Modes of Nutrition | Biology for JAMB PDF Download

Autotrophic Nutrition

Autotrophic nutrition refers to the process by which organisms synthesize their own food using simple inorganic substances. Autotrophs are self-sufficient and do not rely on consuming other organisms for nutrition. There are two types of autotrophic nutrition:

Photosynthesis

• Photosynthesis is the process through which green plants and some other organisms convert light energy into chemical energy to synthesize organic compounds, primarily glucose. It occurs in the chloroplasts of plant cells and involves the following steps:
• Light energy is absorbed by chlorophyll pigments.
• Carbon dioxide (CO₂) from the atmosphere enters the leaves through stomata.
• In the presence of light energy, water (H₂O) from the roots is split into hydrogen and oxygen.
• Hydrogen from water combines with carbon dioxide to form glucose.
• Oxygen is released as a byproduct.

Example: Green plants like wheat, maize, and trees such as mango and coconut trees carry out photosynthesis.

Chemosynthesis

• Chemosynthesis is a process in which certain bacteria and archaea use energy derived from the oxidation of inorganic chemicals to synthesize organic compounds. These organisms are commonly found in deep-sea hydrothermal vents and other extreme environments.

Example: Bacteria in hydrothermal vents utilize chemical energy from sulfur compounds to produce carbohydrates.

Heterotrophic Nutrition

Heterotrophic nutrition involves obtaining organic nutrients by consuming other organisms. Heterotrophs cannot produce their own food and depend on external sources for sustenance. There are several types of heterotrophic nutrition:

Holozoic Nutrition

• Holozoic nutrition is the process of obtaining nutrients by ingesting solid organic matter. This type of nutrition involves the following steps:
• Ingestion: The organism ingests food through the mouth or specialized structures.
• Digestion: The ingested food is broken down into simpler forms by mechanical and chemical processes.
• Absorption: The digested food is absorbed and assimilated into the organism's cells for energy and growth.

Example: Animals such as sheep and humans obtain nutrients through holozoic nutrition by consuming a variety of food, including plants and other animals.

Parasitic Nutrition

Parasitic nutrition refers to the mode of nutrition in which an organism, known as a parasite, lives on or inside another organism, known as the host, and obtains nutrients from it. Parasites harm the host organism in the process. There are different types of parasites:

• Roundworm: Roundworms are parasitic organisms that live in the intestines of animals, including humans, and obtain nutrients from the host's digested food.
• Tapeworm: Tapeworms are parasitic flatworms that attach themselves to the walls of the host's intestines and absorb nutrients from the host's digested food.
• Loranthus: Loranthus is a parasitic plant that attaches itself to the branches of host trees and absorbs nutrients from the host plant.

Saprophytic Nutrition

Saprophytic nutrition involves obtaining nutrients by decomposing dead organic matter. Saprophytes play a vital role in the recycling of nutrients in ecosystems. The process of saprophytic nutrition includes the following steps:

• Secretion: Saprophytes release digestive enzymes onto the dead organic matter.
• Extracellular Digestion: The enzymes break down complex organic compounds into simpler forms outside the organism's body.
• Absorption: The broken-down nutrients are absorbed by the saprophyte's cells for energy and growth.

Example: Fungi such as Rhizopus (bread mold) and mushrooms obtain nutrients through saprophytic nutrition by decomposing dead plants and animals.

Carnivorous Plants

Carnivorous plants are unique types of plants that have adapted to grow in nutrient-poor environments. They capture and digest small animals to supplement their nutrient requirements. There are various mechanisms employed by carnivorous plants:

• Sundew: Sundew plants have sticky tentacles on their leaves that trap small insects. The insect is then digested by the plant's enzymes.
• Bladderwort: Bladderwort plants have bladder-like structures with a vacuum mechanism that traps and digests small aquatic organisms.