Cells are activated by the binding of their antigen and interaction with _____ cells.
A. helper T cells
B. cytotoxic T cells
C. macrophages
D. natural killer cells
Answer: A. helper T cells
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Deer flies (Chrysops spp.) are a major vector in the spread of typhus
Indicate whether the statement is true or false.
Molecules made primarily of carbon and hydrogen are called hydrocarbons. In each of the following hydrocarbons, indicate how many hydrogen atoms are present: 12, 10, 8, or 6
A chain of five carbons joined to each other by single covalent bonds A chain of five carbon atoms with one double bond and the rest single bonds A chain of five carbon atoms with two double bonds and two single bonds A five-carbon molecule with four of the carbons linked by a single covalent bond, and with the fifth carbon attached by a single bond as a branch to the second carbon in the chain A ring of six carbon atoms held together by alternating single and double bonds
What does the curvy line on the above graph represent?
a) Average amount of rainfall on the Galapagos Islands. b) The average beak size of Galapagos finches. c) The diet of the Galapagos finches. d) The number of wet and dry years. e) The average number of droughts.
Which of the following statements about gap junctions is false?
(a) Gap junctions are made of connexons. (b) Molecules up to 1000 daltons in molecular mass can move across gap junctions. (c) Because gap junctions do not allow ions to pass through, they are not used for electrically coupling cells. (d) Gap junctions can close in response to extracellular signals.