Phylum: Protozoa (Amoeba & Plasmodium) | Additional Study Material for NEET PDF Download

Classification

Phylum – Protozoa - Simple, Acellular animals. (According to DOBELL).

Subphylum – Sarcomastigophora (Plasmodroma) - Locomotive organs are flagella or pseudopodia.

Class – Rhizopoda (or sarcodina) - Locomotive organs are pseudopodia.

Order – Lobosa (or Amoebina) - Pseudopodia are with rounded ends called lobopodia.

Genus – Amoeba.

Species – Proteus - Body is variable in shape.

Discovery and History

R.V. Rossenhoff has discovered Amoeba. Termed it as "Little Proteus" on the name of a God of Yunan who
was able to change his shape.

Saint Vincent Named "Amiba" which was further changed to "Amoeba".

Heirsch Field has done detailed study of Amoeba.

- Most of the species of Amoeba are found in freshwater and feeds on Algae and Bacteria.

- It is present in dirty water with mud.

- Culture of Amoeba can be done by Hay infusion process.

Dry and clean leaves, grass, wheat grains are boiled in distilled water for 15 minutes.

After filtration allow to stand for 2-3 days. Bacterial growth will take place.

Half rotten leaves from pond are washed and put into filtrate. Within a week, filtrate will have good numbers of Amoeba.

- Two species of Amoeba are also found in seawater or marine water.

- Amoeba verucosa

- Amoeba striata

- Amoeba radiosa - Found in tropical areas. This is the most common species found in India.

- Amoeba proteus - Present in Temperate atmosphere. The maximum study is done of this species because its structure is like a simple cell and the size is also sufficient.

- Amoeba pelomyxa – (Chaos - chaos) – Giant Amoeba. This is the biggest Amoeba, its structure is uncommon because it is exceptionally multinucleated.

Shape and Size

Amoeba is a microorganism. Size varies from .2 mm to .6 mm . It is colourless and transparent. Shape is variable because pseudopodia are continously forming and disappearing and also because pellicle is absent.

Exceptionally due to presence of pellicle in Amoeba verucosa and striata, pseudopodia are not formed and their shape is fixed.

Body of Amoeba is differentiated into Protoplasmic membrane, Cytoplasm and Nucleus.

Protoplasmic membrane This is the outermost coating. It is 0.2m to 2m in thickness. It is a thin, soft, selectively permeable unit membrane which is capable of regeneration.

Electron microscope shows that hair like extensions are present on whole of the membrane. These are called microvilli. They are mucoprotein in nature. These micorvilli helps Amoeba in adhesion with ground.

Cytoplasm

It is divided into two parts

Outer – Ectoplasm or Ectosarc

Inner – Endoplasm or Endosarc

1. Ectoplasm – It is transparent and present in form of a thin layer. It is devoid of granules and structures. It is differentiated into two areas.
Outer part is made of a watery fluid which is called "Hyaline layer". This layer is thick in pseudopodia and called as "Hyaline cap". It gives strength to pseudopodia. Internal part is made of plasmagel.

- The ectoplasm of Amoeba proteus contains various perpendicular projections. These are called as "longitudinal ridges". These ridges causes friction and helps Amoeba to adhere with the ground.

2. Endoplasm – It is semi transparent and granular. All the structures of Amoeba are present in endoplasm. 

According to "Mast", Endoplasm is divided into two parts. Internal – Plama sol, Peripheral – Plasma gel.

But Electron microscope does not show this type of division. So whole of the endoplasm is considered as Sol in nature as per the modern theory.

Nucleus

Normally Amoeba is uninucleated but exceptionally Amoeba diploidia has two nuclei. While Amoeba pelomyxa is multi nucleated. 

The nucleus of young or baby Amoeba is biconcave but biconvex in adult Amoeba.

A network of protein fibers is present just inside the nuclear membrane. It is honey comb in shape known as "Honey comb lattice". It maintains the shape of nucleus.

Nucleus of Amoeba is massive in nature, it means that chromatin material is more and nucleoplasm is less in quantity. Chromatin material is present in spherical granules known as "Chromidia". These are 500-600 in number Every chromidia is made up of one or two genes.

Cell Organells

CONTRACTILE VACUOLE (C.V.) – It appears like a bubble of clear watery fluid enclosed within delicate condensation membrane. Only one in number. It is formed by union of many small vacuoles. C.V. is present in Endoplasm. Its position is not fixed but usually it is present between nucleus and rear part of Amoeba (Uroid).

Function of CV is osmoregulation. The liquid medium around Amoeba is Hypotonic so water enters in from outside continuously. This extra incoming water is thrown out by C.V.

Functionally C.V. is equivalent to kidney or nephron or uriniferous tubules of higher animals.

Numerous long tubules are related to C.V. These are called Feeding canals or Radiating canals. These canals collect water from cytoplasm and drain into C.V.

Increase in size of C.V. is due to filling of water called Diastole.

When C.V. becomes sufficiently large it bursts near plasmalemma and water is thrown out. This process is
called systole.

Many small vacuoles combines to form a C.V. The maximum energy is used in this process so many Mitochondria surround the C.V.

- The functional ability of C.V. increases when Amoeba is put in distilled water.

- When Amoeba is transferred from fresh water to marine, C.V. disappears.

- When marine amoeba is transferred to distilled water a new C.V. is formed.

Food Vacuole

Many food vacuoles are present in endoplasm Every time when food is ingested, a new food vacuole is formed and full digestion occurs in this vacuole.

Functionally it is closely related to alimentary canal of higher animals.

Water Vacuoles

These are small, non contractile vacuoles filled with water present in endoplasm. Its function is unknown.

Biurets and Triurets

Many bi-pyramidal and tri-pyramidal crystals are present in endoplasm of Amoeba.
These crystals are made up of excretory product carbonyl diurea. Probably these crystals are excreted during
reproduction.

- Stored food of Amoeba is Glycogen and oil drops.

- Every cell organelle like ER, Mitochondria, Golgi complexes, Lysosomes, Ribosomes etc are present in cytoplasm except centriole.

- Endoplasmic reticulum in Amoeba does not contain cisternae.

Locomotion in Amoeba

- Amoeba is a polypodial animal but the locomotion is monopodial. Amoeba uses single pseudopodia in locomotion.

This movement is called amoboid movement.

- A pseudopodium can form at any point on body surface. It first formed a homogenous fluid called hyaline cap.

When this touches substratum, granular endoplasm rush into it resulting elongation and become distinct pseudopodia.

- Speed is .02 – .03 mm / min.

Locomotion in Amoeba is completed in three stages -

1. Adhesion with base - In this process micrvoilli, longitudinal ridges and ions present in water like Ca++, Mg⁺⁺, K⁺ etc. are helpful.

2. Interconversion of Sol and Gel - This is essential for pseudopodia formation.

3. Contraction in body - Amoeba moves forward by this contraction.

Theories Related with Locomotion

1. Rolling Movement theory - This theory was proposed by "Jenings". This type of rolling movement was observed on Amoeba verucosa. This theory is possible for only two species-

• Amoeba verucosa
• Amoeba striata
• Amoeba roll like a football during locomotion.

2. Contraction theory This theory is given by Heitzman & Schultze.
- According to this theory a pseudopodium is formed due to contraction. Contraction occurs in posterior portion of Amoeba while pseudopodia forms in front part or in the direction of locomotion.

This theory is not valid because only contraction is not responsible for pseudopodia formation.

3. Walking movement theory This theory was given by Dellinger. This theory says that pseudopodia forms in the front part. These pseudopodia serves as feet for Amoeba. With the help of these pseudopodia Amoeba lifts up from the ground and feet like pseudopodia causes locomotion. Pseudopodia disappeares in the back part and are appear as wrinkles. These wrinkles are called Uroids. Due to these uroids, Amoeba shows polarity.

This theory is not valid because at the time of locomotion Amoeba is in contact with surface.

4. Surface tension theory Proposed by Berthold. Butschli and Rhumbler supported this theory. According to this theory pseudopodia are formed due to difference in surface tension of body of Amoeba and ground.

5. Fountain Zone theory Proposed by Allen.

According to this, sol is present in periphery while gel is inside. This central gel moves like a fountain in the direction of locomotion. This fountain applies pressure over ectoplasm and thus pseudopodia is formed. 

But this theory was discarded because in Amoeba sol is always inside while gel is always outside.

6. Sol-Gel theory is Based on change in viscosity theory. Proposed by Hyman. Its detail study was done by Pantin and Mast

This theory suggests that pseudopodia are formed due to interconversion of sol and gel.

In locomotion sol flows in the direction of locomotion and breaks the gel barrier. This sol strikes with the ectoplasm. After striking it moves on either side and converts into gel.

In locomotion the gelation process occurs in front while solation (gel - sol) occur in rear.

- Sol continuously strikes with ectoplasm therefore ectoplasm grows in size and spreads outward hence a small hyaline cap as a small bulge representing begining of pseudopodia. This process helps in pseudopodia formation.

- Pseudopodia is a tube-like structure of ectoplasm in which endoplasm is filled. The wall of pseudopodia is made up of gel while sol in inside.

Drawbacks

1. This theory do not explain the sol-gel interconversion.

2. It does not mention about the force by which sol moves forward.

Some theories in favour of sol-gel theory :

(i) Molecular folding unfolding theory 

– Proposed by Goldacre and Lorch. It explains the sol-gel interconversion. This is a Biochemical and biophysical process. The sol form of protoplasm is due to tertiary structure(folded state) of protein. While the gel form is due to secondary structure (Unfolded state) of Protein.

(ii) Contraction Hydraulic theory

Earlier given by Schultze and detailed explanation was given by Rinaldi. It explains how sol moves in the direction of locomotion. According tothis, actin and myosin type of proteins are present in rear portion of Amoeba. These proteins produce hydraulic pressure by contraction. This pressure is maximum in front, minimum in middle and medium in rear.

According to "Huxley" the proteins participating in solution and gelation are similar to actin and myosin of  muscles fibres. 

Nutrition

Nutrition in Amoeba is Holozoic or Zootropic which involve ingestion of food and then digestion and absorption.

Amoeba is omnivorous. It likes to take bacteria, algae, cilliated and flagellated Protozoans. There is no pore for ingestion and excretion of digested food. Any part of plasmalemma can ingest food and excrete digested food.

Some protozoans like Paramoecium contain pore. These are called Cytostome and Cytoproct. (or cytopyge)

Methods of food ingestion (Studied by Rhumbler)
1. Import - Amoeba do not effort in this method. Any moving food when strikes with amoeba it is embedded into the cytoplasm (Passive food ingestion).

2. Invagination - By this process small and non-motile food is ingested. This type of food comes in contact with plasmalemma which invaginates and food is ingested due to invagination of plasmalemma in the form of a food vacuole.

3. Circumfluence - This process is used to ingest large and nonmotile or less active food e.g. Filaments of algae.

In this process cytoplasm of amoeba flows around the food and encircle it.Plasmalemma invaginates and forms a food cup which further converts to a big food vacuole.

4. Circumvallation - By this process amoeba ingests active, motile food. Food is surrounded by several small pseudopodia. Later these pseudopodia unite and forms a food cup. Finally, prey is embedded in the endoplasm.

Amoeba can also ingest colloids from surrounding by pinacytosis and form pinocytic vesicle.

Digestion

Digestion takes place in food vacuoles by means of lysosomal enzymes release from Lysosome which get fuse and merge with food vacuoles. These enzyme work effectively only when medium in food vacuole is alkaline.

- Just like higher animals digestion is completed first acidic and then alkaline phase.

- First HCl produced from fluid of vacuole made food loose, soft and semitransparent. And simultaneously vacuole loses water and become smaller. Then Lysosome release their enzyme into vacuole which made vacuole alkaline.

- Proteolytic enzymes like trypsin, peptidases and lipolytic enzyme lipase are found but carbohydrate-digesting
enzyme or amylolytic enzyme is very less.

- Thus proteins hydrolysed to amino acids and fats to fatty acid and glycerol. Due to increase osmotic concentration water is reabsorbed.

- Food vacuole remain in endoplasm for about 30mts for completing digestion. End product of digestion diffuse out from the vacuole to all part of body.

- Excess amino acid changed to sugar and store as glycogen as reserve food.

- Food vacuole with undigested food is thrown out.

Respiration and Excretion

Both these functions are completed by plasmalemma through diffusion.

Amoeba is an obligate aerobe. It depends only on aerobic respiration. So when Amoeba is put under O₂ less water it dies.

- In view of excretion Amoeba is Ammonotelic.

Reproduction

1. Binary fission - Simplest type of reproduction. It occurs in desirable condition. In this process division is primitive type of mitosis called as Cryptomitosis.

Phases of this division are as under -

i. Prophase - Contractions in C.V. Stops. Numerous small pseudopodia arises on whole of the surface of Amoeba. Amoeba is covered by hyaline caps. Therefore entry of water becomes slow.

Nucleolous and Honey comb lattice in nucleus disappears but nuclear membrane persists.

Chromidia become condensed and clear. Spindle formation starts in nucleus. These are called intranuclear spindles.

ii. Metaphase - Chromidia forms metaphase plate by adjusting themselves in the middle of nuclues. 

Spindles are arranged on different poles of nucleus. These are called multipolar spindle. This is an unique character of binary fission in Amoeba.

iii. Anaphase - Pseudopodia becomes less in number but size increases. Multipolar spindles are converted into bipolar spindles (spindle fibers). Now chromidia separate so that chromidia approaches the two poles of nucleus.

Simultaneously nucleus becomes larges and show constriction in middle.

At the end of Anaphase nucleus is dumble shaped.

iv. Telophase - At this stage nucleus and cytoplasm divides. It results in formation of two daughter Amoeba.

Size of daughter Amoeba is greater than the half of the size of parent Amoeba.

Old C.V. remains in any one of the daughter Amoeba. While the other forms a new one. Binary fission is completed in 30 mt. It maybe repeated after 48 hrs.

2. Sporulation -

i. Sometimes Amoeba reproduces by sporulation in unfavourable conditions.

ii. When excessive energy is spent continously, binary fission ability decreases. To reproduce further it does sporulation. Spore is the resting stage of Amoeba hence it saves energy.

- In sporulation Amoeba retracts its pseudopodia and becomes sphere shaped.

- Nuclear membrane disappears and chromidia disperse in the sets of 2 or 3 chromidia. Every set of chromidia is surrounded by a newly formed nuclear membrane.

- After that cytoplasm divides and breaks in 200 pieces and surrounds each small nucelus. Every piece now secretes a hard and thick coat around itself. This structure is called spore.

- About 200 spores are formed by this process. Coat of spore is made up of chitin.

- Now plasmalemma of parent Amoeba dissolves and spores are spread out.

- When favourable conditions arrive, spore germinates. They absorb water and swallow. Thick coat splits and a young Amoeba comes out.

- In this young stage endomitosis occurs in nucleus so that chromidia increases in number up to 500-600. Nucleus formed by endo mitosis is called Restitution or polyenergid nucleus.

- Spore also helps in dispersion of Amoeba.

3. Encystment and Multiple fission This process is used under unfavourable conditions, like lack of O₂ , lack of food and at high temp. In this case Amoeba secretes a three layered thick coat around itself called cyst. Coat of cyst is made up of chitin like that of spore. It is impermeable to water and permeable to O₂ and CO₂.

Inside cyst amitosis occurs several times so that 500 small Amoeba are formed. These are called pseudopodiospores or Swarm spores.

- On return of favourable conditions cyst spits and Amoeba get freed in water.

- According to modern scientists, multiple fission is very rare. It is not a process of reproduction it is a process of perennation.
- Amoeba is least active inside cyst. This phenomenon is called "Suspended Animation". This is also a process of dispersion but its efficiency is more than spore.

Rejuvenation - This is also called non-functional conjugation. In this process two old amoeba come close to each other and adhere themselves. After a while they get separated. Now these both amoeba are more active than before. (No Exchange of matter.)

Regeneration - Studied by Bruno & Hoger. Amoeba has tremendous power of regeneration.

- Any part of Amoeba which contain at least one chromidia may regenerate but piece without nucleus can not regenerate.

IMMORTALITY IN AMOEBA Studied by Hertman

Amoeba is immortal because its natural death do not occur as a parent Amoeba is converted completely into two daughter Amoeba by binary fission.

Immortality can also be explained on the basis of "Germplasm theory of weisman". According to this theory Amoeba is not differentiated into somatoplasm and Germplasm.

This type of differentiation is present in multicellular animals.

IRRITABILITY

- Amoeba has protoplasmic grade of irritability.

- Maximum taxis movement of Amoeba are negative, these are called phobotaxis.

- Some positive taxis are also present these are called philotaxis.

Types of irritability :

1. Thigmotaxis - Normally phobotaxis, but in response to food it is always philotaxis.

2. Phototaxis - Amoeba likes dim light. So phobotaxis is seen in response to bright light & darkness.

3. Thermotaxis - Optimum temp is 20-25⁰C. When Amoeba is kept suddenly under high temperature it dies but when rise in temp is gradual it forms cyst.

4. Chemotaxis – Amoeba shows phobotaxis when kept under water in which those chemicals are present that are not present normally in water.

5. Galvanotaxis - When low current is passed Amoeba moves toward cathode but in high current it dies.

6. Rheotaxis - Amoeba moves with the flow of water.

7. Geotaxis- Philotaxis because Amoeba like to live in bottom. These animals are called benthos or benthic.

ENTAMOEBA HISTOLYTICA

Entamoeba histolytica is discovered by Lamble. Losch discovered its pathogenic nature.

Entamoeba Histolytica is a parasitic Amoeba and it causes "Amoebic dysentry". A patient with this disease has acidic stools. Stool also contain mucous, blood and cyst of Entamoeba. So this disease is diagnosed by stool test.

Entamoeba Histolytica is a parasite of large intestine(colon) of man. It secretes histolytic enzymes which causes harm to wall of intestine. Entamoeba destroys the mucosa and submucosa of colon and enters in its wall and injest tissue, RBC etc, and form flask shaped ulcer from which mucous and blood comes out and pass into stools of the host. It may also approach in other organs of body like liver, lungs, kidney, brain etc. through blood circulation.

Basically structure of Entamoeba is similar to Amoeba, but C.V. is absent in Entamoeba.

It's food vacuole contains R.B.C., W.B.C. and bacteria as these substance are used as food.

Nucleus of Entamoeba is vesicular i.e. chromatin material is less and Nucleoplasm is more.

Chromidia are arranged on periphery of nucleus. At the center of nucleus a false nucleolus or karyosome or Endosomes occurs. Endosome is surrounded by a small clear shiny and transparent area which is called Halo.

Nucleoplasmic striations connect Halo to chromidia.

Entamoeba Histolytica is monopodial animal. In its rear portion plasmalemma is geletinous and sticky. It helps in sticking of food particles. Food is ingested by the process of invagination. This is the only process of taking food.

Two forms of Entamoeba are there :

(i) Trophozoites or Magna form.(20-30u)

(ii) Precyst or Minuta form.(12-15u)

Trophozoites form is larger than Minuta form. Trophozoites is the adult stage of Entamoeba. This stage of Entamoeba is motile, actively feeding and pathogenic.

Life Cycle - Few daughter Amoeba which are formed by the asexual multiplication of Trophozoites grow in to normal adult whereas few dauthter Amoeba remain small and escape from the lumen of the colon known as minuta form or precystic Amoeba.

Cytoplasm of these minuta contain only one or two granules of glycogen, but contains a dense body called as "Chromatoid body". Possibly it is made up of Ribo nucleoproteins which further disappear.

Minuta secretes a thin but strong coat around itself called cyst. Nucleus of cyst undergo two mitosis and a tetra nucleated cyst is formed. It is carried out from the body by stools of the patient.

This tetra nucleated cyst is the infective stage of Entamoeba for human.

Cyst enters in human by impure water and food. Houseflies also carry these cyst to food. When these cysts reach to colon, their hard coat is damaged. This process is called hatching or excystment. Now Tetra nucleated stage comes out. This is called Metacyst. Metacyst undergo binary fission and eight Entamoeba are formed.

All these Entamoeba enters the wall of colon and after growth converted into Trophozoite. Some medicines used in prevention of diseases caused by Entamoeba Histolytica are Emetine, Diodoquin, Dependal, Carborsone metrogyl, Magma, Amicline.

ENTAMOEBA GINGIVALIS

Size of trophozoite - 12-20u.

It is present in Tartar which is deposited in between teeth. Approximately 70% humans are infected by this.

Some times it also infect gums. It has 2-3 pseudopodia and contain several food vacuole.

Entamoeba gingivalis is a human parasite but it is not pathogenic. It helps some pathogenic protozoa in infection e.g. Trichomonas tinax, Trichomonas buccalis both of these causes pyorrhoea.

- Entamoeba gingivalis does not form cyst.

- It spreads through mouth to mouth by kiss. It trophozoites feeds on bacteria, debris WBC.

- Prevention may be done by using sensoform mouth wash

- Treatment can be done by Garamycin.

ENTAMOEBA COLI. (E. Coli) - (Trophozoite - 20-40 m)

- This species is found in human colon.

- It shows commenselism Host is neither in gain nor in loss.

- It feeds on non digestive food & Bacteria and do not invade colon wall.

- Eight-nuclei are found in the mature cyst.

SPECIAL POINT

1. Pelomyxa is the biggest Amoeba.

2. Amoeba proteus is a free living and solitary animal

3. Amoeba is omnivorous.

4. Amoeba is polypodial where as Entamoeba is Monoipodial

5. Amoeba shows polarity as uroids are present on back.

6. Chromatin material of Amoeba is granular and called chromidia.

7. Gaseous exchange in Amoeba is done through body surface.

8. Excretion of Ammonia is also done through body surface.

9. The universal theory for locomotion in Amoeba is sol-gel theory

10. Mechanism of binary fission in Amoeba is cryptomitosis.

11. General method of reproduction in Amoeba is binary fission.

PLASMODIUM (Malaria Parasite)

CLASSIFICATION

Phylum - Protozoa

Sub Phylum - Plasmodroma

Class - Sporozoa - All members are parasite so locomotive organs are absent

Order - Haemosporidia – Digenetic life cycle

Genus - Plasmodium

- Plasmodium is a member of order Haemosporidia, therefore, it complets its life cycle in two hosts.

- Primary host - Primary host for Plasmodium is human being. Plasmodium completes only asexual life cycle in this host.

- Secondary host - Intermediate host / Carrier host - Female Anopheles serves as secondary host for Plasmodium. Both sexual cycle and sporogony asexual are completed in this host.

- Reserviour host - Monkey is reservoir host for Plasmodium (Dog is also not affected).

- All the stages of Plasmodium life cycle that occurs in human are also found in monkey, but monkey do not suffer or die of malaria.

- Eradication of Plasmodium is not easy due to its several hosts. Another reason is that vaccine cannot be formed because Plasmodium do not induce human body to form antibodies and hence no immunity against
Plasmodium can develop.

- Number of chromosomes in Plasmodium 10

- NMEP - National Malaria Eradication Programme

LIFE CYCLE OF PLASMODIUM IN HUMAN

There are two sites for activity of Plasmodium in human

(i)Liver

(ii) RBC

- All the activities that oocurs in liver are known as "Exo erythrocytic Cycle".

- Whereas activities in RBC are termed as "Erythrocytic Cycle".

INFECTION OF PLASMODIUM IN HUMAN

- Infective stage of Plasmodium for human is sporozoite which are present around 2,00,000 in salivary glands of female Anopheles.

- Sporozoites are spindle or sickle shaped. Body is covered by pellicle which is made up of 11-15 microtubules.

- Sporozoite contains an aperture at the apex called "Micropyle". A structure which covers micropyle is known as Apical cap. It is made up of 3 concentric microtubules.

A pair of secretory organells are related to micropyle. It contains lytic enzymes which helps sporozoite to penetrate human liver cells.

A big oral shaped nucleus is present in middle of sporozoite. Just beneath it, there is a Mitochondria.

- This type of 2,00,000 sporozoites are present in saliva of female Anopheles Micropyle

- An anticoagulent is secreted when female Anopheles bites. It do not allow blood to clot so that Anopheles, can suck blood easily. With the saliva numerous of sporozoites enters in human blood. Within 30 minutes all of these sporozoites approach the liver and no sporozoite is visible in the blood.

PRE ERYTHROCYTIC CYCLE

- The first cycle of Plasmodium in liver is called as Pre erythrocytic cycle.

- Plasmodium starts its life cycle from liver because

(i) To prevent itself from the phagocytic action of WBC

(ii) Plasmodium use glycogen as food and liver is rich in glycogen

(iii) To multiply in number

- Sporozoite enters in the liver cell and become spherical by phagocyting the cytoplasm. Now these are termed as "Cryptozoites"

- Cryptozoites undergo multiple division. This is called "Schizogony". This results in the formation of 1000-1500 small structure called as Cryptomerozoites. At this stage cryptozoite is called "Schizont"

- Finally cell membrane of liver cell & schizont bursts and Cryptomerozoites are now free in blood sinusoids of liver.

- A few of these cryptomerozoites infect RBC and start the erythrocytic cycle.

 - Rest of the cryptomerozoites go back in liver cells and starts the post exoerythrocytic cycle. All these cycles in liver except the first one are called post exoerythrocytic cycles.

- Time taken to complete pre erythrocytic cycle is called Pre patent period. In this period Plasmodium is not visible in blood.

POST EXOERYTHROCYTIC CYCLE

In this cycle Cryptomerozoites infect the liver cells. They phagocyte the cytoplasm and become big and spherical. Now these are known as Metacryptozoite or phanerozoites.

Two types of Metacryptozoites are formed

(i) Micro Metacryptozoites - (MICRO MCZ)

(ii) Macro Metacryptozoites - (MACRO MCZ)

MICRO MCZ are further converted into 100-1000 merozoites by the process of schizogony. The product is called Micro meta crypto merozoite (Micro MCM).

MACRO MCZ also undergo the process of schizogony. It results in the formation of 64 merozoites these are called Macro meta crypto mero zoite (Macro MCM).

- Micro MCM infect only RBC whereas Macro MCM infect liver cells

- This cycle goes on repeating again and again which causes destruction of liver cells. In case of an excessive Malaria, liver may damage and jaundice like symptoms may appear.

ERYTHROCYTIC CYCLE OR GOLGI CYCLE

- This cycle starts at first by cryptomerozoites and further carry on by Micro meta cryptomerozoite.

- Cryptomerozoite infects R.B.C. They phagocyte Haemoglobin of R.B.C & become big & spherical. Then they are called Trophozoites. Later on, a big central vacuole is formed in the cytoplasm of trophozoite. This makes it appear like a "Ring". So this stage is called Signet ring stage. After a while vacuole is lost and trophozoite become irregular in shape. At this stage, Plasmodium looks like Amoeba so this is called as Amoeboid stage. This is active and feeding stage of Plasmodium. It phagocytes Haemoglobin quickly and grows up and occupies whole of the RBC approximately.

Particularly, at this stage reddish brown coloured granules are seen in the cytoplasm. These are called Haemozoin granules. It is the non digested haeme part of haemoglobin.

At the same time bright yellow coloured granules appear in the cytoplasm of RBC. These are called Schuffner's dots which are probablely waste product of Plasmodium. These dots are used in diagnosis of malaria because they are the most clear structures that appear in blood. A stain known as Romanovaski stain is used to observe schuffner's dots.

There are two species of Palsmodium that do not form schuffner's dots.

1. Plasmodium malariae - They form Red coloured granules known as Zeiman's dots

2. Plasmodium falciparum - They form green coloured Maurer's dots/Clefts.

Both of these are also helpful in diagnosis of malaria

Now schizogony occurs in trophozoite and 12-24 Merozoites are formed. They are arranged as petals of flower. So Plasmodium looks like a flower and hence this stage is known as Rosette stage.

Some cytoplasm in this stage remains indivisible. Haemozoin granules are present in this cytoplasm.

Finally, membrane of RBC and schizont bursts and all the material get freed in blood plasma. Merozoites infect new RBC and repeat the erythrocytic cycle again and again. Organells like apical cap, secretory organells etc.  get fused to form Rhoptries stage in merozoites.

Burst RBC is called Ghost RBC. Spleen uptake these ghost RBC from the blood and destroy it. A special type of phagocyting cells called as Macrophages are present in spleen, These cells secrete an enzyme Lysolecithin which destroy ghost RBC.

In case of excessive malarial infected spleen becomes large and swollen. This disease is called Megaly of spleen or spleen index. It is due to increase in number of macrophages and lysolecithin causes swelling.

Excessive malaria infection may also lead to anemia because more lysolecithin secretion occurs which reaches to blood and destructs the healthy RBC's, so decrease in the number of healthy RBC cause Anaemia. This anemia is called Haemolytic anaemia.

The time lapse between infection of Plasmodium and first attack of Malaria is called Incubation period.

- Plasmodium shows biological clock system because erythrocytic cycle is completed exactly within 48-72 hours.

EFFECT OF HAEMOZOIN GRANULES

Due to toxic effects on body, symptoms of Malaria appear.

Initial symptoms of Malaria - Nausea, Constipation, Bodypain, Dyspnoea, weakness in body.

- After 2 or 3 Erythroytic cycles haemozoin granules increase in number and actual symptoms of Malaria now begins to appear. This is called Paroxysm of malaria. It has three stages.

1. Rigor stage :- Alternate contraction and relaxation in muscles causes shivering and cold sensations.

2. Febrile stage :- After some time shivering stops and body temp rises due to contraction of muscles.

Rise in temprature is benificial for patient because internal high temp is unfavourabale for parasite Plasmodium.

3. Differvescent stage :- After rise in temperature excessive sweating occurs and body temperature decreases.

Now patient feels himself healthy. But at this time erythrocytic cycle starts again and fever is repeated at a constant interval of time.

POST ERYTHROCYTIC CYCLE
Sometimes Merozoites formed by erythrocytic cycle escapes from blood and enters the liver cells. These merozoites remain inactive in liver.

After a long time they become active and multiply in number. This causes Malaria again. So after a long time malaria is repeated again this is called Relapse of Malaria.

Post erythrocytic cycle is not found in Plasmodium falciparum. So relapse of malaria do not occur. Longest relapse of Malaria found in Plasmodium malarie may last up to 3 years.

GAMETOCYTE STAGE

When many Erythrocytic cycles completed then merozoites enter the RBC and form a new stage called as Gametocyte or Gamonts or Resistant Trophozoite schizont. Merozoite stage contain Rhoptries.

Gametocyte is the last stage in human. Further development occurs in female Anopheles because high temperature in human is unfavourable for gametocyte formation. There is biological clock system in Plasmodium it means that it form gametes when there is more probability of attack of female anopheles. So gametes are formed in the night, from late evening up to midnight. Gametocytes which reach in female Anopheles are developed and rest which are left in blood are destroyed in the morning.

Two type of gametocytes are formed

(1) Micro gametocyte

(2) Macro gametocyte

These are formed in ratio of 1 : 2 respectively.

LIFE CYCLE OF PLASMODIUM IN FEMALE ANOPHELES

There are two types of cycles :
(1) Gametogony - Sexual cycle

(2) Sporogony - Asexual cycle

Gametocyte is the infective stage of Plasmodium for female Anopheles. When it sucks blood, many stages reach in its Crop but only gametocyte stage remains, rest of all are digested.

GAMETOGENESIS - Microgametocytes undergo the process of Spermatogenesis in which its nucleus is divided into four haploid nuclei by meiotic division. Further, Mitosis occurs and these are converted into 8 nuclei. All nuclei are arranged on periphery. At the site of every nucleus plasmalemma projects outward and eight spindle shaped projections are formed. Every projection contains a nucleus and few cytoplasm. These projections are called Sperms. Sperm formation process is exflagellation. Every sperm detaches itself from microgametocyte by constricting at its base. So eight sperms are formed by a single microgametocyte. 

Macrogametocytes form ovum by the process of Oogenesis in which meiosis occurs and one ovum and three polar bodies are formed. Polar bodies are destroyed further. A projection appears on ovum which is called reception cone. This is the penetration site of sperm at the time of fertilization. Zygote is formed as a result of fertilization. Whole of this process up to zygote formation occurs in lumen of crop. Zygote can form in any type of mosquito e.g. Anopheles, Culex and Ades etc but further development of zygote is possible only in female Anopheles. This is the host specialisation of Plasmodium.

DEVELOPMENT OF ZYGOTE

Proposed by "Grassi". This theory says that all zygotes are converted into long worm like structures called Ookinete or vermicule. With the help of gliding and wringling movements These ookinete enters the crop wall and are place beneath the outermost layer called peritoneum of crop wall.

A thin and elastic coat is secreted around these zygotes by both zygote and cells of crop wall. This stage is called Oocyst. At this stage 50-100 small projections of oocyst are found on the crop wall.

II. SPOROGONY- Oocyst takes nutrition from crop wall and develop into 5-6 times bigger structure called sporont. Many small vacuoles are now formed in the cytoplasm of sporont. Nucleus of sporont is converted by free nuclear divisions into approximately 10,000 nuclei. All these nuclei are arranged on periphery of vacuoles. Later on cytoplasm is divided and converted into 10,000 parts around every nucleus, with the result 10,000 sporozoites are formed. This sporont is called as sporocyst.

Outermost layer of crop and wall of sporont bursts and these sprozoites are now free in haemocoel of mosquito. 

Haemocoel is a blood filled cavity. This blood is colourless and called haemolymph.

All sporozoites are stored in salivary glands. About 2,00,000 sporozoites are stored in salivary glands of mosquito which further infect to human through saliva.

SPECIES OF PLASMODIUM :- About 60 species are known but only four are pathogenic

(1) Plasmodium vivax

(2) Plasmodium ovale (Not found in India, Found in Phillipens & Africa)

(3) Plasmodium falciparum

(4) Plasmodium malariae

Most common is - Plasmodium vivax and very rare is - Plasmodium ovale

COMPARATIVE STUDY

- Malaria caused by Plasmodium falciparum is called lethal malaria. It is also termed as sub tertian fever, tropical fever, cerebral fever, black water fever, Malignant fever or Aestivo-autumnale fever. This is the most dangerous malaria because infected RBC adhere and form thrombus which may interfere the blood circulation.

Carotid artery is feeding artery of brain so when, this artery is blocked by thrombus then brain may suffer from less blood circulation which is unfavourable for it. Longer duration of this condition may cause death.

When thrombus is formed in coronary arteries, which gives nutrition to heart, heart attack may occur. Loss of Haemoglobin through urine(Haematuria) occur in which colour of urine changes from yellow to black hence it
is also called as 'Blackwater fever'.

Double signett ring and crescent gametocyte are characteristic of Plasmodium falciparum.

- Malaria by Palsmodium malarie is difficult to diagnose because this species may remain dormant in liver for a very long period.

HISTORY OF MALARIA

1. Mc. Culloh - Named Malaria

2. Lancisi - Suspect that there is any relation in between mud mosquito and malaria.

3. Charles laveran - discovered Plasmodium

He observed Plasmodium first in RBC of human and revealed that malaria is caused by Palsmodium.

4. Sir Ronald Ross - Proved the relation between mosquito and Malaria. He saw oocyst first on crop of female Anopheles. About 25,000 mosquitoes were dissected by Sir Ronald Ross in his life.

Female Anapheles is the carrier of Plasmodium. The discovery of sir Ronald Ross was awarded by Noble Prize on 29th of August 1902. Hence this day is celebrated as "Malaria day"

It was an incident that Sir Ronald Ross died of Malaria.

5. Grassi - Studied the life cycle of Plasmodium in female Anopheles.

6. Mc. Collum - Explained in detail the sexual cycle of Plasmodium.

7. Shortt, James, Huff & tate - studied the life cycle of Plasmodium in human.

8. Golgi & celli - explained erythrocytic cycle so this is also called golgi cycle.

9. Schauddin - Detailed study of Plasmodium vivax life cycle in human and mosquito.

10. Rudzinska - Study of ultra structure of Plasmodium by electron microscope.

CONTROL OF MALARIA

(1) Direct - by killing Plasmodium

(2) Indirect- by killing mosquitoes

(1) Indirect - following procedures are used to kill mosquitoes.

(a) Insecticides like - DDT (It is now banned) Gamaxene, Melathion etc. are sprayed.

(b) Biological control - This is the more suitable procedure. In this larvivorous fishes are used. They eat larva of mosquitoes. e.g. Gambussia Trout, minnows, stickle back.

(2) Direct method - Plasmodium is destroyed by chemotherapy

(a) Old medicines like Quinine - it is obtained from Cinkona as quinine sulphate salt. It destroys only those stages of plasmodium which are present in blood.

(b) Mapacrine - It destroys merozoites present in blood

(c) Paludrine and sulphadoxine - These medicines destroy all the stages either in blood or in liver. But are not generally used because they cause harm to liver cells.

(d) The most effective medicine for Malaria is Deraprim. It destroys gametocytes.

SPECIAL POINTS

(1) 29th August is Malaria day

(2) Plasmodium is a member of Sporozoa class

(3) Monkey acts as Reservoir host of Plasmodium

(4) Lysolecithin secreted by spleen destroys infected RBC's

(5) Normally primary host is the host in which parasite completes its sexual life cycle but in Plasmodium human is primary host exceptionally. Although sexual cycle is completed in mosquito and asexual in human. 

(6) Maximum amount of Haemozoin granules is present in gametocyte stage.

(7) Temperature of Malaria patient may rise up to 104-1050 F.

(8) Some other symptoms and side effects may appear from malaria like Anaemia, Jaundice, Megaly, Thrombosis, Insomnia.

(9) The most effective medicine for Malaria is Deraprim. It destroys gametocytes.

(10) Number of lymphocytes is increased in malaria infection.

(11) Shivering characteristic of malaria is caused by merozoites are liberated with toxin from RBC.

(12) Number of chromosome in Plasmodium - 10

(13) Merozoite stage of Plasmodium contain Rhoptries.