Module 2: Foundations In Biology Cells Flashcards
What two lenses does a light microscope have?
Objective lens
Eyepiece lens
Objective lens
Produces magnified image
Magnified again by the eyepiece lens
What is illumination?
Provided by light underneath the sample
Opaque specimens can be illuminated from above
Sample prep: dry mount
Solid specimens can be viewed whole/cut into thin slices (sectioning)
Specimens placed on a slide and cover slip placed over
Sample prep: wet mount
Specimens suspended in a liquid such as water or oil
Cover slip placed at an angle
Sample prep: squash slides
Wet mount is first prepared
Lens tissue used to gently press down the cover slip
Squash slides are a good technique for soft samples
Sample prep: smear slides
Edge of slide used to smear sample
Creates thin, even coating on other slide
Cover slip then placed over sample
Diffraction
Bending of light as it passes close to the edge of an object
How do stains work?
Increase contrast as different components of a cell take up stains to different degrees
Thecytosol
Aqueous interior of cells - often transparent
Preparing a sample for staining
Place on slide
Air dry
Heat fixed via flame
Specimen will adhere to microscope slide and then take up stains
How do crystal violet/methylene blue stains work?
Positively charged dyes are attracted to negatively charged materials in cytoplasm
How do conga red/nigrasin stains work?
They are negatively charged and are repelled by negatively charged cytasol
These dyes stay outside cells, leaving cells in stained against a stained background
What is the purpose of differential staining??
Distinguish between two types of organisms that would otherwise be hard to identify
What is the gram stain technique?
Used to separate bacteria into two groups
What is the acid-fast technique
Used to differentiate species of Mycobacterium from other bacteria
Production of pre-prepared slides: fixing
Chemicals are used to preserve specimens in as near-natural state as possible
Production of pre-prepared slides: sectioning
Specimens dehydrated with alcohols
Placed in a mould with wax/resin to form hard block
Can then be sliced thinly with a knife (microtome)
Production of pre-prepared slides: staining
Specimens also treated with multiple stains to show different structures
Production of pre-prepared slides: mounting
Specimens then secured to a microscope slide and a cover slip placed on top
Risk management of stains
Many stains used in the preparation of slides are toxic or irritants
What is electron microscopy
A beam of electrons is used to illuminate the specimen
What is different about electron microscopy
More detail of cell ultra structure can be seen because electrons have a much smaller wave length than light waves
Can specimen be damaged when using an electron microscope
Yes
Disadvantage of using an electron microscope
Very expensive
Require a controlled environment and dedicated space
TEM (transmission electron microscope)
Beam of electrons transmitted through specimen
Focussed to produce an image
Has best resolution with a resolving power of 0.5nm
SEM (scanning electron microscope)
Beam of electrons sent across the surface of a specimen
Reflected electrons are collected
Resolving power is 3-10nm so resolution is not as good
3D images produced
Sample prep for electron microscopes
Involves fixation using chemicals or freezing, staining with heavy metals and dehydration with solvents
Sample prep for TEM
Set in resin then sometimes restained
Sample prep for SEM
May be fractured to expose the inside
Cooked with heavy metals
Light microscope
Expensive or inexpensive
Inexpensive to buy/operate
Electron microscopes
Expensive/inexpensive
Expensive to buy/operate
Light microscope
Small and portable or large and installed??
Small and portable
Electron microscopes
Small and portable or large and installed???
Large and installed
Light microscope
Simple or complex sample prep
Simple sample prep
Electron microscope
Simple or complex sample prep
Complex sample prep
Light microscope
Vacuum required or not required
Vacuum not required
Electron microscope
Vacuum required/not required
Vacuum required
Magnification on light microscope
Up to x2000 magnification
Magnification on electron microscope
Over x500 000 magnification
Resolving power on a light microscope
200nm
Resolving power on an electron microscope
3-10 nm
Light microscope
Specimens living or dead?
Either living or dead
Electron microscope
Specimens living or dead??
Specimens dead
Artefacts
Visible structural detail caused by processing the specimen
Examples of artefacts
Air bubbles
Loss of continuity in membranes
Distortion of organelles
Empty space in cytoplasm
Mitochondria function
Aerobic respiration
Produce or release ATP
Self replicate
How many mitochondria does a typical cell have
More than 1000
Where is mitochondria found?
In the cytoplasm of a cell
Where are there large numbers of mitochondria
In the muscle and liver cells
Chloroplasts
Photosynthetic organelle
Function of a chloroplast
Absorbs wavelengths of light for photosynthesis
Function of the Rough Endoplasmic Reticulum (REM)
Protein synthesis (translation 2nd stage)
Function of Smooth Endoplasmic Reticulum (SER)
Lipid synthesis
Make steroid hormone (lipid based)
Examples of steroid hormones
Oestrogen
Testosterone
Progesterone
Function of the Golgi
Modifying and packaging the products
Transportation from RER to the Golgi
Protein uses vesicles
Vesicles leave the cell via the cell surface membrane and a protein is contained within this vesicle
Where are ribosomes found?
Free in cytoplasm
Attached to the cisternae
What do ribosomes do when they are free in the cytoplasm
They synthesise proteins to be used in a cell
What do ribosomes do when attached to cisternae
Used outside of the cell
1000mm = how many metres
1m
1000 ūm is how many mm?
1 mm
1000 nm is how many ūm??
1 ūm
What is the nucleus?
The information centre
Why does the nuclear membrane have pores?
The nuclear membrane is pitted with nuclear pores allowing transport of macromolecules from cytoplasm
What is the nucleolus?
The site of ribosome and RNA production
What is the chromatin?
Cells of DNA bound to protein in cell division
The chromatin aggregates to form chromosomes
Function of the centrioles
Produce spindle fibres
Why is the production of spindle fibres important??
Made in meiosis and mitosis
Separate chromosomes and chromatids
Cell surface membrane
Partially permeable
Forms a barrier
Controls what enters/leaves the cell
Has receptors for molecules
Recognition by immune system cells
How old are prokaryotic cells?
First appeared around 3.5 billon years ago
May have been among the earliest forms of life on earth
Extremeophiles
Scientists believe these early cells were adapted to living in extremes of salinity, PH and temperature
Today these organisms can be found in hydrothermal vents and salt lakes
Are prokaryotic organisms unicellular or multicellular
Unicellular with a relatively simple structure
Structure of a prokaryotic organism
DNA is not contained within a nucleus
Few organelles
Organelles they do have are not membrane bound
DNA in prokaryotes
Generally only have one molecule of DNA, a chromosome, supercoiled to make it more compact
What is a group of operons
Grouped genes on the chromosome
Ribosomes in prokaryotic cells
Ribosomes are smaller in prokaryotes than in eukaryotic cells
They are necessary for protein synthesis
Cell walls in prokaryotic cells
Have cell walls made from peptidoglycan
Complex polymer formed from amino acids and sugars
Where is the energy for the rotation of flagella from?
From the process of chemiosmosis
How is the flagella attached to the cell
Attached to the cell membrane
By a basal body and rotated by a molecular motor
Function of a molecular motor on a flagellum
A molecular motor caused the hook to rotate giving the filament a whip like movement, which propels the cell
How old are eukaryotic cells?
Appeared 1.5 billion years ago
Structure of eukaryotic cells
Much more complex than prokaryotic cells
DNA present in a nucleus and exists as multiple chromosomes which are supercooled and each one wraps round a number of proteins called histones
Role of the cartilage
Keep trachea and bronchi open
Prevent collapse under low pressure
C-shaped to allow expansion of oesophagus
Helps support the trachea whilst allowing it to move and flex during breathing
Goblet cells function
Secrete mucus, mucus traps pathogens, reducing the risk of lung infections
Ciliated epithelial cells function
Function of moving particles over epithelial surface in structures such as trachea, bronchi and nasal cavities
Move trapped particles up to throat
Smooth muscle function
Allows lumen to constrict by contracting
Elastic tissue function
When breathing in the fibres stretch to allow alveoli and airways to expand
When breathing out they recoil, helping to reduce the volume of alveoli and expel air from lungs
Blood vessels function
Many blood vessels to take substances to and from the alveoli
Deliver CO2 to alveoli for exhaling, remove O2 from alveoli and deliver to tissues
Maintain concentration gradient for diffusion, short diffusion distance
Squamous epithelial cells function
In alveoli
Allow oxygen from the air to enter the blood in the capillaries of the lung and provide thin surface for gaseous exchange
Why are there so many air sacs in the lungs??
Many alveoli are needed because they have a large SA and there is a gaseous exchange between air sacs and surrounding capillary blood vessels
What type of epithelium is in the walls of the air sacs
Squamous epithelium
