Kingdom Protista – Phylum Protozoa

The first page introduces Kingdom Protista and Phylum Protozoa. The word is written in the source as derived from protos meaning first or primitive and zoon meaning animal.

General Characters of Phylum Protozoa

1. They are unicellular and mostly microscopic.
2. They may be free-living and found in fresh water, marine water or damp soil. Some are parasites, while a few are saprophytes and commensals.
3. The body may be naked or covered with a definite pellicle.
4. The protoplasm is divisible into outer ectoplasm and inner endoplasm.
5. Locomotory organs may be pseudopodia in Rhizopoda, cilia in Ciliata and flagella in Flagellata, while locomotory organs are absent in Sporozoa.
6. Respiration takes place through the general body surface by diffusion.
7. Nutrition may be holozoic (animal-like), holophytic (plant-like), saprophytic or parasitic.
8. Reproduction occurs by both sexual methods such as conjugation or syngamy and asexual methods such as budding, binary fission or multiple fission.

Classification of Protozoa

The notes classify Protozoa into four classes mainly on the basis of locomotory organs.

Paramecium

Habit and Habitat

• Paramecia are freshwater organisms found in lakes, rivers, streams, reservoirs and ponds.
• They are abundantly found in stagnant water where organic matter is plentiful.
• They feed upon bacteria, small protozoa and other dead and decaying matter in water with the help of oral cilia.
• Reproduction takes place by both asexual and sexual methods. Asexual reproduction occurs by transverse binary fission and sexual reproduction by conjugation.

General Shape

The source describes Paramecium as slipper-like or slipper-shaped because the living cell resembles the sole of a shoe or slipper. The cytoplasm is divided into an outer distinct part called ectoplasm and an inner granular part called endoplasm.

Structure of Paramecium

1. Cilia

Cilia are longitudinal hair-like structures distributed over the pellicle. At the posterior end they are generally larger and thicker and form a caudal tuft. Each cilium arises from the centre of a hexagonal depression in the pellicle.

The source describes two functional types:

2. Pellicle

The pellicle is described as a thin, plastic, double-layered membrane covering the cytoplasm of Paramecium. Under microscopic view it shows numerous hexagonal depressions. A cilium arises from the centre of each depression, while thread-like structures associated with trichocysts occur near the depressions.

3. Trichocyst

Trichocysts are oval, elongated and bag-like structures arranged perpendicularly near the inner wall of the pellicle. They may evert as sticky thread-like substances, helping the organism attach to a substratum and probably contributing to defence.

4. Oral Groove

The oral groove is a large depression on the ventro-lateral side of the body. It leads to the buccal cavity and then into a funnel-shaped structure called the gullet. The source states that the cytopharynx helps in the production of new food vacuoles.

5. Cytopyge

The cytopyge is a temporary aperture near the posterior end on the ventro-lateral side. It is also called the anus or anal aperture, through which undigested material and other excretory wastes are eliminated.

6. Nucleus

Paramecium shows nuclear dimorphism and contains two types of nuclei:

7. Food Vacuoles

Many non-contractile food vacuoles occur in the cytoplasm. They move through the endoplasm in a circulating manner described in the source as cyclosis. Their shape and size vary with the quantity of food particles. Food vacuoles are also called gastrioles in the scan.

8. Contractile Vacuoles

Two contractile vacuoles occur on the dorsal surface in the anterior and posterior regions. They are star-shaped and perform osmoregulation. The source also states that they assist in removal of carbon dioxide and excretory products. Each is surrounded by about 6–8 radial canals.

Reproduction in Paramecium

Paramecium reproduces by both asexual and sexual methods. The most common asexual method is transverse binary fission, while the sexual method described in detail is conjugation.

A. Transverse Binary Fission

1. A fully developed Paramecium stops feeding and becomes less active.
2. The body starts elongating.
3. The micronucleus divides mitotically.
4. The macronucleus divides amitotically.
5. The oral groove starts disappearing and a constriction appears at the centre of the body.
6. A new oral groove develops on each side of the constriction.
7. The constriction deepens and ultimately partitions the cytoplasm.
8. The anterior daughter is called the proter and the posterior daughter the opisthe.
9. The two daughter Paramecia separate and begin independent life.

A single binary fission is stated to take about 30–120 minutes, depending on temperature, food availability and population density. In 24 hours it may occur about 2–3 times, producing about 4–8 individuals.

Why Does Paramecium Never Get Old?

B. Sexual Reproduction – Conjugation

1. The macronucleus of each conjugant starts disappearing and the micronucleus undergoes meiosis to produce four haploid micronuclei.
2. Three of the four haploid nuclei disappear in each conjugant.
3. The remaining nucleus divides unequally to form a larger stationary or female pronucleus and a smaller migratory or male pronucleus.
4. A protoplasmic bridge forms between the conjugants and exchange of migratory male pronuclei takes place.
5. The pronuclei in each conjugant unite to form a diploid synkaryon or zygote nucleus.
6. The two Paramecia separate and are called ex-conjugants.
7. The zygote nucleus of each ex-conjugant divides three times to form eight nuclei. The source states that four become macronuclei, three degenerate and one remains as a micronucleus.
8. The remaining micronucleus divides into two; the source then describes each daughter Paramecium as having one micronucleus and two macronuclei.
9. Further mitotic divisions of the micronuclei and the Paramecia occur.
10. The source concludes that eight Paramecia are formed after conjugation of each conjugant.

Significance of Conjugation

• It helps in restoration or regeneration of cytoplasmic parts of the body and makes Paramecium efficient for binary fission.
• Fusion of nuclear materials helps heredity and variation.
• Formation of new macronuclei assists control of metabolic activities.
• The source states that four daughter Paramecia are formed from each ex-conjugant, helping multiplication of the population.

Autogamy

The source states that it was first reported in Paramecium aurelia, a binucleate species, and occurs in a single individual. The macronucleus breaks and disintegrates, while the two micronuclei divide first by meiosis and then by mitosis. The notes state that eight haploid daughter nuclei are formed.

Cytogamy

It resembles conjugation in that two small Paramecia temporarily unite by their oral surfaces. The source states that the male and female pronuclei of the same individual fuse to form a synkaryon, as in autogamy.

Malarial Parasite – Plasmodium vivax

Habit and Habitat

• The source describes it as cosmopolitan in distribution and mostly found in tropical and subtropical parts of the world.
• Plasmodium is described as a digenetic intracellular parasite living in human liver cells or red blood cells and in the wall of the stomach of the female Anopheles mosquito.
• The notes list four species responsible for malaria: P. vivax, P. falciparum, P. malariae and P. ovale.

Structure of Plasmodium

A. Trophozoite

A fully grown parasite is described as an amoeboid and uninucleated trophozoite. Its body is covered by a plasma membrane. A distinct nucleus with nucleolus is present in the cytoplasm.

• Cytoplasm contains dark Palade’s granules.
• Endoplasmic reticulum occurs as smooth or rough vesicles.
• Mitochondria are very few in number and are described as having peripheral cristae.
• Food vacuoles containing haemozoin are present.

B. Sporozoite

Sporozoites are described as small, sickle-shaped, uninucleated and motile forms of the parasite. The source states a length of about “10–15” and labels the form as capable of wriggling movements. Each sporozoite consists of pellicle, cytoplasm and nucleus.

Life Cycle of Plasmodium vivax

The source describes Plasmodium vivax as a digenetic parasite completing its life cycle in two alternate hosts:

Asexual Cycle in Human – Schizogony

1. Pre-erythrocytic Phase

1. After the bite of an infected female Anopheles mosquito, numerous sporozoites circulate in the blood for about half an hour and then enter liver cells.
2. Inside the liver cell they obtain nutrition, increase in size and become rounded uninucleated structures called schizonts.
3. The schizont undergoes schizogony or multiple fission to form a large number of merozoites.
4. After the infected liver cell releases them, these merozoites are called cryptomerozoites.
5. Cryptomerozoites invade fresh liver cells and begin the exo-erythrocytic phase.

2. Exo-erythrocytic Phase

1. Cryptomerozoites enter fresh liver cells.
2. They obtain nutrition, grow and again become rounded schizonts.
3. Schizogony produces many spindle-shaped merozoites.
4. These are released as metacryptozoites.
5. The source divides them into small, numerous micro-metacryptozoites, which enter RBCs and begin the erythrocytic phase, and larger, fewer macro-metacryptozoites, which re-enter liver cells and continue the exo-erythrocytic phase.

3. Erythrocytic Phase

1. Micro-metacryptozoites enter fresh RBCs.
2. Inside the RBC a circular trophozoite forms and begins active feeding on haemoglobin.
3. A vacuole develops centrally and the nucleus moves toward the side, producing the signet-ring stage.
4. The source states that digestive enzymes break haemoglobin into haematin and globin. Globin is consumed while haematin contributes to formation of the pigment haemozoin.
5. The trophozoite develops pseudopodia and becomes the amoeboid stage.
6. It becomes more or less circular and forms a schizont.
7. The schizont undergoes schizogony or multiple fission to form about 12–24 nuclei, each later surrounded by cytoplasm to form merozoites.
8. The source mentions small red Schüffner’s granules in the cytoplasm of the infected RBC.
9. The infected RBC bursts, releasing about 12–24 merozoites and haemozoin with other substances into the blood; the source links this release with malaria fever.
10. Some merozoites enter fresh RBCs to repeat the cycle, while others develop into microgametocytes and megagametocytes that are taken up by a female Anopheles mosquito.

Sexual Cycle of Plasmodium vivax in Female Anopheles Mosquito

1. Microgametocytes and macrogametocytes enter the body of a healthy female Anopheles mosquito when it sucks blood from an infected human.
2. In the mosquito midgut, the microgametocyte acts as the male gamete-forming stage and the macrogametocyte as the female gamete-forming stage.
3. The nucleus of the microgametocyte divides into about 6–8 nuclei; each develops a protruded structure to form 6–8 flagellated microgametes. The source calls this process exflagellation.
4. The macrogamete develops a bulging structure called the cone of reception through which a microgamete enters.
5. The nuclei of the microgamete and macrogamete fuse to form a zygote nucleus.
6. The rounded zygote is initially inactive and later becomes an elongated active structure called the ookinete.
7. The ookinete invades the stomach wall of the mosquito and forms a cyst. The rounded zygote nucleus inside the cyst forms an oocyst.
8. The oocyst first undergoes meiosis followed by mitotic divisions, producing thousands of haploid nuclei.
9. Each haploid nucleus becomes surrounded by cytoplasm to form immature sporozoites, described in the source as sporoblasts.
10. After maturity, spindle-shaped sporozoites are released by bursting of the cyst wall.
11. Sporozoites wriggle through the mosquito and enter the salivary glands.

Symptoms of Malaria Fever

The source describes malaria as an important parasitic disease of humans and states that the major damage occurs in the human host rather than the mosquito.

1. Prodromal Stage

The notes list mild headache, nausea, loss of appetite and drying of the mouth, including during the incubation period.

2. Paroxysm Stage

This is described as the actual attack of malaria, with terrible chills and shivering, nausea, vomiting, drying of the mouth and a coated tongue.

The source further states that excessive damage to RBCs can lead to anaemia.

Treatment of Malaria Fever – As Listed in the Scanned Notes

Page 18 lists the following medicines in its treatment section:

Difference Between Plasmodium vivax and Plasmodium falciparum

Control Measures of Malaria Parasite – As Listed in the Source

1. Destruction of Breeding Places

The source recommends draining swamps and stagnant water to reduce mosquito breeding places. It also states that where water cannot be drained, kerosene oil may be sprayed over the water surface.

2. Destruction of Larvae and Pupae

The notes mention spraying kerosene, Paris green powder and DDT over the water surface to kill larvae and pupae.

3. Biological Control

The source lists fishes that feed on insect larvae and pupae, such as sticklebacks, trout, minnows and Gambusia, for introduction into water reservoirs. It also mentions ducks and cleaning floating plants as useful measures.

4. Destruction of Adult Mosquitoes

Page 20 lists burning sulphur or tar and the use of DDT and other insecticides as methods for destroying adult mosquitoes.

5. Personal Protection

The source lists mosquito repellents, mosquito cream, anti-mosquito mats and mosquito nets as methods for keeping mosquitoes away.