The three main parts of a seed are the embryo, endosperm, and the seed coat.
The embryo is the “baby plant” produced during fertilization. It contains the tissues that later become the leaves, stem, and roots of the plant.
The endosperm surrounds the embryo, protecting it and serving as a source of nourishment. It is made up mostly of starch, as well as oil and protein.
The seed coat is the outer covering of the seed. It is usually hard and protects the seed from damage. It also prevents: (1) loss of water, (2) entry of parasites, and (3) germination during unfavourable environmental conditions.
The cotyledon (seed leaf) is sometimes mentioned as another main part of the seed but, strictly speaking, it is actually part of the embryo.
In some plants (such as peas), the mature seed does not have an endosperm because it was used up during the development of the embryo. In these cases, food storage becomes the role of the cotyledon.
The outer, thicker layer of the seed coat is called the testa.
The inner, more delicate layer is called the tegmen.
Other parts of the seed coat:
The seed embryo is made up of:
Seeds are differentiated according to their number of cotyledons (seed leaves).
The two main types of seeds are the:
Seed dispersal is divided into:
The five main modes of seed dispersal are through gravity, ballistic, wind, water, and animals.
Gravity causes fruits to fall from the plant when ripe. The seeds can then grow where they fall or be carried away. Seeds that are dispersed this way include those of apples, coconuts, passionfruit, and those with harder shells.
Some fruits have a built-in line of weakness that eventually splits (dehiscence) and allows it to expel seeds. Plants that disperse seeds this way include the dwarf mistletoe, exploding cucumber (or squirting cucumber), euphorbia, geranium, hairy bittercress, impatiens, and witch hazel.
Plants with seeds or fruits that can float and flutter away include dandelions, maples, and tumbleweeds.
Plants that use water for seed dispersal include water lilies, palm trees, and mangroves.
Seed dispersal by animals is called zoochory.
Epizoochory is when seeds are transported on the outside of animals, such as when burr sticks to an animal’s fur (or someone’s clothes) and is carried away by the animal.
Endozoochory is the dispersal of seeds through ingestion by animals, mostly birds and mammals.
Aside from epizoochory and endozoochory, which are explained above, other ways that animals carry out seed dispersal include:
The plants that disperse seeds by epizoochory (on the outside of animals) include:
The seeds of most tree species are dispersed by endozoochory (ingestion by birds, mammals, and other animals).
Free printable versions of the seeds worksheets below can be downloaded here:
Note on the Worksheets
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