Life Science: Session 4
Seeds vs. Eggs
How do seeds compare to eggs?
Although seeds and eggs — referring to “supermarket” eggs and not the sex cells — appear to be very different, they both arise in the same way and serve the same functions in the plants and animals that produce them. Both develop from the union of male and female sex cells, and both act as structures that protect and supply nutrients to a developing embryo. Eggs and seeds are also both considered to be adaptations to a life on land. They both enclose the embryo in an environment that prevents dehydration, while still allowing gases to flow in and out.
How do seeds develop?
There are other features that make seeds and eggs comparable. In flowering plants, one or more seeds develop within an ovary. The seed coat, which is the hard structure that surrounds the seed, develops from the wall of the chamber where the fertilized egg begins to develop. Inside the seed is a food source—the endosperm— that forms as the result of fertilization. As the embryo grows inside the seed, it uses the endosperm for food. The endosperm develops along with the embryo into one or two seed leaves, or cotyledons, that act as a food source after germination until photosynthesis can take over.
How do eggs develop?
In animals such as birds and reptiles, eggs are fertilized internally. As an egg passes through the female reproductive tract, the egg white is secreted around it, followed by a shell membrane and the shell. As this is happening, the fertilized egg is beginning to develop into an embryo and other parts of a “life support system.” One part is the yolk, which is a food source rich in fats and proteins that is secreted into sac that connects directly to the embryo. Another part connects to the embryo and collects wastes. A third part envelops the embryo in a fluid filled sac, which protects it as it floats freely.
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