Have you ever wondered what you might see if the invisible world around you became visible?
Answer
You would find that almost nothing around you is really empty — every drop of water, every pinch of soil, the air, food and even your own body would be seen to be crowded with living beings.
This is exactly what you will see in this chapter when you actually look:
A single drop of pond or stagnant water on a slide shows Amoeba and Paramecium moving about, and green single-celled algae (Activity 2.4, Table 2.1).
A drop taken from the top of a soil suspension shows bread mould, other moulds, algae and bacteria of many shapes — spherical, comma, spiral and rod-shaped (Activity 2.5, Table 2.2).
A thin onion peel looks like a wall of neat rectangular bricks; a scrape from the inside of your cheek shows polygon-shaped cells.
Fungal growth appears as a powdery or cotton-like patch on a rotting lemon or tomato, and your own gut holds bacteria that help you digest your food.
Why we cannot see them: the human eye can only see objects above a certain size. These organisms are far below that size, so for a very long time they simply remained unknown. A microscope magnifies them 100 to 400 times, which is what makes them visible.
Q2.
How do you think your observation of this hidden world might change the way you think about size, complexity, or even what counts as ‘living’?
Answer
It changes all three ideas.
Idea
What you thought before
What the hidden world shows
Size
Living things are things you can see
There is no lower size limit to life. Bacteria are far smaller than the smallest speck your eye can catch, yet they eat, grow and multiply. At the other end, the yolk of an ostrich egg is a single cell about 130 mm to 170 mm across.
Complexity
Something so small must be simple
A cell is not just a simple bag of liquid. It has a cell membrane, cytoplasm, a nucleus, and in plants plastids and a vacuole — each part with its own special job. A one-celled Amoeba carries out every life process inside that one cell.
What counts as ‘living’
Living and non-living are clearly separate
Viruses are microscopic and acellular — they are not made of cells at all, and they multiply only after entering a living cell. So the boundary of ‘living’ turns out to be far less sharp than it looks.
Did you know? The change also works the other way. Once Hooke saw that cork was made of small empty compartments, the idea that all bodies are built from cells became possible — and that single idea explains a plant, an insect and you.
Q3.
Have you thought how these tiny living beings interact with each other?
Answer
They interact constantly — with each other, with plants and animals, and with us. The chapter gives real examples of each kind of interaction.
They live inside larger organisms and help them.Rhizobium lives in the swollen root nodules of legumes such as beans, peas and lentils; it traps nitrogen from the air and makes it useful to the plant, and the plant shelters and feeds the bacteria. Bacteria in our intestine help in digestion.
They feed on the remains of other organisms. Fungi and bacteria act on fallen leaves, fruit and vegetable peels and even dung, and break these complex substances into simpler, nutrient-rich ones — decomposition. The nutrients go back to the soil, and plants use them again.
They feed one another. Microalgae make their own food using sunlight and become food for many aquatic animals — the beginning of the food chain in a pond.
They compete, and can be kept out. Pickles and murabbas do not spoil because a high concentration of salt or sugar does not allow these organisms to grow on them.
Some of them attack. Viruses may infect plants, animals or even bacterial cells and cause disease.
Why it matters: almost every one of these interactions ends with something being broken down and passed on — nutrients back to the soil, sugar into curd, plant waste into manure. That recycling is the microbes' main job in nature.
Q4.
Share your questions
Answer
Write down the questions the pictures on this page actually raise for you — a good question here is one you could later test with a slide, a microscope or a kitchen experiment.
How to frame one: take something you noticed, add why, how, where or what if, and check that an observation could answer it.
Sample questions:
If a drop of pond water holds so many organisms, how many are there in the whole pond?
Why does bread go mouldy in three days near the sink but not in the refrigerator?
Are the microorganisms in soil from my garden the same as those in soil from a field?
If bacteria live in my gut and help digestion, what happens to them when I fall ill?
An onion peel cell has a cell wall and my cheek cell does not — what does the cheek cell use to keep its shape?
Curd sets overnight in summer but takes much longer in winter. What exactly is temperature doing to the bacteria?
Tip: keep this list in your notebook. At the end of the chapter the book asks you to look back at the questions your friends framed and try to answer them — many of these will already have been answered by then.