Category: Biology Second Paper Lecture Sheet

1. Vertebrate (human) requirements
(i) New host: Sporozoites of malaria parasite require human as new host.
(ii) Merozoite Formation: Merozoites are not formed without a vertebrate host. Therefore, a vertebrate host is required for merozoite formation.
(iii) Schizogony: Hepatic and erythrocytic schizogony of malaria parasites is accomplished in humans or vertebrates.
(iv) Easy availability: Humans are readily available as vertebrate hosts.
(v) Continuity of the species: Production of male and female gametophytes is necessary to maintain the continuity of the species. Gametophytes are produced in human blood. Therefore, vertebrates are essential to prevent species extinction.
2. Invertebrate host (meshki) requirement for sex cycle
(i) Sex cycle: Malaria parasite requires mosquito for sex cycle.
(ii) Carrier of sporozoites: After sexual reproduction, the mosquito carries the sporozoites.
(iii) Easy availability: As an invertebrate host, muskrats are readily available in the vicinity of settlements.
(iv) Nutrition: The sporozoites obtain nutrition from the body of the mosquito.
(v) Life span: The mosquito lives longer than the time required for the malaria parasite to complete its sexual cycle.

Merozoites of the malaria parasite are released from the liver and enter the bloodstream. It disrupts the normal environment of the blood. White blood cells release pyrogens to destroy them. The hypothalamus of the brain is stimulated due to excess pyrogens in the blood. Because of this, chemical substances like prostaglandin, monoamine etc. are secreted from the brain. This message or stimulus reaches the peripheral regions of the body through vasomotor nerves. Peripheral blood vessels are narrowed. Therefore excess heat cannot escape from the body. As a result, body temperature rises more than normal and fever occurs.

The periodic alternation of haploid and diploid states in the life cycle of an organism is called a cycle. The genealogy of the malaria parasite is discussed.
1. Haploid status
(i) Sporozoites: When an Anopheles mosquito biting a healthy human, the sporozoites enter the human body through the saliva of the mosquito. Sporozoites are mobile, slightly curved and both ends of the body are straight. The sporozoites penetrate human liver cells and grow within 30-45 minutes.
(ii) Metacryptomerozotes: Metacryptomerozotes are formed successively from sporozoites. Metacryptomerozites are of two types. Micrometacryptomerozites and macrometacryptomerozites. Micrometacryptomerozites are small in size and have large nuclei. Macrometacryptomerozotes are large in size and have small nuclei. Macrometacryptomerozites invade new liver cells. Micrometacryptomerozites enter the bloodstream and invade red blood cells.
(iii) Merozoite: 12-18 small cells are seen in the cytoplasm of the germ. A nucleus enters each segment. They are arranged in two layers like petals. This condition is called rosette. Each part, including the nucleus, becomes a merozoite.
(iv) Gametocytes: Some merozoites develop into gametocytes. Gametocytes are of two types. Microgametocyte and Macrogametocyte. Microgametocytes are small in size and have large nuclei. Macrogametocytes are large in size and have small nuclei.
(v) Gametes: In the process of exflagellation, the nucleus of each microgametocyte divides into 4-8 pungametes or microgametes. Each macrogametocyte gives rise to one strigamete or macrogamete.
2. diploid state
(i) Zygote: The microgamete enters the macrogametocyte through the fertilization cone. Later their nuclei fuse to form a zygote.
(ii) Uokinete: After 12-14 hours the quiescent spherical zygote becomes elongated and motile. It is called wokkinet or vermicule. Uokinetes are 18-28 microns in length and 3-5 microns in width.
(iii) Oocyst: Within 24 hours the oocinets break through the wall of the mosquito crop and come out and become spherical. It is then covered with a thin film. It is called a oocyst. The oocyst later transforms into a sporozoite.

1. The pellicle of ookinetes is bilayered. The outer coat is wrinkled and the inner coat is smooth.
2. At the tip of the body there are microscopic pores called cytostome. Through these pores, protein-degrading enzymes are secreted and cause damage to the crop of the mosquito.
3. Under the endoplasmic reticulum there are 55-56 microtubules. They are contractile-expandable and aid in movement.
4. Its nucleus is quite large, granular and irregular.
5. Cytoplasm dense and containing brown pigmented granules.
6. It contains mitochondria and ribosomes.

1. The trophozoite is covered by a double-membrane envelope.
2. Its cytoplasm contains dense granular material containing ribonucleoprotein.
3. There are several food cavities in the cytoplasm. It is filled with hemoglobin.
4. Its nucleus is quite large and located laterally.
5. Cytoplasm contains mitochondria, endoplasmic reticulum, Golgibodies etc.

1. Sporozoites are very small, slightly curved and pointed at both ends.
2. It is 10-14µm long and 0.05-1.00µm wide.
3. Its body covering is called pellicle. The pellicle is strong and flexible. It is composed of vertical and contractile microtubules.
4. It has a cup-shaped apical cup at its tip. The apical cup is composed of three ring-like segments.
5. It opens a pair of organs called rhoptry. It secretes enzymes that dissolve liver cell membranes.

The process of sporozoite formation is called sporogony. The oocyst grows by consuming food. Its nucleus divides repeatedly by first mitosis and then meiosis to form many haploid nuclei. Cytoplasm accumulates around each nucleus to form spherical cells. Later round cells transform into sickle or macule shaped sporozoites. About 10,000 sporozoites are produced from each oocyst. The sporozoites reside in the hemocele of the mosquito. At this time, if the mosquito bites a healthy person, the sporozoite enters the person’s body. About 10% of sporozoites enter the human body during a single bite. A mosquito’s salivary gland can contain up to 326,000 sporozoites. The sporozoites remain in the salivary glands of the mosquito for about 60 days. It takes about 10-20 days from stinging to sporozoite formation.

Within 24 hours the ookinetes break through the wall of the mosquito crop and come out and take spherical shape. Then within 40 hours it is covered with a thin film. It is called a oocyst. The nucleus of the oocyst divides first by meiosis and then by mitosis. Meiosis of oocyst is called postzygotic meiosis. A mosquito crop may contain 50-500 oocysts. The resulting oocysts appear spongy and 4-5 times larger in size (50-60 µ).

After 12-14 hours the quiescent spherical zygote becomes elongated and motile. It is called wokkinet or vermicule. Uokinetes are 18-24 microns in length and 3-5 microns in width.

The process of formation of strygametes or ovules is called oogenesis. Each macrogametocyte gives rise to one strigamete or macrogamete. One end of the macrogamete swells to form the fertilization cone. The cone region is called the Fertilization Cone or Reception Cone. The nucleus of the egg is located near the cone.