Feeding

Animals obtain their food either directly from plants or by consuming other animals. Their nutritional needs are met through the food they ingest. Different organisms have unique ways of obtaining and consuming food, known as feeding mechanisms.

Feeding Mechanisms in Some Animals

1. Absorption: Organisms with this mechanism lack a mouth or digestive tract. They absorb nutrients through their body surface, often from the host's intestine. For instance, tapeworms attach to their host using hooks and suckers.

2. Biting and Chewing: Organisms with this mechanism have specialized mouthparts for cutting and grinding food. These include:
   • Labrum (Upper Lip): Helps keep food in the mouth.
   • Labium (Lower Lip): Prevents food from spilling.
   • Mandibles: Used to cut and chew food.
   • Maxillae: Further break down food after cutting.
3. Sucking: Found in organisms like mosquitoes, butterflies, and houseflies. These insects have modified mouthparts designed for sucking liquids.
4. Grinding: Common in mammals such as humans, cattle, and sheep. These animals grind food using strong teeth made of enamel and dentine.
5. Trapping and Absorption: Insectivorous plants use specialized structures to trap prey. Bright colors, scents, and sugary liquids attract insects, which are then digested by enzyme-rich secretions.

Feeding Habits

1. Filter Feeding: Involves straining small food particles or organisms from water. Examples include flamingos and baleen whales. Clams, for instance, use gills to filter food particles:
   • Hair-like cilia create water currents over the gills, trapping food particles.
   • The trapped particles are directed into food grooves for consumption.
2. Fluid Feeding: Animals consume liquids from plants, animals, or liquefied solid food. There are two main types:
   • Wallowers: Absorb nutrients directly from their surroundings. Tapeworms, for example, absorb food through their body surface inside the host.
   • Suckers: Extract fluids from plants or animals. Examples include mosquitoes and aphids.
3. Saprophytic Feeding: Saprophytes, like mushrooms and rhizopus, feed on decaying matter. They release enzymes to break down organic material externally and absorb the nutrients.

Feeding in Hydra

Hydra feed on small aquatic organisms, capturing them with stinging cells (nematocysts) on their tentacles. The prey is passed into the mouth, where digestive enzymes break it down in the gut. Nutrients are absorbed by specialized cells, while waste is expelled through the mouth.

Feeding in Protozoa

Protozoa use a holozoic mode of nutrition. They engulf prey along with water, forming food vacuoles. Enzymes digest the food, and nutrients are absorbed into the cytoplasm. Indigestible materials are expelled through the cell membrane.

Feeding in Mammals

Mammals are classified based on their diet into herbivores (plant-eaters), carnivores (meat-eaters), and omnivores (eat both plants and animals). Most mammals have heterodont dentition, meaning their teeth are specialized for different functions. Types of teeth include:

• Incisors: Used for cutting food.
• Canines: Designed for tearing food.
• Premolars and Molars: Adapted for grinding food.

Humans have two sets of teeth: temporary milk teeth, which appear during childhood, and permanent teeth, which replace the milk teeth as they fall out.