Both are single-celled prokaryotes — no true nucleus and no membrane-bound organelles — which is why both are grouped under Monera. Beyond that, the two differ in size, colour and how they feed. What follows from being a prokaryote: with no internal compartments, everything a bacterial cell does happens in one space. Its DNA lies free in the cytoplasm. This makes the cell small and simple, and also makes it fast — a bacterium can divide in twenty minutes, which is why bacteria colonise new conditions so quickly. Where these organisms live and what they do — from the chapter: Bacteria are found everywhere — soil, water, air, hot springs and other extreme environments where most organisms cannot survive, and even inside human bodies. They live in the gut of ruminants and are responsible for the production of biogas from the dung of these animals. Some are harmful pathogens and cause diseases, but many are useful — Lactobacillus and Rhizobium . Cyanobacteria are autotrophs and decomposers ; besides nutrient cycling, some bacteria break down pollutants such as oil, pesticides and sewage. Did you know? Cyanobacteria were among the first organisms to produce oxygen by photosynthesis. About 2.5 billion years ago that oxygen accumulated in the atmosphere and made the Earth suitable for other forms of life. Their fossils are found in structures called stromatolites , and stromatolites have been found in Rajasthan and Madhya Pradesh — some of the earliest evidence of life on the Earth.

NCERT Solutions for Class 9th Science Chapter 12 Let us explore — Activity 12.4

Book page 235 Updated on2026-09-08

Q1.

In the school laboratory, observe the available permanent slides of bacteria and cyanobacteria under the microscope.

Answer

Place the slide on the stage, focus first on low power (10×) to find the material, then switch to high power (45×) and finally to the oil-immersion objective (100×) if your microscope has one — bacteria are only a few micrometres across and stay a blur at low power.

What you should see:

Bacteria — extremely small, stained dots, rods or spirals. Nothing inside them is resolvable: no nucleus, no chloroplast, no visible organelles. Often they lie in chains or clusters.
Cyanobacteria — noticeably larger, blue-green, usually as unbranched filaments of cells joined end to end (for example Nostoc, Oscillatoria). The colour is spread through the whole cell, not packed into chloroplasts.

Tip: use the fine adjustment only on high power, and reduce the light with the diaphragm — unstained prokaryotes are nearly transparent and are much easier to see in dim, contrasty light than in bright light.

Q2.

Compare them with Fig. 12.6.

Answer

Fig. 12.6 shows the members of Kingdom Monera. Match what is on your slide to the figure point by point.

Feature	Bacteria	Cyanobacteria (blue-green algae)
Cell type	Prokaryote — no membrane-bound nucleus	Prokaryote — no membrane-bound nucleus
Level of organisation	Unicellular	Unicellular, often in filaments or colonies
Size seen under the microscope	Very small dots, rods, spirals	Distinctly larger; chains of cells
Colour	Only what the stain gives	Naturally blue-green
Nutrition	Mostly heterotrophic; some autotrophic	Autotrophic (photosynthesis) — and also act as decomposers

Why both are in the same kingdom despite looking different: the kingdom is decided at the first fork of Fig. 12.5 — cell type. Neither has a true nucleus, so both are Monera, whatever their colour, shape or way of feeding. Compare this with an amoeba, which is also a single cell but does have a true nucleus and therefore goes to Protista.

Q3.

What do you observe?

Answer

Both are single-celled prokaryotes — no true nucleus and no membrane-bound organelles — which is why both are grouped under Monera. Beyond that, the two differ in size, colour and how they feed.

What follows from being a prokaryote: with no internal compartments, everything a bacterial cell does happens in one space. Its DNA lies free in the cytoplasm. This makes the cell small and simple, and also makes it fast — a bacterium can divide in twenty minutes, which is why bacteria colonise new conditions so quickly.

Where these organisms live and what they do — from the chapter:

Bacteria are found everywhere — soil, water, air, hot springs and other extreme environments where most organisms cannot survive, and even inside human bodies.
They live in the gut of ruminants and are responsible for the production of biogas from the dung of these animals.
Some are harmful pathogens and cause diseases, but many are useful — Lactobacillus and Rhizobium.
Cyanobacteria are autotrophs and decomposers; besides nutrient cycling, some bacteria break down pollutants such as oil, pesticides and sewage.

Did you know? Cyanobacteria were among the first organisms to produce oxygen by photosynthesis. About 2.5 billion years ago that oxygen accumulated in the atmosphere and made the Earth suitable for other forms of life. Their fossils are found in structures called stromatolites, and stromatolites have been found in Rajasthan and Madhya Pradesh — some of the earliest evidence of life on the Earth.

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