Amoebas use extensions of their cell membrane (called pseudopodia) to move, as well as, to engulf food. When the pseudopodium traps a bit of food, the cell membrane closes around the meal. This encasement forms a food vacuole. Hope this helps.
Answer: D. They are not well adapted to the Australian climate.
Explanation:
Just took the exam
Answer:
Helper T cells stimulate B-cells to produce antibodies and killer T cells to destroy the non-self cells. Cytotoxic T cells on the other hand are direct attack cells. They can kill the micro organisms by creating pores on the invader's cell.
Explanation:
T lymphocyte mediated immunity of cell mediated immunity do not secrete antibodies but they help stimulate the B cells to produce them. Immature T cells are produced in bone marrow from where they migrate to thymus via blood. In the thymus maturation of T cells occur and then they migrate to lymphoid tissue and get differentiated into three types:
a. Helper T cells: As the name suggests, they help in activating other immune cells, in other terms they are the regulator of virtually all functions of immune system. Protein mediator called lymphokines are produced by these helper T cells in order to regulate the immune functions. Some examples of these lymphokines are: Interleukin-2 interleukin-3, interferon gamma. T helper cells stimulate the B-cells to produce antibodies.
b. Cytotoxic cells or killer T cells: The lymphokine interleukin-2 is responsible for the growth and proliferation of both cytotoxic T cells and suppressor T cells. With the help of receptor proteins on the surface of killer T cells, they bind to the specific antigen. After binding, they secrete a pore forming protein called perforins which create pores on the invaders cell membrane for water to enter into it thereby cell swells and finally lyse.
c. Suppressor T cells: They suppress the function of above two T cells.
The correct answer is - Most killer whales congregate in the areas that are near the Arctic/Antarctic Circles.
The killer whales have a very large distribution, and they can be found in all oceans, apart from the Southern Ocean. It is noted though that the population density of the killer whales differs from place to place. The higher concentrations are found around the Arctic and Antarctic Circles, where there's cool rich waters, while in the lower latitudes they are much rarer. The reason for this probably lies in the fact that most of the animals that are considered to be the prime food source of the killer whales are living in this rich cold waters.
