C3.1 Integration of Body Systems IB Past Paper PDF 2025

First Exams 2025 C3.1 Integration of Body Systems part 2 Theme: Interaction and Interdependence Level of Organisation: Organisms Combined Content SL and HL SL and HL Content From C3.1.11: Modulation of sleep...

First Exams 2025 C3.1 Integration of Body Systems part 2 Theme: Interaction and Interdependence Level of Organisation: Organisms Combined Content SL and HL SL and HL Content From C3.1.11: Modulation of sleep patterns by the IB melatonin secretion as a part of circadian rhythms Students should understand the diurnal pattern of melatonin secretion by the pineal gland and how it helps to establish a cycle of sleeping and waking. SL and HL Content Circadian Rhythms Circadian rhythms are physical, mental, and behavioral changes that follow a 24-hour cycle. These natural processes respond primarily to light and dark and affect most living things, including animals, plants, and microbes (NIH). The secretion of melatonin by the pineal gland helps establish a cycle of waking during daylight, and sleeping during darkness. Circadian Rhythms follow a day-night cycle SL and HL Content SL and HL Content Melatonin and Sleep Blue light suppress the secretion of melatonin from the pineal gland. Melatonin levels increase in the evening, signalling that it is time to sleep. Melatonin levels drop in the morning, helping us feel awake. Daily changes in Melatonin Levels SL and HL Content From C3.1.12: Epinephrine (adrenaline) secretion the IB by the adrenal glands to prepare the body for vigorous activity Consider the widespread effects of epinephrine in the body and how these effects facilitate intense muscle contraction. SL and HL Content Epinephrine Read the linked article on the role of epinephrine, also known as adrenaline, in the fight or flight response. Explain how the release of epinephrine prepares the body for fight or flight. Adrenaline: Fight or Flight SL and HL Content Fight or Flight The release of epinephrine from adrenal glands prepares the body for intense physical activity, and facilitates intense muscle contraction in the following ways: Widening of bronchioles to provide muscles with more oxygen. The liver converts glycogen into glucose, which is released into the bloodstream. The heart pumps harder and faster, providing muscles with a greater supply of oxygen and glucose. Blood flow is redirected away from the brain, skin and digestive system, so that muscles receive more blood. Pupils dilate which improves vision. SL and HL Content From C3.1.13: Control of the endocrine system by the IB the hypothalamus and pituitary gland Students should have a general understanding, but are not required to know differences between mechanisms used in the anterior and posterior pituitary. SL and HL Content Control of the Endocrine System The hypothalamus and pituitary gland work together to regulate the endocrine system. 2-Minute Neuroscience: Hypothalamus & Pituitary Gland SL and HL Content Control of Endocrine System The hypothalamus monitors the body's internal conditions and releases appropriate hormones to the pituitary gland, which then stimulates other glands in the body to release specific hormones. The hypothalamus secretes releasing factors which causes the release of specific hormones from the anterior pituitary gland. The hypothalamus produces hormones that are transported to and stored in the posterior The Hypothalamus and Pituitary Gland pituitary gland. SL and HL Content From C3.1.14: Feedback control of heart rate the IB following sensory input from baroreceptors and chemoreceptors Include the location of baroreceptors and chemoreceptors. Baroreceptors monitor blood pressure. Chemoreceptors monitor blood pH and concentrations of oxygen and carbon dioxide. Students should understand the role of the medulla in coordinating responses and sending nerve impulses to the heart to change the heart’s stroke volume and heart rate. SL and HL Content Baroreceptors and Chemoreceptors Baroreceptors are stretch-sensitive receptors that monitor blood pressure. Chemoreceptors detect changes to blood chemistry, including carbon dioxide and oxygen levels as well as pH. Baroreceptors and chemoreceptors are located in regions of the aorta and carotid arteries. Both baroreceptors and chemoreceptors send signals to the medulla oblongata in the brain stem. SL and HL Content Exercise and Blood Chemistry Exercise increases the rate of respiration in muscle tissue, which changes blood chemistry. Respiring muscle tissue removes oxygen from the blood and releases carbon dioxide. An increase in carbon dioxide levels in the blood will cause a decrease in blood pH through the production of carbonic acid. Chemoreceptors in the aorta and carotid artery monitor changes in blood chemistry, and send signals to the cardiovascular control centre of the medulla oblongata. The medulla oblongata sends signals to the sinoatrial node (pacemaker) via one of two nerves, to increase the rate of heart beats and heart stroke volume. SL and HL Content Rest and Blood Chemistry After exercise, the rate of respiration decreases Blood chemistry changes as less oxygen is used during respiration, and less carbon dioxide is produced. Chemoreceptors in the aorta and carotid artery monitor changes in blood chemistry, and send signals to the cardiovascular control centre of the medulla oblongata. The medulla oblongata sends signals to the sinoatrial node (pacemaker) via one of two nerves to decrease the rate of heart beats. SL and HL Content Changing Blood Pressure and Heart Beat Baroreceptors in the aorta and carotid artery monitor changes in blood pressure, sending signals to the cardiovascular control centre of the medulla oblongata. In response to changing blood pressure, the cardiovascular control centre initiates a series of neural and hormonal adjustments to bring the heart rate back to normal. SL and HL Content From C3.1.15: Feedback control of ventilation rate the IB following sensory input from chemoreceptors Students should understand the causes of pH changes in the blood. These changes are monitored by chemoreceptors in the brainstem and lead to the control of ventilation rate using signals to the diaphragm and intercostal muscles. SL and HL Content Carbon Dioxide and Blood pH When carbon dioxide dissolves in blood plasma, it reacts with water to form carbonic acid, and reduces the pH of the blood. The pH of the blood decreases during physical activities, because respiration increases the amount of carbon dioxide in the blood. Chemoreceptors in the carotid artery and the medulla oblongata monitor changes in the pH of the blood. The respiratory control centre of the medulla oblongata regulates the rate and depth of ventilation, and brings blood pH levels back to a normal pH range of 7.35 to 7.45. SL and HL Content Chemoreceptors Control of Ventilation in the carotid arteries and in the medulla oblongata monitor change in the pH of the blood, and help regulate the ventilation rate. Effect of blood chemistry - stimuli, hyperventilation response and hypoventilation response SL and HL Content Exercise and Ventilation Rate Exercise increases the respiration rate of the muscles, releasing more carbon dioxide in the blood. Higher levels of carbon dioxide in the blood reduces the pH of the blood because carbon dioxide forms carbonic acid. Chemoreceptors in the medulla oblongata monitor the decrease in blood pH. The respiratory control centre of the medulla oblongata sends nerve impulses to the intercostal muscles and diaphragm, increasing the rate and depth of ventilation. SL and HL Content Exercise and Ventilation Rate After exercise, the level of respiration decreases, reducing the carbon dioxide concentration in the blood. Reduced levels of carbon dioxide in the blood increase the pH of the blood because carbon dioxide is removed from the blood. Chemoreceptors in the medulla oblongata monitor the increase in blood pH. The respiratory control centre stops sending signals to the diaphragm and intercostal muscles, and ventilation occurs. SL and HL Content From C3.1.16: Control of peristalsis in the the IB digestive system by the central nervous system and enteric nervous system Limit to initiation of swallowing of food and egestion of faeces being under voluntary control by the central nervous system (CNS) but peristalsis between these points in the digestive system being under involuntary control by the enteric nervous system (ENS). The action of the ENS ensures passage of material through the gut is coordinated SL and HL Content The Enteric Nervous System The autonomic nervous system is responsible for the control of bodily functions which are not under conscious control, such as breathing, control of heartbeat, and digestion. The enteric nervous system is a branch of the autonomic nervous system which controls the movement of food along the digestive system. The enteric nervous system ensures the Peristalsis coordinated movement of material through the digestive system through peristalsis. SL and HL Content Peristalsis Peristalsis is the involuntary relaxation and contraction of muscles, which move contents along the digestive system. Intestinal Peristalsis SL and HL Content SL and HL Content Control of the Digestive System Swallowing of food and egestion of faeces is under voluntary control of the central nervous system. Movement of food from the oesophagus to the rectum by peristalsis is under involuntary control of the enteric nervous system. SL and HL Content Review and Discuss: SL & HL Key Terms Cells Blood Plasma Multicellular Cerebral Cortex (Cerebrum) Tissues Cerebellum Organs Medulla Oblongata Organ Systems Hypothalamus Emergent Properties Pituitary Gland Nervous System Central Nervous System Endocrine System Brain SL and HL Content Review and Discuss: SL & HL Key Terms Spinal Cord Effector Conscious Processes Circadian Rhythms Unconscious Processes Melatonin Sensory Neurons Pineal Gland Interneurons Epinephrine / Adrenaline Motor Neurons Adrenal Glands Nerves Baroreceptors Pain Reflex Arc Chemoreceptors SL and HL Content Review and Discuss: SL & HL Key Terms pH Swallowing Ventilation Egestion Cardiovascular Control Centre Voluntary Control Respiratory Control Centre Involuntary Control Digestive System Peristalsis Autonomic Nervous System Enteric Nervous System SL and HL Content From C3.1 Integration of Body Systems - IB the IB Linking Questions What are examples of branching (dendritic) and net-like (reticulate) patterns of organization? What are the consequences of positive feedback in biological systems? SL and HL Content