NCERT Solutions for Class 9th Science Chapter 11 Let us explore — Activity 11.1

Book page 209 – 210 Updated on2026-09-08

Q1.

Note the following points while observing the technique of cutting in the field. (i) Does the gardener, scientist or horticulturist cut the overgrown branches of a plant at the end of its growing season? (Different plants have different growing seasons). (ii) Observe them prepare the cuttings from a plant for the purpose of growing new plants. Note the average length of the cuttings. (iii) Count the number of nodes and internodes on the cuttings.

Answer

(i) Yes. Gardeners prune the overgrown branches at the end of the growing season, and they take their cuttings from that pruned material.

(ii) and (iii) — record what you actually measure. A typical shoot cutting is about 15 – 20 cm long and carries 3 – 5 nodes, which means 2 – 4 internodes between them.

Plant	Growing season ends	Length of cutting (cm)	Nodes	Internodes
Money plant	All year in warm places	15	3	2
Rose	After the winter flush	20	4	3
Sugarcane (sett)	At harvest	30	3	2

Why the end of the growing season: by then the shoot has finished elongating and has stored food in it, and its buds are mature but still dormant. A cutting taken then has enough reserve to live on until roots form, and it will not waste that reserve on making new leaves first. A cutting taken in mid-growth is soft, watery and wilts before it can root.

Why nodes are counted: a node is the point where a leaf and an axillary bud are attached, and it is the only place on the stem where the tissue that can make new roots and new shoots is present. The internode between two nodes has none. So a cutting with no node cannot become a plant, however long it is — the count of nodes, not the length, is what decides whether the cutting will take.

Tip: collect cuttings in the morning (step 2 of the activity). The stem is fullest of water at that hour, before the day's transpiration has drawn it down, so the cutting starts with the largest possible water reserve.

Q2.

Insert the cuttings up to approximately half of their length in the soil mixed with compost at an angle of about 45– 60° from the soil surface (Fig. 11.2). Water them regularly and observe the change, if any.

Answer

In about two to three weeks, roots appear from the buried nodes and new shoots push out of the nodes above the soil. Compost is mixed into the soil because it holds moisture and keeps the soil loose enough for young roots to push through.

Why slant the cutting instead of pushing it straight down: a slanted cutting keeps a longer stretch of stem inside the soil for the same digging depth, so more nodes are in contact with moist soil. For a cutting pushed to a depth h at an angle θ to the surface, the buried length is

L = h ÷ sin θ
at θ = 45°: L = h ÷ 0.707 = 1.41 h
at θ = 60°: L = h ÷ 0.866 = 1.15 h
straight down (θ = 90°): L = h ÷ 1 = h

So planting at 45° buries about 40 per cent more stem than planting vertically to the same depth — more nodes in the rooting zone, and the buried nodes stay in the warm, moist upper layer of the soil instead of going down into cold subsoil.

Why the lower leaves are removed (step 3): leaves lose water by transpiration. Until roots form, the cutting has no way of replacing that water, so every leaf left on it is a leak. Removing the lower leaves cuts the loss; a few upper leaves are kept so that photosynthesis can still supply sugar for root growth. Buried leaves would also rot and invite fungi.

Check it yourself: plant two money-plant cuttings of the same length, one with all its leaves and one with only the top two. The second usually roots first — evidence that water loss, not leaf number, is the limiting factor at this stage.

Q3.

Water the plant regularly and observe the growth of Plant B along with Plant A. [Grafting]

Answer

Within two to three weeks the graft heals and the buds on the Plant B piece sprout. From then on the shoot, the leaves and the flowers are all of Plant B's variety, while everything below the graft joint stays Plant A. If Plant B was a yellow rose, the plant now carries yellow roses on a wild-rose root system.

Why it works: the piece of Plant B (the scion) is a vegetative part, so it grows by mitosis and keeps every character of Plant B exactly. It has no roots of its own, so it must be joined to Plant A (the stock) in such a way that water and minerals can flow up into it and sugars can flow down. That happens only if the cambium — the thin dividing layer just under the bark — of the two pieces touches. New cells from both cambia meet, form a callus and then join up the xylem and phloem, so the two stems become one plumbing system.

Why the other branches of Plant A are cut (step 4): a branch that is left on the stock competes for the water and food coming up from the roots, and being already established it wins. Removing those branches sends the whole supply into the scion.

Why the joint is wrapped (step 4): a fresh cut is an open wound. The cloth or film keeps it from drying, holds the two pieces pressed together while the callus forms, and keeps insects and fungal spores out until the wound is healed.

Tip: a grafted plant is genetically two plants living as one. If a shoot ever sprouts from below the graft joint, it belongs to the wild stock and will carry the stock's flowers, not the variety you wanted — cut it off as soon as you see it.

Q4.

Water it regularly and observe the growth of new leaves on the twig buried in the soil. After 10 – 15 days, the roots will develop from the area of the twig buried in the soil. [Layering]

Answer

New leaves keep coming out on the buried twig, and after 10 – 15 days roots grow from the buried portion. Once those roots are established, the twig is cut off from the parent and becomes an independent plant — a clone of the parent tree.

Why layering is more reliable than a cutting: a cutting is on its own from the moment it is separated — it must find water with no roots. A layered twig is still attached to the parent the whole time, so water and minerals keep arriving from the parent's roots and sugars keep arriving from the parent's leaves. It cannot wilt. That is why the new leaves keep growing even before any roots have formed.

Why roots form exactly at the buried bend: two things meet there. The soil provides darkness and steady moisture, which is what root primordia need to grow out. And the bend slows the sugars moving down the phloem, so food collects in that stretch of stem and is available to build roots. Nodes buried at that point are where the roots actually emerge.

Try this: lemon, guava, jasmine, bougainvillea and pomegranate all layer easily. Choose a thin, flexible twig, scrape a little bark off the part you bury (this slows the sugar flow further), peg it under the soil and keep it watered — and be patient for a fortnight.

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