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Osmosis is the diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a selectively permeable membrane.

Blood is pumped away from the heart at high pressure in arteries, and returns to the heart at low pressure in veins. The human circulatory system is a double circulatory system.

Most animals carry out sexual reproduction. Sexual reproduction involves the joining of two sex cells (gametes) – the sperm (male gamete) and the egg/ovum (female gamete).