This document is a biology module summary from snaprevise.co.uk about communication, homeostasis, and energy. It covers two topics: communication and homeostasis, including cell signaling, negative and positive feedback, and temperature regulation in endotherms and ectotherms. The second topic discusses excretion as an example of homeostatic control, covering the roles of the liver and kidneys in removing nitrogenous and carbon dioxide waste from the body. The summary is designed to concisely explain the content for exam revision in a clear presentation.

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BIOLOGY
SUMMARY
COMMUNICATION,
HOMEOSTASIS AND ENERGY
MODULE 5

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3. MODULE 5
Communication, Homeostasis & Energy
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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 + CO2
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 H2
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

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