OCR GCSE Biology: Human Physiology and Homeostasis

OCR GCSE Biology: Human Physiology and Homeostasis (B5)

Introduction

This chapter delves into the fascinating world of human physiology, focusing on the circulatory and nervous systems, hormonal responses, and the crucial concept of homeostasis. You'll explore how your body maintains a stable internal environment despite external changes, and the key processes that make this possible.

1. Transport in the Human Body

• Diffusion: The movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient. This is a passive process, meaning it doesn't require energy. Examples include the movement of oxygen from the alveoli to the blood and carbon dioxide from the blood to the alveoli.
• Osmosis: The movement of water molecules from a region of high water potential to a region of low water potential, across a selectively permeable membrane. This is also a passive process. Examples include the absorption of water in the small intestine and the movement of water between blood plasma and cells.
• Active Transport: The movement of molecules across a membrane against their concentration gradient, requiring energy. This is an active process, utilizing ATP (adenosine triphosphate). Examples include the absorption of glucose and amino acids from the small intestine into the bloodstream and the reabsorption of water and glucose in the kidneys.

Practical Task: Investigating the rate of diffusion in different conditions (e.g., temperature, concentration) using agar blocks or a diffusion apparatus.

2. The Circulatory System

• Heart: The muscular organ that pumps blood around the body. It has four chambers: two atria and two ventricles.
• Blood Vessels: Arteries carry oxygenated blood away from the heart, veins carry deoxygenated blood back to the heart, and capillaries facilitate exchange of substances between blood and tissues.
• Blood: Consists of plasma, red blood cells (transport oxygen), white blood cells (fight infection), and platelets (involved in clotting).

Practical Task: Investigating the structure of the heart using a dissected model or diagram.

3. The Nervous System

• Structure: Made up of the brain, spinal cord, and nerves.
• Function: Coordinates responses to stimuli and controls bodily functions.
• Nerves: Bundles of nerve cells (neurons) that transmit electrical impulses.
• Synapses: Gaps between neurons where chemical messengers called neurotransmitters are released to transmit signals.

Practical Task: Measuring reaction time to a stimulus, demonstrating the speed of nerve impulses.

4. Hormonal Responses

• Hormones: Chemical messengers produced by endocrine glands, transported in the bloodstream to target organs.
• Examples: Insulin (regulates blood glucose levels), adrenaline (fight-or-flight response), and thyroxine (regulates metabolism).
• Mechanism of action: Hormones bind to specific receptors on target cells, triggering a response.

Practical Task: Researching the effects of different hormones on the body, considering their role in homeostasis.

5. Homeostasis

• Definition: The maintenance of a stable internal environment despite external changes.
• Importance: Ensures optimal functioning of cells and organs.
• Control Mechanisms: Involve negative feedback loops, where a change in a controlled variable triggers a response that counteracts the initial change.

6. Examples of Homeostasis

• Blood Glucose Regulation: The pancreas releases insulin to lower blood glucose levels and glucagon to raise them.
• Temperature Regulation: The body maintains a constant temperature through sweating, shivering, and vasoconstriction/vasodilation.

Practical Task: Monitoring body temperature and heart rate changes in response to exercise or exposure to cold/hot environments.

Conclusion

Understanding human physiology and homeostasis is crucial for appreciating the complexity and efficiency of the human body. This chapter provides a foundation for further exploration of how our bodies work and the intricate mechanisms that keep us alive and functioning.