Biology Exam Review
- 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
- Do not regulate body temperatures internally, have same internal temp as the surrounding
- 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
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
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
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
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.
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
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
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
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.
- 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.
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
- 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 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