7. describe each of the different types of transport across the membrane:
| passive transport |
| active transport |
| vesicle transport |

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Accepted Answer

# Brief Explanations:
- **Passive Transport**: Movement of substances across a cell membrane without energy input. Includes simple diffusion (small, non - polar molecules like $O_2$, $CO_2$ move down concentration gradient), facilitated diffusion (uses transport proteins like channels or carriers for polar/charged molecules, e.g., glucose via GLUT transporters, still down concentration gradient), and osmosis (diffusion of water across a selectively permeable membrane, towards higher solute concentration).
- **Active Transport**: Requires energy (usually ATP) to move substances against their concentration gradient. Primary active transport uses ATP directly, e.g., $Na^+/K^+$ pump (3 $Na^+$ out, 2 $K^+$ in per ATP hydrolyzed). Secondary active transport uses energy from an ion gradient (e.g., $Na^+$ gradient) to move another substance, like glucose - $Na^+$ cotransport in intestinal cells.
- **Vesicle Transport**: Involves transport of large molecules or particles via vesicles. Endocytosis (cell takes in substances: phagocytosis for large particles like bacteria, pinocytosis for fluid - solute mixtures, receptor - mediated endocytosis for specific molecules like LDL). Exocytosis (cell releases substances: e.g., neurotransmitters from neurons, hormones from endocrine cells, by fusing vesicles with the plasma membrane).

# Answer:
| Transport Type | Description |
| ---- | ---- |
| Passive Transport | Movement of substances across the cell membrane without energy input. Includes simple diffusion (e.g., $O_2$, $CO_2$ movement down concentration gradient), facilitated diffusion (uses transport proteins for polar/charged molecules like glucose down gradient), and osmosis (water diffusion down water potential gradient). |
| Active Transport | Movement of substances across the cell membrane against the concentration gradient, requiring energy (often ATP). Primary active transport (e.g., $Na^+/K^+$ pump) uses ATP directly. Secondary active transport (e.g., glucose - $Na^+$ cotransport) uses an ion gradient for energy. |
| Vesicle Transport | Transport of large molecules/particles via vesicles. Endocytosis (phagocytosis - large particles, pinocytosis - fluid - solute, receptor - mediated - specific molecules) brings substances into the cell. Exocytosis (e.g., neurotransmitter, hormone release) sends substances out by vesicle - membrane fusion. |

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Answer:

Transport Type	Description
Active Transport	Movement of substances across the cell membrane against the concentration gradient, requiring energy (often ATP). Primary active transport (e.g., $Na^+/K^+$ pump) uses ATP directly. Secondary active transport (e.g., glucose - $Na^+$ cotransport) uses an ion gradient for energy.
Vesicle Transport	Transport of large molecules/particles via vesicles. Endocytosis (phagocytosis - large particles, pinocytosis - fluid - solute, receptor - mediated - specific molecules) brings substances into the cell. Exocytosis (e.g., neurotransmitter, hormone release) sends substances out by vesicle - membrane fusion.