Life cycle of Plasmodium :
(i) The life cycle of Plasmodium involves three phases namely schizogony,gamogony and sporogony.
(ii) The parasite enters the human blood stream through the bite of an infected female Anopheles mosquito.
(iii) As it feeds, the mosquito injects the saliva containing the sporozoties.
(iv) The sporozoite within the blood stream enter the hepatic cells of the liver.
(v) It undergoes multiple asexual fission (schizogony) and produces merozoties which are released from liver cells.
(vi) The merozoites penetrate the RBC's. Inside the RBC of blood, the merozoite begins to develop unicellular trophozoites. The trophozoite grows in size and a central vacuole develops p them to one side of cytoplasm and becomes the signet ring stage.
(vii) The trophozoite nucleus divides asexually to produce the schizont.

(viii) The schizont divides and produces mononucleated merozoites.
(ix) Eventually the erythrocyte lyses, releasing the merozoites and haemozoin toxin into the blood stream to infect other erythrocytes.
(x) Lysis of red blood cells results in fever and other symptoms.
(xi) This erythrocytic stage is cyclic and repeats itself approximately every 48 to 72 hours or longer depending on the species of Plasmodium involved.
(xii) The sudden release of merozoites triggers an attack on the RBCs.
(xiii) Occasionally, merozoites differentiate into macrogametocytes and microgametocytes. when these are ingested by a mosquito, they develop into male and female gametes respectively.

1. Effectively dealing with peer pressure:
The biggest reason for teens to start on drugs is due to their friends/peer groups imposing pressure on them. Hence, it is important to have a better group of friends to avoid such harmful drugs and alcohol.
2. Seeking help from parents and peers:
Help from parents and peer group should be sought immediately so that they can be guided appropriately. Help may even be sought from close and trusted friends. Getting proper advice to sort out their problems would help the young to vent their feelings of anxiety and guilt.
3. Education and counselling:
Education and counselling create a positive attitude to deal with many problems and to accept disappointments in life.
4. Looking for danger signs:
Teachers and parents need to look for a sign that indicates a tendency to go in for addiction.
5. Seeking professional and medical assistance:
Assistance is available in the form of highly qualified psychologists, psychiatrists and deaddiction and rehabilitation programmes to help individuals to overcome their problems.

The human immunodeficiency virus belongs to the genus Lentivirus. When observed under the electron microscope, HIV is seen as a spherical virus, 100-120 nm in diameter, containing a dense core surrounded by a lipoprotein envelope. The envelope has .glycoprotein (GP) spikes termed GP 41 and GP 120. At the core, there are two large single-stranded RNA. Attached to the RNA are molecules of reverse transcripte. It also contains enzymes like protease and ribonuclease. The core is covered by a capsid made of proteins. This is followed by another layer of matrix proteins as shown above.

Different types of antigen and antibody reactions: The reaction between soluble antigen and antibody leads to the visible precipitate formation, which is called a precipitin reaction. Antibodies that bring about precipitate formation on reacting with antigens are called as precipitins. Whenever a particulate antigen interacts with its antibody, it would result in clumping or agglutination of the particulate antigen, which is called agglutination reaction. The antibody 'involved in bringing about agglutination reaction is called agglutinin. Opsonisation or enhanced attachment is the process by which a pathogen is marked of ingestion and destruction by a phagocyte. Opsonization involves the binding of an opsonin i.e., antibody, to a receptor on the pathogens. cell membrane. After opsonin binds to the membrane, phagocytes are attracted to the pathogen. So, opsonization is a process in which pathogens are coated with a substance called an opsonin, marking the pathogen out for destruction by the immune system. This results in a much more efficient phagocytosis. The neutralization reactions are the reactions of antigen-antibody that involve the elimination of the harmful effects of bacterial exotoxins or a virus by specific antibodies. These neutralizing substances i.e. antibodies are known. as antitoxins. This specific antibody is produced by a host cell in response to a bacterial exotoxin or corresponding toxoid (inactivated toxin).

Lymphocytes: About 20-30% of the white blood cells are lymphocytes. They have a large nucleus filling most of the cell, surrounded by a little cytoplasm. The two main types of lymphocytes are Band T lymphocytes. Both these are produced in the bone marrow. B lymphocytes (B cells) stay in the bone marrow until they are mature. Then they circulate around the body. Some remain in the blood, while others accumulate in the lymph nodes and spleen. T lymphocytes leave the bone marrow and mature in the thymus gland. Once mature, T cells also accumulate in the same areas of the body as B cells. Lymphocytes have receptor proteins on their surface. When receptors on a B cell bind with an antigen, the B cell becomes activated and divides rapidly to produce plasma cells. The plasma cells produce antibodies. SomeB cells do not produce antibodies but become memory cells. These cells are responsible for the secondary immune response. T lymphocytes do not produce antibodies. They recognize antigen-presenting cells and destroy them. The two important types of T cells are Helper T cells and Killer T cells. Helper T cells release a chemical called cytokine which activates B cells. Killer cells move around the body and destroy cells which are damaged or infected. Apart from these cells neutrophils and monocytes destroy foreign cells by phagocytosis. Monocytes when they mature into large cells, they are called macrophages which performs phagocytosis on any foreign organism. Dendritic cells are called so because it's covered with long, thin membrane extensions that resemble dendrites of nerve cells. These cells present the antigen to T-helper cells. Four types of dendritic cells are known. They are Langerhans, interstitial cells, myeloid and lymphoid cells.

Lymph node has three zones. They are the cortex, paracortex, and medulla. The outer most layer of the lymph node is called cortex, which consists of B-lymphocytes, macrophages, and follicular dendritic cells. The paracortex zone is beneath the cortex, which is richly populated by T lymphocytes and interdigitating dendritic cells. The innermost zone is called the medulla which is sparsely populated by lymphocytes, but many of them are plasma cells, which actively secrete antibody molecules. As the lymph enters, it slowly percolates through the cortex, paracortex, and medulla, giving sufficient chance for the phagocytic cells and dendritic cells to trap the antigen brought by the lymph. The lymph leaving a node carries enriched antibodies secreted by the medullary plasma cells against the antigens that enter the lymph node. Sometimes visible swelling of lymph nodes occurs due to active immune response and increased the concentration of lymphocytes. Thus swollen lymph nodes may signal an infection. There are several groups of lymph nodes. The most frequently enlarged lymph nodes are found in the neck, under the chin, in the armpits, and in the groin.

Thymus is most active during the neonatal and pre-adolescent periods. The. thymus is a fiat and bilobed organ located behind the stemun, above the heart. Each lobe of the thymus contains numerous lobules, separated from each other by connective tissue called septa. Each lobule is differentiated into an outer cortex and an inner medulla. Within each lobule, the developing T cells called thymocytes are arranged into outer cortex and inner medulla. The inner medulla contains immature thymocytes and outer cortex has matured thymocytes. One of its main secretions is the hormone thymosin. It stimulates the T cell to become mature and immunocompetent. By the early teens, the thymus begins to atrophy and is replaced by adipose tissue.

S.No	Primary Immune Response	Secondary Immune Response
1.	It occurs as a result of primary contact with an antigen.	It occurs as a result of second and subsequent contacts with the same antigen
2.	Antibody level reaches peak in 7 to 10 days	Antibody level reaches peak in 3 to 5 days.
3.	Prolonged period is required to establish immunity	It establishes immunity in a short time.
4.	There is rapid decline in antibody level	Antibody level remains high for longer period.
5.	It appears mainly in the lymph nodes and spleen.	It appears mainly in the bone marrow followed by the spleen and lymph nodes

S. No	Active Immunity	Passive Immunity
1.	Active immunity is produced actively by host's immune system	Passive immunity is received passively and there is no active host participation
2.	It is produced due to contact with pathogen or by its antigen.	It is produced due to antibodies obtained from outside
3.	It is durable and effective in protection.	It is transient and less effective
4.	Immunological memory is present	No memory
5.	Booster effect on subsequent dose is possible.	Subsequent dose is less effective
6.	Immunity is effective only after a short period	Immunity develops immediately

Type of innate immunity	Mechanism
1. Anatomical barriers Skin Mucus membrane	Prevents the entry' of microbes. Its acidic environment (pH 3-5) retards the growth of microbes Mucus entraps foreign microorganisms and competes with microbes for attachment.
2. Physiological barriers Temperature Low pH Chemical mediators	Normal body temperature inhibits the growth of pathogens. Fever also inhibits the growth of pathogens The acidity of gastric secretions (HCI) kills most ingested microbes Lysozyme acts as antibacterial agent and cleaves the bacterial cell wall. Interferons induce antiviral state in the uninfected cells. Complementary substances produced from leucocytes lyse the pathogenic microbes or facilitate phagocytosis.
3. Phagocytic barriers	Specialized cells (Monocytes, neutrophils, tissue macrophages) phagocytose and digest whole microorganisms
4. Inflammatory barriers	Tissue damage and infection induce leakage of vascular fluid, containing chemotactic signals like serotonin, histamine, and prostaglandins. They influx the phagocytic cells into the affected area. This phenomenon is called diapedesis.

Helminths are mostly endoparasitic in the gut and blood of human beings and cause diseases called helminthiasis. The two most prevalent helminthic diseases are Ascariasis and Filariasis. Ascaris is a monogenic parasite and exhibits sexual dimorphism. Ascariasis is a disease caused by the intestinal endoparasite Ascaris lumbricoides commonly called the roundworms. It is transmitted through ingestion of embryonated eggs through contaminated food and water. Children playing in contaminated soils are also prone to have a chance of transfer of eggs from hand to mouth. The symptoms of the disease are abdominal pain, vomiting, headache, anemia, irritability, and diarrhoea. A heavy infection can cause nutritional deficiency and severe abdominal pain and causes stunted growth in children. It may also cause enteritis, hepatitis, and bronchitis.
Filariasis is caused by Wuchereria bancrofti, commonly called filarial worm. It is found in the lymph vessels and lymph nodes of man. Wuchereria bancrofti is sexually dimorphic, viviparous and digenic. The life cycle is completed in two hosts, man and the female Culex mosquitoes. The female filarial worm gives rise to juveniles called microfilariae larvae. In the lymph glands, the juveniles develop into adults. The accumulation of the worms blocks the lymphatic system resulting in inflammation of the lymph nodes. In some cases, the obstruction of lymph vessels causes elephantiasis or filariasis of the limbs, scrotum and mammary glands

(i) Plasmodium vivax is a digenic parasite, involving two hosts, man as the secondary host and female Anopheles mosquito as the primary host. The life cycle of Plasmodium involves three phases namely schizogony, gamogony and sporogony (f.g)
(ii) The parasite first enters the human blood stream through the bite of an infected female Anopheles mosquito. As it feeds, the mosquito injects the saliva containing the sporozites.
(iii) The sporozoites within the blood stream enter the hepatic cells of the liver and undergoes multiple asexual fission (schizogony). This produces merozoites which are released from liver cells.
(iv) The merozoites penetrate the RBC's. Inside the RBC of Blood, the merozoite of Plasmodium to develop as unicellular trophozoites. The trophozoite grows in size and a central vacuole develops pushing them to one side of cytoplasm and becomes the signet ring stage.
(v)The trophozoite nucleus then divides asexually to produce the The schizont divides and produces on nucleated merozoites.
(vi) Eventually the erythrocyte lyses, releasing the merozoites and haemozoin toxin into the blood stream to infect other erythrocytes. Lysis of red blood cells results in cycles of fever and other symptoms. This erythrocytic stage is cyclic and repeats itself approximately every 48 to72 or longer depending on the species of Plasmodium involved. The sudden release of merozoites triggers an attack on the RBCs.
(vii) Occasionally, merozoites differentiate into macrogametocytes and microgametocytes When these are ingested by a mosquito, they develop into male and female gametes respectively
In the mosquito's gut, the infected erythrocytes lyse and male and female gametes fertilize to form a diploid zygote called ookinete. The ookinete migrates to the mosquito's gut wall and develops into an oocyte.
The oocyte undergoes meiosis by a process called sporogony to form sporozoites. These sporozoites migrate to the salivary glands of the mosquito. The cycle is now completed and when the mosquito bites another human host, the sporozoites are injected and the cycle begins a new.
The pathological changes caused by malaria, affect not only the erythrocytes but also the spleen and other visceral organs. Incubation period of malaria is about 12 days. The early symptoms of malaria are headache, nausea and muscular pain. The classic symptoms first develop with the synchronized release of merozoites, hemozoin toxin and erythrocyte debris into the bloodstream resulting in malarial paroxysms - shivering chills, high fever followed by sweating. Fever and chills are caused partly by malarial toxins that induce macrophages to release tumor necrosis factor (TNF-a) and interleukin.

S.No	Diseases	Caustive agent	Site of infection	Mode of transmission	Symptoms
1.	Common cold	Rhino viruses	Respiratory tract	Droplet infection	Nasal congestion and discharge sore throat, cough and headache
2.	Mumps	Mumps cirus (RNA virus)Paramyxa cirus	Salivary glands	Saliva and droplet infection	Enlargement of the parotid glands
3.	Measles	Rubella virus (RNA virus Parmyxco),	Skin and respiratory tract	Droplet infection	Sore throat, running nose cough and fever. reddish rashes  on the skin, neck and ears
4.	Viral hepatitis	Hepatitis - B virus	Liver	Parenteral route blood transfusion	Liver damage, jaundice, nausea yellowish eyes, fever and pain in the abdomen
5.	Chicken pox	Varicella-Zoster virus (DNA Virus	Respiratory tract,skin and nervous	Droplet infection and direct contact	Mild fever with itchy skin, rash and blisters

Protozoan Disease :
1. Protozoans are unicellular organisms and can sometimes cause illness.
2. Common protozoal diseases include malaria, giardia, and toxoplasmosis.
The two diseases caused by protozoans are Malaria and Kala-azar.
Causative agent:
1. Malaria -a single-celled parasite of the genus plasmodiu
2. Kala-azar - Leishmania organism.

No	Diseases	Causative agent	Site of infection	Mode of transmission	Symptoms
1.	Shigellosis (Bacillary dysentery)	Shigella sp.	Intestine	Food and water contaminated by faces oral route	Abdominal pain,dehydration, blood and mucus in the stools
2.	Bubonic plague (Black death)	Yersinia pestis	Lymph nodes'	Rat flea vectorXenopsylla cheopis	Fever, headache, and swollen lymph nodes
3.	Diphtheria	Corynebacterium diphtheriae	Larynx, skin nasal and genital passage	Droplet infection	Fever, sore throat, hoarseness and difficulty in breathing
4.	Cholera	Vibrio cholerae	Intestine	Contaminated food and water/faecal oral route	Severe diarrhoea and dehydration
5.	Tetanus)Lock jaw)	Clostridium tetani	Spasm of muscles	Through wound infection	Rigidity of jaw muscle increased heart beat rate and spasm of the muscles of the jaw and face