All Free Biology MCQs with Answers

• A. Sucrose
• B. Lactose
• C. Maltose
• D. Amylose

Explanation: Lactose, a disaccharide composed of glucose and galactose, contains a beta-1,4-glycosidic linkage. In this linkage, the hydroxyl group (-OH) on carbon 1 of glucose is connected to the hydroxyl group on carbon 4 of galactose. This beta configuration means that the oxygen atom involved in the bond formation is below the plane of the ring in the glucose molecule and above the plane in the galactose molecule. Also its a bond between beta glucose and beta galactose.

• A. Cx(H2O)x
• B. C6H12O6
• C. Cx(H2O)y
• D. Cx(HO)y
• E. Cx(H2O2)y

Explanation: Carbohydrates are the instant sources of energy in living organisms. The general carbohydrate formula is Cx(H2O)y, where x and y are integers. This formula represents that carbohydrates are composed of carbon, hydrogen, and oxygen in a ratio of 1:2:1. Glucose, which has the formula C6H12O6, is an example of carbohydrate and is a primary energy source for the body's cells.

• A. 1, 4 glycosidic linkage
• B. 1, 6 glycosidic linkage
• C. 1,2 glycosidic linkage
• D. 1,3 glycosidic linkage

Explanation: Fructose and glucose combine through condensation process to form sucrose. Glucose and fructose join together through a glycosidic bond to form sucrose. A glycosidic bond is a type of covalent bond that connects the two monosaccharides, glucose and fructose, to create the disaccharide known as sucrose. Specifically, the glycosidic bond forms between the anomeric carbon atom of glucose (C1) and the hydroxyl group of fructose (C2). This linkage results in the formation of a new molecule, sucrose, with the molecular formula C₁₂H₂₂O₁₁. Sucrose is commonly found in various plants, particularly in sugar cane and sugar beets. It serves as a major source of energy in the human diet and is commonly known as table sugar or cane sugar.

• A. Monosaccharides
• B. Oligosaccharides
• C. Polysaccharides
• D. Carbohydrates

Explanation: The formula (CH2O)n specifically describes monosaccharides, the simplest form of carbohydrates that consist of single sugar units. This formula fits monosaccharides perfectly, unlike oligosaccharides and polysaccharides, which have more complex structures due to multiple sugar units. While 'carbohydrates' as a general term can be represented by this formula, it lacks the specificity needed to identify the simplest form.

• A. SA node > AV node > Purkinje fibres > ventricles
• B. SA node > Purkinje fibres > AV node > ventricles
• C. AV node > SA node > Purkinje fibres > ventricles
• D. AV node > Purkinje fibres > SA node > ventricles

Explanation: The correct pathway of nerve impulse during the excitation and contraction of the human heart is: SA node > AV node > Purkinje fibres > ventricles. The sinoatrial (SA) node, located in the right atrium, acts as the primary pacemaker of the heart by initiating the electrical impulse. This impulse travels to the atrioventricular (AV) node, located at the junction of the atria and ventricles. From the AV node, the impulse moves to the bundle of His and then to the Purkinje fibres, which distribute the impulse throughout the ventricles, causing them to contract. This sequence ensures the coordinated contraction of the heart muscle, which is essential for efficient blood pumping.

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: During ventricular systole, ventricular pressure exceeds atrial pressure to pump blood into aorta, AV valves closes to prevent backflow of blood into atria and aortic valve opens to allow for blood flow.So B is correct.

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: When pressure is highest in aorta both AV valves and semilunar are closed because ventricular contraction has just completed.So C is correct.

• A. Aortic pressure exceeds ventricular pressure
• B. Left atrial pressure exceeds left ventricular pressure
• C. Right ventricular pressure exceeds right atrial pressure
• D. Pulmonary trunk pressure exceeds ventricular pressure

Explanation: The tricuspid valve is located between the right atrium and the right ventricle of the heart. It closes when the pressure in the right ventricle exceeds that in the right atrium, which occurs during ventricular contraction (systole). This prevents the backflow of blood into the right atrium. Option A refers to conditions affecting the aortic valve, Option B describes conditions for the mitral valve, and Option D pertains to the pulmonary valve, none of which are related to the tricuspid valve.

• A. A
• B. B
• C. C
• D. D

Explanation: During atrial systole, the atria contract to push blood into the ventricles. Therefore, the ventricles are relaxed at this stage. The atrioventricular valves (tricuspid and mitral valves) must be open to allow blood to flow from the atria into the ventricles. Meanwhile, the semilunar valves (aortic and pulmonary valves) remain closed to prevent blood from flowing back into the ventricles from the arteries. Hence, Option B is correct. Options A, C, and D describe states that do not occur during atrial systole.

• A. Ventricular repolarization
• B. Ventricular depolarization
• C. Atrial repolarization
• D. Atrial depolarization

Explanation: The T wave in an ECG (electrocardiogram) represents ventricular repolarization, indicating the recovery of the ventricles before the next contraction.