Biology Lecture Notes on Cells, Ecosystems, and Symbiotic Relationships

Endomembrane System

  • Endoplasmic Reticulum (ER)
    • Transport Network
    • Internal transport network in the cell.
    • Transports proteins and other products that are exported.
    • Types of ER
    • Rough ER:
      • Studded with ribosomes, synthesizes proteins for export.
    • Smooth ER:
      • Lacks ribosomes, involved in enzyme activity, fat, and carbohydrate production, detoxification processes.
  • Golgi Body
    • Functions as the “packaging and shipping center” for materials.
    • Structure: A stack of flat sacs (like deflated beach balls).
    • Process:
    • Materials from the Golgi exit in small vesicles, fusing with the cell membrane to release contents (exocytosis).
  • Vesicles and Vacuoles
    • Vesicles: Small membrane sacs for transport/storing materials.
    • Vacuoles: Large, fluid-filled sacs found typically in plant cells that appear as empty spaces in tissue cross-sections.

Cytoskeleton and Motility

  • Cytoskeleton
    • Network of protein microtubules and microfilaments that supports the cell, assisting in movement.
    • Flagella and Cilia:
    • Hairlike structures; flagella are long, cilia are short, both help in movement of cells or fluids past the cell.

Mitochondria

  • Commonly referred to as the “powerhouse of the cell.”
  • ATP (Adenosine Triphosphate)
    • Consists of adenosine and three phosphate groups.
    • Releases energy when one phosphate group is removed converting it to ADP (Adenosine Diphosphate).
    • Example of ATP Function:
    • ATP donates a phosphate to myosin, which leads to conformational change, allowing muscle contraction through movement against actin.
  • Mitochondria are key in metabolic processes that extract energy from food and convert ADP back to ATP, cycling 500-750 times daily.

Chloroplasts

  • Site of photosynthesis where solar energy is converted into larger organic molecules.

Endosymbiotic Theory

  • Proposed by Lynn Margulis in 1970 in "Origin of Eukaryotic Cells."
  • Suggests:
    • Mitochondria are descended from free-living bacteria that entered a primitive eukaryotic cell.
    • Chloroplasts share a similar origin from free-living photosynthetic bacteria.

Lines of Evidence for Endosymbiotic Theory

  • Mitochondria and Chloroplasts Characteristics:
    • Own circular DNA similar to bacteria.
    • Contains ribosomes resembling those of bacteria.
    • Susceptibility to antibiotics that target bacteria.

Symbiotic Relationships

  • Symbiosis: Relationship between species; can be mutualism, parasitism, or commensalism.
  • Mutualism: Both partners benefit.
    • Example: Bees and flowers; bees pollinate while obtaining nectar.
  • Parasitism: One partner benefits while the other is harmed.
    • Example: Ascaris (intestinal roundworm) affecting humans.
  • Commensalism: One partner benefits without harming the other.
    • Example: Cattle egrets feeding on insects stirred up by grazing cows.

Ecology

  • Definition: Study of organism interactions with each other and their environment.
  • Levels of Organization:
    • Population: Members of a single species in an area.
    • Community: Interacting populations of different species.
    • Ecosystem: Sum of communities and their abiotic environment.
    • Biome: Similar ecosystems sharing climate.
    • Biosphere: All life on Earth.
  • Population Growth:
    • Exponential Growth: Unlimited resources lead to population spikes (J-curve).
    • Logistic Growth: Levels off at carrying capacity (K), often depicted as a sigmoid curve.
  • Factors Affecting Carrying Capacity:
    • Biotic: Presence of predators, prey, or resources.
    • Abiotic: Sunlight, temperature, moisture, nutrients, oxygen levels.