NCERT Solutions for Class 9th Science Chapter 12 Let us study — Activity 12.3
Book page 234 Updated on2026-09-08
Q1.
Study the concept map (Fig. 12.5).
Answer
Fig. 12.5 is a decision tree. You start at the top with any living organism and answer one question at each fork; after at most four questions you are standing in one of the five kingdoms.
Fig. 12.5 redrawn as a decision tree: four questions place any organism in one of the five kingdoms.
Read the map carefully — two details are easy to miss. Protista may or may not have a cell wall (when present it is of cellulose), which is why the map settles Protista on level of organisation and not on the wall. And Fungi and Plantae are separated only at the last fork, by what the wall is made of and how the organism feeds — chitin plus absorption for Fungi, cellulose plus photosynthesis for Plantae.
Q2.
List the criteria which form the basis of five kingdom classification.
Answer
Reading Fig. 12.5 from the top down, the concept map turns on five criteria:
Cell type — prokaryote (primitive nucleus, no bounding membrane) or eukaryote (membrane-bound nucleus).
Level of organisation — unicellular or multicellular.
Cell structure — cell wall present or absent, and if present, made of chitin or cellulose.
Mode of nutrition — autotrophic (makes its own food by photosynthesis) or heterotrophic (depends on others for food).
Ecological role — producer, consumer or decomposer.
Why these five and not others: each one is a property of the cell or of the organism's basic way of living, so it cannot be switched on and off by circumstances. Contrast this with habitat or the ability to fly, which Activity 12.1 showed will put a bat with an eagle. A bacterium cannot acquire a nucleus and a plant cannot start eating other organisms — these are the deepest divisions available.
Q3.
Compare the criteria you have listed after studying the concept map and the criteria given below: Cell type — prokaryote or eukaryote; Cell structure — presence or absence of a cell wall; Level of organisation — unicellular or multicellular; Mode of nutrition — autotrophic or heterotrophic
Answer
All four listed criteria appear in the concept map, in exactly the order the map uses them. The only item on my list that is not in the four given is ecological role (producer / consumer / decomposer), which Fig. 12.5 prints alongside mode of nutrition at the last fork.
Criterion given
Where it acts in Fig. 12.5
What it separates
Cell type
First fork, at the very top
Monera (prokaryote) from all four other kingdoms (eukaryote)
Level of organisation
Second fork, on the eukaryote branch
Protista (unicellular) from Fungi, Plantae, Animalia (multicellular)
Cell structure
Third fork
Fungi and Plantae (cell wall) from Animalia (no cell wall)
Mode of nutrition
Fourth fork
Fungi (heterotrophic, chitin wall) from Plantae (autotrophic, cellulose wall)
Why the order is not interchangeable: the criteria are applied from the most fundamental to the least. Having or not having a nucleus is the single biggest difference between cells, so it splits first. Nutrition is applied last because it separates the finest pair — and even then it must be used together with the wall material, since a mushroom and a moss are both multicellular eukaryotes with cell walls, and only chitin-plus-absorption versus cellulose-plus-photosynthesis tells them apart.
Check it yourself: run yeast through the map. Eukaryote → unicellular → so it should land in Protista. But its cell wall is made of chitin, so the book places it in Fungi. That single exception is a good reminder that a decision tree is a summary, not a law.