1.Theunicellular organism removetheirwastesdirectly through the cell membrane by the process ofdiffusion.

2.Many unicellular organisms like Amoeba throw out their wastes by diffusion from their body surface. Protozoan’s have no organs for excretion. As they live in an aquatic habitat, their wastes are eliminated by diffusion through the plasma membrane.Simple multicellular organisms like Hydra throw out solid waste matter through their mouth. Higher multicellular organisms have well-defined specialized excretory organs. These organs could be simple tubular structures as in flatworms and leech.

The excretory organs of insects (e.g., grasshopper, cockroach and housefly) are also tubular. They remove nitrogenous wastes from the body fluid and help in maintaining the water balance in the body.

In vertebrates, the main organs of excretion and maintenance of water balance are the kidneys.

3. There are two bean-shaped kidneys that lie in the abdominal cavity, one on either side of the vertebral column.

4.Bowman’s capsule is a double-walled cuplike structure which surrounds the dense network of blood capillaries called the glomerulus.