1) Cells and microscopy Flashcards
(91 cards)
1
Q
What is the typical magnification of a light microscope?
A
up to 1500x
2
Q
What is the typical resolution of a light microscope?
A
limit of 200nm
3
Q
How can resolution be improved?
A
use radiation with a shorter wavelength
4
Q
Define magnification
A
the number of times larger an image appears compared to the real specimen
5
Q
Total magnification = ?
A
eye piece magnification x objective magnification
6
Q
Magnification = ?
A
size of image / size of object
7
Q
Define resolution
A
the ability to distinguish between two distinct objects separately and to see detail
8
Q
1mm = _m?
A
1 x 10^-3
9
Q
1μm = _m?
A
1 x 10^-6
10
Q
1nm = _m?
A
1 x 10^-9
11
Q
Why are stains used?
A
to make different parts of the specimen stand out more clearly as often colourless and almost transparent
12
Q
What colour does iodine solution turn starch grains?
A
blue-black
13
Q
Name two stains which can be applied to living cells directly
A
methylene blue
iodine solution
14
Q
Some specimens need to be fixed with _ or _ to make proteins and nucleic acids insoluble (killing cells)
A
acetic acid
alcohol
15
Q
Give 4 features of cell theory
A
- the cell is the basic unit of all life forms (uni/multicellular) and the smallest unit capable of surviving independently
- metabolic processes take place inside cells
- new cells are derived from old cells
- cells possess genetic material passed on from parent to daughter cells
16
Q
Give the journey of light through a light microscope
A
bulb under stage -> condenser lens -> specimen -> objective lens -> eyepiece lens
17
Q
Why does a light microscope contains one or more lenses?
A
to focus light into the eye
18
Q
Give 3 advantages of a light microscope
A
- observation of a wide range of specimens (inc. living), smear preparations and thin sections of tissue
- easy to use (no specialist training required) and transport
- relatively inexpensive
19
Q
Give 1 disadvantage of a light microscope
A
limited resolution so most internal cellular structures are not visible
20
Q
Define electron microscope (EM)
A
microscope that uses a beam of e- as its source of radiation to view a magnified image of an object
21
Q
An electron microscope has a greater _ than a light microscope
A
resolution
22
Q
Describe how an electron microscope works (3 points)
A
- electrons focused onto a fluorescent screen which emits visible light where electrons hit
- forms a photomicrograph (visible image on screen)
- final images are black, grey and white however, colour can be added by specialist computer programs to produce false-colour electron micrographs
23
Q
Give 3 features of a transmission electron microscope (TEM)
A
- thinner specimens (e- less penetrating)
- heavy metals are used to stain specimens (large +ive nuclei scatter e- so don’t hit fluorescent screen and leave a dark area) so structures that take up stain appear as dark images
- 2D, black + white image
24
Q
Give 4 features of a scanning electron microscope (SEM)
A
- e- don’t pass through specimen, instead are reflected off its surface
- beam of e- passed back and forth over surface of specimen in regular pattern
- pattern of reflected e- / scattered e- reflects contours of specimen
- 3D image produced with computer analysis
25
Why would a confocal microscope be used?
to obtain high resolution images and 3D reconstructions
| to produce focused images of thick specimens at various depths using optical sectioning
26
What can fluorescent markers be used for?
the detection of biological objects
27
Name 5 key parts of an electron microscope
```
electron source
magnetic condenser
magnetic objective
magnetic projector
fluorescent screen
```
28
Give 1 advantage of an electron microscope
greater resolving power (0.1nm) with a higher magnification means smaller objects can be seen in more detail
29
Give 5 disadvantages of an electron microscope
* large + expensive
* requires trained personnel and specially designed room
* specimens in near vacuum environment (air molecules absorb e-) so must be dehydrated + dead
* complex staining process
* artefacts may occur due to preparation techniques
30
What does using a preserved form of specimen enable?
the specimen can be cut into sections and treated with a variety of stains to reveal different structures within the tissues and cells
31
Name the 3 stages temporary slide preparation
fixation
staining
mounting
32
What 2 key things does temporary slide preparation require? Why?
70% alcohol and thin glass coverslip
| to exclude dust and air; to protect high power objective lens of microscope
33
Name the 3 stages permanent slide preparation
```
fixation
dehydration
clearing
embedding
sectioning
staining
mounting
```
34
What will a specimen be mounted in if the specimen is likely to dry out or a prolonged examination is likely?
glycerine
35
Which type of blood cell can clearly be seen under a microscope?
erythrocytes (red blood cells)
36
Why do white blood cells require staining?
to distinguish between the different types by showing differences in the shapes of their nuclei
37
What do different structures vary in?
the type / quantity of stain they take up
38
What is the benefit of the staining process being automated in a laboratory?
allows many slides to be prepared at the same time
39
Why may a blood smear be prepared and examined?
to observe the appearance of blood for diagnostic tests (identify cells and pathogens present)
40
Name 3 types of section
longitudinal
transverse
oblique
41
Name 3 differential stains for plants, their final colours and what type of tissue each are suitable for
eosin -> red = cellulose
toluidine -> blue = lignin
or -> purple = cellulose
iodine KI -> blue-black = starch
42
Why is toluidine used for plant vascular tissue?
stains lignified cell walls blue and cellulose cell walls purple
to allow xylem vessels to be distinguished
43
Name 2 Romanowsky stains for blood
Leishman's stain
| Wright's stain
44
Give the 5 steps for using Leishman's stain
1. blood allowed to dry
2. fixation with methanol
3. flooded and left for 2 mins
4. diluted with water and left for 5-7 mins
5. washed until pale pink to the naked eye
45
When is Wright's stain used?
for differential white blood cell counts when infections suspected
46
Give a brief 1 sentence description of how a blood film / smear is made
a sample of blood is spread onto a microscope slide (usually by machine)
47
What happens if a blood smear is too thick?
individual cells cannot be seen
48
What happens if a blood smear is too thin?
small number of cells may not be representative
49
Give the 5 steps for preparing a blood smear by hand
1. small drop of blood at the end of a sterile, clean and dry microscope slide
2. spreader (sterile slide) pushed along slide at a 30 degree angle to spread blood
3. label with patient's details
4. dry in air (cells stick to slide)
5. fixative to apply cells
50
What are the 4 key components of the blood?
plasma
red blood cells
white blood cells
platelets
51
What are the 6 components of blood plasma?
```
water
proteins
glucose
mineral ions
hormones
carbon dioxide
```
52
What are the 7 key functions of the blood?
* delivery of oxygen and nutrients to tissues
* removal of waste from tissues
* immunological protection
* clotting
* transport of cell signalling molecules (e.g. hormones)
* acting as a buffer to regulate body pH (acidity)
* distribution of heat to regulate core body temperature
53
How should biological drawings be drawn? (4)
in pencil
single, clear continuous line
labels and annotations
total magnification used
54
What are the 2 types of leucocytes?
granulocytes and agranulocytes
55
What type of blood cell is an example of a granulocyte?
neutrophil
56
What 3 types of blood cell are examples of agranulocytes?
monocytes
lymphocytes
macrophages
57
What is the function of erythrocytes?
deliver oxygen from lungs to the body and carbon dioxide from tissues to lungs
58
Where are erythrocytes developed?
in the bone marrow
59
How are erythrocytes developed?
from erythropoietic stem cells by erythropoiesis (stimulated by erythropoietin, EPO)
60
How long does the development of erythrocytes take?
7 days
61
What are immature erythrocytes called?
reticulocytes
62
How can red blood cells be identified?
methylene blue stain
63
How long do erythrocytes circulate for?
100 - 120 days
64
Give 3 key features of erythrocytes
* contain haemoglobin (binds reversibly with oxygen to form oxyhaemoglobin)
lacks nucleus and most organelles so...
* large surface area to volume ratio
* biconcave (flexible to squeeze through capillaries)
65
What is the diameter of an erythrocyte?
6.2 - 8.2 μm
66
What is the width of an erythrocyte at its thickest point?
2 - 2.5 μm
67
What two features of an erythrocyte should be included on its biological drawing?
cell surface membrane
| cytoplasm (stained darker at edges and lighter in centre)
68
What is an alternative name for platelets?
thrombocytes
69
What is the function of platelets?
contribute to blood clotting and clot formation
70
Where do platelets develop?
in bone marrow
71
How long to platelets circulate for?
6 - 7 days
72
Give 3 features of platelets
biconcave discs of cytoplasm fragments surrounded by a cell surface membrane
no nucleus
appear as dark purple spots when stained
73
What is the diameter of a platelet?
2 - 3 μm
74
What is the function of leucocytes?
immunological protection
75
Describe granulocytes
contain granules (often lysosomes) in their cytoplasm which stain differently
76
Describe agranulocytes
absence of granules in cytoplasm
77
Leucocytes are _ in size than erythrocytes but _ abundant
larger
| less
78
What is the function of neutrophils?
defend against fungal / bacterial infection by phagocytosis (engulfing / breaking down bacteria)
79
How long do neutrophils circulate for? Why?
5 days
| unable to renew lysosomes so die after breaking down a few pathogens
80
Give 1 key feature of a neutrophil
multi-lobed nucleus - increases flexibility to be able to leave capillaries by squeezing through fenestrations in the capillary wall
81
What 3 features of an neutrophil should be included on its biological drawing?
cytoplasm - stained light blue
cell surface membrane
multi-lobed nucleus - stained deep blue; no. of lobes vary between 2 + 5
82
What are lymphocytes characterised by?
large, deeply stained nucleus surrounded by relatively small cytoplasm
83
What are the 2 types of lymphocyte?
B and T
84
What is the function of B lymphocytes
produce immunoglobins (antibodies)
85
Name the 3 types of T lymphocytes
helper T cells
cytotoxic T cells
natural killer cells
86
What is the function of helper T cells?
produce cytokines and co-ordinate immune response
87
What is the function of cytotoxic T cells?
bind to antigens on virus infected / tumour cells and destroy them
88
What 3 features of an neutrophil should be included on its biological drawing?
cell surface membrane
nucleus - circular; stained dark purple; large
cytoplasm - small quantity; pale purple
89
What is the function of monocytes?
phagocytosis
leave bloodstream and differentiate into tissue macrophages (remove cell debris and attack microorganisms) found in lungs, lymph nodes and liver
90
Monocytes circulate for a _ time than neutrophils because _?
longer
| they are able to replace their lysosomes
91
What 3 features of an neutrophil should be included on its biological drawing?
cell surface membrane
nucleus - darkly stained; kidney bean shaped
cytoplasm - stained purple
