Grade 7 Science Practice Test: How Human Body Systems Work Together

The small intestine is long and lined with tiny fingerlike villi that absorb nutrients into the blood. The large intestine mainly absorbs water.

Alveoli are tiny air sacs surrounded by capillaries, where oxygen moves into the blood and carbon dioxide moves out. The trachea and bronchi are only airways.

Arteries carry blood away from the heart; veins return it. Capillaries are the tiny vessels where exchange with the cells happens.

Working muscles release more energy through cellular respiration, which uses oxygen and produces carbon dioxide. The respiratory and circulatory systems speed up together to keep up.

Muscles pull on bones, and bones act as levers at the joints. The nervous system sends the signal, but the movement itself comes from muscles and bones.

The kidneys filter the blood, removing wastes and extra water as urine. This makes them part of the excretory system.

In a reflex the signal travels to the spinal cord and straight back to the muscles, skipping the slower path through the brain. Hormones work far too slowly for this.

The endocrine system uses hormones carried in the blood to control things like growth. The nervous system sends faster electrical signals along nerves.

White blood cells are part of the immune system and destroy germs. Carrying oxygen is the job of red blood cells, and clotting is the job of platelets.

An organ is made of different tissues that work together on one job. The heart, blood and blood vessels together form an organ system, the circulatory system.