BIOLOGY OF EARTHWORM presentation ppt with labelled idagrams

Earthworms are known as ‘friends of farmers’ because they improve soil fertility and
structure. Their burrowing activities aerate the soil, enhance drainage, and mix organic matter with soil minerals.
They accelerate decomposition and nutrient cycling, benefiting crop productivity. Vermicomposting, a process using
earthworms to convert organic waste into manure, is widely practiced for sustainable agriculture.

1. Biology of Earthworm – Chapter 1 Prepared by: Alumpunsang Doley & Nikita Das

2. Introduction to Earthworm Earthworms are invertebrates belonging to the phylum Annelida and class Oligochaeta. They are widely distributed in moist soil rich in organic matter. Their segmented body and burrowing habits make them important organisms in soil ecosystems. Earthworms play a crucial role in soil aeration, mixing of soil layers, and enhancing soil fertility by decomposing organic matter and recycling nutrients.

3. Habit and Habitat Earthworms live in damp soil, decaying organic matter, humus-rich fields, and gardens. They avoid light and prefer dark and moist conditions. Earthworms create burrows in the soil that increase soil aeration and water absorption. They are nocturnal and emerge from their burrows during the night or after rainfall. Their presence is an indicator of fertile soil.

4. External Features The body of the earthworm is long, cylindrical, and bilaterally symmetrical. It is divided into more than 100 segments or metameres. The dorsal side of the body is dark, while the ventral side is pale. The anterior end has the mouth, while the posterior end bears the anus. Segments 14–16 form a thickened glandular band called the clitellum, which is important for reproduction.

5. Digestive System The digestive system of earthworm is a straight tube running the length of the body. The mouth opens into the buccal cavity, followed by the pharynx, oesophagus, gizzard, and intestine. The gizzard helps in grinding the food into fine particles. The intestine absorbs nutrients and digests organic matter. The undigested waste is expelled through the anus as worm castings, which enrich the soil with nutrients.

6. Circulatory System Earthworms have a closed circulatory system with blood vessels, capillaries, and hearts. Blood is red in colour due to the presence of hemoglobin dissolved in plasma. The dorsal vessel pumps blood forward, while the ventral vessel carries blood backward. The blood is circulated to all parts of the body, ensuring efficient transport of oxygen, nutrients, and waste products.

7. Respiration Respiration in earthworms takes place through their moist skin by simple diffusion. The skin is richly supplied with blood capillaries, which help in the exchange of gases. Oxygen diffuses directly into the blood, and carbon dioxide diffuses out. For this reason, earthworms can only survive in moist conditions and die if their skin dries out completely.

8. Excretory System Excretion in earthworms is carried out by segmentally arranged tubular structures called nephridia. These are of three types – septal, integumentary, and pharyngeal nephridia. Nephridia remove nitrogenous wastes from the body and help maintain water balance. The excretory system ensures homeostasis and the survival of the organism in varied soil conditions.

9. Nervous System The nervous system of earthworm consists of a nerve ring around the pharynx and a ventral nerve cord running the length of the body. The nerve cord bears paired ganglia in each segment, which control local movements. Earthworms respond to touch, light, vibrations, and chemical stimuli through sensory cells present in the epidermis.

10. Reproductive System Earthworms are hermaphrodites, possessing both male and female reproductive organs. Testes are present in the 10th and 11th segments, while ovaries are located in the 13th segment. Fertilization is external and takes place in a cocoon secreted by the clitellum. The cocoon develops into young earthworms after embryonic development, ensuring continuity of the species.

11. Economic Importance Earthworms are known as ‘friends of farmers’ because they improve soil fertility and structure. Their burrowing activities aerate the soil, enhance drainage, and mix organic matter with soil minerals. They accelerate decomposition and nutrient cycling, benefiting crop productivity. Vermicomposting, a process using earthworms to convert organic waste into manure, is widely practiced for sustainable agriculture.