Biology Lecture Notes Review

Algae

  • General Overview
    • Approximately 6000 species of green algae exist, with various lifestyles:
      • Many species live most of their lives as single cells.
      • Other species form colonies or long filaments.
    • Characteristics:
      • Algae possess simple reproductive structures.
      • Lack extensive vascular structures found in higher plants.
      • Eukaryotic organisms who perform oxygenic photosynthesis.
    • Classification based on:
      • Morphology
      • Types of chlorophylls
      • Carbon reserve storage materials
      • Cell wall composition
      • Habitat
    • Mobility: Most green algae are non-motile; however, some may have motile reproductive cells.

Pigments

  • All eukaryotic algae possess chlorophyll a, which gives them a bright green color.
  • Algae are differentiated by their accessory pigments that include:
    • Chlorophyll b, c1, c2, d and various carotenoid pigments.
    • These pigments capture photons of wavelengths not absorbed by chlorophyll a.
  • Specific accessory pigments depending on local light conditions:
    • Green algae living at the ocean/lake surface utilize carotene (a yellow pigment) to trap purple and UV light.
    • Below the surface, red algae use phycobilins, brown algae use fucoxanthin, and golden algae use xanthophylls to capture blue-green light.
  • Evolutionary Note:
    • All land plants are believed to have evolved from green algae possibly due to better adaptation to high light conditions and UV radiation, making them resistant to photobleaching (the destruction of photosynthetic pigments by excess light).

Diatoms

  • Diatoms belong to the larger group known as heterokonts, which include:
    • Autotrophs (e.g., golden algae, kelp)
    • Heterotrophs (e.g., water molds)
  • Diversity: Over 200 genera and approximately 100,000 extant species of diatoms are identified.
  • Structure:
    • Diatoms have frustules, which are two hard cell walls made of silicon oxide.
    • Contains yellowish-brown chloroplasts with pigments, e.g., fucoxanthin.
  • Habitat:
    • Found in various locations including oceans, freshwater, soils, and damp surfaces.
    • Most inhabit open waters while some exist at the water-sediment interface or under damp atmospheric conditions.
  • Ecological Role:
    • Diatoms are significant contributors to oceanic primary production, estimated at 45% of total production.

Euglena

  • Euglena is classified as a flagellated cell, possessing both chlorophyll a and b akin to higher plants.
  • Uniqueness:
    • Can lose its chloroplasts under dark conditions or when exposed to the antibiotic streptomycin.
    • Capable of survival as a heterotroph in these conditions, highlighting its dual affinity to both algae and protozoa.
  • Taxonomy Note:
    • Botanists classify Euglena as an alga, whereas zoologists recognize it as a protozoan.

Classification of Algae

  • Green Algae with Analogous Arrangement/Organization:
    • Ulothrix: Unicellular colonial
    • Chlamydomonas: Unicellular
    • Volvox: Colonial
    • Spirogyra: Filamentous algae

Bacteriophage: T4

  • Introduction to Bacteriophages:
    • Defined as viruses that infect bacteria.
    • Interaction with host cells occurs predominantly through two methods:
      • Lytic Cycle:
        • Complete takeover of the host cell's metabolism, leading to cell lysis (destruction).
        • Steps of Infection:
          1. Attachment to the bacterial cell wall.
          2. Injection of viral DNA into the bacterial cytoplasm.
          3. Viral genome commandeers cellular machinery to produce viral proteins for phage assembly.
          4. Post-assembly, the host cell lyses, releasing new phages to infect other cells.
        • Example: T3 bacteriophage that infects Escherichia coli.
      • Temperate/Latent Phage (Lysogenic Cycle):
        • Coexist with the host cell, replicating alongside it.
        • Steps of Infection:
          1. Attachment to the bacterial cell wall.
          2. Injection of viral DNA into the bacterial cytoplasm.
          3. Integration of viral nucleic acid into the host's chromosome.
          4. Delayed takeover of host processes; replication of phage is deferred.
          5. Waltz into the lytic cycle is prompted by environmental stress to escape cell death.
        • Example: Lambda bacteriophage that infects E. coli.

Lytic and Lysogenic Cycle Details

  • Control Stimuli for Lysogenic to Lytic Transition:
    • Exposure to environmental stressors like radiation and toxic substances can provoke this switch.
  • Key Differences in Results of Infections:
    • Lytic cycle: Viral DNA infection directly correlates to multiplication of viruses and lysis of the host.
    • Lysogenic cycle: A prophage is maintained as part of the host chromosome.

Life Cycle of a Typical Temperate Phage (Coliphage)

  • Steps:
    • Infection
    • Attachment
    • Entry
    • Cellular replication
    • Induction
    • Lysis

Plaque Counting Method for Lytic Bacteriophage

  • Lysis of bacterial cells cultured on agar plates leads to clearings observable by the naked eye, termed plaques.
  • Plaque Assay:
    • Utilizes lysis to gauge phage concentration in samples.
    • Process:
      1. Sample of bacteriophage added to an agar plate inoculated with bacteria to produce a growth lawn.
      2. Count of plaques indicates original phage density.
    • Comparison to Standard Plate Count:
    • Employs serial dilutions for generating countable plates.

Detection of Bacteriophages through Plaque Assay Technique

  • Process:
    • Diluted phage combines with broth culture.
    • Mixture layered onto prepared nutrient agar plates as an agar overlay.
    • Soft agar immobilizes bacterial growth while allowing phage diffusion.
    • Incubation leads to bacterial lawn with plaques representing lysed cells.
    • Number of plaques indicates phage particles/ml or plaque forming units (pfu).

Water Quality Analysis

  • Historical Context:

    • First public well in New York City dug near Bowling Green in 1677.
    • Population growth by 1776 necessitated reservoir construction due to increased demand.
    • Expansion of water sources by drawing from the Catskill and Delaware watersheds.

  • Current Water Supply:

    • NYC’s water system involves three upstate reservoir systems comprised of 19 reservoirs and 3 controlled lakes holding 580 billion gallons of water.

  • Legislation:

    • Total Coliform Rule (1989) established legal limits for total coliform presence in drinking water.
    • Regular monitoring mandated by local governments and the Environmental Protection Agency (EPA):
      • Frequency depends on population size:
        • <1000 people = once/month
        • >2.5 million = approximately 420 times/month
      • <5% of samples allowed to be positive for coliforms.

  • Pathogen Detection:

    • Most water-borne diseases stem from fecal contamination by pathogens.
    • Indicator organisms (like Escherichia coli) are used due to their persistence, abundance, and lower risk in culturing.

  • Testing Method:

    • Conduct tests on water samples to identify presence of indicator organisms to ensure water purity.

  • IDEXX Enterolert System:

    • Recognized detection system approved by the EPA for water quality.
    • Based on the Most Probable Number (MPN) estimation for bacteria in a culture, utilizing proprietary media that selects for Enterococci spp. and fluoresces blue under UV light.
    • Calculating MPN involves sizing analyzation based on fluorescence ratio in small and large wells of IDEXX trays.