Keystone Biology: Cell Processes/Transport Questions and Answers 1 — Questions and Answers
Question 1: A scientist places a sample of red blood cells into a beaker containing a solution with a much higher salt concentration than the cells' cytoplasm. Which of the following outcomes is most likely?
- The red blood cells will shrivel because water will move out of the cells. (Correct answer)
- The red blood cells will swell and burst because water will move into the cells.
- The red blood cells will remain unchanged because the cell membrane is impermeable to water.
- The red blood cells will actively pump salt out to equalize the concentration.
Correct answer: The red blood cells will shrivel because water will move out of the cells.
The solution is hypertonic to the red blood cells, meaning it has a higher solute (salt) concentration and a lower water concentration. Due to osmosis, water moves from an area of higher water concentration (inside the cell) to an area of lower water concentration (outside the cell) across the semipermeable membrane, causing the cells to lose water and shrivel.
Question 2: Which of the following cellular processes requires the direct expenditure of energy in the form of ATP to move substances against their concentration gradient?
- Facilitated diffusion
- Osmosis
- Active transport (Correct answer)
- Simple diffusion
Correct answer: Active transport
Active transport is the process of moving molecules across a cellular membrane through the use of cellular energy (ATP). It is used to move substances from an area of lower concentration to an area of higher concentration, or 'against' the concentration gradient. The other options are forms of passive transport, which do not require ATP because they move substances 'down' the concentration gradient.
Question 3: A single-celled freshwater organism, like a Paramecium, lives in a hypotonic environment. To maintain homeostasis, it must constantly pump out excess water that enters the cell. Which organelle is primarily responsible for this function?
- Mitochondrion
- Contractile vacuole (Correct answer)
- Ribosome
- Nucleus
Correct answer: Contractile vacuole
The contractile vacuole is a specialized organelle that collects excess water from the cytoplasm and expels it from the cell. This process of osmoregulation is crucial for survival in hypotonic (low solute) freshwater environments, as it prevents the cell from swelling and bursting due to the constant influx of water via osmosis.
Question 4: Some large molecules, like hormones or waste products, are packaged into vesicles and transported out of the cell when the vesicle fuses with the plasma membrane. What is this process called?
- Endocytosis
- Phagocytosis
- Pinocytosis
- Exocytosis (Correct answer)
Correct answer: Exocytosis
Exocytosis is the process by which a cell transports molecules (e.g., proteins, hormones, waste) out of the cell. It is an active transport process where a vesicle containing the material fuses with the interior of the plasma membrane, releasing its contents into the extracellular fluid. Endocytosis is the opposite process of bringing material into the cell.
Question 5: Both facilitated diffusion and active transport are processes that move substances across the cell membrane. What is a key characteristic they have in common?
- They both move substances against a concentration gradient.
- They both require the cell to expend energy (ATP).
- They both utilize specific transport proteins embedded in the membrane. (Correct answer)
- They both only transport water molecules across the membrane.
Correct answer: They both utilize specific transport proteins embedded in the membrane.
Both facilitated diffusion and active transport rely on integral membrane proteins to move substances across the cell membrane. In facilitated diffusion, these proteins act as channels or carriers to help molecules move down their concentration gradient. In active transport, protein pumps use energy to move substances against their concentration gradient.
Question 6: A cell's plasma membrane is described as selectively permeable. Which statement BEST explains this property?
- The membrane allows all substances to pass through freely, but only at certain times.
- The membrane allows only water to enter the cell and nothing to leave.
- The membrane blocks all materials from entering or leaving the cell, acting as a rigid wall.
- The membrane allows certain substances to pass through while preventing the passage of others. (Correct answer)
Correct answer: The membrane allows certain substances to pass through while preventing the passage of others.
Selective permeability means that the plasma membrane regulates what enters and leaves the cell. Due to its phospholipid bilayer structure with embedded proteins, it allows small, nonpolar molecules to pass through easily while restricting the passage of large or charged substances, which often require transport proteins. This regulation is essential for maintaining cellular homeostasis.
Keystone Biology: Cell Processes/Transport Questions and Answers 1
A scientist places a sample of red blood cells into a beaker containing a solution with a much higher salt concentration than the cells' cytoplasm.
Which of the following outcomes is most likely?