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NCERT Solutions for Class 9th Science Chapter 11 Let us explore — Activity 11.2

Book page 211 Updated on2026-09-08

Q1.
Do you observe any small, round outgrowths (buds) emerging from the parent yeast cells as shown in Fig. 11.6?
Answer

Yes. Under the compound microscope you see oval yeast cells, and many of them carry a smaller round swelling attached at one end — the bud. Sometimes a bud already carries a bud of its own, so short chains of two, three or four cells are seen.

sugar solution used = 1 g in 10 mL
= 10 g per 100 mL = 10% (w/v)
sugar in the 20 mL taken = (1 g ÷ 10 mL) × 20 mL = 2 g
Why this set-up gives buds within an hour or two: yeast needs a respiratory substrate, warmth and time. Two grams of sugar in the tube is far more than the pinch of yeast can use up, so energy is not the limit. Warmth speeds up the enzymes that drive respiration and cell division. The cotton plug lets carbon dioxide escape while keeping other microbes out, and leaving the tube undisturbed lets the cells settle and multiply without being knocked apart.
Tip: look at the edge of the drop under the coverslip, where the cells are spread in a single layer. In the crowded middle the cells lie on top of one another and buds are easy to miss.
Q2.
Do these features indicate that the yeast is duplicating?
Answer

Yes — the yeast is multiplying, and each bud is a genetic duplicate of the parent cell. But note carefully how it duplicates: the parent does not split into two equal halves. It pushes out a small bud at one point on its wall.

The sequence is:

  1. The parent cell's DNA is copied and its nucleus divides by mitosis.
  2. A small outgrowth appears on the cell wall.
  3. One of the two identical nuclei moves into the outgrowth, along with some cytoplasm.
  4. A wall forms across the neck and the bud is pinched off. It then grows to full size and starts budding itself.
Why the copies are identical: mitosis replicates every chromosome once and then separates the two copies, so each daughter nucleus receives the same number of chromosomes carrying the same information as the parent. There is no meiosis and no second parent, so nothing is reshuffled and nothing new is added. The offspring are therefore clones.
Tip: the word "duplicating" is a fair description of the genetic outcome but not of the shape. Amoeba splits into two nearly equal cells (binary fission); yeast makes a small bud on a large parent (budding). Both are asexual, both use mitosis, but the division of the cytoplasm is equal in one and unequal in the other.
Q3.
How do these observations help you in understanding reproduction in yeast?
Answer

They show, directly under your own microscope, that yeast reproduces asexually by budding — from one parent, without gametes, without a partner, and very fast.

  • One parent. Every bud is attached to a single cell. No two cells were seen fusing, so no gamete and no fertilisation is involved.
  • Genetically identical offspring. The bud is built by mitosis from the parent's own material, so the population in the tube is a colony of clones.
  • Speed. Buds appear within 1 – 2 hours of the yeast becoming active. Since every new cell can itself bud, the number of cells rises very steeply while sugar and warmth last.
  • Conditions matter. Nothing happened until the tube was warm and sugar was available — asexual reproduction is fastest when the environment is favourable, exactly as the chapter says.
Why this is worth knowing outside the laboratory: the same budding is what makes dough rise and what ferments sugar in idli and dosa batter. Carbon dioxide from the respiring, multiplying yeast is trapped in the dough and puffs it up. A warm kitchen makes the batter rise quicker for exactly the reason your test tube had to be kept warm.
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