Topic 2 - Cell Biology

Cell Theory

All living things are made of cells, which are the basic units of life, and all cells arise from other cells.

Spontaneous Generation

A now-disproved theory that living organisms could arise from nonliving matter such as soil, manure, and decaying corpses.

Debunking of Spontaneous Generation

The theory of spontaneous generation was conclusively debunked in 1859.

Temporary Mounts (Wet Mounts)

Prepared slides used because cells and their structures are usually transparent and hard to distinguish under a light microscope.

Purpose of Stains in Microscopy

Chemical solutions applied to a sample to increase contrast between different areas and make them more visible.

Iodine Stain

Used to prepare slides of plant cells because it binds to the starch present.

Methylene Blue Stain

Used to view animal cells because it binds to the nuclei of the cell.

Gram Stain

Used to view bacteria by adhering to the thick peptidoglycan layer of Gram-positive cells.

Peptidoglycan Layer Functions

Provides structural rigidity, maintains cell shape, and protects bacteria from bursting due to internal osmotic pressure.

Eyepiece Graticule

A transparent ruler with a scale or grid placed in the eyepiece lens to measure actual object sizes.

Stage Micrometer

A small, calibrated ruler mounted on the stage of a microscope used to calibrate eyepiece graticules.

Graticule Scale Relationship

Each 100 µm stage micrometer division equals 20 eyepiece graticule divisions (1 graticule division = 5 µm).

Micrometer to Millimeter Conversion

1 mm = 1000 µm.

Magnification Definition

The comparison of the size of an image compared to the actual size of an object.

Magnification Formula

Magnification = image size / actual size.

Image Size Formula

Image size = magnification × actual size.

Actual Size Formula

Actual size = image size / magnification.

Electron Microscope Mechanism

Passes a beam of electrons through the specimen; dense parts absorb electrons, while less dense areas scatter or let them pass.

Electron Microscope Advantages

Much higher resolution than light microscopes; can magnify small objects by about 500,000 times.

Freeze Fracture Microscopy

A technique where frozen samples are broken into pieces and observed using an electron microscope to see internal structures.

Cryogenic Electron Microscopy (Cryo-EM)

Samples are frozen to −180 °C or colder, improving resolution and reducing damage from the electron beam.

Immunofluorescence

A technique where a fluorescent tag is attached to antibodies that bind to antigens, allowing visualization of target molecules.

Fluorescent Tag (Fluorophore)

A molecule chemically attached to aid in the detection of biomolecules such as proteins, antibodies, or amino acids.

Fluorescent Dyes

Dyes that preferentially attach to certain structures and appear as brightly colored spots under light microscopy.

Universal Cell Structures

DNA as genetic material, cytoplasm composed mostly of water, and a lipid-based plasma membrane.

Prokaryotic Cell Characteristics

Unicellular organisms (0.1 to 5.0 µm) with no nucleus or membrane-bound organelles.

Prokaryotic Cell Wall

Located outside the cell membrane; protects against toxins and helps maintain shape.

Prokaryotic Plasma Membrane

Separates the cell's interior from the external environment and controls entry and exit.

Prokaryotic Cytoplasm

Water-based jelly-like fluid that fills the cell, suspends molecules/organelles, and hosts metabolism.

Prokaryotic Naked DNA in a Loop

Located in the nucleoid region without histones; stores genetic information for protein synthesis.

Prokaryotic 70S Ribosomes

Free in the cytoplasm; smaller/lower mass than eukaryotic ribosomes; site of translation.

Prokaryotic Plasmid

Small, circular pieces of DNA transferred between cells via horizontal gene transfer.

Prokaryotic Capsule

Outer layer of polysaccharides that protects the organism and allows surface adhesion.

Prokaryotic Flagellum

Spins to propel the organism through its medium for locomotion.

Prokaryotic Pili

Protein filaments on the cell wall aiding cell adhesion and DNA transfer between cells.

Eukaryotic Cell Characteristics

Larger, more complex, typically multicellular, and features cell compartmentalization.

Advantages of Cell Compartmentalization

Creates higher concentrations, separates toxins, and maintains optimal enzyme conditions.

Eukaryotic Mitochondria

Double membrane-bound organelles that convert glucose into ATP via respiration.

Eukaryotic Nucleus

Contains histone-associated DNA in chromosomes, a nucleolus, and a double membrane with pores.

Smooth Endoplasmic Reticulum

Produces and stores lipids.

Rough Endoplasmic Reticulum

Has attached ribosomes that produce proteins destined for use outside the cell.

Golgi Apparatus

Processes and packages proteins to be released in Golgi vesicles.

Eukaryotic Vesicle

Small sac that transports and releases substances by fusing with the cell membrane.

Eukaryotic Vacuole

Maintains osmotic balance, stores substances, and can have hydrolytic functions.

Eukaryotic Cytoskeleton

System of protein microfilaments and microtubules that holds organelles in place and maintains shape.

Eight Life Processes

Metabolism, response to stimuli, homeostasis, movement, growth, reproduction, excretion, and nutrition.

Paramecium Growth

Enlarges by consuming food and divides into two daughter cells when reaching a certain size.

Chlamydomonas Growth

Grows via photosynthesis and mineral absorption, then divides into two daughter cells.

Paramecium Movement

Beating cilia propel the organism in response to environmental changes.

Chlamydomonas Movement

Rotating flagella move the organism toward more favourable conditions like higher light intensity.

Paramecium Response to Stimuli

Detects changes in water temperature and moves to seek warmer temperatures.

Chlamydomonas Response to Stimuli

Senses light changes using its eyespot and moves toward brighter regions.

Osmoregulation in Paramecium and Chlamydomonas

Collects excess water in contractile vacuoles and expels it through the plasma membrane.

Paramecium Nutrition

Heterotroph that engulfs microorganisms in vacuoles for digestion and absorption.

Chlamydomonas Nutrition

Autotroph that uses a large chloroplast to carry out photosynthesis.

Paramecium Reproduction

Primarily reproduces asexually via binary fission into two daughter cells.

Chlamydomonas Reproduction

Reproduces via binary fission or sexual reproduction once reaching a certain size.

Paramecium Excretion

Metabolic waste collects in vacuoles that rupture at the anal pore or exit via contractile vacuoles.

Chlamydomonas Excretion

Uses the whole surface of its plasma membrane to excrete waste products.

Paramecium Metabolism

Breaks down external organic nutrients obtained from the environment for energy and carbon.

Chlamydomonas Metabolism

Flexible metabolism using heterotrophic chemical carbon or mixotrophic CO2 and acetate utilization.

Animal Cell Wall

Animal cells lack a cell wall entirely.

Plant Cell Wall

Made of cellulose; protects the cell and maintains shape against osmotic pressure.

Fungal Cell Wall

Made of chitin, providing structural support and protection.

Chloroplasts in Animal and Fungal Cells

Both animal and fungal cells completely lack chloroplasts.

Plant Chloroplasts

Contain chlorophyll to convert light energy into chemical energy through photosynthesis.

Animal Cell Vacuoles

May have small vacuoles that store water, nutrients, and waste products.

Plant Cell Vacuoles

Feature a large vacuole that regulates the cell's osmotic potential.

Fungal Cell Vacuoles

Have large vacuoles that degrade molecules and store small molecules like ions.

Centrioles, Lysosomes, and Cilia in Animal Cells

Contain centrioles, lysosomes, and sometimes cilia for division, breakdown, and movement.

Centrioles, Lysosomes, and Cilia in Plant Cells

Plant cells usually lack centrioles, lysosomes, and cilia.

Centrioles, Lysosomes, and Cilia in Fungal Cells

Generally lack cilia and lysosomes; centrioles are absent in most fungi.

Skeletal Muscle Cells (Multinucleate)

Contain multiple nuclei formed by the fusion of many smaller myocytes.

Mature Red Blood Cells (Anucleate)

Lack a nucleus entirely to provide greater hemoglobin capacity for transport.

Aseptate Fungal Hyphae (Multinucleate)

Lack internal cross-walls, causing many nuclei to share a single continuous cellular unit.

Phloem Sieve Tube Elements (Anucleate)

Lack a nucleus and have reduced cytoplasm/organelles for low resistance substance movement.