Cell Theory: Inductive & Deductive Reasoning

Cell Theory

• All living organisms consist of one or more cells.
• Cells are the basic structural and organizational units of all organisms.
• Cells arise from pre-existing cells through cell division.
• In scientific language, theories are well-substantiated explanations based on evidence and repeated testing.
• Inductive reasoning involves drawing general conclusions from specific observations.
• Deductive reasoning involves drawing specific conclusions from general principles.
• The cell theory resulted from inductive reasoning based on observations by scientists like Hooke, Schleiden, and Schwann.
• Deductive reasoning can predict that a newly discovered organism is likely composed of cells, given that all known organisms are.

Microscopy Skills

• Total magnification is calculated by multiplying the magnification of the ocular lens by the magnification of the objective lens.
• To focus, start with the lowest power objective, use the coarse focus knob, and then fine-tune with the fine focus knob.
• A temporary wet mount involves placing the specimen on a slide, adding a drop of water, and covering with a coverslip.
• Staining highlights specific structures.
• Use sharp, joined lines for drawings and straight-edge lines for labels.
• Field of view (FOV) is measured using the diameter under low power.
• The formula to calculate FOV under high power is FOVhigh = (FOVlow × Magnificationlow) / Magnificationhigh.
• Magnification of a micrograph is calculated as the size of the image divided by the actual size of the specimen.
• Actual size is calculated as the size of the image divided by the magnification.
• Quantitative observations involve numerical data.
• Qualitative observations involve descriptive data.

Developments in Microscopy

• Resolution is the ability to distinguish between two separate points.
• Magnification is the increase in apparent size of an object.
• Light microscopes use visible light and have a lower resolution (approximately 200 nm).
• Electron microscopes use electron beams and have a higher resolution (approximately 0.1 nm).
• Fluorescent stains highlight specific structures, such as DNA and proteins.
• Immunofluorescence uses antibodies tagged with fluorescent dyes to visualize specific proteins.
• Freeze-fracture electron microscopy splits the membrane to reveal internal structures.
• Cryogenic electron microscopy visualizes proteins at near-atomic resolution by freezing samples.

Structures Common to All Cells

• All cells have a plasma membrane, cytoplasm, ribosomes, and DNA.

Prokaryote Cell Structure

• The cell wall provides shape and protection.
• The plasma membrane regulates the movement of substances.
• The cytoplasm is the site of metabolic reactions.
• 70S ribosomes facilitate protein synthesis.
• Nucleoid DNA contains genetic material.
• Prokaryotic DNA is not enclosed in a nucleus or associated with histones, hence, it is naked DNA.

Eukaryote Cell Structure

• Eukaryotes have a nucleus and membrane-bound organelles, unlike prokaryotes.
• The plasma membrane regulates transport.
• The cytoplasm contains organelles.
• 80S ribosomes enable protein synthesis.
• The nucleus contains DNA.
• Mitochondria are responsible for ATP production.
• Chloroplasts facilitate photosynthesis in plants.
• The endoplasmic reticulum (ER) synthesizes proteins and lipids.
• The Golgi apparatus modifies and packages proteins.
• Vesicles transport materials.
• Vacuoles store materials and dispose of waste.
• Lysosomes contain digestive enzymes.
• The cytoskeleton maintains cell shape and enables movement.

Processes of Life in Unicellular Organisms

• Common processes include metabolism, homeostasis, excretion, growth, nutrition, movement, reproduction, and response to stimuli.
• Paramecium utilizes cilia for movement and contractile vacuoles for osmoregulation.
• Chlamydomonas utilizes flagella for movement and chloroplasts for photosynthesis.

Differences in Eukaryotic Cell Structure

• Cell walls are present in plants (cellulose) and fungi (chitin) but absent in animals.
• Vacuoles are large in plants and small in animals/fungi.
• Chloroplasts are present in plants but absent in animals/fungi.
• Centrioles are present in animals but absent in plants/fungi.
• Cilia/flagella are present in some animal cells but rare in plants/fungi.

Atypical Cell Structure in Eukaryotes

• Skeletal muscle fibers are multinucleated, long, and striated.
• Aseptate fungal hyphae are long, multinucleated, and lack cell walls between nuclei.
• Red blood cells in mammals lack a nucleus or organelles.
• Phloem sieve tube elements lack a nucleus and rely on companion cells.

Cell Types and Structures in Micrographs

• Prokaryotic cells: look for plasma membrane, nucleoid, ribosomes, and cell wall.
• Eukaryotic cells: look for nucleus, mitochondria, chloroplasts, ER, Golgi, vesicles, ribosomes, cell wall, cilia, flagella, and microvilli.

Drawing and Annotation

• Prokaryotic cell: label the nucleoid, ribosomes, cell wall, and plasma membrane.
• Eukaryotic cell: label the nucleus, mitochondria, ER, Golgi, vesicles, and ribosomes.

Organelles as Discrete Subunits

• Organelles are specialized structures within cells performing specific functions.
• Solid organelles include ribosomes and the cytoskeleton.
• Single-membrane organelles include lysosomes, the Golgi apparatus, and the ER.
• Double-membrane organelles include the nucleus, mitochondria, and chloroplasts.
• The cell wall, cytoplasm, and cytoskeleton are not organelles because they lack a membrane.

Compartmentalization of Nucleus and Cytoplasm

• Compartmentalization protects DNA from damage.
• Separates transcription (nucleus) from translation (cytoplasm).
• In prokaryotes, transcription and translation occur simultaneously in the cytoplasm.
• Post-transcriptional modification occurs only in eukaryotes.

Compartmentalization in the Cytoplasm

• Cytoplasm is divided into specialized regions.
• Increases efficiency of metabolic reactions.
• Isolates harmful substances, such as those in lysosomes.
• Lysosomes and phagocytic vacuoles isolate digestive enzymes to prevent damage to the cell.

Lipid Bilayers

• Phospholipids form bilayers in water due to hydrophobic tails and hydrophilic heads.
• Found in the plasma membrane and organelle membranes.

Lipid Bilayers as Barriers

• Regulate the movement of substances.
• Hydrophobic core forms a barrier to hydrophilic particles.
• Enable compartmentalization and selective permeability.

Simple Diffusion

• Molecules move from high to low concentration.
• Rate is affected by the concentration gradient, particle size, and polarity/charge.
• Examples: Oxygen and carbon dioxide diffusion in cells.

Membrane Proteins

• Integral proteins are embedded in the membrane.
• Peripheral proteins are on the surface or anchored to integral proteins.
• Functions include transport, enzymatic activity, signal transduction, cell recognition, intercellular joining, and attachment to the cytoskeleton.

Osmosis and Aquaporins

• Osmosis involves the movement of water across a selectively permeable membrane.
• Aquaporins are channel proteins that facilitate water movement.

Channel Proteins and Facilitated Diffusion

• Transmembrane proteins with a pore.
• Allow specific ions/molecules to pass.
• Gated by voltage, ligands, or mechanical stimuli.

Pump Proteins and Active Transport

• Transmembrane proteins use ATP.
• Move molecules against their concentration gradient.
• Example: Sodium-potassium pump.

Selective Permeability

• Membranes allow certain substances to pass while restricting others.
• Permeability is affected by size, hydrophobicity, and hydrophilicity.
• Small, nonpolar molecules (e.g., O2) pass easily, while large, polar molecules (e.g., glucose) require channels/pumps.

Glycoproteins and Glycolipids

• Proteins/lipids with carbohydrate chains.
• Function in cell adhesion and recognition (e.g., immune response).

Fluid Mosaic Model

• Includes a phospholipid bilayer, integral and peripheral proteins, glycoproteins and glycolipids, and cholesterol (embedded in the hydrophobic region).