2.1 Cell Structure Flashcards
What is magnification?
How many times bigger the image is than the actual size.
What is resolution?
The ability to separate two objects visually, to see detail.
Why is the resolution of a light microscope limited?
The wavelength of visible light is 400 to 700 nanometres.
What is the role of the objective lens?
To capture light emitted or reflected by the specimen and focus the image.
What is the role of the cover slip?
To be placed over the specimen and protect the lens.
What is the role of the microscope slide?
For placing the specimen onto.
What is the role of the light source and mirror?
To reflect light up through the lens and eyepiece.
Why are specimens stained?
To make the components of a cell easier to identify (differential staining), to provide contrast against the background to make the structure more visible.
How is a light microscope specimen prepared?
Slice specimens to allow light to pass through, fix in wax if fragile before slicing.
How is an electron microscope specimen prepared?
Fixed specimen in gluteraldehyde, dehydrate with ethanol, embed in resin, slice thinly, stain with heavy metal, put on copper grid, place in vacuum before viewing so air particles don’t get in the way.
What is the equation for magnification?
Magnification = image size / actual size
How does a light microscope work?
Uses a number of lenses to view an image through the eye, light passes through the condenser lens then through the specimen, beam of light is focused through objective lens then through eyepiece lens.
How does a Transmission Electron Microscope work?
Generates beams of electrons, electrons pass through thin part of sample less easily so create contrast, sample dehydrated and stained with metal salts, electrons focused on photographic plate.
How does a Scanning Electron Microscope work?
Electrons are reflected off the surface of a metal- salt- stained sample, 3D shapes, can add false color with a computer, use to look at cell surfaces.
What are the advantages of a light microscope?
Relatively cheap, easy to use, portable, can observe living specimens.
What are the disadvantages of a light microscope?
Can’t be used to see very small structures, smaller magnification and larger resolution.
What are the advantages of a Transmission Electron Microscope?
Wavelength is a lot shorter than visual light so very high resolution, better magnification.
What are the disadvantages of a Transmission Electron Microscope?
Expensive, not portable, skills and training needed, vacuum needed to prepare slides, preparing slides is complex, image produced has no color and is 2D.
What are the advantages of a Scanning Electron Microscope?
You can see surface features in detail, better magnification and resolution, 3D image produced.
What are the disadvantages of a Scanning Electron Microscope?
Expensive, vacuum needed for sample preparation, large, skill and training needed, not portable.
What is a light microscope used for?
To look at whole cells and tissues, can see live tissue.
What is a Transmission Electron Microscope used for?
To look at organelles within cells.
What is a Scanning Electron Microscope used for?
To look at cell surfaces.
What features do animal cells and plant cells contain?
A nucleus, ribosomes, rough endoplasmic reticulum, cytoplasm, smooth endoplasmic reticulum, cell surface membrane, Golgi apparatus, mitochondria, vesicles.
What features do only plant cells contain?
Chloroplasts, cell wall, permanent vacuole.
What features do only animal cells contain?
Centrioles.
What is a nucleus?
Largest organelle, surrounded by double membrane called nuclear envelope, contains nucleolus, stores DNA as chromatin, site of DNA replication, controls protein synthesis and cell activities.
What is a nucleolus?
A small, dark structure in the nucleus that synthesises ribosomes.
What is a Rough Endoplasmic Reticulum ?
Cisternae, studded with ribosomes, space between filled with fluid that transports substances, site of protein synthesis.
What is the Smooth Endoplasmic Reticulum?
Cisternae, space between filled with fluid that transports substances, site of lipid synthesis.
What is the Golgi apparatus?
Cisternae, surrounded by vesicles, processes and packages all substances made by the RER and SER, creates vesicles for secretion.
What is a ribosome?
Tiny organelle, light and heavy sub-unit, either float free in cytoplasm or attached to RER, site of protein synthesis.
What is a lysosome?
A small, round organelle, contains digestive enzymes to digest invading cells or apoptosis, specific type of vesicle.
What is a vesicle?
Membrane bags that contain substances, made by the Golgi.
What are mitochondria?
Double membrane bound organelles, contain loop of the mother’s DNA, contain cytoplasm called matrix, sites of aerobic respiration, make ATP in inner folded membrane (cristae).
What are chloroplasts?
Double membrane bound organelles, more membranes stacked inside cells containing chlorophyll, contain cytoplasm called stroma, contain loops of DNA, site of photosynthesis.
What is a cellulose cell wall?
Made of polysaccharide cellulose in plants, has pores called plasmodesmata that connect cells together by there cytoplasm, gives cell support and structure, can function as a carbohydrate store.
What are centrioles?
Two bundles of mitochondria at right angles to each other, essential to cell division as enable movement of chromosomes, involved in movement of substances and formation of cilia.
What is a permanent vacuole?
A membrane containing liquid, pigments, waste, etc, keeps the cell turgid which gives support.
What are cisternae?
Flattened, membrane bound sacks.
What is the cytoskeleton?
The large network consisting of protein fibers and other molecules that gives shape and structure to cells in the body.
What is the role of the cytoskeleton?
Cell support, movement of cilia, flagella or whole cell, changing cell shape (cytokinesis, phagocytosis, endocytosis, exocytosis), muscle contraction, organelles moved or held in place, movement of chromosomes.
Where is a cytoskeleton present?
In all eukaryotic cells.
What are peroxisomes?
Vesicles that usually contain enzymes such as catalase and are moved around the cell by attaching to the cytoskeleton and being moved by protein motors (dynein).
What is division of labour?
Each organelle in a cell has a specific role within the cell.
What is an example of division of labour?
Protein synthesis.
What is the role of the nucleus in protein synthesis?
Contains DNA (protein making instructions).
What is the role of ribosomes/rRNA in protein synthesis?
Read instructions and make chains of amino acids.
What is the role of the Golgi in protein synthesis?
Modifies and packages proteins.
What is the role of vesicles in protein synthesis?
Transport proteins to cell membrane.
What is the role of the cell surface membrane in protein synthesis?
Releases proteins.
What are microtubules?
A structure in the cytoskeleton that can instigate cell movement.
What is tubulin?
A globular protein that can polymerise from the cell cytoskeleton.
What is tubulin essential for?
Movement of polypeptides through RER, movement of vesicles from RER to Golgi, movement of vesicles between cisternae of Golgi, movement of secretory vesicles from Golgi to cell surface membrane.
What is the cell wall of prokaryotic cells made from?
Peptidoglycan.
Where is ATP made in prokaryotic cells?
A mesosome (membrane).
What do prokaryotic cells have instead of a nucleus?
DNA free in cytoplasm (nucleoid), extra DNA loops called plasmids.
What covers a prokaryotic cell’s cell wall?
A capsule.
What external features can prokaryotic cells have?
Pili and flagella.
What are features of plasmids?
Replicated independently of a bacterium’s genophore (bacterial conjugation) and be the cause of antibiotic resistance, commonly used in genetic engineering to make copies of genes or large quantities of proteins or hormones.
How are prokaryotes different to eukaryotes?
Smaller (0.1-5 micrometres), DNA is circular and free in cytoplasm, naked DNA, smaller ribosomes (18-20 nanometre diameter), no ER present, very few organelles, non with double membrane, cell wall always present.
How are eukaryotes different to prokaryotes?
Bigger (up to 40 micrometres), DNA is in a nucleus, DNA is associated with proteins, forming chromosomes, bigger ribosomes (25-30 nanometres), ER present, many double membrane bound organelles, cell wall sometimes present.
