Xylem is a type of complex tissue in plants for upward conduction of water. Which one of the following xylem tissues consists of living cells?
- A.Tracheid
- B.Vessel
- C.Xylem parenchyma
- D.Xylem fibre [ P.T.O.
Correct answer
Explanation
The correct answer is C, Xylem parenchyma. Of the four elements of xylem, only xylem parenchyma is made of living cells; tracheids, vessels and xylem fibres are dead at maturity.
Xylem carries water and dissolved minerals from the roots to the leaves. Its four elements share the work. Tracheids are long, tapering cells with thick lignified walls, and vessels are tubes formed by cells joined end to end, which lose their cross walls; both conduct water, and both are dead, empty cells when working. Xylem fibres give mechanical support. Xylem parenchyma, the only living part, stores food such as starch and fat and helps in the sideways, radial conduction of water. In phloem, by contrast, only phloem fibres are dead.
Option A is wrong because tracheids lose their protoplasm and are dead when they conduct water. Option B is wrong because vessels are also dead, hollow tubes. Option D is wrong because xylem fibres are dead cells with thick walls that only give support.
Exam tip: Xylem: only parenchyma is living; phloem: only fibres are dead.
Practice Questions
View allThe pressure exerted by a 760 mm column of mercury at 0 °C is known as
- A.1 pascal
- B.1 atmosphere
- C.1 bar
- D.1 poise
Show answer
Standard atmospheric pressure at sea level is defined as the pressure of a 760 mm column of mercury at 0 °C. In 1643 Evangelista Torricelli showed that air pressure holds up a column of mercury about 760 mm (76 cm) tall in a glass tube, inventing the mercury barometer.
Read the full explanation →Sound and light waves are
- A.respectively longitudinal and transverse in air
- B.respectively transverse and longitudinal in air
- C.both longitudinal in air
- D.both transverse in air
Show answer
Sound travels as compressions and rarefactions, while light is a transverse electromagnetic wave. In a longitudinal wave the particles of the medium vibrate back and forth along the direction in which the wave moves.
Read the full explanation →Which one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
Show answer
Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
Read the full explanation →A planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
Show answer
Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
Show answer
Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
Read the full explanation →