SEED PLANTSSBI 3C0

SEED PLANT CHARACTERISTICS

All seed plants have the structures that people commonly associate with plant life: roots, stems, and leaves. It is a diverse group that has a huge variety of adaptations in size, shape, colour, and other characteristics.

Seed plants can vary in size from only a few millimetres such as a tiny duckweed plant, to many meters, such as giant conifers.

Their vascular systems can transport water and nutrients very efficiently, often to great heights.

In many species, the vascular system also gives also provides physical support and gives rise to woody growth and massive stems, or tree trunks.

Seed plants provide us with many products, and are the most important producers of food in most of the world’s terrestrial biomes

Unlike nonseed plants, seed plants can undergo sexual reproduction without free water and when individuals are at great distances from one another.

Seeds also provide protection for the early stages of the sporophyte generations, and enable the young sporophyte to survive for long periods of time under unfavourable environmental conditions.

Finally, seeds can be carried a long distance from their parent by the wind, water, or animals.

THERE ARE TWO TYPES OF SEED PLANTS: GYMNOSPERMS AND ANGIOSPERMS.

Gymnosperms are plants with a vascular system that produce seeds that are not in an enclosed structure.

All living gymnosperms are woody (wood-producing) trees or shrubs.

Examples include conifers such as pines, spruces, redwoods, and cedars.

Most confiers have needle or scale like leaves and are evergreens, meaning they retain their leaves throughout the year.

Needles have small surface areas and a thick waxy coating. These characteristics reduce water loss, helping conifers to survive the long dry winters.

The roots of conifers are relatively shallow and extend over large areas, helping anchor the trees. This enables them to grow in areas where the soil is thin.

Conifers provide materials for building and furniture’s, paper, varnishes, turpentine, disinfectants, and fuels.

LIFE CYCLES OF GYMNOSPERMS Involves alteration of generations. The

sporophytes are the large trees and shrubs, many of which bear cones.

The gametophytes are tiny, microscopic plants found on specialized structures on the sporophyte.

The female gametophyte is found inside large female cones of the mature sporophyte.

The male gametophytes are the pollen grains, which are found in the small male cones. Male sex cells are produced within the pollen grains, which are carried by the wind to the female cones.

The male sex cells are then released and fertilize the egg cells inside the microscopic female gametophytes in the cone.

After pollination, each zygote forms a small embryo within a seed. Upon maturity, the seed is released from the cone and develops into a sporophyte.

ANGIOSPERMS

Angiosperms are plants with a vascular system that produce enclosed seeds, which form within flowers. Angiosperms are by far the largest group of plants on earth.

There are more than 250 000 known species of angiosperms- more than all other plant species combined. New species are being discovered almost daily, Angiosperms are commonly known as flowering plants.

Many angiosperms are herbaceous plants, which are plants that lack woody tissue. However, most tree species are also flowering plants.

These plants produce large, colourful flowers such as those on tulips, cherry trees, and roses. The large flowers attract insects, birds, and other organisms to feed on the sugary nectar produced by the flower.

During feeding, these organisms transfer pollen from one flower to another- they pollinate the plants.

Other angiosperms have small, inconspicuous flowers and are pollinated by the wind (ex. Maple, birch, oak trees).

Grasses are also wind pollinated and include the worlds most important food crops- wheat, rice, and corn.

Seeds vary in sizes, some are barely visible to the human eye.

The largest seed is the coconut.

Many seeds can remain dormant for long periods of time. Dormancy is broken only under specific environmental conditions. The seeds then absorb water and expand, and the embryo begins to grow rapidly.

MONOCOTS AND DICOTS

Angiosperms are split into two groups: monocots and dicots.

Monocots produce seeds in which the embryo has only one cotyledon, or seed leaf.

Dicots produce seeds in which the embryo has two cotyledons.

The bulk of most monocots seeds are taken up by the endosperm, a tissue that stores food material.

The bulk of most dicots are taken up by the

two cotyledons, which store food for the developing embryo. Both seeds have a protective layer known as the seed coat that surrounds the entire seed.

LIFE CYCLE OF FLOWERING PLANTS