Class 7 Science Notes Chapter 1 (Nutrition in Plants) – Science Book

Okay, let's begin with the detailed notes for Chapter 1: Nutrition in Plants, tailored for government exam preparation based on NCERT Class 7 Science.

Chapter 1: Nutrition in Plants - Key Concepts & Notes

1. What is Nutrition?

• The process by which organisms take in food and utilize it for growth, repair, maintenance, and carrying out life processes.
• Nutrients: Components of food essential for our body, such as carbohydrates, proteins, fats, vitamins, and minerals.

2. Why is Nutrition Essential?

• To build bodies (growth).
• To repair damaged parts of bodies.
• To provide energy to carry out life processes.

3. Modes of Nutrition
All living organisms require food. Plants can make their food themselves, but animals (including humans) cannot. Based on how organisms obtain food, nutrition is broadly classified into two types:

• a) Autotrophic Nutrition:

  • 'Auto' = self; 'trophos' = nourishment.
  • Organisms make their own food from simple inorganic substances (like carbon dioxide and water).
  • Organisms exhibiting this mode are called Autotrophs.
  • Example: Green plants.

• b) Heterotrophic Nutrition:

  • 'Heteros' = other; 'trophos' = nourishment.
  • Organisms obtain food prepared by other organisms (plants or other animals).
  • Organisms exhibiting this mode are called Heterotrophs.
  • Examples: Animals, humans, non-green plants (like fungi, Cuscuta).

4. Autotrophic Nutrition in Plants: Photosynthesis

• Definition: The process by which green plants synthesize their own food (in the form of glucose/starch) 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' of the plant. Photosynthesis can also occur in other green parts like stems in some plants (e.g., desert plants).
• Key Components Required:
  • Chlorophyll: The green pigment present in chloroplasts (organelles within plant cells, mainly in leaves). Its function is to trap sunlight energy.
  • Sunlight: The ultimate source of energy for photosynthesis.
  • Carbon Dioxide (CO₂): Taken in from the atmosphere through tiny pores on the leaf surface called stomata.
  • Water (H₂O) & Minerals: Absorbed by the roots from the soil and transported upwards to the leaves through vessels (xylem).
• Process Overview:
  1. Roots absorb water and minerals.
  2. Water is transported to leaves via xylem vessels.
  3. Leaves take in CO₂ through stomata.
  4. Chlorophyll traps sunlight energy.
  5. Using sunlight energy, water and CO₂ are converted into carbohydrates (glucose, later stored as starch).
  6. Oxygen (O₂) is released as a byproduct through stomata.
• Chemical Equation for Photosynthesis:

        Sunlight
  CO₂ + H₂O   --------->   C₆H₁₂O₆  +  O₂
  (Carbon Dioxide + Water) Chlorophyll (Glucose + Oxygen)
  

  (Note: This is a simplified representation. Balancing the equation is usually taught in higher classes, but the components are key)
• Products of Photosynthesis:
  • Glucose (Carbohydrate): The immediate food produced. It is often converted to starch for storage in various parts of the plant (leaves, roots, stem, fruits). The presence of starch in leaves is an indicator that photosynthesis has occurred (tested using iodine solution - turns blue-black).
  • Oxygen: Released into the atmosphere, essential for the survival of most living organisms.
• Stomata:
  • Tiny pores usually found on the underside of leaves.
  • Function:
    • Gas exchange (taking in CO₂, releasing O₂ during photosynthesis).
    • Transpiration (release of excess water vapor).
  • Each stoma is surrounded by two guard cells that control its opening and closing.
• Photosynthesis in Non-Green Leaves: Leaves with pigments like red, brown, or violet also contain chlorophyll. The other pigments mask the green color, but photosynthesis still occurs.
• Photosynthesis in Algae: Algae (often seen as slimy green patches in ponds) are simple organisms containing chlorophyll and perform photosynthesis.

5. Other Modes of Nutrition in Plants (Heterotrophic Nutrition)

Some plants lack chlorophyll or grow in conditions where certain nutrients are scarce, leading them to adopt heterotrophic modes.

• a) Parasitic Nutrition:
  • Organisms (parasites) derive nutrition directly from the body of another living organism (host), often harming the host.
  • Example: Cuscuta (Amarbel) - A yellow, tubular plant that lacks chlorophyll. It twines around a host plant and uses specialized structures called haustoria (not explicitly in Class 7 text, but implied by absorption) to absorb ready-made food from the host's vascular tissues.
• b) Insectivorous Nutrition:
  • Plants that trap and digest insects to supplement their nutritional requirements, particularly nitrogen, as they often grow in nitrogen-deficient soil.
  • These plants are green and perform photosynthesis but rely on insects for nitrogen.
  • Examples:
    • Pitcher Plant: Leaf is modified into a pitcher-like structure with a lid. Insects attracted by nectar slip inside and are trapped by downward-pointing hairs. Digestive juices secreted inside the pitcher digest the insect.
    • Venus Flytrap: Leaves have hinged lobes with trigger hairs. When an insect touches the hairs, the lobes snap shut, trapping the insect, which is then digested.
• c) Saprotrophic Nutrition:
  • Organisms (saprotrophs or saprophytes) obtain nutrients from dead and decaying organic matter.
  • They secrete digestive juices onto the matter, converting it into a soluble form, which is then absorbed.
  • Examples: Fungi (like mushrooms, yeast, bread mould), some bacteria. Fungi are often seen growing on stale bread, pickles, leather, or rotting wood, especially during warm and humid conditions.
• d) Symbiotic Nutrition (Symbiosis):
  • A close association between two different organisms where both benefit mutually.
  • Examples:
    • Lichens: A symbiotic association between an alga (contains chlorophyll, provides food through photosynthesis) and a fungus (provides shelter, water, and minerals absorbed from the surroundings).
    • 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.

6. Replenishment of Nutrients in the Soil

• Plants continuously absorb mineral nutrients from the soil, leading to their depletion over time.
• It's essential to replenish these nutrients for healthy plant growth.
• Methods:
  • Adding Manures and Fertilizers: Farmers add organic manure or chemical fertilizers to the soil. Fertilizers are rich in specific nutrients like Nitrogen (N), Phosphorus (P), and Potassium (K) (often referred to as NPK).
  • Nitrogen Fixation by Bacteria: The symbiotic relationship between Rhizobium bacteria and leguminous plants naturally enriches the soil with nitrogen. Growing leguminous crops often helps restore soil fertility.

Key Takeaways for Exams:

• Know the definitions of all key terms (Nutrition, Autotroph, Heterotroph, Photosynthesis, Chlorophyll, Stomata, Parasite, Host, Insectivorous, Saprotrophy, Symbiosis, Lichens, Rhizobium).
• Understand the process of photosynthesis: requirements, site, products, and the equation components.
• Be able to identify the mode of nutrition based on examples (Cuscuta - Parasitic, Pitcher Plant - Insectivorous, Fungi - Saprotrophic, Lichen/Rhizobium - Symbiotic).
• Understand why insectivorous plants trap insects (Nitrogen).
• Know the components and benefits of symbiotic relationships (Lichen, Rhizobium).
• Understand why soil nutrients get depleted and how they are replenished (Fertilizers, Manure, Nitrogen Fixation by Rhizobium in legumes).

This covers the essential points from NCERT Class 7, Chapter 1, focusing on details relevant for government exam preparation. Remember to correlate these notes with the diagrams in the NCERT textbook for better understanding.