A.1 Communication

Communication studies how the body detects changes inside and outside it, passes that information between its systems and responds so that conditions such as core temperature, blood pH and blood glucose stay within narrow limits. The same mechanisms raise heart rate and breathing to meet the demands of exercise, protect health in heat and cold, and break down in conditions such as type 2 diabetes and heat stroke.

The questions behind the topic

The topic is built around one central question: how does the body collect information about its internal environment, send it where it is needed and use it to keep conditions right for its cells to work? Each subtopic answers part of that question. Everyday situations in sport and health make it concrete:

• Why does heart rate rise before a race has even started?

• How does the body hold its core temperature close to 37 °C during a long run on a hot day?

• Why is a rise in carbon dioxide, more than a fall in oxygen, the main signal that increases breathing during exercise?

• How can a trained endurance athlete pump the same volume of blood at rest with far fewer heartbeats than an untrained person?

• Why does regular exercise help people with type 2 diabetes control their blood glucose?

• Why do some athletes spend weeks training in the heat or at altitude before a major competition? (HL)

What the topic covers

Inter-system communication introduces the two signalling systems: the nervous system, which sends fast electrical impulses along neurons, and the endocrine system, which releases hormones into the blood. It includes the sympathetic nervous system and parasympathetic nervous system, the receptors that start nervous responses, and hormones such as epinephrine, insulin and the reproductive hormones. Maintaining homeostasis shows how these signals are organised into feedback loops. Transport describes the heart, blood vessels, blood and lungs, whose output the loops adjust.

How the subtopics connect

The three subtopics describe one chain of events, shown in the concept map. A change, such as the start of a sprint or a hot afternoon, is detected by a receptor and passed on along nerves or carried by hormones. A control centre in the brain compares the information with a set point and sends signals to an effector that reverses the change. This is homeostasis by negative feedback.

Many of the effectors are in the heart, the blood vessels and the respiratory muscles. The result of most homeostatic responses during exercise is therefore a change in heart rate, stroke volume, blood flow or minute ventilation. For example, a rise in blood carbon dioxide lowers blood pH; chemoreceptors detect it, the respiratory control centre increases breathing, and the extra carbon dioxide is breathed out. Communication, homeostasis and transport all appear in that single loop.

The map also shows links beyond the topic. The oxygen that the cardiovascular and respiratory systems deliver is used by the oxidative system to resynthesise ATP, which is why VO₂ max depends on both systems. Motor neurons from the same nervous system activate motor units in skeletal muscle, which links communication to how muscles generate movement. The anticipatory rise in heart rate before competition is a sympathetic response to rising arousal, the same response that sport psychology studies as part of anxiety.

Health and performance

Almost every idea in the topic matters through both lenses of the course:

Communication links to every other part of the course. Within the same theme, fluid loss through sweating causes dehydration and cardiovascular drift, and long-term training produces chronic adaptations in the heart and lungs. In biomechanics, proprioceptors in muscles, tendons and joints give the information that keeps a movement accurate and the body balanced. In sport psychology, the sympathetic nervous system is the physical side of anxiety: a raised heart rate, faster breathing and sweating before a performance are the same responses as those at the start of exercise.

How SL and HL differ

HL students study everything SL students study, plus additional higher level material. In this course that extra material is mostly added inside subtopics rather than as separate subtopics. Most pages are therefore read by everyone, and contain sections with headings ending “(HL only)” that SL students can skip. Questions on the HL material appear only in the HL papers.

In Communication, no subtopic is HL only, and Inter-system communication and Transport contain no HL material: both levels study them in full. Maintaining homeostasis has one HL-only part:

• the acute responses and long-term adaptations to exercising in heat, humidity, cold and at altitude, including heat illness, hypothermia and hypoxia;

• why the effect of an environment depends on the type, intensity and duration of the activity;

• strategies to support performance and health in these conditions, such as heat acclimatisation, pre-cooling, clothing for the cold and altitude training, with an evaluation of each.

Assessment

Questions on Communication appear in all three parts of the external assessment. Paper 1A asks multiple-choice questions, for example which hormone raises blood glucose or which receptor detects a change in blood pressure. Paper 1B gives data from a study, such as heart rate or core temperature recorded during exercise, and asks students to describe trends, calculate changes and evaluate the method. Paper 2 asks short-answer and extended-response questions. HL-only material on environmental responses appears only in the HL papers.

The topic tends to produce these kinds of question:

• labelling the data booklet’s diagrams of the endocrine glands, the heart and its conduction system, the circulatory and respiratory systems, and hormone levels across the menstrual cycle;

• drawing and annotating a negative feedback loop for temperature, blood glucose or blood pH;

• calculating cardiac output ($\dot{Q}$ = HR × SV) or minute ventilation from data, with units;

• sketching and describing heart rate before, during and after exercise, including the anticipatory rise;

• explaining a response step by step, from the stimulus to the effector;

• evaluating strategies for exercising in the heat or at altitude (HL).