A type of gland that secretes an oily substance that softens and protects hair is a(n) ________ gland.

The human immunodeficiency virus (HIV) only affects a specific class of cells in the immune system called helper T cells, and not other types of T cells. Which is the best explanation for this observation?

The concentration of solutes in most soil is lower than the concentration of solutes in root cells, so water enters the roots by

A microbiologist Gram stains a bacterium and finds the bacterium to be pink to red in color. This identifies the

Each myofibril consists of two types of filaments, a thick actin filament and a thin myosin filament.

A slow-twitch muscle fiber

What hypothesis were Ellison and Gotelli testing when they manipulated concentrations of nutrients available to pitcher plants?

Based on the theory of endosymbiosis, which of the following would you expect to find in a chloroplast?

What is the function of the simple squamous cells found in the glomeruli of the kidney?

Scientists measured the pressure in the xylem of redwood trees at different heights and found that the higher they made their measurements, the lower the pressure. They extrapolated this to a pressure of zero, and concluded that the tallest a tree could grow is 122–130 meters. The tallest known tree on Earth is 112.7 meters. Which of the following most likely limits the height of trees?