Cells: Basic Units of Life Quiz

Cells: Basic Units of Life

• Cells are the fundamental units of all living organisms.
• All organisms are composed of cells, from single-celled bacteria to complex multicellular organisms.
• Cells carry out all the processes necessary for life, including metabolism, growth, and reproduction.
• Cells vary greatly in size and shape depending on their specific function.

Cell Structure

• Plasma membrane: A selectively permeable barrier that encloses the cell's contents. It regulates the passage of materials into and out of the cell.
• Cytoplasm: The jelly-like substance filling the cell, containing organelles.
• Nucleus: The control center of the cell, containing DNA, the genetic material.
• Ribosomes: Involved in protein synthesis. Found either free-floating or bound to the endoplasmic reticulum.
• Endoplasmic Reticulum (ER): A network of membranes involved in the synthesis, modification, and transport of proteins and lipids. Rough ER has ribosomes; smooth ER lacks ribosomes.
• Golgi apparatus: Processes, packages, and distributes proteins and lipids. Modifies and sorts proteins transported from the ER.
• Mitochondria: The "powerhouses" of the cell, responsible for cellular respiration and energy production.
• Lysosomes: Contain enzymes that break down waste materials and cellular debris.
• Vacuoles: Storage compartments for water, nutrients, and waste products. Plant cells often possess a large central vacuole.
• Cytoskeleton: A network of protein fibers that provides structural support, facilitates cell movement, and aids in intracellular transport. Includes microtubules, microfilaments, and intermediate filaments.

Cell Division

• Cell cycle: A series of events that leads to cell growth and division. Includes interphase, mitosis, and cytokinesis.
• Interphase: The period of growth and activity between cell divisions. DNA replicates during this stage.
• Mitosis: The process of nuclear division, resulting in two genetically identical daughter nuclei. Consists of four phases: prophase, metaphase, anaphase, and telophase.
• Cytokinesis: The division of the cytoplasm to form two separate daughter cells. Different in animal and plant cells.
• Cell differentiation: The process by which cells become specialized for specific functions. Differentiated cells have different sets of proteins and carry out specific tasks in the body.

Cell Signaling

• Cell signaling: A complex process by which cells communicate with each other. Crucial for coordinating cellular activities.
• Signaling pathways: Series of molecular events that transmit a signal from the cell surface to the nucleus.
• Receptors: Proteins on the cell surface or within the cell that bind to signaling molecules.
• Second messengers: Molecules that relay the signal inside the cell after the receptor is activated.
• Types of signaling:
  • Endocrine signaling: Hormonal signals that travel throughout the body.
  • Paracrine signaling: Signals that act on nearby cells.
  • Synaptic signaling: Nerve impulses that transmit signals across synapses.
  • Contact-dependent signaling: Signals transmitted across cell membranes.
• Importance of cell signaling: Crucial for growth, development, homeostasis, responses to the environment, and maintaining overall health. Disruptions in signaling pathways can lead to disease, including cancer.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells: Simple cells lacking a nucleus and membrane-bound organelles. E.g., bacteria.
• Eukaryotic cells: Complex cells with a nucleus and membrane-bound organelles. E.g., plant and animal cells. These are generally much more complex than prokaryotic cells.