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Questions and Answers
What characterizes diffusion across a cell membrane?
What characterizes diffusion across a cell membrane?
Which transport mechanism allows for the ingestion of large particles like bacteria?
Which transport mechanism allows for the ingestion of large particles like bacteria?
What is an example of a substance that combines with intrinsic factor to enter cells via endocytosis?
What is an example of a substance that combines with intrinsic factor to enter cells via endocytosis?
Which of the following best describes pinocytosis?
Which of the following best describes pinocytosis?
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In which type of cells is pinocytosis particularly rapid?
In which type of cells is pinocytosis particularly rapid?
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What initiates phagocytosis in immune cells?
What initiates phagocytosis in immune cells?
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Which of the following substances is not typically internalized via endocytosis?
Which of the following substances is not typically internalized via endocytosis?
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How does the mechanism of active transport differ from diffusion?
How does the mechanism of active transport differ from diffusion?
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Which process facilitates the transport of glucose into cells?
Which process facilitates the transport of glucose into cells?
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What is a key characteristic of carrier-mediated diffusion?
What is a key characteristic of carrier-mediated diffusion?
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How is the rate of molecular movement across a barrier calculated in passive diffusion?
How is the rate of molecular movement across a barrier calculated in passive diffusion?
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What is the primary mechanism of water transport across a semi-permeable membrane?
What is the primary mechanism of water transport across a semi-permeable membrane?
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Which of the following statements about active transport is accurate?
Which of the following statements about active transport is accurate?
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Which of the following mechanisms is NOT governed by Fick's law?
Which of the following mechanisms is NOT governed by Fick's law?
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Probenecid is used clinically to affect the transport of which substance?
Probenecid is used clinically to affect the transport of which substance?
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What distinguishes endocytosis from other transport mechanisms?
What distinguishes endocytosis from other transport mechanisms?
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What is the main characteristic of a lipid bilayer in relation to water molecules?
What is the main characteristic of a lipid bilayer in relation to water molecules?
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How does active transport differ from diffusion?
How does active transport differ from diffusion?
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What defines simple diffusion through a cell membrane?
What defines simple diffusion through a cell membrane?
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What is facilitated diffusion?
What is facilitated diffusion?
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Which of the following substances is most likely to diffuse through the lipid bilayer easily?
Which of the following substances is most likely to diffuse through the lipid bilayer easily?
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What role do small water-filled pores in capillary membranes play?
What role do small water-filled pores in capillary membranes play?
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Which process is governed by Fick's law?
Which process is governed by Fick's law?
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Which of the following describes lipid diffusion?
Which of the following describes lipid diffusion?
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What process describes the attachment of cell membrane receptors to surface ligands of a particle?
What process describes the attachment of cell membrane receptors to surface ligands of a particle?
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What is the function of lysosomes in phagocytosis?
What is the function of lysosomes in phagocytosis?
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Which agent is NOT found in lysosomes to combat phagocytized bacteria?
Which agent is NOT found in lysosomes to combat phagocytized bacteria?
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What occurs immediately after a phagocytic vesicle forms within a cell?
What occurs immediately after a phagocytic vesicle forms within a cell?
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What happens to indigestible substances post-digestion in a phagocytic vesicle?
What happens to indigestible substances post-digestion in a phagocytic vesicle?
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What do foodstuffs react with inside the cell to release energy?
What do foodstuffs react with inside the cell to release energy?
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Which component is essential for the activation of lysosomal hydrolases?
Which component is essential for the activation of lysosomal hydrolases?
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What mechanism helps push the phagocytic vesicle into the cell?
What mechanism helps push the phagocytic vesicle into the cell?
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Study Notes
Functional Systems of the Cell: Transport of Substances
- The lipid bilayer of the cell membrane acts as a barrier, preventing the movement of water and water-soluble substances between the extracellular and intracellular fluid compartments. It is not miscible with either fluid.
Cellular Transport
-
Passive Transport (Small Molecules):
- Simple Diffusion: Random movement of molecules through intermolecular spaces or with carrier proteins in the membrane, driven by concentration gradient.
- Facilitated Diffusion: Movement of molecules across a membrane with the assistance of a carrier protein, utilizing a concentration gradient. This can be through channels (nonspecific transport) or carriers (specific).
-
Active Transport (Small Molecules):
- Movement of ions or substances against a concentration gradient, requiring energy in addition to kinetic energy (usually ATP). This involves carrier proteins.
-
Large Molecules:
- Exocytosis: Outbound transport of large molecules using vesicles.
- Endocytosis: Inbound transport of large molecules using vesicles. Includes phagocytosis (ingestion of large particles like bacteria or tissue debris), and pinocytosis (ingestion of minute particles and fluids).
Diffusion
- Diffusion is the random movement of molecules.
- Types of diffusion through the cell membrane:
- Simple Diffusion: Molecules move through the membrane without the help of carrier proteins.
- Facilitated Diffusion: Molecules move through the membrane with the assistance/interaction of carrier proteins, which bind chemically to them.
Aqueous Diffusion
- Movement of molecules through the watery extracellular and intracellular spaces.
- Most capillaries have small water-filled pores that allow molecules up to the size of small proteins to diffuse between blood and the extravascular space.
- Governed by Fick's law.
Lipid Diffusion
- Movement of molecules through membranes and other lipid structures, occurring directly in the lipid bilayer if the molecule is lipid-soluble.
- Examples include oxygen, nitrogen, carbon dioxide, and alcohols.
- Governed by Fick's law.
Fick's Law of Diffusion
- Predicts the rate of movement of molecules across a barrier.
- Factors for calculating rate:
- Concentration gradient (C1 - C2).
- Permeability coefficient
- Area
- Thickness
Carrier-Mediated Diffusion
- Movement across the membrane facilitated by a macromolecule (carrier protein).
- Specific for certain chemical structures.
- Saturable process.
- Does not move against a concentration gradient (a type of passive transport).
- Example: Glucose uptake by cells.
Transport by Special Carriers
- Drugs may be transported by mechanisms that carry similar endogenous substances (e.g., amino acid carriers in the blood-brain barrier).
- Not governed by Fick's law.
- Capacity-limited.
- Probenecid: Selective inhibitor for uric acid transport, increasing its excretion (used in gout). Sometimes used with penicillin antibiotics to increase antibiotic blood levels and enhance their effectiveness to fight infections.
Endocytosis
- Involves the movement of large molecules into the cell.
- Pinocytosis: Ingestion of minute particles and fluids.
- Phagocytosis: Ingestion of large particles (bacteria, whole cells, or tissue debris).
Steps of Phagocytosis
- Attachment: Cell membrane receptors attach to surface ligands on particles.
- Evagination: Membrane surrounds the particle.
- Vesicle Formation: A phagocytic vesicle is formed.
- Contraction & Separation: Cytoplasmic fibrils contract, pinching off the vesicle from the membrane.
- The vesicle is now inside the cytoplasm
Lysosomes
- Digestive vesicles formed inside cells.
- Contain acid hydrolases that digest proteins, carbohydrates, and lipids.
- Breakdown products are released into the cytoplasm.
- Contain bactericidal agents (lysozyme, lysoferrin, and low pH) to destroy phagocytized bacteria..
- The remaining indigestible material forms a residual body that is eventually expelled from the cell via exocytosis
Mitochondria
- Site of cellular respiration.
- Breakdown of glucose, fatty acids, and amino acids with oxygen to produce ATP (adenosine triphosphate), a high-energy compound.
- Vital for supplying energy for cellular functions.
Uses of ATP for Cellular Function
- Transport: Active transport of substances through membranes.
- Synthesis: Chemical compound synthesis throughout the cell, such as protein synthesis.
- Mechanical work: Energy for muscle contraction.
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Description
Test your understanding of the various mechanisms that regulate transport across cell membranes, including diffusion, endocytosis, and active transport. This quiz covers key concepts essential for studying cellular physiology and the functions of immune cells. Challenge yourself to identify the processes by which substances move in and out of cells.
