Fertilisation, Seed and Fruit — Part 2: Seeds, fruits and special modes: visual lesson, ISC Class 12 Biology

Lesson

Seeds and fruits

Part 2 — the products of fertilisation, and the exceptions to the usual route.

In this lesson you will

Describe the internal structure of a bean seed and a maize grain
Distinguish albuminous and non-albuminous seeds, true and false fruits
Describe the L.S. of mango and coconut and the significance of seeds, fruits and dispersal
Explain apomixis, polyembryony and parthenocarpy

Diagram

A dicot seed: bean

A bean seed has a seed coat of two layers, the outer testa and inner tegmen. The hilum is the scar where the seed was attached to its stalk; the micropyle lies beside it. The embryo has two large cotyledons storing food and an embryonal axis with plumule and radicle. The endosperm is used up: the seed is non-albuminous (exalbuminous).

Diagram

A monocot grain: maize

In a maize grain the pericarp is fused with the seed coat. Below it lies the aleurone layer, a protein-rich layer around the starchy endosperm. The embryo has a scutellum, a coleoptile over the plumule and a coleorhiza over the radicle. The endosperm persists: the seed is albuminous.

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