13 marksCuriosity Grade 8, Chapter 3, Section 3.5.1, page 39
What are antibiotics? Why do they work against bacteria but not against viruses or protozoa?
Hint. The reason is about what the drug targets.
What they are. If our immune system fails to protect us against an infectious disease, we fall ill and need a doctor, who may give medicines called antibiotics, which kill the bacteria that caused the disease.
Why they work only on bacteria. Antibiotics target parts of bacterial cells that are different from human or other animal cells. That is what makes them useful — they can destroy the bacterium while leaving your own cells unharmed.
Why that same fact limits them. They do not work against viruses or diseases caused by protozoa, because those are not bacteria and do not have the bacterial structures the drug attacks. A virus, as Chapter 2 explained, is not even made of a cell.
Working out which diseases they help with. Use the causal agent column of Table 3.1:
| Disease | Causal agent | Antibiotic useful? |
|---|
| Tuberculosis, cholera, typhoid | Bacteria | Yes |
| Cold, flu, chickenpox, measles, hepatitis A, dengue | Virus | No |
| Malaria | Protozoa | No |
| Ascariasis | Worms | No |
A practical consequence. Since most common colds and coughs are viral, taking an antibiotic for them cannot help — and, as the next questions show, it does real harm.
✦ Answer: antibiotics kill bacteria by targeting parts of bacterial cells that differ from our own, which is exactly why they do not work against viruses or protozoa — those lack the structures the drug attacks.
23 marksCuriosity Grade 8, Chapter 3, Think like a scientist, page 40
How was penicillin discovered?
Hint. It began with a petri dish somebody had discarded.
Who and when. Penicillin was discovered in 1928 by Alexander Fleming, a bacteriologist from London.
What happened. While studying harmful bacteria, he noticed that a mould on a discarded petri dish stopped the bacteria from growing. He realised the mould released a substance that killed the bacteria.
What followed. This chance discovery led to penicillin — the first antibiotic used to treat bacterial infections.
Why the chapter calls it a chance discovery, and why that is not the whole story. The mould landing on the dish was an accident. Noticing that the bacteria had stopped growing around it, and asking why, was not. A discarded plate is normally thrown away without a second look; Fleming's contribution was treating an unexpected observation as worth investigating — precisely the habit Chapter 1 was teaching with its instruction to record everything you notice, including what you were not looking for.
A link back to Chapter 2. A mould is a multicellular fungus. So the first antibiotic came from one microorganism that happened to kill another — a striking illustration that microbes are not simply 'germs'.
✦ Answer: Alexander Fleming, a London bacteriologist, noticed in 1928 that a mould on a discarded petri dish had stopped bacteria growing, realised it released a bacteria-killing substance, and this chance observation led to penicillin, the first antibiotic.
34 marksCuriosity Grade 8, Chapter 3, Section 3.5.1 and Activity 3.7, pages 40-41
What is antibiotic resistance? How does it develop and spread, and what precautions reduce it?
Hint. Fig. 3.5b shows the development in four steps.
What it is. A phenomenon where bacteria that were earlier killed by a given antibiotic are found to survive and multiply despite treatment with that antibiotic. This makes common infections harder to treat and increases the risk of complications, prolonged illness, and even death.
How it develops (Fig. 3.5b):
- When antibiotics kill the bacteria causing illness, they also kill good bacteria that protect the body from infection
- A few bacteria develop resistance to the antibiotic
- Those resistant bacteria grow and take over, because their competitors have been removed
- Some bacteria transfer antibiotic resistance to other bacteria, spreading the problem further
What drives it. The caption is explicit: taking antibiotics when they are not required, or taking an incomplete dose.
How resistant bacteria spread (Fig. 3.5a). Through humans — a patient may spread them directly to other patients or indirectly through healthcare workers or dirty hospital surfaces, and then carry them home into the community. And through plants and animal products — resistance develops in bacteria in animals, spreads through manure or animal faeces into crop soil, and reaches the human digestive system through crop produce and animal food products.
The precautions. Use antibiotics wisely — only when prescribed by a doctor, in the correct dose, and for the right duration. Avoiding unnecessary use prevents the rise of resistant bacteria and keeps antibiotics effective for future generations. Fig. 3.5b adds not giving antibiotic injections to cattle without cause.
✦ Answer: antibiotic resistance is bacteria surviving and multiplying despite an antibiotic that once killed them; it develops when a few resistant bacteria survive, take over the space left by the killed bacteria, and pass resistance to others, driven by unnecessary use and incomplete doses — so the precautions are to take antibiotics only on prescription, in the correct dose, for the full duration.
43 marksCuriosity Grade 8, Chapter 3, Section 3.5.1, pages 41-42
What does the chapter say about traditional medicine systems, and how are non-communicable diseases treated?
Hint. The chapter is careful to state both what traditional systems can and cannot do.
Traditional medicine systems. Ayurveda, Siddha and Unani have been used in India for many years to manage common health problems. They use natural substances like herbs, oils and minerals for managing illnesses and promoting recovery, and they focus on a healthy lifestyle and balanced diet.
The chapter's careful qualification. "While these systems can help with some conditions, and are useful for everyday well-being, they may not be effective for all diseases and at all stages." That balance is worth reproducing exactly — it neither dismisses these systems nor claims they can replace treatment for every condition.
Treating non-communicable diseases. Since no pathogen is involved, there is nothing to kill, so therapy focuses on managing symptoms and improving quality of life, through:
- Medication
- Lifestyle changes
- Rehabilitation
What matters most. Early diagnosis and continuous care are key to control the disease progression and prevent complications. Note both words — early, because chronic diseases develop slowly and are easier to control before damage accumulates; and continuous, because a chronic disease by definition lasts more than three months and is managed rather than cured in a single course.
✦ Answer: Ayurveda, Siddha and Unani use herbs, oils and minerals and stress lifestyle and diet, and while useful for everyday well-being may not be effective for all diseases or at all stages; non-communicable diseases are managed through medication, lifestyle changes and rehabilitation, with early diagnosis and continuous care being key.
Solutions written by the tuition.in editorial team and checked against NCERT Curiosity - Textbook of Science for Grade 8 (hecu103.pdf), Chapter 3 'Health: The Ultimate Treasure', pages 28-45, Reprint 2026-27. HAND-WRITTEN throughout. Page count verified against the printed contents page (hecu1ps.pdf p.18): 18 pages, 28-45, matching exactly. Covers the 5 'Probe and ponder' prompts (p.28), all 7 activities (3.1-3.7), every in-text section (3.1-3.5.1), both 'Our scientific heritage' boxes (Ayurveda; variolation and teekedaars), both 'Be a scientist' boxes (Kamal Ranadive; Maharaj Kishan Bhan), both 'Think like a scientist' boxes (Jenner; Fleming), the 'Ever heard of' box on India's vaccine production, the 11 numbered 'Keep the curiosity alive' exercises (pp.42-45) and the 5 'Discover, design, and debate' projects (p.45). ALL OF TABLE 3.1 TRANSCRIBED FROM THE PDF rather than from memory - 10 diseases with causal agent, site of infection, symptoms and preventive measures, in the book's own three groupings (air-spread: common cold and influenza, chickenpox, measles, tuberculosis; water- and food-spread: hepatitis A, cholera, typhoid, ascariasis; insect-transmitted: malaria, dengue). Exercise Q7's dengue figures were transcribed and re-read: Jan 10, Feb 12, Mar 15, Apr 18, May 22, Jun 40, Jul 65, Aug 65, Sep 65, Oct 30, Nov 30, Dec 20 - so the three peak months are July, August and September at 65 each and the lowest is January at 10, with the rise beginning in June and the fall in October, which matches the monsoon and is the basis of the answer to (iii). Exercise Q10 was answered by route of transmission using Table 3.1: hepatitis A, poliomyelitis and cholera spread by faecal contamination of water, while tuberculosis and chickenpox are airborne and do not. THREE POINTS OF DELIBERATE CAUTION. (1) The 'could climate change lead to NEW types of diseases' prompt is answered as changing WHERE, WHEN and HOW MUCH existing diseases occur, with the emergence of genuinely new diseases flagged as an open research question rather than asserted. (2) The CPR project answer gives the broad current sequence and India's emergency number 112, but states plainly that CPR is a practical skill that cannot be learnt from a written description, that guidelines are periodically revised, and that it must be learnt hands-on from a qualified instructor - which is what the book itself asks by suggesting a doctor demonstrate a mock drill. (3) The four Indian scientists in the reading project are given as starting points describing the FIELD each worked in, with the student told to verify and cite sources and to note disagreement between them, rather than being handed specific dates and claims to reproduce.. Questions are referenced from the NCERT textbook for identification.
