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.