All Free Biology MCQs with Answers

2431. In higher vertebrates, the immune system can distinguish between self-cells and non-self-cells. If this property is lost due to genetic abnormality and it attacks self-cells, then it leads to:

• A. Autoimmune disease
• B. Active immunity
• C. Allergic response
• D. Graft rejection

Explanation: Autoimmunity is a disorder of the body's defense mechanisms in which an immune response is elicited against its own tissues, which are thereby damaged or destroyed. Autoimmunity may be caused due to genetic or environmental factors. This immune system dysfunction can result in a wide range of symptoms and health problems. There are more than 80 known autoimmune diseases, and they can affect virtually any part of the body.

2432. If you suspect a major deficiency of antibodies in a person, to which of the following would you look for confirmatory evidence?

• A. Haemocytes
• B. Serum globulins
• C. Fibrinogen in plasma
• D. Serum albumins

Explanation: Serum globulins are proteins that include gamma globulins(antibodies) and a variety of enzymes and carrier/transport proteins. The specific profile of the globulins is determined by protein electrophoresis(SPEP), which separates the proteins according to size and charge. There are four major groups that can be identified: α-1 globulins, α-2 globulins, beta globulins, and gamma globulins. Once the abnormal group has been identified, further studies can determine the specific protein excess or deficit. Since the gamma fraction usually makes up the largest portion of the globulins, therefore antibody deficiency is mainly related to the low level of serum globulins.

2433. Which of the following immunoglobulins does constitute the largest percentage in human milk?

• A. IgA
• B. IgG
• C. IgD
• D. IgM

Explanation: IgA immunoglobulins are the second most abundant class of immunoglobulins, which are mainly found in sweat, tears, saliva, mucus, colostrum, and gastrointestinal secretions.

2434. Which of the following diseases is caused by a protozoan?

• A. Babesiosis
• B. Blastomycosis
• C. Syphilis
• D. Influenza

Explanation: Babesiosis is a malaria-like parasitic disease caused by infection with Babesia, a parasitic protozoan. Babesiosis has long been recognized as a disease of cattle and other domestic animals until human forms of babesiosis were discovered. Babesia parasites reproduce in the red blood cells of mammals and cause hemolytic anemia, quite similar to malaria. The parasite is transmitted by ticks.

2435. A grafted kidney may be rejected in a patient due to:

• A. Passive immune response
• B. Innate immune response
• C. Humoral immune response
• D. Cell-mediated immune response

Explanation: Cell-mediated immune response(CMIS) consists of T-lymphocytes. It reacts against transplants. Transplantation may result in the rejection of the transplanted organs. The immune system recognizes the protein in the transplanted tissue or organ as foreign and initiates cellular immunity against it.

2436. The active form of Entamoeba histolytica feeds upon:

• A. Food in intestine
• B. Blood only
• C. Erythrocytes, mucosa and submucosa of the colon
• D. Mucosa and submucosa of colon only

Explanation: Entamoeba histolytica(Gr., entos: within+amoeba: change+histones: tissue + lysis: dissolve) is the causative organism of amoebic dysentery or amoebiasis in man. It is a microscopic endoparasite of man. It is commonly found in the upper part of the large intestine(colon) and is very often lodged in the liver, lungs, brain, and testes. In its life cycle, it occurs in three distinct forms (i) trophozoite or magna form, (ii) precystic or minuta form, and (iii) cystic form. Trophozoite is the most active, motile, and feeding form which is pathogenic to man. It lives in the mucous and submucous layers of the colon and feeds on these layers and erythrocytes.

2437. HIV that causes AIDS first starts destroying:

• A. Helper T lymphocytes
• B. Thrombocytes
• C. B lymphocytes
• D. Leucocytes

Explanation: The AIDS retrovirus, called human immunodeficiency virus(HIV), mounts a direct attack on CD4 + T-helper cells because it recognizes the CD4 coreceptors associated with these cells. HIV's attack on CD4 + T cells cripples the immune system in at least three ways. First, HIV-infected cells die only after releasing replicated viruses that infect other CD4 + T cells, until the entire population of CD4 + T cells is destroyed. Second, HIV causes infected CD4 + T cells, to secrete a soluble suppressing factor that blocks other T cells from responding to the HIV antigen. Finally, HIV may block transcription of MHC genes, hindering the recognition and destruction of infected CD4 + T cells, and thus protecting those cells from any remaining vestiges of the immune system. The combined effect of these responses to HIV infection is to wipe out the human immune defense.

2438. Which is the particular type of drug that is obtained from the plant whose flowering branch is shown here?

• A. Hallucinogen
• B. Depressant
• C. Stimulant
• D. Pain killer

Explanation: The plant illustrated in the diagram is Datura. It is a genus of flowering plants in the family Solanaceae. Seeds of Datura stramonium are misused for their hallucinogenic properties because of the presence of anticholinergic alkaloids atropine, hyoscyamine, and scopolamine(= hyoscine). However, even in slight excess, they can cause death. Ingesting or coming into contact with parts of the plant can lead to a range of symptoms, including hallucinations, delirium, blurred vision, dry mouth, and other severe health effects. In some cases, ingesting Datura can be fatal.

2439. At which stage of HIV infection does one usually show symptoms of AIDS?

• A. Within 15 days of sexual contact with an infected person
• B. When the infected retro virus enters host cells
• C. When HIV damages a large number of helper T-lymphocytes
• D. When the viral DNA is produced by reverse transcriptase

Explanation: AIDS is a disorder of the cell-mediated immune system of the body. The virus responsible for AIDS is HIV(Human immunodeficiency virus). There is a reduction in the number of helper T cells which stimulate antibody production by B-cells. This results in the loss of natural defense against viral infection. HIV attacks the immune system, specifically targeting the CD4 cells (T cells). HIV infection progresses through several stages by infecting Helper T cells.

2440. Infection of Ascaris usually occurs by:

• A. Tsetse fly
• B. Mosquito bite
• C. Drinking water containing eggs of Ascaris
• D. Eating imperfectly cooked pork

Explanation: Man acquires infection of Ascaris by directly ingesting Ascaris eggs, containing the infective second-stage larva, with contaminated food or water. The life cycle of Ascaris is monogenetic. There is no vector or intermediate host. Infection with Ascaris, a type of parasitic roundworm, typically occurs through the ingestion of Ascaris eggs.