Bio 100 LAB 1 Study Guide UPDATED

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Microscopy and the Cell

Introduction to Cell Structure

Understanding cell structure is fundamental to biology. The cell theory states that all organisms are composed of cells and all cells arise from pre-existing cells. Cells are the basic units of life, and their structure determines their function.

Cell Theory: (1) All living things are made of cells; (2) All cells come from other cells.
Cell Types: Cells are classified as prokaryotic or eukaryotic based on their internal organization.

Prokaryotic and Eukaryotic Cells

Key Differences Between Prokaryotic and Eukaryotic Cells

Prokaryotic and eukaryotic cells differ in several fundamental ways, including the presence of a nucleus, organelles, and the organization of genetic material.

Characteristic	Prokaryotic Cells	Eukaryotic Cells
Membrane-bound organelles	None	Mitochondria, Chloroplasts, Golgi, ER, etc.
Nucleus	No true nucleus; nucleoid region	True nucleus with nuclear envelope
Organization of DNA	Few proteins, 1 circular chromosome	Multiple linear chromosomes with histones
Type of cell division	No mitosis	Mitosis
Size	Small	Large

Prokaryotic Cells: Lack a true nucleus and membrane-bound organelles. DNA is found in the nucleoid region as a single circular chromosome.
Eukaryotic Cells: Have a true nucleus surrounded by a nuclear envelope and contain multiple membrane-bound organelles. DNA is organized into multiple linear chromosomes associated with proteins.
Endosymbiosis Theory: Mitochondria and chloroplasts contain their own small, circular DNA, similar to prokaryotes, supporting the idea that these organelles originated from free-living prokaryotes incorporated into ancestral eukaryotic cells.

Types of Prokaryotic Organisms

Archaebacteria: Some are methanogenic or reduce sulfur.
Pseudobacteria: Tiny, lack true cell walls (e.g., mycoplasmas).
Bacteria: Have true cell walls.
Cyanobacteria: Also known as blue-green algae; photosynthetic.

Autotrophic Prokaryotes: Produce their own nutrients via photosynthesis or chemosynthesis (e.g., cyanobacteria).
Heterotrophic Prokaryotes: Obtain energy from organic molecules; most bacteria are saprophytic (decompose dead material) or parasitic.

Structure of a Typical Prokaryotic Cell

Cell Wall: Provides strength and protection.
Capsule: Additional protective layer.
Plasma Membrane: Surrounds cytoplasm; too thin to be seen with a light microscope.
Nucleoid: Region containing DNA.
Flagellum: Provides motility.

Eukaryotic Organisms

Overview of Eukaryotic Cell Structure

Eukaryotic cells contain a variety of organelles, each specialized for specific functions. The four main groups of eukaryotes are protists, fungi, plants, and animals.

Mitochondria & Chloroplasts: Involved in energy metabolism.
Endoplasmic Reticulum (ER): Rough ER (with ribosomes) synthesizes proteins; smooth ER synthesizes lipids.
Golgi Apparatus: Processes and packages proteins for export or membrane insertion.

Protists

Protists are the simplest eukaryotes, mostly unicellular, and highly diverse. They can be classified as non-photosynthetic (protozoa and fungus-like protists) or photosynthetic (algae).

Protozoa: Unicellular, motile, heterotrophic, lack cell walls. Examples include Amoeba and Paramecium.
Algae: Photosynthetic, may be unicellular or colonial, most have cell walls. Example: Euglena (photosynthetic, lacks cell wall, can be heterotrophic in the dark).

Examples of Protists

Amoeba: Moves and ingests food by extending pseudopodia; flexible; some are parasitic (e.g., Entamoeba histolytica).
Paramecium: Uses cilia for locomotion; has a macronucleus (asexual reproduction) and micronuclei (conjugation); contains contractile vacuoles for osmoregulation.
Euglena: Has flagella, chloroplasts, and an eyespot for detecting light; can switch between autotrophic and heterotrophic metabolism.

Locomotion in Protists

Amoeba: Moves by pseudopodia (cytoplasmic extensions).
Paramecium: Moves by coordinated beating of cilia.
Euglena: Moves using flagella.
All forms of movement require cytoskeletal elements and ATP.

Multicellular Organisms

Advantages of Multicellularity

Surface-to-Volume Ratio: Limits cell size; as cells grow, volume increases faster than surface area, limiting nutrient uptake and regulation.
Cell Specialization: Allows formation of tissues and organs with specialized functions (e.g., red blood cells for oxygen transport, muscle cells for movement).
Gene Expression: Different cell types express different sets of proteins, determined by specific genes.

Types of Multicellular Organisms

Plants: Multicellular, autotrophic, contain tissues specialized for photosynthesis, support, and storage.
Animals: Multicellular, heterotrophic, diverse cell types (e.g., muscle, nerve, epithelial).
Fungi: Multicellular (except yeasts), heterotrophic, cell walls made of chitin.

Plant Cells

Structure and Specialization

Chloroplasts: Site of photosynthesis.
Cell Wall: Provides structural support.
Large Central Vacuole: Stores water and nutrients.
Lack Centrioles: Unlike animal cells.
Protoplasmic Streaming: Movement of organelles within the cell, mediated by the cytoskeleton.
Root Cells: Specialized for absorption; lack chloroplasts and large vacuole.

Animal Cells

Structure and Specialization

No Cell Wall, Chloroplasts, or Large Vacuole: Distinguishes animal cells from plant cells.
Centrioles: Present in animal cells, involved in cell division.
Organelles: Nucleus, mitochondria, Golgi apparatus, endoplasmic reticulum, lysosomes, peroxisomes, cytoskeleton.
Example: Human cheek cells are typical animal cells; nucleus is visible under the light microscope.

Microscopy: Principles and Practice

Light Microscopy

The light microscope allows visualization of cells and small organisms. Two key concepts are magnification and resolution.

Magnification: Increases the apparent size of an object.
Resolution: The smallest distance at which two points can be distinguished as separate. For the human eye, this is about 0.1 mm; for a light microscope, about 0.1 μm; for a transmission electron microscope, about 0.001 μm.

Measurement and Magnification in Microscopy

To estimate cell size, use a slide with a known scale (e.g., mm graph paper) and compare the field of view to the scale.
Example calculation: If 1.5 boxes (1.5 mm) fit across the field, and a cell is 1/3 the diameter, its size is .

Laboratory Observations

Plant Cells

Onion Cells: Thick cell wall, visible nucleus; size can be estimated by counting cells across the field of view.
Elodea Cells: Observe chloroplasts and protoplasmic streaming (cyclosis).
Potato Cells: Stain with Lugol's reagent to observe starch granules (red for straight chains, blue for branched, purple for both).

Animal Cells

Human Cheek Cells: Stain with methylene blue; observe nucleus and cell shape.

Protists

Amoeba: Observe pseudopodia and cytoplasmic streaming.
Paramecium: Observe cilia, macronucleus, micronuclei, contractile vacuole, and food vacuoles.
Pond Mix: Observe diversity of protists, including Euglena.

Living Cultures and Behavior

Brown Hydra: Observe feeding and movement; hydra are sensitive to vibration and display defensive postures.
Comparison: Hydra feeding behavior differs from that of paramecia or amoeba, which use different mechanisms for locomotion and food intake.

Summary Table: Key Features of Cell Types

Cell Type	Key Features	Examples
Prokaryotic	No nucleus, no membrane-bound organelles, small size, circular DNA	Bacteria, Cyanobacteria
Protist (Eukaryotic)	Unicellular, may have cilia/flagella/pseudopodia, nucleus, organelles	Amoeba, Paramecium, Euglena
Plant	Cell wall, chloroplasts, large central vacuole, nucleus	Elodea, Onion, Potato
Animal	No cell wall, no chloroplasts, nucleus, centrioles	Human cheek cell

Key Terms and Concepts

Organelle: Specialized structure within a cell performing a specific function.
Nucleus: Membrane-bound organelle containing genetic material in eukaryotes.
Chloroplast: Organelle for photosynthesis in plants and algae.
Mitochondrion: Organelle for cellular respiration and energy production.
Cytoskeleton: Network of protein filaments for cell shape and movement.
Pseudopodium: Temporary cytoplasmic projection for movement and feeding in amoeboid cells.
Cilia/Flagella: Hair-like structures for movement.
Vacuole: Storage organelle, large in plant cells.
Magnification: Apparent increase in size of an object.
Resolution: Ability to distinguish two points as separate.

Formulas

Estimating Cell Size:

Magnification Calculation:

Additional info: The notes above expand on the basic laboratory procedures and cell biology concepts, providing definitions, examples, and context for microscopy and cell diversity. This guide is suitable for introductory college biology students preparing for laboratory or exam review.