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 (B)

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 (A)</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 (A)</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 (A)</p> Signup and view all the answers

Passive transport processes require cellular energy.

<p>False (B)</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 (A)</p> Signup and view all the answers

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

<p>False (B)</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 (C)</p> Signup and view all the answers

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

<p>True (A)</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 (A)</p> Signup and view all the answers

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

<p>False (B)</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 (A)</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 (B)</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. (A)</p> Signup and view all the answers

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

<p>False (B)</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. (A)</p> Signup and view all the answers

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

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

Positive feedback systems work to maintain stability within the body.

<p>False (B)</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 (B)</p> Signup and view all the answers

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

<p>True (A)</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 (B)</p> Signup and view all the answers

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

<p>False (B)</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 (C)</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

Flashcards

Tonicity

The ability of a solution to alter the volume of a cell through osmosis.

Isotonic solution

A solution with the same solute concentration as the inside of a cell, causing no change in cell volume.

Hypertonic solution

A solution with a higher solute concentration than the inside of a cell, causing water to move out and the cell to shrink.

Hypotonic solution

A solution with a lower solute concentration than the inside of a cell, causing water to move in and the cell to swell.

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Hydrostatic pressure

The pressure exerted by a fluid against a surface. In the body, this is primarily blood pressure.

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Filtration

The movement of water and dissolved substances from high pressure to low pressure. Driven by hydrostatic pressure.

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Osmotic pressure

The pressure required to prevent water from moving across a selectively permeable membrane, driven by differences in solute concentrations.

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Selectively permeable membrane

A membrane that allows only certain substances to pass through. Water molecules can pass, but larger solutes are blocked.

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What is the cytoskeleton?

A complex network of fibers maintaining the cell's structure, holding organelles in place, and allowing the cell to move and change shape.

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What is passive transport?

The process of molecules moving across the cell membrane, requiring no cellular energy.

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What is simple diffusion?

Movement of a substance across a membrane without the help of any membrane proteins. It relies on the concentration gradient and occurs from an area of high concentration to an area of low concentration.

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What is facilitated diffusion?

Movement of molecules across the membrane with the assistance of membrane proteins. It allows the passage of substances that cannot easily pass through the phospholipid bilayer.

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What is channel-mediated diffusion?

A type of facilitated diffusion that involves the movement of small ions through protein channels.

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What is carrier-mediated diffusion?

A type of facilitated diffusion where a carrier protein binds with a specific molecule and transports it across the membrane, following its concentration gradient (high to low).

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What is a uniport system?

A carrier protein that transports only one type of molecule in one direction.

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What is osmosis?

The movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.

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Co-transport or Symport system

A type of membrane transport protein that moves two substances across the cell membrane simultaneously in the same direction. It often uses the energy from the movement of one substance down its concentration gradient to drive the movement of the other substance against its gradient.

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Countertransport or Antiport system

A type of membrane transport protein that moves two substances across the cell membrane in opposite directions. One substance moves down its concentration gradient, providing energy for the other substance to move against its gradient.

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Primary Active Transport

A type of active transport that directly uses metabolic energy, typically in the form of ATP, to move substances across the cell membrane against their concentration gradients.

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Secondary Active Transport

A type of active transport that indirectly uses energy from the concentration gradient of one substance to move another substance across the cell membrane against its concentration gradient. The energy is supplied by the movement of a substance down its concentration gradient, which is maintained by primary active transport.

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Na+-K+ ATPase (Sodium-Potassium Pump)

A protein responsible for pumping Na+ ions out of the cell and K+ ions into the cell, both against their concentration gradients. It maintains the sodium-potassium gradient, which is essential for many cellular functions.

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Active Transport

The movement of ions across a membrane against their concentration gradient, requiring energy from ATP.

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H+-ATPase (Proton Pump)

The pumping of H+ ions from the cytosol into the lumen of the renal tubule, against their concentration gradient. This process is important for regulating blood pH and urine acidity.

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Secondary Active Transport - Example: Glucose Uptake

The sodium-potassium gradient across the cell membrane, maintained by the Na+-K+ ATPase, is used as a source of energy to drive other membrane transport processes, such as the uptake of glucose into kidney cells.

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Gap junctions

A type of communication where cells have direct channels connecting their cytoplasm, allowing for the synchronization of metabolic activities or electrical signals.

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Cell-cell recognition

Communication between cells that occurs when cells with specific cell-surface molecules bind to each other, triggering a response.

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Paracrine signaling

A type of local signaling where a cell releases a signal molecule that diffuses through the surrounding fluid to nearby target cells.

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Autocrine signaling

A type of local signaling where a cell releases a signal molecule that acts on the same cell that produced it.

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Positive feedback loop

A process where a disturbance is amplified, leading to instability.

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Oxytocin

A hormone released by the pituitary gland that stimulates uterine contractions during childbirth.

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Cervix

The neck of the uterus, which dilates during labor.

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Pituitary gland

The organ responsible for producing and releasing hormones.

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Synaptic signaling

A specialized form of local signaling in the nervous system where nerve cells release chemical messengers called neurotransmitters across a narrow space called the synapse, triggering a response in the target cell.

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Neurotransmitters

Chemical messengers released by nerve cells at synapses to transmit signals to other nerve cells.

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Synapse

The narrow space between a nerve cell and its target cell, across which neurotransmitters diffuse.

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Hormonal signaling

A type of long-distance signaling where a controlling cell releases a hormone that travels through the circulatory system to target cells, often located far away.

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Hormone

A long-distance signaling molecule secreted by a controlling cell that travels through the bloodstream to target cells.

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Target cells

Cells that respond specifically to particular hormones.

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Nervous system

The body's main communication system, responsible for coordinating and controlling various bodily functions.

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Cell communication

The primary means of communication between cells in the body.

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Regulated Variable

The factor that is being controlled or regulated in a homeostatic system. For example, body temperature is the regulated variable in thermoregulation.

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Homeostasis

A mechanism by which a system automatically maintains a stable internal environment despite external changes. It involves sensing a change, initiating a response, and then reducing the change back to a set point.

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Thermoregulation

The process of maintaining a stable body temperature within a narrow range. It's a crucial homeostatic mechanism.

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Thermoreceptors

Sensors in the skin and hypothalamus that detect changes in body temperature.

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Negative feedback

A control system that works by reducing a change in a regulated variable back towards a set point. The response counteracts the initial change.

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Positive feedback

A control system that amplifies a change in a regulated variable, pushing it further away from the set point. Often used for processes that need to complete quickly.

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Insulin

Hormone released by the pancreas (beta cells) in response to high blood glucose. It helps lower blood sugar.

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Glucagon

Hormone released by the pancreas (alpha cells) in response to low blood glucose. It helps raise blood sugar.

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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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