EXCRETORY SYSTEMS

Subject 

Biology

Topic 

EXCRETORY SYSTEMS

Class :

SSS 2

Term :

First Term

Week :

Week 7

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

Respiration in Lower Animals

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

• Say the meaning of the word excretion
• say the importance of excretion in animals
• say the organs of excretion in smaller animals

EXCRETORY SYSTEMS

CONTENT

1. Definition of Excretory Systems
2. The Need for Excretion
3. Contractile Vacuoles
4. Flame Cells in Flatworm
5. Malpighian Tubules in Insects
6. Kidneys in Vertebrates
7. Other Excretory Organs in Mammals
8. Stomata and Lenticels

Definition of Excretory Systems

Excretory systems refer to all the cells and organs of any living organism which enables it to eliminate harmful substances away from the body.

Excretion is therefore the removal of toxic wastes of metabolism from the body of living organisms.

The Need for Excretion

Waste products produced in the body by excretion must not be allowed to remain in the because of the following reasons:

1. Waste products when not removed can interfere with normal metabolic activities of the body.
2. Excretion helps to maintain salt and water balance i.e. homeostasis in the body.
3. Some products are poisonous and must never be allowed to accumulate within the body.
4. The excretory products are harmful to the body and so must be removed.
5. All animals are heterotrophic and may eat some materials as food which is not needed by their bodies. These substances and unwanted products of the chemical activities of the body is excretion.
6. Proteins are used for growth and repair but any excess cannot be stored. The initial waste products of the biochemical processes involving protein is ammonia gas. This compound is very poisonous and must be excreted quickly.

Contractile Vacuoles

Contractile vacuole is an organelle or a tool present in Amoeba and different unicellular organisms or protozoans. It’s a easy machine, a small sac lined with a membrane mendacity freely within the cytoplasm. The cell membrane surrounding the amoeba is a semi permeable to water and since the osmotic strain contained in the animal is bigger than outdoors the animal, water enters the cell by osmosis. To counter this, water is secreted into the contractile vacuole as quick because it enters the physique. As this occurs, the contractile vacuole expands and bursts, thus discharging its contents to the outside by way of a small pore within the cell membrane after which the entire course of is repeated. The vitality required by the contractile vacuole is produced by the mitochondria discovered close to the vacuole. The contents of the contractile vacuole are; water, carbon (iv) oxide and nitrogenous wastes.

A contractile vacuole is a sub-cellular structure involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole

Paramecium

The paramecium is a single-celled organism that propels itself by minute, hairlike projections called cilia. Cilia also create currents that sweep food particles toward the paramecium’s gullet for ingestion. The paramecium gets rid of excess water with the help of a contractile vacuole, which pumps water out of the cell.

Flame Cells in Flatworm

These are two longitudinal excretory canals, which open onto the dorsal surface of the flat worm by a number of minute pores. The main canals give off numerous branches, which ramify among the parenchyma cells. The final branches end in flame cells. These are cells, which have intracellular cavities and ducts, with numerous cytoplasmic branches penetrating between the parenchyma cells. Projecting into the cavity of the cell is a bundle of long cilia which arise from basal granules in the cytoplasm.

These cilia are characterised by their flickering movement which give use to t flame cell is a specialized excretory cell found in the simplest freshwater invertebrates, including flatworms, rotifers and nemerteans; these are the simplest animals to have a dedicated excretory system. Flame cells function like a kidney, removing waste materials. Bundles of flame cells are called protonephridia The name ‘flame cells’.

Malpighian Tubules in Insects

Generally, insects are very successful group of animals because of their ability to conserve water, wings to fly, metamorphosis, and small body structure.  On the other hand, they have an extremely efficient excretory system. The malpighian tubules are the excretory organs. They are found between the midgut and the rectum. One end of each tubule opens into the gut, while the other free end floats in the haemoloel of insects. They are long and extremely slender and penetrate among the visera over. The greater part of the horux and abdomen. In the cockroach for example, they are in six groups with about twelve tubules in each group.

Generalized Anatomy of an Insect

All adult insects have three main body parts—the head, which holds an insect’s primary sense organs; the thorax, which is the attachment site for the legs and wings; and the abdomen, which contains the organs for digestion and reproduction. All of the insect’s soft inner body parts are protected by an external skeleton, or exoskeleton, made of semirigid plates and tubes.

Kidneys in Vertebrates

All vertebrates have a pair of kidneys, which type a part of the excretory system. In mammals, the kidneys are bean-shaped, darkish red in colour and surrounded by fats. The right kidney is barely lower in the body than the left. If a kidney is minimize longitudinally into two, it is going to be seen to include two most important areas: an outer darkish colored cortex and an inner lighter colored medulla. When considered underneath a microscope, a kidney consists of blood vessels, kidney tubules or nephrons and connective tissues. Every nephron begins within the cortex as a tiny cup-shaped construction often known as Bowman’s capsule, which surrounds capillaries known as the glomerulus. The Bowman’s capsule leads right into a coiled tube known as the proximal tubule. This goes down to type a U-shaped structure, the Henle’s loop. Finally, it coils once more to type the distal tubul, which twists and  empties right into a gathering duct. Renal artery, which branches from the merchandise and oxygenated blood to the kidney in order that nitrogenous wastes merchandise (urea) might be eliminated.

Section of the Kidney

Approximately one million nephrons (right) compose each bean-shaped kidney (left). The filtration unit of the nephron, called the glomerulus, regulates the concentration within the body of important substances such as potassium, calcium, and hydrogen, and removes substances not produced by the body such as drugs and food additives. The filtrate, urine, leaves the nephron through the long renal tubule. Chemical signals triggered by the body’s need for water and salt cause the walls of the tubule to become more or less permeable to these substances, which are reabsorbed accordingly from the urine.

The blood that leaves the kidney is deoxygenated and is carried away by renal vein to the inferior (posterior) vena cava. The urine formed passes from each kidney into a ureter. The left and right ureters lead to a muscular sac called the bladder in which urine is stored temporarily. The bladder opens to a short tube, urethra, which leads to the exterior.

Other Excretory Organs in Mammals

1. The skin excretes water, salts and urea. Skin excretes wastes by means of sweat glands, which consists of coiled tubes, opening exteriorly as pores. Sweat is composed of 95% water and 3% dissolved salts (e.g. sodium chloride).
2. Lungs excrete carbon (iv) oxide and water. Carbon (iv) oxide can be harmful if it accumulates too much as it forms carbonic acid is capable of upsetting the delicate acid base balance of the body fluids.
3. Liver, in addition to manufacturing chemicals, the liver helps clear toxic substances, such as drugs and alcohol, from the bloodstream. It does this by absorbing the harmful substances, chemically altering them, and then excreting them in the bile

Structure of the Skin

Humans and other vertebrates are covered with a multilayered tissue called skin. The skin consists of an outer, protective layer (epidermis) and an inner, living layer (dermis). The top layer of the epidermis is composed of dead cells containing keratin, the horny scleroprotein that also makes up hair and nails.

Stomata and Lenticels

In general, plants are much less active than animals and produce waste products at a much slower rate. Hence, they have no need for specialised excretory organs. The main excretory products, which are water, oxygen and carbon (iv) oxide, are got rid of by diffusion through the stomata and lenticels.

Excretion in Stomata

Stomata are pores in the epidermis bounded by specialised epidermal cells known as guard cells. In conjunction with the guard cells, other adjacent and distinctive epidermal cells may exist in opening and closing of the pore. These are known as accessory cells. Stomata are usually found at the aerial parts of the stems and leaves and flower parts. Underground rhizomes and some aquatic plants may possess them. They may be irregularly scattered or arranged in parallel rows. The guard cells are bean shaped and fit together with the pore between them. The size of the pore ulters according to how turgid the guard cells are. This in turns depends on the osmotic pressure within the guard cells. When the pressure is low, the guard cells are flabby and the stoma is closed. When it is high, the guard cells are turgid and the stoma opens.

Excretion in Lenticels

They are structurally differentiated parts of the periderm, which stand out because of the very loose cell arrangement and lack of suberization. They vary greatly in size according to species but can be seen as protrusions of loose substance through cracks in the periderm. In a stem undergoing secondary thickening, the first lenticels usually arise beneath the stoma in the epidermis. The cells below the stomata lose their chlorophyll and divide repeatedly to form a losse mass. Gradually, the region of division penetrates deeper into the cortex, and the place of the division of the cells becomes regularly parallel to the surface so that a lenticels phellogen is formed. This proceeds to cut off more and more loose cells towards the exterior and eventually the epidermis is ruptured.

[mediator_tech]

Prominent plants excretory products are water, carbon (iv) oxide and oxygen. They are excreted through the stomata and lenticels. Green plants like tomato and potato have glands that secretes water, a process called guttation. This is seen at the apex and margin. Other waste products produced by plants are tannins, poisonous nitrogenous alkaloids and anthocyanins, which give colour to the petals of many flowers. In order not to interfere with plants activities, these waste products are converted to harmless insoluble compounds and stored within the plant body, e.g., some plant cells contain calcium oxide, glucose and alkaloid compounds.

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. Outline excretory systems.
2. State 5  significance of excretion in living organisms.
3. Write brief notes of the next: (i) Contractile Vacuoles (ii) Flame Cells in Flatworm (iii) Malpighian Tubules in Bugs (iv) Kidneys in Vertebrates

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