Biology

  The Circulatory System •            Large and complex animals have circulatory systems that consist of tubes, a transport fluid and a means of pumping the fluid. Blood is the transport fluid which contains dissolved substances and cells. •            The tubes are blood vessels through which dissolved substances are circulated around the body. The heart is the pumping organ which keeps the blood in circulation. The types of circulatory system exist in animals: open and closed. •            In an open circulatory system: The heart pumps blood into vessels which open into body spaces known as haemocoel. Blood comes into contact with tissues. •            A closed circulatory system: Found in vertebrates and annelids where the blood is confined within blood vessels and does no...

  INTRODUCTION Transport is the movement of substances within an organism. •            All living cells require oxygen and food for various metabolic processes. •            These substances must be transported to the cells. •            Metabolic processes in the cells produce excretory products which should be eliminated before they accumulate. •            The excretory products should be transported to sites of excretion. Organisms like amoeba are unicellular. They have a large surface area to volume ratio. The body is in contact with the environment. Diffusion is adequate to transport substances across the cell membrane and within the organism. Large multi-cellular organisms have complex structure where cells are far from each other hence diffusion alone cannot meet...