Chapter 1 Cells And Microscopy Flashcards
Define resolution.
Resolution is the minimum distance between two objects in which they can be viewed as separate.
Define magnification.
Magnification refers to how many times larger the image is compared to the object.
How to calculate magnification?
Magnification=
Size of the image / size of the real object
How to calibrate a microscope with an eye piece graticule?
- Line up stage micrometer and eye piece graticule (in eye piece) whilst looking through eye piece. One division on micrometer is equal to 10 micrometres.
- Check how many divisions in the eye piece graticule fit into one division on stage micrometer.
- If 4 EPG divisions fit into one stage micrometer division (which is worth 10 micrometres), we can work out how big is one EPG division, by doing 10 / 4.
- Remove stage micrometer, and use eye piece gracticule to measure size of specimen as you already know 1 EPG = 2.5 micrometres, so stage micrometer is no longer needed.
- When you change magnification and objective lens, we need to calibrate the microscope again.
- Why is differential staining used?
- Crystal violet and methylene blue are two stains used in the same way. How do they work?
- Nigrosin and Congo red are two other stains used in the same way. How do they work?
- Differential staining uses chemicals to stain different parts of a cell in different colours, to make them stand out, as they may be difficult to see.
- Crystal violet and methylene blue are positively charged, so they attract negatively charged materials.
- Nigrosin and Congo red are negatively charged so they cannot enter the cytoplasm of cells, as the cytoplasm [?] repels them. This makes them stain the background and the unstained cells stand out.
- What is gram staining?
- What stain is used to differentiate gram positive bacteria? How does it work?
- What stain is used to differentiate gram negative bacteria? How does it work?
- Why is gram staining essential?
- Gram staining is differential staining to differentiate gram negative and gram positive bacteria.
- Crystal violet staining is used for gram positive bacteria, which is fixed with iodine. The remaining stain is then washed away with alcohol. The gram positive bacteria turns blue / purple with this stain. This stain is retained due to the thicker peptidoglycan cell wall, which absorbs the dye.
- Gram negative bacteria cannot use crystal violet as this bacteria has thinner peptidoglycan cell wall. Instead, a safranin stain is used, which turns the gram negative bacteria red.
- Staining differentiates the 2 different bacteria, so medics can prescribe the right antibiotics for patients with bacterial infections. This is because the 2 bacteria reacts differently to antibiotics, as how they react is determined by the different cell walls.
What are the standard rules for a scientific drawing ?
> Drawing must be in pencil.
Title the drawing / diagram to show what you have drawn.
State magnification / use a scale bar.
Annotate cell components, cells and sections of tissue that are visible.
Do not sketch. Use solid lines that do not overlap.
Do not colour in or shade.
State the general properties of electrons microscopes (both TEM and SEM).
> Electron microscopes have a high resolution as the beam of electrons have a short wavelength. This means that organelles and internal structures can be seem with the microscope.
> Image is created by using an electromagnet to focus beam of negatively charged electrons.
> Electrons would be absorbed by air, so EM must focus electrons within a vacuum. This also means specimen must be in a vacuum; hence, the specimen should be non-living.
> Electron microscopes produces black and white images.
State the differences between a transmission electron microscope and scanning electron microscope.
> In TEM, the specimens studied should be thin and stained. This is because the electrons have to pass through the specimen. Some parts of the specimen absorbs the electrons, making some parts appear darker.
> In SEM, the specimens can be any size, as electrons are not passing through, but they bounce off the surface of the specimen and and scatter in different ways depending on the contour.
> Therefore, the image produced by TEM is a 2D image of the internal structure of cells. The image produced by SEM is 3D.
State the features of a laser confocal microscope.
Laser confocal microscope uses a focused laser beam to create a 2D image (or 3D image in different focal planes). As light is emitted from the specimen, it causes florescence. This microscope has benefits of high resolution and depth selectivity.
It enables scientists to view sections of tiny structures, which would be challenging to physically sections off.
State the structure and function of the nucleus.
Function
> Site of DNA replication and transcription.
> Contains genetic code of each cell.
> Site of ribosome synthesis.
Structure
> The membrane of the nucleus is a double membrane, which is called the nuclear envelope.
> The nuclear envelope has gaps in it, called nuclear pores, which allows substances to leave the nucleus and travel to the rest of the cell.
> The inside of the nucleus is filled with a nucleoplasm (granular, jelly like material). Within the nucleoplasm, is genetic material in the form of chromosomes, which are linear and also wound around a protein called histones.
> Within the nucleoplasm is a smaller sphere called the nucleolus. This is the site of ribosome synthesis.
Describe the structure and function of the endoplasmic reticulum (smooth and rough endoplasmic reticulum).
Structure
> Both types of endoplasmic reticulum has folded membranes called cisternae.
> Structure of RER differs to SER, because it has ribosomes on the cisternae, making it ‘rough’.
Function
> The RER is involved in protein synthesis.
> The SER is involved in the synthesis and store of lipids and carbohydrates.
Describe the structure and function of the Golgi Apparatus.
Structure
> Has folded membranes called cisternae.
Function
> Modifies proteins and packages them into vesicles. The vesicles carry proteins to where they are needed- in or out of the cell.
Describe the structure and function of lysosomes.
Structure
> Lysosomes are vesicles which contain hydrolytic enzymes.
Function
> Hydrolyses phagocytic cells.
> Completely breaks down dead cells.
> Exocytosis- releases enzymes to outside of cell to destroy material.
> Digest old and worn out organelles to reuse the materials.
Describe the structure and function of mitochondrion.
Structure
> Double membrane
> Inner membrane highly folded to form structure called cristae.
> Fluid in interior of mitochondrion called matrix.
> Loops of mitochondrial DNA.
Function
> Site of aerobic respiration.
> Site of ATP production.
