🌿 Chapter 5: Life Processes 🌿
(Part 2) Autotrophic Nutrition - How Plants Make Their Own Food - Your Complete Notes for CBSE Grade 10
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1. What is Autotrophic Nutrition?
Term Breakdown:
| Term | Meaning | Example |
|---|---|---|
| Auto | Self | Plants |
| Troph | Nutrition | Algae |
| Autotroph | Self-feeder | Cyanobacteria |
Key Concept: Autotrophs create their own food from simple inorganic substances using light or chemical energy. "Auto" = Self, "Troph" = Nutrition. Autotrophs are 'self-feeders'. They create their own food from simple inorganic substances. This process of self-feeding is called autotrophic nutrition. The most common form is photosynthesis.
2. Photosynthesis Overview
Definition: Process where plants convert light energy into chemical energy (food) using chlorophyll.
The Basic Recipe
| Ingredients | Source | Role |
|---|---|---|
| Carbon Dioxide (CO₂) | Air via stomata | Carbon source for glucose |
| Water (H₂O) | Soil via roots | Hydrogen source |
| Sunlight | Sun | Energy source |
| Chlorophyll | Chloroplasts | Captures light energy |
Ingredient 1: Sunlight - The primary energy source. The 'Cook': Chlorophyll - The green pigment that absorbs sunlight. Ingredient 2: Carbon Dioxide - Taken from the air (CO2). Ingredient 3: Water - Absorbed from the soil (H2O).
3. Chemical Equations
Word Equation:
Carbon Dioxide + Water → Glucose + Oxygen
Balanced Chemical Equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
4. The 3-Step Process of Photosynthesis
| Step | Process | What Happens |
|---|---|---|
| 1. Absorption | Light capture | Chlorophyll absorbs sunlight |
| 2. Conversion | Energy transformation | Light energy → Chemical energy; Water split into H + O |
| 3. Reduction | Food production | H combines with CO₂ to form carbohydrates |
5. Stomata Mechanism
| Condition | Guard Cells | Stomata | Effect |
|---|---|---|---|
| Water (In) | Swell/bend | Open | CO₂ enters |
| Water (Out) | Shrink/limp | Closed | Conserves water |
How CO2 Enters the Leaf: Through tiny pores on the leaf surface called stomata. These pores are opened and closed by guard cells. Guard cells swell with water to open the pore, and shrink to close it, controlling gas exchange.
6. Cellular Level: Chloroplasts
| Part | Function |
|---|---|
| Outer membrane | Protective covering |
| Inner membrane | Selective transport |
| Stroma | Site of dark reactions |
| Thylakoids | Site of light reactions |
| Grana | Stacks of thylakoids |
| Chlorophyll | Green pigment in thylakoids |
The Green Pigment: Found in cell organelles called chloroplasts. These are the "green dots" you can see in leaf cells under a microscope. Their main job is to trap energy from sunlight.
7. Raw Materials & Their Journey
Water Transport:
Root hairs → Root cortex → Xylem → Leaves → Mesophyll cells
Carbon Dioxide Pathway:
Atmosphere → Stomata → Air spaces → Spongy layer → Palisade cells
Essential Minerals from Soil:
| Mineral | Function |
|---|---|
| Nitrogen | Protein synthesis |
| Phosphorus | ATP/DNA formation |
| Magnesium | Chlorophyll component |
| Iron | Enzyme activation |
Water (H2O): A key ingredient for photosynthesis, taken up from the soil by the roots. Nitrogen: Used to make proteins and other compounds. Taken up as inorganic nitrates or nitrites. Other Minerals: Plants also need essential minerals like phosphorus, iron, and magnesium from the soil to build their body.
8. Products & Their Fate
Immediate Products:
- Glucose: Used for energy via respiration
- Oxygen: Released as by-product
| Organism | Immediate Energy | Storage Form |
|---|---|---|
| Plants | Glucose | Starch |
| Animals | Glucose | Glycogen |
| Both | ATP | Fat |
Uses of Glucose in Plants:
- Respiration (energy)
- Converted to starch (storage)
- Make cellulose (cell walls)
- Produce proteins (with N)
- Form fats (energy reserve)
Immediate Energy: Carbohydrates (like glucose) are used right away for the plant's life processes. Plant Storage: Extra energy is stored as starch, serving as an internal energy reserve for later use. Human Storage (Analogy): This is similar to how humans store extra energy from the food we eat as glycogen in our body.
9. Factors Affecting Photosynthesis
| Factor | Effect | Example |
|---|---|---|
| Light intensity | Increases rate up to saturation | More light = faster rate |
| CO₂ concentration | Limits at low levels | 0.03% to 0.1% optimal |
| Temperature | Optimal 25-35°C | Too high/low denatures enzymes |
| Water availability | Essential raw material | Drought stops process |
| Chlorophyll content | Affects light absorption | Yellow leaves = less photosynthesis |
10. Exam-Focused Q&A
Q1. Why are plants called autotrophs?
Ans: Because they can synthesize their own food from inorganic substances using sunlight.
Q2. Name the tissue that transports water to leaves.
Ans: Xylem tissue.
Q3. What happens to the rate of photosynthesis on a cloudy day?
Ans: It decreases due to reduced light intensity, which slows down the light-dependent reactions.
Q4. Why do farmers add nitrogen fertilizers to soil?
Ans: Nitrogen is essential for protein synthesis and chlorophyll formation, which boosts plant growth and photosynthesis.
Q5. How would you test a leaf for starch?
Ans:
- Boil leaf in water to kill cells
- Boil in alcohol to remove chlorophyll
- Wash with water
- Add iodine solution
- Blue-black color indicates starch presence
11. Real-World Applications
Agricultural Practices:
- Greenhouse farming: Controls CO₂, temperature, light
- Irrigation: Ensures water availability
- Crop rotation: Maintains soil nutrients
Environmental Significance:
- Oxygen production for atmosphere
- Carbon dioxide consumption reduces greenhouse effect
- Base of food chains
12. Comprehensive Glossary
📚 Exam Focus
Important Topics
- Definition of autotrophs
- Photosynthesis equation
- Role of chlorophyll
- Stomata and guard cells
- Factors affecting photosynthesis
Question Types
- Multiple Choice Questions (MCQs)
- Short Answer Questions (SA)
- Long Answer Questions (LA)
- Diagram-based Questions
Marking Scheme
- MCQs: 1 mark each
- SA: 2-3 marks each
- LA: 4-5 marks each
- Total: ~15-20 marks in board exams
💡 Study Tips
Understand Concepts
Focus on understanding concepts, not just memorizing facts.
Use Diagrams
Draw diagrams to explain processes and relationships.
Practice Questions
Solve previous year questions and sample papers.
Relate to Real Life
Connect biological concepts to everyday examples.
📚 Additional Resources
Check out our YouTube channel for video explanations of these concepts!
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