New Senior Secondary Mastering Biology Chapter 11 Suggested answers to Exercise and Reading to learn p.1/4

Suggested answers to Exercise and Reading to

    learn

    (Note: The overseas examination boards bear no responsibility for the suggested answers

    contained in this publication. Answers for HKCEE and HKALE questions are not available due

    to copyright restrictions.)

Ch 11 Cell cycle and division

    Exercise

    Multiple-choice questions (p. 11-25)

    1 B 2 B 3 B

    4 C 5 D 6 B

Short questions (p. 11-26)

    7 a i 2 / two 1m

     ii 8 / eight 1m

     b 38 1m

    8 i Chromosomes line up in the middle of the cell 1m

     ii Prophase 1m

     iii Anaphase 1m

     iv DNA replication / synthesis 1m

     OR

    Chromosomes copying / duplication 1m

     v Telophase 1m

9 a 12 chromatids 1m

     Chromatids separated from each other 1m

     Labels: centromere, chromatids 1m x 2

     b Any three from: 1m x 3

    DNA molecules are replicated.

     New organelles e.g. mitochondria are made.

     Proteins are made.

     Energy stores increase.

    ? Oxford University Press 2009

New Senior Secondary Mastering Biology Chapter 11 Suggested answers to Exercise and Reading to learn p.2/4

10

    Number of Mass of DNA / Nucleus chromosomes arbitrary units

    A 8 600

    B 8 600

    C 8 300

    D 4 150

     0.5m x 4

Structured questions (p. 11-26)

    11 a Add stain in a fixed root tip 1m

    Tear the root tip into small pieces 1m

     Gently press the cover slip 1m

     Warm the slide over a hotplate / hot water bath 1m

     b Telophase is the longest stage. 1m

     Anaphase is the shortest stage. 1m

     Correct manipulation of figures to compare any two stages 1m

     c Use the equation to work out actual time of each stage 1m

    Add up the total of four stages 1m

    OR

     Add up all 4 percentages 1m

    Substitute into equation 1m

12 HKCEE Biology 1994 I Q3c

    ? Oxford University Press 2009

New Senior Secondary Mastering Biology Chapter 11 Suggested answers to Exercise and Reading to learn p.3/4

13 a i B 1m

     ii D / C and D 1m

     iii A and B / A, B and C 1m

     (C in ii or iii but not both)

    b Any three from: 1m x 3

     Synthesis / replication of DNA

     Synthesis of proteins

     Replication / synthesis / production of organelles

     Storage of energy

     c DNA content was halved 1m

     because two separate cells have been formed. 1m

     d No 1m

     Diploid amount of DNA presents in both the cell undergoing mitosis and meiosis I

     1m

     OR

    During meiosis, reduction of the amount of DNA does not occur until the second

    division. 1m

     e Chromosomes at the end of the meiosis I consist of chromatids still attached at

    centromere. 1m

    Chromosomes at the end of the meiosis I are a random assortment of parental and

    maternal chromosomes. 1m

    Essays (p. 11-27) 14 Each chromosome is replicated into two identical chromatids / strands / copies. 1m

    Chromosomes shorten / thicken. 1m

    Nuclear membrane disintegrates. 1m

    Chromosomes / chromatids move to / line up in the middle of the cell. 1m

     Sister chromatids separate and move to opposite poles. 1m

     Each pole / end receives all genetic information / identical copies of each chromosome.

     1m

     New nuclear membranes form around each set of chromosomes. 1m

     Communication 3m

    ? Oxford University Press 2009

New Senior Secondary Mastering Biology Chapter 11 Suggested answers to Exercise and Reading to learn p.4/4

15 Process: Any six from: 1m x 6

     Meiosis consists of two nuclear divisions.

     During prophase I, chromosomes shorten / thicken and appear as two chromatids.

     Homologous chromosomes pair up.

     Nuclear membrane breaks down.

     During metaphase I, the homologous pairs line up in the middle of the cell.

    During anaphase I, chromosomes of each homologous pair are pulled apart / separate and

    move to opposite poles.

    At telophase I, a set of chromosomes arrives at each pole / new nuclear membranes form

    around each set of chromosomes / at each pole.

     During prophase II, chromosomes usually stay in their shortened form.

    During metaphase II, chromosomes consisting of pairs of chromatids line up in the middle

    of the cells.

     During anaphase II, chromatids are pulled apart / separate and move to opposite poles.

    At telophase II, the nuclear membranes reform / cytokinesis occurs, producing four haploid

    cells.

     Importance within life cycles and in genetic variation: Any four from: 1m x 4

     Life cycles:

     Meiosis produces haploid gametes.

    It avoids doubling of chromosome number with each generation / preserves a constant

    number of chromosomes.

     Genetic variation:

    The haploid cells produced, whether gametes or spores, are genetically variable since the

    alignment of homologous pairs with respect to the poles in metaphase I is completely at

    random.

     Random fertilization of gametes promotes genetic variation.

     Communication 2m

Reading to learn (p. 11-28)

    1 Limited magnifying power of early microscopes 1m

    Lack of cell staining techniques 1m

    2 ‘Chromosome’ means ‘coloured body’ 1m

    because chromosomes become coloured when stained with special dyes. 1m 3 Flemming was the first to stain and observe chromosomes in cells. 1m

    The stained chromosomes allow scientists to observe their distribution during cell division.

     1m

    This leads to further understanding of different stages of mitosis and the reduction of

    chromosome number in meiosis. 1m

    ? Oxford University Press 2009