CHAPTER 2 - BASIC COMPONENTS OF LIVING SYSTEMS Flashcards
Microscopy, Magnification and Calibration, More microscopy, Eukaryotic cell structure, Ultrastructure of plant cells, Prokaryotic and Eukaryotic Cells
1
Q
How many types of microscopes are there?
A
3 - Light, Transmission electron micrscope, Scanning Electron Microscope
1
Q
What is Cell theory
A
Both plants and animal tissue is composed of cells
Cells are the basic unit of life
Cells only develop from existing cells
2
Q
Benefits of Light Microscopy
A
Easily Available
Cheap
Can be used out in the field
Can observe both dead and prepared specimens
3
Q
How many lenses does a (compound) light microscope have?
A
2 - Eyepiece and objective
4
Q
How many different slides preparation types are there?
A
4 - Wet mount, Dry Mount, Squash slides, Smear Slides
5
Q
How are Dry Mounts prepared?
A
Solid Specimens are viewed whole or cut into very Thin slices with a sharp blade - this is called sectioning.
The specimen is placed on the centre of the slide and a cover slip is placed on top
6
Q
What would a dry mount be used to view?
A
eg. Hair, pollen, dust, muscle tissue and plant tissue
7
Q
How is a wet mount prepared?
A
Specimens are suspended in a liquid such as water or immersion oil
A cover slip is placed on from an angle
8
Q
What would a wet mount be used to view?
A
Aquatic samples and other living organisms
9
Q
How is a squash slide prepared?
A
Wet mount is first prepared,
then a lens tissue is used to gently press down on the cover slip
10
Q
What are squash slides used to view?
A
Root tip squashes, other soft samples
11
Q
How are Smear slides prepared?
A
the edge of a slide is used to smear the sample, creating a thin, even coating on another slide.
A cover slip is then placed over the top of the sample
12
Q
What are smear slides used to view?
A
Blood, other thick liquids
13
Q
Outline the importance of microscopes in the study of living organisms
A
Microscopes allowed scientists to investigate cell structure, observe the tiniest details of plants, animals, and fungi, and learn about the presence of microbes.
14
Q
Suggest, with reasons, why cell theory was not fully developed before the mid-19th century
A
Prior to the mid-19th century microscopes were of too low a magnification to see and identify cells and cell components
15
Q
suggest reasons why specimens must be thin during microscopy
A
So light can be seen through
Details can be seen
16
Q
suggest why when preparing a wet mount the refraction index (ability to bend light) of the medium should be roughly he same as the glass.
A
reduce / prevent, diffraction between liquid and glass
prevent / reduce distortion of
image
17
Q
A cover slip must be placed onto the wet mount at an angle suggest why
A
reduce / prevent air bubbles being trapped
18
Q
explain why when using basic light microscopy the sample’s image tend to have low contrast
A
the whole sample is illuminated at once from below
so most cells do not absorb a lot of light
19
Q
what is resolution in a basic light microscope limited by?
A
resolution is limited by the wavelength of light
and diffraction of light as it passes through the sample
20
Q
what is diffraction
A
diffraction is the bending of light as it passes close to the edge of an object
21
Q
what parts of cells are often transparent
A
the cytosol (aqueous interior) and other structures
22
Q
explain why staining is used in microscopy
A
Staining provides contrast
Different Organelles absorb stain differently allowing identification
23
Q
explain how to prepare a sample for staining
A
Placed on a slide an allowed to air dry
Passed it through a flame
Specimen will then adhere to the microscope side and will take up stain
24
Explain how crystal violet or methylene blue dyes perform in staining samples
Positively charged dyes
Attracted to negatively charged materials in cytoplasm
Stains of cell components
25
Explain how the dyes nigrosin or Congo red perform in staining samples
Negatively charged
Repelled by negatively charged materials in cytoplasm
This means that they stay out of cells
Leaves the cells unstained
Which then stand out against the stained background
26
What are the techniques using the dyes nigrosin or Congo red called?
Negative stain technique
27
Explain what differential staining is
Differential staining distinguishes between two types of organisms that are hard to identify
Can also distinguish between two different organelles of a single organism within a tissue sample
28
what is gram stain technique used for?
Gram stained technique is used to separate bacteria into two groups
Gram-positive
Gram Negative
29
How are Gram Stains prepared?
Crystal violet is applied to bacterial specimen on a slide
Iodine is then applied to fix the dye
The slide is then washed with alcohol
30
explain how gram positive bacteria are identified using the gram stain technique
Gram positive bacteria retain crystal violet stain and will appear blue/purple
31
How is gram negative bacteria identified
Gram negative bacteria have thinner walls and therefore lose the crystal violet stain
Then stained with safranin dye - called a COUNTERSTAIN
Bacteria will then appear red
32
Describe the effect of the antibiotic penicillin on gram positive and negative bacteria
Gram positive are susceptible to the antibiotic penicillin, which inhibits the formation of cell walls
gram-negative have much thinner cell walls and are not susceptible to penicillium
33
What is acid-fast technique used for
Differentiate species of Mycobacterium from other bacteria
34
explain how acid-fast technique is carried out
Lipid solvent is used to carry carbolfuchsin dye into the cells being studied
Cells are then washed with a dilute acid-alcohol solution
Mycobacterium are not affected by the acid-alcohol and retain the carbolfuchsin stain, which is bright red.
Other bacteria lose the stain and are exposed to a methylene blue stain - which is blue
35
explain the process of 'fixing' on slides that have been pre-prepared
chemicals like formaldehyde are used to preserve specimens in as near natural state as possible
36
explain the process of 'sectioning' on slides that have been pre-prepared
Specimens are dehydrated with alcohols
Then placed in a mould with wax or resin to form a hard block.
this can be then thinly sliced with a knife called a microtome
37
explain the process of 'staining' on slides that have been pre-prepared
specimens are often treated with multiple stains to show different structures
38
explain the process of 'mounting' on slides that have been pre-prepared
the specimens are then secured to a microscope slide and a coverslip is placed on top
39
Why must a risk assessment be carried out?
many of the stains used in preparations of slides are toxic,
risk assessment is used to identify any procedures involved that may result in harm.
40
Use your knowledge of gram positive and gram negative bacteria:
Suggest why gram -negative infections are more difficult to treat than gram positive
Gram negative have thinner cell wall
Penicillin disrupts cell wall formation
Less cell wall formation (in gram negative)
Prevents entry of penicillin (1)
41
Rules for the production good scientific drawings
- include title
- magnification
- sharp pencil for drawing and labels
- while unlined paper
- as much proportion of paper as possible
- smooth continuous lines
- no shade
- clear defined structures
- ensure proportions are correct
- no crossing of label lines and no arrow heads
- labels barrel and drawn with ruler
42
Magnification formula
Magnification = Image size/actual size
43
What is the difference between magnification and resolution
Magnification is the ratio of the image size to the object size
Resolution is the ability to distinguish two separate points
44
Explain why a light microscope will not usually magnify images to greater than 1500x
The resolution of a light microscope is not sufficent
45
What are the disadvantages of light microscopes
Resolution is limited
46
How can you tell the difference between images created by an electron microscope and one created by a transmission electron microscope
A SEM Image is in 3D and has surface view
A TEM image allows you to see
inside the organelles
47
Unit conversions for microscopy
1000 nanometres = 1 micrometre
1000 micrometres = 1 millimetre
1000 millimetres = 1 metre
48
What are the advantages of scanning electron microscope and transmission electron microscope
+ high resolution, so image can be magnified more and will still show more detail
+ SEM also give 3D images with depth of field and are good for viewing surfaces
49
What are the disadvantages of scanning electron microscope and transmission electron microscope
- Large and very expensive
- Require trained operatives
- the sample must be dried out and therefore is dead, so they cannot be seen in real time and it may also affect the shape of the features seen
- need false colour for micrographs
50
How do you use an eyepiece graticule?
Use a x4 objective lens first
Bring both the eye piece graticule and stage micrometer divisions into focus using the course adjustment and fine focusing knobs
Line up the eyepiece graticule and stage micrometer divisions.
Take a reading of how many eyepiece graticule divisions corrospond to the stage micrometer divisions
As every stage micrometer division equates to 0.1 mm you can calculate the equal Lange length of the eyepiece graticule divisions
From there calculate one eye piece graticule division
In both mm and micrometers
51
State the correct names of the scale used on the stage of the microscope and the scale of the eyepiece
Stage Micrometer
Eye Piece Graticule
52
A blood smear is stained with raisin and harmatoxylin, explain what the observer should expect to see using the light microscope
Red blood cells and white blood cells
The nucleus of the white blood cell
53
State the differing magnification of a light, scanning electron and transmission electron microscope
- Light - 1000- 2000x
- SEM - 50,000- 500,000x
- TEM - 300,000 - 1,000,000
54
State the differing resolution of a light, scanning electron and transmission electron microscope
Light - 50- 200 nm
SEM - 0.4-20nm
TEM - 0.05 - 1nm
55
Uses of light, scanning electron, transmission electron microscopes
Light: viewing cells and tissues
Scanning : viewing surface of cells and organelles
Transmission: detailing organelles (ultra structure)
56
Explain why the resolution of an image can be increased by using beams of electrons
Beams of electrons have shorter wave length than light
Electron beams are still diffracted
But the shorter wavelength means the individuals be as can be much more closer together before they overlap
This means objects that are much smaller and closer together can be seen with more detail without diffraction blurring the image
57
What is an eyepiece graticule
used to find out size of specimen
Fit into eyepiece
transparent ruler with numbers
no units
58
What is a stage micrometer
used to work out size of specimen
placed on a stage
microscope slide with accurate scale
it has units
used to work out value of divisions in eyepiece graticule
at a particular magnification
59
Suggest why it is important to calibrate the lens going to be used to view the specimen
Scale on eyepiece graticule is always the same
Magnification of other lenses changes
Need to calibrate eyepiece graticule for each lens to know actual measurements represented by eyepiece graticule at different magnifications
necessary to calculate real size of objects seen.
60
Suggest why you should put all measurements into the same units before carrying out nay calculations
Simplifies calculations
Reduces room for errors
61
What is contrast?
Difference in shade or colour between two objects
62
Explain how diffraction limits resolution
diffraction happens when light passes through structures
light waves spread out
(light waves) overlap
Individual objects do not appear separate
Causes blurring
63
Explain why eyepiece graticules do not have Units
Arbitrary units
Calibrated for each lens
Using stage micrometer
64
Improvements to increase VALIDITY in the way slides are produced
validity - refers to maintain control variables
sharp blade - thin slices to individual cells are visible /resolution is high
wet mount - prevents dehydration
squash slides - easier to see individual cells and allows light to penetrate tissue
65
What are artefacts?
visible structures
produced due to the preparation process
not a feature of the specimen
66
Define ultrastructure
those features that can be seen using an electron microscope
67
explain what is a disadvantage to the process of using an electron microscope
specimens can often be damaged by the electron beam
Complex preparation process can create artefacts
68
explain what takes place in a transmission electron microscope (TEM)
a beam of electrons is transmitted through a specimen
Focused to produce an image.
69
explain what takes place in a scanning electron microscope (SEM)
Beam of electrons is sent across the surface of a specimen
Reflected electrons are collected.
Produces 3D images of surfaces
70
Explain how a specimen is prepared for electron microscopes
Fixation using chemicals or freezing
Staining with heavy metals
Dehydration with solvents.
TEM samples will be set in resin and may be stained again
SEM samples may be fractured to expose the inside so will need to be coated in heavy metals
71
why is fixation used in sample prep for electron microscopes
Prevents Decomposition
72
why is dehydration used in sample prep of sample for electron microscopes
dehydration prevent vaporisation of water
vaporisation would damage sample
73
why is embedding in resin used for prep of sample for electron microscopes
Embedding allows thin slices to be obtained
74
why is staining with heavy metals used for prep of sample in electron microscopes
staining with heavy metals creates contrast
75
Light Vs Electron
Light:
Cheap
Small and portable
Simple prep
No vacuum required
Live specimens can be viewed
- Low mag and resolution
CSPVL
Electron is exact opposite
76
give an example of an artefact in light microscopes
air bubbles being trapped undercover slip
77
give an example of an artefact in an electron microscope
-loss of continuity of membranes
- distortion of organelles
- empty space in cytoplasm
78
explain how a florescent microscope uses florescence to magnify images
Higher light intensity is used to illuminate a specimen
Treated with a florescent chemical
Florescence absorbs and re radiates the light
in a longer and lower energy wave length
Produces a magnified image
79
What is a focal point?
the distance that gives the sharpest focus
80
TEM vs SEM microscopes
TEM:
+Greater Mag/ resolution (1)
+more detail (1)
- 2D images (1)
- very thin specimen (1)
- more preparation processes and artefacts (1)
SEM
+ 3D images
+ thin specimens not needed
- lower magnification/ resolution
- only surface details seen
81
Define florescence
chemical that absorbs and re-radiates light
82
What occurs in laser scanning confocal microscopy
A laser moves a single spot of focused light across a specimen
Causes illumination of dyed components
Emitted light from the specimen is filtered through pinhole aperture
83
What is a cell
Basic unit of all living things
84
What are the two types of cell?
Prokaryotic
Eukaryotic
85
What are Prokaryotes
Single celled organisms
Single undivided internal area
86
What type of organisms are made up from Eukaryotic cells?
Animals, Plants, Fungi
87
What do Eukaryotic cells contain?
Membrane bound organelles
Nucleus and nucleolus
Vesicles
Golgi
Mitochondria
Cytoskeleton
SER
RER
Cytosol
Centriole
Cell surface membrane
Ribosome
Microtubule Network
88
Nucleus information
Contains coded genetic information (DNA)
Biggest organelle
Has double membrane (Envelope)
Contains Nuclear pores allowing movement of molecules
Contains histones, which form with DNA to form Chromatin, which further coils into Chromosomes
89
Describe the Nucleolus
Responsible for producing ribosomes
Composed of proteins and RNA
90
Describe Mitochondria
Site of final stages of cellular respiration (production of ATP)
Contain Double membrane
Inner membrane is highly folded, forming Cristae
Fluid interior called matrix
Contains small amount of (mt)DNA
91
Describe vesicles
Membranous sacs
Responsible for storage and transport
Single membrane containing fluid
92
Describe Lysosomes
Specialised vesicles
Contain Hydrolytic Enzymes
Responsible for breakdown of waste material
Responsible for breakdown of pathogens ingested by phagocytic cells
Play role in Apoptosis
93
Describe the Cytoskeleton
Network of fibres
Necessary for shape and stability of a cell
Holds organelles in place
Composed of Microfilaments, Microtubules and intermediate fibres
94
Describe microfilaments
Contractile fibres formed from the protein Actin
Responsible for cell contraction during cytokinesis
95
Describe microtubules
Globular Tubulin proteins polymerise to form tubes
forms scaffold like structures
Determines shape of cell
acts as tracks for the movement of organelles and vesicles
Spindle fibres are important in cell division
96
Describe intermediate fibres
These fibres give mechanical strength to cells
97
Eukaryotic cells
DNA is linear
Nucleus present (DNA inside)
No cell wall in animals, cellulose cell wall in plants, or chitin in fungi
Many organelles
Flagella made if microtubule proteins
Larger ribosomes
Example: human liver cell
98
Prokaryotic Cells
DNA is circular
No nucleus (DNA is free in the cytoplasm)
Cell wall is made of a polysaccharide but not cellulose or chitin
Few organelles and no membrane bound organelles eg.mitochondria
Flagella made of the protein flagellin, arranged in a helix
Small ribosomes
Example: E. Coli bacteria
99
What do plant cells contain that animals dont?
Cell wall with plasmodesmata
Vacuole
Chloroplasts
100
Description of Plasma membrane
Membrane found on the surface of animal cells and inside the cell wall of plant cells and prokaryotic cells.
Made mainly of lipids and proteins.
101
Function of Plasma membrane
Regulates the movement of substances into and out of the cell.
Also has receptor molecules of which allow it to respond to chemicals like hormones
102
description of Cell wall
Rigid structure that surrounds plant cells
Made mainly of the carbohydrate cellulose
103
Function of cell wall
Supports plant cells
104
what are cell walls made of?
Cellulose
105
description of Ribosome
small organelle that either floats free on cytoplasm or attached to the rough endoplasmic reticulum.
106
Function of Ribosome
Site of Translation
107
what are ribosomes made of?
2 Sub-units (Large and Small)
Comprised of proteins and RNA.
108
Description of Rough endoplasmic reticulum
The surface is covered with ribosomes
109
Function of Rough endoplasmic reticulum
Folds and processes proteins that have been made at the ribosomes
110
Function of Smooth endoplasmic reticulum
Synthesises and processes lipids
111
Description of Mitochondrion
Usually oval shaped. Have a double membrane- the inner one is folded to form cristae.
Inside is the matrix which contains enzymes involved in respiration
112
Description of a Chloroplast
A small, flattened structure found in plant cells.
double membrane,
Contains membranes inside called thylakoids membranes.
These membranes are stacked up in some parts of the chloroplast to form grana.
Grana are linked together to form lamellae
113
Function of Chloroplasts
The site where photosynthesis takes place.
Some parts of photosynthesis happen in the grana and other parts happen in the stroma (a thick fluid found in chloroplasts)
114
Description of a Centriole
Small, hollow cylinders made of microtubules (tiny protein cylinders).
Found in animal cells but only some plant cells.
115
Function of Centriole
Involved in the separation if chromosomes during cell division
116
Description of Cilia
Small, hair like structures found on the surface membrane of sine animal cells.
They have an outer membrane and a ring of nine pairs with protein microtubules inside with two microtubules in the middle.
117
Function of Cilia
The microtubules allow the cilia to move.
This movement is used by the cell to move substances along the cell surface.
118
Flagellum Description
On eukaryotic cells are like cilia but longer.
They stick out from the cell surface and are surrounded by the plasma membrane
119
Function of Flagellum
The microtubules contract to make flagellum move.
Flagella are used like outboard motors to propel cells forward (eg. when a sperm cell swims)
120
Description Cytoskeleton
Network of protein threads. In eukaryotic cells the protein threads are arranged as microfilaments (small solid strands) and microtubules (tiny protein cylinders)
121
Function of Cytoskeleton
The microfilaments and microtubules support the cells organelles keeping them in position
strengthen the cell and maintain its shape
Responsible for movement of materials within the cell.
Proteins of the cytoskeleton can also cause the cell to move
122
Protein Production
-proteins made at ribosomes
-ribosomes on Rough ER make proteins that are excreted or attached to the cell membrane. The free ribosomes in the cytoplasm make proteins that stay in the cytoplasm.
ER=Exctretion
-new proteins produced at the rough ER are folded and processed (eg.sugar chains are added) in the rough ER
-then they're transported to the Golgi apparatus in vesicles
-at the Golgi apparatus the proteins undergo further processing (eg.sugar chains are trimmed and more are added)
-the proteins enter more vesicles to be transported around the cell eg.glycoproteins (found in mucus) move to the cell surface and are secreted.
123
What is a lysosome and why is the membrane that surrounds it so important?
A specialised Vesicle
Contains enzymes which require low pH and would break down other organelles should they escape
124
Explain why cells need to be compartmentalised, and describe 3 examples of compartmentalisation within an animal Cell
Reactions require different conditions
Damage would be caused due to hydrolytic enzymes
Eg. Nucleus, vesicles lysosomes, mitochondria, Golgi body, endoplasmic reticulum, chloroplast
125
Compare the structure and function of the rough and smooth Endoplasmic reticulum
Rough ER has ribosomes attached AND the smooth ER does not have ribosomes attached
The rough ER is the site of proteins synthesis/modification
Smooth ER is the site of lipid synthesis
126
Describe the structure and function of the cytoskeleton
Microfilaments
which are contractile fibres made of actin cause cell contraction during cytokinesis
Microtubules
which are formed from the cylindrical protein Tubulidentata and form scaffold-like structures;
used in movement of organelles and segregation of chromosomes in cell division
Intermediate fibres
give mechanical strength to cells
127
Discuss how the structure of microfilaments and microtubules means these components of the cytoskeleton are involved in the movement of cells but the intermediate fibres are not
Microfilaments are composed of actin which is contractile
Microtubules are composed of Tubulidentata which polymerises. Contraction and polymerisation lead to a change in the length of the filaments, this results in the movement of the cell.
Intermediate fibres have a fixed length for stability
128
Features of Cellulose cell wall
Freely permeable
Gives the cell shape
Contents of cell press against the cell wall making it rigid
Defence mechanism against invading pathogens
129
Description of Vacuoles
Membrane lined sacs in cytoplasm
Contains cell sap
Most are permanent
Membrane in vacuole called Tonoplast
If Vacuoles appear in animal cells, they are small and transient (not permanent)
130
Function of Vacuoles
Maintains Turgor so that the contents of cell push against the cell wall and maintain rigid framework
131
When did Prokaryotic cells first appear and what conditions were they present in
3.5 billion years ago
Hostile conditions
132
What name are given to organisms that live in extreme conditions
Extremophiles
133
Where are Extremophiles found?
Hydrothermal vents
Salt lakes
(more recently) Digestive systems
134
Are prokaryotes always unicellular?
YES
135
Are Eukaryotes Always Multicellular?
NO
136
Describe the DNA in a Prokaryotic Cell
Only contain one molecule of DNA - a chromosome- which is supercoiled to make it more compact
Genes on the chromosome are often grouped into operons, meaning a number of genes are all switched on or off at the same time
137
Describe Prokaryotic Ribosomes
70S (as opposed to 80S found in Eukaryotes)
Relative size is determined by the rate at which the form sediment in solution
Less Complicated than Eukaryotic Ribosomes
138
Describe the Prokaryotic Cell Wall
Made from peptidoglycan
Complex polymer formed from amino acids and sugars
139
Describe Prokaryotic Flagella
Doesn't have 9+2 Arrangement (seen in eukaryotes)
Thinner than Eukaryotic flagella
Energy required to make the filament rotate comes from chemiosmosis, not ATP (in Eukaryotic cells)
Attached to cell membrane of bacterium by a basal body and rotated by molecular motor
140
What is the Endosymbiosis theory?
Mitochondria and chloroplasts (and possibly other eukaryotic organelles) were formerly free-living bacteria/ Prokaryotes
These prokaryotes were taken inside another cell as an endosymbiont
Lead to the evolution of eukaryotic cells
140
Prokaryotes vs Eukaryotes Nucleus
P: Not present
E: Present
141
Prokaryotes vs Eukaryotes DNA
P: Circular
E: Linear
142
Prokaryotes vs Eukaryotes DNA Organisation
P: Proteins fold and condense DNA
E: Associated with Proteins called histones
143
Prokaryotes vs Eukaryotes Extra chromosomal DNA
P: Circular DNA called Plasmids
E: Only present in certain organelles such as chloroplasts and mitochondria
144
Prokaryotes vs Eukaryotes Ribosomes
P: 70S
E: 80S
145
Prokaryotes vs Eukaryotes Organelles
P: Non membrane bound
E: Both Membrane and non membrane bound
146
Prokaryotes vs Eukaryotes Cell walls
P: Peptidoglycan
E: Chitin in Fungi
Cellulose in Plants
Not present in animals
147
Prokaryotes vs Eukaryotes Cytoskeleton
P: Present
E: Present, more complex
148
Prokaryotes vs Eukaryotes Reproduction
P: Binary Fission
E: Asexual or Sexual
149
Prokaryotes vs Eukaryotes Cell type
P: Unicellular
E: Unicellular or Multicellular
150
Prokaryotes vs Eukaryotes Cell surface membrane
P: present
E: Present
151
List three structural differences between prokaryotic cells and eukaryotic cells
Nucleus in Euk, none in Pro
DNA is circular in Pro, Linear in Euk
Cell wall Is made of peptidoglycan in Pro, Chitin/cellulose in Euk
152
Suggest why the lack of membrane-bound organelles doesn't stop prokaryotic cells making proteins
Contain Ribosomes
Capable of replicating proteins
153
Some Antibiotics kill bacteria by disrupting the formation of peptidoglycan molecules. Explain why these antibiotics kill bacteria and why they do not have any effects on eukaryotic cells
Bacteria Cell walls made from peptidoglycan
Prevents growth and replication of bacteria, unable to form cell wall
Eukaryotes either have no cell walls, or they are made from chitin/cellulose
Hence no cell wall would be disrupted
