NCERT Class 11-Biology: Chapter –5 Morphology of Flowering Plants Part 8

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Question 6:

Sunflower is not a flower. Explain.

Answer:

Sunflower is not a flower, but it is a kind of inflorescence called capitulum in which the receptacle is flattened. It bears numerous sessile and small florets. The youngest floret is in the centre and oldest lies at the periphery. Whole cluster of florets gets surrounded by bracts, known as involucre. Two kinds of florets are recognised in sunflower:

(i) Ray Florets - Arranged on the rim of receptacle having distinct yellow and strap-shaped petals. These florets are female, sterile and are always zygomorphic and may be arranged in one or more whorls.

(ii) Disc florets - Grouped in the centre, bisexual and actinomorphic.

Question 7:

How do you distinguish between hypogeal germination and epigeal germination? What is the role of cotyledon (s) and the endosperm in the germination of seeds?

Answer:

Difference between hypogeal germination and epigeal germination:

Difference between Hypogeal Germination and Epigeal Germination
Difference between hypogeal germination and epigeal germination

Hypogeal germination

Epigeal germination

Epicotyl grows first

Hypocotyl grows first

Only plumule is pushed out of the soil

It pushes cotyledons and other parts of the seed out of the soil.

Cotyledons remain non-green, non – photosynthetic

Cotyledons become green and photosynthetic.

Example – Castor, Beans

Example – Maize, Rice

Role of Cotyledons and Endosperm in the germination of seeds –

They contain reserved food materials. When seed imbibes water, enzymes get activated, hydrolyze reserve food material and make it available for the germinating seed.

Question 8:

Seeds of some plants germinate immediately after shedding from the plants while in other plants they require a period of rest before germination. The later phenomena is called as dormancy. Give the reasons for seed dormancy and some methods to break it.

Answer:

Dormant seeds remain under non-germination conditions only for a specific period of time that may vary from days to years. This specific period is called dormancy period.

Reasons for seed dormancy –

  • Impermeable and hard seed coat

  • Presence of chemical inhibitors like abscisic acid

  • Immature embryo

  • Methods to break seed dormancy are –

  • Washing away of inhibitors due to rain

  • Maturation of embryo

  • Inactivation of growth inhibitors due to heat or cold treatment.

  • Weakening and decomposition of seed coat by microorganisms.

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