Why don't na+ ions move across the plasma membrane of neurons and down their concentration gradient all the time? a. the plasma membrane is not permeable to na+ ions. b. the na+/k+ pump is required and it only operates when atp is plentiful c. a na+ channel is required and it is usually closed. a & c. a, b, & c.

Match the following terms describing electrical events with the correct phases of the cardiac cycle. the ventricular muscle cells depolarize at the start of this phase. during this phase, na+ entry through the funny channels causes the pacemaker potential of sa nodal cells to gradually become less negative until it reaches threshold. the ventricular muscle cells repolarize right before this phase. the cytosolic concentration of calcium in the contractile cells of the ventricle is highest during this phase. a. isovolumetric relaxation b. ventricular ejection c. isovolumetric contraction d. ventricular filling

In 2015, about ten percent of total u.s. energy consumption was from renewable energy sources. renewable energy plays an important role in reducing greenhouse gas emissions. when renewable energy sources are used, the demand for fossil fuels is reduced. sanjay and his family want to cut back on their use of non-renewable resources at home. they are thinking of an alternate way to heat their home without adding more greenhouse gases or pollutants to the environment. which renewable resource would not fit into their plan? a) solar power b) burning wood c) constructing a wind turbine eliminate d) generating hydroelectric power

Explain why biological control methods are generally environmentally superior to chemical pest control methods.