Embryo

An embryo is the first stage of growth for any living thing made of many cells. In animals that come from eggs and sperm joining together, this growth starts right after the egg and sperm meet. When they join, they form a single cell called a zygote. This cell quickly grows by splitting into 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 wall inside the mother’s womb.

After attaching, the embryo keeps changing. It goes through steps like forming layers that become the body’s parts and building the nervous system. It also grows 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 that, 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 1300s. It comes from a Medieval Latin word embryo. This Latin word came from an ancient Greek word ἔμβρυον (émbryon), which means "young one." The Greek word is related to another word, ἔμβρυος (émbryos), meaning "growing in." Both words are made from smaller parts: ἐν (en) meaning "in" and βρύω (brýō) meaning "to swell, to be full." The Latin form of the Greek word is embryum.

Development

Main article: Animal embryonic development

In animals, embryonic development starts 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 study embryos from many plants and animals. They learn about important topics like stem cells, how living things grow, how cells divide, and how genes work. Some big discoveries from studying embryos have even won the Nobel Prize. For example, scientists found special cells in frog embryos that help form the brain and nervous system. They also 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. This helps 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. It has helped many families have children. Scientists also try to find ways to make embryos healthier before they are placed in a mother’s body. Some scientists have tried to change genes in embryos to stop diseases, but this is very debated and not widely accepted.

These same methods also help farm animals have more babies. They can also help endangered animals like northern white rhinos, cheetahs, and sturgeons have more babies when 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. This keeps them safe for the future and helps protect many 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 tiny animal babies from long ago. These fossils come from the Precambrian time and especially from the Cambrian period. Fossils of dinosaur babies have also been found, helping us learn about how these ancient animals grew.