Which one of the following plant tissues has dead cells ?
- A.Epidermis
- B.Parenchyma
- C.Collenchyma
- D.Sclerenchyma
Correct answer
Explanation
The correct answer is D, Sclerenchyma. Sclerenchyma cells are dead at maturity, with thick walls hardened by lignin.
Sclerenchyma is the tissue that makes plants hard and stiff. Its cells are long and narrow, and their walls are so thickened with lignin that often almost no space is left inside; once the wall is complete, the living contents die. It occurs as fibres and sclereids in stems, around vascular bundles, in the veins of leaves and in the hard coverings of seeds and nuts, such as the husk of coconut. Jute and hemp fibres are sclerenchyma.
A is wrong because epidermis is a single layer of living cells covering the plant. B is wrong because parenchyma is made of living, thin-walled cells that store food and carry out photosynthesis. C is wrong because collenchyma is made of living cells thickened at the corners, giving flexibility to stems and leaf stalks.
Exam tip: parenchyma and collenchyma are living; sclerenchyma is dead and lignified.
Practice Questions
View allImagine 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
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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.
Read the full explanation →Cinnabar is an ore of which one of the following?
- A.Copper
- B.Zinc
- C.Mercury
- D.Manganese
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Cinnabar is mercury sulphide, HgS, the chief ore from which mercury is obtained. Cinnabar is a bright red mineral.
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