Review Questions

Study of malaria - an example of biological method:

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

Observations about malaria:

By that time there were four major observations about malaria.

1. Malaria and marshy areas have some relation
2. Quinine is an effective drug for treating malaria.
3. Drinking the water of marshes does not cause malaria.
4. 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.

Hypothesis about malaria:

The hypothesis made in this case was:

"Plasmodium is the cause of malaria."

The 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 people ill with malaria should have Plasmodium in their blood."

An experiment about malaria:

The next step was to test the deduction through experiments which were designed "Blood of 100 malarial patients was examined under a microscope. To have a control group, the blood of 100 healthy persons was also examined under a microscope."

Results about malaria:

The results of the 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 appearance of symptoms). The results were quite convincing and proved that the hypothesis "Plasmodium is the cause of malaria" was true.

Hypothesis: If some people have Plasmodium in their blood but they do not show any symptoms of malaria, then plasmodium is present in them in incubation period.

Principles of ratio and proportion:

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.

In every proportion of two ratios, there are four terms i.e. the first and fourth terms are called extremes, and the second and third are called means. So, in the above proportion 'a' and 'd' are extremes while 'b' and 'care means. The basic rule used to solve problems through ratios and proportion is that the product of the extremes is equal to the product of means. When three values in a proportion are known, the fourth one (X) can be calculated by using this rule.

For example, a biologist can calculate how many birds would 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