Honors Biology – Homeostasis, Muscles & Cell Transport
Endocrine System
Contains glands that secrete hormones (chemical messengers) into the bloodstream.
Feedback Mechanism
Maintains a living system’s internal conditions within certain limits even as external conditions change.
Positive Feedback
Moves the system away from homeostasis by amplifying the effects of a product or event. Occurs when something must happen quickly. Ex: childbirth, fruit ripening.
Negative Feedback
Counteracts a disruption in homeostasis to re-establish internal stability.
Negative Feedback Loop Order
Receptor (sensor) → Change detected → Stimulus → Control center → Effector (response) → Returns to homeostasis.
Body too hot (thermoregulation)
Thermoregulation center in brain → blood vessels dilate, heat escapes → sweat glands secrete sweat that evaporates → cooling → return to homeostasis.
Body too cold (thermoregulation)
Blood vessels constrict → skeletal muscles shiver to generate heat → return to homeostasis.
Blood glucose too high
Pancreas releases insulin → cells take up glucose → liver stores glucose as glycogen → blood glucose decreases.
Blood glucose too low
Pancreas releases glucagon → liver breaks down glycogen → releases glucose into blood → blood glucose increases.
Insulin
Hormone that helps decrease blood glucose.
Glucagon
Hormone that helps increase blood glucose.
Pancreas
Organ that secretes insulin or glucagon from specialized cells into the bloodstream.
Liver (glucose role)
Stores glucose as glycogen; breaks down glycogen and releases glucose into blood.
Diabetes
Metabolic disease causing high blood glucose levels (hyperglycemia).
Type I Diabetes
Insulin not produced by beta cells → glucose stays in blood.
Type II Diabetes
Prolonged overproduction of insulin → cells desensitized → insulin ineffective.
Muscular System Functions
Enables movement, supports bodily functions, generates heat, maintains posture, stabilizes joints.
Skeletal Muscle
Attached to bones via tendons; voluntary movement (walking, grasping).
Smooth Muscle
Within organs (digestive tract); involuntary actions (digestion, circulation).
Cardiac Muscle
In heart; rhythmic contractions for blood circulation.
Plasma Membrane Functions
1. Selectively permeable 2. Separates cytoplasm from outside 3. Receives chemical messengers and passes info to cell.
Lipid Bilayer
Made of phospholipids; determines what enters/leaves based on charge and size.
Anchor Proteins
Keep cells attached, forming tissues.
Identifier Proteins
Help immune system distinguish self vs. foreign; have unique carbohydrate chains.
Enzymatic Proteins
Catalyze metabolic reactions; active site exposed to cytoplasm.
Receptor Proteins
Receive chemical messengers; specifically shaped for certain messengers.
Channel Proteins
Provide hydrophilic channel for ions/water to pass.
Carrier Proteins
Change shape to shuttle specific substances across membrane.
Cholesterol
Located between fatty acids to stabilize and strengthen flexible cell membrane.
Concentration
Amount of solute per unit volume of solution.
Distilled Water
H₂O = 100%, Solute = 0%.
Living Cells (approx)
H₂O ≈ 70%, Solutes ≈ 30% (glucose, salt, O₂, CO₂, etc.).
Concentration Gradient
Difference in solute concentration between two areas.
Equilibrium
Solute and H₂O molecules equally distributed; continue moving evenly.
Passive Transport
No energy required.
Active Transport
Requires energy (ATP).
Diffusion
Movement of molecules from high to low concentration without ATP.
Simple Diffusion
Through phospholipid bilayer; small non-polar molecules (lipids, steroids).
Facilitated Diffusion
Through transport proteins; charged/polar substances (glucose, ions).
Large Polymers (proteins, polysaccharides)
Too large to diffuse; must be hydrolyzed (broken down) first.
Osmosis
Passive transport of water.
Hypertonic Solution
Higher solute concentration (lower water).
Isotonic Solution
Same solute concentration as cell.
Hypotonic Solution
Lower solute concentration (higher water).
Animal Cell in Hypertonic
Shrinks (crenation).
Animal Cell in Hypotonic
Swells and may burst (lysis).
Animal Cell in Isotonic
Normal.
Plant Cell in Hypertonic
Plasmolysis (membrane pulls away from cell wall).
Plant Cell in Hypotonic
Turgor pressure (cell pushes against wall).
Plant Cell in Isotonic
Flaccid.