Cell Biology: Cell Structure Exam Questions with Verified Answers| Graded A

Cell Biology: Cell Structure Exam Questions with Verified Answers| Graded A 1. **Explain the endosymbiotic theory and provide evidence supporting it.** The endosymbiotic theory suggests that certain organelles, such as mitochondria and chloroplasts, originated as free-living bacteria that were engulfed by ancestral eukaryotic cells. Evidence includes similarities in size, double membranes, their own circular DNA, and the ability to replicate independently. 2. **Describe the role of the nucleolus in ribosome biogenesis.** The nucleolus is responsible for the synthesis and assembly of ribosomal RNA (rRNA) and proteins to form the small and large subunits of ribosomes, which are then transported to the cytoplasm for translation. 3. **What are the main functions of the smooth endoplasmic reticulum (SER) in cellular metabolism?** The SER is involved in lipid synthesis, detoxification of drugs and toxins, and calcium ion storage, particularly in muscle cells. 4. **How does the structure of the phospholipid bilayer contribute to its selective permeability?** 2 The phospholipid bilayer has hydrophilic heads that face outward and hydrophobic tails that face inward, allowing selective passage of substances. Small, non-polar molecules can diffuse freely, while larger, polar molecules require transport proteins. 5. **Compare the structure and function of mitochondria and chloroplasts.** Mitochondria are double-membraned organelles that generate ATP through cellular respiration. Chloroplasts, also double-membraned, perform photosynthesis in plants, converting light energy into chemical energy. Both contain their own DNA and ribosomes. 6. **What is the role of lysosomes in apoptosis, and how does this process benefit the organism?** Lysosomes release hydrolytic enzymes that break down cellular components during apoptosis (programmed cell death). This process is essential for development, removing damaged cells, and maintaining tissue homeostasis. 7. **Describe how the cytoskeleton contributes to both cell shape and intracellular transport.** The cytoskeleton is composed of microtubules, microfilaments, and intermediate filaments. It maintains cell shape, anchors organelles, and facilitates movement of materials within the cell through motor proteins like dynein and kinesin. 8. **Explain the role of membrane proteins in cell signaling and transport.** 3 Membrane proteins serve as receptors in cell signaling, binding to ligands and initiating intracellular pathways. They also act as channels, carriers, or pumps to regulate the transport of molecules across the membrane. 9. **What are peroxisomes, and how do they contribute to cellular metabolism?** Peroxisomes contain enzymes that catalyze reactions involving hydrogen peroxide, breaking down fatty acids and detoxifying harmful substances. They also participate in the synthesis of lipids and bile acids. 10. **How does the structure of cilia and flagella facilitate their function in cellular movement?** Both cilia and flagella are composed of microtubules arranged in a 9+2 pattern, anchored by a basal body. Dynein arms cause sliding of microtubules, leading to a bending motion that propels the cell or moves fluid across the cell surface. 11. **Discuss the importance of vesicular transport in maintaining cellular homeostasis.** Vesicular transport allows cells to move large molecules, like proteins and lipi