Cellular Transport and Exchange Notes

Transport of Molecules In and Out of Cells

• Nutrients and oxygen must enter the cell for respiration and chemical reactions.

• Waste products must exit the cell to prevent interference with reactions and poisoning.

Diffusion

• Definition: Passive movement of particles from high to low concentration.

• Occurs in liquids and gases, not solids.

• Driven by kinetic energy; no energy required.

• Greater concentration gradient = higher rate of diffusion.

• Examples in organisms:

  • Gas exchange: O2 into cells, CO2 out of cells.

  • Glucose exchange: glucose into cells.

• Factors affecting diffusion rate:

  • Molecule size: smaller = faster.

  • Temperature: higher = faster.

  • Concentration gradient: higher = faster.

  • Distance: shorter = faster.

  • Surface area: larger = faster.

Surface Area to Volume Ratio

• Small organisms (e.g., Amoeba):

  • High SA:V ratio.

  • Efficient diffusion for nutrient/waste exchange.

  • No transport system needed.

• Large organisms:

  • Low SA:V ratio.

  • Diffusion insufficient; need transport systems.

  • Examples: blood/circulatory system (animals), xylem/phloem (plants).

Osmosis

• Definition: Passive diffusion of water from dilute to concentrated solution across a semi-permeable membrane.

• Cell membranes are selectively permeable.

• Water potential: dilute = high, concentrated = low.

• Water moves from high to low water potential.

• Animal Cells:

  • Hypotonic solution: cell bursts (lysis).

  • Hypertonic solution: cell shrivels.

  • Isotonic solution: no net movement.

• Plant Cells:

  • Hypotonic solution: cell becomes turgid.

  • Hypertonic solution: cell becomes flaccid, then plasmolysed.

Reverse Osmosis

• Removes salt from seawater using pressure and a semi-permeable membrane.

• Requires energy.

Active Transport

• Movement of particles from low to high concentration, requiring energy.

• Occurs against the concentration gradient.

• Requires energy from respiration.

• Examples:

  • Nutrient uptake in root hair cells.

  • Glucose absorption in villi cells of the intestine.

Experiment

• Visking tubing with sucrose solution in water demonstrates osmosis.

• Water moves into the tubing, increasing its mass.

Gaseous Exchange

• Breathing: Moving air in and out of the lungs.

• Gas exchange: Transfer of gases from high to a low concentration.

• Cellular respiration: Releasing energy from glucose breakdown.

Characteristics of an Efficient Gas Exchange Surface

• Large surface area.

• Thin epithelium.

• High concentration gradient.

• Rich blood supply.

• Moist surface.

Internal Structure of a Leaf

• Waxy Cuticle : reduce water loss from the surface of the leaf.

• Upper Epidermis: allow light to pass through

• Mesophyll:

  • Palisade Layer: maximum photosynthesis takes place.

  • Spongy Layer: oxygen and carbon dioxide can easily diffuse in and out of the cells.

• Veins: transporting and circulating water and minerals in xylem vessels and food and other nutrients in phloem vessels along the plant.

• Lower Epidermis: gaseous exchange occurs.

Negative Impact of Smoking on Human Health

• Tar :Prevents the cilia lining the trachea from beating upwards.

• Nicotine: makes smoking addictive.
  *Carbon monoxide: binds with haemoglobin in red blood cells instead of oxygen..