Question

1. define passive transport.
2. how do molecules move across a cell membrane during diffusion?
3. how is facilitated diffusion different from regular diffusion?
4. what type of proteins assist with moving water through the cell membrane during osmosis?
5. what does active transport require?
6. what do pumps force molecules to do?
7. what is bulk transport used for?
8. summarize the following processes of endocytosis.

a. phagocytosis:
b. pinocytosis:
c. receptor - mediated endocytosis:

1. what is one similarity and one difference between endocytosis and exocytosis?

Explanation:

1. Passive transport is the movement of substances across a cell membrane without the use of energy. It occurs along a concentration gradient.
2. During diffusion, molecules move from an area of higher concentration to an area of lower concentration across the cell membrane. This is a passive process driven by the random motion of molecules.
3. Facilitated diffusion is different from regular diffusion in that it requires the assistance of transport proteins (carrier or channel proteins) to move substances (usually larger or polar molecules) across the cell membrane, while regular diffusion can occur without such proteins for small, non - polar molecules.
4. Aquaporins are the type of proteins that assist with moving water through the cell membrane during osmosis.
5. Active transport requires energy, usually in the form of ATP, to move substances against their concentration gradient (from an area of lower concentration to an area of higher concentration).
6. Pumps force molecules to move against their concentration gradient, using energy to transport them from an area of lower concentration to an area of higher concentration.
7. Bulk transport is used for the movement of large amounts of substances or large particles into (endocytosis) or out of (exocytosis) the cell. It involves the formation of vesicles.

19.
a. Phagocytosis: A type of endocytosis where large particles, such as bacteria or dead cells, are engulfed by the cell. The cell membrane extends around the particle to form a phagosome.
b. Pinocytosis: A form of endocytosis where the cell takes in small droplets of extracellular fluid along with any dissolved molecules. It is non - specific.
c. Receptor - mediated endocytosis: A more specific form of endocytosis. Receptor proteins on the cell surface bind to specific ligands, and then the cell membrane invaginates to form a vesicle, bringing in the ligand - receptor complexes along with some extracellular fluid.

1. Similarity: Both endocytosis and exocytosis are forms of bulk transport and involve the formation of vesicles. Difference: Endocytosis is the process of bringing substances into the cell, while exocytosis is the process of releasing substances out of the cell.

Answer:

1. Passive transport is the movement of substances across a cell membrane without energy input, along a concentration gradient.
2. Molecules move from high to low concentration across the cell membrane by random motion.
3. Facilitated diffusion uses transport proteins; regular diffusion doesn't (for small non - polar molecules).
4. Aquaporins.
5. Energy (usually ATP).
6. Move against their concentration gradient.
7. Movement of large amounts of substances or large particles into or out of the cell.

19.
a. Engulfing large particles like bacteria by extending the cell membrane to form a phagosome.
b. Taking in small droplets of extracellular fluid and dissolved molecules non - specifically.
c. Specific binding of ligands to receptors on the cell surface followed by membrane invagination to form a vesicle.

1. Similarity: Both are forms of bulk transport involving vesicles. Difference: Endocytosis brings substances in; exocytosis releases substances out.