Egg and sperm (nouns, “EG” and “SPURM”)
These are two types of reproductive cells, or gametes. Each contains half of the genetic information necessary to form a complete organism. When an egg and a sperm fuse, they combine into a new cell called a zygote. The zygote contains all the genetic information it needs to become a new individual. This new cell then divides over and over, eventually forming a complete organism with the same genes in each cell.
In sexual reproduction, an egg and a sperm combine to make a new individual. Eggs are often relatively large and don’t move on their own. Some contain nutrients, which help feed a growing organism as it develops.
Sperm, in contrast, are small and mobile. A single sperm is also called a spermatozoon (sper-MAH-toe-ZOH-on). Many sperm together can be called sperm, or spermatozoa (sper- MAH-toe-ZOH-ah). Most have long, whiplike tails. When an organism releases sperm, they use the tails to swim toward the egg. The head of a sperm contains proteins and DNA. The proteins help the sperm cell enter the egg cell.Once that happens, the sperm releases its DNA to pair with the egg’s DNA.
In humans and in many animals such as mammals and birds, ovaries produce eggs, and testes produce sperm. But eggs and sperm are found all over the living world. Some plants develop egg cells called ovules and sperm cells called pollen. Some fungi and algae produce eggs and sperm, too. In some species, one individual can produce both sperm and eggs. Others can produce sperm at one time, and eggs at another.
In a sentence
Scientists are working out how to get around eggs and sperm — producing mice with sperm alone, or with only eggs.
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Power Words
More About Power Wordsalgae: Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.
birds: Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
cell: The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Mostorganisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size, mental maturity or sometimes even shape. (as with towns) The conversion of wildland to host communities of people. This development can include the building of roads, homes, stores, schools and more. Usually, trees and grasslands are cut down and replaced with structures or landscaped yards and parks.
DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
egg: A reproductive cell that contains half of the genetic information necessary to form a complete organism. In humans and in many other animals, ovaries produce eggs. When an egg fuses with a sperm, they combine to produce a new cell, called a zygote. This is the first step in the development of a new organism.
environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature andhumidity (or even theplacement of things in the vicinity of an item of interest).
fuse: (v.) To merge two things together, often along some seam. (n.)Some cord, tube or other material that can burn and eventually ignite an explosive. Or an electrical device that breaks an electrical circuit when it overheats, thus preventing electrical wires from getting hot enough to causea fire.
gamete: A reproductive cell containing half of the genetic material required to produce an individual. In humans, those gametes are an egg and sperm. In plants, they are a pollen grain and ovum.
gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
generation: A group of individuals (in any species) born at about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans. The term also is sometimes extended to year classes of other animals or to types ofinanimate objects (such as electronics or automobiles).
genetic: Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.
mammal: A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
nutrient: A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.
organism: Any living thing, from elephants and plants to bacteria and other types of single-celled life.
ovaries: See ovary.
protein: A compoundmade from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are thehemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.
species: A group of similar organisms capable of producing offspring that can survive and reproduce.
sperm: A reproductive cell that contains half of the genetic information necessary to form a complete organism. In humans and in many other animals, testes produce sperm. When a sperm fuses with an egg, the two combine to produce a new cell, called a zygote. This is the first step in the development of a new organism."
zygote: A cell that forms when two gametes fuse. in humans, those gametes are an egg and sperm. In plants, the gametes are pollen grains and ova.
About Bethany Brookshire
Bethany Brookshire was a longtime staff writer at Science News Explores. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.
