Every Book Back multiple-choice question from Human Health and Diseases (12th Standard Zoology, Samacheer Kalvi) — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Malaria caused by Plasmodium is transmitted through
- A. Air
- B. Contact
- C. Fleas on food
- D. Mosquito bitesCorrect
Explanation. Malaria is a vector-borne disease caused by the protozoan parasite Plasmodium. It is transmitted to humans through the bites of infected female Anopheles mosquitoes during their blood meals.
Q2
A 30 year old woman has bleedy diarrhoea for the past 14 hours, which one of the following organisms is likely to cause this illness?
- A. Streptococcus pyogens
- B. Clostridium difficile
- C. Shigella dysenteriaeCorrect
- D. Salmonella enteritidis
Explanation. Bloody diarrhea is a classic symptom of bacillary dysentery. This intestinal disease is caused by the pathogenic bacterium Shigella dysenteriae, which is transmitted through contaminated food and water.
Q3
Which of the following disease is spread through droplet nuclei?
- A. Tularemia
- B. Listeriosis
- C. Chicken poxCorrect
- D. Mumps
Explanation. Chickenpox is highly contagious and spreads from person to person through airborne droplet nuclei or direct contact. These microscopic infectious droplets remain suspended in the air and can be inhaled by others.
Q4
Exo-erythrocytic schizogony of Plasmodium takes place in -------
- A. RBC
- B. Leucocytes
- C. Stomach
- D. LiverCorrect
Explanation. During the life cycle of Plasmodium, the sporozoites first infect the host's liver cells. In the liver, they undergo multiple asexual division, a process known as exo-erythrocytic schizogony, to produce merozoites.
Q5
The sporozoites of Plasmodium vivax are formed from ------------
- A. Gametocytes
- B. Sporoblasts
- C. OocystsCorrect
- D. Spores
Explanation. In the mosquito host, sexual reproduction leads to the formation of oocysts on the stomach wall. These oocysts undergo multiple divisions, or sporogony, to produce numerous infectious sporozoites.
Q6
Poliomyelitis which causes infantile paralysis enters the body through.........
- A. Skin
- B. Mouth and noseCorrect
- C. Ears
- D. Eyes
Explanation. Poliovirus, the causative agent of poliomyelitis, is typically transmitted via the faecal-oral route or through respiratory droplets. It enters the human body through the mouth and nose.
Q7
Amphetamines are stimulants of the CNS, whereas barbiturates are ----
- A. CNS stimulant
- B. both a and b
- C. hallucinogenic
- D. CNS depressantsCorrect
Explanation. While amphetamines increase central nervous system activity and act as stimulants, barbiturates reduce brain activity and slow down body functions, thereby acting as central nervous system depressants.
Q8
Marijuana is extracted from
- A. Dried leaves and flowers of hemp plantCorrect
- B. Ergot fungus
- C. Roots of hemp plant
- D. Cocoa plant
Explanation. Marijuana is a cannabinoid drug obtained from the Indian hemp plant, Cannabis sativa. It is prepared from the dried leaves and female flowers of this plant.
Q9
Choose the correctly match pair.
- A. Amphetamines - StimulantCorrect
- B. LSD - Narcotic
- C. Heroin - Psychotropic
- D. Benzodiazepine - Pain killer
Explanation. Amphetamines are synthetic drugs that stimulate the central nervous system, increasing alertness and energy. Other choices are mismatched as LSD is a hallucinogen, heroin is a narcotic, and benzodiazepines are tranquilizers.
Q10
The Athlete's foot disease in human is caused by-------
- A. Bacteria
- B. FungiCorrect
- C. Virus
- D. Protozoan
Explanation. Athlete's foot is a common skin infection of the feet. It is caused by a group of fungi called dermatophytes, specifically Tinea pedis, which thrive in warm, moist environments.
Q11
Cirrhosis of liver is caused by chronic intake of ------
- A. Opium
- B. AlcoholCorrect
- C. Tobacco
- D. Cocaine
Explanation. Chronic and excessive consumption of alcohol leads to progressive liver damage, characterized by scarring and loss of functional tissue, a medical condition known as liver cirrhosis.
Q12
The sporozoite of the malarial parasite is present in ----
- A. saliva of infected female Anopheles mosquito.Correct
- B. RBC of human suffering from malaria.
- C. Spleen of infected humans.
- D. Gut of female Anopheles mosquito.
Explanation. Sporozoites represent the infective stage of the malarial parasite Plasmodium. They migrate to and are stored in the salivary glands of infected female Anopheles mosquitoes, ready to be injected during a bite.
Q13
Haemozoin is
- A. A precursor of haemoglobin.
- B. A toxin from Streptococcus.
- C. A toxin from Plasmodium species.Correct
- D. A toxin from Haemophilus species.
Explanation. Haemozoin is a toxic crystalline pigment produced by Plasmodium species as a byproduct of hemoglobin digestion. Its release into the bloodstream during RBC rupture triggers the characteristic fever and chills.
Q14
The drug synthesised from Datura is
- A. HallucinogenCorrect
- B. Depressant
- C. Stimulant
- D. Pain killer
Explanation. Datura species contain tropane alkaloids that affect the central nervous system. These substances act as potent hallucinogens, causing altered sensory perceptions, illusions, and delusions when ingested.
Q15
Match the pathogens with respective diseases caused by them and select the correct match using the codes given below.
A. Leishmania donavani - i. Amoebiasis
B. Wuchereria bancrofti - ii. Kala - azar
C. Trypanosoma gambiense - iii. Sleeping sickness
D. Entamoeba histolytica - iv. Filariasis
- A. A-ii, B-iv, C-iii, D-iCorrect
- B. A-ii, B-iv, C-i, D-iii
- C. A-iii, B-i, C-ii, D-iv
- D. A-i, B-iv, C-iii, D-ii
Explanation. Leishmania donovani causes Kala-azar, Wuchereria bancrofti causes filariasis, Trypanosoma gambiense causes sleeping sickness, and Entamoeba histolytica causes amoebiasis. This matching corresponds to the first option.
