Unit-3 Plant Physiology: Seeds Structure and Germination

Vocabulary flashcards covering the key terms and concepts from seeds, their structure, germination, and related experiments.

Fruit

The enlarged ripened ovary with its wall forming the fruit wall around the seed; protects the seed and aids in seed dispersal (e.g., mango, pea pod).

Seed

The ripened ovule containing the embryo; the seed coat protects the embryo and seeds contain food material for nourishment during germination (e.g., bean seed, peas).

Grain

A type of fruit in which the fruit-wall and the seed coat are fused to form a protective layer (as in maize, wheat).

Monocotyledonous seed

Seeds that contain one cotyledon (seed leaf); examples include maize and other grasses.

Dicotyledonous seed

Seeds that contain two cotyledons; examples include pea, gram, and bean.

Albuminous seed

Endosperm persists; seeds with thin, membranous cotyledons (e.g., poppy, custard apple in dicots; cereals, millets, palm in monocots).

Exalbuminous seed

Non-endospermic seeds where cotyledons store food and become thick and fleshy (e.g., gram, pea, mango, mustard; Vallisneria, orchids, amorphophallus in monocots).

Testa

The outer hard brownish covering of the seed coat; protects inner parts from injury and pathogens.

Tegmen

The thin inner layer lying next to the testa; also protective.

Hilum

A distinct whitish oval scar indicating where the ovule (seed) was attached to the ovary wall.

Micropyle

A tiny pore near the hilum; allows water entry for germination and diffusion of gases during embryo growth.

Cotyledon

Seed leaf; food starchy tissue within the seed; two in dicots (beans) and one in many monocots (scutellum in maize).

Radicle

The embryonic root that develops into the root system.

Plumule

The embryonic shoot; develops into the shoot and leaves.

Epicotyl

Region of the axis between cotyledons and plumule; elongates in germination (above-ground growth).

Hypocotyl

Region of the axis below the cotyledons; elongates in germination (below-ground growth or if cotyledons stay underground in hypogeal).

Coleorhiza

Protective sheath around the radicle in monocots such as maize.

Coleoptile

Protective sheath around the plumule in monocots such as maize.

Endosperm

Tissue rich in stored food (starch, proteins) inside the seed; present as a large central mass in grains like maize.

Aleurone layer

Outermost layer of the endosperm in many seeds, rich in protein.

Scutellum

Single cotyledon of maize; absorbs food from the endosperm during germination.

Hypogeal germination

Germination where cotyledons remain underground; epicotyl elongates (e.g., pea, gram).

Epigeal germination

Germination where cotyledons are pushed above the ground; hypocotyl elongates (e.g., castor, bean).

Vivipary

Germination of a seed inside the fruit while still attached to the parent plant (e.g., mangroves like Rhizophora).

Dormancy

A period when the embryo is inactive in a dry seed; physiological maturation occurs and germination requires favorable conditions.

Germination

The process by which a seed develops into a seedling, involving revival of the dormant embryo under suitable conditions.

Optimum temperature

Moderately warm temperature range (about 25°C to 35°C) favorable for germination. Some tropical seeds require higher temperatures.

Oxygen

Gas required for respiratory energy during germination; seeds germinate only with adequate oxygen.

Water

Essential for germination; hydrates seed, ruptures seed coat, and enables enzymatic breakdown of stored food.

Micropyle and water uptake

Micropyle is the main entry point for water uptake during germination and also allows gas exchange.

Three-bean experiment

Experiment showing how varying water and oxygen exposure affects germination depending on position in water or air.

Seedling

The young plant that emerges after germination, which later becomes a mature plant and can produce flowers and seeds.

Embryo

The developing plant inside the seed, comprising radicle (root) and plumule (shoot).

What is the main function of the seed coat?

The seed coat (composed of testa and tegmen) primarily protects the embryo and its stored food from injury, desiccation, and pathogen attack.

How do monocotyledonous and dicotyledonous seeds differ in their cotyledon count?

Monocotyledonous seeds possess a single cotyledon (e.g., maize), whereas dicotyledonous seeds have two cotyledons (e.g., pea, gram, bean).

What is the primary role of cotyledons in seed development and germination?

Cotyledons serve as storage organs for food reserves (especially in exalbuminous seeds) or as structures for absorbing nutrients from the endosperm to nourish the developing embryo during germination.

What vital substances enter the seed through the micropyle during germination?

Water, essential for initiating metabolic activity and rupturing the seed coat, and oxygen, necessary for the embryo's respiration, enter through the micropyle.