PLEASE HELP I BEG YOU IM GONNA CRY :( 17. There are 3 populations of turtles. One population has a large shell, one population has a medium shell, and one population has small shells. To survive, turtles must have a large shell, to protect them from the turtle-eating predator. Over the next 100 years, the large shell turtles keep having babies, while the small and medium turtles slowly die. What type of Natural Selection is taking place?
a Disruptive Selection
b Directional Selection
c Stabilizing Selection
d None of the above

18. In the JuJu forest, there are plenty of tall and short trees. The tall-neck giraffe has plenty of food, and produces many tall giraffe babies. The short-neck giraffe has plenty of food and produces many short giraffe babies. The average-neck giraffe has a serious problem because he cannot eat from the tall trees, nor can he eat from the short trees. What type of Natural Selection is taking place?
a Disruptive Selection
b Directional Selection
c Stabilizing Selection
d None of the above

19. In the human population, people that are extremely skinny (anorexic) are having health problems. People that are extremely over-weight (obese) are also having health problems. People that are in the middle (average weight) seem to have the least amount of health problems. What type of Natural Selection is taking place?
a Disruptive Selection
b Directional Selection
c Stabilizing Selection
d None of the above

Turtle, (order Testudines), any reptile with a body encased in a bony shell, including tortoises. Although numerous animals, from invertebrates to mammals, have evolved shells, none has an architecture like that of turtles. The turtle shell has a top (carapace) and a bottom (plastron). The carapace and plastron are bony structures that usually join one another along each side of the body, creating a rigid skeletal box. This box, composed of bone and cartilage, is retained throughout the turtle’s life. Because the shell is an integral part of the body, the turtle cannot exit it, nor is the shell shed like the skin of some other reptiles.

There are approximately 356 species of turtles living on land in all continents except Antarctica and in both salt water and fresh water. Tortoises (family Testudinidae) live exclusively on land and have anatomic features distinguishing them from other turtles, but the term tortoise has long been used to refer to other terrestrial testudines as well, such as the box turtle and the wood turtle. Similarly, terrapin was sometimes used to describe any aquatic turtle but is now largely restricted to the edible diamondback terrapin (Malaclemys terrapin) of the eastern United States.

Despite turtles’ broad distribution, there are not and never seem to have been a great many species of turtles at any time over the course of their long evolutionary history. The small number of species, however, does not equate to a lack of diversity. There are turtles with carapace lengths (the standard way to measure turtles) of less than 10 cm (4 inches), as in the flattened musk turtle (Sternotherus depressus), and of more than 1.5 metres (4.9 feet), as in the leatherback sea turtle (Dermochelys coriacea). Some species live in seasonally cold climates with growing seasons of only about three months; others live in the tropics and grow year-round. Some tortoises rarely see water, while other turtles spend virtually their entire lives in it, be it in a single small pond or traveling the vast open ocean.

Such exploitation is not a recent phenomenon. For example, the Native Americans who settled Florida quite possibly ate its giant tortoises to extinction as early as 11,500 years ago. The first colonists of Madagascar eliminated that island’s giant tortoise (Geochelone grandidieri) between 2,300 and 2,100 years ago, and European settlers and sailors eliminated giant tortoises from the island of Mauritius during the 1700s and from Réunion by the 1840s. Every sea turtle species has long been killed for meat, with its eggs being harvested from beach nests as soon as they are laid. This practice now endangers many populations of sea turtles. Before 1969, for example, more than 3,000 female leatherback sea turtles emerged from the ocean annually to nest on the beaches of Terengganu, Malaysia. In the 1990s only 2 to 20 females appeared each year. Their disappearance resulted from years of excessive egg harvesting and the capture and slaughter of juveniles and adults during their migratory search for food. By the 2010s the species was virtually absent from Terengganu.

Overharvesting is not confined to large species. In China, turtles large and small are used for both food and medicine. By the early 1990s, many local populations of turtles had disappeared within the country, so turtles began to be imported from around the world. Some species, such as the three-striped box turtle, or golden coin turtle (Cuora trifasciata), are so popular for traditional Chinese celebrations and in traditional Chinese medicine that aquaculturists raise them and can sell individual turtles for tens of thousands of dollars (U.S.), an amazing price for a reptile less than 20 cm (about 8 inches) long.

Form And Function

The turtle’s shell is an adaptation that protects it from predators, which compensates for the reptile’s slow crawling speed. The carapace and plastron each arose from two types of bone: dermal bones that form in the skin and endochondral bone (bone arising from cartilage) derived from the skeleton. Evolution has intricately linked these two types of bone to produce the shell of modern turtles. The carapace consists of 10 trunk vertebrae and their ribs, which are overlain by and fused to dermal plates. Another series of dermal plates forms the perimeter of the carapace. The plastron usually contains four pairs of large plates and a single one centred near the front (the anteromedial plate); these plates are large dermal bones, although the anterior ones may contain parts of the shoulder girdle. The shell is variously modified and shaped to meet the needs of defense, feeding, and movement.

Explanation:

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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