1.4 Membrane transport Flashcards
What is diffusion?
Diffusion is the movement of particles from a region of high concentration to a region of low concentration due to random motion of particles.
Differentiate between simple and facilitated diffusion.
Simple diffusion doesn’t require assistance, occurring across a membrane if a concentration gradient exists. Facilitated diffusion requires specific channel or carrier proteins to help substances cross the membrane.
What affects the rate of diffusion across a membrane?
Factors include temperature, membrane’s surface area, size of particles, and the concentration gradient of diffusing particles.
Define osmosis.
Osmosis is the passive movement of water molecules from a lower to a higher solute concentration across a partially permeable membrane.
What is active transport?
Active transport is the movement of particles against a concentration gradient, requiring energy in the form of ATP.
Explain the role of sodium-potassium pumps in neurons.
Sodium-potassium pumps help maintain resting potential by moving sodium and potassium ions against their concentration gradients, critical for nerve impulse transmission.
Differentiate between endocytosis and exocytosis.
Endocytosis is the process where cells intake substances by engulfing them in the cell membrane, whereas exocytosis involves ejecting substances out of the cell.
What are phagocytosis and pinocytosis?
Phagocytosis is the ingestion of solid particles by cells (“cell eating”), and pinocytosis is the ingestion of liquid particles (“cell drinking”).
How is osmolarity in tissues estimated?
By bathing samples in hypertonic and hypotonic solutions, observing changes in mass or volume to estimate the osmolarity of the tissue.
Why is matching osmolarity important in medical procedures involving tissue or organ transplants?
To prevent osmosis that could cause cells to swell or shrink, potentially damaging them and affecting the success of the transplant.
What is the significance of vesicles in cellular processes like endocytosis and exocytosis?
Vesicles transport materials within cells, enabling the movement of substances in and out of the cell through endocytosis and exocytosis.
Describe the structure and function of potassium channels in axons.
Potassium channels are specialized protein structures in cell membranes, allowing selective passage of K+ ions. In axons, they play a crucial role in repolarization during action potentials, restoring the negative charge inside the neuron by facilitating the outward flow of K+ ions, thus ensuring the rapid transmission of nerve impulses.
How do vesicles form and merge with the plasma membrane during exocytosis?
In exocytosis, vesicles containing substances to be expelled merge with the plasma membrane in a process facilitated by membrane fluidity. This involves vesicle docking, where vesicles are guided and attached to specific sites on the membrane, followed by membrane fusion, where vesicle and plasma membranes blend to release contents outside the cell.
Explain the encapsulation process in endocytosis.
During endocytosis, the cell membrane flexibly indents to envelop substances or particles. Membrane proteins recognize and bind to the target molecules, triggering membrane invagination. This invagination deepens, eventually pinching off into the cytoplasm as a vesicle, encapsulating the substance within.
How does membrane fluidity facilitate endocytosis and exocytosis?
Membrane fluidity, imparted by the lipid bilayer composition and cholesterol presence, allows the membrane to be dynamic and adaptable. This fluidity enables the membrane to form vesicles during endocytosis by bending and folding inward and to merge or separate easily during exocytosis, ensuring efficient transport of materials in and out of the cell.
