Biology Revision for "O" level examinations

Types of joints 1.       Movable joints      The bones of these joints are separated by a pad of flexible cartilage. There are two type of movable joints: a.        Slightly movable joints: -are found adjacent between adjacent vertebrae. The cartilage between the joints (called intervertebral disc) absorbs shock. They can be displaced due to injury. Other e.g. Pivot joints: between neck and cranium. b.       Synovial joints: the bones are held together by ligaments and are separated by synovial fluid. The fluid lubricates the joints, preventing the joints and cartilage caps of the bone from rubbing against each other. e.g. hinge joints: elbow, and knee         ball and socket: at shoulder and hips 2.       Immovable joints       These joints are held firmly in position by fibers. They exist betwee...

How the xylem vessel carries water ROOT PRESSURE Water that is present in the soil, is absorbed by osmosis into the root hairs of plants. The water then travels through the cortex of the root, from cell to cell. A root pressure is therefore created, and this forces water from the cortex into the xylem vessel CAPILLARITY Through capillarity, water moves up the xylem in a continuous stream. The water molecules are attracted to the walls of the vessels (adhesion) and they are also attracted to each other (cohesion). This cause an upward movement of water in the xylem, against gravity TRANSPIRATION PULL Transpiration occurs in leaves of plants. This loss of water causes a vacuum to be created in the xylem. There is therefore a high water pressure at the bottom, and a lower water pressure at the top of the xylem. Therefore, there is an upward pull of water.