#32 Summary of Cell and Nuclear division

1. Growth of a multicellular organism is a result of parent cells dividing to produce genetically identical daughter cells.

2. During cell division the nucleus divides first, followed by division of the whole cell.







3. Division of a nucleus to produce two genetically identical nuclei is achieved by the process of mitosis.

4. Mitosis is used in growth, repair, asexual reproduction and cloning of cells during an immune
response.

5. Although a continuous process, mitosis can be divided for convenience into 4 phases: prophase,
metaphase, anaphase and telophase. The phase between successive nuclear and cell divisions is
called interphase. Replication of DNA takes place during interphase so that the new cells will each have identical DNA.

6. The period from one cell division to the next is called the cell cycle. It has four stages or phases: G1
is a growth stage, S (for synthesis) is when the DNA replicates, G2 is a second growth stage, and nuclear and cell division. G1, S and G2 are collectively known as interphase.

7. In a life cycle involving sexual reproduction, the gametes have one set of chromosomes, a condition
known as haploid. The cell produced by fusion of the gametes, the zygote, has two sets of chromosomes, a condition known as diploid. In such a life cycle it is therefore essential that a type of nuclear division occurs which reduces the number of chromosomes from two sets to one set. This type of nuclear division is called meiosis and must take place at some point in the life cycle before fertilisation.

8. All the cells in the human body are diploid, apart from the gametes, which are haploid.

9. Cancers are a result of uncontrolled cell division.

10. A number of physical and chemical factors can increase the chances of cancer. Agents which are
known to have caused cancer are described as carcinogenic. Examples are asbestos (chemical) and
ionising radiation (physical).

11. Certain viruses, such as papilloma virus, can cause cancer. Genetic predisposition or inheritance of
certain mutant genes may also contribute to the risk of cancer.

Multiple - choice Test 

1. What explains why organisms use mitosis to produce new cells for growth and repair?

A Daughter cells are genetically identical to the parent cell.
B Daughter cells are not able to divide again.
C Daughter cells have the same genes switched on as the parent cell.
D Daughter cells look identical to the parent cell.

2. Which event in the mitotic cell cycle ensures that daughter cells are genetically identical?

A A spindle is formed.
B DNA replicates to form sister chromatids.
C The centriole replicates.
D The nuclear envelope disappears.

3. The photomicrograph shows a cell during the mitotic cell cycle.

Which of the following describes this cell?

A an animal cell in anaphase of mitosis
B an animal cell in metaphase of mitosis
C a plant cell in prophase of mitosis
D a plant cell in telophase of mitosis

4. Which two processes in humans require the production of daughter cells that are not genetically identical to the parent cell?

A gamete production and asexual reproduction
B gamete production and fertilisation
C growth and fertilisation
D growth and repair

5. The tumour suppressor gene, p53, codes for a protein which helps to prevent some cancer cells from multiplying. Another gene codes for a protein, RAD51, which encourages the repair of damaged DNA.
Which row shows the circumstances most likely to result in uncontrolled cell division of a cancerous cell?

6. Which statement is correct?

A A haploid cell is a eukaryotic cell containing only one of each pair of homologous chromosomes.
B A haploid cell is a prokaryotic cell containing one complete set of chromosomes.
C A diploid cell is a eukaryotic cell containing only two chromosomes.
D A diploid cell is a prokaryotic cell containing two complete sets of chromosomes.

7. The diagram shows an animal life cycle.

8. Some events that occur in the mitotic cell cycle are listed.

1 Centrioles begin to move towards opposite poles of the cell.
2 Centrioles produce a spindle.
3 Chromatids are pulled to opposite poles of the cell.
4 Chromosomes line up on the equator of the cell.
5 Chromosomes become longer and thinner.
6 Nuclear envelope and nucleoli disappear.

Which row correctly matches one of these events with each stage of mitosis?

9. Some events in the development of a cancer are listed.

1 Tumour cells invade other tissues.

2 Cell subjected to carcinogens.

3 Tumour increases in size.

4 Cell does not respond to signals from other cells and continues

to divide.

5 Genes that control the mitotic cell cycle mutate.

Which sequence of events describes the development of a cancer?

A 1 → 2 → 5 → 4 → 3

B 2 → 5 → 4 → 3 → 1

C 3 → 1 → 2 → 5 → 4

D 4 → 3 → 1 → 2 → 5

10. The diagram shows the four pairs of chromosomes found in the nuclei of the body cells of an adult fruit fly, Drosophila.

Answers for Multiple-choice Test 

1 A

2 B

3 A

4 B

5 B

6 A

7 A

8 D

9 B

10 A

End-of-chapter questions

1 During  prophase  of mitosis, chromosomes  consist of rwo chromatids.  At which stage of the cell cycle is the second chromatid  made?

 A  cytokinesis
 B  G1
 C  G2
 D  S

2 Growth of cells and  their  division   are balanced   during   the  cell cycle.  Which   column   shows  the  consequences    that would follow  from  the  two  errors  shown   in  the  table?

3 Adiploid  cell undergoes    a cell cycle  including    mitosis.   Which   diagram   correctly   shows  the  changes   in  chromosome number during   interphase?

4 a    Distinguish   between   the  following   terms:
     i  haploid   and  diploid                        
    ii centromere    and  centriole
  b Briefly explain  what   is meant   by the  following   terms:
     i autosome
     ii homologous chromosomes


5 Thediagram  shows  three  cells  (labelled   A, B and  C)  from  a root  tip  which   have  been  stained   to show  chromosomes.

a  Identify the  stage  of mitosis   shown   by each  cell.
b    Describe what   is happening     at each  stage.


 6    Diagram    1 shows  the  life cycle  of a simple  plant   known   as a liverwort.   Liverworts   have  two  multicellular    stages in life cycle:  one  is haploid   and  produces   gametes;   the  other   is diploid   and  produces   spores.

a    Copy  diagram   1 and  write  'mitosis'   on  one  of the  arrows  in the  life cycle where  mitosis   would   take  place.[1]
b    Write  'meiosis'  where  meiosis  would   need  to  take  place.[1]
c    Explain   why  meiosis  is needed   in  this  life cycle.[3]
d    Diagram   2 shows  a cell of a liverwort   plant   dividing   by mitosis.   Only   two  of the  many   chromosomes are shown  for  simplicity.
i What   stage  of mitosis   is shown? [1]
ii    Is this  cell haploid   or diploid?   Explain   your  answer.[3]
iii Draw  prophase   for  the  same  cell  (assume  the  cell has  only  two  chromosomes,  as in diagram   2).[1]
e    Diagram   3 shows  the  same  cell at telophase.   The  cell is beginning to divide  and  a new  cell wall  is forming, spreading   out  from  the  middle   of the  cell.  Copy  the  diagram   and  add  drawings   of the  chromosomes     as they would   appear  at this  stage.[1]

 [Total: 7]

7    Microtubulesare tiny  tubes  made  of protein   subunits   which   join  together.   The  protein   is called  tubulin.    Colchicine isa natural chemical   which   binds  to  tubulin   molecules,    thus  preventing    the  formation    of microtubules.

a Why should  the  binding   of colchicine    to  tubulin    molecules   interfere   with   the  formation    of microtubules?                 [2]

b What structure   or structures    involved   in  mitosis   are made  of microtubules?       [2]                                                                
c When cells treated   with  colchicine    are observed,   the  dividing   cells are all seen  to  be in  the  same  stage  of mitosis. Suggestwith  reasons  the  identity   of this  stage.        [3]                                                                                                                      

[Total: 7]

 Diagram1 shows  chromosomes     in  the  nucleus   of a diploid   cell.

a  Draw the  nucleus   of a gamete   produced    from  this  cell. [1]
b What type  of nuclear   division   would   be used  in  the  production     of the  gamete? [1]
c  Draw a diagram   to show  what   the  nucleus   would   look  like  in  anaphase   of mitosis.[3]

Diagrams 2 and  3 below  show  the  same  diploid   nucleus   as in  diagram1. However, the  chromosomes have been shaded.

d   State what  the  different   types  of shading   represent   in  each  nucleus.[2]

e  Draw a karyogram    based  on  the  diploid   nucleus   shown   in all 3 diagrams.[3]

[Total: 10]

9    Humans   have  46  chromosomes   in each  body  cell.  Six cells are shown   in the  diagram   below.

 a    Copy  the  diagram.   For  e  ch cell,  insert  in the  circle  the  number   of chromosomes   it contains. [3]

b   What   type  of nuclear   division   takes  place  at X? [1]

[Total: 4]

Answers to End-of-chapter questions

 1 D
 2 B
 3 D
 4 a i haploid (cell or organism) has one set of chromosomes;
         diploid has two sets of chromosomes;
      ii centromere is region of a chromosome that holds two chromatids together;
        centriole is an organelle;
         found (in pairs) just outside nucleus;
        microtubule organising centres/starting points for growing microtubules (for spindle);
 b i a non-sex chromosome;
    ii a pair of chromosomes that have the same structure;
        same genes;
       pair up during meiosis (forming a bivalent);
     found in diploid cells;
5 a A anaphase; B prophase; C metaphase;
  b Information for this answer can be found in Figure 5.10 on page 92 in the Coursebook.

Exam-style questions

6 a ‘mitosis’ label added to one of the ‘growth’ arrows or to the arrow between gamete-producing stage and gametes; [1]
  b ‘meiosis’ label added to arrow between spore- producing stage and unicellular spores;           [1]
 c  gamete-producing  stage is haploid and spore- producing stage is diploid;
    chromosome number would double every generation if no meiosis;
    because life cycle includes sexual reproduction; haploid gametes fuse to form diploid     zygote/when gametes fuse chromosome number, doubles/changes, from one set to two sets/gametes must be haploid and there is a diploid stage in the life cycle;           [max. 3]
 d i     metaphase;                                                     [1]
   ii    haploid;
       if it were diploid there would be, four pairs of chromatids/two long pairs of chromatids and               two short pairs of chromatids, lined up on the equator;
         chromosomes are lined up separately/not paired in homologous pairs as they would be in               meiosis;3]
   iii  prophase drawing shows two single chromosomes, each with a centromere (not paired chromatids), ‘randomly’ distributed, surrounded by cell surface membrane but with no spindle;                                                                                                                  [1]
e  a long and a short chromatid, each with a centromere, are shown inside each new nucleus;  [1]                                                            
                                                                                                                     [Total: 11]
7  a microtubules are made out of tubulin molecules; the tubulin molecules stick together in a particular pattern to form the microtubules,
so the presence of colchicine would interfere  with this; AW                                                  [2]
   b spindle;
      centrioles;                                                             [2]
  c  (held up in) prophase;
     spindle cannot form (due to presence of colchicine);
     so metaphase cannot occur;
      metaphase, normally follows prophase/is next stage of mitosis;     [max. 3]

[Total: 7]

8  a  one long, one short and one hooked chromosome present inside a circle (nucleus);   [1]               b meiosis;                                                                   [1]
    c  six chromatids  about half way between equator and each pole (12 chromatids in all);
       two long, two short, two hooked in each direction;
        centromere leading for each chromatid;            [3]
   d in diagram 2, shading represent sets of chromosomes/one type of shading represents set of chromosomes from mother, other type of shading represents set of chromosomes from father; AW
in diagram 3, shading represent homologous pairs of chromosomes/differently numbered chromosomes; AW                                          [2]
  e  only chromosomes drawn (no nuclear envelope); three separate homologous pairs drawn side by side;
pairs arranged in order of size, starting with largest;                                                              [3]

[Total: 10]

9  a  body cells 46;
       sperm and egg 23;
       zygote 46;                                                         [3]
   b mitosis;                                                               [1]

[Total: 4]