② Cells (short answers)

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Questions and Answers

Compare and contrast the main structural differences between prokaryotic and eukaryotic cells, focusing on the presence or absence of membrane-bound organelles.

Prokaryotic cells lack membrane-bound organelles like a nucleus, while eukaryotic cells possess them. Prokaryotes have a simpler structure with DNA in a nucleoid region, whereas eukaryotes have a complex structure with DNA enclosed in a nucleus.

Explain the significance of the surface area to volume ratio in the context of cell size and function. How does this ratio limit cell size?

As a cell increases in size, the surface area to volume ratio decreases. A lower ratio limits the rate at which substances can cross the membrane to supply the volume of the cell which also affects how quickly waste can be removed.

Describe the endosymbiotic theory and provide two pieces of evidence that support the idea that mitochondria and chloroplasts were once independent prokaryotic cells.

The endosymbiotic theory suggests that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by a larger cell. Evidence includes their own DNA/ genetic material (circular DNA) and double membranes.

Outline the function of the following cell structures: ribosomes, endoplasmic reticulum (ER), Golgi apparatus, and lysosomes, and explain how they work together in protein production and processing.

Ribosomes synthesize proteins. The ER (rough ER) modifies and transports proteins. The Golgi apparatus further processes proteins. Lysosomes digest cellular waste. The ribosomes create the protein, the ER and Golgi modify and package, and the lysosomes break down any waste from that process. Signup and view all the answers

Compare and contrast the structures and functions of plant and animal cells, highlighting the unique features of each, such as cell walls in plant cells and centrioles in animal cells.

Plant cells have cell walls, chloroplasts, and a central vacuole, while animal cells have centrioles and lack cell walls and chloroplasts. Plant cells use chloroplasts for photosynthesis, animal cells contain centrioles which are involved in cellular division. Signup and view all the answers

Briefly explain how the arrangement of phospholipids in a cell membrane contributes to its selective permeability.

Phospholipids arrange in a bilayer with hydrophobic tails facing inward and hydrophilic heads facing outward, creating a barrier that only allows small, nonpolar molecules to pass through easily. Signup and view all the answers

Differentiate between simple diffusion, facilitated diffusion, and active transport, including the role of membrane proteins and energy (ATP) in each process.

Simple diffusion moves molecules down their concentration gradient without assistance or energy. Facilitated diffusion uses membrane proteins to assist molecules down their concentration gradient without energy. Active transport uses membrane proteins to move molecules against their concentration gradient, requiring energy (ATP). Signup and view all the answers

Describe the processes of endocytosis and exocytosis, and explain how they enable cells to transport large molecules or particles across the plasma membrane.

Endocytosis is the process by which cells engulf external materials by folding the plasma membrane inward to form a vesicle. Exocytosis is the process by which cells expel substances by fusing a vesicle with the plasma membrane and releasing its contents outside the cell. Signup and view all the answers

Explain the importance of water potential in plant cells, and how it affects turgor pressure and plasmolysis.

Water potential determines the direction of water movement into or out of the plant cell. High water potential inside the cell leads to turgor pressure (cell swells), while low water potential leads to plasmolysis (cell shrinks). Signup and view all the answers

Describe how the sodium-potassium pump works and its significance in maintaining the resting membrane potential in nerve cells.

The sodium-potassium pump uses ATP to actively transport 3 sodium ions out of the cell and 2 potassium ions into the cell, creating an electrochemical gradient and maintaining a negative charge inside the cell, which is crucial for nerve impulse transmission. Signup and view all the answers

Define the term 'stem cell' and explain the difference between totipotent, pluripotent, and multipotent stem cells.

A stem cell is an undifferentiated cell that can divide and differentiate into various specialized cell types. Totipotent cells can differentiate into any cell type (including embryonic), pluripotent cells can differentiate into almost any cell type (excluding embryonic), and multipotent cells can differentiate into a limited range of cell types. Signup and view all the answers

List three specific examples of specialized cells in the human body and describe how their structure relates to their function.

Nerve cells (neurons) have long extensions to transmit signals. Red blood cells lack a nucleus and are shaped like biconcave discs to maximize oxygen-carrying capacity. Muscle cells are elongated and contain contractile filaments for movement. Signup and view all the answers

Explain the role of cholesterol in the cell membrane and the effect it has on membrane fluidity at different temperatures.

Cholesterol maintains membrane fluidity by preventing phospholipids from packing too tightly at low temperatures and by restricting movement at high temperatures. Signup and view all the answers

Describe the extracellular matrix (ECM) and the function it performs in animal tissues.

The extracellular matrix (ECM) is a network of proteins and carbohydrates outside of cells that provides structural support, cell adhesion, and cell signalling in animal tissues. Signup and view all the answers

Outline the role of the nuclear envelope and nuclear pores in regulating the transport of molecules between the nucleus and the cytoplasm.

The nuclear envelope separates the nucleus from the cytoplasm, and the nuclear pores in the envelope regulate the movement of molecules (like mRNA and proteins) between the nucleus and the cytoplasm. Signup and view all the answers

Describe the function of aquaporins and explain why they are important for water transport across cell membranes.

Aquaporins are channel proteins that facilitate the rapid transport of water across cell membranes. They are important because they greatly enhance water permeability, which is crucial in tissues that require high rates of water transport, such as kidney tubules. Signup and view all the answers

Explain the process of receptor-mediated endocytosis and its importance in selectively importing specific molecules into the cell.

Receptor-mediated endocytosis involves receptors on the cell surface binding to specific target molecules, triggering the invagination of the membrane and formation of a vesicle containing the selected molecules. It is important for selectively importing nutrients, hormones, and other essential substances. Signup and view all the answers

Compare and contrast the roles of microfilaments, intermediate filaments, and microtubules in the cytoskeleton.

Microfilaments (actin) provide cell shape and movement; intermediate filaments provide structural support and stability; and microtubules (tubulin) provide tracks for intracellular transport and cell division. Signup and view all the answers

Describe how cell junctions (tight junctions, adherens junctions, desmosomes, gap junctions) enable cells to interact and communicate in tissues.

Tight junctions create a barrier to prevent leakage between cells. Adherens junctions and desmosomes provide strong adhesion. Gap junctions allow direct communication and passage of small molecules between cells. Signup and view all the answers

Explain the role of the cell wall in bacterial cells and describe how it differs from the cell wall in plant cells.

In bacterial cells, the cell wall (made of peptidoglycan) provides structural support and protection against osmotic lysis. In plant cells, the cell wall (made of cellulose) also provides support and shape, but it has a different composition and more complex structure. Signup and view all the answers

Flashcards

Main cell types

Prokaryotic and eukaryotic cells are the two basic types of cells. Prokaryotes lack a nucleus and other membrane-bound organelles, while eukaryotes possess these features.

Stem Cell

Stem cells are undifferentiated cells that can differentiate into specialised cells. They are important for growth, repair, and renewal in tissues.

Cell membrane function

Cell membranes control the movement of substances in and out of cells. They are selectively permeable, allowing some molecules to pass through while blocking others.

Cellular transport

Cellular transport mechanisms include passive (diffusion, osmosis) and active transport (requires energy).

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Key cell structures

Cell structures include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, and mitochondria, each with specific functions.