Biology 2.2 Cell division & Stem Cells

What is a chromosome

A linear DNA molecule tightly coiled around proteins
Contains genes

How many chromosomes do human body cells contain

46 chromosomes
23 pairs

What are sex chromosomes

A pair of chromosomes that determines sex
Males have an X and a Y chromosome
Females have two X chromosomes

What is mitosis

A form of cell division that produces two daughter cells
Both genetically identical to the parent cell with the same number of chromosomes
46 chromosomes
Involves one division

Why is mitosis important in organisms

Asexual reproduction
Growth
Repair of damaged cells
Cell replacement

What is meiosis

A form of cell division involved in the formation of gametes
Chromosome number is halved
23 chromosomes
Involves two divisions producing four gametes

What are gametes

Sex cells
Sperm cells and egg cells
Contain half the chromosome number

Why is meiosis important for sexual reproduction

Increases genetic variation
Ensures that the resultant zygote has a full set of chromosomes

Compare mitosis and meiosis

Mitosis occurs in all non reproductive cells
Meiosis occurs only in reproductive cells
Mitosis produces two daughter cells
Meiosis produces four daughter cells
Mitosis daughter cells are genetically identical
Meiosis daughter cells are genetically different
Mitosis daughter cells have 46 chromosomes
Meiosis daughter cells have 23 chromosomes
Mitosis occurs for growth repair and replacement of damaged cells
Meiosis occurs for the formation of gametes during sexual reproduction

What is cancer

Non communicable disease
Uncontrolled mitosis results in the formation of a primary tumour
Tumour cells break off and spread to other tissues forming secondary tumours

What are stem cells

Cells that are unspecialised and capable
of differentiating into a range of different
cell types

What is meant by differentiation

The process by which stem cells become
specialised and have a specific function
Some genes switch on or off determining
cell type

Why is cell differentiation important

Enables the formation of specialised
tissues with specific functions
for example muscle tissue

What are embryonic stem cells

Stem cells found in very early embryos
that are unspecialised and capable of
differentiating into any cell type

What is the function of embryonic stem cells

Enable the growth and development of
tissues in human embryos

Where can embryonic stem cells be collected from

Donor stem cells removed from embryos
grown in vitro
Patient’s own stem cells removed from the
umbilical blood before birth

What are adult stem cells

Stem cells that can differentiate into a
limited range of cell types
for example bone marrow stem cells

What is the primary function of adult stem cells

Replacement of dead cells
for example replacement of red blood cells
which only live for 120 days

Describe the potential uses of stem cells in medicine

Treat disease for example heart disease
and type 1 diabetes
Used to repair damaged tissue for example
brain damage
Used in scientific research
Growing organs for transplants

What are the ethical issues related to the use of stem cells in medicine

The embryos used to provide stem cells
are destroyed which is seen as unethical
and a waste of potential human life
Could lead to the farming of embryos for
stem cells
May lead to the reproductive cloning
of humans

Where are stem cells found in plants

Meristems

Where is meristem tissue found

In regions of the plant where cells are
continuously dividing
for example root tips and shoot tips