Seeds are an important part of plant development. They contain an embryo, which can develop into a new plant when grown under optimum conditions.
Typically, a seed contains an embryo, endosperm and a seed coat. The seed coat allows water to penetrate the seed, triggering germination.
Definition
A seed is a mature fertilized ovule containing an embryo (the seedling), and its food store, enclosed within a protective seed coat. The endosperm, a bulky, food-storing organ, forms an important supply of nutrients for the developing plant.
Most seeds are edible, containing a variety of protein-rich compounds, including most carbohydrates and some fats. They are also an important source of some nutrients essential for human health, such as vitamins A, B, C, E and K and minerals like iron, magnesium, zinc and copper.
The majority of human calories comes from seeds, especially those from cereals, legumes and nuts, although they are also important sources of many cooking oils and some beverages and spices. The storage proteins of the seed embryo or endosperm differ in their amino acid content and physical properties, for example, wheat gluten provides the elastic property to bread dough.
In addition to their food-producing function, seeds play an important role in plant reproduction. They contain DNA from a pollen grain (male parent) and an ovule (female parent).
Origin
Seed plants (spermatophytes) are one of the dominant species in most environments. They produce seeds in a wide range of shapes and sizes that allow them to disperse themselves widely through wind, water or by attaching to other organisms such as animal fur or feathers.
They also have a wide variety of ways to help their seeds reach an appropriate location at the right time for germination and growth. Examples include pine seeds with a wing to help them fly or sea-bean seeds that float in the ocean and can be blown across large areas of land.
The origin of seed development and anatomy has been a long-standing challenge for plant biologists. However, with the advent of molecular genetics and genome analysis, a better understanding of the developmental processes behind seeds is possible.
Structure
A seed is a tiny structure enclosing the embryo of a plant within a protective outer covering. When the conditions of growth are favorable, it gives rise to a new plant from its store of nutrients, usually through germination.
A typical seed consists of three parts: the cotyledon, endosperm and embryo. The cotyledon or embryonic leaf is the first part of a seed to appear when it germinates.
In most plants, the cotyledon contains a food store called endosperm which is stored temporarily and will be used when the seedling grows from the embryo. Monocotyledonous seeds contain one cotyledon, while dicotyledonous seeds have two.
The cotyledon, endosperm, and embryo are surrounded by an outer covering called the seed coat. The seed coat helps protect the seed from physical, mechanical, temperature-related and water damage. It can be thin and soft as in beans or thick and hard like in locust or coconut seeds.
Function
Seeds are the characteristic reproductive bodies of both angiosperms (flowering plants) and gymnosperms (conifers, cycads, ginkgos). They are usually tiny in size, occupy a small space, and make negligible demands on the environment.
They are essential for a wide variety of functions. For example, they serve as a food source for humans and other animals. They also help balance ecosystems, protect watersheds and mitigate erosion, moderate climate, and provide shelter for many animal species.
These functions are accomplished by a wide range of processes including dispersal, germination and seed dormancy. The dispersal of seeds depends on a number of factors, including the permeability of the seed coat and how much water is available in the surrounding environment.
Germination is the process by which the embryo in the seed swells, splitting the seed coat and permitting water to penetrate. It is a necessary step for many seeds to begin life, although some seeds can develop without it.
