1
Q
What does the cell theory state about the cell?
A
The cell is the smallest structural and functional unit capable of carrying out life processes.
2
Q
What are cells the building blocks of?
A
All plant and animal organisms.
3
Q
Where do new cells come from?
A
From pre-existing cells.
4
Q
Why are cells across all organisms similar?
A
Because of the continuity of life, they are fundamentally similar in structure and function.
5
Q
What determines an organism’s structure and function?
A
The individual and collective capabilities of its cells.
6
Q
When did scientists first learn that cells existed?
A
After the invention of the microscope in the 17th century.
7
Q
Are the cells of hummingbirds, humans, and whales different in size?
A
No — they are about the same size; larger organisms just have more cells.
8
Q
What is the basic unit of life?
A
The cell.
9
Q
What life functions can a cell perform?
A
Metabolism, growth, response, and reproduction.
10
Q
About how many different cell types are in the human body?
A
Around 200.
11
Q
Where do all cells come from?
A
Pre-existing cells.
12
Q
What are organisms made of?
A
One cell (unicellular, e.g., bacteria, yeast, some algae, protozoa) or many cells (multicellular, e.g., humans, plants, animals, fungi).
13
Q
About how many cells make up the human body?
A
~37 trillion cells.
14
Q
In terms of structure and function, how are cells across organisms?
A
Cells are fundamentally similar.
15
Q
What are the three major subdivisions of most cells?
A
Plasma membrane, nucleus, cytoplasm.
16
Q
What are the three main parts of a eukaryotic cell?
A
Plasma membrane, nucleus, and cytoplasm.
17
Q
What is the cytoplasm?
A
The gel-like portion inside the cell that contains cytosol (fluid) and organelles.
18
Q
What are organelles?
A
Specialized structures within the cell that carry out specific functions.
19
Q
What does the cytoskeleton do?
A
Provides structural support, framework, and tracks for movement inside the cell.
20
Q
What are the main components of the cytoskeleton?
A
Microtubules, microfilaments, and intermediate filaments.
21
Q
What are the three main types of cytoskeleton filaments?
A
Microtubules, microfilaments, and intermediate filaments.
22
Q
Function of microtubules?
A
Highways for organelle and vesicle movement; also form spindle fibers during cell division.
23
Q
Structure of microtubules?
A
Hollow tubes made of tubulin
Highway for organelle and vesicle movement
24
Q
Function of microfilaments?
A
Shape, crawling, and contraction of the cell (act in motility if stimulated by signals).
25
Structure of microfilaments?
Thin strands made of actin.
26
Function of intermediate filaments?
Provide tough scaffolding; resist mechanical stress; give the cell structural stability.
27
Structure of intermediate filaments?
Rope-like fibers made of various proteins.
28
What is the structure of the plasma membrane?
A lipid bilayer studded with proteins and small amounts of carbohydrate.
29
What is the function of the plasma membrane?
Acts as a selective barrier, controlling traffic in and out of the cell.
30
What is the structure of the nucleus?
DNA and specialized proteins enclosed by a double-layered membrane.
31
What is the function of the nucleus?
Control center of the cell; stores genetic information, provides blueprint for protein synthesis and cell replication.
32
What is the cytoplasm?
The portion of the cell interior not occupied by the nucleus.
33
What does the cytoplasm contain?
Organelles and the cytosol, where many metabolic reactions occur.
34
What is the structure of mitochondria?
Rod- or oval-shaped, double membrane; inner membrane folded into cristae.
35
What is the function of mitochondria?
Energy production; major site of ATP synthesis, citric acid cycle, and electron transport chain.
36
What is the structure of ribosomes?
Granules of RNA and protein; some free in cytoplasm, some attached to rough ER.
37
What is the function of ribosomes?
Sites of protein synthesis (“workbenches” of the cell).
38
What is the structure of the endoplasmic reticulum (ER)?
Extensive network of fluid-filled tubules and sacs; rough ER studded with ribosomes, smooth ER lacks ribosomes.
39
What is the function of rough ER?
Protein synthesis and processing.
40
What is the function of smooth ER?
Lipid synthesis, detoxification, calcium storage.
41
What is the structure of the Golgi apparatus?
Stacks of flattened membranous sacs.
42
What is the function of the Golgi apparatus?
Modifies, packages, and distributes proteins and lipids.
43
What is the structure of lysosomes?
Membranous sacs containing hydrolytic enzymes.
44
What is the function of lysosomes?
Digestive system of the cell; break down debris, organelles, and foreign material.
45
What is the structure of peroxisomes?
Membranous sacs containing oxidative enzymes.
46
What is the function of peroxisomes?
Detoxification; break down harmful substances like hydrogen peroxide.
47
What is the structure of the nucleus?
Double membrane enclosing DNA and associated proteins.
48
What is the function of the nucleus?
Control center of the cell; stores genetic info and directs protein synthesis.
49
What is another name for the plasma membrane?
The cell membrane.
50
What does the plasma membrane surround?
Every cell.
51
What does the plasma membrane separate?
Intracellular fluid (ICF) from extracellular fluid (ECF).
52
What is the primary function of the plasma membrane?
Controls movement of molecules into and out of the cell; acts as a selective barrier.
53
What is the plasma membrane mostly made of?
Lipids, proteins, and some carbohydrates.
54
What is the structure of the lipid bilayer?
Hydrophilic polar heads (face water on both sides).
## Footnote
Hydrophobic nonpolar tails (face inward, away from water).
55
What is the structure of a phospholipid molecule?
A hydrophilic polar head (charged, water-loving) and two hydrophobic nonpolar tails (uncharged, water-fearing).
56
In the plasma membrane, where are the hydrophilic heads located?
Facing the water of the intracellular fluid (ICF) and extracellular fluid (ECF).
57
In the plasma membrane, where are the hydrophobic tails located?
Facing inward, away from water, forming the core of the bilayer.
58
What is the overall organization of the plasma membrane?
A phospholipid bilayer with polar heads on the outside and nonpolar tails on the inside.
59
Why is the plasma membrane described as 'fluid'?
Molecules are not fixed; they move around, making the membrane dynamic and flexible.
60
Why is the lipid bilayer described as 'fluid in nature'?
Its molecules can move laterally, making the membrane flexible and dynamic.
61
What does the fluid mosaic model describe?
The plasma membrane as a mosaic of proteins embedded in or attached to a dynamic lipid bilayer.
62
What role does cholesterol play in the plasma membrane?
It contributes to membrane fluidity and stability.
63
Where are membrane proteins located?
Attached to or inserted within the lipid bilayer.
64
What are glycoproteins?
Carbohydrates bound to membrane proteins.
65
What are glycolipids?
Carbohydrates bound to lipids in the membrane.
66
What is the role of glycoproteins and glycolipids?
They contribute to cell recognition, communication, and stability of the membrane.
67
What is the role of cholesterol in the plasma membrane?
Helps stabilize and regulate fluidity of the membrane.
68
What are the main components of the plasma membrane?
Phospholipids, proteins, cholesterol, and carbohydrates.
69
What are examples of membrane proteins?
Channels, carriers, receptors, and enzymes.
70
Why is the membrane called 'fluid'?
Phospholipids and proteins can move laterally within the layer.
71
Why is it called 'mosaic'?
Because of the scattered arrangement of proteins and other molecules within the bilayer.
72
What is the function of channel proteins?
Form water-filled channels across the lipid bilayer for selective transport.
73
What is the function of carrier proteins?
Transport molecules across the membrane by binding and carrying them.
74
What is the function of docking marker proteins?
Serve as acceptors for vesicles, ensuring they dock at the right spot.
75
What is the function of membrane enzymes?
Catalyze specific reactions at the membrane surface.
76
What is the function of receptor proteins?
Bind signal molecules (ligands) to trigger cellular responses.
77
What is the function of cell adhesion molecules (CAMs)?
Link cells together to form tissues.
78
What is the function of self-recognition markers?
Identify cells as belonging to the same type (important for immune recognition).
79
What feature of the plasma membrane allows self-recognition?
Short sugar chains on the outer membrane (glycoproteins and glycolipids).
80
Do all cells have the same self-recognition markers?
No, different cell types have different markers.
81
Why are self-recognition markers important?
They allow cells to identify and interact with one another.
82
What is different about cancer cells in terms of self-recognition?
Cancer cells have abnormal cell markers.
83
What does permeable mean?
Allows substances to pass through.
84
What does impermeable mean?
Does not allow any substances to pass through.
85
What does selectively permeable mean?
Allows some substances to pass through while restricting others.
86
What is passive transport?
Movement across the membrane that does not require cellular energy (ATP).
87
What is active transport?
Movement across the membrane that does require energy (ATP).
88
What drives passive transport?
Concentration and/or electrical gradients (not ATP).
89
What drives active transport?
ATP expenditure, often moving substances against their gradient.
90
What determines if a substance can cross the membrane passively (without ATP)?
1) Its lipid solubility, and 2) its size.
91
Which molecules are highly soluble in lipids and can cross easily?
Uncharged, nonpolar molecules.
92
Which types of molecules have difficulty crossing the lipid bilayer without help?
Charged or polar molecules (they usually need assistance).
93
Why do nonpolar molecules pass more easily through the membrane?
Because they dissolve in the lipid bilayer.
94
What is diffusion?
The passive movement of molecules from an area of high concentration to low concentration.
95
What drives diffusion?
The concentration gradient (chemical gradient).
96
What does 'net diffusion' mean?
The overall movement of molecules until concentrations are equal inside and outside the membrane.
97
Do molecules stop moving once equilibrium is reached?
No — they continue random motion, but movement is balanced in both directions.
98
Is energy (ATP) required for diffusion?
No, it is passive.
99
What is net diffusion?
The difference between the number of molecules moving from area A → B and area B → A.
100
When does net diffusion occur?
When there is a concentration gradient (unequal distribution).
101
What happens at dynamic equilibrium?
Molecules continue moving randomly, but movement in both directions is equal (no net diffusion).
102
What is required for diffusion?
A concentration gradient and random molecular motion (no ATP needed).
103
When does diffusion occur across a membrane?
If the substance can permeate the membrane (penetrating solute).
104
When does diffusion NOT occur?
If the substance cannot permeate the membrane (nonpenetrating solute).
105
What determines whether a solute can cross the membrane?
Its size and lipid solubility (nonpolar vs polar).
106
What is a penetrating solute?
A solute that can cross the membrane → diffusion occurs.
107
What is a nonpenetrating solute?
A solute that cannot cross the membrane → no diffusion.
108
What is the electrical gradient?
The force causing positively charged ions to move toward negatively charged areas, and vice versa.
109
What is the concentration gradient?
The difference in concentration across a membrane that drives diffusion.
110
What is the electrochemical gradient?
The combined influence of both electrical and concentration gradients acting on ion movement.
111
Do ions move only because of concentration gradients?
No, ion movement depends on both concentration and electrical gradients.
112
In passive diffusion, how do molecules move according to the concentration gradient?
From high concentration → low concentration.
113
How do ions move according to the electrical gradient?
Positively charged ions move toward negative areas; negatively charged ions move toward positive areas.
114
What is the electrochemical gradient?
The combined effect of concentration and electrical gradients acting together on ion movement.
115
At equilibrium, molecules stop moving across the membrane. True or False?
False — molecules continue to move randomly, but there is no net diffusion.
116
Oxygen enters cells from the blood by which transport process?
Simple diffusion (down its concentration gradient).
117
If Na⁺ is high outside the cell and the inside is negative, which way will Na⁺ move?
Into the cell (favored by both concentration and electrical gradient).
118
If a solute is nonpenetrating, will diffusion occur across the membrane?
No — nonpenetrating solutes cannot cross, so no diffusion occurs.
119
Cholesterol in the plasma membrane mainly contributes to what property?
Membrane fluidity.
120
K⁺ is high inside the cell and the outside is negative — which way does K⁺ move?
It depends → concentration pushes K⁺ out, but electrical may pull K⁺ in. That’s the electrochemical gradient.
121
Which of the following is NOT a function of the plasma membrane? a) Acts as a barrier between ICF and ECF b) Controls movement of molecules in/out of the cell c) Serves as a storage site for calcium d) Involved in cell recognition
c) Serves as a storage site for calcium (this is a function of bone, not the plasma membrane).
122
What is a cation?
A positively charged ion (formed by losing electrons).
123
What is an anion?
A negatively charged ion (formed by gaining electrons).
124
What happens when like charges interact?
They repel each other.
125
What happens when opposite charges interact?
They attract each other.
126
Example of a common cation?
Na⁺, Ca²⁺, K⁺, Mg²⁺.
127
Example of a common anion?
Cl⁻, HCO₃⁻, PO₄³⁻, SO₄²⁻.
128
Sodium (Na⁺) is an example of a…
Cation (positive ion).
129
Chloride (Cl⁻) is an example of a…
Anion (negative ion).
130
Which molecules can diffuse directly across the lipid bilayer without help?
Small, nonpolar, lipid-soluble molecules (O₂, CO₂, fatty acids, steroid hormones).
131
Which molecules cannot cross the membrane without help?
Charged ions (Na⁺, K⁺, Ca²⁺, Cl⁻) and large polar molecules (glucose, amino acids, proteins).
132
The plasma membrane is permeable to what type of molecules?
Small, nonpolar, lipid-soluble molecules.
133
The plasma membrane is impermeable to what type of molecules?
Large polar molecules and ions.
134
Which of the following is NOT permeable to the plasma membrane without help? a) Oxygen (O₂) b) Carbon dioxide (CO₂) c) Sodium (Na⁺) d) Fatty acids
c) Sodium (Na⁺) — ions require channels/carriers.
135
Do O₂ and CO₂ need protein channels to cross the plasma membrane?
No — they are small, nonpolar, lipid-soluble molecules that diffuse freely.
136
Do Na⁺ and K⁺ need channels or pumps to cross the plasma membrane?
Yes — charged ions cannot diffuse freely; they require protein channels or pumps.
137
What is an example of a pump that moves ions across the membrane?
The sodium-potassium pump (Na⁺/K⁺ pump).
138
Why can oxygen diffuse across the membrane but sodium cannot?
Oxygen is nonpolar and lipid-soluble; sodium is charged and needs a protein channel.
139
Which of the following does NOT require protein channels or pumps to cross the plasma membrane? a) Sodium (Na⁺) b) Potassium (K⁺) c) Carbon dioxide (CO₂) d) Calcium (Ca²⁺)
c) Carbon dioxide (CO₂).
140
Is the sodium-potassium pump an example of passive or active transport?
Active transport (requires ATP).
141
What does the sodium-potassium pump move across the membrane?
Sodium (Na⁺) out of the cell, potassium (K⁺) into the cell.
142
Why is ATP needed for the sodium-potassium pump?
Because it moves ions against their concentration gradients.
143
The sodium-potassium pump helps maintain what key condition of the cell?
The electrochemical gradient (high Na⁺ outside, high K⁺ inside).
144
What is a solute?
The substance dissolved in a solution (e.g., salt).
145
What is a solvent?
The liquid that dissolves the solute (e.g., water).
146
What is a solution?
A mixture of solute + solvent.
147
In osmosis, which part of the solution moves across the membrane?
The solvent (water).
148
What is osmosis?
The net movement of water across a selectively permeable membrane.
149
How can water cross the plasma membrane?
By squeezing between lipid molecules or through aquaporins.
150
What are aquaporins?
Specialized protein channels that allow rapid water movement across the membrane ('aqua' = water, 'porin' = tunnel).
151
Does osmosis require energy (ATP)?
No — it is a passive process.
152
What is the driving force for osmosis?
The concentration gradient of water.
153
What does 'net diffusion of water' mean?
Water molecules move both ways, but more water moves toward the higher solute concentration.
154
What happens if solute concentration outside the cell is higher than inside?
Water leaves the cell.
155
What happens if solute concentration outside the cell is lower than inside?
Water enters the cell.
156
What does 'net diffusion' mean?
Molecules move randomly both ways, but more move in one direction overall.
157
In osmosis, which way does water move?
From the side with low solute (high water) → to the side with high solute (low water).
158
Why does water move toward the higher solute side?
That side has less water; osmosis balances water distribution.
159
What is the definition of osmosis?
The net diffusion of water across a selectively permeable membrane.
160
What does diffusion mean?
Molecules move from high concentration → low concentration.
161
What does net diffusion mean?
Overall movement is in one direction, even though molecules move randomly both ways.
162
In osmosis, water moves toward which side of a membrane?
Toward the side with more solute (because that side has less water).
163
Why does water move during osmosis?
Water is “nosy” and balances solute concentration by moving from high water (low solute) → low water (high solute).
164
What is osmosis in one sentence?
Net diffusion of water across a membrane toward the side with higher solute concentration.
165
What does “net diffusion” mean?
Molecules move randomly both ways, but more move in one direction overall.
166
In osmosis, which way does water move?
From the side with low solute (high water) → to the side with high solute (low water).
167
What is the relationship between solute concentration and water concentration?
They are inversely related — ↑ solute = ↓ water; ↓ solute = ↑ water.
168
If a solution has 0% solute, what is the water concentration?
100% water concentration (pure water).
169
If a solution has 10% solute, what is the water concentration?
90% water concentration.
170
What drives osmosis?
A difference in water concentration (due to unequal solute concentrations).
171
In osmosis, water moves from _______ to _______.
From high water concentration (low solute) → to low water concentration (high solute).
172
When does osmosis stop?
When solute and water are evenly distributed (equilibrium).
173
What happens if a membrane separates unequal solutions of a penetrating solute?
Both solute and water move down their gradients until equilibrium.
174
What happens when a membrane is permeable to both water and solute?
Both water and solute move until concentrations equalize.
175
In osmosis, if the solute is penetrating, what is the final outcome?
Equal solute and water concentration on both sides (steady state).
176
What is the driving force for water and solute movement in this case?
Concentration gradients of both solute and water.
177
How does this differ from nonpenetrating solutes?
With nonpenetrating solutes, only water moves — leading to cell shrinkage or swelling.
178
What happens when a solute is nonpenetrating?
The solute cannot cross the membrane, so only water moves.
179
In osmosis with nonpenetrating solutes, which way does water move?
From the side with higher water concentration (low solute) → to the side with lower water concentration (high solute).
180
What happens to the volume of the side with higher solute concentration?
It increases, as water moves into it.
181
What happens to the volume of the side with lower solute concentration?
It decreases, as water leaves.
182
Why does steady state eventually occur?
Water redistribution balances out the concentrations, even though the solute itself does not move.
183
What determines if a substance can cross the membrane unassisted?
Lipid solubility (nonpolar, uncharged can cross) and size of the particle.
184
Define diffusion.
Net movement of molecules from high → low concentration.
185
Define osmosis.
Net diffusion of water from low solute (high water) → high solute (low water).
186
What is the difference between penetrating and nonpenetrating solutes?
Penetrating solutes and water both move until equal; nonpenetrating solutes can’t cross, so only water moves.
187
Why are nonpenetrating solutes important for cells?
They determine tonicity (isotonic, hypotonic, hypertonic).
188
What happens to an RBC in isotonic, hypertonic, and hypotonic solution?
Isotonic = no change; Hypertonic = shrink; Hypotonic = swell/burst.
189
What is the role of the Na⁺/K⁺ pump?
Active transport: moves 3 Na⁺ out and 2 K⁺ in, using ATP.
190
Which molecules cross the plasma membrane without help?
Small, nonpolar, lipid-soluble molecules (O₂, CO₂, fatty acids, steroid hormones).
191
Which molecules require assistance (channels, carriers, or pumps)?
Charged ions (Na⁺, K⁺, Ca²⁺, Cl⁻) and large polar molecules (glucose, amino acids, proteins).
192
What is the difference between penetrating and nonpenetrating solutes?
Penetrating solutes and water both move until equalized; nonpenetrating solutes can’t cross, so only water moves.
193
What happens when pure water is separated from a solution containing a nonpenetrating solute?
Water moves into the solute side by osmosis.
194
Why can the two sides never become equal in this case?
The solute cannot cross the membrane, so only water moves.
195
What eventually limits osmosis in this scenario?
Hydrostatic pressure builds as volume increases, opposing further water movement.
196
What is hydrostatic (fluid) pressure?
The pressure exerted by a standing/stationary fluid on an object.
197
What is osmotic pressure?
A measure of the tendency for water to move into a solution due to the relative concentration of nonpenetrating solutes and water.
198
What major force controls water movement in and out of cells?
Osmosis.
199
What is tonicity?
The effect a solution has on cell volume.
200
What happens to a cell in an isotonic solution?
Cell volume remains constant (no net water movement).
201
What happens to a cell in a hypotonic solution?
Water enters → cell swells (may burst/lyse).
202
What happens to a cell in a hypertonic solution?
Water leaves → cell shrinks (crenates).
203
What happens to RBCs in a hypotonic solution?
They swell and may burst (lysis).
204
What happens to RBCs in a hypertonic solution?
They shrink (crenation).
205
What happens to RBCs in an isotonic solution?
They remain normal in size/shape (no net water movement).
206
In an isotonic solution, what happens to the cell?
Stays the same (no net water movement).
207
In an isotonic solution, how does water move?
Water moves equally in and out.
208
Memory tip for isotonic solution?
ISO = Equal.
209
In a hypotonic solution, what happens to the cell?
Cell swells (may burst/lyse).
210
In a hypotonic solution, how does water move?
Water moves into the cell.
211
Memory tip for hypotonic solution?
HYPO = Hippo (big).
212
In a hypertonic solution, what happens to the cell?
Cell shrinks (crenates).
213
In a hypertonic solution, how does water move?
Water moves out of the cell.
214
Memory tip for hypertonic solution?
HYPER = Skinny cell.
215
Why do large, poorly lipid-soluble molecules need assistance crossing the plasma membrane?
They cannot cross on their own.
216
What does the cell provide to move large, poorly lipid-soluble molecules?
Mechanisms for assisted transport.
217
What are the two types of assisted membrane transport?
1. Carrier-mediated transport
2. Vesicular transport.
218
What proteins are involved in carrier-mediated transport?
Carrier proteins that span the plasma membrane.
219
How do carrier proteins work?
They change shape so binding sites on either side of the membrane can be exposed.
220
What are the two forms of carrier-mediated transport?
Active and passive.
221
What are the 3 important characteristics of carrier-mediated transport?
Specificity, Saturation, Competition.
222
Is facilitated diffusion active or passive?
Passive (no energy required).
223
How do molecules move in facilitated diffusion?
Down their concentration gradient (high → low).
224
What proteins are required for facilitated diffusion?
Carrier proteins in the plasma membrane.
225
How do carrier proteins work in facilitated diffusion?
Solute binds → carrier protein changes shape → solute released on other side.
226
Compare simple diffusion and facilitated diffusion.
Simple diffusion: Molecules move directly through the lipid bilayer (no carrier needed), down concentration gradient, passive.
Facilitated diffusion: Requires carrier proteins, moves molecules down concentration gradient, still passive (no ATP).
227
What does specificity mean in carrier-mediated transport?
Each carrier protein only transports one (or a few closely related) specific substances.
228
What is cystinuria?
A genetic disorder where a defective carrier protein in kidney cells fails to reabsorb cysteine (amino acid).
229
Why does cystinuria occur?
Loss of specificity or function in the carrier protein → cysteine stays in urine instead of being reabsorbed.
230
What is the consequence of cystinuria?
High cysteine levels in urine crystallize into cystine stones.
231
What does saturation mean in carrier-mediated transport?
Carriers have limited binding sites.
232
What is Transport Maximum (Tm)?
The maximum transport rate once all carriers are occupied.
233
Can transport rate increase beyond Tm?
No, it cannot.
234
What happens if glucose carriers (SGLT1 & SGLT2) in the kidney are saturated?
Excess glucose cannot be fully reabsorbed → glucose appears in urine.
235
What does glucose in urine indicate about carrier-mediated transport?
The carriers have reached their Transport Maximum (Tm).
236
What does competition mean in carrier-mediated transport?
Similar molecules (e.g., glycine and alanine) compete for the same transporter.
237
What happens when molecules compete for the same carrier?
Transport of each is reduced, but they can still be absorbed.
238
What carrier is defective in Hartnup disease?
The carrier for neutral amino acids (e.g., tryptophan, glycine, alanine).
239
Why is tryptophan loss especially important in Hartnup disease?
Leads to niacin deficiency, causing pellagra-like symptoms.
240
What are key symptoms of Hartnup disease?
Sun-sensitive rash, neurological symptoms, diarrhea.
241
What is passive transport?
Movement down the concentration gradient (high → low) without energy.
242
Give two examples of passive transport.
Simple diffusion and facilitated diffusion.
243
What is active transport?
Movement against the concentration gradient (low → high) that requires energy (ATP).
244
What protein is involved in active transport of sodium and potassium?
Sodium-potassium pump (Na⁺ out, K⁺ in using ATP).
245
Is facilitated diffusion active or passive?
Passive.
246
What does facilitated diffusion require?
A carrier or channel protein.
247
Give an example of a molecule that uses facilitated diffusion.
Glucose.
248
Why does glucose need facilitated diffusion?
It is large and polar, so it cannot cross the membrane directly.
249
Define osmosis.
Movement of water across a semipermeable membrane from low solute (high water) → high solute (low water).
250
What is the driving force for osmosis?
Concentration gradient (no energy required).
251
What stops osmosis?
Hydrostatic (fluid) pressure balances osmotic pressure.
252
What is osmotic pressure?
The tendency of water to move into a solution due to concentration of nonpenetrating solutes.
253
What is hydrostatic pressure?
Pressure exerted by a standing or stationary fluid.
254
How do osmotic and hydrostatic pressure interact?
Osmosis draws water in, hydrostatic pressure pushes water out → equilibrium occurs when they balance.
255
Define tonicity.
The effect of a solution on cell volume.
256
What happens in an isotonic solution?
No net water movement → cell volume stays constant.
257
What happens in a hypotonic solution?
Water enters the cell → cell swells (may lyse).
258
What happens in a hypertonic solution?
Water leaves the cell → cell shrinks (crenation).
259
How do kidneys prevent cells from shrinking or swelling?
By balancing solute and water levels in extracellular fluid (ECF).
260
Why do large or polar molecules need assisted transport?
They cannot cross the lipid bilayer directly.
261
What are the two types of assisted transport?
Carrier-mediated transport and vesicular transport.
262
What are the three important characteristics of carrier-mediated transport?
Specificity, saturation (Transport Maximum, Tm), and competition.
263
What is Transport Maximum (Tm)?
The point at which all carrier binding sites are full, so transport cannot increase further.
264
What happens when concentration increases beyond Tm?
No further increase in transport rate.
265
What percentage of glucose is reabsorbed by SGLT2 in the kidney?
~90%.
266
What percentage of glucose is reabsorbed by SGLT1?
~10%.
267
What happens when glucose carriers saturate?
Excess glucose appears in the urine.
268
What does competition mean in carrier-mediated transport?
Different molecules (e.g., glycine and alanine) compete for the same transporter.
269
What happens in Hartnup disease?
Defective neutral amino acid carrier → tryptophan not absorbed → niacin deficiency symptoms (rash, neurological issues, diarrhea).
270
What is passive transport?
Movement down concentration gradient, no energy.
271
Examples of passive transport?
Simple diffusion, facilitated diffusion.
272
What is active transport?
Movement against concentration gradient, requires energy (ATP).
273
Example of active transport?
Sodium-potassium pump (Na⁺ out, K⁺ in using ATP).
274
What is osmosis?
Passive diffusion of water across a membrane.
275
What happens to a cell in an isotonic solution?
Stays the same.
276
What happens to a cell in a hypotonic solution?
Swells (may burst/lyse).
277
What happens to a cell in a hypertonic solution?
Shrinks (crenates).
278
What are the two types of assisted membrane transport?
Carrier-mediated transport and vesicular transport.
279
What are the three properties of carrier-mediated transport?
Specificity, saturation, competition.
280
What is transport maximum (Tm)?
The maximum rate of transport once all carriers are saturated.
281
What proteins are required for facilitated diffusion?
Carrier proteins.
282
What is the key difference between simple diffusion and facilitated diffusion?
Simple: moves directly through lipid bilayer, no protein.
## Footnote
Facilitated: requires a carrier protein.
283
How does the rate of simple diffusion change with concentration?
Increases continuously (no limit).
284
How does the rate of carrier-mediated transport change with concentration?
Increases at first, but plateaus at Transport Maximum (Tm) once carriers are saturated.
285
What key feature distinguishes carrier-mediated diffusion from simple diffusion on a graph?
Carrier-mediated shows a plateau (Tm), simple diffusion does not.
286
What is the simplest form of active transport?
A proton (H⁺) pump, which moves a single type of ion.
287
What does the sodium-potassium (Na⁺–K⁺) pump do?
Pumps Na⁺ out of the cell and K⁺ into the cell, against their gradients, using ATP.
288
What kind of transport is the Na⁺–K⁺ pump an example of?
Active transport (specifically, counter-transport of two substances in opposite directions).
289
What does the Na⁺/K⁺ pump move per cycle?
3 Na⁺ out, 2 K⁺ in.
290
Does the Na⁺/K⁺ pump require energy?
Yes, it uses ATP.
291
Why is the Na⁺/K⁺ pump important?
Maintains sodium and potassium gradients across the cell membrane.
292
What type of transport is the Na⁺–K⁺ pump?
Primary active transport (uses ATP directly).
293
How many ions are exchanged in the Na⁺–K⁺ pump per cycle?
3 Na⁺ out, 2 K⁺ in.
294
Why is ATP required for the Na⁺–K⁺ pump?
ATP phosphorylation drives the conformational change to move ions against their gradients.
295
What gradients does the Na⁺–K⁺ pump maintain?
High Na⁺ outside, high K⁺ inside.
296
What are 3 key roles of the Na⁺/K⁺ pump?
Generates electrical signals in nerve and muscle cells.
## Footnote
Helps regulate cell volume by controlling solute concentrations inside the cell.
## Footnote
Provides energy (indirectly) for the cotransport of glucose and amino acids in intestinal and kidney cells.
297
What is this process called?
Secondary active transport.
298
Why do large concentrations of dextrose cause RBCs to shrink?
Because water moves out of the cells down its concentration gradient.
299
Why is normal saline used as IV fluid after blood loss?
It is isotonic to blood, so it replaces lost fluid without causing RBCs to shrink or swell.
300
Why is 20% dextrose reserved for extreme hypoglycemia?
It rapidly raises blood sugar but is very concentrated, so it can pull water out of cells (risky if not carefully monitored).
301
What is secondary active transport?
Transport that uses the energy from one ion’s gradient (set up by the Na⁺/K⁺ pump) to move another substance.
302
In the thyroid, what does the sodium-iodide symporter (NIS) do?
Uses the Na⁺ gradient to pull iodide (I⁻) into thyroid follicular cells.
303
Why is iodide transport into the thyroid important?
It’s required for thyroid hormone synthesis.
304
What is primary active transport?
Direct use of ATP to move substances against their gradient (e.g., Na⁺/K⁺ pump).
305
What is secondary active transport?
Uses the energy stored in the gradient from primary active transport (often Na⁺) to move another molecule (e.g., Na⁺-glucose cotransporter, Na⁺-iodide symporter).
306
Key difference between primary and secondary active transport?
Primary = ATP directly; Secondary = relies on ion gradient created by primary transport.
307
How does the Na⁺/K⁺ pump support secondary active transport?
By creating a Na⁺ gradient that powers cotransport of glucose or amino acids into cells.
308
Where does glucose and amino acid absorption via secondary active transport occur?
Intestinal and kidney cells.
309
What is the difference between primary and secondary active transport?
Primary active transport: Directly uses ATP (e.g., Na⁺/K⁺ pump).
## Footnote
Secondary active transport: Uses ion gradients created by primary transport to move other molecules (e.g., Na⁺-glucose symporter).
310
What is symport vs antiport?
Symport: Both molecules move in the same direction.
## Footnote
Antiport: Molecules move in opposite directions.
311
Does secondary active transport require energy?
Yes, but it uses “secondhand” energy from ion gradients instead of ATP directly.
312
How does secondary active transport move molecules?
It couples movement of one molecule down its concentration gradient with another molecule moving uphill (against its gradient).
313
Example of secondary active transport in the body?
Na⁺ gradient driving glucose or amino acid uptake in intestinal/kidney cells.
314
What happens to a cell in an isotonic solution?
Stays the same (water in = water out).
315
What happens to a cell in a hypotonic solution?
Swells (water moves in).
316
What happens to a cell in a hypertonic solution?
Shrinks (water moves out).
317
What is facilitated diffusion?
Passive transport using a carrier protein, moving substances from high → low concentration.
318
What is active transport?
Uses ATP directly to move substances against their gradient (low → high).
319
What is the Na⁺/K⁺ pump?
A primary active transport pump that moves 3 Na⁺ out and 2 K⁺ in per cycle using ATP.
320
What is secondary active transport?
Uses the Na⁺ gradient (created by the Na⁺/K⁺ pump) as “secondhand” energy to move other molecules uphill.
321
Symport vs Antiport?
Symport = both substances move the same way; Antiport = substances move in opposite directions.
322
What are the 3 main roles of the Na⁺/K⁺ pump?
Generates electrical signals in nerve & muscle cells.
Helps regulate cell volume.
Provides energy for secondary active transport (e.g., glucose & amino acids).
323
Why is ATP required for the Na⁺/K⁺ pump?
ATP phosphorylation drives conformational changes that move ions against their gradients.
324
How does the Na⁺ gradient help glucose absorption?
It drives glucose into intestinal and kidney cells via a Na⁺-glucose symporter.
325
How does the thyroid use secondary active transport?
The sodium-iodide symporter (NIS) uses the Na⁺ gradient to pull iodide into thyroid follicular cells for thyroid hormone synthesis.
326
Why do RBCs shrink in high dextrose solution?
Water moves out (hypertonic environment).
327
Why is normal saline given for blood loss?
It is isotonic, so it restores volume without shrinking or swelling RBCs.
328
Why is 20% dextrose reserved for severe hypoglycemia?
It raises blood sugar quickly but is so concentrated it can pull water out of cells, making it risky.
329
How does glucose enter intestinal epithelial cells?
By secondary active transport with Na⁺ (Na⁺-glucose symporter) at the luminal border.
330
What provides the energy for glucose secondary active transport?
The Na⁺ gradient created by the Na⁺/K⁺ pump (which uses ATP).
331
After glucose enters the cell, how does it move into the blood?
By facilitated diffusion through a passive glucose carrier at the basolateral border.
332
What role does the Na⁺/K⁺ pump play in glucose absorption?
Pumps Na⁺ out of the cell, keeping intracellular Na⁺ low and maintaining the gradient that drives glucose uptake.
333
What is vesicular transport? STUDY
Movement of large particles across the membrane inside membrane-enclosed vesicles.
334
Does vesicular transport require energy? STUDY
Yes — it is an active form of transport.
335
What are the two main forms of vesicular transport? STUDY
Endocytosis: Brings materials into the cell.
Exocytosis: Moves materials out of the cell.
336
What is pinocytosis?
“Cell drinking” – the cell engulfs extracellular fluid and dissolved solutes into small vesicles.
337
What is receptor-mediated endocytosis? STUDY
Specific molecules bind to receptors on the membrane, then the cell engulfs them in a vesicle.
338
What is the key difference between pinocytosis and receptor-mediated endocytosis?
Pinocytosis is non-specific (any solutes/ECF), while receptor-mediated is highly specific for certain molecules.
339
What is endocytosis? STUDY
The process where a cell brings material inside by wrapping it in a vesicle made from its plasma membrane.
340
What is phagocytosis?
“Cell eating” – the cell engulfs large particles (e.g., white blood cells engulfing bacteria).
341
How does phagocytosis work?
The membrane extends around the target → encloses it in a vesicle → vesicle fuses with a lysosome → contents are digested.
342
What type of cells commonly use phagocytosis?
White blood cells (e.g., macrophages, neutrophils).
343
What is exocytosis? STUDY
A vesicular transport process where materials are moved out of the cell — essentially the reverse of endocytosis.
344
What are the two main purposes of exocytosis?
Secretion of large polar molecules (e.g., hormones, enzymes, proteins).
Addition of components (e.g., channels or receptors) to the plasma membrane.
345
Where do exocytosis vesicles come from? STUDY
They are produced by the Golgi complex and bud off to deliver products to target sites.
346
Give an example of exocytosis. STUDY
Secretion of hormones or digestive enzymes into the extracellular space.
347
Where are secretory vesicles produced?
In the Golgi complex.
348
What ensures that secretory vesicles dock at the correct site on the plasma membrane?
Specific protein pairing between v-SNAREs (vesicle) and t-SNAREs (target membrane).
349
What happens after docking?
The vesicle fuses with the plasma membrane and releases its contents outside the cell.
350
Why must endocytosis and exocytosis stay balanced?
To keep the cell’s surface area and volume constant.
351
How much membrane can be internalized during active endocytosis?
More than 100% of the plasma membrane in one hour.
352
How does the cell prevent losing too much membrane during endocytosis?
Exocytosis rapidly replaces the internalized membrane.
353
Are cells selective in what enters and leaves?
Yes — selectivity depends on the transport mechanisms available.
354
What is diffusion through the lipid bilayer?
Movement of nonpolar molecules (e.g., O₂, CO₂, fatty acids) down their concentration gradient (high → low). Passive process.
355
What is diffusion through protein channels?
Movement of small ions (e.g., Na⁺, K⁺, Ca²⁺, Cl⁻) down their electrochemical gradient through open channels. Passive process.
356
What is osmosis?
Passive movement of water down its concentration gradient (from high water concentration → low water concentration, or toward higher solute concentration).
357
What is the driving force in all three (lipid bilayer diffusion, channel diffusion, osmosis)?
A concentration gradient (no energy required).
358
What is facilitated diffusion?
Passive transport of polar molecules (e.g., glucose) down their concentration gradient via a carrier protein.
359
What is primary active transport?
Active transport where ions/molecules (e.g., Na⁺, K⁺, amino acids) move against their concentration gradient using ATP (e.g., Na⁺/K⁺ pump).
360
What is secondary active transport?
Uses energy stored in an ion gradient (usually Na⁺) created by primary active transport to move other molecules (e.g., glucose, amino acids, some ions) uphill.
361
What is pinocytosis?
“Cell drinking” – uptake of small fluid volumes + solutes into vesicles.
362
What is receptor-mediated endocytosis?
Highly selective uptake of large molecules (e.g., proteins, hormones) via binding to surface receptors.
363
What is phagocytosis?
“Cell eating” – engulfment of large particles (e.g., bacteria, debris) into vesicles.
364
What is exocytosis?
Active process where secretory vesicles (e.g., hormones, enzymes, proteins) fuse with plasma membrane and release contents outside the cell.
365
Why must cells communicate?
To coordinate body functions.
366
What are the two main types of intercellular communication?
Direct communication → cell-to-cell contact.
Indirect communication → chemical messengers travel through extracellular fluid or blood.
367
How does indirect intercellular communication work?
A signaling cell releases a chemical messenger → messenger travels through extracellular fluid or blood → binds to receptors on a target cell.
368
What are the four types of extracellular chemical messengers?
Paracrines
Neurotransmitters
Hormones
Neurohormones
369
What are gap junctions?
Channels that allow small ions and molecules to pass directly between cells without entering extracellular fluid.
370
What role do surface membrane markers play?
Allow brief cell-to-cell contact, enabling immune cells (e.g., phagocytes) to recognize and destroy harmful cells (like cancer) while sparing healthy ones.
371
Neurotransmitters — released by? target?
Released by neurons, act on nearby cells across a synapse (e.g., neurons, muscle, glands).
372
Paracrines — released by? target?
Released by local non-neuronal cells, act on nearby cells in the same tissue.
373
Hormones — released by? target?
Released by endocrine gland cells, travel via bloodstream to distant target cells.
374
Neurohormones — released by? target?
Released by neurons into the blood (not into a synapse), act on distant target cells via bloodstream.
375
Compare the 4 types of extracellular chemical messengers.
Neurotransmitters → Neurons → Act across synapse on nearby cells (neuron, muscle, gland).
Paracrines → Local non-neuronal cells → Act on nearby cells in same tissue.
Hormones → Endocrine gland cells → Travel in blood to distant target cells.
Neurohormones → Neurons → Released into blood (not synapse), act on distant target cells.
376
What are paracrines?
Short-range chemical messengers that act only on nearby cells in the same tissue.
377
Example of a paracrine?
Histamine — secreted by mast cells in connective tissue.
378
What does histamine do?
Causes vasodilation → more blood flow → immune cell recruitment.
379
What are neurotransmitters?
Short-range messengers released by neurons across a synapse to act on nearby target cells (e.g., neurons, muscles, glands).
380
Example of neurotransmitter action?
A neuron releasing a neurotransmitter that binds to a muscle cell to cause contraction.
381
What are hormones?
Long-distance messengers released by endocrine gland cells into the blood.
382
How do hormones act?
Only on target cells with the right receptors.
383
What are neurohormones?
Hormones released into the blood by neurons (instead of endocrine glands).
384
Example of neurohormones?
Oxytocin and vasopressin from the hypothalamus.
385
How do the 4 types of chemical messengers differ?
By their source, distance traveled, and how they reach target cells.
386
What do they all have in common?
All are released from one cell type and act on specific target cells.
387
What is signal transduction?
The process by which incoming signals are conveyed to the cell’s interior for execution.
388
How do messengers signal a cell?
By binding to a specific membrane receptor.
389
What are the 2 main ways receptors cause a response?
Opening/closing ion channels (first messenger).
Activating a second-messenger system.
390
What opens chemically gated channels?
Binding of a chemical messenger (e.g., acetylcholine).
391
What happens when ions move through the channel?
The cell’s charge changes → electrical signal.
392
In muscle, what does this electrical signal trigger?
Contraction.
393
What happens when the messenger is removed?
The channel closes.
394
What is a first messenger?
The extracellular messenger that binds to the receptor.
395
What is a second messenger?
Intracellular relay molecules that pass on the signal, causing slower but longer-lasting cellular changes.
396
Why is membrane function important for homeostasis?
It allows cells to survive and perform specialized tasks, maintaining the body’s balance.
397
What do many specialized tasks require?
Energy production + regulation of the intracellular environment.
398
What are the 3 main categories of membrane transport?
Diffusion, carrier-mediated transport, vesicular transport.
399
Diffusion through lipid bilayer – substances & type?
Nonpolar molecules (O₂, CO₂, fatty acids), passive.
400
Diffusion through protein channels – substances & type?
Small ions (Na⁺, K⁺, Ca²⁺, Cl⁻), passive.
401
Osmosis – what moves?
Water only, passive, from high → low water concentration.
402
Facilitated diffusion – energy use? example?
Passive, uses carriers (e.g., glucose).
403
Primary active transport – energy use? example?
Uses ATP directly, moves ions uphill (Na⁺/K⁺ pump).
404
Secondary active transport – energy use?
Uses ion gradient (usually Na⁺) from primary active transport to drive other molecules.
405
Paracrines – source & range? example?
Local cells → nearby cells; e.g., histamine (mast cells → blood vessels).
406
Neurotransmitters – source & range?
Neurons → nearby cells across synapse (muscle, neuron, gland).
407
Hormones – source & range?
Endocrine glands → distant target cells via blood.
408
Neurohormones – source & range? example?
Neurons release into blood → distant cells; e.g., oxytocin, vasopressin.
409
Signal transduction definition?
Process by which signals are conveyed to cell’s interior via receptors.
410
2 main mechanisms of signal transduction?
Opening/closing ion channels (first messenger) OR activating second-messenger pathways.
411
Chemically gated channels – steps?
Messenger binds → ion flow → change in charge → electrical signal → muscle contraction → channel closes when messenger removed.
412
Second-messenger pathways – key idea?
First messenger (outside) triggers second messenger (inside) → slower but longer-lasting cellular effects.
413
How does this chapter tie to homeostasis?
Membrane transport + communication allow cells to survive, specialize, and coordinate body balance.
414
Which process requires ATP?
C) Primary active transport ✅
415
Osmosis definition?
Water moves down gradient → higher solute concentration.
416
Exocytosis helps maintain cell surface area by?
A) Recycling vesicle membranes to plasma membrane ✅
417
Which messenger is released by neurons but travels through blood to distant targets?
D) Neurohormone ✅
418
Which best describes a second messenger?
C) An intracellular relay molecule activated by a first messenger ✅
419
Which best describes the role of membranes in homeostasis?
B) Membranes allow regulated exchange to support cellular function ✅
420
Main function of skin epithelium?
Protection.
421
Main function of lung epithelium?
Protection + gas exchange.
422
Main function of thyroid epithelium?
Secretion.
423
Main function of liver epithelium?
Secretion.
424
Main function of kidney epithelium?
Filtration.
425
Main function of intestinal epithelium?
Absorption.
426
General feature of epithelial cells?
Tightly packed together.
427
Loose connective tissue – function?
Connects skin to muscle, surrounds vessels/organs, cushions organs, provides nutrients to epithelium.
428
Adipose tissue (fat) – function?
Stores energy, insulates body, cushions organs.
429
Dense connective tissue – examples & function?
Tendons (muscle → bone), ligaments (bone → bone); transmit force, stabilize joints.
430
Cartilage – function & locations?
Smooth surfaces for joints, flexibility; found in ear, nose, airway.
431
Bone – function?
Support, protection, blood cell production, calcium storage.
432
Blood – function?
Transport (O₂, nutrients, wastes), immune defense, clotting.
433
What is the main function of epithelial tissue?
Covers body surfaces, lines organs, forms glands; functions include protection, absorption, secretion, filtration, gas exchange.
434
What is the main function of connective tissue?
Supports, connects, and anchors body structures; roles include transport, storage, cushioning, flexibility, and defense.
435
How are epithelial cells arranged?
Tightly packed, forming continuous sheets.
436
How are connective tissue cells arranged?
Scattered within an extracellular matrix (fibers + ground substance).
437
Does epithelial tissue have blood supply?
No, it’s avascular (relies on diffusion from connective tissue).
438
Does connective tissue have blood supply?
Yes, most types are vascular (except cartilage).
439
Examples of epithelial tissue?
Skin (protection), lungs (gas exchange), intestine (absorption), glands (secretion), kidney (filtration).
440
Examples of connective tissue?
Loose connective, adipose, dense connective (tendons, ligaments), cartilage, bone, blood.
