diffusion and exchange
This process moves molecules from high to low concentration.
what is diffusion
In this system, blood stays inside vessels at all times.
What is a closed circulatory system
This organ pumps blood throughout the body.
What is the heart
These vessels carry blood away from the heart.
What are arteries
Fish use this type of circulation.
What is single circulation
These tiny vessels are where gas exchange occurs.
What are capillaries
Insects use this fluid instead of blood.
What is hemolymph
This ventricle pumps blood to the lungs.
What is the right ventricle
These smaller vessels control blood flow by constricting or dilating.
What are arterioles
Mammals and birds use this type of circulation.
What is double circulation
Oxygen diffuses into these cells at the capillaries.
what are red blood cells (rbc)
This type of system bathes organs directly in hemolymph.
What is an open circulatory system
This ventricle has the thickest walls.
What is the left ventricle
These vessels experience the highest pressure.
What are arteries
These cells carry oxygen.
What are red blood cells (RBCs)
CO₂ diffuses out of tissues because this gradient is higher in tissues.
What is CO₂ concentration
This system allows higher pressure and faster oxygen delivery.
What is a closed circulatory system
These structures prevent backflow in the heart.
what are valves
These vessels are only one cell thick.
What are capillaries
These cells fight infection.
What are white blood cells (WBCs)
This pressure (paired with osmotic pressure) drives fluid movement in capillaries.
what is hydrostatic pressure
Flatworms rely on this simple cavity instead of a circulatory system.
What is a gastrovascular cavity
The “lub‑dub” sound comes from these structures closing.
What are the AV and semilunar valves
The term for narrowing arterioles to reduce blood flow.
What is vasoconstriction
These receptors detect CO₂ changes and help regulate heart rate.
What are chemoreceptors