Body Systems and Senses — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The heart is a strong muscle that pumps blood through the whole body.
The heart pumps continuously to keep blood moving so every cell in the body receives oxygen and nutrients.
2. Blood vessels called arteries carry oxygen-rich blood away from the heart.
Arteries have thick walls that handle the high pressure of blood being pushed out of the heart.
3. Blood vessels called veins return blood to the heart from the body.
Veins have thinner walls and one-way valves that help blood flow back toward the heart.
4. The lungs add oxygen to the blood and remove carbon dioxide as we breathe.
In the lungs, oxygen passes from air sacs into the blood while carbon dioxide moves out to be exhaled.
5. When you exercise, your heart rate speeds up to deliver more oxygen.
A faster heart rate moves more oxygen-rich blood to working muscles during exercise.
6. Tiny blood vessels called capillaries connect arteries to veins inside body tissues.
Capillaries are so thin that oxygen and nutrients can pass through their walls into nearby cells.
7. Blood carries oxygen from the lungs to every cell in the body.
Cells need oxygen to release energy from food, so blood must keep delivering it constantly.
8. Blood returning to the heart from the body is low in oxygen and high in carbon dioxide.
After cells use oxygen, the leftover carbon dioxide is carried back through veins to be exchanged in the lungs.
9. The circulatory system works closely with the respiratory system to exchange gases.
The circulatory and respiratory systems work together so oxygen reaches cells and carbon dioxide is removed.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Heart
→ Pumps blood through the body
Carries blood back to the heart
Artery
→ Carries oxygen-rich blood away from the heart
Pumps blood through the body
Vein
→ Carries blood back to the heart
Add oxygen to the blood
Lungs
→ Add oxygen to the blood
Carries oxygen-rich blood away from the heart
Each part of the circulatory system has a specific role: pumping, carrying blood out, returning blood, or exchanging gases.