Chapter 2 notes biology-class 9th

Chapter 2  notes biology-class 9th

Give an example of solving biological problem keeping in view the study of malaria.

 Introduction: 

Malaria is a disease of chills and fevers with recurring attacks. Scientists observed that this disease was common in low, marshy areas.

The word “Malaria” was derived from two Latin words: i) Mala means bad. ii) Aria means air. 

So, the meaning of malaria becomes bad air. Quinine from cinchona bark was an effective remedy for malaria.

Observations: 

i) In 1878, a French army physician Laveran began to search for the cause of malaria.
ii) He observed the blood of malarial patients under microscope and found some tiny creatures in it.
iii) His discovery was not believed by other biologists.
iv) Two year later same results were drawn by another physician and three years later same observations were found third time.
v) The organism was given the name Plasmodium.

Hypothesis: 

Regarding malaria the hypothesis made was: “Plasmodium is the cause of malaria”

Deduction:

 Regarding malaria deduction was made from above hypothesis is: “If plasmodium is the cause of malaria, then all person ill with malaria should have plasmodium in their blood.”
Experiments:
• Then blood of 100 malarial patients was examined under microscope.
 • The results showed that all malarial patients had plasmodium in their blood. While 7 out of 100 healthy persons also had plasmodium in their blood.
• In the healthy people plasmodium was in incubation period (The period between the entry of parasite in host and the appearance of symptoms.)
• The result was convincing and proved the hypothesis.

 How Plasmodium enter in Man:

 Now next step was that how plasmodium gets into the blood of man? In this regard biologists were having following observations:
i) Malaria is associated with marshes
ii)  Drinking water of marshes does not cause malaria.

In this regard, A.F.A King made his observations in 1883. His observations were: 

i) People who slept outdoors in open spaces suffered more from malaria than www.allonlinefree.com those who slept indoors.
ii) People who slept under mosquito nets did not suffer from malaria. iii) Person who slept near smoky fire also did not suffer from malaria.
On the basis of these observations King suggested a hypothesis:
“Mosquitoes transmit Plasmodium and so are involved in the spread of malaria.” For this hypothesis, following deductions were made:
i) “Plasmodium should be present in mosquitoes”
ii) “A mosquito can get Plasmodium by biting a malarial patient”

Experiment of Ronald Ross: 

To test these deductions Ronald Ross, a British army physician performed his experiments in 1880’s in India.
• 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.
• Next step was to allow the infected mosquito to bite a healthy person. But this was a risky work as that healthy person can be suffered from malaria. So he selected sparrows for his experiment.
• He allowed a female Culex mosquito to bite a malarial sparrow.
• Then he allowed those mosquitoes to bite a healthy sparrow.
• The healthy sparrow also suffered from malaria.
• In this way he proves that plasmodium is the real cause of malaria and they are transmitted by mosquitoes.
In 1898, an Italian biologists performed same experiments on human beings and find the same results. This confirmed that mosquitoes are involved in the spread of this disease.

Theory:

 When a hypothesis has been proved by consistent results it becomes a theory.

Scientific Principle or Law: 

When a theory can explain many natural phenomena and consistently supported by experiments, and also universally accepted by scientists it becomes a scientific principal or Law.