70. Which altered sixth codon of the beta-globin gene produces the haemoglobin change associated with sickle-cell anaemia?
[NEET — 3 May 2026]
- (A) CAG
- (B) GUG
- (C) AUG
- (D) GAG
Answer: (B) GUG
Explanation: Sickle-cell disease results from a point mutation in the beta-globin coding sequence. The sixth mRNA codon changes from GAG, encoding glutamic acid, to GUG, encoding valine. The resulting haemoglobin S can polymerise under low oxygen conditions, distorting red cells.
69. Why do veins possess valves whereas most arteries do not?
[RRB Technician Grade III — 10 March 2026, Shift 3]
- (A) Veins carry low-pressure blood and need backflow prevention
- (B) Arteries are deep and muscle-supported
- (C) Arteries always carry oxygen-rich blood
- (D) Veins carry higher-pressure blood
Answer: (A) Veins carry low-pressure blood and need backflow prevention
Explanation: Venous blood generally returns towards the heart at lower pressure than arterial blood. Valves within many veins prevent reversal of flow, especially in the limbs where blood moves against gravity. Arteries withstand strong pulses using thick, elastic muscular walls.
68. What are the smallest vessels with walls only one cell thick, formed by branching arteries?
[RRB ALP CBT-I — 17 February 2026, Shift 1]
- (A) Arteries
- (B) Capillaries
- (C) Veins
- (D) Arterioles
Answer: (B) Capillaries
Explanation: Arterioles branch into capillary networks within organs. Capillaries have walls mainly one endothelial cell thick, allowing short diffusion distances for gases, nutrients and waste. Their blood ultimately drains through venules into veins. Arteries and arterioles possess thicker muscular walls.
67. What is the fluid matrix of blood in which its cellular elements remain suspended?
[RRB Group D — 6 February 2026, Shift 1]
- (A) Platelets
- (B) Red blood cells
- (C) Plasma
- (D) White blood cells
Answer: (C) Plasma
Explanation: Plasma is the straw-coloured liquid matrix of blood and makes up approximately fifty-five percent of blood volume. It consists predominantly of water with proteins, salts, nutrients, hormones and wastes. Red cells, white cells and platelets are suspended within it.
66. Which of these is not itself a tissue?
[RRB Group D — 4 February 2026, Shift 3]
- (A) Nerves
- (B) Red blood cells
- (C) Muscles
- (D) Blood
Answer: (B) Red blood cells
Explanation: Blood is classified as specialised connective tissue, and muscles and nerves consist of organised tissue structures. A red blood cell is an individual cellular component of the blood tissue, not a distinct tissue in itself. Mature human RBCs also lack nuclei.
65. In human blood, oxygen is mainly transported by which component?
[RRB Group D — 3 February 2026, Shift 1]
- (A) Blood platelets
- (B) Lymph
- (C) Red blood corpuscles
- (D) White blood corpuscles
Answer: (C) Red blood corpuscles
Explanation: Red blood corpuscles contain haemoglobin, which binds oxygen reversibly in lung capillaries and releases it in tissue capillaries. Their biconcave shape increases exchange efficiency. White cells defend against infection and platelets support clotting; neither is the principal oxygen carrier.
64. The blood pressure observed when the heart relaxes is called ______.
[RRB NTPC Graduate Level CBT-II — 13 October 2025, Shift 2]
- (A) Diastolic pressure
- (B) Pulse pressure
- (C) Venous pressure
- (D) Systolic pressure
Answer: (A) Diastolic pressure
Explanation: Diastolic pressure is the minimum arterial pressure during ventricular relaxation between heartbeats. In a commonly quoted reading of 120/80 mmHg, 80 represents the diastolic component. Systolic pressure is measured during ventricular contraction, while pulse pressure is their numerical difference.
63. Which statements about blood are correct?
(1) It contains plasma and different cell types.
(2) Haemoglobin gives blood its red appearance.
[UPPSC PCS Prelims — 2025, GS Paper I]
- (A) Only statement 1
- (B) Both statements 1 and 2
- (C) Neither statement
- (D) Only statement 2
Answer: (B) Both statements 1 and 2
Explanation: Blood comprises liquid plasma and formed elements: erythrocytes, leucocytes and platelets. Its familiar red colour is mainly due to haemoglobin, an iron-bearing oxygen transport protein inside erythrocytes. Both statements correctly describe the composition and appearance of circulating blood.
62. Which vessels carry oxygenated blood away from the heart to most parts of the body?
[RRB NTPC Undergraduate CBT-I — 18 August 2025, Shift 2]
- (A) Veins
- (B) Venules
- (C) Capillaries
- (D) Arteries
Answer: (D) Arteries
Explanation: Systemic arteries convey oxygen-rich blood from the left ventricle through the aorta towards tissues. The pulmonary artery is a notable exception: it carries oxygen-poor blood from the right ventricle to the lungs. Veins usually direct blood back towards the heart.
61. What is the scientific name for white blood cells?
[SSC Stenographer — 6 August 2025, Shift 1]
- (A) Erythrocytes
- (B) Leucocytes
- (C) Thrombocytes
- (D) Platelets
Answer: (B) Leucocytes
Explanation: Leucocytes, also spelt leukocytes, are the nucleated defensive cells of blood. They include neutrophils, eosinophils, basophils, lymphocytes and monocytes. Erythrocytes are red blood cells, while thrombocytes or platelets chiefly participate in arresting bleeding after vessel damage.
