Biological Processes in Heterotrophs

Heterotrophs and Nutrition

Heterotrophs are living beings which feed on organic matter produced by other living things. They transform this matter to obtain nutrients and energy.

The Process of Digestion

1. Ingestion: The intake of food into the body through the mouth.
2. Digestion: The transformation of food into nutrients which the body can absorb. There are two types:
   • Intracellular digestion: Takes place inside the cells of single and primitive multicellular organisms.
   • Extracellular digestion: Takes place inside the digestive tube and not in individual cells.
   The transformation of food is both mechanical and chemical.
3. Absorption: The passage of nutrients from the digestive system into the blood. The blood carries the nutrients to the cells.
4. Egestion: The elimination of undigested and waste products from the digestive system. These products are transformed into faeces and expelled from the organism.

Types of Respiration

• Cutaneous respiration: Gas exchange is carried out through the skin, which is very thin and moist.
• Branchial respiration: Gas exchange takes place through the gills. Gills are thin extensions on the surface of the body, surrounded by blood vessels.
• Tracheal respiration: Gas exchange takes place through internal tubes.
• Pulmonary respiration: Gas exchange takes place in the lungs. Lungs are internal cavities which have very thin, damp walls of blood vessels.

The Circulatory System

1. Open circulatory system: The circulating fluid is pumped by the heart. From here, it flows through the body cavity, directly to the internal organs.
2. Closed circulatory system: The blood always circulates inside blood vessels, pumped by a heart. The vessels deliver blood to the body cells and return it to the heart.

Interaction with the Environment (Topic 3)

All living beings interact with their environment and with other living beings to survive.

Elements of Interaction

1. Stimuli: These are detectable changes in the internal or external environment. They can be physical, chemical, and biotic.
2. Receptors: These are structures which receive stimuli from the external or internal environment.
3. Coordination systems: These consist of organs which process information received by the receptors and produce a response.
4. Responsive organs: These are structures which produce responses, such as muscles and glands in animals.

Nervous and Endocrine Systems

The nervous system regulates the body's activities and responses. It works by means of specialized cells called neurons which transmit information in the form of nerve impulses.

The endocrine system regulates and coordinates body functions.