1. AMOEBA PROTEUS (A PROTOZOAN)

Amoeba proteus is a unicellular organism, it is usually colorless and looks like jelly – like mass .Amoeba is can only be seen through an electron microscope. Amoeba is a protozoan that has no definite shape. It is clear and transparent; it has only one thin membrane.

1. Habitat:

It is found in muddy water, at the bottom of ponds and ditches. Another name for pseudo podia is false feet.

2. Function of Organelles of Amoeba

1. Plasma lemma (Cell membrane)

This is a thin membrane which protects the amoeba and allows the exchange of material.

2. Protoplasm

This consists of a dark central nucleus and the cytoplasm.

3. Ectoplasm

This is the granular outer zone of the cytoplasm.

4. Endoplasm

This is the granular inner zone of the cytoplasm.

5. Nucleus

It is spherical in shape; it controls the metabolic activities of the organism.

6. Contractile Vacuole

It helps in excretion and osmoregulation.

7. Food Vacuole

They are numerous food vacuoles of different sizes and shape, they are bounded by a membrane enclosing food in a droplet of water. It is here that digestion of food takes place in Amoeba.

8. Pseudopodia or “Fast Feet”

Pseudopodia are not permanent structures as they appear and disappear all the time. They are used for movement and to evolved food.

3. Mode Of Life Of Amoeba

• Movement: Amoeba move using Pseudopodia. Amoeba put out his Pseudopodia in the direction where it want to move and its whole body move in that direction.
• Feeding: Amoeba feed on small micro organisms or on decayed foods particles that may be present in water. When Amoeba comes across a food particle it surrounds it with its Pseudopodia in the presence of a droplet of water in a structure called the food vacuole. It is inside this food vacuole that food gets digested. The useful part of the food is absorbed and the undigested part is left behind as waste as the organism move away from the spot.
• Gaseous Exchange and Respiration: Amoeba obtains dissolved oxygen for respiration from surrounding water and also sends out carbon dioxide into the surrounding water. These exchanges occur by simple diffusion through the thin plasma lemma. Oxygen diffuses into the surrounding water.
• Excretion and Osmoregulation: Carbon dioxide gets dissolved in the cytoplasm it collects in a little space called the contractile vacuole. This contractile vacuole finally burst when it is full releasing it content into the surrounding water. A new vacuole may then be formed in another part of a cell. Entry of water into the cytoplasm is due to the fact that, the water in the cytoplasm is more concentrated than the surrounding water.

NB: Amoeba in marine environment lacks a contractile vacuole because the concentration of water in it cytoplasm is equal to the concentration of the surrounding water. So the amount of water entering the cytoplasm is equal to the amount of water leaving the cytoplasm to the surrounding.

• Reproduction: Amoeba reproduces asexually by binary fission. The parent cell divides into two identical daughter cells.
• Irritability: Amoeba has no sense organ but is able to detect environmental changes or danger near it. If it is touch with a sharp object like needle the stimulated region contracts away from the stimulus by forming Pseudopodia in the opposite direction and moving away. But when Amoeba senses the presence of food, it moves towards it.
• Encysting: During unfavorable conditions such as draught when ponds dry up, Amoeba protects itself by forming a thick outer covering called a cyst. It remains inside this cyst until favorable conditions return. The cyst then breaks open and the Amoeba then comes out and lives a normal life again. Sometimes, where inside the cyst, Amoeba undergoes multiple fission releasing young ones when the cyst open.

4. Economic Importance Of Amoeba

-Amoeba causes Amoebic dysentery.

2. THE MALARIA PARASITE (PLASMODIUM SPECIES)

The malaria parasite (Plasmodium species) is the causative agent for malaria. Four species of Plasmodium are pathogenic to man. They are:

• Plasmodium falciparium ( most virulent)
• Plasmodium virax
• Plasmodium ovale
• Plasmodium malaria

Plasmodium is transmitted from man to man by the bite of an infected female anopheles mosquito. The female anopheles mosquito acts as a vector for the malaria parasite. This is because it has piercing and sucking mouth parts with which it can pierce the skin and suck blood.

The male anopheles mosquito does not have piercing mouth parts, it has only sucking mouth parts. The male anopheles mosquito feeds on plant juice.

1. Life Cycle Of Malaria Parasite

When an infected female anopheles mosquito is sucking blood from a healthy person, it injects some of the saliva containing sporozoites (Infective form of the parasite) into the blood stream. The sporozoites are carried by blood to the liver where they enter the liver cell. In the liver cell, they develop into schizonts which later divide to give merozoites. The liver cell burst and releases the merozoites into the blood stream. This cycle that occurs in the liver is called pre-erythrocytic cycle. The development of sporozoites to schizonts is asexual and is known schizogony. The merozoites enter red blood cell where they develop into trophozoites. The trophozoites develop into schizonts which later form merozoites. The red blood cells burst releasing merozoites and metabolic waste of parasite into the blood stream. Metabolic waste is responsible for fever associated with malaria. The destruction of red blood cells leads o anaemia. Some of the merozoites from the liver enter the red blood cell; develop into male and female gametes which fuse to form a zygote called ookinete. These zygotes divide to form sporozoites which enter the salivary gland of the mosquito.

2. Effects Of Malaria

- Toxins from parasite cause fever.

- Destruction of red blood cells causes malaria.

- Can cause enlargement of the spleen.

- People living in malaria endemic areas are re-infected.

3. Signs And Symptoms Of Malaria

Symptoms include; fever, flu-like, illness, shaking chills, head ache, muscle ache, tired. Nausea, vomiting and diarrhea may occur. Anemia and jaunalice may occur. Infection with falciparium species may leads to kidney failure.

4. Prevention and Control Of Malaria

• Anti-malaria drugs should be taken periodically as prescribed by the doctor.
• By destruction of adult mosquito using insecticides.
• By sleeping under impregnated mosquito nets.
• Breathing places like ditches, pools should be filled or drained.
• Clear all pushes in the surrounding as mosquitoes hide there in the day and come out to bite in the night.
• Fishes like Gambusia and panchax that feed on mosquito larvae should be introduced into areas where mosquitoes breed. Eg: rice field.
• Windows and door nets can be coated with mosquito repellant.
• Bore holes on empty tins before throwing to prevent water from collecting inside and forming breeding ground for mosquitoes.
• Oil, example: kerosene should be sprayed on stagnant water to suffocate mosquito larvae.

3. SPIROGYRA

Structure:

Spirogyra jogensis is simple multicellular green algae. It is found on or below the surface of fresh water, ponds, ditches and slow running stream. It forms a slimy bright-green tangled mass called colony. Each spirogyra is an unbranched filament. It consists of a single row of cylindrical cell joined end-to-end.

• All the cells are identical. Each cell has a thick cellulose cell wall lined inwardly by the cytoplasm.
• In the cytoplasm is a large central vacuole containing cell sap.
• A single nucleus is suspended in the centre of eac0h cell by cytoplasmic strands.
• There is also a part of chloroplast in the form of spiral bands.
• Each chloroplast has protein like bodies called pyrenoids.
• The pyrenoids serve as food reserve or where food is stored.

1. Mode Of Life Of Spirogyra

• Feeding: Spirogyra is capable of manufacturing its food by the process of photosynthesis. It produces glucose which is stored in the pyrenoids.
• Movement: Spirogyra cannot move except carried along by water currents.
• Reproduction: Spirogyra reproduces asexually by binary fission and sexually by conjugation. Conjugation begins when two filaments lie side by side to each other. Lateral out growths form on the adjacent of each conjugant. At the point of contact, the cross wall dissolve resulting in conjugation till formation. The male gamete migrates into the adjacent cell. Fusion of the gamete results in zygospore formation which then germinates and gives rise to a filament by transverse division.

1. FUNGI

Fungi are found in damp tropical countries. They are sometimes considered to be plants that have lost their chlorophyll. Types of fungi include; Rhisopus nigricans (bread mould), yeast, mushroom, mucor penicillium, Candida, etc…

1. General Characteristics Of Fungi

-Fungi lack chlorophyll.

-Fungi are either saprophytic or parasitic.

-They have cell wall made of chitin.

-They store food as glycogen.

-They reproduce by means of spores.

-Simplest forms are unicellular. Eg: yeast and majority consist of slender filaments called hyphae.

1. The Bread Mould (Rhizopus nigricans)

Rhizopus is a common mould fungus which grows on moist decaying bread, fruits and other organic matter.

1. Structure:

Structure of a Rhizopus nigricans

Rhizopus can be seen with the naked eye as a white fluffy mss. When observed under the microscope, it is seen as inter women fine threads called hyphae. These hyphae are called mycelium. There are three types of hyphae:

5. The horizontal hyphae is called the stolon
5. The root-like hyphae called rhizoids and
5. The sporangiophore (reproductive hyphae)

Walls of the hyphae are made up of chitin. At the tip of the sporangiophore is the sporangium which when mature is black and contains spores. A dome shaped structure called columella occupies the center of the sporangium. The Rhizoids grow down into the substrate (stale bread). Rhizoids serve as anchoring and feeding hyphae.

1. Mode Of Life Of Rhizopus

• Nutrition: Rhizopus carries out saprophytic nutrition. i.e. It feeds on dead decaying food matter. The Rhizoids secretes enzymes into the substrate such as moist bread. The enzymes digest the food substances in the bread which are then absorbed by the Rhizoids into the hyphae. This type of digestion outside the body or cells of the organism is known as extracellular digestion and it occurs in all saprophytes.
• Reproduction: Rhizopus reproduces both sexually and asexually (more frequent). Asexual reproduction is by means of spores.