Vacuoles in an amoeba (a one-celled eukaryote) Vacuoles are little pockets in the cytoplasm of a cell where a cell stores food. You can see them with a good light microscope. Vacuoles are mostly made of water and amino acids. They have a lipid membrane around them to keep out the salty water [...]
Human sperm cells with flagella (under a microscope) About two billion years ago, the first eukaryote cells evolved from the earlier prokaryote cells. These eukaryote cells also evolved a new way to move themselves around. Even though some eukaryote cells have flagella that look like the ones in prokaryote cells, they don't work the same [...]
Krystie has Tay-Sachs disease Tay-Sachs is a disease where your lysosomes aren't working right. It's a disease you get in your DNA from your parents. Both your mother and your father have to have the disease in their DNA in order for you to get it. It is not catching. One of the [...]
RNA molecule: A single strand of RNA, seen under an electron microscope The RNA molecule was probably one of the earliest steps towards life on Earth. RNA is short for "ribonucleic acid". That's a very long, complicated molecule made out of amino acids linked together. The amino acids are made out of atoms of [...]
A cell dividing into two cells One of the main ways we define whether something is alive is whether it can reproduce - if it can make a new version of itself. The first things we know about that could reproduce were molecules of RNA, more than four billion years ago. RNA could reproduce, but often [...]
An onion skin cell (seen through a microscope) You can see the nucleus inside each cell The earliest cells, and all prokaryote cells, don't have a nucleus. Inside these simple cells, the DNA molecules just float around in the cytoplasm. This is a nice simple arrangement, but it's risky - the DNA often [...]
A mitochondrion (seen through a microscope) About two billion years ago, in the Proterozoic, there were only prokaryotic cells on Earth. Mitochondria probably started out as independent cells that were especially good at digesting food. These cells were extra good at digesting because they had evolved to have two membranes. The inside membrane, [...]
Lysosomes (under an electron microscope) Prokaryote cells don't have lysosomes, so the first lysosomes probably evolved about the same time as the other pieces of eukaryote cells. That was about two billion years ago. Like the vacuoles and the Golgi bodies and the other parts of a cell, lysosomes (LIE-sew-somes (like HOMES)) are [...]
Highly magnified view of a cell wall Around four billion years ago, some of the amino acid molecules that were on the planet Earth began to join together into bigger molecules with hundreds of atoms in them, called lipids. This happened in the water in the oceans on Earth, because there wasn't any land [...]
One cell of a plant (magnified 22,500 times) Thanks to Ohio State University A cell is the smallest living thing (unless you count viruses), and all bigger living things are made of cells. Both plants and animals are made of cells. We don't know yet whether there are cells on any other planet [...]
