A-LEVEL BIOLOGY MODULE 5: Communication, Homeostasis & Energy

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A-LEVEL BIOLOGY MODULE 5: Communication, Homeostasis & Energy TOPIC 1 Communication & Homeostasis Need for communication Organisms must maintain certain conditions Optimal conditions for cells and

1 A-LEVEL BIOLOGY MODULE 5: Communication, Homeostasis & Energy TOPIC 1 Communication & Homeostasis Need for communication Organisms must maintain certain conditions Optimal conditions for cells and enzymes Cell signalling Communication between cells Neuronal system Hormonal system Homeostasis = regulation of internal environment Despite external changes Temperature ph Water content Blood pressure Negative feedback Reversal of change back to optimal level Change detected by sensors Effectors act to oppose change Optimal condition restored Positive feedback Change exaggerated Stimulus = change in environment that initiates a response Can be external or internal environment Response = reaction to stimulus Endotherms Maintain constant body temperature Internal sources of heat Activity possible in cool temperatures Higher caloric requirements Adaptations: Sweat glands on skin Capillaries near skin surface Hairs on skin Ectotherms External environment controls body temp Less food required More energy available for growth Warm up by lying on hot surfaces When active, muscles generate some heat Rely heavily on behaviour to help maintain body temp TOPIC 2 Excretion as an Example of Homeostatic Control Excretion = removal of metabolic waste from body Metabolic waste = unneeded byproducts of normal metabolism Carbon Dioxide Harmful in excess (disturb ph balance) Carried in blood buffer system Removed by lungs Nitrogenous waste Excess amino acids deaminated in liver Converted into ammonia then urea Urea excreted in urine by kidney Mammalian liver Blood flow Oxygenated blood in hepatic artery Deoxygenated blood in hepatic portal vein (also carries products of digestion) Blood exits via hepatic vein Oxygenated and deoxygenated blood mixes in sinusoids Liver cells ( hepatocytes ) Cuboidal with microvilli Multifunctional Kupffer cells Specialised macrophages in sinusoids Break down old RBCs into bilirubin Deamination Amino acids keto acids + ammonia Ornithine cycle Ammonia + CO 2 urea Urea excreted by kidney Kidney Nephron = functional unit Filter waste from blood Structure and function Bowman s capsule: ultrafiltration PCT: selective reabsorption including glucose reabsorption Loop of Henle: water reabsorption DCT: osmoregulation Blood vessels: Glomerulus Afferent arteriole Efferent arteriole Peritubular capillaries Vasa recta Vanule In PCT: Reabsorption of salts, glucose and H 2 O 85% of water reabsorbed here In descending limb: Salts added; water removed Water potential decreases In ascending limb: Salts removed (active) Water potential increases In collecting duct: Water removed; water potential decreases Ultrafiltration Blood enters glomerulus via afferent arteriole Afferent diameter > efferent diameter Therefore blood is under high pressure Small solutes enter bowman s capsule 3 layers to pass through: Capillary endothelium Basement membrane Epithelial cells of bowman s capsule Super concise & exam board specific videos, notes & summaries by A* students at snaprevise.co.uk

The Excretory System. Biology 20

The Excretory System. Biology 20 The Excretory System Biology 20 Introduction Follow along on page 376 What dangers exist if your body is unable to regulate the fluid balance of your tissues? What challenged would the body have to respond