1
Q
Q: How do you prepare a temporary wet mount?
A
A: Specimen → drop of water/stain → lower coverslip at angle → blot excess liquid.
2
Q
Q: Why lower the coverslip at an angle?
A
A: Prevents air bubbles.
3
Q
Q: Why use a coverslip?
A
A: Prevents drying. Protects objective lens. Flattens specimen.
4
Q
Q: Why are stains used?
A
A: Increase contrast. Make structures visible.
5
Q
Q: How do you correctly focus a light microscope?
A
A: Start low power → coarse focus → fine focus → adjust light → higher power (fine focus only).
6
Q
Q: What is total magnification?
A
A: Eyepiece × objective.
7
Q
Q: What is an eyepiece graticule?
A
A: Scale in eyepiece with arbitrary units. Must be calibrated.
8
Q
Q: What is a stage micrometer?
A
A: Slide with known scale (usually 1 mm ÷ 100 = 10 µm per division).
9
Q
Q: Why must calibration be repeated?
A
A: Each objective lens gives different magnification.
10
Q
Q: How do you calculate the value of one eyepiece unit?
A
A: Stage micrometer length (µm) ÷ eyepiece divisions counted.
11
Q
Q: How do you measure a specimen?
A
A: Number of eyepiece divisions × value per division.
12
Q
Q: Why are cells hard to see without staining?
A
A: They are mostly transparent.
13
Q
Q: What is differential staining?
A
A: Using multiple stains to distinguish cell components or cell types.
14
Q
Q: How do stains bind to structures?
A
A: Chemical attraction (often charge-based).
15
Q
Q: What does methylene blue stain?
A
A: DNA → nuclei stain blue.
16
Q
Q: What does iodine stain?
A
A: Starch → blue-black.
17
Q
Q: What is Gram staining used for?
A
A: Distinguishing Gram-positive and Gram-negative bacteria.
18
Q
Q: Why do Gram-positive bacteria stay purple?
A
A: Thick peptidoglycan wall retains crystal violet.
19
Q
Q: Why do Gram-negative bacteria stain pink?
A
A: Thin peptidoglycan wall loses violet stain, takes counterstain.
20
Q
Q: Limitation of staining?
A
A: Can kill or distort cells.
21
Q
Q: Nucleus — structure?
A
A: Double membrane with pores. Contains chromatin and nucleolus.
22
Q
Q: Nucleus — function?
A
A: Controls cell activity. Contains DNA.
23
Q
Q: Nucleolus — function?
A
A: Makes rRNA. Assembles ribosomes.
24
Q
Q: Rough ER — structure?
A
A: Flattened sacs with ribosomes attached.
25
Q: Rough ER — function?
A: Synthesises proteins for secretion or membranes.
26
Q: Smooth ER — function?
A: Lipid synthesis. Carbohydrate metabolism.
27
Q: Golgi apparatus — function?
A: Modifies, sorts, packages proteins. Forms lysosomes.
28
Q: Ribosomes — structure?
A: 80S. rRNA + protein. Two subunits.
29
Q: Ribosomes — function?
A: Translation.
30
Q: Mitochondria — key features?
A: Double membrane. Cristae. Matrix with circular DNA and ribosomes.
31
Q: mitochondria function?
A: Aerobic respiration. ATP production.
32
Q: Lysosomes — function?
A: Intracellular digestion. Apoptosis.
33
Q: Chloroplasts — key features?
A: Double membrane. Grana. Stroma. Circular DNA.
34
Q: chloroplast function?
A: Photosynthesis.
35
Q: Plasma membrane function?
A: Controls movement. Cell signalling.
36
Q: Plasma membrane — structure?
A: Phospholipid bilayer with proteins, cholesterol, glycoproteins.
37
Q: Centrioles — function?
A: Spindle formation in cell division.
38
Q: Cell wall (plant) — function?
A: Support. Prevents osmotic bursting.
39
Q: Cilia/flagella — structure?
A: 9+2 microtubules.
40
Q: Cilia/flagella function?
A: Movement.
41
Q: Where does a protein for secretion start being made?
A: On ribosomes attached to the rough ER.
42
Q: Why are some ribosomes attached to rough ER?
A: They are making proteins for secretion or membranes.
43
Q: What happens to a protein once it enters the rough ER?
A: It is folded and processed inside the ER lumen.
44
Q: How does a protein leave the rough ER?
A: It is packaged into transport vesicles.
45
Q: Where do transport vesicles from the rough ER go?
A: To the Golgi apparatus.
46
Q: What happens to proteins in the Golgi apparatus?
A: They are modified (e.g. glycosylation), sorted, and packaged.
47
Q: How do proteins leave the Golgi?
A: In secretory vesicles.
48
Q: What happens when a secretory vesicle reaches the plasma membrane?
A: It fuses with the membrane and releases the protein by exocytosis.
49
Q: What is exocytosis?
A: Vesicle membrane fuses with plasma membrane, releasing contents outside the cell.
50
Q: How are the organelles interrelated in protein secretion?
A: Ribosome → Rough ER → Transport vesicle → Golgi → Secretory vesicle → Plasma membrane.
51
Q: What is the cytoskeleton?
A: A network of protein fibres within the cytoplasm.
52
Q: What are the main components of the cytoskeleton?
A: Microfilaments, intermediate filaments, microtubules.
53
Q: What does the cytoskeleton do to provide mechanical strength?
A: Maintains cell shape and prevents cell collapse.
54
Q: How does the cytoskeleton aid transport within cells?
A: Microtubules act as tracks for movement of vesicles and organelles.
55
Q: What moves materials along microtubules?
A: Motor proteins (using ATP).
56
Q: How does the cytoskeleton enable cell movement? (3)
A:
- Forms spindle fibres in cell division.
- Enables movement of cilia and flagella.
- Microfilaments allow cell shape changes.
57
Q: What is a key structural difference between prokaryotic and eukaryotic cells?
A: Prokaryotes have no nucleus. Eukaryotes have a membrane-bound nucleus.
58
Q: Where is DNA found in prokaryotes?
A: Free in the cytoplasm (nucleoid region).
59
Q: What is the form of DNA in prokaryotes?
A: Single circular DNA molecule. May also have plasmids.
60
Q: What is the form of DNA in eukaryotes?
A: Linear chromosomes associated with histone proteins.
61
Q: Do prokaryotes have membrane-bound organelles?
A: No.
62
Q: Give examples of membrane-bound organelles in eukaryotes.
A: Mitochondria, ER, Golgi, chloroplasts.
63
Q: Ribosome size in prokaryotes?
A: 70S.
64
Q: Ribosome size in eukaryotes?
A: 80S (in cytoplasm).
65
Q: Typical size of prokaryotic cells?
A: Small (about 1–5 µm).
66
Q: Typical size of eukaryotic cells?
A: Larger (about 10–100 µm).
67
Q: What is the prokaryotic cell wall made of?
A: Peptidoglycan (murein).
68
Q: What is the plant eukaryotic cell wall made of?
A: Cellulose.
69
Q: How do prokaryotic flagella differ from eukaryotic flagella?
A:
- Prokaryotic: made of flagellin, rotate.
- Eukaryotic: 9+2 microtubules, whip-like movement.
70
Q: How is prokaryotic cytoplasm different?
A: No compartmentalisation.
71
Q: How is eukaryotic cytoplasm different?
A: Compartmentalised by membrane-bound organelles.
72
Q: What do both prokaryotic and eukaryotic cells have?
A:
- Plasma membrane
- Cytoplasm
- Ribosomes
- DNA
73
Q: Why is water a polar molecule?
A: Oxygen is more electronegative than hydrogen → uneven charge distribution → partial negative O, partial positive H.
74
Q: How does hydrogen bonding occur between water molecules?
A: The δ⁺ hydrogen of one water molecule is attracted to the δ⁻ oxygen of another molecule.
75
Q: What is a hydrogen bond?
A: A weak electrostatic attraction between δ⁺ hydrogen and δ⁻ oxygen of neighbouring molecules.
76
Q: Why is water a good solvent?
A: It is polar and can surround charged or polar substances.
77
Q: Why is water’s solvent property important in cells?
A:
- Metabolic reactions occur in solution.
- Ions dissolve for reactions.
78
Q: Example in eukaryotes?
A: Cytoplasm is aqueous → enzymes and substrates dissolve for respiration.
79
Q: Example in prokaryotes?
A: Bacterial cytoplasm contains dissolved enzymes and nutrients for metabolism.
80
Q: Why is water suitable as a transport medium?
Q: Why is water suitable as a transport medium?
81
Q: Example in eukaryotes (transport)?
A:
- Blood plasma transports glucose, ions, urea.
- Xylem transports water in plants.
82
Q: Example in prokaryotes (transport)?
A:
- Dissolved nutrients diffuse through cytoplasm.
- Aquatic bacteria rely on dissolved substances in surrounding water.
83
Q: Why does water have a high specific heat capacity?
A: Hydrogen bonds require energy to break.
84
Q: Why is high specific heat capacity important?
A: Resists rapid temperature changes.
85
Q: Example in eukaryotes (cooling)?
A:
- Sweating in humans.
- Stable internal temperature for enzyme function.
86
Q: Example in prokaryotes?
A: Stable aquatic environments prevent enzyme denaturation in bacteria.
87
Q: Why is water a good habitat?
A:
- High specific heat capacity → stable temperature.
- Ice less dense than water → floats.
88
Q: Why is floating ice important?
A: Insulates water below → organisms survive in winter.
89
Q: Example organisms?
A:
- Prokaryotes: aquatic bacteria.
- Eukaryotes: fish, algae.
90
Q: Why does water have high surface tension?
A: Strong cohesion due to hydrogen bonding.
91
Q: Biological importance?
A:
Surface habitat for some organisms.
Helps water move in continuous columns in plants.
92
Q: What is a monomer?
A: Small, basic molecular unit that can join to form a polymer.
93
Q: What is a polymer?
A: Large molecule made from repeating monomer units.
94
Q: Give examples of biological monomers.
A:
- Glucose (carbohydrates)
- Amino acids (proteins)
- Nucleotides (nucleic acids)
- Fatty acids + glycerol (lipids)
95
Q: Give examples of the corresponding polymers.
A:
- Starch, glycogen, cellulose (from glucose)
- Proteins (from amino acids)
- DNA/RNA (from nucleotides)
- Triglycerides (from fatty acids + glycerol)
96
Q: What is a condensation reaction?
A: Joins monomers → polymer + water.
97
Q: Example of condensation in carbohydrates?
A: Glucose + glucose → maltose + water.
98
Q: What is a hydrolysis reaction?
A: Breaks polymer → monomers, using water.
99
Q: Example of hydrolysis in proteins?
A: Protein + water → amino acids.
100
Q: Why are condensation and hydrolysis important?
A:
- Condensation: builds complex molecules needed for structure & function.
- Hydrolysis: releases monomers for energy, growth, repair.
101
Q: Which elements are present in carbohydrates?
A: Carbon (C), Hydrogen (H), Oxygen (O)
102
Q: Which elements are present in lipids?
A: Carbon (C), Hydrogen (H), Oxygen (O)
103
Q: Which elements are present in proteins?
A: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Sulfur (S)
104
Q: Which elements are present in nucleic acids?
A: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P)
105
Q: Why do proteins contain sulfur?
A: Sulfur is in some amino acids (cysteine, methionine) → forms disulfide bonds.
106
Q: Why do nucleic acids contain phosphorus?
A: In the phosphate group → forms backbone of DNA/RNA.
107
Q: What is a hexose monosaccharide?
A: A sugar with 6 carbon atoms (e.g., glucose).
108
Q: How does α-glucose differ from β-glucose?
A: Position of OH on carbon 1:
- α: OH below the ring
- β: OH above the ring
109
Q: Why is the α/β difference important?
A: Determines the type of polysaccharide formed (starch vs cellulose).
110
Q: What is the ring structure of glucose?
A: Forms a 6-membered ring (pyranose) in solution.
111
Q: Properties of glucose?
A:
- Soluble in water
- Reducing sugar (can donate electrons)
- Source of energy in cells
112
Q: What is a pentose monosaccharide?
A: A sugar with 5 carbon atoms (e.g., ribose).
113
Q: Structure of ribose?
A: 5-membered ring (furanose) in solution.
114
Q: Role of ribose?
A: Component of RNA and ATP.
115
Q: Difference between hexose and pentose?
A: Hexose → 6 carbons, 6-membered ring; Pentose → 5 carbons, 5-membered ring.
116
Q: What is a disaccharide?
A: Two monosaccharides joined by a glycosidic bond.
117
Q: How is a glycosidic bond formed?
A: Condensation reaction → water removed → covalent bond between sugars.
117
Q: How is a glycosidic bond broken?
A: Hydrolysis reaction → water added → bond splits.
118
Q: Examples of disaccharides?
A:
Sucrose → glucose + fructose
Lactose → glucose + galactose
Maltose → glucose + glucose
119
Q: Biological importance of disaccharides?
A: Energy source → can be hydrolysed to monosaccharides for respiration.
120
Q: What is a polysaccharide?
A: Long chain of monosaccharides joined by glycosidic bonds.
120
Q: How are polysaccharides formed?
A: Condensation of many monosaccharides → glycosidic bonds.
120
Q: Structure of amylose?
A: Long, unbranched chain of α-glucose. Forms a coiled helix.
121
Q: Biological roles of polysaccharides?
A:
- Energy storage: starch (plants), glycogen (animals)
- Structural: cellulose (plants), chitin (fungi/insects)
121
Q: How are polysaccharides broken down?
A: Hydrolysis of glycosidic bonds → monosaccharides released.
121
Q: What is starch?
A: A plant energy storage polysaccharide made of α-glucose.
122
Q: Structure of amylopectin?
A: Long α-glucose chain with branched side chains (1–6 glycosidic bonds).
123
Q: Why does starch coil?
A: Hydrogen bonding between glucose units → compact storage.
124
Q: Biological role of glycogen?
A: Energy storage in liver and muscles.
124
Q: Why is glycogen highly branched?
A: Allows rapid release of glucose for energy.
124
Q: What is cellulose?
A: Plant structural polysaccharide made of β-glucose.
124
Q: Structure of cellulose?
A: Straight, unbranched chains of β-glucose. Chains form microfibrils via hydrogen bonds.
124
Q: What is glycogen?
A: Animal energy storage polysaccharide made of α-glucose.
125
Q: Biological role of starch?
A: Energy storage in plants; hydrolysed to glucose when needed.
125
Q: Structure of glycogen?
A: Highly branched α-glucose chains (more branched than amylopectin).
126
Q: Why is cellulose strong?
A: Hydrogen bonds between chains → high tensile strength.
126
Q: Biological role of cellulose?
A: Provides structural support in plant cell walls.
127
Q: How does glucose’s structure relate to its role as an energy source?
A: Small, soluble monosaccharide → easily transported in blood/cytoplasm → rapidly respired for ATP.
127
Q: How does glycogen’s structure relate to its function?
A: Highly branched → rapid hydrolysis → fast glucose release for energy.
Compact → efficient storage in liver/muscle.
127
Q: How does cellulose’s structure relate to its function?
A:
β-glucose chains → straight
Hydrogen bonds → strong microfibrils
Function: Provides structural support in plant cell walls.
127
Q: Structure of fatty acids?
A: Long hydrocarbon chain + carboxyl group (–COOH).
127
Q: How does starch’s structure relate to its function?
A:
- Amylose → coiled → compact storage
-Amylopectin → branched → glucose can be quickly released
- Function: Plant energy storage.
127
Q: Difference between saturated and unsaturated fatty acids?
A:
- Saturated → no C=C double bonds, straight chain
- Unsaturated → ≥1 C=C double bond, kinked chain
128
Q: What is a triglyceride?
A: One glycerol molecule + three fatty acids joined by ester bonds.
128
Q: Function of triglycerides?
A: Energy storage, insulation, protection.
129
Q: What is a phospholipid?
A: Glycerol + 2 fatty acids + phosphate group.
130
Q: Key feature of phospholipids?
A: Amphipathic → hydrophilic head (phosphate) + hydrophobic tails (fatty acids).
131
Q: Biological role of phospholipids?
A: Form bilayers in plasma membranes → barrier and compartmentalisation.
132
Q: How is a triglyceride synthesised?
A: Condensation reaction → 3 fatty acids + glycerol → 1 triglyceride + 3 water molecules.
133
Q: What bond forms between fatty acids and glycerol?
A: Ester bond.
134
Q: How is a triglyceride broken down?
A: Hydrolysis reaction → triglyceride + 3 water molecules → glycerol + 3 fatty acids.
135
Q: Biological importance of synthesis and breakdown?
A:
Synthesis → stores energy efficiently
Breakdown → releases fatty acids and glycerol for respiration or other reactions.
136
Q: What properties of triglycerides make them good energy stores?
A: Long hydrocarbon chains → high chemical energy per gram → compact energy storage.
137
Q: Are triglycerides hydrophilic or hydrophobic?
A: Hydrophobic → insoluble → stored without affecting water potential.
138
Q: Other functions of triglycerides?
A: Insulation and protection (cushioning organs).
139
Q: What structural feature gives phospholipids their function in membranes?
A: Amphipathic → hydrophilic head + hydrophobic tails → forms bilayer → barrier and compartmentalisation.
140
Q: How does the hydrophobic core affect membrane function?
A: Prevents polar molecules crossing → controls substance movement.
141
Q: What structural property of cholesterol affects membranes?
A: Small rigid molecule → hydrophobic with small hydroxyl → inserts between phospholipids.
142
Q: How does cholesterol relate to membrane function?
A: Stabilises membrane → maintains fluidity → prevents membranes becoming too rigid or too fluid.
143
Q: Other roles of cholesterol?
A: Precursor for steroid hormones and vitamin D.
144
Q: What is a peptide bond?
A: A covalent bond between the amino group of one amino acid and the carboxyl group of another.
145
Q: How is a dipeptide formed?
A: Condensation reaction → 2 amino acids join → 1 dipeptide + 1 water molecule.
146
Q: How is a polypeptide formed?
A: Repeated condensation of many amino acids → polypeptide + water molecules.
147
Q: How is a peptide bond broken?
A: Hydrolysis reaction → water added → peptide bond splits → amino acids released.
148
Q: Biological importance of peptide bond formation/breakdown?
A:
Formation → builds proteins needed for structure, enzymes, transport.
Breakdown → releases amino acids for recycling or energy.
149
Q: What happens during a condensation reaction between two amino acids?
A: The –COOH group of one reacts with the –NH₂ group of another and a molecule of water is released.
150
Q: What is the primary structure of a protein?
A: The specific sequence of amino acids in a polypeptide chain.
151
Q: What bonds hold the primary structure together?
A: Peptide (covalent) bonds.
152
Q: Why is the primary structure important?
A: It determines how the protein will fold into higher levels of structure.
153
Q: What is the secondary structure of a protein?
A: The regular folding of the polypeptide backbone.
154
Q: What two shapes form the secondary structure?
A: Alpha helix and beta pleated sheet.
155
Q: What stabilises the secondary structure?
A: Hydrogen bonds.
156
Q: Between which groups do hydrogen bonds form in secondary structure?
A: Between the C=O and N–H groups of the peptide backbone.
157
Q: Are hydrogen bonds strong or weak compared to covalent bonds?
A: Weak individually, but strong collectively.
158
Q: What is the tertiary structure of a protein?
A: The overall 3D shape of a single polypeptide chain.
159
Q: What determines the tertiary structure?
A: Interactions between R groups (side chains).
160
Q: What type of bond forms between two cysteine R groups?
A: A disulfide bond.
161
Q: What type of bond is a disulfide bond?
A: A strong covalent bond.
162
Q: Between which R groups do ionic bonds form?
A: Between oppositely charged R groups.
163
Q: What type of bond is an ionic bond in proteins?
A: An electrostatic attraction between charged side chains.
164
Q: What are hydrophobic interactions?
A: Non-polar R groups clustering together away from water.
165
Q: Why do hydrophobic R groups move towards the centre of the protein?
A: To avoid contact with water.
166
Q: What are hydrophilic interactions?
A: Polar or charged R groups interacting with water.
167
Q: Where are hydrophilic R groups usually found in a globular protein?
A: On the outside surface.
168
Q: Which bonds/interactions stabilise tertiary structure?
A: Hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions.
169
Q: What is the quaternary structure of a protein?
A: The association of two or more polypeptide chains.
170
Q: What holds quaternary structure together?
A: The same interactions as tertiary structure (hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions).
171
Q: Does every protein have a quaternary structure?
A: No, only proteins with multiple polypeptide chains.
172
Q: Which levels of protein structure depend on hydrogen bonding?
A: Secondary and tertiary (and sometimes quaternary).
173
Q: Which level of structure is directly determined by DNA?
A: Primary structure.
174
Q: How can a change in primary structure affect the protein?
A: It can alter bonding and folding, changing the tertiary structure and function.
175
Q: What is a globular protein?
A: A protein that is compact and roughly spherical in shape.
176
Q: Why are globular proteins spherical?
A: The polypeptide chain folds tightly due to R group interactions.
177
Q: Why are globular proteins soluble in water?
A: Hydrophilic R groups face outward and interact with water.
178
Q: Where are hydrophobic R groups located in globular proteins?
A: Folded into the centre, away from water.
179
Q: Which levels of structure do globular proteins have?
A: Primary, secondary, tertiary, and sometimes quaternary.
180
Q: What type of bonds stabilise globular proteins?
A: Hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions.
181
Q: What is a conjugated protein?
A: A protein with a non-protein component called a prosthetic group.
182
Q: What is a prosthetic group?
A: A non-protein molecule permanently attached to a protein.
183
Q: How does a prosthetic group affect function?
A: It enables the protein to perform a specific biological role.
184
Q: Why is haemoglobin described as a conjugated protein?
A: It contains haem prosthetic groups.
185
Q: What is the prosthetic group in haemoglobin?
A: A haem group containing an iron (Fe²⁺) ion.
186
Q: What is the function of haemoglobin?
A: To transport oxygen in the blood.
187
Q: How does haemoglobin bind oxygen?
A: Oxygen binds reversibly to the Fe²⁺ ion in each haem group.
188
Q: What level of structure allows haemoglobin to carry four oxygen molecules?
A: Quaternary structure (four polypeptide chains).
189
Q: Why must haemoglobin be soluble?
A: It is transported in blood plasma and inside red blood cells.
190
Q: What type of protein is amylase?
A: A globular enzyme.
191
Q: What is the function of amylase?
A: To catalyse the hydrolysis of starch into maltose.
192
Q: How does the structure of amylase relate to its function?
A: It has a specific tertiary structure forming an active site complementary to starch.
193
Q: Why is the active site specific?
A: The precise folding of the polypeptide creates a specific 3D shape.
194
Q: What happens if the tertiary structure of amylase changes?
A: The active site changes shape and the enzyme may no longer function.
195
Q: What type of protein is insulin?
A: A globular protein hormone.
196
Q: What is the function of insulin?
A: To regulate blood glucose concentration.
197
Q: How does insulin’s structure relate to its function?
A: Its specific tertiary structure allows it to bind to complementary receptors on target cells.
198
Q: How many polypeptide chains make up insulin?
A: Two polypeptide chains linked by disulfide bonds.
199
Q: Why are disulfide bonds important in insulin?
A: They stabilise its specific 3D shape.
200
Q: Why does the spherical shape of globular proteins suit their function?
A: It allows them to be soluble and interact easily with other molecules.
201
Q: Why are globular proteins more metabolically active than fibrous proteins?
A: Their compact structure allows binding sites and functional regions.
202
Q: Why can a change in primary structure affect protein function?
A: It alters folding, which changes the tertiary structure and shape of binding sites.
203
Q: What is the overall shape of fibrous proteins?
A: Long, extended and fibrous.
204
Q: Are fibrous proteins soluble or insoluble in water?
A: Insoluble in water.
205
Q: Why are fibrous proteins insoluble?
A: They have many hydrophobic R groups and form long parallel chains.
206
Q: What is the main function of fibrous proteins?
A: Structural support and mechanical strength.
207
Q: Are fibrous proteins metabolically active?
A: No, they are mainly structural.
208
Q: How does their shape relate to function?
A: Their long fibres provide strength and support to tissues.
209
Q: What is the function of collagen?
A: Provides tensile strength to tissues.
210
Q: Where is collagen found?
A: Tendons, ligaments, skin and bones.
211
Q: Why is collagen important in tendons?
A: It allows tendons to withstand pulling forces.
212
Q: Why is collagen described as strong?
A: It resists stretching and provides high tensile strength.
213
Q: What is the function of keratin?
A: Provides protection and structural support.
214
Q: Where is keratin found?
A: Hair, nails and the outer layer of skin.
215
Q: How does keratin relate to its protective role?
A: It forms tough, durable structures.
216
Q: What is the function of elastin?
A: Allows tissues to stretch and recoil.
217
Q: Where is elastin found?
A: Artery walls, lungs and skin.
218
Q: Why is elastin important in arteries?
A: It allows arteries to stretch when blood is pumped and recoil afterwards.
219
Q: Why are fibrous proteins suitable for structural roles?
A: They are long, strong, insoluble and form fibres.
220
Q: How do fibrous proteins differ from globular proteins?
A: Fibrous proteins are structural and insoluble; globular proteins are compact and soluble.
221
Q: Which fibrous protein provides tensile strength?
A: Collagen.
222
Q: Which fibrous protein allows stretch and recoil?
A: Elastin.
223
Q: Which fibrous protein forms protective outer structures?
A: Keratin.
224
Q: What is a key role of calcium ions (Ca²⁺) in muscle cells?
A: They bind to proteins to initiate muscle contraction.
225
Q: What is a role of Ca²⁺ at synapses?
A: They trigger vesicles to release neurotransmitters.
226
Q: What structural role does Ca²⁺ have in organisms?
A: Formation of bones and teeth (calcium phosphate).
227
Q: What is the role of Na⁺ in neurones?
A: Involved in depolarisation during an action potential.
228
Q: How does Na⁺ contribute to membrane potential?
A: By creating an electrochemical gradient across membranes.
229
Q: What transport process commonly involves Na⁺?
A: Co-transport (secondary active transport).
230
Q: What is the role of K⁺ in neurones?
A: Involved in repolarisation of the membrane.
231
Q: How does K⁺ help maintain resting potential?
A: By diffusing out of the cell through potassium channels.
232
Q: What does the concentration of H⁺ determine?
A: pH.
233
Q: Why is H⁺ concentration biologically important?
A: It affects enzyme activity and protein structure.
234
Q: What process uses a gradient of H⁺ across membranes?
A: ATP synthesis by chemiosmosis.
235
Q: How is ammonium used in plants?
A: As a nitrogen source for amino acid synthesis.
236
Q: Why is ammonium important for protein production in plants?
A: Nitrogen is required to form amino groups.
237
Q: What is the role of nitrate ions in plants?
A: Used to synthesise amino acids and nucleotides.
238
Q: Why are nitrate ions important for growth?
A: They provide nitrogen for proteins and DNA.
239
Q: What is the role of hydrogencarbonate ions in blood?
A: Act as a buffer to maintain pH.
240
Q: How does HCO₃⁻ relate to carbon dioxide transport?
A: CO₂ is transported in blood as hydrogencarbonate ions.
241
Q: What is a role of chloride ions in neurones?
A: Contribute to membrane potential.
242
Q: What digestive role do Cl⁻ ions have?
A: Form hydrochloric acid (HCl) in the stomach.
243
Q: What structural role do phosphate ions have in cells?
A: Component of DNA and RNA backbone.
244
Q: What is the role of phosphate in ATP?
A: Involved in energy transfer via phosphate bonds.
245
Q: What membrane structure contains phosphate?
A: Phospholipids in cell membranes.
246
Q: What does OH⁻ concentration influence?
A: pH (alkalinity).
247
Q: Why are OH⁻ levels important in cells?
A: They affect enzyme activity and metabolic reactions.
248
Q: Which ions are directly involved in action potentials?
A: Na⁺ and K⁺ (and sometimes Cl⁻).
249
Q: Which ions are involved in pH regulation?
A: H⁺, HCO₃⁻ and OH⁻.
250
Q: Which ions are essential for plant nitrogen metabolism?
A: NO₃⁻ and NH₄⁺.
251
Q: What reagent is used in the Biuret test?
A: Biuret reagent (sodium hydroxide + copper(II) sulfate).
252
Q: How is the Biuret test carried out?
A: Add Biuret reagent to the sample and mix.
253
Q: Is heating required for the Biuret test?
A: No.
254
Q: What is a positive Biuret test result?
A: Blue solution turns lilac/purple.
255
Q: What does a purple colour in the Biuret test indicate?
A: Presence of peptide bonds/protein.
256
Q: What does Benedict’s test detect?
A: Reducing sugars.
257
Q: How is Benedict’s test carried out?
A: Add Benedict’s reagent to the sample and heat in a water bath.
258
Q: Why must Benedict’s test be heated?
A: The reaction requires heat to occur.
259
Q: What is the colour change in a positive Benedict’s test?
A: Blue → green/yellow/orange/brick-red precipitate.
260
Q: What does the colour in Benedict’s test indicate?
A: The concentration of reducing sugar.
261
Q: What causes the colour change in Benedict’s test?
A: Cu²⁺ ions are reduced to Cu⁺, forming a precipitate.
262
Q: Why do non-reducing sugars not react in Benedict’s test initially?
A: They lack a free aldehyde or ketone group.
263
Q: How do you test for non-reducing sugars?
A: First hydrolyse with dilute hydrochloric acid.
264
Q: Why is acid added when testing for non-reducing sugars?
A: To hydrolyse the glycosidic bonds.
265
Q: What must be done after heating with acid?
A: Neutralise with sodium hydrogencarbonate.
266
Q: What is done after neutralisation?
benedicts
A: Add Benedict’s reagent and heat again.
267
Q: What indicates a positive result for non-reducing sugars?
A: A colour change after hydrolysis but not before.
268
Q: What does the iodine test detect?
A: Starch.
269
Q: How is the iodine test carried out?
A: Add iodine solution to the sample.
270
Q: Is heating required for the iodine test?
A: No.
271
Q: What is a positive iodine test result?
A: Orange-brown turns blue-black.
272
Q: What causes the blue-black colour in the iodine test?
A: Iodine molecules fit inside the coiled structure of starch.
273
Q: How is the emulsion test carried out?
A: Add ethanol to the sample and shake.
274
Q: What is done after adding ethanol?
A: Add water.
275
Q: What is a positive emulsion test result?
A: A white, cloudy emulsion forms.
276
Q: Why does a cloudy emulsion form?
A: Lipids dissolve in ethanol but are insoluble in water.
277
Q: Why must samples be neutralised before adding Benedict’s reagent?
A: Benedict’s reagent requires alkaline conditions.
278
Q: What does a colorimeter measure?
A: The absorbance of light by a coloured solution.
279
Q: What is absorbance proportional to?
A: The concentration of the coloured substance.
280
Q: What happens to light as concentration increases?
A: More light is absorbed.
281
Q: Why must the solution be coloured for colorimetry?
A: Because absorbance of specific wavelengths is measured.
282
Q: Why is a specific wavelength of light selected?
A: To maximise absorbance and increase accuracy.
283
Q: How is the concentration of an unknown sample determined?
A: Measure its absorbance and read the value from the calibration curve.
284
Q: What must be used to zero a colorimeter?
A: A blank containing all reagents except the substance being tested.
285
Q: Why is a blank solution used?
A: To account for absorbance caused by solvents or reagents.
286
Q: Why must cuvettes be clean and handled carefully?
A: Fingerprints and scratches affect light transmission.
287
Q: Why should cuvettes be placed in the same orientation each time?
A: To reduce variation in light path.
288
Q: How can reliability be improved in colorimetry?
A: Repeat measurements and calculate a mean.
289
Q: How can accuracy be improved?
A: Use calibrated equipment and precise measuring apparatus.
290
Q: How is validity ensured in colorimetry?
A: Control variables such as wavelength, temperature and volume.
291
Q: What variables must be controlled in a colorimetry experiment?
A: Temperature, pH, total volume and wavelength.
292
Q: How can air bubbles affect results?
A: They scatter light and alter absorbance readings.
293
Q: Why must solutions be mixed thoroughly?
A: To ensure uniform concentration.
294
Q: What happens if concentration is outside the calibration range?
A: The result is unreliable.
295
Q: If absorbance doubles, what happens to concentration (within linear range)?
A: It also doubles.
296
Q: Why may a calibration curve stop being linear at high concentrations?
A: The solution absorbs most light, reducing proportionality.
297
Q: What causes substances to separate in chromatography?
A: Different affinities for the stationary and mobile phases.
298
Q: What is the stationary phase in paper chromatography?
A: The chromatography paper (cellulose).
299
Q: What is the stationary phase in thin layer chromatography (TLC)?
A: A thin layer of silica gel or alumina on a plate.
300
Q: Why must the solvent level be below the baseline?
A: To prevent the sample dissolving directly into the solvent.
301
Q: What is the formula for Rf?
A: Rf = (distance moved by substance) ÷ (distance moved by solvent).
302
Q: Why may proteins need to be hydrolysed before chromatography?
A: To break them into amino acids.
303
Q: Why might a locating agent be needed for sugars?
A: Many sugars are colourless.
304
Q: What can chromatography separate in nucleic acid analysis?
A: Nitrogenous bases or nucleotides.
305
Q: How can an unknown be identified?
A: By comparing its Rf value with known standards.
306
Q: Why must measurements be taken from the centre of spots?
A: To increase accuracy.
307
Q: How can resolution be improved?
A: Use a suitable solvent and avoid large sample spots.
308
Q: Why is TLC often more effective than paper chromatography?
A: It provides better separation and clearer spots.
309
Q: What is a polynucleotide?
A: A polymer of many nucleotide monomers joined together.
310
Q: What bond joins nucleotides in a polynucleotide?
A: A phosphodiester bond.
311
Q: More precisely, which carbon atoms are involved in the phosphodiester bond?
A: The 5′ phosphate of one nucleotide and the 3′ carbon of the sugar on the next.
312
Q: What type of reaction forms a phosphodiester bond?
A: A condensation reaction.
313
Q: What gives a polynucleotide directionality?
A: The 5′ to 3′ arrangement of phosphodiester bonds.
314
Q: Why are phosphodiester bonds important for DNA stability?
A: They form strong covalent bonds in the backbone.
315
Q: Which level of DNA structure depends on phosphodiester bonds?
A: The primary structure (base sequence).
316
Q: Why must cells be lysed in DNA extraction?
A: To break open cell and nuclear membranes and release DNA.
317
Q: What is the role of detergent in DNA extraction?
A: It disrupts phospholipid membranes.
318
Q: Why may protease be added during extraction?
A: To break down proteins associated with DNA.
319
Q: What is the role of salt in DNA extraction?
A: It neutralises negative charges on DNA, allowing strands to clump.
320
Q: Why is cold alcohol added in DNA precipitation?
A: DNA is insoluble in cold alcohol.
321
Q: Why is the alcohol added slowly down the side of the tube?
A: To form a separate layer and improve DNA precipitation.
322
Q: Why should cold conditions be maintained?
A: To reduce enzyme activity (e.g., DNases).
323
Q: What type of bond holds complementary bases together in DNA?
A: Hydrogen bonds.
324
Q: How many hydrogen bonds form between A and T?
A: Two.
325
Q: In which directions do DNA strands run?
A: One runs 5′ → 3′, the other 3′ → 5′.
326
Q: What type of bonds form the sugar–phosphate backbone?
A: Strong covalent phosphodiester bonds.
327
Q: What does semi-conservative replication mean?
A: Each new DNA molecule contains one original strand and one new strand.
328
Q: When does DNA replication occur in the cell cycle?
A: During the S phase of interphase.
329
Q: What is the role of helicase in DNA replication?
A: It unwinds the DNA double helix.
330
Q: What is the role of DNA polymerase?
A: It synthesises new DNA strands.
331
Who demonstrated that DNA replication is semi-conservative?
Meselson and Stahl.
332
What organism was used in the Meselson–Stahl experiment?
Escherichia coli.
333
What isotope was used to make the original DNA heavy?
15N.
334
What isotope was bacteria transferred to for replication?
14N.
335
After one replication in 14N
what was observed?
336
What did the intermediate density after one replication show?
Each DNA molecule contained one heavy and one light strand.
337
After two replications in 14N
what was observed?
338
Why did the results support semi-conservative replication?
They matched the predicted pattern for semi-conservative replication.
339
Why did the results not support conservative replication?
Conservative replication would have produced separate heavy and light DNA after one replication.
340
What was the overall conclusion of the experiment?
DNA replicates semi-conservatively.
341
Why is semi-conservative replication important?
It helps conserve genetic information accurately.
342
What is the role of enzymes in cells?
They catalyse metabolic reactions by lowering activation energy.
343
What is meant by intracellular enzymes?
Enzymes that catalyse reactions inside cells.
344
What is catalase an example of?
An intracellular enzyme.
345
What reaction does catalase catalyse?
The breakdown of hydrogen peroxide into water and oxygen.
346
What is meant by extracellular enzymes?
Enzymes that are secreted to work outside cells.
347
What is amylase an example of?
An extracellular enzyme.
348
What reaction does amylase catalyse?
The hydrolysis of starch into maltose.
349
What determines an enzyme’s specificity?
Its tertiary structure.
350
What is the active site?
The region of an enzyme where the substrate binds.
351
What is meant by enzyme specificity?
Only a specific substrate fits the active site.
352
What is the lock and key hypothesis?
The active site is complementary to the substrate from the start.
353
What is the induced-fit hypothesis?
The active site changes shape slightly when the substrate binds.
354
What is an enzyme-substrate complex?
A temporary complex formed when substrate binds to the active site.
355
What is an enzyme-product complex?
A temporary complex after the reaction has occurred.
356
How do enzymes lower activation energy?
By stabilising the transition state and reducing bond strain.
357
What is the temperature coefficient (Q10) formula?
Q10 = (rate at higher temp ÷ rate at lower temp)^(10 ÷ temperature difference).
358
What does a Q10 of 2 indicate?
The rate doubles for every 10°C increase.
359
What is a serial dilution?
A stepwise dilution where each solution is diluted by the same factor.
360
Why are serial dilutions used?
To produce a range of known concentrations.
361
What is a cofactor?
A non-protein substance required for enzyme activity.
362
What is a coenzyme?
An organic molecule that assists enzyme function.
363
What is the role of chloride ions in amylase activity?
They act as a cofactor.
364
Why are vitamins important in enzyme reactions?
They are sources of coenzymes.
365
What is a competitive inhibitor?
A molecule that competes with the substrate for the active site.
366
How does a competitive inhibitor affect enzyme activity?
It reduces rate but effect can be overcome by increasing substrate concentration.
367
What is a non-competitive inhibitor?
A molecule that binds away from the active site.
368
How does a non-competitive inhibitor affect enzyme activity?
It changes enzyme shape and reduces maximum rate.
369
What is a reversible inhibitor?
An inhibitor that can detach from the enzyme.
370
What is a non-reversible inhibitor?
An inhibitor that permanently binds to the enzyme.
371
What is end-product inhibition?
When the final product inhibits an earlier enzyme in the pathway.
372
What is a membrane’s role as a barrier?
It is partially permeable and controls movement of substances.
373
Where are membranes found in cells?
At the cell surface
374
Why are membranes sites of chemical reactions?
They contain embedded enzymes.
375
How do membranes enable cell signalling?
They contain receptor proteins.
376
What is the fluid mosaic model?
A model describing membranes as a phospholipid bilayer with proteins embedded.
377
What forms the bilayer of membranes?
Phospholipids.
378
What is the role of cholesterol in membranes?
It stabilises membrane fluidity.
379
What are glycoproteins involved in?
Cell recognition and signalling.
380
What are glycolipids involved in?
Cell recognition.
381
What is the role of membrane receptors?
They bind hormones or drugs.
382
How does temperature affect membranes?
High temperatures increase fluidity and permeability.
383
How do solvents affect membranes?
They disrupt phospholipids and increase permeability.
384
What is diffusion?
Net movement of molecules from high to low concentration.
385
What is facilitated diffusion?
Passive movement through channel or carrier proteins.
386
Does diffusion require ATP?
No.
387
What is active transport?
Movement against concentration gradient using ATP.
388
What are endocytosis and exocytosis?
Bulk transport processes requiring ATP.
389
What is ATP?
Adenosine triphosphate
390
What happens in G1 phase?
Cell growth and organelle production.
391
What happens in S phase?
DNA replication.
392
What happens in G2 phase?
Preparation for mitosis.
393
What is mitosis?
Nuclear division producing identical nuclei.
394
What is cytokinesis?
Division of cytoplasm.
395
What is the purpose of checkpoints?
To ensure each stage is completed correctly before proceeding.
396
What happens in prophase?
Chromosomes condense and spindle forms.
397
What happens in metaphase?
Chromosomes align at the equator.
398
What happens in anaphase?
Sister chromatids separate.
399
What happens in telophase?
Nuclear envelope reforms.
400
What is the significance of meiosis?
It produces haploid gametes and genetic variation.
401
What is independent assortment?
Random distribution of homologous chromosomes.
402
What is crossing over?
Exchange of genetic material between homologous chromosomes.
403
What are homologous chromosomes?
Pairs of chromosomes with the same genes at the same loci.
404
How many divisions occur in meiosis?
Two.
405
What is produced at the end of meiosis?
Four genetically different haploid cells.
406
How are erythrocytes specialised?
They lack a nucleus and contain haemoglobin.
407
How are neutrophils specialised?
They have a lobed nucleus and many lysosomes.
408
How are squamous epithelial cells specialised?
They are thin for short diffusion distance.
409
How are ciliated epithelial cells specialised?
They have cilia to move substances.
410
How are sperm cells specialised?
They have a flagellum and many mitochondria.
411
How are palisade cells specialised?
They contain many chloroplasts.
412
How are root hair cells specialised?
They have a large surface area for absorption.
413
How are guard cells specialised?
They change shape to open and close stomata.
414
What is a tissue?
A group of similar cells working together.
415
What is an organ?
A structure made of different tissues working together.
416
What is an organ system?
A group of organs working together.
417
What are stem cells?
Undifferentiated cells that can divide and specialise.
418
Where are adult stem cells found?
In bone marrow and other tissues.
419
How are erythrocytes and neutrophils related?
They differentiate from the same bone marrow stem cell.
420
Where are plant stem cells found?
In meristems.
421
What do xylem vessels differentiate into?
Dead cells specialised for water transport.
422
What do phloem sieve tubes differentiate into?
Living cells specialised for translocation.
423
Why does an enzyme’s tertiary structure determine its specificity?
The precise 3D folding forms an active site with a specific shape and chemical environment complementary to one substrate.
424
How does induced fit improve catalysis?
Substrate binding causes slight active site change that strains bonds and stabilises the transition state.
425
Why does increasing temperature initially increase enzyme activity?
More kinetic energy increases successful collisions and enzyme–substrate complex formation.
426
Why does high temperature reduce enzyme activity?
Hydrogen and ionic bonds break
427
How does pH affect enzyme activity?
Changes in H+ concentration disrupt ionic bonds
428
Why does increasing substrate concentration eventually stop increasing rate?
All active sites become occupied (enzyme saturation)
429
How does a competitive inhibitor affect Vmax and Km qualitatively?
Vmax unchanged
430
How does a non-competitive inhibitor affect Vmax?
Vmax decreases because functional enzyme concentration is reduced.
431
Why can increasing substrate concentration overcome competitive inhibition?
Substrate outcompetes inhibitor for active site binding.
432
Why can’t increasing substrate concentration overcome non-competitive inhibition?
Inhibitor binds elsewhere and changes enzyme shape.
433
Why is end-product inhibition important in metabolism?
It prevents wasteful overproduction and conserves resources.
434
What is meant by membrane fluidity?
Phospholipids can move laterally within the bilayer.
435
How does cholesterol regulate membrane fluidity?
Restricts phospholipid movement at high temps and prevents packing at low temps.
436
Why is the membrane partially permeable?
Hydrophobic fatty acid tails prevent passage of polar/charged molecules.
437
How do channel proteins differ from carrier proteins?
Channels form pores; carriers change shape to transport molecules.
438
How does temperature increase membrane permeability?
Increases phospholipid movement and disrupts bilayer stability.
439
How do organic solvents increase membrane permeability?
They dissolve phospholipids
440
Why does a larger surface area to volume ratio increase diffusion rate?
More membrane area per unit volume for exchange.
441
Why does shorter diffusion distance increase rate?
Molecules reach destination more quickly.
442
How does ATP enable active transport?
Hydrolysis of ATP provides energy for carrier protein conformational change.
443
Why is mitosis important in multicellular organisms?
Growth
444
How does DNA content change during the cell cycle?
It doubles during S phase and halves per nucleus after mitosis.
445
What is the role of spindle fibres in mitosis?
Attach to centromeres and separate sister chromatids.
446
What would happen if a checkpoint failed?
Uncontrolled division and possible tumour formation.
447
Why does meiosis produce genetic variation?
Independent assortment and crossing over create new allele combinations.
448
How does crossing over increase variation?
Exchange of genetic material between homologous chromosomes forms new allele combinations.
449
Why does meiosis halve chromosome number?
Two divisions occur after one DNA replication.
450
Why are daughter cells genetically different after meiosis?
Random assortment and recombination.
451
Why are erythrocytes efficient at oxygen transport?
Biconcave shape increases SA and no nucleus maximises haemoglobin space.
452
How are neutrophils adapted to their function?
Lobed nucleus aids movement; many lysosomes digest pathogens.
453
Why do palisade cells have many chloroplasts?
Maximise light absorption for photosynthesis.
454
Why do root hair cells increase mineral uptake?
Large surface area increases absorption.
455
What is differentiation?
Process by which cells become specialised through selective gene expression.
456
How can stem cells produce different specialised cells?
Different genes are switched on/off.
457
Why are xylem vessels dead at maturity?
Lignification removes contents to form hollow tubes for water transport.
458
Why do phloem sieve tubes require companion cells?
They lack many organelles and rely on companions for metabolic support.
459
How would you improve reliability in an enzyme practical?
Repeat trials and calculate a mean.
460
How would you improve validity in a membrane permeability experiment?
Control temperature
461
Why must serial dilutions be mixed thoroughly?
To ensure uniform concentration before the next dilution.
462
How is Q10 used in exam calculations?
Substitute rates and temperature difference into formula carefully using correct exponent.
A-level biology OCR
flashcards
Decks in class (24)
# Cards
-
Final SC module 2479
-
2.1.1 cell structure31
-
2.1.2 Biological molecules98
-
2.1.3 Nucleotides and nucleic acids20
-
2.1.4 Enzymes49
-
2.1.5 Biological membranes141
-
2.1.6 Cell division, cell diversity and cellular organisation51
-
3.1.1 Exchange surfaces18
-
3.1.2 Transport in animals0
-
4.1.1 Communicable diseases, disease prevention and the immune system159
-
4.2.1 Biodiversity28
-
4.2.2 Classification and evolution35
-
5.1.1 Communication and homeostasis0
-
wrong bio ppq's46
-
A2 Photosynthesis + respiration128
-
A2 Homeostasis and temperature control8
-
bio member 232
-
3.1.3 transport in plants62
-
action potentials gpt cards47
-
respiration151
-
Neuronal communication24
-
Photosynthesis36
-
Cellular control74
-
Patterns of inheritance66
