NCERT Class 12 Biology: Chapter – 8 Human Health and Diseases Part 9

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Question 22:

What are lifestyle diseases? How are they caused? Name any two such diseases.

Answer: Lifestyle diseases are the diseases caused because of the way a person lives his life or his daily habits and routine. These diseases occurs because of:

1. Unhealthy eating.

2. Intake of substances like alcohol, drugs and cigarettes etc.

3. Lack of physical activity and exercise.

Lifestyle disorders are:

1. Type II Diabetes: High or low blood sugar level is caused due to unhealthy eating, excessive stress and lack of exercise etc.

2. Hypertension: Increased blood pressure due to extreme stress and lack of exercise.

Question 23:

If there are two pathogenic viruses, one with DNA and other with RNA, which would mutate faster? And Why?

Answer: If there are two pathogenic viruses, one with DNA and other with RNA than the one having RNA would mutate faster because RNA being a single stranded structure is quiet unstable and is able to mutate at a faster rate. Hence, the organism would have a shorter life span and would evolve rapidly.

Long Answer Type Questions

Question 1:

Represent schematically the life cycle of a malarial parasite.

Answer: Malaria is a mosquito born disease caused by female anopheles mosquito.

Symptoms of Malaria:

1. Headache

2. Fever, chills, and sweating.

3. Muscular Fatigue and pain.

4. Spleen Enlargement

5. Nausea and Vomiting.

Life cycle of Malarial Parasite:

Life Cycle of Malarial Parasite

1. The female anopheles mosquito transmits the motile infective form called sporozite to a vertebrate host such as humans.

2. These Sporozoites infect the liver where they asexually multiply and mature to form Schizonts.

3. These Schizonts rupture and release Merozoites.

4. Now, Merozoites enter RBC՚s where they multiply asexually and infect the RBC leading to cycles of fever.

5. He ring stage trophozites mature into schizonts which release merozites or parsites.

6. Some parasites form gametophytes.

7. The gametophytes produced are ingested by the female anopheles mosquito when it bites the infected person.

8. The parasites then multiply in the gut of the mosquito known as sporogonic cycle.

9. Now, these microgametes enter macrogametes and form zygotes.

10. These zygotes now become motile and elongated called as sporozite.

Question 2:

Compare the life style of people living in the urban areas with those of rural areas and briefly describe how the life style affects their health.


Rural Area and Urban Area
S. no.Rural areaUrban area
1.Lack of health facilities.Health facilities are present.
2.Poor SanitationBetter sanitation facilities.
3.Poor living conditions.Better living conditions.
4.Unavailability of basic necessities like water electricity etc.Availability of basic necessities like water, electricity
5.Poor hygiene conditions.Good hygiene conditions.
6.More physical labour is doneLess physical labour.