Excretory Mechanism in Earthworm

Subject 

Biology

Topic 

Excretory Mechanism in Earthworm

Class :

SSS 2

Term :

First Term

Week :

Week 8

Instructional Teaching Materials :

• pictures of the excretory system of animals
• Sample alimentary canal of animal

Reference 

• Scheme of Work
• On-line Information
• Textbooks
• Workbooks

Earlier Tutorials 

The pupils have earlier information on

EXCRETORY SYSTEMS

that was beforehand taught as a topic before this specific lesson

Behavioural Objectives :  On the conclusion  of this lesson, the learners will likely be able to

• Describe the excretory mechanism of an earthworm.
• Describe the excretory system of insects.
• Describe the process of urine formation in the excretory mechanism of mammals.

EXCRETORY SYSTEMS AND MECHANISMS

CONTENT

1. Excretory Mechanism in Earthworm
2. Excretory System in Insects
3. Excretory Mechanism in Mammals

Excretory Mechanism in Earthworm

The nephridia is the excretory organ of earthworm. Each segment of the nephridia contains a pair of tubes. Each nephridium is a long coiled tube derived by the growth of ectoderm, and opens into the coelomic fluid of the segment anterior to the nephridiophore. The first part is called the nepridiopore, and it has a minute flattered funnel with the upper lip large than the lower lip. The upper lip is formed mainly of a large central cell which is thickly ciliated on the inner surface of the funnel. The lower lip on the other hand consists of a thickened cluster of small cells which are not ciliated. All the cilia beat into the lumen of the tube. The nephrostome leads into an intrcellular ducts which bears two rows of lateral cilia. Beyond the septum, the tube is narrower and ciliated. It goes into several loops and then becomes the wider brown, ciliated tube which terminates at the nephridiophore. The opening of this pore is regulated by a sphincter. The nephridia of the earthworm are generally supplied with many fine capillaries which ramify among the coils.

Generalized Anatomy of an Earthworm

The earthworm shows the well-developed segmentation that is characteristic of all animals in the phylum Annelida. Although the major nervous, circulatory, and digestive organs are located near the head, more posterior segments contain peripheral structures for all of these systems. These posterior segments are virtually identical to each other. Earthworms are hermaphroditic, possessing both male and female internal reproductive organs.

Excretory System in Insects

Tissues in insects produce nitrogenous waste in the form of soluble potassium urate, which is librated into the blood and taken up by the cells lining the malpighian tubules. The tubules are muscular and their writhing movements facilitate the absorption of urate by stirring up the blood. In the cells of the tubule, the potassium urate reacts with water and carbon (iv) oxide (from respiration) to form potassium trioxocarbonate (iv) and uric acid. The former is reabsorbed into the blood to such an extent that the proximal end of the malpighian tubule becomes filled with solid crystals of uric acid. Water is further reabsorbed by the folded walls of the rectal glands so that by the time urine leaves the body, it is very much more concentrated than the blood.

The remarkable ability of insects to conserve water has contributed towards their success as a group. This is largely due to the action of their malpighian tubules and rectal glands. Insects conserve water more effectively than any other group of animals because they do not drink water. They pass out semisolid waste (uric acid), which contains very little quantity of water.

Excretory Mechanism in Mammals

We shall focus our attention on the formation of urine. The kidneys of mammals accomplish this task by purifying the blood. Some toxic substances such as nitrogenous salt, sodium salt, potassium salt, calcium salt, and urea are removed from the body through this means.

In urine formation, three processes take place:

1. Ultra filtration
2. Selective re-absorption, and
3. Tubular secretion.

Now, as the blood circulates round the glomerulus, ultra filtration occurs. Small molecules such as water, urea, mineral salts, sugar, and plasma solutes pass through the one-cell thick walls of the capillaries and the Bowman’s capsule into the capsular space. Bigger molecules like plasma, protein and the blood cells cannot pass through the barrier which thus acts as a filter. A high pressure in the glomerulus is essential for the filtration process. This is brought about in the following ways:

1. The blood entering the kidney is already at high pressure because the renal artery branches off from the dorsal aorta at only a short distance from the heart.
2. The blood vessel leaving each glomerulus is narrower than the one entering it, thereby increasing the pressure of the blood in the glomerulus further.

The fluid that filters into the Bowman’s capsule is known as glomerula filtrate. It flows down the tubule, and as it passes down the proximal part of the tubule and the Henle’s loop, selective reabsorption take place. In this process, water and useful substances like sugar, amino acid and salts are reabsorbed into the surrounding blood capillaries. The filtrate then moves into the distal part of the tubule. Here, large waste molecules like creatinine are secreted into the tubules. If necessary, ions (hydrogen, potassium and hydrogen carbonate) are secreted into the tubules to keep the osmotic concentration of the blood constant. The fluid that eventually remains in the tubules is concentrated and is known as urine.

An average of 1.5 litres of urine is produced daily. The amount of urea excreted will depend on the protein content of the daily diet. The filtered blood leaving the kidney by the renal vein contains:

1. Less oxygen and glucose, and more carbon (iv) oxide, as a result of cellular respiration and
2. Less nitrogenous wastes, salt and water as a result of excretion.

The urine formed trickles down the ureter and collects in the bladder. When the bladder is full, it contracts discharging the urine out of the body through the urethra.

The mechanism used in urine formation includes the following:

1. Active transports
2. Varying permeability of tubules and
3. Passive diffusion and osmosis.

The Excretory System

Presentation

The topic is obtainable step-by-step

Step 1:

The subject instructor revises the sooner issues

Step 2.

He introduces the topic new topic

Step 3:

The class coach permits the pupils to current their very personal examples and he corrects them when the desires come up

Conclusion :

The class coach wraps up or conclude the lesson by giving out temporary observe to summarize the topic that he or she has merely taught.

The class coach moreover goes spherical to ensure that the notes are correctly copied or correctly written by the pupils.

He or she does the required corrections when and the place  the desires come up.

EVALUATION

1. Describe the excretory mechanism of an earthworm.
2. Describe the excretory system of insects.
3. Describe the process of urine formation in the excretory mechanism of mammals.

Conclusion 

The topic wraps up the subject by giving the learners a complete notice and she or he makes certain that the learners copy the notes accurately . She or he marks the notes and he does the mandatory corrections