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Cell Division and Genetic Variation

In this worksheet, students study how cell division occurs and how genetic diseases come about. It is a continuation of the 'Variation and the role of Reproduction' worksheet in Year 10.

Key stage:  KS 4

Curriculum topic:  Biology: Cell Biology

Curriculum subtopic:  Cells as a Basic Structural Unit

Difficulty level:  

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QUESTION 1 of 10

Our bodies must replace thousands of cells that are lost every day, from areas such as the skin. The body also needs to produce new cells, for growth and to repair wounded skin. Cells of large organisms like us have the ability to differentiate and become specialised according to their function. 

The process with which the cells divide is called cell division and there are two types: mitosis and meiosis. It is all about the chromosomes in the nucleus and how they are represented in the new cells. 

 

 

The photograph above shows a cell just before it is to be split into two daughter cells, as they are called. Notice how the nucleus has duplicated (doubled).

The diagram below shows the stages of cells during mitosis and meiosis:

 

 

Stages of mitosis:

1) Chromosomes duplicate.

2) The chromosomes are arranged along the equator of the cell on the spindle: a structure which aids cell division (see diagram below).

 

 

3) One strand of each chromosome moves to the poles of the cell.

4) Two genetically identical cells are formed.

Note: the 2n in the mitosis diagram. It means that the number of chromosomes in the mother and daughter cells is the same; n is the number of chromosomes of each organism.

 

Stages of meiosis:

1) Homologous chromosomes (chromosomes in a pair that carry similar information) pair up.

2) One from each pair moves to one pole of the cell and one division takes place.

3) One strand from each pair moves to the opposite poles and a second division occurs. The daughter cells contain half the number of the mother cell: n instead of 2n.

 

Meiosis is used only to produce haploid cells (cells with half the genetic material). These cells are the gametes, the sex cells, sperm and egg or ovum. They have half the genetic material, because when they fuse during fertilisation, the genetic material will become diploid again. Diploid is the full set of chromosomes.

 

Sexual reproduction with meiosis produces genetic variation within a species. In large organisms, offspring are not genetically identical to their parents. This makes them new individuals, who, apart from a different appearance, also have a different ability to fight disease and adapt to their environment; hopefully better than that of their parents! Therefore, meiosis is the type of genetic division that improves survival of a species.

What is the purpose of cell division? Three answers apply.

growth of organisms

repairing wounded areas of the body

to send messages to the brain and nerves

cells divide out of control

replacement of dead cells

How are cells of large organisms different to those of small?

they divide better

they are identical

they differentiate

What is the name of the process that produces new cells?

cell multiplication

cell division

cell addition

What are the new cells called?

daughter cells

sister cells

son cells

What type of cell division produces diploid daughter cells?

mitosis

meiosis

What type of cell division produces haploid cells?

mitosis

meiosis

What happens to chromosomes before cell division?

they are halved

they are duplicated

they remain the same

Along which part of the cell are chromosomes arranged at the beginning of cell division?

the middle

the equator

the centre

What are homologous chromosomes?

pairs of chromosomes that carry similar information

chromosomes that are far from each other in cell division

chromosomes that duplicate

What does meiosis create within a species?

identical organisms

genetic variation

genetic similarity

  • Question 1

What is the purpose of cell division? Three answers apply.

CORRECT ANSWER
growth of organisms
repairing wounded areas of the body
replacement of dead cells
EDDIE SAYS
Genetic division ensures growth of organisms, repairing wounded areas of the body and the replacement of dead cells.
  • Question 2

How are cells of large organisms different to those of small?

CORRECT ANSWER
they differentiate
EDDIE SAYS
Cells of large organisms have the ability to differentiate, which means that a less specialised cell becomes a more specialised cell type.
  • Question 3

What is the name of the process that produces new cells?

CORRECT ANSWER
cell division
EDDIE SAYS
Cell division is the process through which new cells are produced.
  • Question 4

What are the new cells called?

CORRECT ANSWER
daughter cells
EDDIE SAYS
New cells are called daughter cells.
  • Question 5

What type of cell division produces diploid daughter cells?

CORRECT ANSWER
mitosis
EDDIE SAYS
Mitosis produces diploid daughter cells, identical to the mother cells.
  • Question 6

What type of cell division produces haploid cells?

CORRECT ANSWER
meiosis
EDDIE SAYS
Meiosis produces haploid cells: cells with half the genetic material of the mother cell.
  • Question 7

What happens to chromosomes before cell division?

CORRECT ANSWER
they are duplicated
EDDIE SAYS
Chromosomes duplicate before cell division.
  • Question 8

Along which part of the cell are chromosomes arranged at the beginning of cell division?

CORRECT ANSWER
the equator
EDDIE SAYS
At the beginning of cell division chromosomes are arranged along the equator.
  • Question 9

What are homologous chromosomes?

CORRECT ANSWER
pairs of chromosomes that carry similar information
EDDIE SAYS
Homologous chromosomes are pairs of chromosomes that carry similar information. One homologous chromosome is inherited from the organisms father, the other from its mother.
  • Question 10

What does meiosis create within a species?

CORRECT ANSWER
genetic variation
EDDIE SAYS
Meiosis creates genetic variation within a species.
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