Movement of Substances in Cells

Movement of Substances in and out of Cells

• Cells need glucose, oxygen, water, and salts for energy production and remove waste like ammonia and carbon dioxide. These substances pass through the cell membrane.
• Movement across membranes can occur via diffusion, osmosis, or active transport.

Diffusion

• Definition: Passive movement of particles from a high concentration to a low concentration.
• Mechanism: Particles with kinetic energy constantly move, causing them to spread out evenly.
• Example: Food coloring in water diffuses throughout the entire glass.
• Passive: No energy needed; happens automatically.

Explaining Diffusion

• Concentration Gradient: Particles move down a concentration gradient, from high to low particle concentration.
• Factors affecting rate of diffusion:
  • Temperature: Higher temperatures increase particle kinetic energy, therefore increasing the rate of diffusion.
  • Size of molecules: Smaller molecules diffuse faster than larger molecules.
  • Diffusion distance/Membrane thickness: Shorter distances across thinner membranes speed up diffusion.

Large Concentration Gradients

• Greater difference in concentrations between regions results in faster diffusion.
• No net movement: Regardless substances still move (into or out of cell) but overall there's no significant net movement.

Larger Diffusion Surface Area

• Larger surface areas increase the rate of diffusion.
• Increased surface area allows more particles to move across the membrane at once.

Surface Area to Volume Ratio

• Important for cell function, as cells need to exchange substances with their surroundings.
• High surface area to volume ratio is ideal for diffusion; Smaller cells have a higher ratio than larger ones, better facilitating diffusion.

Diffusion in Larger Organisms

• Larger organisms have a smaller surface area to volume ratio.
• Respiratory systems (like lungs) are necessary for sufficient gas exchange.
• These systems increase the surface area to efficiently transport oxygen and remove carbon dioxide.

Osmosis

• Definition: Passive diffusion of water molecules from a dilute solution (more water) to a concentrated solution (less water) through a selectively permeable membrane.
• Mechanism: Water moves to equalize the concentration of water on both sides of the membrane.
• Example: Water moves across a semi-permeable membrane.

Cells and Osmosis

• Keywords:

  • Solution: Liquid with dissolved solid.
  • Concentrated solution: Higher solute concentration (less free water).
  • Dilute solution: Lower solute concentration (more free water).
  • Distilled water: Pure water ( no solutes).

• Higher concentration gradients of water lead to faster osmosis.

• Cell membranes in cells are selectively permeable, allowing water to enter and exit cells.

Putting Animal and Plant Cells in Different Solutions

• Hypotonic solution: More water outside the cell; cell swells. Animal cells may burst (lyse), while plants become turgid.
• Isotonic solution: Equal water concentration inside and outside the cell; no net movement. Both animal and plant cells maintain normal shape.
• Hypertonic solution: More water inside the cell; cell shrinks or shrivels. Animal cells may crenate, while plants become plasmolysed.

Active Transport

• Definition: Movement of particles through a cell membrane against their concentration gradient.
• Mechanism: Requires energy (from respiration) and transport proteins.
• Example: Absorption of mineral salts by plant root cells, nutrient absorption in the small intestine.

Examples of Active Transport

• Animals: Glucose absorption in the small intestines.
• Plants: Mineral ion uptake by root cells.

This quiz explores the processes involved in the movement of substances in and out of cells, focusing on diffusion, osmosis, and active transport. Understanding these mechanisms is crucial for grasping how cells obtain nutrients and remove waste. Test your knowledge on concentration gradients and factors influencing diffusion rates.