Biology

Cell Cycle and Cell Division

Question:

lt is said that the one cycle of cell division in human cells (eukaryotic cells) takes 24 hours. Which phase of the cycle, do you think occupies the maximum part of cell cycle?

Answer:

G1  phase of interphase is of longest duration. It takes about 10 hours in 24 hour cell cycle.

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Cell Cycle and Cell Division

Q 1.

Name the pathological condition when uncontrolled cell division occurs.

Q 2.

Which tissue of animals and plants exhibits meiosis?

Q 3.

Name a cell that is found arrested in diplotene stage for months and years. Comment in 2-3 lines how it completes cell cycle.

Q 4.

What attributes does a chromatid require to be classified as a chromosome?

Q 5.

Given that the average duplication time of E.coli is 20 minutes, how much time will two E.coli cells take to become 32 cells?

Q 6.

At what stage of cell cycle does DNA synthesis take place?

Q 7.

A cell has 32 chromosomes. It undergoes mitotic division. What will be the chromosome number (n) during metaphase? What would be the DNA content (C) during anaphase?

Q 8.

lt is said that the one cycle of cell division in human cells (eukaryotic cells) takes 24 hours. Which phase of the cycle, do you think occupies the maximum part of cell cycle?

Q 9.

Two key events take place during S phase in animal cells, DNA replication and duplication of centriole. In which parts of the cell do events occur?

Q 10.

Mitosis results in producing two cells which are similar to each other. What would be the consequence if each of the following irregularities occur during mitosis?
(a) Nuclear membrane fails to disintegrate
(b) Duplication of DNA does not occur
(c) Centromeres do not divide
(d) Cytokinesis does not occur

Q 11.

Name a stain commonly used to colour chromosomes.

Q 12.

In which phase of meiosis are the following formed? Choose the answers from hint points given below.
(a) Synaptonemal complex________
(b) Recombination nodule________
(c) Appearance/activation of________
enzyme recombinase
(d) Termination of chiasmata________
(e) Interkinesis________
(f) Formation of dyad of cells________
Hints: (1) Zygotene, (2) Pachytene, (3) Pachytene, (4) Diakinesis, (5) After Telophase-l/before Meiosis-ll, (6) Telophase-I /After Meiosis-I.

Q 13.

Between a prokaryote and a eukaryote, which cell has a shorter cell division time?

Q 14.

Which of the phases of cell cycle is of longest duration?

Q 15.

Mitochondria and plastids have their own DNA (genetic material). What is known about their fate during nuclear division like mitosis?

Q 16.

Label the diagram and also determine the stage at which this structure is visible.
ncert-exemplar-class-11-biology-solutions-cell-cycle-cell-division-3

Q 17.

State the role of centrioles other than spindle formation.

Q 18.

Write briefly the significance of mitosis and meiosis in multicellular organism.  

Q 19.

The following events occur during the various phases of the cell cycle, name the phase against each of the events.
(a) Disintegration of nuclear membrane________
(b) Appearance of nucleolus________
(c) Division of centromere________
(d) Replication of DNA________

Q 20.

Which part of the human body should one use to demonstrate stages in mitosis?

Q 21.

lt is observed that heart cells do not exhibit cell division. Such cells do not divide further and exit______ phase to enter an inactive stage called_______of cell cycle. Fill in the blanks.

Q 22.

If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone?

Q 23.

What attributes does a chromatid require to be classified as a chromosome?

Q 24.

The diagram shows a bivalent at prophase-l of meiosis. Which of the four chromatids can crossover?
ncert-exemplar-class-11-biology-solutions-cell-cycle-cell-division-1

Q 25.

Comment on the statement – Telophase is reverse of prophase.

Q 26.

Write brief note on the following:
(a) Synaptonemal complex
(b) Metaphase plate

Q 27.

Both unicellular and multicellular organisms undergo mitosis. What are the differences, if any, observed in the process between the two?

Q 28.

While examining the mitotic stage in a tissue, one finds some cells withl 6 chromosomes and some with 32 chromosomes. What possible reasons could you assign to this difference in chromosome number. Do you think cells with 16 chromosomes could have arisen from cells with 32 chromosomes or vice versal.

Q 29.

Comment on the statement – Meiosis enables the conservation of specific chromosome number of each species even though the process per se, results in reduction of chromo-some number.

Q 30.

An organism has two pair of chromosomes (i.e., chromosome number = 4). Diagrammatically represent the chromosomal arrangement during different phases of meiosis-ll.

Q 31.

An anther has 1200 pollen grains. How many pollen mother cells must have been there to produce them?

Q 32.

How does cytokinesis in plant cells differ from that in animal cells?

Q 33.

What are the various stages of meiotic prophase-l? Enumerate the chromosomal events during each stage.

Q 34.

Differentiate between the events of mitosis and meiosis.