Embryo

An embryo is the very first stage of growth for any living thing made up of many cells. In animals that come from eggs and sperm joining together, this special growth starts right after the egg and sperm meet. When they join, they form a single cell called a zygote, which quickly grows by splitting into more and more cells.

These tiny cells, called blastomeres, clump together to make a ball. As they keep growing, they form a hollow space inside, turning into a structure known as a blastula or, in mammals like humans, a blastocyst. This tiny ball then moves and attaches to the safe wall inside the mother’s womb.

After attaching, the embryo keeps changing. It goes through important steps like forming the three main layers that become all the body’s parts, building the nervous system, and growing all the body’s tissues and organs. In humans, this growing life is called an embryo for the first nine weeks after the sperm meets the egg, after which it is called a fetus. In many other animals, the word “embryo” is used for any early stage of growth before the baby is born or hatches.

Etymology

The word "embryo" has been used in English since the middle of the 14th century. It comes from a Medieval Latin word embryo, which itself came from an ancient Greek word ἔμβρυον (émbryon) meaning "young one." This Greek word is related to another word, ἔμβρυος (émbryos), meaning "growing in." Both of these words are built from smaller parts: ἐν (en) meaning "in" and βρύω (brýō) meaning "to swell, to be full." The Latin version of the Greek word would be embryum.

Development

Main article: Animal embryonic development

In animals, embryonic development begins when a female egg cell and a male sperm cell join to form a zygote, a single cell. This zygote then divides into many cells, forming a multicellular embryo. The process has several stages, including rapid cell division, forming layers of cells, and developing structures that will become organs.

Main article: Plant embryonic development

Further information: Sporophyte

Flowering plants create embryos when a female ovule and male pollen combine to form a zygote. This zygote divides into many cells, forming an embryo inside a seed. The seed also contains nutrient-rich tissue and a protective outer covering. The plant embryo goes through stages and eventually develops into a seedling when it grows from the seed.

Research and technology

Biological processes

Scientists around the world study embryos from many plants and animals to learn about important topics like stem cells, how living things change over time, how cells divide, and how genes work. Some big discoveries made by studying embryos have even won the Nobel Prize. For example, scientists found special groups of cells in frog embryos that help form the brain and nervous system, and they discovered genes that decide how body parts are arranged in fruit flies.

Assisted reproductive technology

Doctors use special methods to help create or change embryos to help people and animals have healthy babies. These methods are very helpful for people who have trouble having children and for farmers who want the best traits in their animals. One common method is called in vitro fertilization, or IVF, which has helped many families have children. Scientists also try to find ways to make embryos healthier before they are implanted in a mother’s body. Some scientists have even tried to change genes in embryos to stop diseases, but this is very controversial and not widely accepted.

These same methods are also used to help farm animals produce more babies or to help endangered animals like northern white rhinos, cheetahs, and sturgeons have more babies when they are needed.

Cryoconservation of plant and animal biodiversity

Scientists collect and store embryos, seeds, and other important parts of plants and animals at very cold temperatures to keep them safe for the future. This helps protect many different species from disappearing. There are special places around the world, like the Frozen Ark in the UK and the San Diego Zoo in the United States, that store these materials. There are also many seed banks, like the Svalbard Global Seed Vault in Norway, that keep millions of plant samples safe.

Fossilized embryos

Main article: Fossil embryos

Scientists have found very old fossils of animal embryos from long ago, starting from the Precambrian time and especially many from the Cambrian period. Even fossils of dinosaur embryos have been uncovered, giving us clues about how these ancient creatures developed.