Intro to Biology: Modules 1-3

Levels of Organization in the Human Body

Cells → Tissues → Organs → Organ Systems → Organism

Cell

Basic unit of life.

Tissue

Group of similar cells performing a specific function.

Organ

Two or more tissues working together (ex: heart).

Organ System

Multiple organs coordinating (ex: digestive system).

Organism

The complete human body.

Plasma Membrane

The plasma membrane is selectively permeable.

Structure of Plasma Membrane

Phospholipid bilayer with proteins, cholesterol, and carbohydrates.

Primary Function of Plasma Membrane

Acts as a selective barrier → regulates what enters and exits the cell.

Homeostasis

Maintains homeostasis by controlling exchange of nutrients, gases, and wastes.

Carbohydrates

Provide quick energy; some structural roles.

Examples of Carbohydrates

Glucose, starch, glycogen.

Lipids

Long-term energy storage, insulation, form membranes, hormones.

Examples of Lipids

Fats, oils, phospholipids, steroids.

Proteins

Structure, transport, enzymes, hormones, defense.

Examples of Proteins

Hemoglobin, collagen, enzymes.

Nucleic Acids

Store and transmit genetic information.

Examples of Nucleic Acids

DNA, RNA.

Anabolic Reactions

Build larger molecules from smaller ones; require energy.

Example of Anabolic Reaction

Building proteins from amino acids.

Catabolic Reactions

Break down larger molecules into smaller ones; release energy.

Example of Catabolic Reaction

Breaking down glucose during cellular respiration.

Importance of Energy

Energy (in the form of ATP) is needed for muscle contraction & movement, active transport across membranes, building molecules (anabolism), maintaining body temperature, and overall survival of cells and systems.

Atoms

Protons (+), neutrons (0), electrons (-).

Chemical Bonds

Ionic (electron transfer, e.g., NaCl), Covalent (electron sharing; polar vs. nonpolar), Hydrogen bonds (weak attractions between polar molecules, e.g., H₂O interactions).

Transport materials & signals

Transport materials & signals via proteins.

Electrical properties

Nerve impulses and gradients.

Phospholipid bilayer

Structure consisting of hydrophilic heads and hydrophobic tails, with embedded proteins.

Selective Permeability

Can pass freely: nonpolar, hydrophobic, small uncharged molecules (O₂, CO₂, lipids); Cannot pass freely: polar molecules, charged ions (glucose, Na⁺) requiring transport proteins.

Transporters

Membrane proteins that carry molecules across (e.g., glucose).

Receptors

Bind signals and trigger intracellular response.

Enzymes

Catalyze reactions.

Anchors

Link internal and external structures.

Passive Transport

No energy required; moves from high to low concentration.

Active Transport

Requires energy (ATP) to move molecules from low to high concentration.

Diffusion

Movement down concentration gradient until equilibrium.

Osmosis

Diffusion of water across membrane; 'Water follows solute.'

Tonicity

Isotonic → no net water movement; Hypertonic → cell loses water (shrivels); Hypotonic → cell gains water (swells/lyses in animals; turgid in plants).

Facilitated Diffusion

Involves channels that open/close to let molecules down gradient and carriers that bind + transport specific molecules.

Aquaporins

Specialized water channels.

Primary Active Transport

Direct use of ATP; Example: Sodium-potassium pump (Na⁺/K⁺ pump) maintains gradients for nerve/muscle function.

Secondary Active Transport

Uses gradient created by primary active transport; Example: Na⁺ gradient drives glucose uptake.

Bulk Transport

Moves large molecules (proteins, polysaccharides) using vesicles; requires energy.

Exocytosis

Vesicles fuse with membrane to release contents (e.g., insulin).

Phagocytosis

'Cell eating,' engulf particles (e.g., neutrophils).

Pinocytosis

'Cell drinking,' uptake of fluid.

Receptor-mediated Endocytosis

Specific ligand binding (e.g., cholesterol uptake).

Diffusion vs Facilitated Diffusion

Diffusion = directly across membrane; Facilitated = requires protein (still passive).

Primary vs Secondary Active Transport

Primary uses ATP directly; Secondary is gradient-driven.

Cell Wall

Rigid cellulose structure; protection, shape, support. (plants only)

Nucleus

Stores DNA; controls protein synthesis; nuclear pores regulate molecule exchange.

Nucleolus

Inside nucleus; assembles ribosomes.

Chromatin → Chromosomes

DNA + proteins; chromosomes visible only during cell division.

Nucleoid (prokaryotes)

Region with DNA, not membrane bound.

Ribosomes

Build proteins by reading mRNA; free-floating (cytosol) or bound (RER).

Rough ER

Protein synthesis + folding; studded with ribosomes.

Smooth ER

Lipid synthesis; detoxification; calcium storage.

Golgi Apparatus

Modifies, tags, and packages proteins & lipids → sends to membrane, lysosomes, or out of the cell.

Lysosomes (animals only)

Digestive enzymes; break down macromolecules & worn organelles.

Peroxisomes

Break down fatty acids; detoxify hydrogen peroxide.

Mitochondria

'Powerhouse'; site of cellular respiration; makes ATP.

Chloroplasts (plants only)

Photosynthesis; convert light energy into glucose; contain chlorophyll.

Vesicles

Small transport sacs.

Vacuoles

Large storage organelles; Animals → small, store glycogen/waste; Plants → large central vacuole maintains turgor pressure + stores water/sugars.

Cytoskeleton

Microtubules → vesicle tracks; Intermediate filaments → anchor organelles; Microfilaments → shape, muscle contraction.

Cilia (animals)

Short, numerous; move substances (respiratory tract).

Flagella (some animals, some plant sperm)

Long, whip-like; cell movement (e.g., sperm).

Endomembrane System

Pathway of Protein Synthesis.

Prokaryotes

No nucleus (DNA in nucleoid); No membrane-bound organelles; Have ribosomes, plasma membrane, cytoplasm, often a cell wall (peptidoglycan).

Eukaryotes

Organisms with DNA enclosed in a nucleus, including plants, animals, fungi, and protists.

Chromatin/Chromosomes

DNA + proteins; chromosomes are visible only during cell division.

Lysosomes

Digest macromolecules, worn organelles, and pathogens; found only in animals.

Chloroplasts

Site of photosynthesis that produces glucose and oxygen; found only in plants.

Cilia

Short, numerous extensions that move substances across the cell surface.

Flagella

Long, whip-like extensions that move the entire cell.

Memory Trick (Protein Pathway)

Nasty Rats Run Good Secret Experiments → Nucleus → Ribosome → Rough ER → Golgi → Secretory Vesicle → Exocytosis.