jan 30

When discussing concentration, molarity is often referenced as the standard measure for concentration, although the term used was incorrectly referred to as "molybdenum."
Molarity is typically defined as the number of moles of solute per liter of solution.

The concept of osmolarity is introduced, which provides a comparison of solute concentrations in different solutions.
Terminology related to osmolarity:
- Isosmotic: Two solutions that have the same osmotic pressure.
- Hyperosmotic: A solution with a higher osmotic pressure than another solution (more solute outside the cell than inside).
- Hyposmotic: A solution with a lower osmotic pressure than another solution (less solute outside the cell than inside).

The cell's volume changes in response to the environment and is influenced by the osmotic conditions of its surroundings.
The need for comparison between two solutions is emphasized to define osmotic terms.

Examples of drawing diagrams to illustrate the osmotic conditions:
- Different solutions (labelled as A, B, and C) to visualize the concentrations of solute particles inside and outside of cells.
- For hyperosmotic solutions, the diagram should illustrate more solute particles outside the cell than inside, implying a potential for water movement out of the cell.

The discussion includes the equilibrium state that solutes (non-penetrating and penetrating) attempt to reach between different concentrations within a system.
It is noted that pressure may oppose equilibrium and that equilibrium is not always achieved, depending on various factors.

Transport mechanisms, such as diffusion and active transport, are introduced:
- Diffusion: The process where solutes move from an area of higher concentration to an area of lower concentration until equilibrium is established.
- This is a natural process that does not require energy.
- Active Transport: The process by which solutes, such as potassium, move against their concentration gradient (from low to high concentration), requiring energy (ATP).

Endocytosis: A form of active transport wherein substances from outside the cell are engulfed by the cell membrane to form a vesicle, bringing them inside the cell.
- Requires energy (ATP) for the process.

Core principles influencing the rate of diffusion include:
- Directly related to temperature: Higher temperatures increase the rate of diffusion, while lower temperatures decrease it.
- Inversely related to molecular weight and size: Larger molecules diffuse slower than smaller molecules.

Diffusion can occur in an open system or across a membrane partition:
- An open system example: A petri dish with agar and dye, illustrating how the dye disperses in the absence of barriers.
- The principles of diffusion apply to molecules that lack charge, contrasting with ions that require additional considerations due to their charge.

Explanation on kinetic movement includes:
- Larger numbers may indicate slower diffusion rates, emphasizing that kinetic energy affects the movement of smaller particles more effectively than larger ones.

Factors influencing membrane permeability for various solutes (e.g., glucose):
- Glucose is presented as a larger molecule, needing transport proteins to cross cell membranes due to its size and polarity.
- Electrochemical gradients impact the transport of ions primarily.

Lipophilic molecules can easily cross the phospholipid bilayer due to their affinity for lipids. This property facilitates their movement through cell membranes.

Inside cells, potassium ions are typically present in higher concentrations compared to outside, while chloride ions are more concentrated outside the cell.
The presence of specific channels (e.g., selective for potassium ions) allows for the regulated movement of these ions across membranes.
At equilibrium, the currents of potassium may balance, contributing to the resting membrane potential of the cell.

The concept of resting membrane potential is briefly mentioned, with a reference to an external video resource for further understanding.