Seed is the characteristic reproductive body of flowering plants and some gymnosperms. It consists of a miniature undeveloped plant and stored food reserves, all enclosed in a protective coat or shell.
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What is a seed?
A seed contains a miniature plant embryo and a store of food in a protected shell or husk. The stored food in seed plants is typically a combination of starch, oil and protein.
A complete embryo and the food reserves in a seed allow it to survive being dispersed away from its parent plant, even in hostile conditions such as extreme heat or dryness. This ability is the key to seed germination.
In gymnosperms (naked seeded plants), one sperm cell fertilizes an egg cell in a megagametophyte to form the seed. However, the megagametophyte can develop in different shapes – most commonly anatropous (curved), orthotropous (straight) and campylotropous (crown shaped).
In some seed plants, such as dicotyledonous plants with non-endospermic endosperm, the embryo is embedded within a layer of the nutrient tissue known as endosperm. In the monocotyledonous seeds of grasses and palms, the embryo is surrounded by the proteinaceous aleurone layer. Seeds can also have additional appendages such as wings (as in yew and nutmeg), hairs (from the Corydalis species) or an aril (a fleshy outgrowth from the funicle or raphe in coniferous seeds). These can aid in their dispersal, or provide a source of nutrients.
How do seeds grow?
Seeds need to find the right conditions for germination and growth. They must also be dispersed, or moved from one place to another, so they can reach their destination. This can be done in many ways. For example, pine seeds have a wing for wind dispersal. Orchid seeds have a dustlike coating that can be carried efficiently by the wind. Buoyant seeds, like those from Mucuna or Dioclea, float on water.
Inside a seed is a tiny plant embryo and stored food, called endosperm. Cells inside the seed are deciding whether they should grow into part of a root, stem, or leaf. This is how a seed becomes a seedling. Some seeds have a hard outer shell that protects the embryo and endosperm. Other seeds have a soft, flexible seed coat that allows it to absorb water and begin growing. This process is called imbibition. Once the seed is in the right conditions, parts of the embryo break through the seed coat and grow downward.
What are seeds made of?
Seeds usually contain an embryo, stored food, and a protective coating. Depending on the kind of plant, the embryo is either fertilized by two sperm cells transferred from pollen (triploid), or unfertilized and empty (zygotic). In gymnosperms such as pines and spruces, the seeds are naked, and they form a cone around the seed when ripe.
In angiosperms, the embryo is covered by a seed coat that may be hard or soft and a thick layer of nutritious tissue called endosperm. Some seeds, however, do not have endosperm. These are called exalbuminous seeds, and they include beans, peas, garden peas, squash, and sunflowers.
The endosperm in most seeds is absorbed by the developing embryo. The embryo then grows within cotyledons, the first leaflike structures that develop from the embryonic axis. There can be one cotyledon (Monocotyledons) or two (Dicotyledons). The tip of the embryo is called the plumule, and the radicle develops from the hypocotyl. Sheath-like structures called coleoptiles and colleorhiza surround the cotyledons and plumule.
What are seeds used for?
Seeds are a source of food for humans and animals. Most seeds are eaten and provide a significant proportion of the world’s total calories, especially cereal grains, legumes (beans, peas and lentils) and nuts. Seeds also provide oils for cooking and margarine, spices and medicines (including gin) and a wide variety of plant products.
RDs can help clients incorporate seed foods into their diets to reap health benefits. Seeds are high in protein, healthy fats and minerals and can be incorporated into meals and snacks that fit a client’s dietary preferences and nutrient needs.
Seeds are an excellent source of energy and can boost optimal immune, hormonal and cardiovascular function. They are a good option for clients with food allergies and can be used to replace nuts in recipes that can cause a reaction, as well as provide a snack that is portable and ideal for pre- or postworkout fuel. Seeds also are an easy way to add texture and crunch to foods.
