Principles of Biology I - Laboratory Manual - Spring 2022 - Hunter college

Microscopy and the Cell

  • Objectives:
    • Study cell structure and characteristics of different cell types.
    • Identify organelles (nuclei, chloroplasts, mitochondria).
    • Learn which organelles cannot be seen with a light microscope.
    • Become familiar with the light microscope.
  • Cell Theory: (1) All organisms are made of cells, and (2) all cells come from other cells.
  • Prokaryotic Cells
    • Lack a true nucleus and membrane-bound organelles.
    • Most lack internal membranes (except photosynthetic bacteria and cyanobacteria).
    • DNA is in the nucleoid region as a single, circular chromosome with few proteins.
    • Do not divide by mitosis.
  • Eukaryotic Cells
    • Contain a true nucleus with a double membrane (nuclear envelope).
    • Have several linear chromosomes, DNA packaged with histones and proteins.
    • Contain more DNA than prokaryotic cells.
    • Divide by mitosis.
    • Contain organelles (mitochondria, chloroplasts, Golgi, endoplasmic reticulum).
  • Organelle DNA: Mitochondria and chloroplasts contain small, circular, protein-devoid chromosomes, resembling prokaryotic chromosomes.
    • Endosymbiosis Theory: Ancestors of mitochondria and chloroplasts were free-living organisms incorporated into prokaryotic cells.
  • Prokaryotic Organisms
    • Archaebacteria: Some methanogenic, some reduce sulfur.
    • Pseudobacteria: Tiny, lack true cell walls (e.g., mycoplasmas).
    • Bacteria: Have true cell walls.
    • Cyanobacteria: Blue-green algae.
    • Autotrophic prokaryotes: Photosynthetic bacteria and cyanobacteria produce their own nutrients.
    • Heterotrophic prokaryotes: Obtain energy from preformed organic molecules; most are saprophytic, some are parasitic.
    • Can be single-celled, multicellular, or colonial.

Prokaryotic Cell Structure

  • Cytoplasm surrounded by a cell membrane (too thin to see with a light microscope).
  • DNA in the nucleoid region.
  • Cell walls for strength and protection.
  • May have a capsule for protection and flagella for motion.

Eukaryotic Organisms

  • Have true nuclei and specialized organelles.
    • Mitochondria and chloroplasts: Energy metabolism.
    • Rough endoplasmic reticulum (with ribosomes): Protein synthesis.
    • Golgi apparatus: Processes proteins for export or cell membrane insertion.
  • Four groups: Protists, fungi, plants, and animals.

Protists

  • Simplest eukaryotic organisms; mostly unicellular.
    • Some form simple colonies.
    • Some are multinuclear.
    • Classified as non-photosynthetic (protozoa and protists resembling fungi) and photosynthetic (algae).
Protozoa
  • Diverse group, mostly unicellular, motile, and heterotrophic.
    • Lack cell walls.
    • Examples: Amoeba and Paramecium.
    • Amoeba: Inhabit soils, fresh water, and marine environments; move and ingest food using pseudopodia; some are parasitic (e.g., Entamoeba histolytica).
    • Paramecium: Single-celled, live in fresh water; use cilia for locomotion; have a macronucleus (asexual reproduction) and micronuclei (conjugation/sexual reproduction); contain an oral groove (cell mouth), food vacuoles, and contractile vacuoles (expel excess water taken up by osmosis).
Algae
  • Variety of single-celled and colonial forms; all are photosynthetic.
    • Most have cell walls.
    • Free-living or colonial; some can be very large (e.g., seaweeds).
    • Example: Euglena (in pond mix), which lacks a cell wall and can be heterotrophic in the dark.
    • Euglena: Single-celled, live in pond water; photosynthetic in light, heterotrophic in dark; have chloroplasts, nucleus, contractile vacuole, flagella, and eyespot (senses light direction).

Protist Locomotion

  • Amoeba: Move by extending a pseudopodium.
  • Paramecia: Move by beating cilia.
  • Euglena: Move by flagella.
  • All three types of motion involve cytoskeletal elements and require ATP for energy.

Multicellular Organisms

  • Fungi, plants, and animals are true multicellular organisms.
  • Unicellular organisms have size limits due to the surface-to-volume ratio; multicellularity allows cells to specialize.
  • Cells associate to form tissues and organs with specialized functions.
  • Cells produce different sets of proteins based on their structure and function; instructions for these proteins are in the genes (DNA).

Plant Cells

  • Advanced multicellular autotrophic organisms; contain many types of tissues.
  • Leaf Cells: Specialized for photosynthesis; have chloroplasts, a cell wall, and a large central vacuole; lack centrioles; have nuclei and mitochondria.
    * Protoplasmic streaming (movement of chloroplasts and organelles) is mediated by the cytoskeleton.
  • Root Cells: Lack chloroplasts and a vacuole; specialized for nutrient and water absorption.
  • Animal Cells
    • Have many different cell types (liver cells, muscle cells, etc.).
    • Lack chloroplasts, cell walls, and vacuoles; contain centrioles; have nucleus, mitochondria, Golgi, and endoplasmic reticulum.

Introduction to the Microscope

  • Magnification increases the apparent size of an object.
  • Resolution is the clarity or sharpness of an image.
  • Resolution: Smallest distance two points can be separated and still be observed as distinct entities.
  • Resolution of human eye: Approximately 0.1 mm.
  • Best light microscopes: Resolution of approximately 0.1 micrometer (
    0.1 * 10^{-6} m
    ), 1000 times better than the human eye.
  • Transmission electron microscopes: Resolutions 100 times better than light microscope (0.001 micrometer) and magnifications better than 100,000X.

Measurement and Magnification

  • Estimate object size by determining the diameter of the visual field using a practice slide with 1 cm^2 of mm graph paper.
    • Place the slide under the 10x objective and determine how many boxes align on a diameter of the field of view.

Onion Cells

  • Examine a thin sheet of onion tissue under low power; notice the thick cell wall and nucleus position.
    • Estimate the long dimension of an onion cell.
    • Determine no. of onion cells that run end-to-end across a diameter to calculate individual cell size.
      *Examine under high power (40x objective), but no measurments.
      *Stain with acetocarmine to see what difference the staining makes.
      *Also, note your size (micrometers) and magnification with the drawing so you know how big it is relative to real-life.

Elodea

  • Observe edge of cells, see edge.
  • Watch chloroplasts material is moved along inside of the cell wall.
    *Capture as many details as possible in your sketch.

Potato

  • Cut a as thin as possbile.
    *Stain it with two drops of Lugol's reagent.
    *Straight starch chains will be red.
    *Brached will be straight.
    *If it mixes, than the cell turns purple.

Human Cheek cell

  • Scrape the lining.
    *place both coverslip and methylane blue drops over the slide.
  • Focus under low power, than scan the slide under high. will look blue in the middle.
    *Compare how do these new sells are from the ones seen.