Cells and Tissues – Chapter 3 Answer Key
Understanding the building blocks of life is the cornerstone of biology, and Chapter 3 of most introductory textbooks focuses on cells and tissues. Below is a comprehensive answer key that covers every major question, diagram label, and concept‑check in the chapter. Use this guide to verify your answers, clarify misconceptions, and deepen your grasp of cellular structure, tissue classification, and the functional relationships that drive organismal biology.
1. Multiple‑Choice Review
| # | Question (Paraphrased) | Correct Answer | Explanation |
|---|---|---|---|
| 1 | Which organelle is the “powerhouse” of the cell? Also, they can differentiate into multiple cell types** | Pluripotent stem cells give rise to many, but not all, cell lineages. In real terms, mitosis** | Mitosis results in two genetically identical daughter cells, essential for growth and repair. Epithelial tissue** |
| 6 | A muscle that contracts involuntarily and is found in the walls of the digestive tract is: | **B. | |
| 7 | The process by which a cell divides its nucleus is called: | A. Mitochondrion | Mitochondria generate ATP through oxidative phosphorylation, supplying energy for most cellular activities. Because of that, cytoplasm** |
| 3 | Which of the following is NOT a characteristic of eukaryotic cells? | ||
| 5 | Which tissue type lines body cavities and surfaces? | ||
| 8 | Which of the following statements about stem cells is true? Now, modify, sort, and package proteins** | Proteins receive carbohydrate tags (glycosylation) and are directed to their final destinations. | |
| 9 | The primary function of the Golgi apparatus is to: | **D. | **D. Practically speaking, |
| 2 | The fluid that fills the interior of a cell is called: | **C. | **C. Consider this: |
| 4 | The extracellular matrix (ECM) is primarily composed of: | **A. Plus, | |
| 10 | In plant cells, the rigid outer layer that provides structural support is the: | **B. Also, | B. Cell wall |
2. Short‑Answer Clarifications
Q1. Define the term “cell theory” and list its three main postulates.
A: Cell theory states that (1) all living organisms are composed of one or more cells, (2) the cell is the basic unit of structure and function in living things, and (3) all cells arise from pre‑existing cells.
Q2. Compare and contrast the plasma membrane and the cell wall.
A:
- Plasma membrane – a phospholipid bilayer with embedded proteins; semi‑permeable, controls entry/exit of substances, present in all cells.
- Cell wall – a rigid polysaccharide layer (cellulose in plants, chitin in fungi, peptidoglycan in bacteria); provides mechanical support, protection, and shape; absent in animal cells.
Q3. Explain why the endoplasmic reticulum (ER) is divided into rough and smooth regions.
A: Rough ER is studded with ribosomes, making it the site of protein synthesis for secretory and membrane proteins. Smooth ER lacks ribosomes and functions in lipid synthesis, detoxification, and calcium storage.
Q4. List the four basic tissue types in animals and give one example organ for each.
A:
- Epithelial – skin (epidermis)
- Connective – bone (femur)
- Muscle – heart (cardiac muscle)
- Nervous – brain (cerebral cortex)
Q5. What is the significance of the “tight junctions” found in epithelial cells?
A: Tight junctions seal adjacent cells together, preventing the passage of molecules between them and thereby maintaining distinct compartments (e.g., the intestinal lumen vs. the bloodstream).
3. Diagram Labeling – Key Points
| Diagram | Structures to Label | Key Features to Remember |
|---|---|---|
| **A. So | ||
| D. But plant Cell | Cell wall, chloroplast, central vacuole, plasmodesma, same organelles as animal cell | Chloroplast – thylakoid stacks (grana); central vacuole – stores water, pigments, waste. |
| E. Skeletal Muscle Fiber | Sarcolemma, sarcoplasm, myofibrils, sarcoplasmic reticulum, mitochondria, nuclei (peripheral) | Myofibrils contain repeating sarcomeres with actin (thin) and myosin (thick) filaments. That said, cross‑section of Skin** |
| **B. | ||
| C. Animal Cell | Nucleus, nucleolus, nuclear envelope, mitochondrion, rough ER, smooth ER, Golgi, lysosome, ribosome, cytoskeleton, plasma membrane | Nucleus – largest organelle, contains DNA; mitochondria – double membrane, inner folds (cristae). Neuron** |
4. Conceptual Application – Problem Solving
Problem 1 – Osmosis in Plant Cells
A leaf cell is placed in a 0.5 M sucrose solution. Predict the movement of water and describe the resulting cellular changes.
Solution: Water moves outward from the cell (higher water potential inside) to the hypertonic sucrose solution by osmosis. The central vacuole shrinks, the plasma membrane pulls away from the cell wall (plasmolysis), and the cell becomes flaccid, reducing turgor pressure No workaround needed..
Problem 2 – Tissue Regeneration
Explain why epithelial tissue heals faster than nervous tissue after injury.
Answer: Epithelial cells have a high mitotic rate and are in direct contact with the basal lamina, which provides growth signals. In contrast, most neurons in the central nervous system are post‑mitotic and lack solid regenerative cues, leading to slower or incomplete repair.
Problem 3 – Energy Yield
Calculate the net ATP gain from one molecule of glucose undergoing aerobic respiration (glycolysis, Krebs cycle, oxidative phosphorylation).
Answer:
- Glycolysis: 2 ATP (substrate‑level) + 2 NADH → ~5 ATP
- Pyruvate → Acetyl‑CoA (link reaction): 2 NADH → ~5 ATP
- Krebs cycle: 2 ATP (GTP) + 6 NADH + 2 FADH₂ → ~20 ATP
- Oxidative phosphorylation (electron transport chain): total ~34 ATP
Net total ≈ 36–38 ATP per glucose molecule (depending on shuttle efficiency).
5. Frequently Asked Questions (FAQ)
Q: Why do some cells have multiple nuclei?
A: Multinucleated cells, such as skeletal muscle fibers, arise from the fusion of myoblasts during development. Multiple nuclei ensure sufficient transcriptional capacity to support the large cytoplasmic volume and high protein synthesis demand.
Q: How do cells maintain a constant internal pH?
A: Through buffer systems (bicarbonate, phosphate), ion transporters (Na⁺/H⁺ exchangers, H⁺‑ATPases), and organelle regulation (mitochondrial buffering). These mechanisms quickly neutralize excess acids or bases.
Q: What distinguishes connective tissue proper from specialized connective tissue?
A: Connective tissue proper (e.g., loose and dense connective tissue) primarily consists of fibroblasts and an ECM of fibers and ground substance. Specialized connective tissue (e.g., cartilage, bone, blood) contains unique cells (chondrocytes, osteocytes, erythrocytes) and specialized matrices (calcified, avascular, or fluid) Which is the point..
Q: Can a cell survive without a nucleus?
A: Mature erythrocytes (red blood cells) lack nuclei yet survive for ~120 days because they rely on stored hemoglobin and glycolysis for energy. That said, most cells require a nucleus for gene expression and long‑term viability And that's really what it comes down to. Took long enough..
Q: What is the role of the cytoskeleton in intracellular transport?
A: The microtubule network serves as tracks for motor proteins (kinesin, dynein) that ferry vesicles, organelles, and macromolecules. Actin filaments allow short‑range movement and cell shape changes, while intermediate filaments provide tensile strength That's the part that actually makes a difference. No workaround needed..
6. Integrative Summary
Chapter 3 weaves together the microscopic architecture of life—from the nanometer‑scale organelles that orchestrate metabolism to the macroscopic tissues that perform coordinated functions. Mastery of this material hinges on three core ideas:
- Compartmentalization: Membrane‑bound organelles isolate biochemical pathways, increasing efficiency and regulation.
- Specialization: Different tissue types (epithelial, connective, muscle, nervous) exhibit distinct structural adaptations that match their physiological roles.
- Dynamic Interplay: Cells communicate via junctions, signaling molecules, and the extracellular matrix, creating a responsive, integrated organism.
By internalizing the answer key above, you not only confirm your factual knowledge but also develop a conceptual framework that will aid in higher‑level topics such as histology, developmental biology, and pathophysiology Took long enough..
7. Self‑Check Checklist
- [ ] Can you identify each organelle in a cell diagram and state its primary function?
- [ ] Do you understand why the plasma membrane is selectively permeable?
- [ ] Are you able to classify a given tissue sample into one of the four basic types?
- [ ] Can you explain the steps and energy yield of aerobic respiration?
- [ ] Have you practiced labeling diagrams of plant cells, animal cells, and specialized tissues?
If you answered “yes” to all items, you are well prepared for quizzes, lab practicals, and future chapters that build upon the fundamentals of cells and tissues. Keep this key handy as a reference point while studying, and revisit any sections that feel uncertain. Mastery of the microscopic world is the gateway to unlocking the complexities of whole‑organism biology.
