Biology Exam 3 Study Guide PDF

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HOMEOSTASIS Define homeostasis, and provide examples a. Homeostasis (from Greek “standing the same”): the maintenance of the internal environment for proper biochemical and physiological function, at both the cellular and organismal levels b. What needs to be maintained? Anything that impacts biochemistry/enzyme function must be maintained within an appropriate range c. EXAMPLES: i. Molecule concentration/ water balance (hydration) ii. Kinetic energy of molecules (level of motion= temperature) iii. Acid-base balance (pH) d. Relies on a NEGATIVE FEEDBACK LOOP Summarize the principles and mechanisms of active vs. passive transport at the cellular and organismal levels a. List some of the hydration and nourishment challenges of multicellularity and living on land, and outline different solutions to these problems a. Explain the significance of negative vs. positive feedbacks a. Negative Feedback: processes that are inhibited by their own outcomes, resulting in self-regulating systems i. A change in the system elicits a response that opposes or resists that same change, thus keeping the output near a SET POINT ii. EXAMPLES: 1. Body temp. Goes up --> increased temperature elicits sweating -> body temperature goes down 2. Body temperature goes down --> decreased temperature elicits shivering--> body temperature goes up

3. Hydration level increases--> thirst is suppressed while the kidneys dump more water--> hydration level decreases 4. Hydration level decreases --> thirst is provoked while the kidneys retain more water--> hydration level increases iii. Negative feedback regulation in response to increased body temperature in humans: 1. Increased body temperature causes the hypothalamus to trigger and increases sweating and blood vessel dilation, thus increasing the rate of heat dissipation so body temperature will fall iv. Important in constraining internal conditions around a set point (homeostasis) v. Spermatogenesis: negative feedbacks constrain sperm production vi. Oogenesis/menstrual cycle: combination and sequencing of negative and positive feedbacks result in a monthly cycle b. Positive Feedback i. The outcome of a process amplifies rather than diminishes the process, thus creating a “runaway train” type of scenario that drives a system away from the set point 1. Not involved in homeostasis, since they drive the system OUT of balance..... but still useful and necessary at times 2. Usually associated with a temporary physiological changes and emergencies 3. Examples: childbirth, vomiting, blood clotting, the “fight or flight” amp up response ii. Drive systems rapidly away from set point Describe the different categories of hormones and the roles they play in homeostasis a. Hormones: long-distance signaling molecules in MULTICELLULAR organisms that are important in DRIVING and COORDINATING cell activities and responses to the environment (including homeostasis)

i. Carried via bulk flow ii. Produced by the endocrine system iii. Evoke targeted responses in key cells 1. May act at the surface by binding a cell-surface receptor 2. Hydrophobic hormones may pass through the cell membrane into the cell, where they can initiate responses, such as turning on a transcription factor b. Different Categories of Hormones i. Amines: derived from Amino acids 1. Must be built specially as part of a dedicated metabolic pathway 2. Hydrophilic: soluble in water, not lipids 3. Names ending in -ine ii. Peptides: short amino acid chains; essentially very short simple proteins 1. Can be built simply by stringing together amino acids in different combinations, as cells already do to build proteins 2. Hydrophilic 3. Names ending in -in iii. Steroids: ring-structure molecules 1. Must be built specially as part of a dedicated metabolic pathway 2. Hydrophobic: soluble in lipids, not water 3. Names ending in –ol or –one iv. Cell surface-receptors 1. Peptide and amine hormones are hydrophilic and bind to cellmembrane receptors activating second messenger pathways, which change the functional state of the target cell v. Intracellular receptors 1. Steroid hormones are hydrophobic and diffuse into the target cell, where they bind a cytoplasmic or nuclear receptor that allows

them to act as transcription factors to alter the gene expression of the cell c. Signal control example: constraining blood sugar levels in humans i. The pancreas produces both the hormones insulin and glucagon 1. Insulin: signals the liver and body cells to take up sugar from the blood stream 2. Glucagon: signals the liver to release more sugar into the blood stream ii. High blood glucose stimulates the production of insulin but inhibits the production of glucagon iii. Low blood glucose stimulates the production of glucagon but inhibits the production of insulin d. Another view of hormone-managed homeostasis of glucose in the bloodstream, via negative feedback loops i. Increase in blood glucose stimulates pancreas production of insulin but inhibits pancreas production of glucagon, and vice-versa e. Different species can respond wildly differently to the same hormones i. Example: Thyroid-Stimulating Hormone (TSH) 1. Mammals: TSH regulates metabolism via the thyroid 2. Amphibians: TSH triggers metamorphosis 3. Birds: TSH triggers feather molt 4. Snails: TSH influences the number of eggs and sperm produced f. How do cells “hear” chemical messages? Via chemoreceptors i. How? Binding triggers the response pathway ii. No ACTIVE chemoreceptors = no response g. A single cell may have multiple ACTIVE vs. INACTIVE chemoreceptors of different types and varying sensitivity h. Different cells may respond to a signal differently, and even a SINGLE cell may exhibit different responses at different times

i. Depends on what??? Depends on which chemoreceptors are active, and how sensitive they are 1. LOW hormone levels only trigger the most sensitive chemoreceptors; when hormone levels are higher less sensitive receptors and their responses kick in too. i.

Hormones elicit specific responses in target cells i. Nature of the response depends on which hormone receptors and associated response (signal transduction) pathways they express.

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A single hormone can evoke a wide variety of responses in different cells, such that different tissues of the body often respond differently to the same hormone i. Example: the plant hormone auxin causes shoot cells to elongate but inhibits root cells from elongating, amid other myriad functions ii. Example: ADH is best known for regulating urination in mammals, but an ADH receptor in the rodent brain seems to play a role in mating behavior 1. Mice: promiscuous – don’t form lasting pairings 2. Prairie voles: highly monogamous- pair bond for life a. Insertion of a brain receptor gene for ADH (along with its regulatory sequences) from the prairie vole into mice results in less promiscuous mice iii. Example: estrogen, testosterone, and other hormones associated with reproduction have different effects in different tissues of men vs. Women

k. Hormonal control of human gametogenesis i. Gonads produce gametes (and hormones) ii. Gametogenesis is under hormonal control iii. The hypothalamus/pituitary/gonad endocrine axis 1. Hypothalamus and pituitary (brain) 2. Gonads (testes and ovaries) 3. Negative feedback constrains sperm production at a constant level

4. Feedback shift on a cycle for monthly egg production l. Control of spermatogenesis i. Hypothalamus ---> (+) stimulates GnRH (gonadotropin-releasing hormone) ii. Pituitary -----> (+) stimulates LH (luteinizing hormone) and FSH (follicle stimulating hormone) iii. LH stimulates testosterone production and FSH stimulates sperm production iv. In turn inhibits the production of LS and FSH by the pituitary gland v. Negative Feedback: sperm production constant and constrained vi. What would added GnRH do to the system? 1. The amount of LH, FDH, and testosterone produces would all go up vii. The increased testosterone would in turn have what impact on the system? 1. It would result in greater suppression of LH and FSH production by the pituitary gland, tending to push LH and FSH back down (or at least resisting it further rises in their levels) viii. Now suppose more testosterone was added to the system, what effect would this initially have? 1. It would tend to lower LH and FSH ix. As LH and FSH production decrease in response to increased testosterone, what would tend to happen to testosterone production? 1. It would tend to go back down x. What kind of feedback is this? 1. Negative xi. Suppose that the LH and FSH receptors on the testes have become more insensitive to binding—they aren’t activated as easily by LH and FSH. What would the overall outcome be?

1. The negative feedback would remain, but LH and FSH production would consistently be depressed below normal m. Control of oogenesis i. Follicular phase: beginning 1. Hypothalamus stimulates GnRH secretion 2. Pituitary stimulates LH and FSH in low levels to ovaries 3. Ovaries in turn inhibit low levels of estradiol to the pituitary 4. The uterus also responds to estradiol: the ovaries coordinate egg production with uterine development (pair the ovarian and uterine cycles) a. Arteries to uterine lining (endometrium) constrict---> menstruation 5. Negative feedback: LH and FSH stay present but low ii. Follicular phase: early to middle 1. Stimulated by the FSH, follicle structures, each containing an oocyte (egg cell), begin to grow on the ovary and produce estradiol 2. Estradiol, heightening to mid-levels by the extra estradiol production contributed by the follicles, continues to inhibit the hypothalamus and pituitary but now stimulates the endometrium to thicken (the arteries feeding it are no longer constricted) 3. Negative feedback: LH and FSH stay present but low iii. Follicular phase: end 1. As the follicles continue to grow, they produce more and more estradiol pushing it to high levels, at which point it flips from inhibiting to stimulating LH and FSH production 2. The surge in LH prompts the dominant ovarian follicle to cough up its egg= ovulation 3. Positive Feedback: LH and FSH ramp up

iv. Luteal phase 1. The one mature follicle becomes the corpus luteum, which produces progesterone to maintain the uterine lining 2. The other follicles degenerate and stop producing estradiol, causing it to drop back down to mid-levels 3. Negative feedback reestablished: LH and FSH return to low constant level n. Questions: i. Estradiol binds receptor proteins on the cells of the hypothalamus and pituitary. When bound, these receptor proteins activate a pathway that inhibits LH and FSH production by the gland cells. Suppose now that the gland cells actually have more than one receptor: one of these inhibits LH and FSH production when bound by estradiol, but the other is attached to a different pathway that actually stimulates LH and FSH production when bound to estradiol. What would be the outcome of this? 1. The two receptors would be in competition, so suppression vs stimulation would always be dependent on whichever receptor pathway was more strongly activated overall Outline the two main strategies and three main mechanisms of homeostasis a. Conformity: evolutionarily adapt or physiologically adjust the internal variable to match that of the external environment i. Be adapted to internal conditions to simply reflect external conditions 1. Example: the organism’s biochemistry (enzymes etc.) works well under the prevailing environmental temperature, rather than the organism needing to maintain an internal temperature different from that of the outside 2. Example: adjust the internal solute concentration of the cell to match that of the outside environment, rather than constantly adjusting water against the gradient

b. Regulation: actively set and maintain the given internal variable at a set point consistently different from that of the external environment i. Constantly work to actively maintain the difference c. For any given variable, an animal may be a conformer, a regulator, or something in between i. May be a conformer for one variable but a regulator for another ii. Something in between: may conform or regulate up to a point- for example, mainly conform but begin to regulate if the environment falls outside a broad acceptable range. d. Passive i. Morphological: different body shapes maximize vs. Minimize relative proportion of organism’s mass that is exposed to the environment surface area for heat exchange with the environment 1. Thicker body: lower proportion of body mass at the surface= less heat exchange 2. Thinner body: higher proportion of body mass at the surface= more heat exchange ii. Chemical: carbonate buffering of blood pH e. Behavioral i. Reflexive: touch a hot surface, hand jerks away ii. Conscious: choose to move to another environment f. Physiological/ biochemical i. Sweating vs. Shivering, increased vs. Decreased blood flow, uncoupling of cellular respiration from ATP production, etc. ii. Negative feedbacks are very important in active homeostatic control 1. Negative feedback loop: the outcome of a process back and inhibits the process, making it self-limiting or self-defeating. Relate the characteristics, advantages, and disadvantages of thermoconformer and thermoregulator animals

a. Thermoconformer i. Poikilotherms (“variable temperatures”): have a body temperature that simply changes with the environment b. Thermoregulator i. Homeotherms (“constant temperatures”): maintain a specific body temperature (set point) constantly c. We can classify animals by whether they regulate their body temperature (Poikilotherms and Homeotherms) and by whether they have the ability to generate heat metabolically in order to achieve homeothermy i. Ectotherms (“outside temperatures”): have NO ability to maintain temperature metabolically, but may still achieve some homeothermy behaviorally (by moving to stay in a good temperature environment) 1. Generally temperature conformers a. Are frequently poikilothermic: their body temperature tends to vary with the environment b. Those that do achieve a degree of body temperature regulation (homeothermy) tend to do so primarily via behavioral means ii. Endotherms (“inside temperatures”): DO have the ability to maintain a set temperature metabolically and thus do achieve homeothermy 1. Generally temperature regulators a. Primarily utilize physiological mechanisms to maintain an internal set point for body temperature (which may vary with age) b. Capitalize on heat produced as a byproduct of metabolism: use metabolic reactions (=biochemistry) to establish an internal temperature that is warmer than that of the environment

i. All metabolic reactions produce heat as a byproduct, the key is having processes that are dedicated to doing so c. Advantage: effectively maintain an optimal temperature for enzymes; higher body temperature allows for generally higher metabolic rates and thus activity levels (not being sluggish in the cold) d. Disadvantage: higher energy cost= greater food demands e. All biochemical reactions generate heat as a byproduct, but only endotherms have metabolic mechanisms expressly dedicated to heat generation i. Examples: 1. Shivering: muscle contraction requires ATP to occur and generate heat as a byproduct. Shivering is the rapid twitching of muscles for no purpose other than just to generate heat 2. Burning of brown fat via UPC1: UPC1 (uncoupling Protein 1). Cellular respiration involves using the energy insugar to set up a separation of protons across the inner membrane of the mitochondrion. These proteins then pass down their electrochemical through ATPase to generate ATP. UPC1 is a channel in the membrane that opens and allows the protons to simply pass through down their electrochemical gradient, without passing through ATPase. The energy release

associated with this transit that would normally have been captured as ATP is instead simply disippated as heat d. So what’s the difference between ecto- vs. Endo- and poikilo- vs. Homeothermy exactly? i. Concept one: do you do something to try to maintain a constant internal body temperature against changing environmental temperatures, rather than just allowing your body temperature to be at the mercy of the environment? 1. Yes: you are a homeotherm 2. No: you are a poikilotherm ii. Concept two: More specifically, do you have the ability to burn energy for the express purpose of generating heat as your method of maintaining a certain set body temperature? 1. Yes: you are an endotherm 2. No: you are an ectotherm e. A passive strategy: circulation layout and thermoregulation i. One challenge endotherms face: problem of constantly having to spend energy to replace heat that is lost to the environment ii. Specifically problematic is waterfowls and dolphins, since they have thin feet and fins from which heat is rapidly lost to the surrounding cold water iii. A passive solution: run the blood vessels that circulate through these limbs close together to recapture some of the heat via countercurrent exchange before it is simply lost to the environment f. The cost of thermoregulation i. The key to endothermy is having metabolic pathways/ physiological activities whose whole purpose is the heat release

1. Endothermy involves deliberately converting energy stores to heat- like burning the energy for no other purpose; heat is the intended product rather than just a byproduct 2. Examples: shivering (using ATP for rapid muscle contractions for no other reason that just because it also produces heat), allowing protons from the cellular battery to flow through an open channel rather than ATP synthase (so that the energy shift will be entirely dissipated as heat rather than capturing some of it as ATP) QUESTIONS: g. Endotherms typically maintain an internal temperature set point that is higher than that of their environment, always (as opposed to holding the same or a lower temperature than their environment). Why- how does this make sense? i. Because it’s easier to generate heat than to shed heat h. The warmer an organism is, the faster its biochemical reactions and thus metabolism can be, which is generally a good thing. Why don’t all animals adopt the strategy of endothermy then, with the warmer the better? i. Because maintaining a temperature higher then the environment has a large energy cost, and the warmer the set point relative to the external environment the greater the cost i.

Would an ectothermic homeotherm also be expected to maintain a body temperature higher than that of the surrounding environment? i. No

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Most marine animals are poikilothermic ectotherms rather than endoderms. Why us ectothermy/poikilothermy a particularly effective strategy in the ocean? i. Because the ocean tends to have a fairly constant temperature year round without any great fluctuations

k. What makes sweating so effective? Identify the mechanism below that correctly explains why sweating works so well

i. Warm water carries heat from the inside to the surface of our body, where it warms even more and evaporates taking the heat with it Sketch the Kleiber curve and explain why it has the shape it does. a. In 1929, Max Klieber built respiration chambers to measure oxygen consumption rate of animals as a function of body mass and other variables b. Oxygen consumption rate = aerobic cellular respiration rate = energy use rate = metabolic rate c. Energy demand does increase with size, but not linearly: larger animals use more energy overall, but actually use less energy per unit mass d. The metabolic rate increases with mass, scaling to the ¾ power: metabolic rate = 70 x mass ^¾ i. That is, metabolic rate is proportional to mass 0.75 ii. End result: the metabolic increase is smaller than the mass increase, meaning larger animals have a lower metabolic rate pound for pound

LEARNING CATALYTIC QUESTIONS 1. Which of the following terms are associated with endothermy? a. Thermoregulation b. Set point c. Physiological/biochemical mechanisms 2. Why does the relative cost of homeostasis—and especially endothermy—decrease with increasing body size? a. Larger animals have lower perc...