Ch : Cell Division

Question 1

What is cell continuity?

Answer 1

All cells develop from pre-existingcells

Question 2

What are chromosomes?

Answer 2

Coiled threads of DNA and protein that become visible in the nucleus during cell division

Question 3

What is a gene?

Answer 3

A section of DNA containing the instructions for the formation of a protein

All the genes in an organism make up its genome

Question 4

What is a haploid cell?

Answer 4

A cell with one set of chromosomes
e.g. sperm cells
Symbolised with the letter ‘n’

Question 5

What is a diploid cell?

Answer 5

A cell with two sets of chromosomes
e.g. cheek cell
Symbolised with the ‘2n’

Question 6

What is a homologous pair?

Answer 6

2 chromosomes of similar size with the same gene sequence
In diploid cells, one chromosome from each pair comes from the mother and one from the father

Question 7

What is the cell cycle?

Answer 7

Changes that take place in a cell during the period between one cell division and the next

Question 8

What is interphase?

Explain interphase

Answer 8

The phase in the cell cycle when the cell is not dividing

-Longest phase of cell cycle
-Chromosomes are elongated and form part of a mass called chromatin
-The early stage produces organelles (mitochondria and chloroplasts) and enzymes and proteins needed for growth
-Chromosomes produce replicates of themselves at the end

Question 9

What is mitosis

Answer 9

A form of nuclear division in which one nucleus divides to form two nuclei, each containing the same number of chromosomes with identical genes

Question 10

Briefly explain mitosis

Answer 10

-New cells formed are called daughter cells
-Takes place in cells not associated with the reproductive system (somatic cells)
-Interphase, prophase, metaphase, anaphase, telophase
(I Party Monday And Tuesday)

Question 11

Explain prophase

Answer 11

DIAGRAM***
-Chromatin starts to condense
-Chromosomes become visible as double stranded structures
-The strands are held together by a centromere
-Each strand has identical genes
-Nucleolus disappears
-Spindle fibres appear in cytoplasm
-Nuclear membrane starts to break down

Question 12

Explain Metaphase

Answer 12

-Nuclear membrane completes full breakdown
-Spindle fibres from each pole attaches to each centromere
-Chromosomes line up across middle of the cell

Question 13

Explain Anaphase

Answer 13

-Spindle fibres contract
-Centromeres split
-One chromosome is pulled to each pole
-Anaphase is the shortest phase

Question 14

Explain Telophase

Answer 14

-Chromosomes lengthen and become hard to distinguish
-Spindle fibres break down
-Nucleoli and nuclear membranes begin to reform
- Original nucleus has divided into two nuclei (same set of genes but half the organelles and biomolecules than parent cell)

Question 15

Explain how cells divide in animal cells

Answer 15

A cleavage furrow appears and becomes deeper until the cell splits in two

Question 16

Explain how cells divide in plant cells

Answer 16

-Rigid cell wall prevents cleavage furrow from forming
-Vesicles (membrane-enclosed sacs) gather in the area between the two nuclei
-Vesicles contain cellulose to form a new cell wall
-Vesicles form the cell plate
-Cell plate enlarges to join cell membrane around the cell
-Two cell walls form with a middle lamella between them

Question 17

What is the function of mitosis in unicellular organisms

Answer 17

-Method of asexual reproduction

Question 18

What is the function of mitosis in multicellular organisms

Answer 18

-Used for growth and repair of cells in animals and plants
-Allows single celled zygote to become an embryo

Question 19

What is cancer?

Answer 19

A group of disorders in which certain cells lose their ability to control the rate of mitosis and the number of times it takes place

-Mitosis is normally tightly controlled
-Uncontrolled mitosis produces a tumour (mass of cells)

Question 20

What are benign tumours?

Answer 20

-Not life-threatening
-Cells stop dividing after some time
-Do not invade other tissues
-Can be surgically removed
-E.g. warts, skin tags, most breast tumours

Question 21

What are malignant tumours?

Answer 21

-May be life-threatening
-Can move from one place to another in the body (metastasis)
-Cells divide indefinitely

Question 22

What are the causes of cancer?

Answer 22

-Normal genes mutate to form cancer causing genes (oncogenes)
-Carcinogens cause these mutations, e.g. cigarette smoke, asbestos

Question 23

What treatment types are available for cancer?

Answer 23

-Surgery
-Radiation
-Chemotherapy

Question 24

What is meiosis?

Answer 24

A form of nuclear division in which the 4 daughter nuclei contain half the chromosome number of the parent nucleus

Question 25

Explain meiosis

Answer 25

-When meiosis takes place in a diploid cell, all daughter cells are haploid -If these cells are capable of joining with another haploid cell from the opposite sex, they are called sex cells/gametes

Question 26

What are the functions of meiosis?

Answer 26

1. Allows for sexual reproduction, involving gametes, while still maintaining the parental chromosome number 2. Allows for new combinations of genes to be formed (variation)