Topic 2.1 Flashcards
In order to investigate onion cells, a stained temporary mount was made. Suggest a food stain to use
Iodine solution or methylene blue
Why do onion cells need to be stained
To observe the cells
Nuclei and cell walls absorb the stain more strongly
So they can be distinguished
What is the advantage of making a temporary mount of cells
Temporary mounts are quick to prepare: the cells can be observed whilst alive
A scientist wishes to study yeast cells using a light microscope. How should the slide be prepared
To create a temporary mount, yeast cells should be placed on a slide with a droplet of iodine solution to stain the organelles. A cover slip should be placed over the cell. Remove air bubbles
Stains are used for a number of different purposes when preparing slide. Give 3 examples of how they can be used
-increases contrast, so different parts of a cell can be distinguished
- to observe the location of certain chemicals in the cell
- to differentiate between organisms that can be hard to tell apart
Starch granule
Carbohydrates stored in amyloplasts (plastids specialised for storage). Plastids are unique to plants. Non photosynthetic plastids usually store materials.
Chloroplast
Specialised plastids containing chlorophyll. They contain dense stacks of membrane (grana) within a colourless Stroma. They are the site of photosynthesis
Cell wall
A semi-rigid structure outside the plasma membrane. It is composed of cellulose and supports the cell
Made of peptidoglycan
Mitochondria
Ovoid (oval shape) structures bounded by a double membrane called the envelope. They are the cell energy transformers. Converting chemical energy into ATP. The inner membrane is folded to form cristae with matrix on the inside containing all the enzymes needed for respiration
Cytoplasm
Contains dissolve structures, enzymes and the cell organelles and structures. The site of translation in the cell
Plant cell- endoplastic reticulum
A network of tubes and flattened sacs, may be smooth or have attached ribosomes
Nuclear membrane
A double layered structure with pores
Ribosomes
Manufactures proteins (site of protein production), made of RNA and proteins. May be free in the cytoplasm or attached to endoplasmic reticulum
Golgi apparatus
A series of flattened, disc-shaped sacs, stacked one on top of the other and connected with the ER. The Golgi stores, modifies and packages proteins. It tags proteins so that they go to their destination
Nuclear pore
Allows communication between the nucleus and the rest of the cell
Rough endoplasmic reticulum
Primary site of protein synthesis, a series of flattened sacs enclosed by a membrane with ribosomes on the surface, it folds and processes proteins made on ribosomes
Smooth endoplasmic reticulum
A site for lipid and carbohydrate metabolism, including hormone synthesis, a system of membrane-bound sacs, it processes and produces lipids
Lysosome
A vesicle containing digestive enzymes, bounded by a single membrane, contain transport enzymes that break down food and foreign matter
Centrioles
Are associated with nuclear (cell) division. They are hollow cylinders composed of a ring of microtubules arranged at right angles to each other
Plasmids
Small, circular DNA molecules that can reproduce independently. They can transfer from one cell to another and between species ( conjugation ) this property accounts for the transmission of antibiotic resistance between bacteria, plasmids are also used as vectors in genetic engineering.
Fimbriae
Hairlike structures that are shorter, straighter and thinner than flagella, they are used for attachment
Glycocalyx
Viscous gelatinous layer outside the cell wall
Composed of polysaccharide and or polypeptide, if it is attached to the wall it is called a capsule. Protects the bacteria from the hosts immune attacks
Flagellum
Used for locomotion (movement), tail-like structure which rotates to move the cell
Sample preparation- dry mount
Solid specimens are viewed whole or cut into very thin slices ( called sectioning) the specimen is placed on the centre of the slide and a cover slip is placed over the sample. Hair, pollen, dust and insect parts can be used
Sampling preparation-wet mount
Specimens are suspended in a liquid such as water or an immersion oil. A cover slip is placed on from an angle. Aquatic samples and other living organisms can be viewed this way
Sampling preparation-Squash slides
A wet mount is prepared, then a lens tissue is used to gentle press down the cover slip
Sampling preparation-smear slides
The edge of the slide is used to smear the sample, creating a thin, even coating on another slide. A cover slip in placed over the sample-blood.
Nucleus
Surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus. The nucleus also contains chromatin and a nucleolus which is the site of ribosome production
Golgi apparatus
A series of fluid filled, flattened and curved sacs with vesicles surrounding the edges, it processes and packages proteins and lipids, also produces lysosomes
Cytoskeleton
Provides mechanical strength as well as aiding transport within cells and enabling cell movement
Protein transport
1.Proteins are produced on ribosomes
2.proteins which are provided on the surface of RER are folded and processed in the RER
3. The proteins are transported from the RER to the Golgi apparatus in vesicles
4. They are modified in the Golgi apparatus
5. Golgi apparatus packages proteins into vesicles to be transported around cells to where they’re required
6. Some of the proteins such as extra cellular enzymes leave the cell by exocytosis
Capsule
Protective slimy layer which helps retain moisture and adhere to surfaces
Pili
Hair-like structures which attach to other bacterial cells
Eyepiece graticule
Acts like a ruler, allowing structures to be measured under a microscope.
stage graticule ( stage micrometer )
A microscope slide with an accurate measuring scale, used to calibrate the value of the eyepiece divisions at different magnifications
What are the 5 steps to calibrate an eyepiece graticule
- Set up microscope to the required magnification to view sample
- Place a stage graticule on the stage
- Line up the 2 scales (the stage and eyepiece graticules)
- Count the number of divisions on the eyepiece graticule equivalent to each division on the stage micrometer
- As the length equivalent to each division on the stage micrometer are known
Why is staining used in microscopy
Provides contrast to distinguish between different structures in the sample
What is differential staining
When multiple stains are used, and each stain binds to a specific cell structure, staining each cell differently so the structures can be easily identified
Acetic orcein
Binds to DNA and stains chromosomes dark red
Eosin
Stains the cytoplasm dark red or pink
Iodine
Stains starch blue-black ( appears violet under microscope)
Iodine in potassium iodide solution
Stains cellulose yellow
Haematoxylin
Stains RNA/DNA a purple/blue colour
Methylene blue
Is an all-purpose stain, often used to stain DNA blue
What is a wet mount used for
Live specimens such as aquatic animals
What is a dry mount used for
Specimens like hairs, parts of insects, pollen, parts of flowers
Wet Mount technique
- Use a pipette to put a drop of water on a slide
- Use tweezers to place specimen in water
- Put the cover slip on by standing the it upright on the slide, next to the water droplet
- Carefully tilt it down onto specimen
- Avoid air bubbles ( they obstruct view of image)
- Add stain (making sure its not toxic to specimen)
Dry mount technique
1.Slide specimen thinly so light can pass through
2.use tweezers to put on slide
3 place coverslip on top
Using a light microscope
- Clip slide onto stage
- Select the lowest power objective lens
- Use the coarse adjustment knob to move the objective lens into focus to just above the slide
- Look down eyepiece and adjust focus, moving lens away from slide using the fine adjustment knob, until clear image appears
- If higher magnification is needed, swap to a higher powered objective lens and refocus
How do you measure the diameter of an irregularly shaped object
Measure the greatest distance from one side to another
How should drawings be done; microscopy
-no shading
-labelled
-take up at-least half the page
-label lines should be horizontal, drawn with a rule, exactly touch object, no arrowheads
-drawing lines completely connected
-a scale should be given (magnification)
-drawn in pencil
