16. The "Biological Concept of Species" from Mayr in 1942 is based on D. ability to interbreed. He considered reproductive isolation to be a key factor in the determination of one species from another. Why are the other answers not correct? Allopatric populations are those that live in different locations (allo- means different). Morphology and type specimens are key factors in identifying species, but they weren't part of Mayr's biological concept.

17. Populations of two different species with overlapping ranges are called sympatric species.

18. Incompatible male and female reproductive structures are an example of an intrinsic isolation mechanism. Intrinsic means internal, so the mechanism is within the animal. An extrinsic factor is one that is not part of the animal. Allopatric species do not live in the same areas, so it would not matter if their male and female parts are incompatible.

19. A method of both heat gain and loss would be conduction. Conduction is the transfer of heat energy via direct contact between two surfaces. So if an animal like a snake is sitting on a warm rock to warm itself up then the snake is gaining heat. If an animal chooses to swim in a cool river in order to lose heat, then that is also conduction.

20. The environmental factor most responsible for timing seasonal events in temperate time zones is the day length. The day length is a factor that stays consistent from year to year, unlike temperature and precipitation.

21. A - fresh water fish need to lose water to keep the homeostasis in their blood.

22. B - a camel has a wider range of tolerable temperatures to reduce water loss. If a person had a 7 degree temperature change we would start sweating and losing water, but a camel need to hold onto to as much water as possible.

23. B - the exoskeleton of an insect is like both the skin and bones of a mammal. So it serves to give the insect structure and protection and also to maintain the fluids in the insect. However, you could also make a case that the exoskeleton can decrease water gain for those insects that live in the water or are able to live in moist environments.

24. C - Plants with deep tap roots are able to draw water from deeper water sources. This means that they are in less competition with surface plants that remove water from the top of the soil.

25. C - these fungi help to basically extend the plant root system and help the plants get more water and minerals from the soil

26. C or B - I can think of two possible ways to look at this question. By growing low to the ground the pines are more protected from the constant winds on the mountain passes that can cause them to lose more water to evaporation. However, this species of pine is also known for helping to prevent erosion and to hold areas of snowpack in place, therefore also ensuring itself a more consistent supply of water. I suggest that you look at your course materials to see which of these examples was discussed.