Chapter 1 Cells & Microscopy Flashcards
What is magnification?
Number of times larger an image appears when compared to the actual specimen.
Achieved by the eyepiece objective (x10) and the objective lens (x4, x10, or x40).
How is total magnification calculated?
Total magnification = eyepiece magnification x objective magnification.
Maximum magnification of LM = x1500; magnifying beyond this results in a blurred image.
What does resolution determine?
The ability to distinguish between 2 separate points, i.e., clarity of the image.
What is the limit of resolution for light microscopes?
Max resolution of LM & CLSM = 200nm.
What is the maximum resolution of electron microscopes?
Higher resolution as they use a beam of electrons with shorter wavelengths (~λ = that of x-rays).
Why do we preserve specimens?
To enable them to be cut into sections and treated with different stains.
This reveals different structures.
What is the function of the eyepiece in a light microscope?
Magnifies specimen but does not resolve the image.
What role does the turret serve in a light microscope?
Holds objective lenses and rotates to enable selection of objective lens.
What is the function of the stage in a light microscope?
Supports the slide in the correct position at 90° to the illumination source.
What is the purpose of the condenser in a light microscope?
Focuses light from the illuminator source onto the specimen.
What does the iris diaphragm control?
The level of light reaching the specimen.
What is the first step in preparing a temporary slide?
Fixation: use 70% alcohol.
What is the advantage of using differential stains?
Improves contrast between different tissues and/or structures.
What are the steps in preparing a permanent slide?
- Fixation 2. Dehydration 3. Clearing 4. Embedding 5. Sectioning 6. Differential staining 7. Mounting.
What is the maximum magnification of Transmission EM (TEM)?
Several hundred thousand times, typical value = 500,000.
What is the key difference between TEM and Scanning EM (SEM)?
TEM produces images of cell ultrastructure; SEM produces images of cell surface and topography.
What type of image does a confocal laser scanning microscope (CLSM) produce?
Focussed images of thick specimens at various depths.
What is a key advantage of electron microscopes?
Greater resolution (~0.1nm) and higher magnifications.
What is a disadvantage of electron microscopes?
Specimens must be dead and placed in a vacuum.
What is the first step in using a light microscope?
Insert x10 eyepiece lens into the eyepiece.
What is an eyepiece graticule?
A scale bar placed in the eyepiece of a light microscope.
What is the purpose of calibrating the microscope and eyepiece graticule?
Converts graticule units into real units (mm, µm).
What is cell theory?
- A cell is the basic unit of all life forms 2. All living organisms are made up of one or more cells 3. Metabolic processes occur inside living cells 4. All new cells are derived from pre-existing cells 5. Cells possess genetic material which can be passed on to daughter cells 6. A cell is the smallest unit of an organism capable of surviving independently.
What is the impact of microscopes on biology?
Enables scientists to see & examine cells in detail.
What is the maximum resolution of SEM?
Typical value = 10 nm (5-50nm).
What is the function of the iris diaphragm in a light microscope?
Controls the level of light reaching the specimen.
What does 1 EPG unit equal in micrometers?
25 µm
1 EPG unit is derived from the calculation of 2000 µm divided by 80 eyepiece graticule units.
How is the width of a plant cell calculated using the eyepiece graticule?
Width of plant cell = 23 x 25 µm = 575 µm
This calculation uses the calibrated value of each eyepiece graticule unit.
What is the formula for calculating the field of view (FOV) in microscopy?
FOV = area of circle = πr² (units = mm²)
Assumes radius is measured in mm.
What are the general principles for biological drawings?
- Use a sharp pencil only
- Use clear, continuous lines
- Do not use any shading
- Accuracy is paramount
- Magnification & illumination should be considered
- Drawing should occupy at least half the available space
- Correct mistakes with a good quality eraser
- Include a title and scale
These principles are essential for all written exam papers.
What is the difference between a label and an annotation in biological drawings?
A label = what the structure is; An annotation = a descriptive comment
Annotations can include details like color, intensity of stain, and size.
What should you assess when evaluating the quality of a drawing in an exam?
- Are label lines ruled and horizontal?
- Are lines drawn with a sharp pencil?
- Are lines continuous?
- Is the magnification stated?
- Is there a scale bar?
- Are there arrow heads on label lines?
- Are all structures that are labelled visible?
These criteria help in determining the quality of the biological drawing.
What is the purpose of low power drawings in microscopy?
- Show the distribution of main tissues within an organ
- Identify tissues and delimit different tissues with boundary lines
- No individual cells should be drawn
- No gaps between tissues
Low power drawings typically provide an overview of tissue arrangement.
What is the purpose of high power drawings in microscopy?
- Show accurate detail as microscopy allows
- Draw only 3-5 representative adjacent cells
- Detail of only one cell may be needed
- Don’t shade in nuclei
High power drawings focus on cellular structures and arrangements.
What is the formula for calculating magnification?
Magnification = image size / actual size of specimen
Ensure all measurements are in the same units for accuracy.
What are the key differences between light microscopes and electron microscopes?
- Light Microscope: Uses light, max magnification x 1500, can view live specimens
- Electron Microscope: Uses electron beams, max magnification > x 1,000,000, cannot view live specimens
Electron microscopes have higher resolution but require more complex preparation.
What steps are involved in preparing a blood smear?
- Place a drop of blood on a slide
- Use a second slide to spread the blood
- Air dry the smear
- Stain with Leishman’s stain
- Rinse and air dry again
- Add a fixative
Proper preparation is crucial for observing individual cells.
What are the functions of blood?
- Delivery of oxygen
- Delivery of nutrients
- Removal of waste products
- Immunological protection
- Clotting
- Transport of signaling molecules
- Regulation of pH
- Distribution of heat
Blood plays a vital role in maintaining homeostasis.
What is the composition of blood?
53.3% plasma, 45% RBC, 0.7% WBC, 1% platelets
The composition indicates the different components and their proportions in blood.
What is the typical size range of erythrocytes?
6.2-8.2 µm diameter, 2-2.5 µm thick
Erythrocytes are designed for flexibility and efficient gas transport.
How are erythrocytes produced?
Produced in bone marrow by erythropoiesis, stimulated by erythropoietin (EPO)
The process takes approximately 7 days and results in reticulocytes.
What is the purpose of a haemocytometer?
To count cells in a sample
It provides a standardized method for cell counting in laboratory settings.
What steps are involved in loading a haemocytometer?
- Clean the haemocytometer
- Moisten the slide
- Insert the capillary tube into the cell suspension
- Fill the area between the coverslip and slide
- Equilibrate before counting
Proper loading ensures accurate cell counting.
What is the purpose of the haemocytometer?
To count cells in a suspension.
How do you prepare the haemocytometer for counting cells?
Place it on a damp tissue in a Petri dish for at least two minutes to equilibrate.
What magnification should be used first when examining the haemocytometer?
Low power objective lens.
What is the North-West rule in cell counting?
Count cells touching the middle line on the north or west side but not on the south or east side.
What is the typical volume of a haemocytometer?
0.004 mm³.
What formula is used to calculate the number of cells per cm³?
(mean number of cells in 0.004 mm³) x 250 x dilution factor.
What cell sizes can flow cytometry analyze?
Between 0.2-150 µm diameter.
What are the main applications of flow cytometry?
- Determining different cell types in heterogeneous populations
- Analyzing cell size and volume
- Analyzing activity of cell surface molecules
- Determining sample purity.
What is the role of the laser in flow cytometry?
To scatter light as cells pass through the beam.
What does Forward Scatter (FS) correlate with in flow cytometry?
Cell size.
What does Side Scatter (SS) indicate?
Density of the particle/cell.
How does flow cytometry differentiate between apoptotic and necrotic cells?
Using propidium iodide and Annexin V to assess cell viability.
What is the function of Annexin V in flow cytometry?
To detect apoptotic cells by binding to phosphatidylserine.
What are the advantages of using flow cytometers?
- Count a large number of cells quickly
- Determine different cell types
- Assess physical characteristics
- Measure DNA and protein content.
What are the disadvantages of using flow cytometers?
- Expensive to purchase
- Require large laboratory space
- Need highly trained technicians.
What is the structure of the cell surface membrane?
Typically 7 nm wide, mainly made of phospholipids with embedded proteins and cholesterol.
What is the primary function of the nucleus?
Contains genetic material (DNA) and carries instructions for protein production.
What is the function of the nucleolus?
Produces rRNA and assembles ribosomes.
What defines the rough endoplasmic reticulum (RER)?
Has ribosomes attached to its outer surface.
What is the primary role of the Golgi apparatus?
Modifies, sorts, and packages proteins and lipids.
What are lysosomes and their function?
Membrane-bound organelles containing hydrolytic enzymes for breaking down waste.
What is the role of centrioles in animal cells?
Organize microtubules during mitosis and meiosis.
What is the structure and function of chloroplasts?
Disc-shaped organelles involved in photosynthesis, surrounded by a double membrane.
What is the function of a large permanent vacuole in plant cells?
Acts as a reservoir for water and provides cell support.
What is the main role of the cell wall in plant cells?
Provides shape, strength, and support.
What is the main function of ribosomes in plant cells?
Synthesize proteins
Ribosomes are involved in the light independent stage of photosynthesis (Calvin cycle).
What does a large permanent vacuole in a mature plant cell act as?
A reservoir for water
It also contains dissolved salts, sugars, and organic acids, providing support to the plant cell.
What is the composition of the cell wall in plant cells?
Cellulose
Cellulose is a polysaccharide made from β-glucose arranged in microfibrils.
What is the primary role of plasmodesmata in plant cells?
Enable materials and chemicals to be transferred between cells
This is important in the symplast pathway.
What is circular DNA in prokaryotic cells characterized by?
Being naked and free DNA
It contains genetic information for replication and protein synthesis.
What are plasmids?
Very small circular pieces of DNA
They are capable of replicating independently of the main DNA and can carry antibiotic resistance genes.
What is the function of mesosomes in prokaryotic cells?
Possible site of aerobic respiration
Mesosomes are formed by invaginations of the cell surface membrane.
What are pili?
Hair-like structures that extend through the cell wall
They enable bacteria to adhere to each other or other surfaces.
What is the role of flagella in bacteria?
Enable motility and movement
Some bacteria have multiple flagella.
True or False: 80s ribosomes are found in prokaryotic cells.
False
80s ribosomes are only found in eukaryotic cells.
What are the seven characteristics of living cells represented by ‘MRS GREN’?
- Movement
- Respiration
- Sensitivity
- Growth
- Reproduction
- Excretion
- Nutrition
These characteristics are common to all living cells.
What is the role of the nucleolus in eukaryotic cells?
Synthesis of ribosomal subunits and assembly of ribosomes
It is involved in protein synthesis.
What is the function of the Golgi apparatus?
Processes, modifies, and packages proteins
It also forms lysosomes and Golgi vesicles for transport.
How do prokaryotic and eukaryotic cells differ in terms of DNA arrangement?
Prokaryotic cells have single circular DNA loops while eukaryotic cells have linear DNA arranged as chromosomes
This is a key distinction between the two cell types.
What are the three types of cytoskeletal filaments?
- Microfilaments
- Intermediate filaments
- Microtubules
Each type has distinct functions in maintaining cell shape and enabling movement.
What is the primary function of motor proteins?
Transport organelles and molecules within the cytoskeleton
Motor proteins move along cytoskeletal filaments using energy from ATP.
What is the fluid mosaic model of cell membranes?
Describes the structure and composition of cell membranes
It features phospholipids and proteins that can move laterally within the membrane.
What are the main components of cell membranes?
- Phospholipids
- Proteins
- Cholesterol
These components contribute to the structure and function of cell membranes.
What do phospholipids account for in cell membranes?
75% of all cell membranes
They form a bilayer that is crucial for membrane structure.
What is the role of cholesterol in cell membranes?
Regulates membrane fluidity
Cholesterol increases fluidity at low temperatures and stabilizes the membrane at high temperatures.
Fill in the blank: Passive movement across cell membranes includes ______.
Diffusion
It is a process that does not require ATP input.
What effect do unsaturated fatty acids have on cell membranes?
They prevent close packing of phospholipids at low temperature, keeping cell membranes fluid
This maintains movement of membrane proteins and substances across membranes.
What is diffusion?
Passive movement of molecules down the concentration gradient across a partially permeable membrane until equilibrium is reached.
What factors affect the rate of simple diffusion?
- Concentration gradient
- Size of molecule
- Kinetic energy of molecules
- Polarity of the molecule
- Surface area
Define facilitated diffusion.
Passive movement of molecules down the concentration gradient through specialized proteins across a partially permeable membrane.
What are channel proteins?
Integral proteins that form channels or pores, allowing specific ions to cross the membrane.
What is an example of molecules transported by facilitated diffusion?
Water soluble molecules and ions, e.g., Na+, Cl-.
What is active transport?
Movement of molecules against the concentration gradient requiring ATP input.
What is bioaccumulation?
The accumulation of molecules within the cell beyond equilibrium in active transport.
What distinguishes active transport from facilitated diffusion?
- Requires ATP
- Moves against the concentration gradient
- Accumulates molecules within the cell
What is endocytosis?
Process where the cell membrane folds in to form a small vesicle or vacuole.
What is phagocytosis?
The process by which cells take in solid material in large quantities.
What is pinocytosis?
The process by which cells take in liquid material in large quantities.
What is exocytosis?
The process of removing waste products or secreting useful products from the cell.
Describe the emulsion test for lipids.
Add ethanol to a sample, shake, then add distilled water and observe for emulsion formation.
What does a qualitative test for lipids indicate?
Presence or absence of a substance, avoiding false negatives.
What is a semi-quantitative emulsion test?
A test that scales the positive result as low/medium/high based on controlled sample quantity.
What is the purpose of a colorimeter in the beetroot experiment?
To quantitatively assess the leakage of betanin from beetroot cells over a range of temperatures.
What happens to membrane permeability at higher temperatures?
Increases due to denaturation of membrane proteins and disruption of the membrane structure.
How does ethanol affect cell membranes?
Causes membrane disintegration by forming temporary bonds with phospholipid heads.
What are limitations of the beetroot experiment?
- Damage to cell walls
- Differences in blotting techniques
- Variability in cylinder positioning
- Inconsistent swirling
What are improvements suggested for the beetroot experiment?
- Perform replicates
- Standardize cutting and blotting techniques
- Stir solution after removing the cylinder
What are betalins?
A class of red and yellow pigments found in beetroot that give color to plants.
What is the effect of increased kinetic energy on phospholipid molecules?
They move more, become spaced out, and create gaps in the cell membrane.
What causes betanin molecules to leak from beetroot cells?
Disruption of the tonoplast and cell surface membrane due to increased temperature.
