EN हिं

NCERT Solutions for Class 9th Science Chapter 2 Pause and Ponder — Why do eukaryotic cells need these organelles?

Book page 19 Updated on2026-09-08

Q4.
Do white flowers contain any pigment? Give reasons.
Answer

A truly white flower contains no coloured pigment in its petals. Its plastids are leucoplasts — plastids that lack pigment and are therefore colourless.

  • Colour is produced when a pigment absorbs some wavelengths of light and reflects the rest. Chlorophyll absorbs red and blue and reflects green; a chromoplast pigment absorbs blue and reflects yellow, orange or red.
  • A white petal absorbs almost nothing. Air spaces between its cells scatter and reflect all wavelengths of visible light back together, and light containing all wavelengths is seen as white.
  • So white is not a pigment at all — it is the appearance of a petal that has none.
all wavelengths absorbed → black
red and blue absorbed, green reflected → green
all wavelengths reflected → white
Why it happens: it is the same reason foam on milk, crushed ice and clouds look white although water is colourless — countless tiny surfaces scatter every colour equally. In a white petal the scattering surfaces are the air-filled gaps between cells. A useful check: crush a white petal in water and no colour comes out, whereas a red rose petal or a marigold petal releases its colour at once.
Did you know? Many ‘white’ flowers such as jasmine are far from plain to the insects that visit them — their petals carry patterns visible in ultraviolet light, which bees can see and we cannot. Some white flowers also carry colourless flavonoids that are pigments in the chemical sense but absorb only in the UV.
Q5.
Draw a well-labelled schematic diagram of a plant or an animal cell using these clues — (i) Nucleus appears as a dark and round body inside the cell. (ii) ER spreads like a network of extended nuclear envelope. (iii) Mitochondria and chloroplasts are rod shaped. You may refer to Fig. 2.10.
Answer

Here is a schematic plant cell drawn to those three clues. Copy this layout, then label it.

cell wall cell membrane nucleus (dark round bodywith nucleolus) endoplasmic reticulum(network from the nucleus) mitochondrion (rod) chloroplast (rod) large centralvacuole cytoplasm
Schematic plant cell: the nucleus is a dark round body, the ER spreads out from the nuclear envelope as a network, and mitochondria and chloroplasts are drawn rod-shaped.

What your diagram must show to earn full marks:

  • A double outer boundary — the thick cell wall outside and the thin cell membrane just inside it.
  • A round, densely shaded nucleus with a smaller dark nucleolus inside it.
  • The endoplasmic reticulum shown as a network of tubes and sheets continuous with the outer membrane of the nuclear envelope.
  • Rod-shaped mitochondria and rod-shaped chloroplasts (the chloroplasts shaded green).
  • The large central vacuole, with cytoplasm as a layer between it and the wall.
Tip: if you draw an animal cell instead, remove the cell wall, remove the chloroplasts, make the outline rounded and irregular, keep the vacuole small, and add a lysosome and the Golgi apparatus.
Was this helpful? Report an error