IX Biology Solved Questions for class 9th Chapter: Why do we fall ill?
Q1. What does the word health mean? Ans: For our grandmothers, being able to go out to the market or to visit neighbours is .being well., and not being able to do such things is .poor health.. Being interested in following the teaching in the classroom so that we can understand the world is called a healthy attitude. While not being interested is called the opposite. .Health is therefore a state of being well enough to function well physically, mentally and socially.
Q2. How does the health of an organism depend upon the surroundings?
Ans: Human beings live in societies. Our social environment, therefore, is an important factor in our individual health. We live in villages, towns or cities. In such places, even our physical environment is decided by our social environment. Consider what would happen if no agency is ensuring that garbage is collected and disposed. What would happen if no one takes responsibility for clearing the drains and ensuring that water does not collect in the streets or open spaces? So, if there is a great deal of garbage thrown in our streets, or if there is open drain water lying stagnant around where we live, the possibility of poor health increases. Therefore , public cleanliness is important for individual health.
Q3. What do we mean by “disease”?
Ans: Disease (disturbed ease) in other words, literally means being uncomfortable. However, the word is used in a more limited meaning. We talk of disease when we can find a specific and particular cause for discomfort. This does not mean that we have to know the absolute final cause; we can say that someone is suffering from diarrhoea without knowing exactly what has caused the loose motion When there is a disease, either the functioning or the appearance of one or more systems of the body will change for the worse. These changes give rise to symptoms and signs of disease.
Q4. What are symptoms?
Ans: Symptoms of disease are the things we feel as being .wrong.. So we have a headache, we have cough, we have loose motions, we have a wound with pus; these are all symptoms. These indicate that there may be a disease.
Q5. How do you distinguish between acute and chronic diseases?
Ans: Some diseases last for only very short periods of time, and these are called acute diseases. We all know from experience that the common cold lasts only a few days. Other ailments can last for a long time, even as much as a lifetime, and are called chronic diseases. An example is the infection causing elephantiasis. Acute and chronic diseases have different effects on our health. Any disease that causes poor functioning of some part of the body will affect our general health as well. This is because all functions of the body are necessary for general health. But an acute disease, which is over very soon, will not have time to cause major effects on general health, while a chronic disease will do so. As an example, think about a cough and cold, which all of us have from time to time. Most of us get better and become well within a week or so. And there are no bad effects.
Q6. What are the various causes of diseases?
Ans: It is useful to think of the immediate causes of disease as belonging to two distinct types. One group of causes is the infectious agents, mostly microbes or micro-organisms. Diseases where microbes are the immediate causes are called infectious diseases. This is because the microbes can spread in the community, and the diseases they cause will spread with them. On the other hand, there are also diseases that are not caused by infectious agents. Their causes vary, but they are not external causes like microbes that can spread in the community. Instead, these are mostly internal, non infectious causes.
Q7. Name some common infectious diseases
Ans: Common examples of diseases caused by viruses are the common cold, influenza, dengue fever and AIDS. Diseases like typhoid fever, cholera, tuberculosis and anthrax are caused by bacteria. Many common skin infections are caused by different kinds of fungi. Protozoan microbes cause many familiar diseases, such as malaria and kalaazar. All of us have also come across intestinal worm infections, as well as diseases like elephantiasis caused by different species of worms.
Q8. Explain the effect of antibiotic penicillin on bacterial cells.
Ans: Taxonomically, all bacteria are closely related to each other than to viruses and vice versa. This means that many important life processes are similar in the bacteria group but are not shared with the virus group. As a result, drugs that block one of these life processes in one member of the group is likely to be effective against many other members of the group. But the same drug will not work against a microbe belonging to a different group. As an example, let us take antibiotics. They commonly block biochemical pathways important for bacteria. Many bacteria, for example, make a cell-wall to protect them. The antibiotic penicillin blocks the bacterial processes that build the cell wall. As a result, the growing bacteria become unable to make cell-walls, and die easily.
Q9. Why are human cells not affected by penicillin?
Ans: Human cells don’t make a cell-wall anyway, so penicillin cannot have such an effect on us. Penicillin will have this effect on any bacteria that use such processes for making cell-walls.
Q10.. Why are antibiotics ineffective against viruses?
Ans: Viruses have very few biochemical pathways of their own, and that is the reason why antibiotics do not work against viral infections. If we have a common cold, taking antibiotics does not reduce the severity or the duration of the disease. However, if we also get a bacterial infection along with the viral cold, taking antibiotics will help. Even then, the antibiotic will work only against the bacterial part of the infection, not the viral infection.
Q 11. How do communicable or infectious diseases spread?
Ans: Many microbial agents can commonly move from an affected person to someone else in a variety of ways. In other words, they can be communicated, and so are also called communicable diseases. Such disease-causing microbes can spread through the air. This occurs through the little droplets thrown out by an infected person who sneezes or coughs. Someone standing close by can breathe in these Diseases can also be spread through water. This occurs if the excreta from someone suffering from an infectious gut disease, such as cholera, get mixed with the drinking water used by people living nearby. The cholera causing microbes will enter new hosts through the water they drink and cause disease in them. Such diseases are much more likely to spread in the absence of safe supplies of drinking water. The sexual act is one of the closest physical contact two people can have with each other. Not surprisingly, there are microbial diseases such as syphilis or AIDS that are transmitted by sexual contact from one partner to the other. However, such sexually transmitted diseases are not spread by casual physical contact. Casual physical contacts include handshakes or hugs .sports, like wrestling, or by any of the other ways in which we touch each other socially.
Q 12.How does AIDS spread?
An: Other than the sexual contact, the AIDS virus can also spread through blood-to-blood contact with infected people or from an infected mother to her baby, by sharing of same syringe and having unprotected sex.
Q13. What are vectors? Name some vector transmitted diseases.
Ans: Many diseases will be transmitted by other animals. These animals carry the infecting agents from a sick person to another potential host. These animals are thus the intermediaries and are called vectors. The commonest vectors we all know are mosquitoes. In many species of mosquitoes, the females need highly nutritious food in the form of blood in order to be able to lay mature eggs. Mosquitoes feed on many warm-blooded animals, including us. In this way, they can transfer diseases from person to person. Eg. Malaria, rabies.
Q14. The disease-causing microbes enter the body through different means. Where do they go then?. Do all microbes go to the same tissue or organ, or do they go to different ones?
Ans: Different species of microbes seem to have evolved to home in on different parts of the body. In part, this selection is connected to their point of entry. If they enter from the air via the nose, they are likely to go to the lungs. This is seen in the bacteria causing tuberculosis. If they enter through the mouth, they can stay in the gut lining like typhoid causing bacteria Or they can go to the liver,like the viruses that cause jaundice. But this needn.t always be the case. An infection like HIV, that comes into the body thru the sexual organs, will spread to lymph nodes all over the body. Malaria-causing microbes, entering through a mosquito bite, will go to the liver, and then to the red blood cells. The virus causing Japanese encephalitis, or brain fever, will similarly enter through a mosquito bite. But it goes on to infect the brain.
Q15. The signs and symptoms of a disease depend upon the tissue or organ targeted. Explain.
Ans: The signs and symptoms of a disease will thus depend on the tissue or organ which the microbe targets. If the lungs are the targets, then symptoms will be cough and breathlessness. If the liver is targeted, there will be jaundice. If the brain is the target, we will observe headaches, vomiting, fits or unconsciousness.
Q16.How does HIV damage our body?
Ans: In HIV infection, the virus goes to the immune system and damages its function. Thus, many of the effects of HIV-AIDS are because the body can no longer fight off the many minor infections that we face everyday. Instead, every small cold can become pneumonia.
Q17.How do we kill microbes?
Ans: One way is to use medicines that kill microbes.Microbes can be classified into different categories. They are viruses, bacteria, fungi or protozoa. Each of these groups of organisms will have some essential biochemical life process which is peculiar to that group and not shared with the other groups. We can use a drug, that blocks the bacterial synthesis pathway without affecting our own.
Q18. What feature of our body protects us from catching infectious diseases?
Ans: The immune system of our body is normally fighting off microbes. We have cells that specialise in killing infecting microbes. These cells go into action each time infecting microbes enter the body. If they are successful, we do not actually come down with any disease. The immune cells manage to kill off the infection long before it assumes major proportions.
Q19. Describe the principle behind vaccination.
Ans: By providing vaccination, we can .fool the immune system into developing a memory for a particular infection by putting something, that mimics the microbe we want to vaccinate against, into the body. This does not actually cause the disease but this would prevent any subsequent exposure to the infecting microbe from turning into actual disease.
Q20. Name some diseases for which vaccines are available.
Ans: Many such vaccines are now available for preventing a whole range of infectious diseases, and provide a disease-specific means of prevention. There are vaccines against tetanus, diphtheria, whooping cough, measles, polio and many others.
Q21. Who were awarded nobel prize for discovery of treatment of peptic ulcer?
Ans: Robin Warren and Barry Marshall discovered for the first time, that the area of peptic ulcer contained many small curved Bacteria named Helicobacter pyroli . They also found that amoxicillin an antibiotic effective in killing the bacteria, could also cure the peptic ulcers.
Q22. List some general principles of prevention. Ans: 1. prevention of overcrowding 2. sanitation 3. safe drinking water 4. taking good nutrition 5. proper habits 6. freedom from addictions 7. exercise 8. relaxation
23. State any two conditions essential for good health. Ans. Two conditions that are essential for good health are: 1. Person should be physically fit and fine. 2. He should have good social and economic conditions. 3. Clean environment.
24. State any two conditions essential for being free of disease. Ans. Two conditions essential for being disease-free are: 1. Person should take balance diet. 2. Personal and community hygiene.
25. Are the answers to the above questions necessarily the same or different? Why?
Ans. To some extent they are the same, because if the conditions that are essential for good health are maintained, then automatically the chances of getting a disease will be minimized. But at the same time, we can say that they are different because being health or good health means physical, mental and social well-being while being disease-free means not suffering from a particular disease(s).
26 . List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?
Ans. Common symptoms which indicate sickness are: (i) Headache (ii) Cough and (iii) Dysentery
If I see any one of the above symptoms, I’ll immediately go the doctor. It is because any of these symptoms can be the sign of sickness or disease. Ignoring it may lead to increase in the disease. The doctor will make his diagnosis and if need be, he’ll get some tests done and then start medication, if need arises.
27. In which of the following case do you think the long-term effects on your health are likely to be most unpleasant? a) if you get jaundice, b) if you get lice, c) if you get acne. Why?
Ans. a) In case of jaundice as liver does not functions properly so it will have drastic long term effect on the body. b) In case of lice it can remain for long time but will not have an adverse effect on the body.
c) Acne can remain for a long time but will not affect the body adversely.
28. Why we are normally advised to take bland and nourishing food when we are sick?
Ans. When we are sick the normal body functions get disturbed. In such situation food that is easily digestible and contains adequate nutrients are required for the speedy recovery. Thus bland and nourishing food is given during sickness
29. How are acute diseases different from chronic diseases?
Ans: Acute disease – Diseases which last for short periods of time and are severe are called acute diseases.
Chronic disease – Diseases which are long lasting are called chronic diseases.
30. What is the full form of AIDS? Name the causal organism.
Ans: AIDS – Acquired Immuno deficiency syndrome It is caused by HIV – Human Immuno deficiency virus.
31. State two conditions essential for keeping good health.
Ans: Conditions for keeping good health are
(a) Public and personal hygiene (b) Regular exercise, sleep and relaxation.
(c) Proper habits. (d) Nutrition
32. Define (a) health (b) disease.
Ans Health – It is defined as a state of complete physical, mental and social well being and not merely the absence of disease or infirmity.
Disease – A disease in the malfunctioning of body organs due to one reason or the other.
34. Why are antibiotics not effective for viral disease?
Ans: Antibiotics block the bacterial pathways without affecting the pathways of humans. In the case of viruses, they have very few biochemical pathways of their own. They use the metabolic machinery of host and grow and reproduce.
35. Explain giving reasons –
(a) Balanced diet is necessary for maintaining health body. (b) Health of an organism depends upon the surrounding environmental conditions.
Ans: a) Balanced diet contain all the nutrient required for maintaining proper health as well as needed for growth and repair. Lack of single nutrient causes deficiency diseases.
b) surrounding environmental conditions plays an important role in the maintenance of health.
For ex we feel depressed if –
(i) surrounding are dirty or polluted
(ii) garbage is not collected or disposed off
(iii) drains are not cleaned and water collects in the streets or open spaces.
Unclean surrounding causes the entry of germs via air, water, food or vectors and makes the person unhealthy