxygen as a byproduct
• Maintains atmospheric oxygen levels (21%)
• Essential for respiration of all aerobic organisms

3. Carbon Dioxide Removal:

• Absorbs CO₂ from atmosphere
• Helps regulate atmospheric carbon levels
• Reduces greenhouse effect

4. Energy Storage:

• Converts light energy into chemical energy
• Energy stored in glucose molecules
• Transferred through food chains

5. Ecological Balance:

• Supports entire ecosystem
• Foundation of all food webs
• Maintains life-supporting atmosphere

Without photosynthesis, life as we know it would not exist on Earth.

Formulas and Equations

Quick Revision Points

1. Nutrition is the process of obtaining and utilizing food for energy and growth
2. Autotrophs (green plants) make their own food through photosynthesis
3. Heterotrophs (animals, non-green plants) depend on others for food
4. Photosynthesis requires chlorophyll, sunlight, CO₂, and water
5. Chloroplasts are the sites of photosynthesis in plant cells
6. Stomata regulate gas exchange and transpiration
7. Guard cells control stomatal opening and closing
8. Plants need 17 essential elements for normal growth
9. Parasitic plants obtain food from living hosts using haustoria
10. Insectivorous plants trap insects for mineral nutrition
11. Saprophytes feed on dead organic matter
12. Symbiosis is a mutually beneficial relationship between organisms

Common Mistakes to Avoid

1. Confusing autotrophic with heterotrophic nutrition
2. Thinking all plants have green leaves (desert plants have green stems)
3. Believing insectivorous plants don't photosynthesize (they do!)
4. Assuming stomata remain open all the time
5. Thinking photosynthesis occurs only in leaves (can occur in green stems too)
6. Confusing total parasites with partial parasites
7. Forgetting that oxygen is a byproduct of photosynthesis
8. Not understanding the difference between light and dark reactions

Exam Preparation Tips

For CBSE Class 7 Science Exam

1. Understand, Don't Memorize: Focus on understanding processes rather than rote learning
2. Practice Diagrams: Draw chloroplast structure, stomatal mechanism, and parasitic plants
3. Learn Definitions: Be clear with terms like nutrition, photosynthesis, autotroph, heterotroph
4. Remember Examples: Know at least 2-3 examples for each type of nutrition
5. Solve NCERT Questions: Complete all exercises from the textbook
6. Compare and Contrast: Make tables comparing different concepts
7. Use Mnemonics: Create memory aids for nutrient categories (NPK for primary nutrients)
8. Revise Equations: Practice writing the photosynthesis equation correctly
9. Time Management: Allocate time based on marks for each question
10. Previous Year Questions: Solve past papers to understand question patterns

Study Schedule Recommendation

• Week 1: Understand basic concepts and definitions
• Week 2: Study photosynthesis in detail with diagrams
• Week 3: Learn heterotrophic nutrition types
• Week 4: Practice questions and revision
• Day Before Exam: Quick revision using notes and formulas

Important Diagrams to Practice

1. Structure of Chloroplast
2. Cross-section of Leaf showing Stomata
3. Open and Closed Stomata with Guard Cells
4. Photosynthesis Process (Flowchart)
5. Parasitic Plant (Cuscuta) on Host
6. Pitcher Plant Structure
7. Venus Flytrap Mechanism
8. Lichen (Symbiotic Relationship)

Conclusion

Understanding nutrition in plants is essential not only for academic success but also for appreciating how life sustains itself on Earth. Plants are the foundation of our food chains and oxygen supply. This comprehensive guide covers all aspects of nutrition in plants for class 7 CBSE students, including modes of nutrition, the photosynthesis process, heterotrophic nutrition, and practice questions.

By mastering these concepts, students will develop a strong foundation in biology that will benefit them in higher classes. Regular revision, diagram practice, and solving extra questions will ensure excellent performance in examinations.