T lymphocytes and cancer cell, SEM
T lymphocytes and cancer cell. Coloured scanning electron micrograph (SEM) of T lymphocyte cells (green) attached to a cancer cell. T lymphocytes are a type of white blood cell that recognise a specific site (antigen) on the surface of cancer cells or pathogens and bind to it. Some T lymphocytes then signal for other immune system cells to eliminate the cell. The genetic changes that cause a cell to become cancerous lead to the presentation of tumour antigens on the cell's surface. Magnification: x2300 when printed at 10 centimetres wide.
© STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY
Hippopotamus mouth. The hippopotamus (Hippopotamus amphibius) is a large and heavy African herbivore. It can reach a length of over 3 metres, and can weigh over 3 tonnes. It has sharp canines that are used to attack mating rivals and defend itself. It can open its mouth to an angle of 150 degrees, compared to 45 degrees in humans. It feeds on vegetation in rivers and lakes in sub-Saharan Africa, emerging at night to feed on grasses. The hippopotamus communicates with a variety of grunts and rumbling noises.
© Mark Newman/Science Photo Library
Great white shark
Great white shark (Carcharodon carcharias). This is the largest of the predatory sharks, reaching a length of over 6 metres. It mainly eats seals, turtles and fish. It has a notorious reputation as an attacker of humans, but it does not feed on humans, and is thought to attack them by mistake in many cases. It lives throughout the warm seas of the world, and often follows ships into coastal waters. It can reach speeds of 40 kilometres per hour. Like other sharks, it is able to detect tiny traces of blood in the water and follow them to their source.
© Louise Murray/Science Photo Library