All Free Biology MCQs with Answers

2071. Which of the following is a sentimentally arranged excretory system?

• A. Protonephridium
• B. Metanephridium
• C. Malpighian tubules
• D. Nephrons

Explanation: Metanephridia are segmentally arranged excretory organs, with repeated units occurring in successive body segments of animals such as earthworms. The likely alternative is protonephridia, but these are flame-cell systems rather than segmentally repeated metanephridia.

2072. The distal blind end of the malpighian tubules bathes freely in____________?

• A. Digestive tract
• B. Intestines
• C. Haemocoel
• D. Coelom

Explanation: Malpighian tubules are blind-ended tubes whose closed ends lie in the haemocoel, bathing in haemolymph and absorbing nitrogenous wastes from it. The likely distractor is the intestine, because the tubules empty into the gut, but their blind ends are surrounded by haemolymph in the haemocoel.

2073. Which of the following kidney stones are most common?

• A. Calcium oxalate
• B. Calcium phosphate
• C. Uric acid
• D. All of these

Explanation: Calcium oxalate stones are the most common type of kidney stone and form when calcium combines with oxalate in concentrated urine. The likely distractor is “all of these,” because calcium phosphate and uric acid stones also occur, but they are less common than calcium oxalate stones.

2074. Which of the following nephrons play important role in production of concentrated urine?

• A. Crotical
• B. Medullary
• C. Juxtramedullary
• D. None of these

Explanation: Juxtamedullary nephrons have long loops of Henle extending deep into the medulla, along with vasa recta that support the countercurrent mechanism for concentrating urine. The likely mistake is cortical nephrons, which are more numerous but have shorter loops and contribute less to urine concentration.

2075. The mechanism of regulation, generally between organism and its environment, of solutes and the gain and the loss of water is called________?

• A. Homeostasis
• B. Hemostasis
• C. Osmoregualtion
• D. Thermoregulation

Explanation: Osmoregulation is the control of water balance and the concentration of dissolved salts in an organism relative to its environment. It maintains suitable water potential and ion concentration in body fluids. Students may choose homeostasis, but homeostasis is the broader maintenance of a stable internal environment, whereas osmoregulation specifically concerns water and solutes.

2076. According to Lamarch evolution occurred as the result of__________?

• A. Natural selection
• B. The theory of recapitulation
• C. Inheritance of acquired characters
• D. Over production

Explanation: Lamarck proposed that organisms acquire adaptations through use and disuse and pass those acquired characters to their offspring. Natural selection is Darwin's mechanism, while overproduction is a condition contributing to Darwinian selection. Students may choose a because natural selection is the modern explanation for adaptation, but it was not Lamarck's proposed mechanism.

2077. In the human body, fats are stored in the__________?

• A. Epidermis
• B. Adipose tissue
• C. Liver
• D. Epithelium

Explanation: Most long-term fat storage occurs in adipose tissue, whose cells store triglycerides in large lipid droplets and also provide insulation and cushioning. The liver processes and stores some fat but is not the principal storage tissue, and the epidermis and epithelium are not normal fat depots. Students may choose the liver because it handles lipid metabolism, but metabolism is different from the main site of storage.

2078. Steroids, a biologically active organic compound, are derived from __________?

• A. Hormones
• B. Chemicals
• C. Cholesterol
• D. Carbohydrates

Explanation: Steroids are a class of lipids formed from the four-ring structure of cholesterol, which serves as their main precursor. Students may choose hormones because many steroids act as hormones, but hormones are products or functions of some steroids, not their source.

2079. They are widespread as protective coatings on fruits and leaves?

• A. cholesterol
• B. waxes
• C. chitin
• D. all of these

Explanation: Waxes are lipids that form water-resistant protective coatings on the surfaces of leaves and fruits, reducing water loss and blocking pathogens. Cholesterol is a membrane lipid mainly found in animals, while chitin is a structural polysaccharide, so choosing either confuses their functions with those of waxes.

2080. Accumulation of lipid molecules in brain cells lead to__________?

• A. paralysis
• B. oedema
• C. mental retardation
• D. all of these

Explanation: In some lipid-storage disorders, lipids accumulate in brain cells and damage neurons, causing progressive mental impairment or mental retardation. Students may choose paralysis because severe neuronal damage can eventually affect movement, but the characteristic result stated here is mental retardation.