Seed is a miniature embryonic plant surrounded by stored food and protected by a tough covering. It is the product of a fertilized ovule in flowering plants and gymnosperms.
Researchers are studying the genes that control ovule and seed development. Their work will help us understand how seeds evolved.
They store food
Seeds are the characteristic reproductive body of flowering plants and some gymnosperms (conifers, cycads, and ginkgoes). They contain an embryo, a miniature undeveloped plant, stored food, and a protective coat. The embryo has the potential to grow into a new plant, and the food provides it with the energy it needs until it can start making its own food through photosynthesis.
The swollen part of the seed called the cotyledon stores the food needed to fuel germination. Different seeds store their food reserves in different ways, including relying on large deposits of the nutrient tissue, endosperm, or using proteins found in embryonic leaves.
Despite the many functions of seeds, they are all designed to be easily carried by animals and transported to sites where they can grow. To facilitate this, some seeds have hooks or burrs to latch onto animal fur or to rub against rocks. Other seeds are packaged in edible surroundings such as fruits, which provide a convenient way to transport them.
They travel
Seeds have developed adaptations to help them travel from one place to another. Some seeds are shaped like wings or have parachute-like parts that let them float on the wind. These seeds, such as dandelion seeds, may travel many miles before they find a suitable spot for germination.
Other seeds are shaped with barbs or hooks that attract animal dispersers and cling to fur or feathers. These seeds are called hitchhikers and often end up in places far from their parent plant. Some seeds are surrounded by fruit to encourage animals to eat them and allow the seeds to pass through the digestive tract.
In this book, students investigate how different types of seeds travel by using hands-on activities such as dropping seeds into an electric fan and observing the movement of each seed. They can also collect and sort seeds on a fuzzy cloth to see how they stick. After completing the activities, students can compare and contrast the different ways seeds travel to find out which method is most successful in each environment.
They attract animals
Seeds come in all shapes and sizes – some have fleshy appendages to entice animal dispersers; others, like black elder seeds, have hooks, barbs or sticky hairs that catch on fur and feathers; and still others, like dandelions, have wings for wind dispersal. Those that rely on animals for dispersal can be vulnerable to declines in (or even extinction of) those animals. For example, Montoya et al found that fruit bats are essential dispersers of black elder and that forest patches with high densities of flying foxes have significantly more black elder trees than adjacent unforested cells.
Plants lure animal dispersers by producing tasty nuts, fruits or seeds. Once an animal eats a seed, it is digested and passed along to new locations in its faeces. This internal dispersal is called frugivory. Plants also disperse their seeds through water, wind and gravity. Some plants, such as ferns and mosses, lack seeds and depend instead on spores to reproduce.
They germinate
Seeds contain an embryo and a store of food reserves packed inside a protective coat. Once the right conditions are met, a seed will germinate into a tiny plant known as a seedling. The seeds of most plants require the right temperature, water, oxygen and light for germination to occur. Some seeds also require a period of after-ripening before germination can take place.
The first step of germination, called imbibition, occurs when the seed absorbs water through its outer seed coat. This causes it to swell and soften, allowing water to enter its inner cells. The seed cell then starts converting starch to sugar, which provides the energy for germination.
The seed’s radicle and root begin to grow, and the seed coat eventually ruptures. As the radicle and root emerge, they begin absorbing underground water and nutrients. During the germination process, the seed also begins releasing volatile compounds like smoke and carbon dioxide. These molecules help with germination by increasing the rate of metabolic reactions and reducing water loss.
