Seed Development and Dissemination

10 Questions

What is the primary function of a seed?

To carry plants over periods unfavorable for growth

What is the result of double fertilization in seed development?

Formation of a zygote and a primary endosperm nucleus

What is the correct sequence of events in seed development?

Endosperm develops, then zygote nucleus divides, then embryo develops

What is the characteristic difference between seeds of monocotyledonous and dicotyledonous plants?

Number of cotyledons

What is the primary function of the nucellus in the early stages of seed development?

To act as a nutritive source for the embryo

What is the term for the process by which animals, including humans, help disperse seeds?

Seed dispersal

Which type of seeds often has endosperm persisting as a food reserve?

Monocotyledonous seeds

What is the term for the food storage tissue that persists in seeds of sugar beet and a few other species?

Perisperm

What is the function of the cotyledons in seeds that store food in the endosperm?

To act as absorbing organs

What is the term for the scar left on the seed where it broke from the stalk or funiculus during harvesting?

Hilum

Study Notes

Seed Development and Structure

Seeds provide a mechanism for plants to carry over periods unfavorable for growth, maintain a reserve supply of potential plants, and disseminate plants.
Seeds ensure the renewal or continuance of plant populations, and many animals, including humans, cooperate in this process.

Embryo Development

The embryo develops from the zygote and the seed coat develops from the integuments of the ovule.
Double fertilization involves the fusion of egg and sperm nuclei to form a zygote nucleus and the fusion of polar nuclei with a second sperm nucleus to form a primary endosperm nucleus.

Seed Formation

The zygote nucleus remains quiescent for a short time, while the primary endosperm divides rapidly and forms the endosperm tissue.
The zygote nucleus then divides, resulting in a file of 4-8 cells, with the basal cell elongating and pushing the other cells into the endosperm.
Further divisions result in a globular stage, then a heart-shaped stage after the two cotyledons develop, and finally into a mature embryo surrounded by a seed coat.

Monocotyledonous and Dicotyledonous Plants

The main distinction between seeds of monocotyledonous and dicotyledonous plants is the occurrence of one or two cotyledons, respectively.

Nucellus, Endosperm, and Integuments

The nucellus, endosperm, and integuments undergo changes characteristic of the plant group during embryo development.
In most plants, the nucellus and endosperm are only required for initial stages of development and are used up as a nutritive source.
In some plants, the endosperm persists as a food reserve, and in monocotyledonous plants, it often persists in seeds as the primary food source during germination.

Kinds of Seeds

Seeds of angiosperms differ in two ways: they have one or two cotyledons and store food either in the embryo, in the endosperm, or more rarely, in nucellar tissue.
Food stored in the embryo is conveyed to meristematic regions through vascular tissues, while food stored in the endosperm is absorbed through epidermal cells.

Examples of Seeds

The common bean is an example of an exalbuminous seed, with a fruit that is a pod containing seeds with a hilum, micropyle, and raphe.
In some cases, the cotyledons become specialized to act as absorbing organs, such as the scutellum in grasses.