chapter 2| solving a biological problem part2

Study Of Malaria - An Example Of Biological Method

   malaria is a common disease in many countries including Pakistan.  

history :In ancient times (more than 2000 years ago), physicians were familiar with malaria. They described it as a disease of chills and fevers with recurring attacks. They also observed that the disease was more common among people living in low, marshy areas. It was thought that the stagnant water of marshes poisoned the air and as a result of breathing in this “bad air”, people got malaria. This belief led to the name of this disease. The Italian words “mala” means bad and “aria” means air. For further clarification of the observation, some volunteers drank stagnant water from the marshes. They did not develop malaria.

In the 17th century when the New World (America) was discovered, many plants from America were

sent back to Europe to be used as medicines. The bark of a tree known as quina-quina was very

suitable for curing fevers. It was so beneficial that soon it was impossible to carry enough bark to

Europe. Some dishonest merchants began to substitute the bark of another tree, cinchona which

closely resembled quina-quina. This dishonesty proved much valuable for mankind. Cinchona bark

was found to be excellent for treating malaria. We now know the reason: cinchona bark contains

quinine that is effective in treating the disease

At that time, physicians treated malaria with cinchona without understanding the cause of malaria.

Two hundred years later, it was found that some diseases are caused by tiny living organisms. After

this discovery, it also became a belief that malaria, too, might be caused by some microorganism.

In 1878, a French army physician Laveran began to search for the “cause” of malaria. He took a

small amount of blood from a malarial patient and examined it under microscope. He noticed some

tiny living creatures. His discovery was not believed by other scientists. 

Two years later, another physician saw the same creatures in the blood of another malarial patient. Three years after the second discovery, the same creatures were observed for third time. The organism was given a name Plasmodium.

In the last part of nineteenth century, many different causes of malaria were being suggested. By

that time, there were four major observations about malaria.

• Malaria and marshy areas have some relation.

• Quinine is an effective drug for treating malaria.

• Drinking the water of marshes does not cause malaria.

• Plasmodium is seen in the blood of malarial patients.

We know that a scientist uses whatever information and observation he has and makes one or

more hypotheses. The hypothesis made in this case was;

“Plasmodium is the cause of malaria.”

Scientist does not know whether his hypothesis is true or not, but he accepts it may be true and

makes deductions. One of the deductions from the above hypothesis was;

“If Plasmodium is the cause of malaria, then all person ill with malaria should

have Plasmodium in their blood.”

The next step was to test the deduction through experiments which were designed as;

“Blood of 100 malarial patients was examined under microscope. For the purpose of having a

control group, the blood of 100 healthy persons was also examined under microscope.”

The results of experiments showed that almost all malarial patients had Plasmodium in their

blood while 07 out of 100 healthy persons also had Plasmodium in their blood (now we know that

Plasmodium in the blood of healthy people was in incubation period i.e. the period between the

entry of parasite in host and the appearance of symptoms). The results were quite convincing and

proved that the hypothesis “Plasmodium is the cause of malaria” was true.

Malaria has killed more people than any other disease. The account of malaria is an example of

a biological problem and of how such problems are solved.

Next biological problem was to learn about “How Plasmodium gets into the blood of man”. Biologists  were having following observations;

• Malaria is associated with marshes.

• Drinking water of marshes does not cause malaria.

From these observations, it can be concluded that Plasmodium was not in the marsh water. But it

must be carried by something that comes to marsh water. In 1883, a physician A. F. A. King, listed

20 observations. Some important observations of King were:

• People who slept outdoors were more likely to get malaria than those who slept indoors;

• People who slept under fine nets were less likely to get malaria than those who did not use such

nets; and

• Individuals who slept near a smoky fire usually did not get malaria.

On the basis of these observations King suggested a hypothesis:

“Mosquitoes transmit Plasmodium and so are involved in the spread of malaria.”

Following deductions were made considering the hypothesis as true i.e. If mosquitoes are involved

in the spread of malaria then;

“Plasmodium should be present in mosquitoes.”

“A mosquito can get Plasmodium by biting a malarial patient.”

In order to test the above deductions, Ronald Ross: a British army physician working in India in 1880’s; performed important experiments. He allowed a female Anopheles mosquito to bite a malarial patient. He killed the mosquito some days later and found Plasmodium multiplying in mosquito’s stomach.

The next logical experiment was to allow an infected mosquito (having Plasmodium) to bite a

healthy person. If hypothesis was true, the healthy person would have got malaria. But scientists

avoid using human beings for experiments when results can be so serious. Ross used sparrows and

redesigned his experiments. He allowed a female Culex mosquito to bite on the sparrows suffering

from malaria. Some of the mosquitoes were killed and studied at various times. Ross found that

Plasmodium multiplied in the wall of mosquito’s stomach and then moved into mosquito’s salivary

glands. He kept some mosquitoes alive and allowed them to bite healthy sparrows. Ross found that

the saliva of the infected mosquito contained Plasmodia (plural of Plasmodium) and these entered

the sparrow’s blood. When he examined the blood of these previously healthy sparrows, he found

many Plasmodia in it. In fact quinine was the only effective remedy for malaria from the 17th to

the 20th century.

Figure 2.1 : Malaria in sparrow and man is transmitted by Culex and Anopheles mosquitoes respectively

In the end, the hypothesis was tested by direct experimentation on human beings. In 1898, Italian

biologists allowed an Anopheles mosquito to bite a malarial patient. The mosquito was kept for a

few days and then it was allowed to bite a healthy man. This person later became ill with malaria. In

this way, it was confirmed that mosquitoes transmit Plasmodium and spread malaria. (Figure 2.1)

Theory, law and principle

When a hypothesis is given a repeated exposure to experimentation and is not falsified, it increases

biologists’ confidence in hypothesis. Such well-supported hypothesis may be used as the basis for

formulating further hypotheses which are again proved by experimental results. The hypotheses

that stand the test of time (often tested and never rejected), are called theories. A theory is

supported by a great deal of evidence.

Productive theory keeps on suggesting new hypotheses and so testing goes on. Many biologists

take it as a challenge and exert greater efforts to disprove the theory. If a theory survives such

doubtful approach and continues to be supported by experimental evidence, it becomes a law or

principle. 

A scientific law is a uniform or constant fact of nature. It is an irrefutable theory. Examples

of biological laws are Hardy-Weinberg law and Mendel’s laws of inheritance.

When a female mosquito pierces the skin with her mouthparts, she injects a small amount of

saliva into the wound before drawing blood. The saliva prevents the blood from clotting in her

food canal.

 Data Organization And Data Analysis

Data organization and data analysis are important steps in biological method. Data can be defined

as the information such as names, dates or values made from observations and experimentation.

Data organization

In order to formulate and then to test hypotheses, scientists collect and organize data. Prior to

conducting an experiment, it is very important for a scientist to describe data collection methods. It

ensures the quality of experiment. Data is organized in different formats like graphics, tables, flow

charts, maps and diagrams.

Data analysis

Data analysis is necessary to prove or disprove a hypothesis by experimentation. It is done through

the application of statistical methods i.e. ratio and proportion. When a relation between two

numbers e.g. ‘a’ and ‘b’ is expressed in terms of quotient (a/b), it is called the ratio of one number

to the other. Ratio may be expressed by putting a division (÷) or colon (:) mark between the two

numbers. For example the ratio between 50 malarial patients and 150 normal persons is 1:3.

Proportion means to join two equal ratios by the sign of equality (=). For example; a:b = c:d is a

proportion between the two ratios. This proportion may also be expressed as a:b::c:d. When three

values in a proportion are known, the fourth one (X) can be calculated.

For example, a biologist can calculate how many birds will get malaria when he allows infected

mosquitoes to bite 100 healthy sparrows. In the previous experiment he noted that when he allowed

mosquitoes to bite 20 sparrows, 14 out of them got malaria. Now he uses the proportion rule.

The welts that appear after the mosquito leaves is not a reaction to the wound but an allergic

reaction to the saliva. In most cases, the itching sensation and swellings subside within several

hours.

Statistics are thus a means of summarizing data through the calculation of mean value. This step

is very important as it transforms raw data into information, which can be used to summarize and

report results

Mathematics: As An Integral Part Of Scientific Process

Biological method also involves the use of applied mathematics to solve biological problems. Major

biological problems in which knowledge of mathematics is used include gene finding, protein

structure, and protein-protein interactions etc. Bioinformatics refers to the computational and

statistical techniques for the analysis of biological data.