Q: A solution has a pH of 4. What is the molarity of protons $$[H^+] in $$this solution?

$$[H^+] = 1 \times 10$$^{-4}$$~\text{M}$$

Question 1

Which of the following best explains why ice floats on liquid water, and why this property is crucial for aquatic life in cold climates?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds in ice force water molecules into a rigid lattice, spacing them farther apart than in liquid water. This insulates the water below, allowing aquatic life to survive during winter.

Question 2

A scientist discovers a new sugar with the molecular formula $$C_5H_{10}O_5$. Which of the following best describes this molecule?

Accepted Answer

It is a pentose monosaccharide, likely to form a ring structure in aqueous solution.

Question 3

Which of the following statements about the permeability of biological membranes is correct?

Accepted Answer

Membranes with a high proportion of unsaturated fatty acids are more permeable to small, nonpolar molecules than membranes with mostly saturated fatty acids.

Question 4

A solution has a pH of 4. What is the molarity of protons $$[H^+] in $$this solution?

Accepted Answer

$$[H^+] = 1 	imes 10$$^{-4}$$~	ext{M}$$

Question 5

Which of the following best describes the difference between starch and cellulose?

Accepted Answer

Starch is composed of $$\alpha-$$glucose monomers with $$\alpha-1$$,4-glycosidic linkages, forming a helical structure, while cellulose is composed of $$\beta-$$glucose monomers with $$\beta-1$$,4-glycosidic linkages, forming straight fibers.

Question 6

Which of the following scenarios best illustrates the process of facilitated diffusion?

Accepted Answer

Glucose moves into a red blood cell through a carrier protein (GLUT-1) down its concentration gradient without the use of ATP.

Question 7

Which of the following best explains why proteins are effective as enzymes?

Accepted Answer

Proteins have diverse three-dimensional structures with specific active sites that bind substrates and lower activation energy, increasing reaction rates.

Question 8

A researcher adds sodium hydroxide ($$NaOH) to a $$solution containing carbonic acid ($$H_2CO_3) $$and bicarbonate ($$HCO_3$$^-$$). What will happen to the concentration of bicarbonate ions?

Accepted Answer

The concentration of bicarbonate ions ($$HCO_3$$^-$$) will increase as OH$$^-$$ ions react with H_2CO_3$ to form $$HCO_3$$^-$$ and $$H_2O.$$

Question 9

Which of the following is a correct statement about the secondary structure of proteins?

Accepted Answer

It is stabilized by hydrogen bonds between the backbone atoms of the polypeptide chain, forming structures such as $$\alpha-$$helices and $$\beta-$$pleated sheets.

Question 10

Which of the following best describes the role of glycoproteins in cell membranes?

Accepted Answer

They serve as identification badges, allowing cells to recognize each other and communicate, which is critical for immune response and tissue formation.

Question 11

Which of the following best explains why unsaturated fatty acids increase membrane fluidity?

Accepted Answer

The double bonds in unsaturated fatty acids create kinks, preventing tight packing of the lipid tails and increasing fluidity.

Question 12

Which of the following is a direct consequence of the first law of thermodynamics in biological systems?

Accepted Answer

Energy cannot be created or destroyed, so cells must convert energy from one form to another, such as chemical energy in glucose to ATP.

Question 13

A patient is diagnosed with cystic fibrosis, a disease caused by a defective chloride channel protein (CFTR). Which of the following best describes the molecular basis of this disease?

Accepted Answer

A mutation in the CFTR gene leads to a misfolded or nonfunctional chloride channel, disrupting ion transport and causing thick mucus buildup.

Question 14

Which of the following best describes the difference between active and passive transport across a cell membrane?

Accepted Answer

Active transport moves substances against their concentration gradient using energy (often from ATP), while passive transport moves substances down their gradient without energy input.

Question 15

Which of the following best explains why cellulose is resistant to digestion by most animals?

Accepted Answer

Most animals lack enzymes that can hydrolyze $$\beta-1$$,4-glycosidic linkages found in cellulose.

Question 16

Which of the following is a property of water that results directly from its polar covalent bonds and bent molecular shape?

Accepted Answer

Water molecules can form hydrogen bonds with each other, leading to high cohesion, surface tension, and a high specific heat.

Question 17

Which of the following best describes the process of osmosis in a biological context?

Accepted Answer

Water moves across a selectively permeable membrane from regions of low solute concentration to regions of high solute concentration.

Question 18

Which of the following is a correct statement about the central dogma of molecular biology?

Accepted Answer

Genetic information flows from DNA to RNA to protein, with DNA serving as the template for RNA, which is then translated into protein.

General Biology: Study Notes on Biomolecules, Cell Theory, and the Chemical Basis of Life

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