Homeostasis in a Changing
Environment
Big Idea 2.D: Growth and dynamic homeostasis
are influenced by changes in the environment
Essential Knowledge
• 2D1: All biological systems from cells to organisms
to populations, communities, and ecosystems are
affected by complex biotic and abiotic interactions
involving exchange of matter and free energy.
• 2D2: Homeostatic mechanisms reflect both
common ancestry and divergence due to
adaptation in different environments.
• 2D3: Biological systems are affected by disruptions
to their dynamic homeostasis.
Organisms Respond to External Environments
What was this called???
External Environment
Made up of Biotic Things: Living
External Environment
And Abiotic Things: Not Living
TPS: With your partner, make a list
of 4 other biotic and 4 other
abiotic factors that may affect
organisms in an environment.
Case Study: Biofilms
• Bacterial cells attach to each other to form
biofilms (a protective protein matrix cover)
• Communal group for protection and shared nutrients
• Grow with limited nutrients.
Cells Interact with Biotic/Abiotic Factors
Organisms Interact with Biotic/Abiotic Factors
• Organisms access to nutrients is affected by other
factors
• i.e. symbiosis, predator-prey, nutrient availability etc
Interactions Among
Organisms
Symbiosis:
relationship b/t 2
species
•Mutualism (+,+)
•Commensalism (+,0)
•Parasitism (+,-)
Mutualism
• Both Species Benefit
• Rhinos and oxpeckers
Commensalism
• One member is helped, the other neither
benefits or is harmed
• Cows and Cattle Egrets
Parasitism
• + and - relationship
• parasite benefits,
host loses
• parasite usually
smaller than host
Leech Bite, Thailand
Lamprey
Ecosystems’ Stability is based upon
interactions w/ biotic or abiotic factors
Evolution of Homeostatic
Mechanisms
• Some mechanisms
are conservedshowing common
ancestry
• Others have changed,
demonstrating
divergent evolution
(due to changing
envs)
Case Study: Nitrogenous
Waste Removal
• All animals produce N byproducts
• Animals in diff. envs. have evolved different
mechanisms for excreting these wastes
Ammonia,
NH3
• Toxic byproduct of protein degradation
• In dilute concentrations is no big deal, so
aquatic orgs can excrete it into water
Urea
• Mammals convert NH3 into urea  travels
through blood to kidneys and is excreted w/
water and other substances as urine
Solid Uric
Acid
• In birds and reptiles
(and some desert
mammals) N waste is
excreted as a solid
• Prevents H2O loss
and buildup of H2O
waste in shell of an
egg
Evolution of Circulatory System Shows Common
Ancestry and Divergence
Evolution of Circulatory System Shows Common
Ancestry and Divergence
Disruptions at the Molecular/Cellular Level Affect
Organisms Homeostasis
• Exs: viral infection of a cell, allergies,
or dehydration in Willis’s body ;)
Disruptions to Ecosystems Affect Homeostasis
• Exs: food chain disruptions, natural
disasters, salination (adding salt)