Chapter 3 - Section 3.3 - Study Guide - Assess Your Learning Outcomes - Page 109: 15

The mechanisms of transport described earlier can be categorized based on their requirement for a membrane, dependence on a plasma membrane, occurrence through artificial membranes, and reliance on ATP. Additionally, I'll note which processes cease when ATP is unavailable (e.g., upon death): **1. Mechanisms that Require a Membrane:** - **Facilitated Diffusion:** Requires a membrane because it involves specific membrane proteins (transporters or channels) that facilitate the movement of molecules across the lipid bilayer. - **Active Transport (Primary and Secondary):** Requires a membrane because it relies on specific membrane proteins (e.g., pumps, transporters) that actively move molecules against their concentration gradients. **2. Mechanisms that Require a Plasma Membrane:** - **All the mechanisms mentioned (Facilitated Diffusion, Active Transport, Vesicular Transport):** These processes occur at or involve the plasma membrane, which separates the cell's internal environment from the extracellular environment. **3. Mechanisms that Can Occur Through Artificial Membranes:** - **Simple Diffusion:** Simple diffusion can occur through artificial lipid bilayers, such as synthetic liposomes or lipid membranes in laboratory experiments. It does not require specific membrane proteins. - **Facilitated Diffusion:** Facilitated diffusion, in some cases, can also be reconstituted using artificial lipid bilayers and purified transport proteins. This is often done in laboratory settings for research purposes. - **Active Transport (Primary and Secondary):** Active transport processes, particularly primary active transport, can be reconstituted using artificial membranes and purified transport proteins. This allows for the study of transport mechanisms in controlled environments. - **Vesicular Transport:** Vesicular transport, such as endocytosis and exocytosis, involves the formation of membrane-bound vesicles. While these processes are typically associated with cellular membranes, they can also be mimicked using artificial liposomes in laboratory experiments. **4. Mechanisms that Require ATP:** - **Active Transport (Primary and Secondary):** Both primary and secondary active transport processes require the energy input provided by ATP. ATP hydrolysis is necessary to move molecules against their concentration gradients. - **Vesicular Transport (Endocytosis and Exocytosis):** Vesicular transport processes also rely on ATP indirectly. ATP is required for various cellular processes, including the formation of vesicles (endocytosis) and the fusion of vesicles with the plasma membrane (exocytosis). Therefore, these processes cease if ATP is unavailable, as upon death. **5. Mechanisms that Cease Without ATP:** - **Active Transport (Primary and Secondary):** Active transport processes cease if ATP is unavailable because they rely on the energy from ATP hydrolysis to function. Without ATP, these processes cannot actively move molecules across the membrane. - **Vesicular Transport (Endocytosis and Exocytosis):** As with active transport, vesicular transport processes cease if ATP is unavailable. The formation of vesicles during endocytosis and their fusion with the plasma membrane during exocytosis both require ATP-dependent cellular machinery. In summary, mechanisms like simple diffusion, facilitated diffusion, and certain aspects of vesicular transport can occur through artificial membranes. However, active transport (both primary and secondary) and vesicular transport (endocytosis and exocytosis) are ATP-dependent processes that cease when ATP is unavailable, such as in the absence of cellular energy supply, as occurs upon death.

The mechanisms of transport described earlier can be categorized based on their requirement for a membrane, dependence on a plasma membrane, occurrence through artificial membranes, and reliance on ATP. Additionally, I'll note which processes cease when ATP is unavailable (e.g., upon death): **1. Mechanisms that Require a Membrane:** - **Facilitated Diffusion:** Requires a membrane because it involves specific membrane proteins (transporters or channels) that facilitate the movement of molecules across the lipid bilayer. - **Active Transport (Primary and Secondary):** Requires a membrane because it relies on specific membrane proteins (e.g., pumps, transporters) that actively move molecules against their concentration gradients. **2. Mechanisms that Require a Plasma Membrane:** - **All the mechanisms mentioned (Facilitated Diffusion, Active Transport, Vesicular Transport):** These processes occur at or involve the plasma membrane, which separates the cell's internal environment from the extracellular environment. **3. Mechanisms that Can Occur Through Artificial Membranes:** - **Simple Diffusion:** Simple diffusion can occur through artificial lipid bilayers, such as synthetic liposomes or lipid membranes in laboratory experiments. It does not require specific membrane proteins. - **Facilitated Diffusion:** Facilitated diffusion, in some cases, can also be reconstituted using artificial lipid bilayers and purified transport proteins. This is often done in laboratory settings for research purposes. - **Active Transport (Primary and Secondary):** Active transport processes, particularly primary active transport, can be reconstituted using artificial membranes and purified transport proteins. This allows for the study of transport mechanisms in controlled environments. - **Vesicular Transport:** Vesicular transport, such as endocytosis and exocytosis, involves the formation of membrane-bound vesicles. While these processes are typically associated with cellular membranes, they can also be mimicked using artificial liposomes in laboratory experiments. **4. Mechanisms that Require ATP:** - **Active Transport (Primary and Secondary):** Both primary and secondary active transport processes require the energy input provided by ATP. ATP hydrolysis is necessary to move molecules against their concentration gradients. - **Vesicular Transport (Endocytosis and Exocytosis):** Vesicular transport processes also rely on ATP indirectly. ATP is required for various cellular processes, including the formation of vesicles (endocytosis) and the fusion of vesicles with the plasma membrane (exocytosis). Therefore, these processes cease if ATP is unavailable, as upon death. **5. Mechanisms that Cease Without ATP:** - **Active Transport (Primary and Secondary):** Active transport processes cease if ATP is unavailable because they rely on the energy from ATP hydrolysis to function. Without ATP, these processes cannot actively move molecules across the membrane. - **Vesicular Transport (Endocytosis and Exocytosis):** As with active transport, vesicular transport processes cease if ATP is unavailable. The formation of vesicles during endocytosis and their fusion with the plasma membrane during exocytosis both require ATP-dependent cellular machinery. In summary, mechanisms like simple diffusion, facilitated diffusion, and certain aspects of vesicular transport can occur through artificial membranes. However, active transport (both primary and secondary) and vesicular transport (endocytosis and exocytosis) are ATP-dependent processes that cease when ATP is unavailable, such as in the absence of cellular energy supply, as occurs upon death.