Seeds contain everything a new plant needs to grow, but are tightly packed in a tough protective coat. Once conditions are right, a seed will absorb water (imbibition), swell up and then burst open.
Seeds are used for many purposes, including food (grain seeds like wheat and corn, legume seeds like beans and lentils, nut seeds like peanuts) and landscaping. They also play a vital role in plant reproduction and evolution.
Definition
The rudiments of a future plant, often covered with a protective shell or fruit. Seeds contain an embryonic “plant” with cotyledons (the first leaves) and the roots of the developing plant, as well as a food reserve called endosperm and a nutrient-rich covering called a seed coat.
Plants produce seeds for reproduction and dispersal, and they are the primary source of many foods including wheat, rice, corn, beans, peas and peanuts. Some seeds are naked and exposed to the environment, like those of conifers; others are enclosed in fruit like berries, nuts, or tomatoes.
In sports, a player or team is seeded in order to arrange competition so that more skilled contestants do not meet early in the tournament. In business, seed money or capital is a small amount of funding provided to help develop and start a company. The term is derived from the fact that a single seed can grow into a lush forest.
Origin
Seeds are one of the most dramatic innovations in plant evolution. They allow plants to reproduce after the union of male and female cells. Seeds perpetuate the hereditary characteristics contributed by both cells.
The seeds of angiosperms (flowering plants) and gymnosperms (conifers and cycads) are enclosed in a protective shell called a testa or caryopsis. They contain an embryo surrounded by a supply of food for its early development, called the endosperm.
The embryo has one cotyledon or seed leaf in monocots and two cotyledons in most dicots. It is pressed closely against the endosperm so that it absorbs the endosperm’s nutrients directly. The seed coat may have many different shapes and textures. Seeds can be discoid (flat), ellipsoid, lenticular, ovoid, or reniform. Some seeds are striped with parallel or longitudinal lines or ridges. Other seeds are spherical, or subglobose. The seeds of some plants, such as certain grasses and bananas, do not have any asexual means of reproduction. In such cases, the seeds must be propagated by planting.
Functions
Seeds have several functions, including nourishment of the embryo inside and dispersal to new locations. They also provide a means of plant reproduction and protect the embryo from predators and the elements.
The food reserve within a seed is called the endosperm, which provides nutrients to the developing plant during germination. It is absorbed through an area of the seed coat called the micropyle and the raphe. Seeds with a micropyle and raphe usually have a kidney-shaped appearance.
Many seeds are able to wait for environmental conditions to be suitable for their germination. This is known as physiological dormancy and it can be broken down by a process called stratification, which involves subjecting the seeds to alternating periods of cold and warm temperatures.
Other seeds are unable to break down their biological dormancy. These are known as non-endospermic or exalbuminous seeds and include beans, peas and a range of nuts. These seeds can be triggered into germination by a period of moist chilling or by the passage through the digestive system of animals.
Uses
Seeds are the source of many edible crops including cereals, legumes, nuts and seeds for beverages such as coffee and tea. Some seeds have medicinal properties such as chamomile seeds for making a soothing herbal tea and flax seeds for omega-3 fatty acids. Seeds are also used to propagate grasses and ornamental plants such as flowers, shrubs and trees.
Most seeds carry the food needed for a new plant to grow and they are protected by the embryo, endosperm and testa. The stored food is converted to growth by the cotyledons.
The ability of seeds to wait for the right conditions to stimulate germination is what distinguishes them from single-celled spores that cannot do so. This behavior is called dormancy. Seeds that require some sort of external stimulus to break down physiological dormancy include those whose seed coat needs to be scarified (skracked, scratched or softened by chemicals like acids) or passed through an animal’s digestive system.
