Class 7 Science Notes Chapter 1 (Chapter 1) – Examplar Problems Book

Alright class, let's get straight into Chapter 1, 'Nutrition in Plants', from your Science Exemplar book. This is a foundational chapter, and understanding it well is crucial, not just for your class exams but also for various competitive government exams where basic science is tested.

Chapter 1: Nutrition in Plants - Detailed Notes

1. What is Nutrition?

• The process by which organisms take in food and utilize it to obtain energy for growth, repair, and carrying out various life processes.
• Nutrients: Components of food like carbohydrates, proteins, fats, vitamins, and minerals that are essential for our body (and for plants!).

2. Modes of Nutrition
Organisms obtain food in different ways. In plants, we primarily see two modes:

• a) Autotrophic Nutrition:
  • 'Auto' means self; 'trophos' means nourishment.
  • Organisms that make their own food from simple inorganic substances (like carbon dioxide and water) are called autotrophs.
  • Green plants are the primary examples of autotrophs. They use photosynthesis.
• b) Heterotrophic Nutrition:
  • 'Heteros' means other; 'trophos' means nourishment.
  • Organisms that cannot synthesize their own food and depend on other organisms (plants or animals) for their nutrition are called heterotrophs.
  • Plants exhibiting this mode lack chlorophyll or have specific adaptations.

3. Autotrophic Nutrition: Photosynthesis - The Food Factory of Plants

• Definition: The process by which green plants synthesize their own food (glucose) using carbon dioxide and water in the presence of sunlight and chlorophyll. Oxygen is released as a byproduct.
• Site of Photosynthesis: Primarily occurs in the leaves, which are often called the 'food factories' or 'kitchens' of the plant. Photosynthesis can also occur in other green parts like stems in some plants (e.g., desert plants).
• Essential Requirements:
  • Sunlight: The ultimate source of energy, trapped by chlorophyll.
  • Chlorophyll: The green pigment present in chloroplasts (organelles within plant cells, mainly in leaves) that absorbs sunlight energy.
  • Carbon Dioxide (CO₂): Taken in from the atmosphere through tiny pores on the leaf surface called stomata. These pores are surrounded by guard cells that regulate their opening and closing.
  • Water (H₂O): Absorbed by the roots from the soil and transported to the leaves through pipe-like vessels called xylem.
• Process Summary: Chlorophyll traps solar energy. This energy is used to combine CO₂ and water to produce glucose (a simple carbohydrate/sugar) and oxygen.
• Equation:
  Carbon Dioxide + Water --- (Sunlight / Chlorophyll) ---> Glucose (Carbohydrate) + Oxygen
  6CO₂ + 6H₂O --- (Sunlight / Chlorophyll) ---> C₆H₁₂O₆ + 6O₂
• Products:
  • Glucose (C₆H₁₂O₆): The food produced. It is immediately used by the plant for energy or converted into starch (a complex carbohydrate) for storage in leaves, fruits, stems, roots, etc. (Iodine test is used to detect the presence of starch - turns blue-black).
  • Oxygen (O₂): Released into the atmosphere through stomata, essential for the survival of most living organisms.

4. Heterotrophic Nutrition in Plants
Some plants cannot perform photosynthesis or need additional nutrients. They adopt heterotrophic modes:

• a) Parasitic Nutrition:
  • Parasite: An organism that lives on or inside another organism (the host) and derives nutrition from it, often harming the host.
  • Parasitic plants develop special structures called haustoria (sucking roots) to penetrate the host tissue and absorb readymade food.
  • Example: Cuscuta (Amarbel) - A yellow, wiry plant commonly seen growing on host trees. It lacks chlorophyll.
• b) Insectivorous Nutrition:
  • These plants grow in soil deficient in certain nutrients, especially nitrogen.
  • They trap and digest insects to supplement their nitrogen requirement.
  • They do perform photosynthesis for carbohydrates but rely on insects for nitrogenous compounds.
  • Examples:
    • Pitcher Plant (Nepenthes): The leaf is modified into a pitcher-like structure with a lid. Insects attracted by nectar slip inside and are digested by enzymes secreted within the pitcher.
    • Venus Flytrap (Dionaea): Has hinged leaf blades with trigger hairs. When an insect touches the hairs, the trap snaps shut.
    • Sundew (Drosera): Has tentacles covered in sticky glands that trap insects.
• c) Saprotrophic Nutrition:
  • Saprotrophs: Organisms that obtain nutrients from dead and decaying organic matter. ('Sapro' means rotting).
  • They secrete digestive juices onto the dead/decaying matter, converting complex substances into simpler soluble forms, which are then absorbed.
  • Examples: Fungi (like Mushrooms, Yeast, Bread Mould) and some bacteria. Fungi are often seen growing on stale bread, pickles, leather, or during rainy seasons.
• d) Symbiotic Nutrition:
  • Symbiosis: A close and long-term interaction between two different biological species where both organisms benefit mutually. ('Sym' means together; 'biosis' means living).
  • Examples:
    • Lichens: A composite organism arising from the symbiotic association between algae (which has chlorophyll and provides food through photosynthesis) and fungus (which provides shelter, water, and minerals absorbed from the substrate).
    • Rhizobium Bacteria and Leguminous Plants: Rhizobium bacteria live in the root nodules of leguminous plants (like peas, beans, gram). The bacteria convert atmospheric nitrogen into a usable form (nitrogen fixation) for the plant. In return, the plant provides food and shelter to the bacteria.

5. Replenishment of Nutrients in the Soil

• Plants continuously absorb mineral nutrients from the soil, leading to their depletion.
• Farmers replenish these nutrients by adding:
  • Manures: Organic matter derived from decomposed plant and animal waste.
  • Fertilizers: Chemical substances rich in specific nutrients like Nitrogen (N), Phosphorus (P), and Potassium (K) - often called NPK fertilizers.
• Natural Replenishment: The symbiotic relationship involving Rhizobium bacteria naturally enriches the soil with nitrogen. Crop rotation involving leguminous plants is a traditional method.

Multiple Choice Questions (MCQs)

Here are 10 questions to test your understanding. Choose the best option:

1. Which of the following is the ultimate source of energy for photosynthesis?
   a) Water
   b) Carbon Dioxide
   c) Sunlight
   d) Chlorophyll

2. The green pigment essential for trapping light energy during photosynthesis is:
   a) Stomata
   b) Guard cells
   c) Chlorophyll
   d) Xylem

3. Cuscuta (Amarbel) is an example of a:
   a) Saprotroph
   b) Parasite
   c) Autotroph
   d) Symbiont

4. Insectivorous plants trap insects primarily to obtain:
   a) Carbon dioxide
   b) Water
   c) Nitrogen
   d) Sunlight

5. The tiny pores on the surface of leaves through which gases are exchanged are called:
   a) Guard cells
   b) Chloroplasts
   c) Stomata
   d) Haustoria

6. Which part of the plant absorbs water and minerals from the soil?
   a) Leaves
   b) Stem
   c) Roots
   d) Flowers

7. Lichens represent a symbiotic association between:
   a) Fungus and Bacteria
   b) Algae and Bacteria
   c) Algae and Fungus
   d) Plant roots and Fungus

8. The food synthesized by plants during photosynthesis is stored mainly as:
   a) Glucose
   b) Protein
   c) Starch
   d) Fats

9. Which of the following organisms exhibits saprotrophic nutrition?
   a) Pitcher plant
   b) Cuscuta
   c) Mushroom
   d) Lichen

10. Rhizobium bacteria, found in the root nodules of leguminous plants, help in fixing:
    a) Atmospheric oxygen
    b) Atmospheric nitrogen
    c) Carbon dioxide
    d) Soil phosphorus

Answer Key:

1. c) Sunlight
2. c) Chlorophyll
3. b) Parasite
4. c) Nitrogen
5. c) Stomata
6. c) Roots
7. c) Algae and Fungus
8. c) Starch
9. c) Mushroom
10. b) Atmospheric nitrogen

Revise these notes thoroughly. Focus on the definitions, examples, and the 'why' behind different processes like why insectivorous plants trap insects or how symbiosis works. Good luck with your preparation!