Re Production Gallery

Illustration of the human placenta

Illustration of the human placenta. The placenta is an organ that develops in the female uterus during pregnancy. Through it, and an umbilical cord (at lower right), the blood supply of the mother is linked to the fetus. A rich supply of placental blood vessels (red and blue, at centre) allow for nutrients and oxygen to be transferred from mother to fetus. And it allows waste products from the fetus to pass back to the mother. Apart from being a vital link between mother and fetus, the placenta also produces hormones. By the end of pregnancy it has grown about 20cm wide and 2.5cm thick. Shortly after birth, the placenta is expelled from the uterus as the afterbirth

© JOHN BAVOSI/SCIENCE PHOTO LIBRARY

Sea cucumber

Sea cucumber (Thelenota sp.) spawning. Microscopic sex cells (gametes) are being released to allow fertilisation (the fusing of a male and a female sex cell). The resulting larvae may grow into adult sea cucumbers. This marine invertebrate is a member of a group of animals (echinoderms) that includes starfish. A sea cucumber lives on the sea floor, crawling on its projecting tube feet, but mostly remaining motionless and gathering its food from the water. It feeds on microscopic sea life (plankton) and also extracts nutrients from the surrounding mud. Sea cucumbers range in length from 2 centimetres to 2 metres. They are found worldwide. Photographed in the Red Sea

© PETER SCOONES/SCIENCE PHOTO LIBRARY

Dividing yeast cells, SEM

Dividing yeast cells. Coloured scanning electron micrograph (SEM) of Schizosaccharomyces pombe yeast cells dividing. S. pombe is a single-celled fungus that is studied widely as a model organism for eukaryotic cell division. It is a rod-shaped yeast that grows by elongation at its ends. It replicates by binary fission. When it reaches a certain size its genetic material (deoxyribonucleic acid, DNA) separates to opposite ends of the cell and a division septum (wall) grows across the centre of the cell, dividing it into two daughter cells that are identical to the parent cell. Magnification: x2400 when printed 10cm wide

© STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY