HCB Midterm

Section 1: Cell Structure & Organelles

Multiple Choice

The smooth endoplasmic reticulum (SER) plays a key role in detoxification because it contains:
A) Ribosomal RNA and transfer enzymes
B) Enzymes that modify and break down hydrophobic toxins
C) Glycoproteins that label proteins for export
D) Lysosomal hydrolases
E) RNA polymerases
The major functional distinction between the rough and smooth ER lies in:
A) Presence or absence of membrane-bound ribosomes
B) The ability to replicate DNA
C) The composition of their lipid bilayers
D) The number of nuclear pores connected to each
E) Whether they contain their own genome
In the Golgi apparatus, proteins are commonly modified to become functional by:
A) Adding carbohydrate groups to form glycoproteins
B) Removing phosphate groups to form nucleotides
C) Inserting chlorophyll molecules for energy transfer
D) Fusing directly with lysosomes for degradation
E) Attaching fatty acids for immediate secretion
Lysosomes are specialized organelles that:
A) Produce ATP through oxidative phosphorylation
B) Contain acid hydrolases active at low pH for macromolecule breakdown
C) Store starch granules for later conversion to glucose
D) Perform protein folding during synthesis
E) Generate ribosomal subunits for export
In eukaryotic cells, ribosomes are located:
A) Inside the nucleus and mitochondria
B) Bound to the rough ER or freely suspended in cytosol
C) Embedded in the plasma membrane and lysosomes
D) Within the Golgi lumen and nuclear pores
E) Only in the nucleolus

True/False
6. Ribosomes are surrounded by a membrane that separates them from cytoplasm. False
7. Mitochondria and chloroplasts both contain their own DNA. True

Diagram Analysis
8. Label the nucleus, nucleolus, nuclear envelope, and rough ER on a diagram of an animal cell.
9. Annotate a mitochondrion diagram showing matrix, cristae, and intermembrane space; describe each’s function.
10. Interpret a diagram comparing a plant and animal cell — highlight three structures unique to plants.

Short Answer
13. Describe the structural relationship between the nucleus and the ER.
14. Explain how compartmentalization benefits eukaryotic cells.
15. What is the role of peroxisomes in cellular metabolism?
16. Why are chloroplasts considered semiautonomous organelles?
17. How does the vacuole contribute to plant cell rigidity?
18. Compare and contrast free and bound ribosomes by function and products.
19. Identify the pathway of a secreted protein from synthesis to exocytosis.
20. Explain why cell fractionation is used and what can be learned from it.

Section 2: Cell Function & Membrane Transport

Multiple Choice

Which type of molecule can most easily diffuse directly through a phospholipid bilayer?
A) Ions like Na⁺ or Cl⁻
B) Large polar molecules such as glucose
C) Small nonpolar molecules such as O₂ or CO₂
D) Proteins and polysaccharides
E) Charged amino acids
The main role of cholesterol in the plasma membrane is to:
A) Anchor peripheral proteins in place
B) Stabilize membrane fluidity across temperature changes
C) Increase the rate of simple diffusion
D) Strengthen covalent bonds between phospholipids
E) Facilitate ATP production across the bilayer
A cell moving ions against their concentration gradient is performing:
A) Facilitated diffusion
B) Passive diffusion
C) Active transport requiring ATP
D) Osmosis through aquaporins
E) Exocytosis of membrane proteins
When an animal cell is placed in a hypertonic solution, it will most likely:
A) Swell and burst due to water gain
B) Shrink as water leaves the cytoplasm
C) Remain unchanged due to osmotic balance
D) Increase membrane fluidity to compensate
E) Undergo plasmolysis like a plant cell
The uptake of specific molecules such as LDL cholesterol via coated pits is known as:
A) Simple diffusion
B) Osmotic pressure
C) Receptor-mediated endocytosis
D) Facilitated diffusion
E) Secondary active transport

True/False
26. Osmosis involves the net movement of water from low solute concentration to high solute concentration.
27. Facilitated diffusion requires a membrane protein but does not require ATP.

Diagram Analysis
28. On a phospholipid bilayer diagram, label hydrophilic heads, hydrophobic tails, integral proteins, and cholesterol molecules.
29. Interpret a diagram showing a U-tube osmosis experiment; indicate which side the water level will rise and why.
30. Label each step of receptor-mediated endocytosis on a cell membrane diagram (ligand binding, pit formation, vesicle creation).

Short Answer
33. Explain how temperature and phospholipid saturation affect membrane fluidity.
34. Describe how channel proteins and carrier proteins differ in their mechanism of transport.
35. Explain how the sodium–potassium pump maintains membrane potential in animal cells.
36. Define tonicity and describe how it relates to osmotic balance.
37. How do large polar molecules like glucose enter the cell?
38. Describe the structure and function of aquaporins in maintaining water homeostasis.
39. Explain how vesicles contribute to both exocytosis and endocytosis.
40. Provide a specific biological example of active transport in plant or animal cells.

Section 3: Cytoskeleton, Microscopy, & Endomembrane System

Multiple Choice

The largest cytoskeletal filaments, composed of tubulin subunits, are primarily responsible for:
A) Providing tensile strength to resist stretching
B) Facilitating intracellular transport and spindle formation
C) Anchoring actin to the plasma membrane
D) Forming nuclear pores for mRNA export
E) Driving cytoplasmic streaming via myosin
Actin filaments (microfilaments) are most directly involved in which cellular activity?
A) DNA replication in the nucleus
B) Muscle contraction and cell motility
C) Vesicle packaging in the Golgi apparatus
D) ATP synthesis in mitochondria
E) Protein translation on ribosomes
In animal cells, microtubules originate from the:
A) Basal bodies located in chloroplasts
B) Centrosome near the nucleus
C) Ribosome clusters on the rough ER
D) Golgi cis face
E) Nuclear envelope folds
Intermediate filaments differ from microtubules and microfilaments because they:
A) Are composed of keratin and provide structural reinforcement
B) Form rapidly disassembling networks during mitosis
C) Function as enzymatic sites for phosphorylation
D) Are only present in plant cells
E) Serve as tracks for kinesin-driven vesicle transport
The cis face of the Golgi apparatus functions mainly to:
A) Anchor ribosomes for translation
B) Receive vesicles from the rough ER for processing
C) Store hydrolytic enzymes
D) Export completed proteins to the plasma membrane
E) Synthesize phospholipids for mitochondria

True / False

Microtubules are composed of actin subunits arranged in helical coils.
Dynein arms attached to microtubules generate motion in cilia and flagella through ATP-driven sliding.

Diagram Analysis

48. Label a cross-section of a cilium showing the 9 + 2 microtubule arrangement and indicate the position of dynein arms.
49. Annotate a Golgi apparatus diagram to distinguish the cis and trans faces, and explain the direction of vesicle traffic.
50. Identify microtubules, microfilaments, and intermediate filaments on an electron micrograph; compare their relative diameters and primary functions.

Short Answer

53. Explain how kinesin and dynein differ in the direction of vesicle movement along microtubules.
54. Describe the “cisternal maturation” model of the Golgi apparatus and how it contrasts with vesicular transport models.
55. List three key functions of the smooth ER and relate them to specific cell types where it is abundant.
56. Contrast the functional outputs of the rough ER and smooth ER in a secretory cell.
57. Describe the process of autophagy and how lysosomes participate in it.
58. Compare plasmodesmata and gap junctions in terms of structure and function.
59. Explain the role of integrins in linking the extracellular matrix (ECM) to the cytoskeleton.
60. Describe how tight junctions contribute to selective permeability in epithelial tissue.

Section 4: Cell Communication & Signaling

Multiple Choice

Which type of signaling involves hormones that travel long distances through the bloodstream to reach target cells?
A) Autocrine signaling
B) Paracrine signaling
C) Endocrine signaling
D) Synaptic signaling
E) Direct cell junction signaling
Local regulators like growth factors that act on nearby cells without entering the bloodstream are examples of:
A) Endocrine signaling
B) Autocrine signaling
C) Paracrine signaling
D) Feedback inhibition
E) Signal amplification
G-proteins become active when:
A) GDP is replaced by GTP on the alpha subunit
B) They bind directly to a ligand molecule
C) They are degraded by the lysosome
D) ATP is converted to cAMP in the cytosol
E) The receptor is endocytosed into the nucleus
Second messengers like cAMP and calcium ions are important in signaling because they:
A) Amplify and distribute the signal inside the cell
B) Replace the need for receptors on the membrane
C) Prevent phosphorylation of target proteins
D) Degrade enzymes that block receptor activity
E) Transport ligands directly to the nucleus
Which receptor type is located inside the cytoplasm rather than on the plasma membrane?
A) G-protein coupled receptor (GPCR)
B) Ligand-gated ion channel
C) Receptor tyrosine kinase (RTK)
D) Intracellular receptor
E) Voltage-gated channel

True / False

Signal transduction pathways often amplify the original extracellular signal through enzyme cascades.
All ligands bind to membrane receptors located on the cell surface.

Diagram Analysis

68. Label a GPCR signaling pathway, including receptor, G-protein, effector enzyme (adenylyl cyclase), and second messenger (cAMP).
69. Annotate a diagram showing phosphorylation cascades in a receptor tyrosine kinase pathway.
70. Identify the difference between autocrine and paracrine signaling on a schematic showing distance of ligand diffusion.

Short Answer

73. Define cell signaling and explain why it is essential for maintaining homeostasis.
74. Describe the three stages of cell signaling: reception, transduction, and response.
75. Explain the role of kinases and phosphatases in regulating signal pathways.
76. Give one example of a human disease caused by faulty cell signaling or receptor malfunction.
77. Discuss ligand specificity and how receptor conformation affects activation.
78. Explain how amplification occurs in a phosphorylation cascade.
79. Describe how receptor proteins’ structures allow for high signal selectivity.
80. Explain the role of nitric oxide (NO) as a short-lived signaling molecule.

Section 5: Labs, Math, & Experimental Analysis

Multiple Choice

During the cell fractionation lab, tetrazolium was used to:
A) Stain DNA to identify nuclei
B) Detect cellular respiration by reduction to a red compound
C) Measure protein concentration through color change
D) Visualize membranes under UV light
E) Precipitate lipids for centrifugation
Methylene blue served what role in respiration assays?
A) It acted as an oxidizing agent to indicate electron transfer
B) It bound to sugars to identify carbohydrate content
C) It served as a pH indicator for acidic vacuoles
D) It reacted with nitrogenous waste to form a gas
E) It neutralized enzymes in the mitochondrial fraction
In the GMO detection lab, PCR amplification was used to:
A) Separate proteins by charge
B) Amplify target DNA regions to detect transgenic sequences
C) Visualize plant pigments in chloroplasts
D) Measure enzyme activity in bacteria
E) Identify carbohydrate polymers in plant tissue
In gel electrophoresis, the buffer solution serves to:
A) Supply ions to carry current and maintain pH
B) Denature the DNA before migration
C) Dissolve agarose and sample dyes
D) Bond DNA fragments to the gel matrix
E) Provide nutrients for enzyme catalysis
Which compound in the sucrose buffer mixture maintained a stable pH during cell fractionation?
A) NaCl
B) EDTA
C) Tris-HCl
D) Sucrose
E) Acetone

True / False

86. The color change in methylene blue from blue to colorless indicates reduction during respiration.
87. Positive and negative controls in the GMO lab are used to validate PCR accuracy and reliability.

Diagram Analysis

88. Label a gel electrophoresis diagram showing sample wells, direction of migration, and band separation.
89. Annotate a mitochondria activity diagram showing tetrazolium reduction and color change zones.
90. Identify parts of a micropipette (plunger, tip ejector, volume adjustment dial) and describe each’s function.

Short Answer

93. Explain why calibration of micropipettes is critical for experimental accuracy.
94. Describe the steps and purpose of DNA extraction in the GMO lab procedure.
95. Explain the importance of including both GMO and non-GMO food controls during PCR.
96. Describe why DNA fragments migrate toward the positive electrode during electrophoresis.
97. Discuss factors that influence how bands separate on an agarose gel.
98. Explain how enzyme activity can be measured using redox indicators like methylene blue or tetrazolium.
99. Describe how centrifugation separates organelles according to density and size.
100. Suggest one procedural improvement for any of the labs that could increase accuracy or reproducibility.

Section 6: Plant Tissue Culture + Plants

What are the key aseptic techniques that prevent contamination during plant tissue culture?
Why is sterilization of instruments and media critical in tissue culture?
What is meristematic tissue, and why is it preferred as an explant in plant tissue culture?
Define callus. What does the formation of a callus indicate about cell totipotency?
Describe how auxins and cytokinins influence shoot and root development in vitro.
What steps are involved in surface sterilization of explants before inoculation?
How can hormone concentration affect whether a plant culture develops roots, shoots, or undifferentiated tissue?
List at least three structural differences between monocots and eudicots.
What patterns in leaf veins, flower parts, and vascular bundles can be used to identify monocots vs. eudicots?
Explain vegetative propagation, and give two examples of natural asexual reproduction in plants.
Describe one artificial method of asexual reproduction and its agricultural significance.