Transport in Living Organisms

Transport is the process by which metabolic materials, nutrients, gases, and waste products are moved from one part of an organism to another. In small organisms, simple diffusion suffices, but complex multicellular organisms require specialized systems.

1. The Need for Transportation

The necessity of a transport system is primarily dictated by the Surface Area to Volume Ratio (SA:V). Small, unicellular organisms (like Amoeba) have a large SA:V ratio, allowing materials to diffuse directly through their cell membranes. As organisms increase in size and complexity, their volume increases much faster than their surface area, making the distance to the center of the body too great for diffusion alone to sustain life. Hence, specialized transport systems are needed to bridge this gap.

2. Materials for Transportation

• Excretory products: Carbon dioxide, urea, and excess salts moved to excretory organs.
• Gases: Oxygen from respiratory surfaces to cells; CO2 from cells to respiratory surfaces.
• Manufactured food: Glucose/sucrose from leaves to other plant parts via the phloem.
• Digested food: Amino acids and glucose from the gut to cells.
• Hormones: From endocrine glands to target organs.
• Water and Minerals: Absorbed from soil and distributed through the plant.

3. Channels for Transportation

A. Mammalian Circulatory System

• The Heart: A muscular pump that drives blood through the vessels.
• Arteries: Carry oxygenated blood (except the pulmonary artery) away from the heart under high pressure. They have thick, elastic walls.
• Veins: Carry deoxygenated blood (except the pulmonary vein) toward the heart under low pressure. They possess valves to prevent backflow.
• Capillaries: Tiny, thin-walled vessels where gas and nutrient exchange occurs between blood and tissues.
• Specific Vessels:
  • Hepatic Portal Vein: Transports nutrient-rich blood from the gut to the liver.
  • Pulmonary Artery: Carries deoxygenated blood to the lungs.
  • Pulmonary Vein: Carries oxygenated blood from the lungs to the heart.
  • Aorta: The main artery carrying oxygenated blood to the body.
  • Renal Artery/Vein: Supply and drain blood from the kidneys.

B. Plant Vascular System

• Xylem: Conducts water and dissolved mineral salts from the roots to the leaves. It also provides mechanical support (lignified).
• Phloem: Translocates manufactured food (sucrose) from the leaves to other parts of the plant (storage organs and growing points).

4. Media and Mechanisms of Transport

A. Transport Media

• Cytoplasm: Media for intracellular transport in unicellular organisms.
• Cell Sap: Found in plant vacuoles.
• Blood: Composed of plasma, red blood cells (transport O2), white blood cells (immunity), and platelets (clotting).
• Lymph: A colorless fluid that returns excess tissue fluid to the circulatory system.

B. Mechanisms

• Diffusion: Movement of molecules from high to low concentration.
• Osmosis: Movement of water through a semi-permeable membrane.
• Plasmolysis: Shrinking of plant cell cytoplasm away from the cell wall in a hypertonic solution.
• Turgidity: State where the plant cell is swollen due to water intake, providing support.
• Transpiration Pull: Suction force created by evaporation from leaves that draws water up the xylem.
• Root Pressure: Osmotic pressure within the roots that pushes water upward.
• Active Transport: Movement against a concentration gradient using energy (ATP).