Mini-Lesson

Interaction: Body Systems & Defence (HL)

Organs integrate into a coordinated body. This HL lesson covers C3.1 Integration of body systems and C3.2 Defence against disease.

You will compare nervous and hormonal control, map key brain regions, and study innate and adaptive immunity, vaccines and monoclonal antibodies.

Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.

C3.1 Integration

Integration and the brain (HL)

The body is coordinated by interacting nervous (fast, electrical, precise) and endocrine (slower, chemical, widespread) systems, with feedback loops.

Key brain regions:

Cerebral cortex: conscious thought and voluntary action.
Cerebellum: coordinates movement and balance.
Medulla oblongata: controls heart and breathing rate.
Hypothalamus & pituitary: link nervous and hormonal control.

Calculate

Your turn — calculate

1A person has a stroke volume of 75 mL and a heart rate of 68 beats per minute. Calculate the cardiac output.

mL/min

Hint: cardiac output = stroke volume × heart rate = 75 × 68.

C3.2 Defence

Innate and adaptive immunity

Innate defences are fast and non-specific: skin and mucous barriers, blood clotting, and phagocytes.

Adaptive immunity is specific: B-lymphocytes make antibodies, and memory cells give a faster, stronger secondary response. Vaccines exploit this, and high uptake gives herd immunity.

Calculate

Your turn — calculate

2A vaccine gives 95% protection. In a group of 400 vaccinated people who are all exposed, calculate the expected number not protected.

people

Hint: 5% are unprotected, so 0.05 × 400.

C3.2 Defence

Antibodies and epidemiology (HL)

Monoclonal antibodies are identical antibodies from one B-cell clone; because each binds a single antigen, they are used in diagnosis (e.g. pregnancy tests) and therapy.

Epidemiology tracks disease spread. Concerns include antibiotic resistance, HIV/AIDS (a retrovirus that destroys helper T-cells) and zoonoses that jump from animals to humans.

Sort it

Sort each item into its group

Sort each process into the correct control or defence system.

Nervous control

Hormonal control

Immune defence

Quick check

Question

?The region of the brain that coordinates fine movement and balance is the...

Quick check

Question

?The secondary immune response is faster and stronger than the primary response because of...

Quick check

Question

?Compared with nervous control, hormonal (endocrine) control is generally...

Match it

Match each item to its partner

Match each structure or term to its role.

Item

Partner

Quick check

Question

?Monoclonal antibodies are useful in diagnosis because they...

Recap

The big ideas to take away

C3.1 (HL): nervous vs hormonal control; cerebellum, medulla, hypothalamus/pituitary

C3.2: innate vs adaptive immunity; memory cells and the secondary response

C3.2 (HL): monoclonal antibodies; epidemiology, HIV, zoonoses, resistance

Skills: cardiac output = stroke volume × heart rate

Press Finish to see your score.

🏆

Mini-lesson complete!

⭐⭐⭐

You have worked through Theme C: Interaction — Body Systems & Defence for IB Diploma Biology. 🎉

Your stars: 0 / 0

Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.

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