Grade 7 Chapter 4: Nutrition in Living Organisms

Introduction to Nutrition

Nutrition is the process of taking in food and utilizing it for energy, growth, and repair of the body. All living organisms need food to survive and perform various life processes. The way organisms obtain and use their food varies greatly across the living world.

Autotrophic Nutrition

Autotrophic nutrition is a mode of nutrition where organisms produce their own food from simple inorganic substances like carbon dioxide and water, using light energy or chemical energy.

Photosynthesis: Food Production in Plants

Green plants are autotrophs. They make their own food through a process called photosynthesis.

• Definition: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy (food) using carbon dioxide and water.
• Raw Materials:
  • Carbon Dioxide ($CO_2$): Taken from the atmosphere through stomata on leaves.
  • Water ($H_2O$): Absorbed from the soil by roots.
  • Sunlight: Energy source, captured by chlorophyll.
  • Chlorophyll: The green pigment present in chloroplasts, responsible for absorbing sunlight.
• Products:
  • Glucose ($C_6H_{12}O_6$): The food (sugar) produced.
  • Oxygen ($O_2$): Released as a byproduct into the atmosphere.
• Equation: $6CO_2 + 6H_2O + \text{Sunlight Energy} \xrightarrow{\text{Chlorophyll}} C_6H_{12}O_6 + 6O_2$

Role of Stomata and Transport

• Stomata: Tiny pores mainly on the underside of leaves, responsible for the exchange of gases ($CO_2$ intake, $O_2$ release) and transpiration (water vapor loss).
• Xylem: Plant tissue that transports water and minerals from the roots to the leaves.
• Phloem: Plant tissue that transports the food (glucose) prepared in the leaves to all other parts of the plant.

Heterotrophic Nutrition

Heterotrophic nutrition is a mode of nutrition where organisms cannot synthesize their own food and depend on other organisms for their nutritional needs.

1. Saprophytic Nutrition

• Definition: Organisms obtain nutrients from dead and decaying organic matter. They secrete digestive juices onto the dead matter and absorb the digested nutrients.
• Examples: Fungi (e.g., mushrooms, yeast, bread mould), and some bacteria. They play a crucial role as decomposers in ecosystems.

2. Parasitic Nutrition

• Definition: Organisms (parasites) obtain food from another living organism (host) without killing it, but often causing harm. The host is usually weakened.
• Examples:
  • Plants: Cuscuta (Dodder plant) which lacks chlorophyll and grows on other plants.
  • Animals: Lice, bedbugs, tapeworm, leeches.

3. Insectivorous Plants

• Definition: These are green plants that perform photosynthesis but also trap and digest insects to obtain essential nutrients, primarily nitrogen, which they cannot get sufficiently from the soil they grow in.
• Examples: Pitcher plant, Venus flytrap, Sundew. They have specialized structures to catch insects.

4. Symbiotic Nutrition (Symbiosis)

• Definition: A relationship between two different organisms where both organisms benefit from each other.
• Examples:
  • Lichens: An association between an alga (provides food through photosynthesis) and a fungus (provides shelter, water, and minerals).
  • Rhizobium bacteria: Live in the root nodules of leguminous plants (e.g., peas, beans). The bacteria convert atmospheric nitrogen into a usable form for the plant, and in return, the plant provides food and shelter to the bacteria.

Summary

• Nutrition: Process of obtaining and utilizing food.
• Autotrophic Nutrition: Organisms make their own food (e.g., green plants via photosynthesis).
• Photosynthesis: Uses $CO_2$, $H_2O$, sunlight, chlorophyll to produce glucose and $O_2$.
• Heterotrophic Nutrition: Organisms depend on others for food.
  • Saprophytic: From dead and decaying matter (e.g., fungi).
  • Parasitic: From living hosts, causing harm (e.g., Cuscuta, lice).
  • Insectivorous: Trap insects for nitrogen (e.g., Pitcher plant).
  • Symbiotic: Mutual benefit (e.g., lichens, Rhizobium).