2.1.1 Cell structure Flashcards
Describe how a light microscope works
Light is transmitted through thin layer of a specimen supported on a glass slide
The light is focused through the eyepiece leans and objective lens to produce a magnified image
Produces 2D coloured images
Living samples
Resolution (200nm) and magnification (1500x) are low
Cheap and fast
Describe how a transmission electron microscope works
A beam of electrons is passed through a specimen
The beam of electrons is focused to produce a magnified image
Produces 2D black and white images
Non-living samples
Resolution (0.2nm) and magnification (500,000x) are high
Expensive and requires training
Describe how a scanning electron microscope works
A beam of electrons is reflected across the surface of the specimen
The reflections are collected to produce a magnified image
Produces 3D black and white images
Non-living specimens
Resolution (10nm) and magnification (100,000x) are high
Expensive and requires training
State dry mount slide preparation of a solid specimen
Solid specimen is cut into thin slices
The specimen is placed on the centre of the slide
Apply a stain to the specimen
The cover slip is placed over the sample using a scalpel or forceps
Explain why staining is used in light microscopy
Differential staining: The increase contrast allows the components to become distinguished and identified
Outline how a light microscopic image must be drawn and annotated
Use sharp pencil, no shading, smooth lines
State title, scale bar, magnification
Label lines must not cross or have arrowheads Label lines must be drawn with a ruler
Drawing must take up at least half the page
State the magnification formula
Magnification = size of image/actual size of object
Define magnification and resolution
Magnification - factor by which the image is larger than the actual specimen
Resolution - The ability to distiguish between two structures
Describe the relative differences in magnication and resolution between light microscopy, TEM and SEM.
Learners are not required to recall exact resolutions or magnification
Light microscopy - low magnification and resolution
TEM and SEM - high magnifictaion and resolutiton
Explain the calibration and use of the eyepiece graticule and stage micrometer in light microscopy
- Line up stage micrometer and eyepiece graticule
- Count how many divisions on the eyepiece graticule are in one division of the micrometer
- Each division on the micrometer is 10μm. Calculate the length of one division on the eyepiece graticule
- The calibration can be used to measure the actual size of an object in light microscopy
Describe the structure of the nucleus
Outline functions of Nuclear envelope, Nuclear pores and Nucleolus
Nuclear envelope - double membrane which surrounds the nucleus
Nuclear pores - allow substances in and out of the nucleus
Nucleolus - within the nucleus and contains proteins and RNA that assemble ribosomes
Outline the function of the nucleus
Outline the function of DNA molecules within the cell
The nucleus contains DNA molecules
DNA directs the synthesis of proteins within the cell
DNA controls the metabolic activities within the cell
Describe the structure of the endoplasmic reticulum
Rough and smooth
A compact structure made up of cisternae
Cisternae - Network of flattened membrane-bound sacs
Outline the function of the endoplasmic reticulum
Rough and smooth
Rough - synthesis and transport of proteins
Smooth - synthesis of lipids and carbohydrates
Describe the structure of the golgi apparatus
A compact structure made up of cisternae
Cisternae - Network of flattened sacs enclosed by membranes
Outline the function of the golgi apparatus
Modifies proteins
Packages proteins into vesicles
Describe the structure of ribosomes
Ribosomes are non-membrane bound organelles made up of RNA molecules made in the nucleolus of the cell
Outline the function of ribosomes
Protein synthesis
Describe the structure of mitochondria
Outline the name and function of the inner membrane and fluid interior
The mitochondria consists of a double membrane
Folded inner membrane called cristae, containing enzymes for aerobic respiration
Fluid interior called the matrix, containing mitochondrial DNA (so mitochondria can produce their own enzymes and reproduce themselves)
Outline the function of the mitochondria
Mitochondria is the site of aerobic respiration to produce ATP
Describe the structure of chloroplasts
Describe thykaloids, granum, lamallae and stroma
Chloroplasts consist of a double membrane
Thykaloids - network of membranes, which forrm flattened sacs
Grana - stacks of thykaloids, containing chlorophyll
Lamallae - membranes which join granum together
Stroma - fluid interior, containing chloroplast DNA
Outline the function of chloroplasts
Site of photosynthesis
Describe structure and function of lysosomes
Lysosomes are specialised vesicles
Lysosomes contain hydrolytic enzymes which breakdown waste material in the cell
Outline the structure and function of the cell wall
Plant, bacterial and fungal
Plant - Cellulose
Bacterial - Peptidoglycan
Fungal - Chitin
The cell wall provides structure and support to the cell
Contrast eukaryotic cells and prokaryotic cells
Prokaryotes
Prokaryotes
- small, make up unicellular organisms
- no membrane bound organelles, no nucleus
- unassociated circular DNA
- small ribosomes (70s)
- peptidoglycan cell wall
Contrast eukaryotic cells and prokaryotic cells
Eukaryotes
Eukaryotes
* large, make up multicellular organisms
* membrane bound organelles, contains nucleus
* associated linear DNA
* large ribosomes (80s)
* cellulose/chitin cell wall
Outline the function of organelles involved in protein production and secretion
Nucleus - DNA molecules code for specific proteins
RER - Site of protein synthesis
Golgi apparatus - Proteins modified and packaged
Vesicles - Transportation of proteins around the cell along the cytoskeleton
Plasma membrane - Secretory vesicles fuse to membrane for secretion by exocytosis of proteins
Describe the structure and function of the flagella and cilia
The cytoskeleton enables cell movement via cilia and flagella
These structures are both hair-like extensions that protrude from the cell surface and contain microtubules that are responsible for moving them as they contract
Describe the stucture and function of centrioles
Centrioles consist of small, hollow cylindrical proteins called microtubules.
Centrioles help chromosomes separate during cell division.
Centrosomes migrate to oppoite sides of poles and produce spindle fibres to separate chromosomes
Outline the functions of the microfilaments of the cytoskeleton
Microfilaments - solid strands that are mostly made of the protein actin.
Microfilaments aid in cellular movement and cell contraction.
Outline the function of microtubules in the cytoskeleton
Microtubules are tubular (hollow) strands that are mostly made of the protein tubulin. Organelles and other cell contents are moved along these fibres.
Microtubules aid in intracellular movement by forming ‘tracks’ along which organelles can move e.g. vesicles through the cell, chromosomes along spindle fibres.
Outline the function of intermediate fibres in the cytoskeleton
Intermediate fibres provides the cell with mechanical strength, forming a kind of ‘scaffolding’ that helps to maintain the shape of the cell.
It also supports the organelles, keeping them in position.
Outline the general importance of the cytoskeleton within the cell
- Mechanical strength of the cell
- Transport within the cell
- Cell movement
Describe how a laser scanning confocal microscope works
A specimen is treated with a fluorescent dye
Fluorescence is the absorption and re-radiation of light
A single spot of focused light (laser) moves across a specimen
The light is re-radiated by fluorescent components of the specimen
The re-radiated light is focused through a narrow pin-hole and detected to produce a magnified image
Can produce 2D images or 3D images by creating images from different planes
Produces coloured images
High resolution as the narrow pinhole blocks out any re-radiated light that is out of focus
Why may a wet mount be used for a microscopic slide
To prevent dehydration of a specimen
Why is it important for a specimen to be thin for a light microscopic slides and what are the methods for achieving this?
To allow individual cells to be seen
To allow maximum light to penetrate the tissue
Using a sharp blade to ensure the specimen is thin
Selected the thinnest slides for observation
Why must a cover slip be placed at an angle over a specimen when preparing a microscopic slide?
To prevent the formation of air bubbles
