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Organisms Respond to External Events
• I.e. taxis or kinesis– Many animals change
speed based on light (pillbugs run wild when exposed to light)
– Many animals change direction in response to stimuli (sharks swim towards blood)
• Plants grow towards light (phototropism)
Biotic vs. Abiotic Factors
Biotic = Living
• Animals• Plants• Fungi• Bacteria/
Archaeans
Abiotic = Non-living
• Sunlight• Water• Vitamins/
Minerals/ Nutrients• Temperature
Cells Are Affected by Both Biotic/Abiotic Factors
• i.e. bacterial cells attach to each other to form biofilms
• Cells shrink/grow depending on water availability
• Cells stop growing after a certain density (except in the case of cancers)
Organisms Interact with Biotic/Abiotic Factors
• Organisms access to nutrients is affected by other factors
• i.e. symbiosis, predator-prey, nutrient availability etc
Symbiosis-Two species living together
• Mutualism-both benefit
• Commensalism- one benefits, other unaffected
• Parasitism- one benefits at other’s expense
"live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance".
Evolution of Homeostatic Mechanisms
• Some mechanisms are conserved- showing common ancestry
• Others have changed, demonstrating divergent evolution
i.e. nitrogenous waste removal
• All animals produce nitrogen byproducts
• Animals in different environments have evolved different mechanisms for excreting these wastes
Ammonia
• Toxic byproduct of protein degradation
• In dilute concentrations is no big deal, so aquatic organisms can excrete it into water
Urea
• Mammals convert ammonia into urea
• Urea travels through the blood to the kidneys and is excreted with water and other substances as urine
Solid Uric Acid
• In birds and reptiles (and some desert mammals) nitrogen waste is excreted as a solid
• Prevents water loss and buildup of water wastes in the shell of an egg
Disruptions at the Molecular/Cellular Level Affect Organisms
• I.e. viral infection of a cell• Allergies• Dehydration
Disruption of One Organisms Affects Others
• I.e. disrupting the food chain• If you break one
link of the chain, everyone is affected• Toxins in one
organism get passed on
Biomagnification
• Toxins get concentrated as they move up the food chain
• So small amounts of mercury can become extremely toxic to polar bears (or humans!)
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