Q.Give an example of a rod shaped virus.

Concept and Intuition

Vaccines are classified by what they contain:

• Inactivated (killed) whole-agent vaccines: the entire pathogen, chemically or physically killed so it can't cause disease but still triggers immunity — classic examples are Rabies and Influenza (and Salk/IPV polio).
• Live attenuated vaccines: a weakened but still-living pathogen (e.g. Measles, BCG, oral/Sabin polio).
• Toxoid vaccines: an inactivated bacterial toxin, not the whole organism — e.g. Diphtheria and Tetanus.

Step-by-Step Solution

1. Check (A) Influenza, Rabies — both are prepared as killed, whole-pathogen vaccines. Matches "inactivated whole agent" cleanly.
2. Check (C) Diphtheria, Tetanus — these are toxoid vaccines (inactivated toxin only, not the whole bacterium), so this doesn't fit "whole agent."
3. Check (D) Hepatitis-A (inactivated), Measles (live attenuated) — mixed …

Concept and Intuition

"Ringworm" is a common name for dermatophytosis, a superficial infection of

the skin, hair, or nails caused by a group of keratin-digesting fungi collectively

called dermatophytes (genera Trichophyton, Microsporum, Epidermophyton). The

infection produces the classic dry, scaly, circular ("ring-shaped") lesion with a

raised, active, itchy border — the name comes from the ring-like appearance, not

from any actual worm involvement.

Step-by-Step Solution

1. Consider the causative-agent categories: virus, bacteria, fungi, protozoan.
2. Recall that dermatophyte infections (ringworm, athlete's foot, jock itch) are specifically caused by a group of fungi adapted to digest keratin in skin, hair, and nails. …

Concept and Intuition

Malarial fever is periodic because it is driven by the synchronous rupture of infected RBCs. When a whole cohort of erythrocytic schizonts bursts at once, it releases merozoites together with the toxin haemozoin, which triggers the chill–fever–sweat paroxysm. So the fever interval equals the length of the erythrocytic cycle:

• 48-hour cycle → fever on day 1, day 3, day 5 … Counting inclusively, that is every third day → tertian.
• 72-hour cycle → fever every fourth day → quartan.

Three species run a 48-hour cycle and are therefore all "tertian"; they are then separated by severity, and that adjective is what the question is testing:

• P. falciparum — enormous parasitaemia, sequestration in capillaries, cerebral malaria → malignant tertian, the killer.
• P. vivax — high relapse rate but rarely fatal → benign tertian.
• P. ovale — the least aggressive, geographically restricted species → mild tertian.
• P. malariae — 72-hour cycle → quartan, not tertian at all.

Step-by-Step Solution

1. The word tertian eliminates P. malariae (option D), which causes quartan malaria. …

Concept and Intuition

Epidemiologists distinguish emerging diseases (newly identified, not previously seen in humans, e.g. many novel viral diseases) from re-emerging diseases (known diseases that had declined in incidence but have reappeared, often in new areas or with new drug-resistant strains). The question's wording — "existed in the past but now showing incidence... in new geographical areas" — matches the re-emerging category exactly.

Step-by-Step Solution

1. Parse the definition given: prior existence + renewed incidence + spread to new areas = re-emerging disease.
2. Check option (A): Tuberculosis labelled "Re-emerging" — matches; TB had declined with antibiotics but has resurged (including multidrug-resistant TB) and spread into new regions. …

Concept and Intuition

Several early scientists contributed to the discovery and study of microorganisms, but their specific legacies differ: Antonie van Leeuwenhoek first observed and described microorganisms ("animalcules") under a microscope; Christian Gottfried Ehrenberg named and classified various microbes including "bacterium"; but it was Louis Pasteur who conclusively demonstrated that microorganisms are responsible for causing specific diseases, establishing what is known as the germ theory of disease, and is celebrated as a founding figure of bacteriology/microbiology.

Step-by-Step Solution

1. Rule out Ehrenberg — he named organisms and coined terms, but is not specifically credited with germ theory.
2. Rule out Leeuwenhoek — he discovered microorganisms via microscopy, a foundational but earlier step, and is not linked to virology or germ theory specifically.
3. Rule out Butler — not a recognised founder of germ theory or bacteriology in this context. …

Concept and Intuition

Disease causative-agent classification is a staple of the "Human Health and Disease" chapter: common cold is viral (rhinovirus), pneumonia is commonly bacterial (Streptococcus pneumoniae) though it can also be viral, typhoid is bacterial (Salmonella typhi), while ring worm is a classic superficial mycosis caused by keratin-digesting dermatophyte fungi, producing the characteristic ring-shaped lesions on skin.

Step-by-Step Solution

1. Common cold → viral. …

Concept and Intuition

Assertion–Reason questions often hinge on getting causality the right way round. Dengue fever's actual cause is infection by the dengue virus (genus Flavivirus), transmitted through the bite of an infected female Aedes aegypti mosquito. As the disease progresses (particularly in its severe form, dengue haemorrhagic fever/dengue shock syndrome), the virus damages bone marrow megakaryocytes and triggers immune-mediated platelet destruction, causing thrombocytopenia. This low platelet count in turn impairs the body's clotting ability and can cause bleeding manifestations. So "failure of clot reaction" is a symptom/complication that follows from the disease, not the thing that causes the disease in the first place — the Assertion inverts this relationship and is therefore false.

The Reason is a separate, self-contained clinical statement: because platelet counts can fall so low in dengue, transfusion of platelet concentrates is indeed a standard supportive treatment in moderate-to-severe cases. This statement is true regardless of whether the Assertion's causal claim is correct.

Step-by-Step Solution

1. Identify the true cause of dengue fever: infection by the dengue virus via mosquito bite — not a primary clotting disorder.
2. Recognise that reduced platelets/clotting failure are consequences of the infection (via bone-marrow suppression and immune platelet destruction), not its cause. This makes the Assertion false. …

Concept and Intuition

Diagnostic tests target different aspects of disease: the Widal test detects the host's antibody response (agglutinins) to specific S. typhi somatic (O) and flagellar (H) antigens, becoming positive as antibody titres rise during infection. ELISA is a more general antigen/antibody-detection technique used across many diseases (e.g., HIV). Western blot is typically used as a confirmatory test after ELISA (e.g., for HIV). Liver function tests assess general liver health/damage and are not disease-specific diagnostic confirmations for typhoid.

Step-by-Step Solution

1. Recognise "typhoid" as the causative context (Salmonella typhi).
2. Recall that its diagnostic hallmark test, taught in standard biology courses, is the Widal test (agglutination test). …