NCERT Solutions for Class 9th Science Chapter 2 Plastids and Vacuoles — In-text Questions

Book page 19 Updated on2026-09-08

Q1.

Are there any other plastids in plant cells that contain any pigments other than the green pigments?

Answer

Yes — the chromoplasts.

Plastid	Pigment	Function	Where you find it
Chloroplast	Chlorophyll (green)	Photosynthesis; temporary storage of food	Leaves, green stems
Chromoplast	Yellow, orange or red	Gives bright colour	Flower petals, fruits
Leucoplast	None — colourless	Stores starch, oils or proteins	Potato tuber, taro (Colocasia), seeds, roots

The Greek roots make the names easy: chroma means colour, leukos means white or colourless.

Why it happens: all three are plastids, that is, members of one family of double-membrane organelles that make and store food. They differ only in which pigment they hold and what they are asked to store. Because they belong to one family, a plastid can change type — this is why a green tomato turns red as it ripens, as chloroplasts are converted into chromoplasts, and why a potato exposed to light turns green as leucoplasts develop chlorophyll.

Q2.

How do flowers, fruits, and vegetables acquire varied colours?

Answer

From the pigments held in their chromoplasts — pigments other than chlorophyll, which may be yellow, orange or red.

In the petals of a flower and in the flesh and skin of a fruit, the plastids carry these coloured pigments instead of chlorophyll.
The bright colour is not decoration. It attracts pollinators to flowers so that pollination happens, and it attracts fruit-eating animals, which then carry the seeds away and help in seed dispersal.

green fruit (chloroplasts, chlorophyll)
→ ripening: chlorophyll broken down, chromoplast pigments revealed and made
→ red, orange or yellow ripe fruit — a signal that the seeds are ready

Why it happens: a plant cannot move, so it must persuade animals to move on its behalf. Colour is the cheapest long-distance signal it has. The timing is what makes it work: the fruit stays green and unattractive while the seeds are still immature, and turns colour only once they are ready to be dispersed. So the change of pigment is really a piece of communication between a plant and an animal.

Did you know? Not every plant colour comes from chromoplasts. Many reds, blues and purples — in jamun, beetroot or a rose — come from pigments dissolved in the cell sap of the vacuole, not from plastids at all.

Q3.

But where are water, minerals, and waste materials stored in the cell?

Answer

In the vacuole. In a mature plant cell there is usually one large central vacuole, surrounded by a single selectively permeable membrane and filled with a watery fluid called cell sap.

It stores water, minerals, sugars and waste material.
By holding a large volume of water it maintains pressure inside the cell, which keeps the plant cell firm.
Animal cells sometimes have vacuoles too. They are much smaller, and are used for the temporary storage of materials.

Why it happens: a plant has no kidneys and no way of excreting most waste, so it stores it instead — safely locked away in the vacuole where it cannot interfere with the cytoplasm. The same sac solves a second problem at the same time. Filling one big bag with water pushes the cytoplasm and organelles into a thin layer against the wall, which puts them close to the surface for exchange, and it lets the cell grow large cheaply — a cell can increase its volume by taking in water instead of by making expensive new cytoplasm.

Q4.

Why do plants look wilted when they do not get enough water?

Answer

Because the vacuole loses water, so the cells stop pressing outwards and the plant can no longer hold itself up.

enough water → vacuole full → cell sap presses membrane against the wall → cell turgid → plant stands firm
too little water → vacuole loses water → pressure inside falls → cell flaccid → leaves and stem droop = wilting

Why it happens: a young stem or a leaf has no wood to hold it up. Its stiffness comes entirely from turgor pressure — the outward push of water-filled cells against their own walls, like air in a bicycle tyre. When the soil dries, the cell sap becomes relatively more concentrated than the soil solution, water is drawn out of the vacuoles, and the ‘tyres’ go flat. The wall is still rigid, but a rigid wall around a half-empty cell no longer presses against its neighbour, so the whole tissue goes limp.

Check it yourself: water a wilted money-plant in the evening and look at it next morning. It stands up again because the vacuoles have refilled by osmosis — proof that wilting is a water-pressure effect and not damage, provided it is caught early.

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