Download Edexcel AS/A level Biology

G
N
I
K
HIN
T
There are many different ways of getting information across. This article assumes
knowledge of cell division in its readers:
1. How well does a question and answer format work for imparting this information?
2. Are bullet points helpful or would continuous text make the explanations more
effective?
3. Try a different approach – work with a partner and choose two alternative ways of
getting this information across. Each take one method and work it through – then
compare notes and decide which you prefer and why.
4. How would you explain cancer to people who are not studying A level Biology and do
not know what mitosis and the cell cycle are?
CANCER – MITOSIS OUT OF
CONTROL
In 2013 an estimated 8.2 million people around the world died from different forms of cancer.
The article below suggests answers to some common questions about cancer.
What is cancer?
Cancer is an umbrella term that covers more than 200 different
diseases. However, most cancers have some features in common:
●
●
●
7 Behaviour
Thinking
canBigger
be learned
8
1 2.3
8
Cancer cells do not respond to the normal mechanisms that
control cell growth – they divide rapidly to form a mass of
abnormally growing cells called a tumour.
Malignant tumours split and release small groups of cells into
the blood and tissue fluid. They circulate and often lodge in
different areas of the body, forming secondary tumours.
Cancer cells divide more rapidly and usually live longer than
normal cells.
Alternative ways of getting information across include formal continuous prose, a series of diagrams,
flow diagrams, a more relaxed and friendly style of writing … and any others you can think of ! For a
non-scientific audience you have to think about the words you use – and how pictures might help.
Most cancers result from mutations which occur in the DNA of a
normal body cell as it reproduces:
●
●
●
Now let us look at the biology behind these questions and answers. You already know about cell
division and mutation, so you can answer these questions now. If you are going to continue your
biology studies to A level, you may like to revisit these pages after you have learned more about
communicable diseases and the immune system in Topic 6.
Several different mutations may work together to increase
the likelihood of cancer, e.g. by interfering with the accurate
replication of the DNA, decreasing the efficiency of the
DNA repair mechanisms or increasing the likelihood of the
chromosomes breaking during mitosis.
A single mutation changing a proto-oncogene to an oncogene
can cause cancer. Proto-oncogenes code for proteins which
stimulate the cell cycle. Oncogenes produce uncontrolled
amounts of stimulating proteins.
Tumour-suppressor genes code for the production of chemicals
which suppress the cell cycle, acting as a brake on cell division.
If the gene mutates, the brake is removed and the cell just keeps
on dividing.
5. At one level there are as many types of cancer as there are types of human cell – any
type of cell can become cancerous, although some are more prone to cancer than
others. At another level, every cancer is different because each one of us is different and
it is our cells which mutate. Describe how the process of cell division can lead to
mutations and therefore cancer.
Activity
You are going to produce an article for a popular magazine explaining about one of the following forms of
cancer. You must explain what happens to the cells of your body and why in each case the risk of
developing cancer is increased. You can add as much extra information about detection, screening,
prevention and even treatment as you like – but the key points to focus on are the biology of the cancer.
Write about EITHER
What causes cancer?
976547_PH_143: Scanning electron micrograph of cancer cells eg SPL
M132/0667
Two main factors affect whether an individual will develop a form
of cancer:
Genetics: some people are more likely than others to experience
a mutation which results in cancer, and some people are
born with a mutation which gives them a very high risk of
developing particular cancers.
● Environment: factors such as the tar in cigarette smoke, ionising
radiation, the chemicals in alcoholic drinks and asbestos are
carcinogenic – they increase the risk of mutations in vulnerable
cells which can result in cancer.
If a genetically vulnerable person encounters carcinogenic
environmental factors, their risk of developing cancer somewhere
in their body increases even more.
1 Breast cancer resulting from mutations in the BRCA1 and BRCA2 tumour suppressor genes
●
fig A Kidney cancer cells.
Why is control of the cell cycle lost?
About 15% of human cancers are the result of viral infections
which cause changes in the cells, affecting the control of the cell
cycle and leading to cancer.
Command wo
rd
If you are aske
d to
describe som
ething, you
need to give
a clear and
concise acco
unt of it.
Pull out all the
important
pieces of info
rmation as a
starting point.
OR
2 Cervical cancer caused by the human papilloma virus
● Reference used: Written by Ann Fullick
Where else will I encounter these themes?
1.1
126
1.2
1.3
1.4
2.1
2.2
2.3
YOU ARE
HERE
2.4
3.1
3.2
3.3
4.1
4.2
4.3
4.4
127