Which of the following secrete spicules?
a. sperm
b. porocytes
c. choanocytes
d. amoeboid cells
Ans: d. amoeboid cells
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Why are phosphorylation and dephosphorylation reactions commonly used to regulate signal transduction pathways?
A. Phosphate groups are efficient second messengers B. Protein kinases and phosphatases are abundant in most cells C. The hydrolysis of bound GTP generates GDP, which can change the activity of proteins bound to GDP D. The addition or removal of a phosphate group can expose or hide potential binding sites in proteins or change protein activity
Which organ filters blood that has collected wastes from cells throughout the body and maintains the homeostasis of body fluids?
a. kidneys b. heart c. lungs d. Pacemaker
Which immune system cell must be presented with antigen by an antigen-presenting cell such as a macrophage, in order to become appropriately activated?
A) B lymphocyte B) plasma cell C) macrophage D) T lymphocyte E) natural killer cell
Living as a member of a group may have all of the following advantages except what?
A. increased feeding rate B. members learn about new food sources from other members C. greater protection from predators D. more individuals scan the environment for dangers E. being more resistant to disease and parasites