ESSENTIAL BIOLOGY 02: CELLS
1. What are the three fundamental statements of cell theory?
i. All organisms are composed of one or more cells.
ii. Cells are the smallest units of life.
iii. All cells come from pre-existing cells.
2. When Hooke first observed what he called ‘cells’ of cork under the microscope, it was the
first time that the cell hypothesis had been proposed. Soon after, cell theory became more
widely accepted. A theory is as close to ‘truth’ as we expect to find in Science – it must be
supported by indisputable evidence. What are some of the scientific advances and discoveries
that have helped strengthen belief in cell theory?
The invention and developing of microscopes, light and electron microscopes has made it
possible to see cells and parts of the cell in all kinds of organism.
We have not been able to find any living entity that is not made of at least one cell.
The experiment by Louis Pasteur in 1860s support that living things come from preexisting cells.
A sterilized chicken broth that was sealed remained free from organisms.
After the seal was removed and the broth exposed to the outside environment, the broth was
invaded by organisms (bacteria and mold) again.
3. Some types of cell seem to break the laws of cell theory.
a. Give two examples of cells which are multinucleated
skeletal muscle cells, many fungal cells and slime molds (belong to protista)
b. What is one organism which can be a ‘giant’ single cell?
The algae Caulerpa has a complex structure with parts that look like leaves and stems and
roots, and although it can grow to be over three feet long, it is actually a single cell. - link
Physarum polycephalum is a plasmodial slime mold. The yellow blob we notice is a huge
single cell. Unlike most cells, which have only one nucleus, this cell contains millions of
nuclei. Physarum plasmodia are usually 3 or 4 cm ( ½ - 1 " ) in diameter, but can get to
be 30 cm (about 1 foot) or more in diameter, and 3 to 5 cm thick. This giant cell moves,
but only pictures taken over several days can show its progress. Its top speed is 1 mm per
hour. - link
ESSENTIAL BIOLOGY 02: CELLS
c. Why are viruses often considered ‘acellular’ or even non-living?
Viruses can not carry out the functions of life on their own. They have no cell structure
like membranes, but are composed of DNA or RNA surrounded by a capsule.
4. The diagram below shows the characteristic rod-shaped structure of E. coli bacteria.
a. What is the magnification of the image?
Scale bar – length in drawing = 25 mm or 25 · 103 µm
Scale bar – length in reality = 2 µm
Magnification is 25 · 103 µm : 2 = 12.5 · 103
or 12500 X
b. By which method (shown here) do bacteria
reproduce?
25 mm
Binary fission
5. Complete this table of SI units of length:
Unit
kilometer
Abbreviation
Metric Equivalent
km
1 000 m
103 m
meter
m
1m
-
centimeter
cm
0.01 m
10-2 m
millimeter
mm
0.001 m
10-3 m
micrometer
μm
0.000 001 m
10-6 m
nanometer
nm
10-9 m
ESSENTIAL BIOLOGY 02: CELLS
6. What is the magnification of these images?
a. Scale bar 10µm measures 40mm on the image.
(40 · 1000 µm divided with 10 µm)
4000 x
b. Scale bar 5µm measures 25mm on the image.
(25 · 1000 µm divided with 5 µm)
5000 x
7. A micrograph has a scale bar of 2µm, which measures 40mm on the image. Measuring the
maximum length of the cell in the image, the ruler reads 180mm. How long is the cell?
Magnification is 40 · 1000 µm divided with 2 µm = 20 000 x
180 · 1000 µm divided with 20 000 = 9 µm
8. What are the advantages of maximizing the surface area: volume ratio in a cell?
The chemical reactions in the cell are proportional to its volume.
Enough surface area to allow efficient rate of exchange of food, waste, gases and heat with
their surroundings.
If the ratio is too small (too big cell) the substances needed will not enter the cell as quickly as
they are required, and the waste products will accumulate. If the ratio is too small the cells may
not loose heat from the metabolism fast enough and overheat.
9. As the volume of a cell increases, what happens to…? (increase/ decrease)
a. Production of waste products.
increase
b. Usage of nutrients and oxygen.
increase
c. The surface area: volume ratio.
decrease
10. Suggest two things a large cell might do to increase its surface area: volume ratio.
i.
Longer and thinner shape
ii.
Infoldings or outfoldings
11. “Unicellular organisms carry out all the functions of life.”
a. Give one example of a unicellular organism.
An amoeba
ESSENTIAL BIOLOGY 02: CELLS
b. What are 6 ‘functions of life’?
metabolism
growth
reproduction
response
homeostasis
nutrition
12. “Multicellular organisms show emergent properties”
Explain, in simple terms, the meaning of this statement.
Emergent properties are those that arise from the interaction of component
parts. The whole is more than the sum of its parts.
For example: consciousness is a property that emerges from the interaction of
nerve cells in the brain. Life itself is an emergent property.
13. What is a stem cell?
A cell in the organism that retain the ability to divide.
14. What type of cell could a liver stem cell become?
It may differentiate into different types of liver cells .
15. Give three examples of specialized cells in multicellular organisms.
Describe how their structure relates to their function.
i.
Red blood cells have no nucleus when mature.
They are filled with hemoglobin to be able to carry as much oxygen as possible.
The shape give them a suitable surface area : volume ratio to exchange the
gases.
The size and shape allow them to pass through narrow capillaries.
ii.
Nerve cells have very long elongations, nerve fibers.
They can conduct electrical impulses.
iii.
Ciliated cells form the lining of the nose and windpipe.
They help to carry the dust and bacteria away from the lungs.
16. Explain briefly how cell differentiation occurs. Refer to ‘genes’ in your answer.
All cells in an organism have the same set of genes. During the development of
the organism, the new cells will block some of their genes and only have access
to the genes they need for their purpose. In the fully developed organism, only
some of the cells in each structure will keep the ability to divide, the others are
differentiated to a special function and have lost the ability to multiply.
For example: The muscle cells use the genes for production of muscle proteins,
but not for production of iris color substances. The iris cells use the genes for
muscle proteins but also the genes for eye color.
ESSENTIAL BIOLOGY 02: CELLS
17. Complete the table below to show how stem cells can be used in medicine.
Therapeutic cloning
Stem cells are removed from the preembryo with the intent of producing
Used to treat… tissue or a whole organ for transplant
back into the person who supplied the
DNA.
Brief method: An egg cell is collected and its
nucleus removed and discarded. A
cell from the patient is taken and its
nucleus taken out and inserted in
the eggshell. This allows to divide
into a pre-embryo. Cells are taken
from this pre-embryo to produce
new tissues for transplantation. The
pre-embryo dies in the process. The
goal of therapeutic cloning is to
produce a healthy copy of a sick
person's tissue or organ for
transplant. This technique would be
vastly superior to relying on organ
transplants from other people. The
supply would be unlimited, so there
would be no waiting lists. The tissue
or organ would have the sick
person's original DNA; the patient
would not have to take
immunosuppressant drugs for the
rest of their life, as is now required
after transplants. There would not
be any danger of organ rejection.
Stem cell transplants
Leukemia, specially in children
Parkinson’s disease
Alzheimer’s disease
Take blood from the umbilical cord
or placenta from a baby.
Remove the red blood cells from
this blood.
Test the remaining fluid for tissue
type.
Check the fluid for disease-causing
organisms.
Store in a special bank for coreblood, in liquid nitrogen.
Kill the bone marrow cells in the
patient, with chemotherapy drug.
Transfer the fluid, with suitable
tissue type, to the patient via a vein
in e.g. the arm. The blood producing
cells move to the bone marrow and
replace the original cells.