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NCERT Solutions for Class 9th Science Chapter 12 Let us study — Activity 12.9

Book page 239 – 240 Updated on2026-09-08

Q1.
Carefully study the salient features of each plant group.
Answer

Read the five groups in order and watch for the one problem each solves. Set out that way, Table 12.3 stops being a list and becomes a sequence.

GroupSalient featuresProblem it solves
ThallophytaBody is a thallus; direct exchange of gases, nutrients and water with the surroundings; mostly aquatic. Example: SpirogyraNone yet — it is simply well suited to water
BryophytaRhizoids, stem-like and leaf-like structures; no vascular tissue; water needed for reproduction. Examples: Marchantia, mossLiving on land — but only where it stays damp
PteridophytaTrue roots, stems and leaves; xylem and phloem; no seeds; water needed for reproduction. Example: fernTransport and support — so the plant can grow tall
GymnospermNeedle-like or scale-like leaves; seeds not enclosed in fruits, exposed on cones; no water needed for fertilisation. Examples: pine, cycadReproduction without water, and survival in cold and dry places
AngiospermWell-developed roots, stems and leaves; sexual reproduction through flowers; seeds enclosed within fruits; seeds dispersed by insects, birds, animals, wind or water. Example: gulmoharEfficient pollination and seed dispersal — hence the widest range of habitats
The one line to remember: from algae to angiosperms the plant groups show a sequence of structural changes that meet the challenges of life on land. Early plants relied on water for support and reproduction; gradually plants evolved transport tissues, then seeds, then flowers.
Q2.
Analyse the salient features, and write the advantages for survival of the group and the exceptions or challenges faced in the given columns.
Answer

Here is Table 12.3 completed. The book's own entries are kept and the blank lines are filled in.

Plant groupAdvantages of the group for survivalExceptions / Challenges
ThallophytaSimple plant body facilitates survival and its dispersal in water. The whole surface absorbs water, minerals and gases directly, so no transport tissue is needed. Many are the base of aquatic food chains and release oxygen.They cannot live on land. With no roots, no cuticle and no vascular tissue they dry out at once out of water, and cannot grow tall or support themselves.
BryophytaThey are plant amphibians. Their body is adapted to live on moist land. Rhizoids anchor them to rock and soil, so they can colonise bare surfaces where nothing else grows, and they hold moisture like a sponge, which helps soil form.They always need moisture. No vascular tissue, so they stay small and low; male gametes must swim, so reproduction stops in dry weather.
PteridophytaThey live on land. They transport food and water to all parts of the plant. True roots reach water deep in the soil and xylem stiffens the stem, so they can grow tall and hold their leaves above competitors.Reproduction does not take place without water. They produce no seeds, so the spore has no food store or protective coat and can germinate only in a damp, sheltered place.
GymnospermLeaves are adapted for dry conditions. They do not require water for reproduction. They form seeds for continuity of life. Needle-like leaves and a thick cuticle survive cold, wind and drought, so they dominate high mountains and cold regions.Seeds are not covered in the form of fruits. Without a fruit there is little help with dispersal, and the exposed seed is easily eaten; pollination depends on wind, so a great deal of pollen is wasted.
AngiospermThey produce flowers, fruits and seeds. They have a well-developed system for reproduction. They produce seeds for continuity of life. Their seeds are covered. Flowers attract pollinators, so far less pollen is wasted; fruits carry the seed away from the parent, so the offspring do not compete with it.Reproduction is dependent on pollination by different agents. They have complex processes through a well-developed tissue system. If the pollinator disappears, seed set fails — so the plant's survival is tied to another species' survival.
The pattern across the whole table: every advantage brings a new dependence. Vascular tissue lets a fern grow tall, but a tall plant must now maintain a pipe system. A seed frees the gymnosperm from water, but the naked seed is vulnerable. A flower makes the angiosperm's reproduction efficient, but ties it to insects, birds or bats. There is no group without a challenge — which is exactly why so many groups still exist side by side today instead of the "best" one replacing the rest.
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