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1 HOMEOSTASIS: Maintaining Living Systems Homeostasis: maintaining a relatively constant, stable internal environment • human body examples: • blood pH =7.4 body temp. = 37°C • blood pressure = 120/80 blood [glucose] = 0.1% Homeostatic Mechanisms: all the body systems help to maintain homeostasis. • Respiratory system: [gases] in blood ° take in O2 (used up) & remove CO2 (produced) • liver and kidney's: monitor and maintain constant blood chemistry Control of Homeostasis STIMULUS RECEPTOR Negative Feedback REGULATOR CENTER Normalcy ADAPTIVE RESPONSE NEGATIVE FEEDBACK MECHANISM Receptors (sensors) • detect unacceptable levels (e.g. if skin gets colder than 37°C temperature sensors detect change). • found all over body • sends signal to appropriate brain center Regulator Center • Brain control centers (e.g. in the hypothalamus) monitor and control body conditions (e.g. pH, temperature, glucose levels) Adaptive Response • An alternate behavior (e.g. shivering) • Directed by regulator center Normalcy • normal state is regained • Once normalcy is attained, sensor stops signaling the regulator center (negative feedback), so adaptive behaviour stops • results in a FLUCTUATION between two levels. 2 Positive feedback mechanisms exist but we will study these later BIOCHEMISTRY & CELL COMPOUNDS Biochemistry: the chemicals of life and their study Organic Chemistry: the study of carbon compounds Why Carbon? 1. has four available covalent bonds -- allows for other atoms to bind. 2. forms strong bonds with itself • forms long chains - straight or branched many combinations • Carbon single bonds rotate • Can form single, double, and multiple ring structures (e.g. glucose, nucleotides) C WATER - Structure, Properties and Importance Water is... • inorganic (contains no carbon) • covalently bonded, but is POLAR • held together by hydrogen bonds δ- O H δ+ H δ+ 3 POLAR – when electrons are not shared equally in a covalently bonded molecule • O has a slight net negative charge • H have a small net positive charge Hydrogen Bonds occur when H bonds with O, F or N • H bonds dotted line • Covalent and ionic bonds much stronger than H bonds • Numerous H bonds add up large effect explains some of the unique properties of water. δ+ H δ- H δ- O O H δ+ H δ+ O δ- δ+ H δ+ H δ+ Water is Essential to All Life • Life began in water • all living organisms are “water-based.” • living organisms have adaptations for maintaining water levels (e.g. human skin, plant stomata) Humans life requires water: i. we are ≈ 70% water. ii. only dissolved substances can enter cell membrane of our cells (e.g. glucose, amino acids). iii. water carries away dissolved cellular wastes and excreted wastes (sweat, urine) 4 can dissolve ions necessary for body processes (e.g. Ca++ for movement, Na+, iv. K+ nerve impulses) v. joints lubricated by a watery fluid vi. brains partially protected against shock by a watery layer vii. sense organs require water: eyes filled with thick fluid; hearing depends upon fluid-filled structure (Cochlea) that transmits vibrations. WATER HAS SEVERAL UNIQUE CHARACTERISTICS • abundant throughout biosphere • H-bonding causes a low freezing point and a high boiling point liquid at body temperature. • H20(l) H20(g) absorbs much heat before it warms up or boils • H20(s) H20(l) gives off much heat before it freezes • ° maintains ocean’s constant temperature ° accounts for cooling effect of sweating high COHESIVENESS (sticks to other materials and itself) good for transporting materials through tubes. • Density? H20(s) < H20(l) ° • ice will form on top Ice protect organisms below. dissolves other polar molecules good solvent in lab and our bodies ° promotes chem. Reactions ° Called the “UNIVERSAL SOLVENT.” ALL DUE TO HYDROGEN BONDING 5 ACIDS, BASES, & BUFFERS • ACIDS: compounds that dissociate in water and release H+ ions. (e.g. HCl, H2CO3, H2O) • BASES: • pH: measures concentration of H+ ions ° ° ° ° • compounds that dissociate in water and OH- ions. (e.g. NaOH, KOH, H2O) range 0 to14. pH ↓than 7.0 is acidic. pH ↑ than 7.0 is basic pH of 7 is neutral (pure water) pH formula: pH = -log[H+] -3 if [H+] = 10 ... pH=-log[10-3] = 3 • pH scale is a logarithmic scale ° ° ° each number on the pH scale = a difference in magnitude of 10. pH of 2 is 10 x more acidic than a pH of 3. pH of 2 is 100 x more acidic than a pH of 4. How does the basicity of ph 10 compare to pH 4? 10 - 4 = 6 ° ° ° tears ____ human blood ____ oven cleaner ____ pH of 10 is 1,000,000 x more basic than a pH of 4. What is the pH of the following (p.29)? ° stomach acid ____ ° beer ____ ° urine ____ • Why is pH important? (remember homeostasis) ° living things need a constant pH ° ∆ pH enzymes denature lose function ° livings cells use buffers keep pH constant. • ° ° BUFFER: chemical that take up excess H+ ions or excess OH- ions. Buffers resist changes in pH when acid or base is added. buffers can be overwhelmed too much acid or base added. • SALT: formed in a neutralization reaction between an acid and a base. e.g. HCl + NaOH ⇒ H2O + NaCl (table salt)