Human Body Systems — Science

  1. Grade 7 — The Digestive System
  2. Grade 7 — Circulatory & Respiratory Systems
  3. Grade 7 — The Nervous System & the Senses
  4. Grade 7 — Homeostasis & How Systems Interact

Apply it in a new setting

Problem 1

A person's heart beats 72 times per minute, and each beat pumps out 70 mL of blood (the stroke volume). Cardiac output is the volume of blood the heart pumps per minute. What is this person's cardiac output, in liters per minute?
Hints

Cardiac output = heart rate × stroke volume.

Multiply 72 beats/min × 70 mL/beat to get mL per minute.

Convert mL to L by dividing by 1000.

Answer and explanation

5.04 L/min

Cardiac output = 72 beats/min × 70 mL/beat = 5040 mL/min.

Convert to litres: 5040 mL ÷ 1000 = 5.04 L.

Cardiac output = 5.04 L/min.

Problem 2

During hard exercise, both your breathing rate and your heart rate climb. Which explanation best accounts for BOTH increases together?
  1. Working muscles use more oxygen and produce more carbon dioxide, so faster breathing takes in more O_2 and faster circulation delivers it and carries CO_2 away.
  2. Exercise thins the blood, so the heart must beat faster to move it.
  3. The lungs physically shrink during exercise, which forces quicker breaths.
  4. A higher body temperature speeds up the heart but has no effect on breathing.
Hints

Look for one cause that explains BOTH systems speeding up at once.

What do exercising muscles need more of, and what waste do they make more of?

The respiratory and circulatory systems cooperate to supply O_2 and remove CO_2.

Answer and explanation

Working muscles use more oxygen and produce more carbon dioxide, so faster breathing takes in more O_2 and faster circulation delivers it and carries CO_2 away.

Exercising muscles demand more oxygen and generate more carbon dioxide.

Breathing speeds up to take in more O_2 and expel CO_2, and the heart speeds up to deliver O_2 to the muscles and carry CO_2 to the lungs — the two systems work together.

Shared O_2 demand and CO_2 removal explain both, therefore A.

Problem 3

The small intestine is lined with millions of tiny finger-like projections called villi. A disease flattens these villi. What is the most direct consequence?
  1. The person can no longer chew food.
  2. Food can no longer be swallowed into the stomach.
  3. Less surface area is available to absorb nutrients, so the person can become malnourished even while eating enough food.
  4. The stomach produces far too much acid.
Hints

Ask what job the villi do in the small intestine.

Villi vastly increase surface area — for what process?

If the absorbing surface shrinks, what happens to nutrient uptake?

Answer and explanation

Less surface area is available to absorb nutrients, so the person can become malnourished even while eating enough food.

Villi hugely increase the intestine's surface area for absorbing digested nutrients into the blood.

Flattening them cuts absorption, so nutrients pass through unabsorbed and the person can be malnourished despite eating enough.

Loss of absorptive surface area is the direct consequence, therefore C.

Problem 4

You touch a hot stove and yank your hand away BEFORE you consciously feel the pain. Which sequence best explains why your hand moves so fast?
  1. Your brain feels the pain, decides to move, and then sends a command down to the hand — all before you notice.
  2. A sensory neuron signals the spinal cord, which sends a motor command straight back to the hand (a reflex), while the pain message travels separately up to the brain.
  3. The muscle itself senses the heat and contracts on its own, with no neurons involved.
  4. Hormones released by the skin travel in the blood and make the muscle contract.
Hints

You move BEFORE feeling pain, so the movement cannot be waiting for the brain to process pain.

A reflex is handled by the spinal cord to save time; the pain signal reaches the brain a moment later.

Which path skips the brain for the movement itself?

Answer and explanation

A sensory neuron signals the spinal cord, which sends a motor command straight back to the hand (a reflex), while the pain message travels separately up to the brain.

In a reflex arc, a sensory neuron carries the signal to the spinal cord, which sends a motor command right back to the hand — no brain needed for the movement.

Meanwhile the pain signal travels on to the brain, arriving slightly later, which is why you move before you feel it.

Spinal-cord reflex plus a separate pain path to the brain, therefore B.

Problem 5

On a hot day you sweat, and the blood vessels near your skin widen (dilate). How do these two responses help keep your body temperature stable?
  1. They generate extra heat to keep your core warm.
  2. They shut down the nervous system to conserve energy.
  3. They permanently lower your body's normal set-point temperature.
  4. They increase heat loss — evaporating sweat and blood flow near the surface release heat — cooling you back toward normal.
Hints

On a HOT day the goal is to lose heat, not make or keep it.

How does evaporating sweat affect skin temperature? Why bring blood close to the surface?

This is negative feedback restoring the normal set point, not changing it.

Answer and explanation

They increase heat loss — evaporating sweat and blood flow near the surface release heat — cooling you back toward normal.

Sweating cools by evaporation, and widened surface vessels bring warm blood near the skin to release heat to the air.

Both responses raise heat LOSS, lowering body temperature back toward the normal set point (negative feedback) — they do not make heat, stop the nervous system, or reset the set point.

Increased heat loss maintains homeostasis, therefore D.

Problem 6

You eat breakfast. How do the nutrients from that meal actually reach a muscle cell in your leg?
  1. They are absorbed into the bloodstream at the small intestine, and the circulatory system carries them to the leg muscle.
  2. They travel straight from the stomach to the leg muscle along nerves.
  3. They diffuse across the open body cavity from the intestine to the leg.
  4. The respiratory system picks them up along with oxygen and delivers them.
Hints

Two systems hand off here: one breaks down and absorbs food, another transports things around the body.

Where are digested nutrients absorbed, and what fluid carries them?

Nerves carry signals, not nutrients; the respiratory system handles gases.

Answer and explanation

They are absorbed into the bloodstream at the small intestine, and the circulatory system carries them to the leg muscle.

Digested nutrients are absorbed through the wall of the small intestine into the blood.

The circulatory system then transports them throughout the body, including to the leg muscle — a digestive-to-circulatory handoff.

Absorbed into the blood, carried by circulation, therefore A.

Problem 7

In the lungs, oxygen moves from the air sacs (alveoli) into the blood, while carbon dioxide moves from the blood into the air sacs. What process drives this exchange?
  1. Active transport, using ATP to pump each gas across the membrane.
  2. Diffusion — each gas moves from where it is more concentrated to where it is less concentrated.
  3. The heart pumping the gases directly across the alveolar wall.
  4. Gravity pulling the denser gas downward into the blood.
Hints

Compare where oxygen is more concentrated (fresh air vs. blood returning from the body) and where CO_2 is more concentrated.

Each gas moves down its OWN concentration gradient, with no energy required.

What is the name for movement from high to low concentration?

Answer and explanation

Diffusion — each gas moves from where it is more concentrated to where it is less concentrated.

Freshly inhaled air is high in O_2 and low in CO_2 compared with the blood arriving from the body.

So O_2 diffuses into the blood and CO_2 diffuses out, each moving down its own concentration gradient — passive diffusion, no ATP or pumping needed.

Gas exchange is diffusion down concentration gradients, therefore B.

Browse all courses