1. The table below shows the chemical characteristics of four substances.

Transcription

1 1. The table below shows the chemical characteristics of four substances. Based on the data, which substance will diffuse through a cell membrane most easily? (A) Substance 1 This answer suggests the student may understand that small size is important for diffusion through membranes, but does not understand that charged ions do not easily pass through membrane lipids because the phospholipid bilayer is hydrophobic. (B) Substance 2 This answer suggests the student may understand that small size is important for diffusion through membranes, but does not understand that although cell membranes have both polar and non-polar properties, polar molecules do not easily pass through the non-polar lipid region of the membrane. (C) Substance 3 This answer suggests the student understands that small size is an important characteristic that allows substances to diffuse through plasma membranes, and that the molecule s nonpolarity is an important characteristic because of the non-polarity of the lipid tails of phospholipids. (D) Substance 4 Page 1 of 5

2 This answer suggests the student may understand that non-polarity is an important characteristic for being able to diffuse through membranes, but does not understand that large molecules do not easily pass through the lipid region of the membrane due to their size. 2. In a person with cystic fibrosis, epithelial cells lining the lungs and digestive system lack a membrane protein needed to remove excess chloride ions from the cell. Which statement best explains how this disorder affects an epithelial cell? (A) The low concentration of chloride ions inside the cell causes water to move from the cell to the cytoplasm, resulting in the cell becoming dehydrated. This answer suggests the student may understand that a low concentration of chloride ions inside the cell would cause water to move out of the cell, but does not understand that the ion concentration inside the cell is high, and that water will flow into the cell and cause it to swell and possibly burst. (B) The high concentration of chloride ions inside the cell causes sodium ions to diffuse into the cell, resulting in the formation of sodium chloride crystals. This answer suggests the student may understand that substances can diffuse across the plasma membrane and that the chloride ion concentration inside the cell is high, but does not understand that sodium ions do not move across the plasma membrane through simple diffusion, and that water would move into the cell and cause the cell to swell. (C) The low concentration of chloride ions inside the cell causes sodium ions to diffuse into the cell, resulting in shrinking and shriveling of the cell. This answer suggests the student may understand that a low concentration of chloride ions inside the cell relative to the concentration outside the cell will cause the cell to shrink and shrivel, but does not understand that only water moves into and out of the cell, that the concentration of chloride ions is higher inside the cell relative to outside, and that the higher ion concentration causes water to move into the cell and causes the cell to swell. Page 2 of 5

3 (D) The high concentration of chloride ions inside the cell causes water to diffuse into the cell, resulting in swelling and bursting of the cell. This answer suggests the student understands that a high chloride concentration inside the cell causes water to diffuse across the plasma membrane into the cell, which causes the cell to swell. 3. The diagram below shows the movement of particles across a cell membrane. Which statement describes the process most likely represented by the diagram? (A) Oxygen is moving into a cell via simple diffusion. This answer suggests the student understands that oxygen can pass through the cell membrane by simple diffusion because oxygen is a small, nonpolar molecule. (B) Sodium ions are moving into a cell via osmosis. This answer suggests the student may understand that water moves across a cell membrane via osmosis, but does not understand that osmosis involves only the movement of water molecules, and not ions. (C) Glucose is being moved into a cell via active transport. Page 3 of 5

4 This answer suggests the student may understand that glucose can move across a cell membrane via active transport, but does not understand that carrier proteins are involved and that the movement is usually against a concentration gradient. (D) Proteins are being moved into a cell via endocytosis. This answer suggests the student understands that proteins could move across a cell membrane via endocytosis, but does not understand that endocytosis involves the membrane wrapping around the molecule. 4. The diagram below shows the movement of ions through the phospholipid bilayer of a cell. Based on the diagram, which statement best explains the movement of the ions through the phospholipid bilayer? (A) The ions can diffuse across the phospholipid bilayer because the ions are moving against the osmotic potential. Page 4 of 5

5 This answer suggests the student may understand that diffusion is the movement of ions from high concentration to low concentration, but does not understand that osmotic potential refers to the movement of water and not the movement of ions. (B) The ions are transported across the phospholipid bilayer because the ions are moving against the concentration gradient. This answer suggests the student may understand that the ions must be transported across the phospholipid bilayer, but does not understand that the ions must be transported because they are charged, and that the ions are not moving against a concentration gradient. (C) The ions can diffuse across the phospholipid bilayer because the ions are nonpolar. This answer suggests the student may understand that diffusion is the movement of a substance from high concentration to low concentration, but does not understand that an ion is charged and requires a channel protein to move across the phospholipid bilayer. (D) The ions are transported across the phospholipid bilayer because the ions are charged. This answer suggests the student understands that the ions are moving from an area of high concentration to an area of low concentration via facilitated diffusion through a protein channel because they are charged. Page 5 of 5