Kids Research Express

Fertilization is the process in which gametes —a male's sperm and a female's egg or ovum—fuse together, producing a single cell that develops into an adult organism. Fertilization occurs in both plants and animals that reproduce sexually—that is, when a male and a female are needed to produce an offspring (see Reproduction ). Fertilization is a precise period in the reproductive process. It begins when the sperm contacts the outer surface of the egg and it ends when the sperm's nucleus fuses with the egg's nucleus. Fertilization is not instantaneous—it may take 30 minutes in sea urchins and up to several hours in mammals. After nuclear fusion, the fertilized egg is called a zygote. When the zygote divides to a two-cell stage, it is called an embryo. Fertilization is necessary to produce a single cell that contains a full complement of genes. When a cell undergoes meiosis , gametes are formed—a sperm cell or an egg cell. Each gamete contains only half the genetic materia

A pollen grain contains a sperm cell that fertilizes an egg. If fertilization is successful, a seed is produced. The pollen grains of each species display unique sculpting of the pollen wall, and fossilized pollen serves to identify ancient species. Pollen grains are microscopic in size, ranging in diameter from less than 0.01mm (about 0.0000004 in) to a little over 0.5 mm (about 0.00002 in). Millions of pollen grains waft along in the clouds of pollen seen in the spring, often causing the sneezing and watery eyes associated with pollen allergies. The outer covering of pollen grains, called the pollen wall, may be intricately sculpted with designs that in some instances can be used to distinguish between plant species. A chemical in the wall called sporopollenin makes the wall resistant to decay.

Pollination is a transfer of pollen grains from the male structure of a plant to the female structure of a plant. The pollen grains contain cells that will develop into male sex cells, or sperm. The female structure of a plant contains the female sex cells, or eggs. Pollination prepares the plant for fertilization , the union of the male and female sex cells. Virtually all grains, fruits, vegetables, wildflowers, and trees must be pollinated and fertilized to produce seed or fruit , and pollination is vital for the production of critically important agricultural crops, including corn, wheat, rice, apples, oranges, tomatoes, and squash. Flowering plants use wind, insects, bats, mammals, and birds to transfer pollen from the stamen, or male portion of the flower, to the stigma, or female portion of the flower. Many plants have evolved closely with certain animals to ensure successful transfer of pollen. For example, many species of rain forest plants can only be pollinated by one parti

In nature, sexual propagation begins when water, wind, insects, birds, or small mammals carry pollen randomly between plants ( see Pollination ). In flowering plants, this transfer of pollen enables the male sex cells, or sperm, of one flower to fertilize the female sex cell, or egg, of a second flower (see Fertilization ). The egg is located at the base of the flower in a structure called an ovule, found within the ovary. Depending on the species, an ovary contains one, several, or many ovules. The ovaries of peach and avocado flowers, for example, have one ovule, while those of watermelon and cantaloupe have many. As the fertilized egg (or eggs) within the ovule begins to develop into an embryonic plant, it produces a variety of hormones that stimulate the outer wall of the ovule to harden into a seed coat. Other biochemical changes in the ovule produce a starchy substance that will be used as a food supply. In this way, the ovule ripens into a seed—a structure containing an embryoni

Plant Propagation, growing new plants from seeds or from parts of existing plants. Plant propagation occurs in nature to ensure survival and spread of species. It is also used commercially to produce seeds and plants for agriculture, horticulture, and forestry. Plant propagation includes sexual propagation, which involves the union of sperm and egg to form seeds, and asexual propagation. Asexual propagation, also known as vegetative propagation, is the growing of new plants from a leaf, stem, or root of a single parent plant (see Vegetative Reproduction ). These two forms of plant propagation transmit genetic information between plants of the same species. Genetic engineering transfers genes from one organism to another that may or may not be of the same species to introduce desirable traits into an organism. These so-called transgenic plants can then be propagated by sexual propagation or asexual propagation .

Ecology Ecology, the study of the relationship of plants and animals to their physical and biological environment. The physical environment includes light and heat or solar radiation, moisture, wind, oxygen, carbon dioxide, nutrients in soil, water, and atmosphere. The biological environment includes organisms of the same kind as well as other plants and animals. Because of the diverse approaches required to study organisms in their environment, ecology draws upon such fields as climatology, hydrology, oceanography, physics, chemistry, geology, and soil analysis. To study the relationships between organisms, ecology also involves such disparate sciences as animal behavior, taxonomy, physiology, and mathematics. An increased public awareness of environmental problems has made ecology a common but often misused word. It is confused with environmental programs and environmental science (see Environment ). Although the field is a distinct scientific discipline, ecology does indeed contribu

Horticulture Horticulture (Latin hortus,”garden”; cultura,”cultivation”), science and art of growing fruits, vegetables, flowers, shrubs, and trees. Horticulture originally meant the practice of gardening and, by extension, now means the cultivation of plants once grown in gardens. In contrast, the term agriculture , by derivation, referred to more open forms of culture such as the production of grains and grasses, known as agronomic crops, which are cultivated on a large scale. The original distinctions have been so blurred that many crops formerly considered either agronomic or horticultural are now categorized sometimes in one field, sometimes in the other, depending on the intended use of the crop. Thus a plant grown for home consumption may be called horticultural; the same plant cultivated for forage is regarded as an agronomic crop. Horticulture includes the growing of fruit (especially tree fruits), known as pomology; production of vegetable crops, called olericulture; producti