Download Biology – The Search for Better Health

Biology – The Search for Better Health
Section 1: What is a healthy organism?

Discuss the difficulties in defining the terms ‘health’ and ‘disease’.
Health is more than merely the absence of disease. The World Health Organisation
(WHO) defines health as ‘a state of complete physical, mental and social well-being,
and not merely the absence of disease or infirmity’.
This definition allows the ‘whole’ person to be taken into account rather than just
whether they have a disease or not. An individual who does not have a disease may
still not be considered healthy. On the other hand, an individual who suffers from
disease could be still classed as healthy.
Physical health refers to the physical state of the body and includes such things as
our level of fitness, body weight, amount of energy and the proper functioning of the
systems in the body.
Mental health is related to our ability to function effectively in society and to cope
with changing situations in our lives.
Social health is our ability to interact, communicate and socialise effectively. One
problem with the WHO definition of health is that is very broad, and if taken literally
it would be very difficult to achieve a healthy status.
The concept of health for individuals is very subjective and depends on their life
circumstances. What is healthy for one may not be regarded as healthy for another.
Different people have different ideas about what is considered an appropriate level
of physical social and mental health. Health is a constantly changing state and is
relative to others and ourselves over a period of time.
Disease can be defined in many ways, but the most common is ‘any condition that
adversely affects the normal functioning of any part of a living thing.’ A problem with
most definitions of disease is that they are quite broad and imprecise. Conditions
that would not be normally classed as diseases could be if the above definition of
disease were to be taken literally. It could mean that a broken arm would be classed
as a disease because it adversely affects the normal functioning of the body.
Another difficulty in defining both ‘health’ and ‘disease’ is caused by the different
ways the terms are used. Terms used by the general public usually have different
meanings to the scientific definitions.

Outline how the function of genes, mitosis, cell differentiation and
specialisation assist in the maintenance of health.
Cell Differentiation: Cells mature and take on different structural features, so that
they become structurally suited to perform a specific function in the body.
Cell Specialisation: Specific genes are switched on in order to perform a particular
function for the body. For example: Nerve cells – have a particular structure and
specific genes that are switched on that allow the transfer of electrochemical
messages.
Differentiation and specialisation enable cells to work together in a healthy body to
carry out complex functions in a controlled way in order to maintain and repair
tissues. If differentiation and specialisation of cells do not occur, the cells would not
be able to function effectively and processes in the body would not be co-ordinated.
Genes and Mitosis:
The maintenance of health is dependent on the information stored in the DNA of
each cell. A gene is a hereditary unit that controls the production of polypeptides
that make up proteins in the cell. These proteins are responsible for normal cell
functioning, growth and repair. A malfunction in a particular gene may result in the
inability of the cells to function properly and lead to the onset of disease.
The information contained in genes also prescribes how and when an organism’s
body tissues are maintained and repaired, so any malfunction in these genes
would be detrimental to healthy cells.
Mitosis is the process of cell division by which identical body cells are produced for
growth, repair of damaged tissue, replacement of worn out cells, and genetic
stability. This results in precise and equal distribution of chromosomes to each
daughter nucleus, so that all resulting cells contain the same number and kind of
chromosomes as each other and the parent cell.
This allows all cells to function normally and tissues in the body to be repaired and
maintained. If cells are damaged through injury or disease, the division of healthy
cells close to the injury or disease site replaces them. Genes code for the proteins
that are responsible for the regulation of the cell cycle and mitosis in healthy cells.
The types of genes responsible for the regulation of the cell cycle and mitosis are:
- DNA repair gene: This codes for proteins that are responsible for the
stopping of the cell cycle while other proteins remove the damaged regions
of DNA and replace them with a new correct sequence. If these genes mutate
they will no longer function correctly, the DNA is not repaired and the
damaged DNA will replicate. As a result the correct proteins necessary for
normal cell functioning growth and repair will not be produced and disease
will occur.
- Proto-oncogenes: These code for proteins that stimulate cell growth and
mitosis.
- Tumour suppressor genes: these code for proteins that slow down or stop
cell growth and mitosis. These genes also code for proteins that induce cell
death if there is an uncontrolled increase in cell numbers
In a healthy cell, these genes tightly regulate cell growth and mitosis. If these genes
are damaged or mutated this regulation is disrupted. Mutations to proto-oncogenes
lead to the expression of oncogenes that would be normally silent. This cause
uncontrolled production of cells and prevents cell death. Mutations to tumour
suppressor genes halt the production of proteins that control cell division and cell
death. This disruption of the normally regulated cell cycle leads to uncontrolled cell
replication which:
- does not allow cells to differentiate, so they cannot perform the
specialised functions necessary for normal body functioning.
- causes the formation of tumours. If the tumour spreads to other tissues,
cancer results.
In some cases, mutations to certain genes could cause uncontrolled cell death, which
leads to degenerative conditions such as Alzheimer’s disease.
Process /
Definition
Structure
Cell
Cells mature and take on different
Differentiation structural features so that they become
suited to perform a specific function in
the body.
Cell
Specific genes are ‘switched on’ in
Specialisation order to perform a particular function
in the body.
Genes
These are hereditary units that control
the production of polypeptides that
make up the proteins in the cell
Mitosis
Explanation
Differentiation and specialisation enable cells to
work together to carry out complex functions in a
controlled and co-ordinated way in order to
maintain and repair tissues. If differentiation and
specialisation of cells do not occur the cells would
not be able to function effectively and processes in
the body will not be co-ordinated.
The maintenance of health is dependant upon the
information stored in the genes. The genes control
the production of proteins that are responsible for
normal cell functioning, growth and repair. Genes
code for the proteins that are responsible for the
regulation of the cell cycle and mitosis. The info
contained in the genes prescribes how/when an
organism’s body tissues are maintained/ repaired.
Mitosis is the process of cell division by It allows all cells to function normally and tissues in
which identical body cells are produced the body to be repaired and maintained. If cells are
to allow for:
damaged through injury or disease, the division of
- Growth
healthy cells close to the injury or disease site
- Repair of damaged tissue,
replaces them.
replacement of worn out cells
Genetic stability - precise and equal
distribution of chromosome to each
daughter nucleus.

Use available evidence to analyse the links between gene expression and
maintenance and repair of body tissues.
Gene expression involves the ‘switching on’ of genes so that the relevant proteins
that they code for are produced. Many genes code for proteins that are responsible
for the control of the maintenance and repair of body tissues. If these genes are
expressed properly then the maintenance and repair of body tissues occurs as it
should. Problems with the normal maintenance and repair processes will occur if
the relevant genes are not expressed properly due to such things as the mutation
of genes.
For example, one particular type of breast cancer is a ‘basal-like’ cancer that is
particularly aggressive and more difficult to control and harder to treat than most
forms of disease.
Mutations to the BRCA1 gene put women at a much higher risk of developing this
form of breast cancer. The BRCA1 mutations are inherited and are carried by one
woman in 800. The presence of these mutated genes increases the risk of developing
this cancer by 85%.
BRCA1 is a tumour suppressor gene found on chromosome 17. It is believed to be
responsible for the coding of proteins involved in the repair of PTEN gene. The PTEN
gene is another tumour suppressor gene that limits the amount of cell division and
encourages cell death. This regulates the cell cycle and prevents the excessive
proliferation of cells that lead to tumours and cancer.
In a normal cell, if there is damage to the PTEN gene, proteins that have been
coded for by the BRCA1 gene would repair it. This repaired PTEN gene would then
be expressed properly and cell division and differentiation would occur to maintain
and repair body tissues. Mutations to the BRCA1 gene would mean that the
proteins that are necessary for the repair of the damaged PTEN gene would not be
produces, and the PTEN would not be repaired and therefore would not be
expressed. This results in a lack of control of the cell cycle and runaway cell division
leading to the formation of tumours.
Outline how the function of genes, mitosis, cell differentiation and specialisation
assist in the maintenance of health. (6 Marks)
A gene is a segment of DNA on a chromosome that specifies a particular
characteristic. One’s DNA is the most integral part of their existence. The genes
coded on this DNA allow for protein synthesis which is essential in ensuring the
maintenance of health. When cells are struck by disease, proteins need to be
produced in order to repair the tissue, or to generate new substances. Genes on the
DNA strand code for the production of these proteins. If a mutation occurs on these
genes, the protein formed may be ineffective in achieving its role, hence it will be
unable to prevent damage to the cell, and hence disease will be likely to onset. An
example of this is when bacterial infections occur. Cells within the bone marrow
have their genes specially designed such that they produce red/white blood cells.
The extra white blood cells produced will then counteract the disease, thereby
assisting in the maintenance of health.
Mitosis is the process in which somatic cells duplicate. This is essential in the
replacement of old and damaged cells, in the generation of new cells for growth and
in the repair of body tissue. As health depends on constant repair within the body,
mitosis serves this role by replacing old cells with new ones. This keeps the body
healthy by removing damaged and old cells. For example, when a person is cut, new
cells will regenerate from older ones via mitosis in order to repair the body tissue
and maintain the health of the organism.
Cell differentiation is when somatic cells have a number of genes on their
chromosomes permanently switched on while others are switched off. This allows
the cell to develop into one with a unique use in the body – ie cell specialization. Cell
differentiation and specialization ensure that the body can perform complex tasks in
a coordinated manner, with different cells taking on different responsibilities. This
creates an efficient system within the body, thereby ensuring the maintenance of
health. For example, the digestive villi in the small intestine are specialized to absorb
nutrients thoroughly – this ensures that the body remains well nourished – an
important and integral aspect of human health.