Cellular Transport, Microscopy, and Cell Structure: Week 1 Study Notes

Cellular Transport Mechanisms

Brownian Motion

Brownian motion describes the random movement of particles suspended in a fluid, resulting from their collision with fast-moving molecules in the fluid. This phenomenon is fundamental to understanding how substances move at the microscopic level.

• Definition: Random movement of substances due to kinetic energy.

• Example: Movement of pollen grains in water observed under a microscope.

Diffusion

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient.

• Definition: Movement of a substance from an area of high concentration to an area of low concentration.

• Key Equation: $J = -D \frac{dC}{dx}$ (Fick's First Law, where J is flux, D is diffusion coefficient, C is concentration, x is position)

• Example: Oxygen diffusing from alveoli into blood capillaries.

Osmosis

Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.

• Definition: Movement of water across a semi-permeable membrane from low solute concentration to high solute concentration.

• Example: Water entering a plant cell, causing it to swell.

Filtration

Filtration is the process by which substances are separated based on size as they pass through a semi-permeable membrane.

• Definition: Separation of substances by size across a semi-permeable membrane.

• Example: Filtration of blood in the kidneys to form urine.

Osmotic Pressure

Osmotic pressure is the minimum pressure required to prevent the movement of solvent (usually water) across a semi-permeable membrane into a region of higher solute concentration.

• Definition: Pressure needed to prevent solvent movement into a concentrated solution.

• Key Equation: $\Pi = iMRT$ (where $\Pi$ is osmotic pressure, i is van 't Hoff factor, M is molarity, R is gas constant, T is temperature)

• Example: Preventing water from entering hypertonic solutions in cells.

Types of Solutions Affecting Cells

Cells respond differently to the concentration of solutes in their environment:

• Hypertonic: Solution has more solute (very concentrated); water leaves the cell, causing it to shrink.

• Isotonic: Solution has the same solute concentration as the cell; no net movement of water.

• Hypotonic: Solution has less solute (dilute); water enters the cell, causing it to swell.

Microscopy: Parts and Functions

Major Parts of the Microscope

Microscopes are essential tools in anatomy and physiology for observing cells and tissues. Understanding their parts and functions is crucial for proper use.

• Arm: Supports major parts; used to hold and carry the microscope.

• Base: Sits on the table surface; supports the microscope.

• Stage: Surface to support microscope slides.

• Upper mechanical stage knob: Moves slide forward and backward.

• Lower mechanical stage knob: Moves slide left and right.

• Coarse adjustment knob: Moves stage up/down for general focusing.

• Fine adjustment knob: Moves stage up/down in small increments for sharp focusing.

• Condenser: Concentrates light onto the slide.

• Iris-diaphragm lever: Adjusts light intensity.

• Lamp: Illuminates the slide.

• On/Off switch: Turns lamp on/off.

• Brightness control knob: Adjusts lamp intensity.

• Revolving nose piece: Holds objective lenses.

• Objectives: Lenses closest to the slide; provide different magnifications.

• Eye piece: Contains ocular lens; closest to the eye.

Objective Lenses Comparison

Objective lenses vary in color, name, and power. They are used for different levels of magnification.

Objective	Name	Scan	Power
Yellow	Low	10X	5X
Blue	High	40X	40X
White	Oil Immersion	100X	100X

Note: The ocular lens (eye piece) typically provides an additional 10X magnification.

Cell Structure and Organelles

Cytoplasm and Its Components

The cytoplasm is the region inside the cell membrane, excluding the nucleus. It consists of the cytoskeleton, cytosol, and organelles.

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide structural support and aid in cell movement.

• Cytosol: Fluid portion containing proteins, water, ions, and nutrients.

• Organelles: Specialized structures performing distinct cellular functions.

Major Organelles: Structure and Function

Organelles are specialized compartments within cells, each with unique structures and functions. The table below summarizes key organelles:

Organelle	Structure	Function
Mitochondria	Double membrane, inner membrane folds (cristae), contains own DNA	Synthesizes the majority of the cell's ATP
Ribosome	Two subunits made of proteins and rRNA	Makes proteins
Peroxisome	Enclosed in a membrane	Metabolizes certain chemicals; breaks down fatty acids; detoxifies
Rough Endoplasmic Reticulum	Series of saclike membranes studded with ribosomes	Synthesizes proteins; modifies and transports proteins
Smooth Endoplasmic Reticulum	Series of tubular membranes without ribosomes	Synthesizes lipids; detoxifies chemicals
Lysosome	Membrane-enclosed vesicle	Digests cellular debris; recycles cell components
Golgi Apparatus	Stack of flattened membrane sacs	Processes, packages, and distributes proteins and lipids
Centrioles	Paired organelles composed of microtubules	Assist in cell division; organize microtubules

Nucleus

The nucleus is the biosynthetic center of the cell, directing the production of nearly all the cell's proteins. It contains the nuclear envelope, chromatin, and nucleolus.

• Nuclear Envelope: Double membrane structure enclosing the nucleus.

• Chromatin: DNA and associated proteins; condenses to form chromosomes during cell division.

• Nucleolus: Site of ribosomal RNA (rRNA) synthesis and ribosome assembly.

Application: Be able to identify major organelles, their functions, and locate them on a cell diagram.

Additional Info

• Microscope Handling: Always carry the microscope with two hands (one on the arm, one under the base).

• Cellular Transport: These mechanisms are essential for maintaining homeostasis in cells and tissues.