第三章 lab 课件 Lab 3: Homeostasis and Exchange Processes

Comprehensive question-and-answer flashcards covering cell membrane physiology, transport mechanisms (diffusion, osmosis, active transport), and laboratory activities on filtration, diffusion, dialysis, osmometry, and hemolysis.

What is homeostasis in human physiology?

Homeostasis is a dynamic state of balance within parameters compatible with life that maintains normal physiological conditions for cells and the organism to function normally.

What is the structural layout of a single phospholipid molecule in the plasma membrane?

It consists of a polar, hydrophilic phosphate 'head' that is attracted to water and non-polar, hydrophobic lipid 'tails' composed of fatty acid chains that repel water.

What are the definitions of intracellular fluid (ICF) and extracellular fluid (ECF)?

Intracellular fluid (ICF) is the fluid interior of the cell, whereas extracellular fluid (ECF) is the fluid environment outside the cell membrane.

What criteria allow substances to pass unaided through the lipid bilayer of the cell membrane?

Only relatively small, non-polar materials—such as oxygen gas, carbon dioxide gas, lipids, and alcohol—can pass through the hydrophobic lipid bilayer unaided.

How do passive transport and active transport differ in terms of cellular energy expenditure?

Passive transport is the movement of substances across the membrane without cellular energy expenditure, whereas active transport requires cellular energy in the form of adenosine triphosphate (ATP).

What is simple diffusion, and how do oxygen and carbon dioxide move across the plasma membrane?

Simple diffusion is the net movement of particles from an area of higher concentration to lower concentration. Oxygen diffuses into cells because its concentration is lower inside, while carbon dioxide diffuses out of cells because its concentration is higher inside cytoplasm.

What is facilitated diffusion, and why is it necessary for certain solutes?

Facilitated diffusion is passive transport that uses specialized membrane proteins (channel or carrier proteins) to transport charged, large polar, or hydrophilic solutes that cannot cross the non-polar lipid bilayer.

How does the glucose transporter move glucose across the cell membrane?

The glucose transporter is a specialized carrier protein that facilitates the inward movement of large, polar glucose molecules into the cell without expending ATP.

How do sodium channels facilitate the movement of sodium ions ($\text{Na}^+$) into cells?

They form membrane pores that allow positively charged $\text{Na}^+$ ions to move down their concentration gradient from extracellular fluid into the cytoplasm.

What is osmosis?

Osmosis is the diffusion of water through a semipermeable membrane toward the area of higher solute concentration (lower water concentration).

What are the effects of hypertonic, isotonic, and hypotonic solutions on cell morphology?

In a hypertonic solution, water leaves the cell causing it to shrivel (crenate); in an isotonic solution, equal water exchange maintains normal shape; in a hypotonic solution, water enters the cell causing it to swell and potentially burst (lyse).

How does filtration differ from diffusion as a passive transport mechanism?

Filtration uses a hydrostatic pressure gradient to push fluid and solutes from a higher-pressure area to a lower-pressure area, whereas diffusion is driven by a concentration gradient.

What is the mechanism, ion stoichiometry, and direction of transport for the sodium-potassium pump ($\text{Na}^+/\text{K}^+$ ATPase)?

Powered by ATP, the sodium-potassium pump extrudes $3\,\text{Na}^+$ ions out of the cell and imports $2\,\text{K}^+$ ions into the cell per cycle, moving both ions against their concentration gradients.

What electrical gradient is maintained across nerve cell membranes?

Nerve cells maintain a negative electrical gradient on the inside of the cell at around $-70\,\text{mV}$ relative to the outside.

What is secondary active transport?

Secondary active transport occurs when an active transport pump uses ATP to establish a concentration gradient (such as high extracellular $\text{Na}^+$), which then drives the passive transport or diffusion of another substance.

What occurs during the filtration procedure in Activity 1 of the lab?

Solid particles of calcium bicarbonate in a water suspension are separated from the liquid as the mixture passes through filter paper in a funnel, leaving solid residue on the filter paper and collecting clear filtrate below.

In Lab Activity 2, how is the rate of diffusion measured using potassium permanganate?

Potassium permanganate crystals are placed into water over concentric rings spaced $1\,\text{cm}$ apart, and the diameter of the purple ring is measured after $5\,\text{min}$ to compute the rate of diffusion in $\text{cm/min}$.

What is the effect of increasing solute concentration on the rate of diffusion in Lab Activity 2?

A higher initial solute concentration (such as using 5-6 crystals instead of 2-3) creates a steeper concentration gradient, which increases the rate of diffusion.

What is dialysis and what clinical condition does it treat?

Dialysis is the diffusion of solutes through a semipermeable membrane; it is used clinically to remove accumulated nitrogenous wastes from the blood of patients with impaired kidney function (azotemia or uremia).

Which chemical indicators are used to test for starch and chloride in Lab Activity 3, and what positive results do they produce?

Lugol solution (iodine) detects starch, turning from yellow to dark blue or purplish; silver nitrate detects chloride, forming a white silver-chloride precipitate or cloudy solution.

What is an osmometer and what does it measure?

An osmometer is an experimental device used to measure the process and rate of osmosis by observing changes in liquid meniscus level over time.

What is the solute concentration inside red blood cells, and what saline solution concentration is isotonic to them?

The solute concentration inside red blood cells is equivalent to approximately $0.9\%$ NaCl ($99.1\%$ water), making a $0.9\%$ NaCl saline solution isotonic to them.

What is hemolysis, and how is it visually confirmed in the lab scintillation vial experiment?

Hemolysis is the breakdown or bursting of red blood cells in a hypotonic environment; visually, the solution becomes clear, allowing text placed behind the vial (such as 'HEMOLYSIS') to be read clearly.

According to the Lab 5 experimental setup table, which vial produces complete hemolysis and why?

Vial 5, which contains $0\,\text{ml}$ of saline and $5\,\text{ml}$ of water; pure water is strongly hypotonic to red blood cells, causing water to diffuse inward until the cells lyse.