Chapter 4 Reading Cell Biology

1. Summarize the relationship between a cell's surface-area-to-volume ratio and its size. As a cell increases in size, its surface area to volume ratio decreases, making it less efficient at exchanging materials. Smaller cells have a higher surface area to volume ratio, allowing for more efficient exchange. 2. Identify the key components of the cell plasma membrane. The plasma membrane is made of a phospholipid bilayer with cholesterol for fluidity and embedded proteins for transport and communication. 3. Explain how the plasma membrane regulates the passage of molecules into and out of the cell. The plasma membrane controls what enters and leaves the cell by allowing small, simple molecules to pass through easily, while bigger or charged molecules need help from proteins. It uses different methods, like active or passive transport, to move things in and out. 4. Describe the diverse functions of the proteins embedded in the plasma membrane. Channel proteins allow molecules to pass through, transport proteins move molecules across, receptor proteins respond to signals, enzymatic proteins speed up reactions, junction proteins connect cells, and cell recognition proteins help identify cells for immune responses. 5. Identify the characteristics common to all cells. All cells have a plasma membrane that surrounds the cell, a semifluid interior called the cytoplasm, and genetic material (DNA) that carries the cell's instructions. 6. Distinguish between prokaryotic and eukaryotic cells. Prokaryotic cells are smaller, simpler, and lack a nucleus, with their genetic material floating freely in the cytoplasm. Eukaryotic cells are larger, more complex, and have a nucleus that contains their genetic material, along with membrane-bound organelles. 7. Identify the general function of the organelles in a eukaryotic cell. The nucleus is surrounded by a nuclear envelope, a double membrane with nuclear pores that allow communication with the cytoplasm. Inside, chromatin (a mix of DNA and proteins) contains genetic information, and ribosomes use RNA from the nucleus to synthesize proteins. 8. State the components of the endomembrane system, and list their functions. The nuclear envelope holds the cell’s DNA and separates it from the rest of the cell. The rough ER has ribosomes and sends proteins to different parts of the cell. The smooth ER makes specific lipids. The Golgi apparatus takes proteins from the ER, modifies them, and ships them out. Vesicles, like lysosomes, break down molecules. 9. Identify the energy roles that chloroplasts and mitochondria play in a cell. Chloroplasts capture solar energy to make carbohydrates, while mitochondria break down carbohydrates to produce ATP. Chloroplasts are larger and in plants, while mitochondria are smaller and in all eukaryotic cells. Both have a double membrane. 10. Describe the structure of a plant cell wall. The cell wall provides support and structure to the cell and is found in plant, fungal, and some protist cells, but not in animals. In plants, the primary cell wall contains cellulose fibrils and other substances that allow it to stretch as the cell grows. The middle lamella, made of adhesive substances, holds plant cells together. Some plants also have a secondary cell wall inside the primary wall, which is stronger due to more cellulose and lignin that adds extra strength. 11. State the purpose of the extracellular matrix. The extracellular matrix (ECM) provides support, allows communication between cells, and guides cell movement. It contains proteins like collagen and elastin, and its rigidity varies across tissues, such as flexible cartilage or rigid bone with added calcium salts. 12. Distinguish among the types of junctions present between eukaryotic cells. Eukaryotic cells have three main types of junctions such as tight junctions which seal cells to prevent leakage, adhesion junctions anchor cells together for strength, and gap junctions allow communication by letting ions and small molecules pass between cells.