NCERT Solutions for Class 9th Science Chapter 12 .9 Fossils as Evidence / 12.10 Biodiversity Under Threat — Pause and Ponder
Book page 24712 Updated on2026-09-08
Q7.
Does the term ‘biodiversity’ relate only to the variety of organisms, or does it encompass other elements?
Answer
It encompasses much more than a list of organisms. Biodiversity is measured at three levels, and the chapter uses all three even though it names the first most often.
Species diversity — the number and variety of different species. This is the obvious level: nearly 300 bird species in Pakke, about 1,300 in India.
Genetic diversity, within a species — the variation among individuals of the same kind. The chapter opens with it: for centuries farmers conserved diverse crop varieties with useful characteristics such as drought tolerance, pest resistance and the ability to grow in nutrient-poor soils, because diversity reduces the risk of crop failure and strengthens food security. All those varieties are one species; the diversity is in their genes.
Ecosystem and habitat diversity — the variety of the places themselves. India's natural landscape ranges from mountains in the north to desert in the west, rainforests in the North East, plateaus in the south and long coastlines. Each region has distinct soil types and climatic conditions, and these diverse habitats together support a wide variety of species.
Why the extra levels matter: a forest with the same number of species but no genetic variation within them is fragile — one new disease can wipe out an entire uniform crop, as has happened repeatedly in agriculture. And a country could in principle keep every species alive in zoos and still have lost its biodiversity, because the interactions — hornbill with fruiting tree, Rhizobium with pulse root, fungus with alga in a lichen — exist only in a functioning habitat. Biodiversity includes those relationships.
Note: the phumdis of Loktak Lake in Manipur are a good example of habitat diversity being irreplaceable. The Sangai deer is endemic to that one floating grassland; protecting the deer without protecting the phumdis would be meaningless.
Q8.
If you find a new organism in a pond, what features will you observe to classify it and why?
Answer
Work down Fig. 12.5 in order — from the most fundamental character to the finest — so that each observation cuts the possibilities roughly in half.
Order
What I observe
Why — what it decides
1
Cell type: is there a membrane-bound nucleus? (needs high magnification or a stain)
No nucleus → Monera, and the enquiry ends there. Nucleus present → go on
2
Level of organisation: one cell or many?
Unicellular eukaryote → Protista. Multicellular → go on
3
Cell wall: present or absent? If present, chitin or cellulose?
No wall → Animalia. Chitin → Fungi. Cellulose → Plantae
4
Mode of nutrition: is it green and making its own food, or absorbing, or ingesting?
Confirms the split between Fungi (absorption) and Plantae (photosynthesis)
5
Body organisation and symmetry; if it is an animal, is there a notochord or a backbone?
Places it within Animalia — non-chordate or chordate, and then the phylum
6
Movement, and how it feeds (pseudopodia, cilia, flagella; tentacles; mouth and anus)
Narrows the group further and often names the organism
7
Reproduction and, finally, DNA comparison
Confirms the placement and shows the closest relatives
Why this order and not another: the point of a key is that each question must be answerable and must eliminate as much as possible. Cell type divides all of life into two; colour or size would divide almost nothing. Starting with a fundamental character also protects you from the trap of Activity 12.1 — that a superficial resemblance (both swim, both are green) can put unrelated organisms together.
Practical note: in a pond sample the commonest finds are protists — Amoeba, Paramecium and Euglena (Fig. 12.7). If your organism moves by pseudopodia, cilia or a flagellum and is a single cell with a true nucleus, that is almost certainly where it belongs.
Q9.
Why do genetic studies provide deep information about living beings?
Answer
Because DNA is the instruction set itself, not one of its outward results. Every visible character — shape, colour, mode of nutrition — is a product of the DNA, so comparing DNA compares organisms at the level where inheritance actually happens.
Four reasons genetic evidence goes deeper than appearance:
It is the direct record of ancestry. Every living cell contains genetic material (DNA) which carries the instructions for its growth and function, and it is copied from parent to offspring. Organisms with similar DNA are considered to have a common ancestry. Similar appearance may or may not mean common ancestry; similar DNA is much harder to fake.
It sees through misleading resemblance. A dolphin looks like a fish and a bat's wing looks like a bird's, but DNA places the dolphin and the bat firmly with the mammals. Equally, DNA reveals hidden differences between organisms that look identical.
It works where structure gives nothing to compare. Two bacteria may look like identical rods under a microscope. There is almost no external character to use. DNA gives thousands of characters instead of two.
It is quantitative. You can measure how much two sequences differ, so relationships can be ranked, not just asserted.
What this actually changed: comparing organisms at the DNA level is exactly what led Carl Woese, in 1977, to propose the three domain system — Bacteria, Archaea and Eukarya. It showed that some organisms lumped together as "bacteria" were as different from each other as either was from us, and that microscopic life forms are far more diverse than previously believed. No amount of looking down a microscope would have revealed that.
Q10.
How can changes in climate affect the biodiversity?
Answer
Climate sets the conditions each species is adapted to. When those conditions shift faster than species can adapt or move, populations shrink and species are lost — and because species depend on one another, the loss spreads.
The main routes, with the mechanism in each:
The habitat itself changes. Each region of India has its own temperature and rainfall, and these diverse habitats support a wide variety of species. Warming shifts the temperature band a species needs to higher altitudes or latitudes. A Himalayan or Western Ghats species can move uphill only until the hill ends — mountain-top and endemic species have nowhere left to go, which is why endemics are the first to be lost.
Timing gets out of step. Flowering, fruiting, breeding and migration are triggered by temperature and rainfall. If a plant flowers earlier but its pollinator emerges on the old schedule, neither succeeds. The Purple Frog comes out only during the monsoon to breed; shift the monsoon and its whole breeding season is disrupted.
More extreme events. Stronger cyclones, longer droughts and heavier floods kill directly and destroy habitat — like the phumdis of Loktak Lake, on which the Sangai deer depends.
Oceans and corals. Warmer, more acidic sea water bleaches corals. Coral reefs, such as those of the Andaman Sea named in the chapter's opening, shelter an enormous number of species; losing the reef loses all of them.
Knock-on losses. The chapter states the principle plainly: when one species disappears, others that depend on it may also decline in number and eventually also disappear. Remove a pollinator and its plants fail; remove the plants and the herbivores follow.
Why "fast" is the key word: the diversity we see today is the outcome of continuous change over a vast span of time — small differences accumulating over many generations. Adaptation is a slow, generational process. Present-day climate change is happening over decades. Long-lived, slow-breeding and already-rare species simply cannot keep up, and it is these that are lost first.