Question

18.) Molecules (like adrenaline or epinephrine) that signal from outside the cell use receptors because:

a. they are hydrophobic and cannot enter the cell

b. they are hydrophilic and cannot enter the cell

19.) Photoautotrophs are essential to life on earth because:

a. they make their own food

b. They provide energy for other organisms

c. they eat harmful insects

d. A and B

e. B and C.

20.) Signaling through receptors allow cells to respond to small differences in the extracellular environment b/c:

a. they are specific.

b. the stoichiometry is one-to-one.

c. they are reversible.

d. one-to-one stoichiometry.

e. the signals are amplified inside the cell.

Answer 1

18. b. they are hydrophilic and cannot enter the cell

The signal molecules are the ligands that will bind to the receptor protein molecule which will stimulate an action. Based on the polarity there are two types; hydrophobic and hydrophilic. The hydrophilic molecules includes acetylcholine, epinephrine, histamine etc.

19. d. A and B

Both the statements are correct as the photoautotrophs make their own food and provide energy for other organisms too.

Photosynthesis is the essential process on earth. It is by photosynthesis the plants as well as the other photoautotrophs synthesize carbohydrates.

20.  e. the signals are amplified inside the cell.

When a receptor protein receives a signal, it usually undergoes a conformational change which in turn go through series of chemical reaction pathway. This pathway can amplify the message their by producing multiple intracellular signal for each receptor.