1 Cell structure Flashcards
1
Q
How to prepare a wet mount slide (using an epidermis from the scale leaf of an onion)
A
- Use forceps to peel off a piece of epidermal tissue (one cell think) from the concave side (inner side) onto the center of a microscope slide
- Add a drop of water and use forceps/mounted needle to help spread out the tissue to obtain a flat layer with no creases
- Place a coverslip at an angle to the slide and move it slowly towards the tissue until water runs under the edge of the slip. Use the forceps/mounted needle to lower the coverslip onto the tissue at an angle to prevent air bubbles forming
- Add a drop of iodine solution to the slide against one edge of the coverslip
- Place a piece of filter paper against the other side of the coverslip so that it can soak up some of the water and “pull” some of the iodine solution to stain a portion of the epidermis (irrigation)
- Carefully blot up any fluid on top of the coverslip before viewing using the microscope
2
Q
What to do if there are any air bubbles
A
if there are any air bubbles, they may be removed by gently tapping the coverslip with the other end of the mounted needle
3
Q
What structures in plant and animal cells are not visible using a light microscope and why?
A
- Cell surface membrane of animal cells
- Tonoplast of plant cells
- They are too thin to interfere with the light waves and so cannot be seen directly but with the use of stains these structures can be observed indirectly
- To see the mitochondrion and Golgi body a magnification of around x1500 is required
4
Q
How to draw cells
A
- Use the available space, but leave room for labels with ruled label lines
- Use an HB pencil to produce thin, clearly visible lines
- Draw continuous lines
- Draw complete cells and include any structures that are visible (do not shade)
- Make sure that the proportions of cell structures are the same as in the cells you are viewing
- Label the cell structure/annotate
5
Q
How to use an eyepiece graticule and stage micrometer scale
A
- The graticule is a glass disc which is placed in the eyepiece of a microscope
- A scale is etched on the disc which is typically 10mm long and is divided into 100 subdivisions
- Needs to be calibrated first for a particular objective lens
6
Q
Conversions for microscope measurements
A
cm, mm, um, nm (x10, x 100, x 1000)
7
Q
How to calibrate the eyepiece graticule
A
- Need to use a stage micrometer which has an etched scale of 2mm long and its smallest subdivisions are 0.01 mm (10um)
- When the eyepiece graticule scale and stage micrometer scales are lined up, the distance between the divisions on the eyepiece graticule can be calculated:
8
Q
How to calculate:
A
- For example, on the micrometer scale, 10 units are equivalent to 40 units on the graticule scale
- Therefore, one unit on the micrometer scale equals 4 units on the graticule scale
- As each unit on the micrometer scale is 10 um, each unit on the graticule equals 10/4=2.5 um
9
Q
What is magnification?
A
- the number of times larger the image is than the actual size of the cellular material
- Magnification beyond x1500 with a light microscope does not provide any more detail, whereas with an electron microscope, it is possible to obtain clear images at magnifications up to x500 000
10
Q
How to calculate magnification?
A
I over AM triangle
11
Q
What is resolution?
A
- the ability to distinguish between two points
- The minimum distance apart that two objects can be in order for them to appear as separate items
- The higher the resolution the clearer, sharper and more detailed the image produced is
12
Q
Compare light and electron microscopes
A
on notes
13
Q
Compare the 2 types of electron microscopes
A
on notes
14
Q
The nucleus and its parts
A
- Usually spherical and is between 10 and 20 um in diameter
- Contains 4 parts: nuclear envelope, nuclear pores, chromatin, and nucleolus
15
Q
Nuclear envelope
A
- Double membrane that surrounds the nucleus
- Its outer membrane is continuous with the endoplasmic reticulum and ribosomes on its surface
- Controls the entry and exit of materials
16
Q
Nuclear pores
A
- Allows the passage of large molecules (mRNA) out of the nucleus, but are too small to allow to allow DNA to leave
- Around 3000 pores in each nucleus and are 40-100 nm in diameter
17
Q
Nucleolus
A
Small spherical region/regions that manufacture rRNA and assemble the subunits of the ribosome
18
Q
Chromatin
A
- The diffuse, thread-like form that chromosomes take up when the cell is not dividing
- When the cell divides the chromatin condenses into chromosomes
- Chromatin is composed of DNA complexed with histone proteins
- Nucleoplasm surrounds it
19
Q
The chloroplast and its parts
A
- Function is photosynthesis
- Found in plant cells
- Flat discs that are usually 3-10 um in diameter and 1 um thick
- Contains 4 parts: chloroplast envelope, grana, stroma, and starch grains
19
Q
Function of the nucleus
A
- Contains genes
- Produces ribosomal subunits
- Controls protein synthesis (through the production of mRNA) by switching genes on/off
- Location for DNA replication before a cell divides
- With its envelope, the nucleus protects the DNA from the rest of the
20
Q
Envelope
A
Double membrane which controls the entry and exit of substances
21
Q
Grana
A
- Each is made up of thylakoids (stack of flattened sacs)
- The thylakoid membranes contain chlorophyll molecules that absorb light energy in the light-dependent stage and produce ATP
22
Q
Stroma
A
- A colorless, jelly-like matrix that contains enzymes necessary for light-independent stage
- Lipid globules are present
- Small circular DNA molecules that contain 70S ribosomes which allow some chloroplast proteins to be made are present
23
Q
Starch grains
A
Act as temporary stores of glucose which are produced during photosynthesis
