What do diffusion and osmosis have in common?
A. They only happen in living cells.
B. They require transport proteins in the membrane.
C. They are passive transport mechanisms.
D. Net movement of substances is against the concentration gradient.
▶️Answer/Explanation
Markscheme
Ans: C
Diffusion and osmosis both have the following in common:
C. They are passive transport mechanisms.
Both diffusion and osmosis are types of passive transport mechanisms that do not require energy input from the cell. Instead, molecules move down their concentration gradient from an area of high concentration to an area of low concentration.
Diffusion is the movement of particles from an area of high concentration to an area of low concentration, while osmosis is the movement of water molecules across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.
Therefore, the correct answer is C. They are passive transport mechanisms.
What is the difference between simple diffusion and facilitated diffusion?
▶️Answer/Explanation
Markscheme
Ans: D
The difference between simple diffusion and facilitated diffusion is that simple diffusion does not require a transport protein, while facilitated diffusion requires a transport protein.
Simple diffusion is the movement of particles from an area of high concentration to an area of low concentration, across a selectively permeable membrane. This process does not require a transport protein because the particles are small enough to pass directly through the membrane.
Facilitated diffusion, on the other hand, is the movement of particles from an area of high concentration to an area of low concentration, across a selectively permeable membrane, with the help of a transport protein. This process requires a transport protein because the particles are too large or too polar to pass directly through the membrane.
Therefore, the main difference between simple diffusion and facilitated diffusion is that facilitated diffusion requires a transport protein, while simple diffusion does not.
What route is used to export proteins from the cell?
A. Golgi apparatus → rough endoplasmic reticulum → plasma membrane
B. Rough endoplasmic reticulum → Golgi apparatus → plasma membrane
C. Golgi apparatus → lysosome → rough endoplasmic reticulum
D. Rough endoplasmic reticulum → lysosome → Golgi apparatus
▶️Answer/Explanation
B
The route that is used to export proteins from the cell is B. Rough endoplasmic reticulum → Golgi apparatus → plasma membrane.
Proteins are synthesized on ribosomes attached to the rough endoplasmic reticulum (ER). They are then transported from the rough ER to the Golgi apparatus, where they are modified, sorted, and packaged for transport to their final destination.
Once the proteins have been processed by the Golgi apparatus, they are packaged into vesicles and transported to the plasma membrane. The vesicles fuse with the plasma membrane, releasing the proteins outside the cell.
Therefore, the correct answer is B. Rough endoplasmic reticulum → Golgi apparatus → plasma membrane.
Why do crop plants dry out when a field is irrigated with water contaminated by sea water?
A. The plants lose water by active transport.
B. The plants gain salt by osmosis.
C. The plants gain salt by diffusion.
D. The plants lose water by osmosis.
Answer/Explanation
Markscheme
D
The correct answer is D. The plants lose water by osmosis. When crop plants are irrigated with water contaminated by sea water, the high concentration of salt in the water creates a gradient across the selectively permeable membrane of the plant cells. This gradient causes water to move out of the cells by osmosis, leading to water loss and dehydration of the plants. Thank you for bringing this to my attention.
Question
The diagram refers to questions 2 and 3. It shows a heterotrophic, unicellular, freshwater organism that has been placed in distilled water. The short arrows show movement of water and the long arrows show a sequence of steps.
What would happen if the unicellular organism was placed in a solution slightly less concentrated than the cytoplasm of the cell, rather than in distilled water?
A. The cell would become larger.
B. More water would be expelled from the cell.
C. X would fill more slowly.
D. X would not appear.
▶️Answer/Explanation
C
Question
Onion (Allium cepa) epidermis was placed in pure water and observed with a light microscope using high magnification.
What would happen to these cells if they were transferred to a hypertonic solution?
A. Cells would gain mass.
B. Cells would take in water by osmosis and swell.
C. Cells would burst open, releasing their content.
D. Cell membranes would detach from walls at some points.
▶️Answer/Explanation
D
Question
Red blood cells from a small mammal were immersed in NaCl (sodium chloride) solutions of different concentrations for 2 hours. The graph shows the percentage of hemolysed (ruptured) red blood cells at each concentration.
What can be deduced from the graph?
A. At Y, the net movement of Na ions between red blood cells and the NaCl solutions is zero.
B. At X, Na and Cl ions disrupt the structure of cell membranes.
C. At Y, the hypertonic NaCl solutions diffuse into the red blood cells.
D. At X, water has moved by osmosis into the red blood cells.
▶️Answer/Explanation
D
Question
Suggest a reason for the difference in the isotonic points for the potato and the carrot tissues.
▶️Answer/Explanation
OR
may have been grown in different soils giving their tissues different contents
OR
may have been stored under different conditions
OR
may be more dehydrated / different water content
OR
different types of tissue / different age
Question
Which process(es) occur(s) by osmosis?
I. Uptake of water by cells in the wall of the intestine
II. Loss of water from a plant cell in a hypertonic environment
III. Evaporation of water from sweat on the skin surface
A. I only
B. I and II only
C. II and III only
D. I, II and III
▶️Answer/Explanation
B
Question
In an experiment on osmosis, red blood cells were immersed in a salt solution for two hours. The micrographs show the appearance of these cells before and after immersion in the salt solution.
What explains the observed changes?
A. The salt solution was hypertonic and entered the red blood cells.
B. The salt solution was hypotonic and disrupted the membranes of the red blood cells.
C. The salt solution was hypertonic and water moved into it from the red blood cells.
D. The salt solution was hypotonic and mineral salts were lost from the red blood cells.
▶️Answer/Explanation
C