Osmosis | Osmolarity | Osmotic Equilibrium | Transport Across the Cell Membrane | Cell Physiology

Summary

This video from Byte Size Med explains osmosis, a type of passive transport where solvents like water move across a semi-permeable membrane to balance solute concentrations. It differentiates between isotonic, hypotonic, and hypertonic solutions, illustrating how they affect cell size. The video also covers osmotic pressure, osmolarity, and osmolality, emphasizing the importance of understanding these concepts for maintaining cellular equilibrium.

Takeaways

• 💧 Passive transport moves substances along a concentration gradient, requiring no metabolic energy like ATP.
• ⚡ Active transport moves substances against a concentration gradient, requiring ATP for energy.
• 🌊 Osmosis is a type of passive transport involving the movement of water (solvent) across a semi-permeable membrane.
• 🔬 In osmosis, water moves from an area of low solute concentration to an area of high solute concentration to reach equilibrium.
• 🧂 The solute is the substance dissolved in a solvent; for example, salt in salt water.
• ⚖️ Osmotic pressure is the pressure needed to stop the movement of water, depending on the number of solute particles.
• 📏 Osmolarity measures solute concentration in terms of osmoles per liter of solution, while osmolality measures it per kilogram.
• 🔄 Isotonic solutions have equal concentrations inside and outside the cell, causing no change in cell size.
• ⬆️ In a hypotonic solution, water enters the cell, causing it to swell due to a higher solute concentration inside.
• ⬇️ In a hypertonic solution, water leaves the cell, causing it to shrink due to a higher solute concentration outside.

Q & A

What is the difference between passive and active transport across a cell membrane?

Passive transport does not require extra metabolic energy and occurs along a concentration gradient from high to low. Active transport requires energy, like ATP, because it moves substances against the concentration gradient, from low to high.

What is osmosis and how does it differ from diffusion?

Osmosis is the movement of the solvent (water) across a semi-permeable membrane, from an area of lower solute concentration to higher solute concentration. Diffusion, on the other hand, is the movement of the solute from high to low concentration until equilibrium is reached.

What role does a semi-permeable membrane play in osmosis?

A semi-permeable membrane allows only certain substances to pass through. In osmosis, it lets water (the solvent) pass but prevents the solute from moving, allowing water to move towards higher solute concentrations to reach equilibrium.

How is osmotic pressure defined, and what does it depend on?

Osmotic pressure is the pressure needed to stop the movement of water across a membrane. It depends on the number of solute particles in the solution, meaning the higher the number of solute particles, the greater the osmotic pressure.

What is the difference between osmolarity and osmolality?

Osmolarity refers to the number of osmoles per liter of solution, while osmolality refers to the number of osmoles per kilogram of solvent. Both measure the concentration of solutes in a solution.

What is meant by the terms isoosmotic, hyposmotic, and hyperosmotic?

Isoosmotic refers to solutions with equal osmolarity. Hyposmotic refers to a solution with lower osmolarity compared to another, while hyperosmotic refers to a solution with higher osmolarity.

What is an ineffective osmole, and why is it called so?

An ineffective osmole is a solute that can freely cross the membrane, which allows it to equalize concentrations quickly, preventing the formation of a sustained osmotic gradient. This makes it ineffective in driving osmosis.

What is tonicity and how is it different from osmolarity?

Tonicity refers to the effect of a solution on cell volume and takes into account the concentration of solutes that cannot cross the membrane, thus contributing to the osmotic gradient. Osmolarity includes all solutes, regardless of their ability to cross the membrane.

How do isotonic, hypotonic, and hypertonic solutions affect cell size?

In an isotonic solution, the concentration of solutes is equal inside and outside the cell, so the cell size remains unchanged. In a hypotonic solution, water enters the cell, causing it to swell. In a hypertonic solution, water leaves the cell, causing it to shrink.

Why does water move towards higher solute concentrations during osmosis?

Water moves towards higher solute concentrations to dilute the solute and achieve equilibrium, where the concentrations of the solute are equal on both sides of the membrane.