Question

1. apply scientific reasoning how are the transport problems of a freshwater organism different from those of a saltwater organism? 5. sep develop models a student draws a fence with several gates as part of a model of cellular transport. explain what the fence and the gates represent, relating their structures to their functions. explain how the model could represent both active transport using protein pumps and facilitated diffusion.

Explanation:

1. Freshwater organisms face osmotic challenges as water moves into their cells due to lower - external solute concentration, requiring mechanisms to expel excess water. Saltwater organisms have the opposite problem, with water moving out of their cells due to higher external solute concentration, so they need to conserve water and excrete excess salts.
2. The fence represents the cell membrane, which is a barrier controlling what enters and leaves the cell. The gates represent transport proteins. In active transport using protein pumps, the gates can use energy (e.g., ATP) to move substances against their concentration gradient. In facilitated diffusion, the gates allow substances to move down their concentration gradient without energy input, just like gates allowing easy passage in one direction.

Answer:

1. Freshwater organisms deal with water influx and need to expel water; saltwater organisms face water efflux and need to conserve water and excrete salts.
2. The fence represents the cell membrane as a barrier, gates represent transport proteins. For active transport, gates use energy to move substances against the gradient; for facilitated diffusion, gates allow substances to move down the gradient without energy.