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Biology Exam Review.docx

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BIOL 1070
T.Ryan Gregory

Biology Exam Review INQUIRY 3: WEEK 8: - CO2 in the air influences overall temperature of planet - The North Pole may become up to 8 degrees warmer unless we slow down GHG emissions - In the high Arctic, near the communities of Resolute and Devon Island, much of the terrestrial environment is dominated by tundra. However, even at very high latitudes, there are both freshwater (rivers, ponds, lakes) and marine (Arctic Ocean) habitats. Endotherms (marine mammals): - Have a thick layer of insulating blubber just under the skin - Generate their own heat through metabolism - “Inside heat” and restricted to mammals and birds Ectotherms: - Do not regulate body temperatures internally, have same internal temp as the surrounding water - Fish, amphibians, reptiles and invertebrates rely on outside heat Plants in the Arctic face a short growing season and challenges related to the cold. Vascular plants in the Arctic tend to be small and freeze tolerant. Lichens are even better suited to these harsh conditions because they lack roots, do not require soil and are tolerant of very low temperatures Populations: Within a group of individuals of the same species living together climate change may affect survival, growth and reproduction. For example, an Arctic plant may thrive as temperatures increase, but they may now dominate an area where a competing species is negatively impacted by increased temperature. Communities: When one considers populations of different species living in the same area, climate change may cause changes in species distribution or frequency within that community. Ecosystems: Within the broader context of an entire ecosystem (e.g. arctic ecosystem), climate change may have many complex effects that influence nutrient cycling between the abiotic and biotic factors. Temperature impacts the motion of molecules. Higher temperatures increase motion, lower temperatures decrease motion. Most macromolecules (e.g. lipids, proteins, nucleic acids) are sensitive to temperature change. For example, there is a class of proteins called enzymes that act as catalysts to speed up reactions within cells. Enzymes typically function best within the normal range of temperatures that the cell experiences. Generally, a decrease in temperature will slow down enzyme function and the reaction will be slower, and an increase in temperature will speed up an enzyme reaction in the short term. Longer term adjustments in enzyme function may occur that help correct any negative effects of temperature perturbances, or in some cases temperature changes will permanently damage macromolecules. Click for larger image. Temperature changes may cause cells to undergo a stress response. For example, most plant or animal cells can tolerate a brief increase in temperature, but if longer the cell may die mostly because enzymes are not functioning properly. The cell stress response usually involves an increase in the amount of heat-shock proteins (HSPs). HSPs are proteins that attach to other proteins and stabilize them. When temperatures decrease back to normal, the HSPs release their bound proteins which then can return to their normal “job” in the cell. At higher levels of organization, temperature changes can have more complex effects. Arctic Char (Salvelinus alpinus) are found in cold arctic lakes, rivers and oceans. As ectotherms, their body temperature is matched to the temperature of the surrounding water. An increase in water temperature will increase the amount of blood the heart pumps per minute. This increased output from the heart, plus other temperature effects on the properties of the blood and blood vessels, will induce multiple changes within the cardiovascular system. Endotherms regulate body temperature (thermoregulation) by sensing changes in internal temperature and altering physiological processes and behavior to bring internal temperatures back to normal. What are physiological processes? An example would be if a caribou is too warm after running away from a predator it will pant to dissipate some of the extra body heat. After panting for a few minutes some of the excess internal heat is lost to the environment, bringing the body temperature back to ~37ºC and then a signal turns off the panting response. In this way, body temperature is regulated (we will discuss this in more detail later). Just to make sure you understand the difference between endotherms and ectotherms, have a look at the x-axis (ambient temperature) and y- axis (body temperature) on this graph. Make sure you could plot a similar graph if you were asked to show the relationship between external and internal body temperature in different animals from the arctic. Homeostasis is the maintenance of a constant internal environment. As you know, endotherms maintain body temperature within narrow limits. Of course, ectotherms don’t maintain a constant body temperature, but other factors (e.g. ions, oxygen) are under homeostatic control. WEEK 9: Challenges of Living in the Arctic:  Processes with which Arctic Animals Exchange Materials with External Environment: 1. Gases – most animals require O2 for metabolism and release CO2 as the respiratory waste product. 2. Nutrients – animals utilize many different types of food, obtaining carbohydrates, fats, and proteins in their diets. 3. Wastes – fluid and solid wastes from digestion and metabolism are released. Animals must also balance the ion composition of their internal fluids. Ions are obtained from food or directly from the environment (especially in aquatic animals).  In cells, exchange occurs across the cell membrane. The fluid surrounding cells is called the interstitial fluid. Complex animals must also have a circulatory fluid that carries gases, wastes, and nutrients to the interstitial fluid. As well, respiratory systems and digestive systems have direct contact with the external environment. Homeostasis and Feedback Mechanisms:  To varying degrees, animals maintain relatively constant internal conditions in the face of a fluctuating external environment. This is particularly pronounced in endotherms (mammals and birds), which regulate body temperature to within a narrow range around a set point, along with other variables such as blood pH, ion concentration, and glucose. Ectotherms (e.g., amphibians, fishes) do not regulate temperature, but do regulate many other internal variables, such as blood [Na+].  Thermoreceptors send information to the hypothalamus in the brain if the skin and body temperature is below or above the set point. This information is integrated in the brain to bring about a response that will regulate body temperature back to the set point. In this way a stimulus brings about a response that compensates for the disturbance. In other words, negative feedback results in lowering a variable that is too high or elevating a variable that is too low.  Not all feedback control is negative. Positive feedback is not as common because it pushes the system farther and farther away from the initial state. For example, during the birthing process in mammals the hormone oxytocin is released and oxytocin stimulates uterine contractions. As the uterine muscles contract, signals are sent that reinforce or strengthen these contractions (positive feedback). This process continues until the fetus is born. In positive feedback loops, there must always be a natural endpoint (infant is born, uterine muscles relax, system returns to “normal”), otherwise serious problems would arise. The Physiology of Climate Change: - Different time scales: acute (short-term), chronic (long-term within an organism’s lifetime), and generational (across multiple generations). Adjustment by individual organisms to chronic stresses is known as acclimatization, whereas the evolution of populations across generations under natural selection is adaptation. - In their natural environment, Arctic plants and animals acclimatize to environmental conditions at that particular time of the year. In the summer months, for example, an Arctic char is more tolerant of warmer water temperatures relative to the winter months. This is because as seasons change, temperature, photoperiod, food availability and a host of other external factors may also change, in turn modifying the physiology of the fish over that period of time. Cell Membrane Acclimatization:  One example of temperature acclimatization occurs at the macromolecular and cellular level. Ectotherms change the composition of their cell membranes with changing temperatures to maintain membrane fluidity. Cell membranes are composed of lipids with embedded membrane proteins. The lipid molecules (e.g. phospholipids, cholesterol, glycolipids) vary in their chemical properties and different lipids have different influences on membrane fluidity. If an Arctic char is exposed to lower water temperatures, body temperatures will decrease and initially cell membranes will become more rigid and less fluid. The fluidity of the membrane affects how the cell functions and therefore the fish will alter the lipid composition over days to weeks to maintain membrane fluidity under these new colder conditions.  . The maintenance of relatively constant membrane fluidity regardless of tissue temperature is called “homeoviscous adaptation”. Ectotherms exposed to seasonal changes in temperature in the Arctic undergo cell membrane acclimatization between seasons. Circadian Rhythms: - Most living things are exposed to a rhythm of light and dark. In plants and animals, many physiological processes and behaviours are linked to a 24 hour cycle (e.g. body temperature in endotherms, sleep patterns, behaviours associated with feeding). If the pattern observed follows a rhythm over 24 hours, this is called a circadian rhythm. - Circadian rhythms are controlled by an endogenous or internal mechanism that acts like a clock. The internal biological clock is set by external light conditions (e.g. travel to a new time zone, eventually your sleep pattern will adjust), but is not dependent on light (e.g. if you live in a cave with complete darkness, you will still sleep for ~8 hours out of every 24 hour period). Longer time cycles also occur, such as circannual rhythms that proceed over the course of a year. WEEK 10: Body Size and Surface Area: - Exchange with the environment and amount of material that must be exchanged are strongly influenced by body size and surface area - One of the important characteristics that changes according to body size is surface area to volume ratio. This is the amount of surface area exposed to the environment relative to the total volume of the object. Smaller objects have higher surface area to volume ratios than larger objects. - The environment is not very efficient for large animals. To compensate for this, many organs involved in exchange do not have simple flat membranes, but folded or convoluted ones that have very high total surface areas. Examples include membranes in the digestive, respiratory, and circulatory systems — in humans, each of these has 25X greater overall surface area than the skin. The key points are: 1) Bigger body size means lower surface area to volume ratio, which means less efficient exchange with the environment. 2) When more surface area is needed, organs may have specialized structures that increase total ar
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