NCERT Solutions Curiosity Chapter 3 Activity 3.6: Let us investigate — Test for fats

Book page 49 Updated on2026-09-05

Q1.

Take a small part of the food items that you tested for the presence of starch in Activity 3.5. Place each food item on a separate piece of paper. Wrap the paper around the food and press it. Be careful not to tear the paper. If a food item contains a little water, allow the paper to dry. Does the paper develop an oily patch? What do you think is the reason for this patch?

Answer

Yes, some foods leave an oily patch — and the reason is the fat present in them.

The test in one line: reagent — none, only a plain piece of paper; result — a greasy, translucent patch that does not dry away.

	What happens
Positive result	A permanent oily patch forms; the paper there looks darker and semi-transparent → fat is present
Negative result	The paper may become damp, but after drying it becomes completely clean and opaque again → fat is absent

Why the patch forms: when the food is pressed, a little fat (oil, ghee or butter) is squeezed out of it and soaks into the paper. Fat does not evaporate the way water does, so the patch stays even after the paper has dried.

Why we wait for the paper to dry: a watery food such as cucumber also makes the paper look wet and dark, and that could easily be mistaken for fat. Water evaporates in a few minutes and the paper becomes clean; an oily patch does not go. Drying the paper is what makes the test fair.

Q2.

Now, hold the paper against light. Can you see the light faintly shining through this patch?

Answer

Yes. Where the fat has soaked in, the paper becomes translucent — the light from the window shines faintly through that spot, while the rest of the paper stays opaque.

Dry paper → light is blocked and scattered → the paper looks opaque and white
Paper soaked with fat → the tiny air spaces between the paper fibres get filled with oil → less scattering → light passes through and the patch glows

Why this second step matters: a crumb or a stain can also make a mark on paper. Holding it against the light is the confirming step — only a fat patch turns translucent. So the full positive result is: a greasy patch that lets light through.

Check it yourself: drop a little mustard oil on one corner of a newspaper and water on another. After ten minutes, hold the sheet up to the window. The oil corner shines through; the water corner has disappeared without a trace.

Q3.

An oily patch on the paper shows that the food item contains fat. Which of these items contain fats? Record your observations in Table 3.3.

Answer

Fill the two fat columns of Table 3.3 — first your prediction, then the observation. Writing the prediction first is part of the activity; it is how you find out whether your guess was right.

Food item	Prediction (Yes/No)	Observation — oily patch?	Fat present? (Yes/No)
Potato	No	Paper becomes damp, dries clean	No
Cucumber	No	Wet patch that dries away completely	No
Boiled rice	No	No greasy mark after drying	No
Boiled gram	No	Almost no patch	No (only a trace)
Peanuts	Yes	Clear translucent patch	Yes
Bread / chapati	No	Plain bread leaves no patch; a ghee-smeared chapati does	No (Yes if oil or ghee is applied)
Butter	Yes	Large bright translucent patch	Yes
Coconut	Yes	Distinct oily patch	Yes
Oil	Yes	Immediate spreading translucent patch	Yes

What the pattern shows: the fat-rich foods are the nuts, seeds, oils and milk fats — peanuts, coconut, butter, oil. The starchy foods — potato, rice, bread — carry almost no fat. This is exactly why a meal of only chapati and rice gives energy but no stored energy, and why a spoon of ghee or a few peanuts is added.

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