Taking out the trash

The idea

Excretion is the biological process of removing harmful metabolic wastes, such as nitrogenous materials, from the body; many unicellular organisms do it by diffusion into surrounding water, while complex multi-cellular organisms use specialised organs.

Wastes inside

The chemical reactions in a body make useful things and also some waste.

What do you think the body should do with harmful wastes?

• Remove them from the body
• Keep them inside
• Turn them into food

Wastes go out

Press Next step.

Getting rid of wastes

When the body uses food and oxygen, harmful by-products appear. Removing them is excretion. A single-celled organism can let the wastes diffuse out from its surface into the water around it. A complex many-celled organism cannot do this for every cell, so it uses specialised organs.

Excretion is the biological process of removing harmful metabolic wastes, such as nitrogenous materials, from the body; many unicellular organisms do it by diffusion into surrounding water, while complex multi-cellular organisms use specialised organs.

Notes

Excretion: removing harmful metabolic wastes (e.g. nitrogenous materials); unicellular organisms use diffusion into water, multi-cellular ones use specialised organs.

Check yourself

What is excretion?

How do many unicellular organisms remove wastes?

What do complex multi-cellular organisms use to remove wastes?

Which of these is an example of a waste that needs to be removed?

• The taking in of food from outside the body. Taking food in from outside the body is nutrition.
• The removal of harmful metabolic wastes from the body — correct. Yes!
• The taking in of oxygen for breaking down food. Acquiring oxygen and using it to break down food is respiration.
• Through specialised organs. Complex multi-cellular organisms use specialised organs.
• By storing all wastes inside the cell. The wastes are harmful and are removed by diffusion into the surrounding water.
• By simple diffusion from the body surface into the surrounding water — correct. Yes!
• Specialised organs — correct. Yes!
• Diffusion from the body surface only. Diffusion from the surface into surrounding water is what many unicellular organisms use.
• Chloroplasts. Chloroplasts hold chlorophyll and are where photosynthesis occurs.
• Chlorophyll. Chlorophyll absorbs light energy in photosynthesis; it is not a waste.
• Nitrogenous materials — correct. Yes!
• Plasma. Plasma is the fluid part of blood.