#hypotonic solution

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Membrane Transportation

If a cell is placed in a hypotonic solution, what is likely to happen?

Water distribution across plasma membrane governed by water potential difference influenced by solute concentration and hydrostatic pressure. In hypotonic situation exterior fluid contains fewer effective impermeable solutes than cytosol, typically below 300 milliosmoles, so extracellular water activity exceeds intracellular. Osmotic pressure inside higher, chemical potential gradient favors net entry via lipid bilayer and aquaporin water channels that permit single-file diffusion at billion molecules per second. Animal cells lacking rigid wall expand, membrane tension rises, spherical shape adopted, cortical actin remodeling limited. If compensatory mechanisms like regulatory volume decrease activating potassium chloride cotransporter and swelling-activated anion channels insufficient, volume increase continues leading to lysis in extreme cases. Plant cells develop increased turgor pressing plasma membrane against wall and become more rigid. Plasmolysis is opposite phenomenon occurring in hypertonic medium where water leaves and protoplast shrinks away from wall. Thus hypotonic placement generally results in water entering cell causing swelling and potentially bursting.

Ref: Alberts et al., Molecular Biology of the Cell, Chapter 11: Hypotonic Swelling and Regulatory Volume Decrease.

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Membrane Transportation

What happens when red blood cells are placed in a hypotonic solution?

Human erythrocytes are discoid cells lacking nucleus and organelles, bounded by lipid bilayer containing aquaporin-1 water channels and Band 3 anion exchanger, supported by spectrin-actin cytoskeleton providing elasticity but limited capacity to expand. Cytoplasm osmolarity about 300 milliosmoles dominated by potassium, chloride and hemoglobin remains nearly isotonic with plasma. Placing these cells into hypotonic solution where extracellular solute osmolarity lower than intracellular creates higher extracellular water chemical potential. Water rapidly enters down gradient via aquaporin-1 at billions of molecules per second and to lesser extent through lipid phase, increasing cell volume. Membrane area expands, cell shape transforms from biconcave disc to sphere. Cytoskeletal network stretches. Continued influx beyond roughly 1.4 times normal volume exceeds tensile strength, causing transient ruptures and release of hemoglobin into surrounding medium. Supernatant becomes red, pellet disappears, phenomenon termed hemolysis. In hypertonic solutions opposite efflux shrinks cells producing crenated appearance. No active water pumping compensates, as Na+/K+ ATPase maintains ion gradients slowly but cannot counter immediate osmotic water entry.

Ref: Guyton and Hall, Textbook of Medical Physiology, Chapter 4: Erythrocyte Osmosis and Hemolysis in Hypotonic Solutions.

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BASICS of PLANT+PYQS

Plant cell becomes turgid when placed in:

Hypotonic solution (C) is correct here. This is core BASICS of PLANT: once you know the definition or pathway step, Hypotonic solution is the clear fit. The wrong ones are A) Hypertonic solution; B) Isotonic solution; D) Concentrated salt. If the topic is about gradients or potentials, water/solutes move from higher to lower of the relevant quantity.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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BASICS of PLANT+PYQS