Unit 8: Organism Regulation, Physiology and Development

WHAT YOU MUST KNOW: 1. The importance of homeostasis from a cell to an organism to an ecosystem. 2. How feedback systems control homeostasis. 3. Examples of positive and negative feedback. 4. How systems are affected by disruptions in homeostasis. 5. How structures (adaptations) have evolved to maintain homeostasis showing common ancestry.

Feedback Loops Used at all levels of organization in living systems. Two types: Negative Feedback Positive Feedback

Negative Feedback They regulate systems or processes Maintains homeostasis at a set point or range The response (or feedback) to the stimulus decreases the occurrence of the stimulus or is opposite of the stimulus. Examples: Lac operon, temperature regulation, plant responses to water limitations, population growth, blood sugar and blood calcium regulation

Positive Feedback Amplifying in nature The response is to amplify or increase the occurrence of the stimulus. Examples: labor, fruit ripening and lactation in mammals

Effects of Disruptions Seen at all levels of organization Molecular and cellular level: Ex: Response to toxins interferes with specific metabolic pathways or cause cell damage Ex: Dehydration Too much water loss causes cellular environment to be too hypertonic. Cellular work stops. Death… Ex: pH change in the bloodstream Ex: blood sugar concentrations

Ecological Disruptions Affects balance of the ecosystems Examples: Invasive species: outcompetes native species or places a rapid stress on natives Natural disturbances: fires, earthquakes etc.

Otherwise, disease, degradation and death are unavoidable.  Note: as long as disruption is not too large and too rapid for homeostatic feedback loops to function, rebound will occur. Otherwise, disease, degradation and death are unavoidable. 

Physiological Interactions Multicellular organisms are organized into organ systems, which contain organs that work together to accomplish life processes. Organ systems also interact for life processes Examples: Stomach and small intestine Plant organs Respiratory and Circulatory System Nervous and Muscular System Kidney and bladder

Animal systems evolved to support multicellular life CHO aa CH CO2 NH3 single cell aa CO2 NH3 O2 CH CHO intracellular waste but what if the cells are clustered? extracellular waste Diffusion too slow! for nutrients in & waste out

Circulatory systems Basic structures needed: circulatory fluid = “blood” tubes = blood vessels muscular pump = heart open closed hemolymph blood

Vertebrate circulatory system Adaptations in closed system number of heart chambers differs 2 3 4 high pressure & high O2 to body low pressure to body low O2 to body What’s the adaptive value of a 4 chamber heart? 4 chamber heart is double pump = separates oxygen-rich & oxygen-poor blood; maintains high pressure

Gas exchange in many forms… one-celled amphibians echinoderms cilia insects fish mammals size • water vs. land • endotherm vs. ectotherm

Evolution of gas exchange structures Aquatic organisms external systems with lots of surface area exposed to aquatic environment Terrestrial Constantly passing water across gills Crayfish & lobsters paddle-like appendages that drive a current of water over their gills Fish creates current by taking water in through mouth, passes it through slits in pharynx, flows over the gills & exits the body moist internal respiratory tissues with lots of surface area

Nitrogen waste Aquatic organisms Terrestrial Terrestrial egg layers can afford to lose water ammonia most toxic Terrestrial need to conserve water urea less toxic Terrestrial egg layers need to conserve water need to protect embryo in egg uric acid least toxic Mode of reproduction appears to have been important in choosing between these alternatives. Soluble wastes can diffuse out of a shell-less amphibian egg (ammonia) or be carried away by the mother’s blood in a mammalian embryo (urea). However, the shelled eggs of birds and reptiles are not permeable to liquids, which means that soluble nitrogenous wastes trapped within the egg could accumulate to dangerous levels (even urea is toxic at very high concentrations). In these animals, uric acid precipitates out of solution and can be stored within the egg as a harmless solid left behind when the animal hatches.

why selective reabsorption & not selective filtration? Nephron Functional units of kidney 1 million nephrons per kidney Function filter out urea & other solutes (salt, sugar…) blood plasma filtered into nephron high pressure flow selective reabsorption of valuable solutes & H2O back into bloodstream greater flexibility & control Each nephron consists of a single long tubule and a ball of capillaries, called the glomerulus. The blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule, that surrounds the glomerulus. Each human kidney packs about a million nephrons. why selective reabsorption & not selective filtration? “counter current exchange system”