The spindle fibre is attached to which of the following specific regions of the chromosomes?
- A.Kinetochore
- B.Chromonema
- C.Telomere
- D.Centriole
Correct answer
Explanation
The correct answer is A, Kinetochore. Spindle fibres attach to the kinetochore, a disc-shaped protein structure on the centromere of each chromosome.
During cell division the spindle, made of microtubules, pulls the copies of each chromosome apart. Each chromosome has a constriction called the centromere, and on either side of it sits a kinetochore, one for each sister chromatid. In metaphase, spindle fibres from opposite poles hook on to the two kinetochores and line the chromosomes up at the equator of the cell. In anaphase the fibres shorten and drag the chromatids to opposite poles. Without a proper kinetochore attachment, chromosomes are shared out wrongly between the daughter cells.
B is wrong because the chromonema is the coiled thread of DNA and protein running along the chromatid, not an attachment site. C is wrong because telomeres are protective caps at the ends of chromosomes. D is wrong because the centriole is not part of the chromosome; in animal cells it sits at the pole and helps organise the spindle.
Exam tip: spindle fibres attach at the kinetochore on the centromere; telomeres cap the ends.
Practice Questions
View allWhich of the following are nitrogen-fixing plants?
1. Alfalfa
2. Amaranth
3. Chickpea
4. Clover
5. Purslane (Kulfa)
6. Spinach
Select the correct answer using the code given below:
- A.1, 3 and 4 only
- B.1, 3, 5 and 6 only
- C.2, 4, 5 and 6 only
- D.1, 2, 4, 5 and 6
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Alfalfa, chickpea and clover are legumes, and legumes fix nitrogen. Plants of the legume family (Fabaceae) carry root nodules that house Rhizobium bacteria.
Read the full explanation →The mass number of an element is NOT changed when it emits
- A.Alpha and Beta radiations only
- B.Alpha and Gamma radiations only
- C.Beta and Gamma radiations only
- D.Alpha, Beta and Gamma radiations
Show answer
Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.
Read the full explanation →Which one among the following statements about facilitated transport in plants is correct?
- A.All passive transports are types of facilitated transport.
- B.Facilitated transport is an example of active transport.
- C.Water moves across plasma membrane by active transport.
- D.Facilitated transport requires assistance of carrier proteins.
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In facilitated transport, molecules cross the membrane with the help of membrane proteins, while still moving down their concentration gradient.
Read the full explanation →Who among the following has coined the term 'Quark', the fundamental particles that make up protons and neutrons in an atomic nucleus ?
- A.Richard Feynman
- B.Murray Gell-Mann
- C.Albert Einstein
- D.Niels Bohr
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The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.
Read the full explanation →Which one of the following is the chemical name of heavy water?
- A.Hydrogen oxide
- B.Deuterium dioxide
- C.Deuterium oxide
- D.Heavy hydrogen oxide
Show answer
Heavy water is D₂O: two atoms of deuterium joined to one atom of oxygen. Deuterium is the isotope of hydrogen with one proton and one neutron in its nucleus, so it is about twice as heavy as ordinary hydrogen.
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