Grade by Grade
B. Life Systems · Human Organ Systems

Body Systems Working Together

B2.3 A2.1 A2.2 A1.5About 45 minutes
Learning goals
  • I can describe how two or more body systems depend on each other.
  • I can explain what happens in several systems when I exercise.
  • I can read, trace and change a simple program that models how my body responds to exercise.
  • I can describe how coded devices like fitness trackers affect everyday life.

Words to know

interrelationship
A connection where two or more things affect and depend on each other.
interdependent
Needing each other to work.
model
A simpler version of something real that helps us understand it. A computer program can be a model.
variable
In coding, a named box that stores a value that can change, like heartRate.
condition
In coding, a test that is true or false, like "heartRate > 80".
wearable technology
Small computers worn on the body, like fitness trackers and smartwatches.

A team, not solo players

A hockey team needs a goalie, defence and forwards. A great goalie alone can't win the game. Your body systems are the same: none of them can keep you alive by itself. They are interdependent: each one needs the others.

People playing pickup hockey on an outdoor rink in a snowy town, seen from a distance.
Playing hockey takes every body system working together: lungs and heart deliver oxygen, muscles and bones move, and the brain controls it all. AI-generated image

How the systems connect

  • Respiratory + circulatory: the lungs bring in oxygen; the blood picks it up and delivers it to every cell. The blood brings carbon dioxide back to the lungs to be breathed out.
  • Digestive + circulatory: the small intestine passes nutrients into the blood, which carries them to every cell.
  • Circulatory + excretory: the blood carries wastes to the kidneys, which filter them out.
  • Nervous + musculoskeletal: nerves tell muscles when to contract, so bones move.
  • Nervous + respiratory + circulatory: the brain stem controls how fast you breathe and how fast your heart beats.
  • Musculoskeletal + respiratory: the diaphragm and rib muscles do the breathing; the ribs protect the lungs.
  • Musculoskeletal + circulatory: bone marrow makes new blood cells.

Why do cells need oxygen and nutrients? Cells use them together to release energy. That makes carbon dioxide and other wastes, which then must be removed.

circulatoryrespiratorydigestiveexcretorymusculo-skeletalnervousoxygencarbondioxidenutrientswastessignalsnew bloodcells
Systems pass things to each other. The circulatory system is the delivery service in the middle: it picks up oxygen and nutrients and drops off wastes.
SystemsWhat passes between them
respiratory → circulatoryoxygen into the blood
circulatory → respiratorycarbon dioxide out of the blood
digestive → circulatorynutrients into the blood
circulatory → excretorywastes carried to the kidneys
nervous → musculoskeletalsignals telling muscles to contract
musculoskeletal → circulatorynew blood cells from bone marrow
Some interrelationships between body systems.
Worked example

Let's follow the body during a sprint

You sprint across the soccer field. What does each system do?

  1. Nervous: your brain sends messages down motor nerves to your leg muscles.
  2. Musculoskeletal: leg muscles contract in pairs and pull on bones; you run.
  3. Circulatory: working muscles need more oxygen and nutrients, so your heart beats faster.
  4. Respiratory: your brain stem senses extra carbon dioxide and you breathe faster and deeper.
  5. Excretory: you sweat to cool down, losing water and salts. Later you feel thirsty and drink.
  6. Digestive: nutrients from your breakfast, already in your blood, are the fuel.

Every system plays a part. When one changes (muscles working harder), others change too (faster heart and breathing).

Modelling the body with code

Scientists use computer programs as models. A model is simpler than the real thing, but it helps us see patterns and make predictions. Here is a program that models how heart rate and breathing rate respond to exercise. It uses two variables (heartRate and breathingRate) and a condition (if... else).

set heartRate to 80
set breathingRate to 20
repeat 4 times
ask "Are you exercising? (yes/no)" and save the answer as exercising
if exercising = yes then
change heartRate by 15
change breathingRate by 5
say "Muscles need more oxygen! Heart and lungs speed up."
else
if heartRate > 80 then
change heartRate by -15
change breathingRate by -5
say "Resting. Heart and lungs slow down."
say heartRate and breathingRate

A body model. Each time through the loop is one minute.

Worked example

Let's trace the program

The answers are: yes, yes, no, no. What does the program say each minute?

  1. Start: heartRate = 80, breathingRate = 20.
  2. Minute 1 (yes): 80 + 15 = 95; 20 + 5 = 25.
  3. Minute 2 (yes): 95 + 15 = 110; 25 + 5 = 30.
  4. Minute 3 (no): is 110 > 80? Yes, so 110 − 15 = 95; 30 − 5 = 25.
  5. Minute 4 (no): is 95 > 80? Yes, so 95 − 15 = 80; 25 − 5 = 20.

It says 95 and 25, 110 and 30, 95 and 25, 80 and 20. The heart and lungs speed up together and slow down together, just like in a real body.

02040608010012001234minuteyesyesnonoexercising?809511095802025302520heart ratebreathingrateper minute
The program's output as a line graph. Heart rate (solid line) and breathing rate (dashed line) go up together while exercising and down together while resting.

Code in your life

Fitness trackers and smartwatches run code like this. Sensors measure your pulse and steps, and the program decides what to show. They can help people stay active and help doctors check on patients. But they are not perfect, they can make people worry about numbers, and they collect personal data, so it's smart to ask who sees that data.

Just for fun

What if your body systems could text each other?

Brain: "RUN!" Muscles: "On it!" Heart: "Speeding up!" Lungs: "huff... puff... sending oxygen!" Stomach: "Is it lunch yet?"

Hands-on activity

Play the body-team game and code it

You need: paper, a pencil, and a family member or two. Optional: a free block-coding app or website your grown-up approves.

  1. Each person is one system (nervous, respiratory, circulatory, musculoskeletal). Write the system on a card.
  2. A caller says an event: "Running for the bus!", "Eating lunch!", "Falling asleep!" Each person says what their system does, in order.
  3. On paper, write a flow chart for one event, with arrows from system to system.
  4. Coding: trace the body program above with your own list of yes/no answers. If you have a block-coding tool, build it and test it. Then change it: make heartRate go up by 20, or add a third variable such as sweat.

What to look for: each step connects one system to another (for example, nerves → muscles → more oxygen needed → faster heart and breathing).

Your turn

1

Which two systems work together to get oxygen to your cells?

2

How does the digestive system depend on the circulatory system?

3

Which system tells muscles when to contract?

4

How does the skeletal system help the circulatory system?

5

In the program, what are the two variables?

6

Trace the program with: no, yes, no, yes. What are the final values?

More practice: warm-up

1

True or false: each body system can work by itself.

2

What do cells need from the blood? Name two things.

3

Which organ removes wastes carried by the blood?

4

What happens to your heart rate when you exercise?

5

What is a fitness tracker?

More practice: on your own

1

Explain why your breathing and heart rate both go up when you exercise.

2

If the kidneys stopped working, how would other systems be affected?

3

In the program, why is the condition "if heartRate > 80" needed?

4

Change the program so exercise adds 20 to heartRate. With answers yes, yes, what is heartRate after 2 minutes?

5

Give one benefit and one problem with fitness trackers.

Challenge

1

You eat a big lunch, then lie down. Describe how the digestive, circulatory and nervous systems work together.

2

The program changes heart rate by exactly 15 each minute. Name one way a real body is different.

3

A person has a lung disease and gets less oxygen. Predict how their circulatory and musculoskeletal systems might be affected.

Check your understanding

Quiz

1.

Oxygen gets from your lungs to your toes by...

2.

Which systems pass nutrients into the blood?

3.

When you run, your heart and breathing rates...

4.

Which system controls how fast your heart beats?

5.

In the program, heartRate is 95. The answer is "no". What is heartRate now?

6.

A fitness tracker uses sensors and...

For parents and teachers

Big idea: body systems are interdependent. Oxygen, nutrients and wastes move between them in the blood, and the nervous system coordinates everything.

How to help at home:

  • After active play, ask: "Which systems were working just now? How do you know?"
  • Trace the program with your child using different yes/no lists; if you have an approved block-coding app, let them build it.
  • Talk about any wearable devices in your family and what data they collect.

Common difficulties:

  • Describing systems separately without saying how they connect. Ask "What does this system give to the other one?"
  • Forgetting the condition when tracing the code ("heartRate > 80" stops it going below 80).