Coordination, excretion and drugs

Learning objectives

• Compare nervous and hormonal signalling.
• Distinguish excretion from egestion.
• Explain negative feedback at an introductory level.

The big idea

Receptors detect changes and effectors produce responses. Nervous pathways coordinate rapid signals, while hormones travel in blood to target tissues; reflex pathways connect detection with a rapid response.

Excretion removes metabolic waste such as urea and carbon dioxide, whereas egestion removes undigested material. Maintaining internal conditions involves feedback. Drugs can alter normal chemical signalling; their effects depend on the substance, dose and receptor interactions.

Investigate and explain

Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.

Related simplified PhET model. Explain what it represents and what the living system does differently.

Open the interactive investigation

Check your understanding