Many cells rely on chemotaxis -- detecting differences in concentrations of chemicals on one side compared to the other -- in order to determine which way to move. Our neutrophils (white blood cells) use this to find and destroy invading bacteria as a part of our immune system. The video at the link on Blackboard (also below) shows chemotaxis of amoeboid cells. In other words, it shows cells migrating toward a region with a high concentration of a chemical, in this case cAMP. Cells start in a large reservoir on top (outside of the field of view) and migrate toward a large reservoir filled with a high concentration of a chemical that attracts the migrating cells (chemoattractant) which is below the field of view. The point of view is looking down on a horizontal surface so the cells are not "falling" but moving on their own to find the chemoattractant.

Around faucet handle is part of a(n) a. lever b. screw c. inclined plane d. wheel and axle

Aheat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. the same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. heat pumps are widely used for home heating. you can think of a heat pump as a refrigerator that is cooling the already cold outdoors and, with its exhaust heat qh, warming the indoors. perhaps this seems a little silly, but consider the following. electricity can be directly used to heat a home by passing an electric current through a heating coil. this is a direct, 100% conversion of work to heat. that is, 19.0 \rm kw of electric power (generated by doing work at the rate 19.0 kj/s at the power plant) produces heat energy inside the home at a rate of 19.0 kj/s. suppose that the neighbor's home has a heat pump with a coefficient of performance of 4.00, a realistic value. note: with a refrigerator, "what you get" is heat removed. but with a heat pump, "what you get" is heat delivered. so the coefficient of performance of a heat pump is k=qh/win. an average price for electricity is about 40 mj per dollar. a furnace or heat pump will run typically 200 hours per month during the winter. what does one month's heating cost in the home with a 16.0 kw electric heater? what does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating?

Immediately upon reaching its lowest point, a falling pendulum bob has its greatest amount of energy, which is the initial amount of potential energy. a. heat; less than b. heat; more than c. kinetic; less than d. kinetic; more than