How Cells Divide

share By Rick Groleau Posted 10.09.01 NOVA Most of the time, when a cell in our bodies divides, each new cell carries a complete set of chromosomes. The cells involved with human reproduction, however, carry only half after division occurs. In this step-by-step explanation, learn about mitosis and meiosis, the two types of cell division. This feature originally appeared on the site for the NOVA program 18 Ways to Make a Baby. Background on Meiosis and Mitosis As viewed from a human perspective, nature seems to have done ingenious engineering to overcome obstacles. Asexual reproduction relies on a process called mitosis, in which the nucleus of a cell divides to create two new nuclei, each containing an identical copy of DNA. Meiosis, on the other hand, is the process by which certain sex cells are created. How exactly does meiosis halve and mix chromosomes?

Transport Videos Page Topics Brownian movement, Osmosis, Elodea Osmosis, Elodea Hypertonic, Elodea Hypotonic, Blood Isotonic, Blood Hypertonic, Blood Hypotonic, Osmosis in Red Onion, Paramecium Contractile Vacuole, Bulk Transport, Paramecium Endocytosis, Paramecium Exocytosis, Links to Transport Videos and Animations. Brownian Movement Brownian movement (motion) is the random movement of suspended particles in a gas or liquid that is caused by the molecular motion (collisions) of surrounding molecules (and particles) of the medium. In biological systems osmosis is defined as the diffusion of water (from an area of high concentration to an area of low concentration) across a selectively permeable membrane. Elodea - Osmosis Elodea is a common freshwater plant that is frequently used to decorate aquariums. Elodea - Hypertonic Solution A hypertonic solution is a solution that contains more (hyper) solutes than the cytoplasm of the cell. Elodea - Hypertonic Cells in a Hypotonic Solution Blood - Isotonic Solution

A Closer Look at Evolutionary Faces To recreate the faces of our early ancestors, some of whom have been extinct for millions of years, sculptor John Gurche dissected the heads of modern humans and apes, mapping patterns of soft tissue and bone. He used this information to fill out the features of the fossils. Each sculpture starts with the cast of a fossilized skull; Gurche then adds layers of clay muscle, fat and skin. Gurche, a “paleo-artist,” even molds the hominids’ eyes out of acrylic plastic, eschewing pre-fabricated versions. The sculpture above is of Lucy’s species, Australopithecus afarensis, which walked the earth roughly three million years ago.

Photosynthesis and Respiration