All Free Biology MCQs with Answers

1981. Embryonic induction is caused by part developing from_____________?

• A. Endoderm
• B. Ectoderm
• C. Mesoderm
• D. Extraembryonic layers

Explanation: Embryonic induction occurs when one group of embryonic cells influences the development of neighbouring cells; the mesoderm acts as an important inducing tissue in early development. Thus, many such developmental signals arise from mesoderm-derived parts. A student may choose ectoderm because it forms structures such as the nervous system, but the question is asking about the inducing tissue, not the tissue being induced.

1982. Which type of respiration is the most effective in frogs?

• A. Coetaneous
• B. Lung
• C. Pulmo-cuntaneous
• D. Through gills

Explanation: Adult frogs use both lungs and moist skin for gas exchange, but pulmonary respiration through the lungs is generally treated as the most effective route for oxygen uptake during active terrestrial life. Students may choose cutaneous respiration because the skin is important in frogs, but it is especially important during rest or when submerged. Option b is the intended answer, although the misspelled alternatives make the item poorly edited.

1983. In which animal respiratory surface are found in more than one organ?

• A. birds
• B. human
• C. fish
• D. frog

Explanation: Frogs use more than one respiratory surface: gases are exchanged through the skin, the lining of the buccal cavity, and the lungs. Humans mainly exchange gases through the alveoli of the lungs, so “human” is the likely distractor. The question asks about respiratory surfaces in more than one organ, not simply the presence of lungs and skin in an animal.

1984. Functional units of lungs are called________?

• A. Alveoli
• B. Air sacs
• C. Parabronchi
• D. None of these

Explanation: Alveoli are the microscopic air sacs where oxygen and carbon dioxide diffuse between the air and pulmonary capillaries, making them the functional units of mammalian lungs. Students may choose air sacs because alveoli are air sacs, but that option is a general description rather than the precise anatomical term.

1985. Lungs are situated in the __________?

• A. Abdominal cavity
• B. Pericardial cavity
• C. Buccal cavity
• D. Thoracic cavity

Explanation: The lungs lie in the thoracic cavity, the chest cavity enclosed by the ribs and diaphragm. The pericardial cavity is specifically the space surrounding the heart, so students may choose it because the heart and lungs are both in the chest.

1986. Transport of oxygen by blood takes place with the help of________?

• A. Erythrocytes
• B. Thrombocytes
• C. Lymphocytes
• D. Leucocytes

Explanation: Erythrocytes transport oxygen because their haemoglobin binds oxygen in the lungs and releases it in body tissues. Students may choose leucocytes because they are also blood cells, but leucocytes provide immune defence and do not normally carry oxygen.

1987. The membrane covering the lungs is a________?

• A. Pleura
• B. Pericardium
• C. Peritoneum
• D. Mesothelium

Explanation: The lungs are enclosed by a double-layered membrane called the pleura, with pleural fluid between its layers to reduce friction during breathing. Students may choose pericardium because it is also a protective membrane, but the pericardium surrounds the heart, not the lungs.

1988. Which Of The Following Produces Harmful Gases_________?

• A. Plants
• B. Motor Vehicles
• C. Bacteria
• D. None of these

Explanation: Motor vehicles produce harmful gases such as carbon monoxide, nitrogen oxides and unburned hydrocarbons through fuel combustion, contributing to air pollution and respiratory disease. Students may choose plants because plants respire and release carbon dioxide, but normal plant respiration is not the main source of the harmful urban gases meant here.

1989. At level above _____ , sound turns into harmful noise pollution?

• A. 80db
• B. 30db
• C. 100db
• D. 120db

Explanation: Sound levels above about 80 dB are commonly regarded as potentially harmful with sufficient exposure and may contribute to noise pollution. Students may choose 120 dB because it is near the pain threshold, but harmful noise begins at lower levels depending on duration and frequency.

1990. __________is a condition in which there is an absence of oxygen supply to an organ's tissues?

• A. Anoxia
• B. Anorexia
• C. Hypoxia
• D. Enuresis

Explanation: Anoxia means complete absence, or near-complete absence, of oxygen supply to tissues, whereas hypoxia means reduced oxygen supply. Anorexia is loss of appetite and enuresis is involuntary urination, so students may choose hypoxia when they remember oxygen deficiency but overlook the word “absence.”