Which of the following cells do not contain nucleus? 1. Root hair cells 2. Red blood cells 3. Platelets 4. Monocytes Select the correct answer using the code given below.
- A.1 only
- B.2 and 3 only
- C.1, 2 and 4
- D.2, 3 and 4
Correct answer
Explanation
The correct answer is B, 2 and 3 only. Mature human red blood cells and platelets have no nucleus. Red blood cells lose their nucleus as they mature in the bone marrow; this gives their biconcave disc shape more room for haemoglobin to carry oxygen, but it also means they cannot divide or repair themselves and live only about 120 days. Platelets, or thrombocytes, are not whole cells at all: they are small fragments broken off from large bone-marrow cells called megakaryocytes, so they too lack a nucleus. They help the blood to clot and live about a week to ten days. Option A is wrong because root hair cells are living plant cells of the root epidermis, each with a nucleus, which grow out to absorb water and minerals. Option C is wrong because it includes root hair cells and monocytes, both of which have a nucleus. Option D is wrong because monocytes, the largest white blood cells, have a large kidney-shaped nucleus; all white blood cells are nucleated. Exam tip: in human blood, RBCs and platelets have no nucleus; every type of WBC has one.
Practice Questions
View allWhich one of the following plant tissues has dead cells ?
- A.Epidermis
- B.Parenchyma
- C.Collenchyma
- D.Sclerenchyma
Show answer
Sclerenchyma cells are dead at maturity, with thick walls hardened by lignin. Sclerenchyma is the tissue that makes plants hard and stiff.
Read the full explanation →Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by
- A.the Right-Hand Thumb rule and it would be in the downward direction.
- B.the Left-Hand Thumb rule and it would be in the downward direction.
- C.the Right-Hand Thumb rule and it would be in the upward direction.
- D.the Left-Hand Thumb rule and it would be in the upward direction.
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For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.
Read the full explanation →Which one of the following statements is true for sound waves propagating in air?
- A.Sound is an electromagnetic wave and transverse in nature
- B.Sound is a mechanical wave and longitudinal in nature
- C.Sound is a mechanical wave and transverse in nature
- D.Sound is an electromagnetic wave and longitudinal in nature
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Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.
Read the full explanation →Which one of the following is primarily responsible for conduction of current in a metal?
- A.Bound electrons
- B.Free electrons
- C.Both bound and free electrons
- D.Ions
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In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.
Read the full explanation →Which one of the following statements is correct about the magnification of an optical microscope?
- A.Magnification increases with the increase in focal length of eyepiece
- B.Magnification increases with the increase in focal length of objective
- C.Magnification does not depend upon the focal length of eyepiece
- D.Magnification decreases with the increase in focal length of eyepiece
Show answer
A compound microscope magnifies more when both its lenses have short focal lengths. In a compound microscope the objective forms a real, enlarged image, and the eyepiece magnifies it further like a simple magnifier.
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