Solvent Properties of Water in Metabolism and Transport

Solvent Properties of Water

• A solvent is a liquid in which a solute dissolves, while a solute is the substance that dissolves in a solvent.
• Solvation is the interaction of a solvent with a dissolved solute, and water forms hydrogen bonds with the solute, creating a hydration shell around it.
• Not everything dissolves in water; nonpolar molecules without a charge (hydrophobic) do not dissolve in water and clump together when exposed to water.

Role of Water as a Medium for Metabolism

• Cytosol is the liquid part of the cytoplasm, common to all cells, composed of about 80% water and containing dissolved salts, fatty acids, sugars, amino acids, and proteins such as enzymes.
• Water is necessary for cellular metabolism as it dissolves reactants and enzymes, allowing catabolic and anabolic reactions to occur.
• Catabolic reactions break down large molecules into smaller ones, while anabolic reactions build larger molecules from smaller ones.

Transport in Plants and Animals

• Mineral ions are transported in xylem sap in plants.
• Sucrose and other products of photosynthesis are transported in phloem sap in plants.
• In animals, blood transports:
  • Salt ions (Na+ and Cl-)
  • Amino acids (both negative and positive charges)
  • Proteins (antibodies and those used in blood clotting)
  • Glucose (polar molecule, freely soluble and carried in plasma)
  • Waste products of metabolism (urea, later removed from the blood at the kidney)
  • A small amount of dissolved gases (CO2 and O2)

Physical Properties of Water

• Water's physical properties make it the medium of life.
• Physical properties include:
  • Buoyancy: a force exerted upwards on an object, which can cause it to float or sink.
  • Viscosity: a measure of a fluid's tendency to flow, with thicker fluids having higher viscosity.
  • Thermal conductivity: a measure of a material's ability to move heat across a temperature gradient, with water having high thermal conductivity.
  • Specific heat capacity: the quantity of heat needed to raise the temperature of a chemical per unit mass, with water having the highest specific heat capacity of any liquid.

Cell Structure and Function

• Similarities between prokaryotic and eukaryotic cells:
  • All cells have a plasma membrane.
  • All cells contain genetic material.
• Structures common to cells in all living organisms:
  • Plasma membrane
  • Cytoplasm
  • DNA
  • Ribosomes

Prokaryotic Cell Structure

• Prokaryotic cells lack a nucleus, mitochondria, and membrane-bound organelles.
• They have a simple cell structure without compartments.
• Prokaryotic cells were the first cells to evolve and are mostly small in size.
• Functions of structures in prokaryotic cells:
  • Plasma membrane: regulates what materials enter and exit the cell.
  • Cytoplasm: a gel-like fluid substance where metabolic reactions occur.

Eukaryotic Cell Structure

• Differences in eukaryotic cell structures between animals, fungi, and plants:
  • Plastids: present in plant cells, including chloroplasts for photosynthesis and amyloplasts for starch storage.
  • Cell wall: present in fungal and plant cells, composed of chitin in fungi and cellulose in plants.
  • Vacuole: present in fungal and plant cells, used for storage and pressurizing the cell.
  • Centrioles: present in animal cells, used for organizing the assembly of structures composed of microtubules.

Atypical Cell Structure in Eukaryotes

• Discrepancies:
  • Red blood cells: lack a nucleus.
  • Aseptate fungal hyphae: have many nuclei.
  • Skeletal muscle fibers: have many nuclei.
  • Phloem sieve tube elements: lack a nucleus.

Evolution of Multicellularity

• Multicellularity: an organism composed of many cells, where cells specialize and lose the ability to live independently.
• Evolution of multicellularity:
  1. Formation of cellular clusters from single cells.
  2. Differentiation of cells within the cluster for specialized functions.