Biology Key Concepts: Cell Theory, Organisms, and Microscopy

Metabolism

Chemical reactions for survival

Reproduction

Producing offspring (sexually/asexually)

Sensitivity

Responding to stimuli (internal/external)

Homeostasis

Maintaining stable internal environments

Excretion

Removing waste products

Nutrition

Exchanging materials with environment

Growth/Movement

Moving and changing shape

Organism

Any living system functioning as an individual life form

Cell Theory

The three tenets are: 1. The cell is the smallest unit of life; 2. All living things are composed of cells; 3. Cells only arise from pre-existing cells.

Cell membrane

Separates internal and external content

Cytosolic fluid

Provides medium for chemical reactions

DNA

Carries instructions for cell activities

Ribosomes

Make proteins to carry out instructions

Striated muscle

Fused cells forming multinucleated fibres

Aseptate fungal hyphae

Lack internal partitions (continuous cytoplasm)

Sieve tube elements

Connected by plasmodesmata (shared metabolism)

Red blood cells

Lack nuclei (cannot reproduce)

Metric System Units

1 metre (m), 10⁻³ millimetre (mm), 10⁻⁶ micrometre (μm), 10⁻⁹ nanometre (nm), 10⁻¹² picometre (pm)

Light Microscopes

View living specimens in natural colour, lower magnification and resolution, use glass lenses to bend light

Electron Microscopes

View dead specimens in monochrome, higher magnification and resolution, use electromagnets to focus electrons

Magnification Formula

M = I ÷ A, where M = Magnification, I = Image Size, A = Actual Size

Actual Size Formula

Actual Size = Image Size ÷ Magnification

Image Size Formula

Image Size = Actual Size × Magnification

Prokaryotes

Simple cells lacking a nucleus ('pro' = before; 'karyon' = nucleus)

Eukaryotes

Complex cells with a nucleus ('eu' = true; 'karyon' = nucleus)

Nucleoid

Region containing DNA (not membrane-bound)

Plasmids

Autonomous DNA molecules

Ribosomes (Prokaryotic)

70S (smaller than eukaryotic)

Cell wall (Prokaryotic)

Made of peptidoglycan for stability

Plasma membrane

Cell boundary

Cytosol

Internal cell fluid

Pili

Hair-like extensions for attachment/conjugation

Flagella

Whip-like projections for movement

Slime capsule (glycocalyx)

Outer coat preventing desiccation

Pathogenicity (Bacteria vs Archaea)

Bacteria can be pathogenic; Archaea are not pathogenic

Cell wall (Bacteria vs Archaea)

Bacteria have peptidoglycan present; Archaea have no peptidoglycan

Membrane lipids (Bacteria vs Archaea)

Bacteria have ester-linked; Archaea have ether-linked

DNA (Bacteria vs Archaea)

Bacteria have naked DNA; Archaea have DNA bound to histones

RNA polymerase (Bacteria vs Archaea)

Bacteria have one type; Archaea have several types

Introns (Bacteria vs Archaea)

Bacteria have introns rare; Archaea can have introns

Nucleus

Main distinguishing feature of eukaryotes, stores DNA

Compartmentalization

Possession of membrane-bound organelles

Ribosome (Eukaryotic)

80S, site of protein synthesis

Mitochondria

Site of aerobic respiration (ATP production)

Chloroplast

Site of photosynthesis (plants only)

Sap Vacuole

Internal fluid storage, pressure regulation (plants only)

Centrioles/Centrosomes

Involved in cell division (animals)

Living organisms

Can maintain all conditions needed for existence.

Smallest self-sustaining unit

A single cell.

Viruses

Not considered living organisms due to lack of metabolism and reliance on host cells for reproduction.

Abiogenesis

The process by which life arises naturally from non-living matter.

Four Stages of Life's Origin

1. Non-living synthesis of organic compounds; 2. Organic monomers assembled into complex polymers; 3. Certain polymers became capable of self-replication; 4. Molecules became packaged into membranes.

Challenges of Proving Abiogenesis

Pre-biotic Earth conditions can't be exactly replicated and first protocells didn't fossilize.

Pre-biotic Earth Conditions

Required conditions for spontaneous organic compound formation include a reducing atmosphere, high UV radiation, volcanic eruptions, higher temperatures, and a water source.

Miller-Urey Experiment

Demonstrated non-living synthesis of organic material through a series of steps involving boiling water, mixing with gases, and exposing to electrical discharge.

Spontaneous Membrane Formation

In water, fatty acids form micelles and attract glycerol heads to form bilayers, creating hydrophobic barriers.

RNA as First Genetic Material

RNA is presumed to be the first genetic material due to the DNA-Protein Paradox.

DNA-Protein Paradox

Proteins require DNA to be synthesized, while DNA requires proteins to self-replicate.

Self-replication

Can self-replicate

Catalytic activity

Has catalytic activity (ribozymes, rRNA)

Stability of DNA

DNA is more stable; proteins are more diverse

Capabilities of RNA

RNA has both capabilities

Polarity of Water

Causes lipids to form spontaneous bilayers

Thermal properties of Water

Maintains stable internal conditions (homeostasis)

Solvent properties of Water

Dissolves polar/charged substances (good medium for metabolism)

Reagent properties of Water

Required for condensation polymerization (building complex molecules)

Origin of Water on Earth

Theory: Water originated on distant asteroids (where it could form ice)

Goldilocks Zone

Range of distance from a star where liquid water can exist

LUCA

Last Universal Common Ancestor (LUCA)

Universality of genetic code

Almost all organisms share the genetic code

Conserved gene sequences

Certain genes broadly conserved across bacteria and archaea

Obligate anaerobe

Suggest LUCA was: Obligate anaerobe (couldn't survive O₂)

Chemoautotroph

Suggest LUCA was: Chemoautotroph (energy from oxidation)

Thermophilic

Suggest LUCA was: Thermophilic (survived extreme heat)

Biosignatures

Chemicals produced by cellular processes

Stromatolites

Layered sedimentary deposits formed by cells

Molecular clock

Estimates divergence time based on mutations

Endosymbiosis

Eukaryotes evolved from prokaryotes via endosymbiosis

Evidence for Endosymbiosis

Membranes: Double membrane (originally in vesicle)

D DNA

Have own DNA (naked and circular)

Cell Differentiation

Process of developing specialized tissues in multicellular organisms

Neurons

Can be >1m long (but only 10μm wide) to signal over distance

Muscle fibres

Fused cells up to 12cm long

Ova

Very large compared to sperm (provides cell contents)

Surface Area to Volume Ratio (SA:Vol)

Metabolism rate: Function of cell volume; Material/heat exchange rate: Function of surface area

SA:Vol ratio decrease

As cells grow, volume increases faster than surface area

Cell death consequence

If metabolic rate exceeds exchange rate → cell dies

Cell division solution

Cells divide and remain small

Microvilli

Increase surface area without changing volume

Squamous cells

Higher SA:Vol than cuboidal

Villi

Ruffled projections in tissues

Biconcave shape

Shape of red blood cells

Invaginated membranes

Found in kidney tubules

Unicellular organisms

Single-celled organisms (Euglena, Amoeba)

Multicellular organisms

Multiple cells aggregated (Daphnia, Hydra)

Differentiation process

Every cell in multicellular organism is a clone of original parent cell

Zygote

Parent cell in sexual reproduction (fertilized egg)

Selective gene expression

Different genes expressed in different cells causing specialization

Stem cells

Can continually divide and replicate (self-renewal) and have the ability to differentiate (potency)

Totipotent stem cells

Can form ANY cell type and develop into complete organisms (Example: Zygote, morula cells)