Cell Biology: Cell Structure and Functions
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Questions and Answers

Which of the following is NOT an example of a physical phenomenon utilizing positive feedback?

  • Blood clotting mechanisms
  • Regulation of blood glucose levels (correct)
  • Excitation of membranes
  • Birth of a baby

    • Positive feedback mechanisms amplify the effect of a disturbance, contributing to stability.

    False

    What is the primary role of gap junctions in cell communication?

    Gap junctions facilitate direct communication between adjacent cells by allowing the passage of small molecules and electrical signals.

    The process of cell-cell recognition involves the docking of cells with specific ____-bound molecules, initiating communication between them.

    <p>membrane</p> Signup and view all the answers

    Which type of cell signaling involves the release of a signal molecule that acts on the same cell that produced it?

    <p>Autocrine signaling</p> Signup and view all the answers

    Match the following types of cell communication with their descriptions:

    <p>Direct contact communication = Cells communicate via physical contact through channels or adhesion molecules. Local signaling communication = Cells communicate through the release of signal molecules that diffuse through the surrounding fluid. Long-distance signaling communication = Cells communicate via hormones or other messengers that travel through the bloodstream.</p> Signup and view all the answers

    Cell communication is essential for maintaining homeostasis in the body.

    <p>True</p> Signup and view all the answers

    Give an example of local regulator that acts in both paracrine and autocrine fashion.

    <p>Growth factors</p> Signup and view all the answers

    Which of the following is NOT a component of the cytoskeleton?

    <p>Phospholipids</p> Signup and view all the answers

    Passive transport processes require cellular energy.

    <p>False</p> Signup and view all the answers

    What type of molecules can pass through the plasma membrane via simple diffusion?

    <p>small and lipid-soluble molecules</p> Signup and view all the answers

    In carrier-mediated facilitated diffusion, a carrier moves a solute down its _______ gradient across the plasma membrane.

    <p>concentration</p> Signup and view all the answers

    Match the transport process with its description:

    <p>Simple diffusion = Movement of small, lipid-soluble molecules down their concentration gradient. Facilitated diffusion = Movement of molecules with the help of membrane proteins. Active transport = Movement of molecules using cellular energy. Osmosis = Movement of water across a semipermeable membrane.</p> Signup and view all the answers

    Which of these molecules uses facilitated diffusion to cross the plasma membrane?

    <p>Glucose</p> Signup and view all the answers

    Uniport system involves a carrier that transports two substances in one direction.

    <p>False</p> Signup and view all the answers

    Name the two main types of facilitated diffusion.

    <p>channel-mediated diffusion and carrier-mediated diffusion</p> Signup and view all the answers

    Which of the following is an example of a symport system?

    <p>Na+-sugar transporter</p> Signup and view all the answers

    Primary active transport requires direct input of metabolic energy, such as ATP.

    <p>True</p> Signup and view all the answers

    What is the ratio of Na+ to K+ ions transported by the Na+-K+ pump?

    <p>3:2</p> Signup and view all the answers

    The Na+-K+ pump helps regulate cell volume by reducing intracellular ion concentration, which controls ______.

    <p>osmolarity</p> Signup and view all the answers

    Match the following transport systems with their characteristics:

    <p>Symport = Transports two substances in the same direction Antiport = Transports two substances in opposite directions Primary active transport = Requires direct energy input like ATP Secondary active transport = Energy derived from ion gradient</p> Signup and view all the answers

    Which of the following is a function of the Na+-K+ pump?

    <p>Maintains a sodium concentration gradient across the membrane</p> Signup and view all the answers

    Secondary active transport directly uses ATP for the movement of substances.

    <p>False</p> Signup and view all the answers

    What type of pump transports H+ ions into the lumen of the renal tubule?

    <p>H+-ATPase</p> Signup and view all the answers

    What does a selectively permeable membrane allow to move across it?

    <p>Water molecules</p> Signup and view all the answers

    Osmotic pressure is determined by the valence, weight, and size of the particles in a solution.

    <p>False</p> Signup and view all the answers

    What is the force that drives osmosis?

    <p>osmotic pressure</p> Signup and view all the answers

    A solution with a higher solute concentration than a cell's intracellular fluid is called a ______ solution.

    <p>hypertonic</p> Signup and view all the answers

    Match the solution type to its effect on a cell

    <p>Isotonic = Cell maintains normal volume Hypertonic = Cell shrinks Hypotonic = Cell swells</p> Signup and view all the answers

    Which of the following best describes the function of hydrostatic pressure in the body?

    <p>It is the pressure exerted by blood against the walls of the blood vessels.</p> Signup and view all the answers

    Filtration is the movement of water and solutes based on the difference in solute concentrations.

    <p>False</p> Signup and view all the answers

    If a cell is placed in a hypotonic solution, what will happen to the cell?

    <p>The cell will swell.</p> Signup and view all the answers

    What is the primary function of thermoreceptors in the human body?

    <p>To monitor body temperature</p> Signup and view all the answers

    Positive feedback systems work to maintain stability within the body.

    <p>False</p> Signup and view all the answers

    What hormone is secreted by the pancreas to lower blood glucose levels?

    <p>Insulin</p> Signup and view all the answers

    The process of regulating body temperature is known as ______.

    <p>thermostasis</p> Signup and view all the answers

    Which of the following is an example of a negative feedback mechanism?

    <p>Blood glucose regulation</p> Signup and view all the answers

    Homeostatic control systems can be separated into positive feedback and negative feedback categories.

    <p>True</p> Signup and view all the answers

    What type of blood vessels dilate to promote heat loss during increased body temperature?

    <p>Skin blood vessels</p> Signup and view all the answers

    Match the physiological functions with their corresponding feedback type:

    <p>Body temperature regulation = Negative feedback Childbirth contraction = Positive feedback Blood glucose level regulation = Negative feedback Blood clotting = Positive feedback</p> Signup and view all the answers

    What triggers the secretion of neurotransmitter molecules in synaptic signaling?

    <p>Electrical signal along a nerve cell</p> Signup and view all the answers

    Hormones act only on the cells that are adjacent to the secreting cell.

    <p>False</p> Signup and view all the answers

    What is the space called that lies between a nerve cell and its target cell?

    <p>synapse</p> Signup and view all the answers

    In long-distance signaling, the controlling cell secretes a signaling molecule known as a _____

    <p>hormone</p> Signup and view all the answers

    Which of the following describes synaptic signaling?

    <p>Involves electrical signals and neurotransmitter release</p> Signup and view all the answers

    The _____ system is responsible for long-distance communication in the body through hormones.

    <p>circulatory</p> Signup and view all the answers

    Match the types of signaling to their descriptions:

    <p>Synaptic signaling = Local signaling through neurotransmitters Long-distance signaling = Communication via hormones Nervous system = Body's primary communication and control system Target cells = Cells that respond to signals from controlling cells</p> Signup and view all the answers

    What is the primary role of the nervous system?

    <p>Communication and control system</p> Signup and view all the answers

    Study Notes

    The Cell and Its Functions

    • Cells are the fundamental units of all living organisms.
    • A human cell has three primary parts:
      • Cell membrane (plasma membrane): controls substance movement.
      • Nucleus: controls cell activities.
      • Cytoplasm: the area between the nucleus and the plasma membrane, containing cytosol and organelles.
      • Cytosol (intracellular fluid): contains dissolved nutrients, ions, proteins, and waste.
      • Organelles: specialized structures with specific functions within the cytoplasm.

    Cell Membrane Composition

    • Composed of lipids, proteins, and carbohydrates.
    • Lipids (45%)
      • Phospholipids: lollipop-shaped molecules with a hydrophilic head and hydrophobic tails. Form a bilayer.
      • Cholesterol: helps maintain membrane stability.
    • Proteins (50%)
      • Integral proteins: extend across the entire membrane.
      • Peripheral proteins: associated with the inner or outer surface of the membrane.
    • Carbohydrates (5%)
      • Glycolipids and glycoproteins: attached to lipids and proteins, form the glycocalyx.

    Membrane Lipid Functions

    • Impermeable to water-soluble molecules.
    • Lipid-soluble molecules, like oxygen and carbon dioxide, cross easily.

    Membrane Protein Functions

    • Channels: allow specific substances to pass through.
    • Carriers or pumps: move substances across the membrane.
    • Enzymes: catalyze specific chemical reactions.
    • Receptors: bind to hormones and other molecules, initiating cellular responses.
    • Linker proteins: connect membrane to other proteins and the cytoskeleton.

    Membrane Carbohydrates Functions

    • Cell identity markers, enabling cell-cell recognition.
      • Sperm recognizing egg
      • Immune cells recognizing self vs. non-self.
    • Helps cells adhere to each other.

    The Nucleus

    • Largest organelle, the "control center" of the cell.
    • Contains DNA (instructions for protein synthesis).
    • Surrounded by a double membrane, the nuclear envelope, which has pores for ribosome and protein passage.
    • Contains nucleoplasm and nucleolus (site for ribosome subunit formation).

    Mitochondria

    • Organelles specialized for ATP synthesis.
    • Have a double membrane with inner folds called cristae.
    • Contain oxidative phosphorylation enzymes used in cellular respiration to produce ATP.
    • The number of mitochondria in a cell relates to the energy demands of that cell.

    Ribosomes

    • Non-membranous organelles composed of proteins & rRNA (ribosomal RNA).
    • Exist in free or bound forms (attached to rough ER).
    • Responsible for protein synthesis.
    • Formed in the nucleolus, then they travel to the cytoplasm.

    Endoplasmic Reticulum

    • A complex network of tubules, vesicles, and flattened sacs, extending from the nuclear envelope.
    • Rough ER (RER) has ribosomes attached and responsible for protein secretion.
    • Smooth ER (SER) lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium ion storage.

    The Golgi Apparatus

    • Refines, packages, and ships proteins and lipids.
    • Modifies proteins via glycosylation.
    • Forms lysosomes and secretory vesicles.

    Lysosomes

    • Contain digestive enzymes (hydrolases) for intracellular digestion.
    • Breakdown of organelles, bacteria, and other substances.

    Peroxisomes

    • Contain enzymes, primarily catalase, to break down hydrogen peroxide.
    • Involved in detoxification.
    • Break down fatty acids and other molecules.

    Proteasomes

    • Degrade damaged or unneeded proteins.

    The Cytoskeleton

    • Network of fibers (microfilaments, intermediate filaments, microtubules) that maintain cell shape and allow movement.
    • Holds and moves organelles.

    Transport Across Cell Membrane

    • Passive transport (no energy required):
      • Diffusion (simple and facilitated): movement of substances down a concentration gradient.
      • Osmosis: movement of water across a selectively permeable membrane down a concentration gradient.
    • Active transport (requires energy):
      • Primary active transport: uses ATP; example Na+-K+ ATPase (pump).
      • Secondary active transport: uses energy from an ion concentration gradient; example Na+-glucose symporter.
    • Vesicular transport (movement of substances in vesicles):
      • Endocytosis (taking substances into the cell): phagocytosis, pinocytosis, receptor-mediated endocytosis.
      • Exocytosis (releasing substances out of the cell).

    Body Fluids

    • Water is the most important molecule in the human body.
    • Approximately 60-70% of body weight is water.
      • Intracellular fluid (ICF): inside the cells.
      • Extracellular fluid (ECF): outside the cells:
        • Intravascular fluid: plasma (in the blood vessels).
        • Interstitial fluid: surrounds the cells.

    Forces Affecting Exchange of Body Fluids

    • Osmosis: the movement of water across a selectively permeable membrane to equalize solute concentration.

    • Tonicity: the ability of a solution to cause a cell to gain or lose water.

      • Isotonic: same solute concentration as the cell (no net water movement).
      • Hypertonic: higher solute concentration than the cell (water moves out, cell shrinks).
      • Hypotonic: lower solute concentration than the cell (water moves in, cell swells)

    • Filtration: movement of water and dissolved substances from a region of high to a low pressure across a selectively-permeable membrane.

    Homeostasis

    • Maintaining a stable internal environment despite external changes.
    • Essential for cell survival.
    • Involves receptors, afferent pathways, control centers, efferent pathways, and effectors.
    • Regulation mechanisms(Examples: Body Temperature; Blood Glucose Levels). -Negative feedback, Positive Feedback.

    Cell Communication

    • Essential for coordination of cellular activities.
    • Direct contact: gap junctions for direct cytoplasmic communication.
    • Local signaling (paracrine & autocrine signaling): signaling molecules act on nearby target cells.
    • Long-distance signaling: hormones travel through the circulatory system.

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