Class 7 - Chapter 1: Nutrients CBSE Baord

                                               

CBSE Science

Class 7 - Chapter 1: Nutrients

Revision Notes • By Pratap Sanjay Sir

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🌿

Class 7 Science: Ch-1 Nutrients

CBSE Digital Notebook • By Pratap Sanjay Sir

Basics Photosynthesis Stomata Heterotrophic Insectivorous ✨ 3 Experiments 🔬

📌 Class 7 Revision Notes

NCERT / CBSE Aligned Notes

Chapter 1: Nutrition in Plants

Handcrafted Study Notes & Interactive Lab Experiments • Pratap Sanjay Sir

🍎 What are Nutrients & Nutrition?

➥ Nutrients: Components of food that are necessary for our body. These include carbohydrates, proteins, fats, vitamins, and minerals.

➥ Nutrition: The process of taking in food by an organism and its utilization by the body to produce energy, build body tissues, and repair damaged parts.

💡 Major Components of Food

🍞

Carbohydrates

Energy giving

🥚

Proteins

Body building

🧈

Fats

Reserve energy

🥕

Vitamins

Disease protection

🥦

Minerals

Growth & health

🌱 Modes of Nutrition in Living Organisms

⟹ There are mainly two modes of nutrition:

1

Autotrophic Nutrition

• ➥ The word "auto" means self and "trophic" means nourishment / nutrition. Thus, autotrophic means self-nutrition.
• ➥ Organisms that prepare their own food from simple inorganic substances are called autotrophs.
• ➥ Examples: Green plants and cyanobacteria (blue-green algae).

☀️ Photosynthesis (Food Making Process in Plants):

Photosynthesis is how green plants make their own food using sunlight. They use a green pigment called chlorophyll present in chloroplasts to convert carbon dioxide and water into glucose (sugar) and oxygen.

Chemical Word Equation:

6CO₂ (Carbon dioxide) + 6H₂O (Water) ──[Sunlight & Chlorophyll]──➔ C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen)

⟹ Process of Photosynthesis occurs in 3 key steps:

1. Absorption: Absorption of light energy from the sun by green chlorophyll.
2. Conversion & Splitting: Conversion of solar energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
3. Reduction: Reduction of carbon dioxide to carbohydrates (glucose/starch).

Diagram: Photosynthesis in a Green Leaf

🔬 Stomata (Leaf Pores)

• ➥ What are Stomata? Tiny microscopic pores present on the surface of leaves (mostly on the lower epidermis) surrounded by kidney-shaped guard cells.
• ➥ Gas Exchange: Allows carbon dioxide (CO₂) to enter the leaf for photosynthesis and releases oxygen (O₂).
• ➥ Transpiration: Enables evaporation of excess water vapor from leaf surfaces, which creates a suction pull for sap and cools down the plant.
• ➥ Opening & Closing: Guard cells swell when water flows into them (opening the stomatal pore) and shrink when water is lost (closing the pore).

Open Stomatal Pore Turgid Guard Cells • Gas Exchange Active

Closed Stomatal Pore Flaccid Guard Cells • Prevents Water Loss

🦁 Heterotrophic Nutrition

Definition: Mode of nutrition where organisms cannot synthesize their own food and must depend on autotrophs or other organisms directly or indirectly.

Examples: Animals, non-green plants, fungi, and humans.

⟹ Types of Heterotrophic Nutrition:

🍄 1. Saprotrophic Nutrition

"Sapro" = Rotten

Organisms secrete digestive juices directly onto dead and decaying organic matter and convert it into a solution, absorbing nutrients from it.

Examples: Fungi (Mushroom, bread mould, yeast) and certain bacteria.

🌿 2. Parasitic Nutrition

Host & Parasite

Organisms derive nutrients by living on or inside another living organism (the host) without giving any benefit and usually causing harm, but without immediately killing it.

Examples: Cuscuta (Amarbel - non-green climbing plant), tapeworm, lice, leech.

🍽️ 3. Holozoic Nutrition

Ingestion & Digestion

The mode of nutrition in which solid or liquid complex food is ingested, digested, absorbed, assimilated, and egested by the body.

(i) Herbivores 🌿 Eat only plants/grass.
e.g., Cow, deer, goat.

(ii) Carnivores 🥩 Eat flesh of other animals.
e.g., Lion, tiger, eagle.

(iii) Omnivores 🥗 Eat both plants & animals.
e.g., Humans, bears, crows.

Note (Detritivores): Animals that feed on organic debris and decomposing plant/animal matter. Example: Earthworm (farmer's friend).

🤝 4. Symbiotic Relationship (Symbiosis)

Mutual Benefit

A close, cooperative relationship between two different species living together where both organisms benefit mutually.

Prime Example - Lichen:

• Alga: Contains chlorophyll and makes food through photosynthesis.

• Fungus: Provides shelter, water, and minerals to the alga in exchange.

🪴 Special Topic: Insectivorous Plants (Insect-Eaters)

What are Insectivorous Plants?

Green plants that trap and feed on insects to fulfill their nutritional needs (especially Nitrogen) are known as insectivorous (carnivorous) plants.

❓ Why do they eat insects if they are green?

Even though they have green leaves and synthesize carbohydrates by photosynthesis, they grow in waterlogged bogs and swampy soils that are extremely deficient in Nitrogen. They digest insects using special enzymes to extract nitrogenous compounds needed for protein synthesis.

🏺

Pitcher Plant (Nepenthes)

Leaf lamina is modified into a pitcher-like jug. The leaf apex forms a lid. Inside are downward-pointing hairs.

Drowns & digests in fluid

🪤

Venus Flytrap

Leaves act as two hinged lobes with sensitive trigger hairs. Snaps shut instantly within 0.1s when touched!

Rapid snapping trap

✨

Sundew (Drosera)

Covered with sticky glandular hairs that glisten like dew in the sun. Traps prey like sticky flypaper.

Sticky tentacle trap

Anatomy of Pitcher Plant Trap

🔬 Laboratory Experiments: Proving Photosynthesis

CBSE practical activities to test starch formation and required conditions. Switch between tabs below and click the interactive "Test with Iodine" buttons to see live color change!

🧪 Experiment 1: To Prove That Green Plants Produce Starch During Photosynthesis (Chlorophyll is Essential)

Materials Required:

• Variegated leaf (e.g., Croton, Money plant, or Coleus with white & green patches).

• Beaker, test tube, burner, tripod stand, water, alcohol, iodine solution, petri dish.

Step-by-Step Procedure:

1. Destarch the potted plant by keeping it in complete darkness for 72 hours.
2. Keep in bright sunlight for 6 hours. Pluck a variegated leaf and trace green areas.
3. Boil the leaf in water to break cell walls, then boil in alcohol over a water bath to remove chlorophyll (decolorize).
4. Wash the pale white leaf in warm water and place it in a petri dish.
5. Add drops of dilute iodine solution over it.

Interactive Test Bench

Untested Leaf

✅ Observation & Inference:

Only the initially green portions containing chlorophyll turned blue-black (presence of starch). Non-green white areas remained pale brown. This proves chlorophyll is essential for photosynthesis!

☀️ Experiment 2: To Prove That Light is Necessary for Photosynthesis (Black Paper Strip Test)

Materials Required:

• Healthy potted green plant, strip of black opaque paper or tin foil, paper clips, alcohol, iodine.

Step-by-Step Procedure:

1. Keep potted plant in the dark for 3 days to completely destarch its leaves.
2. Cover a middle section of an attached leaf on both sides with black paper using paper clips.
3. Expose the setup to direct sunlight for 4 to 6 hours.
4. Pluck the leaf, remove black paper, and decolorize by boiling in alcohol (water bath).
5. Wash with water and test the entire leaf with iodine solution.

Simulated Leaf with Black Strip

Black Strip

✅ Observation & Inference:

The exposed parts (top and bottom) turn blue-black as they could perform photosynthesis and make starch. The middle part blocked from sunlight shows no starch. Hence, sunlight is necessary!

💨 Experiment 3: To Prove That Carbon Dioxide (CO₂) is Necessary for Photosynthesis (Moll's Half-Leaf Experiment)

Materials Required:

• Destarched potted plant, wide-mouthed glass bottle with split cork, Potassium Hydroxide solution (KOH), iodine.

Step-by-Step Procedure:

1. Add concentrated KOH solution into a clean wide-mouthed glass bottle. (KOH absorbs any CO₂ inside the bottle).
2. Insert the front half of a destarched leaf into the bottle through the split cork, leaving the other half outside in fresh air. Seal with vaseline.
3. Place the apparatus in bright sunlight for 4 to 5 hours.
4. Pluck the leaf and test both halves for starch using iodine solution.

Moll's Half-Leaf Apparatus Test

Inside (KOH) No CO₂

Outside Has CO₂

✅ Observation & Inference:

The outer half in air turns blue-black (photosynthesis occurred). The inner half in KOH stays pale yellowish-brown because KOH absorbed all CO₂. This proves CO₂ is essential for photosynthesis!

⚡ Quick Recall: Test Your Concept

Click to check your understanding right away!

Q1: Which chemical solution is used to test the presence of starch in a leaf?

Q2: Why do pitcher plants trap and digest insects?

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