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OCR A Biology A-Level > 2.1.1 Cell Structure > Flashcards

2.1.1 Cell Structure Flashcards

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1
Q

What are microscopes used for and why are different types used to study cells + give examples of types

A

To observe and identify cell structure and to study cells at different levels of detail, for example light or electron microscopes

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2
Q

Tell me about the resolution and magnification of a light microscopes and what it is generally used for

A

Max resolution - 0.2 micrometers (um)
Max magnification - x1500
They are used to observe larger structures, such as entire cells or nuclei

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3
Q

What are the advantages of light microscopes

A
  • small and cheap
  • preparation can be straightforward
    -produce colour images
    -can observe living specimens
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4
Q

Tell me about electrons microscopes generally, their resolution, magnification and use and how

A

-electrons are used to form an image
-max resolution - 0.0002 um / 0.2 nm
- max magnifcation - many millions
- used to observe small structures inside cells such as cell membranes, ribosomes

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5
Q

What are the limitations of electron microscopes

A

-large and expensive
-complex preperation process
-viewed in a vacuum, no live specimens
-always black and white

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6
Q

What are the two types of electron microscopes and which has a lower max resolution

A

Transmission electron microscopes
Scanning electron microscopes
SEM has a lower max resolution then TEM

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7
Q

How does a transmission electron microscope work, and what does it produce

A

-Uses electromagnets to transmit beams of electrons through specimen, dense parts absorb more, making them appear darker
-Image is high resolution
-2D
-Internal structures can be seen

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8
Q

How does a scanning electron microscope work and what does it produce

A

-Pass a beam of electrons across the surface of a specimen and then detect the rate at which electrons bounce back
-Produce image that is 3D and shows the surface of specimens

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9
Q

How do light/optical microscopes work and what are some key components of apparatus

A

-Light is directed at thin layer of matter on a glass slide
-Light focused through several lenses, image visible through eye peice
-mag can be increased by rotating objective lens

Apparatus
-eye peice lens
-objective lens
-stage
-light source
-course and fine focus

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10
Q

What other tools would be included in setting up a light microscope to view a sample

A

-Scalpel
-Scissors
-Forceps
-Pipette

-Slides
-Coverslip
-Staining solution

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11
Q

Explain the featues of the components of an optical microscope

A

-Objective lenses - x4 (low power) x10 (medium power) x40 (high power)
-Course focus - for focusing the low and medium power objective lenses
-FIne focus - for focusing the high power objective lenses
-Condenser - Controls intensity of light
-Stage - slide is placed onto stage
Turret - Rotates the objective lenses

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12
Q

Describe how you would set up to examine a liquid specimen with a light microscope

A

-add few drops of specimen to slide
-coverslip to remove air bubbles
-wear gloves to ensure no cross contaminiation

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13
Q

How many methods are there to view a solid specimen under a light microscope and name them

A

3 methods
-Just using a stain
-Chemically fixing the sample
-Freezing the sample

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14
Q

Describe the method of viewing a solid sample with a light microscope using a stain

A

-cut the sample into a thin layer
-light must be able to go through the sample
-add the stain, the coverslip to remove air bubbles

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15
Q

Describe the method of chemically fixing a sample to view to under a light microscope

A

-fix cells to make rigid using formaldehyde
-dehydrate using ethanaol solution
-impregnate using parafinn
-cut using a microtome
-stain and mount using resin
-apply coverslip

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16
Q

Describe the method of freezing a sample to view using a light microscope

A

-freeze sample using CO2 or liquid nitrogen
-cut using cryostat
-place on a slide and stain
-add coverslip to remove bubbles

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17
Q

Why when using a light microscope do we always start on the low power objective lens

A

-It is easier to find what you are looking for in the field of view
-It helps to prevent damage to the lens or coverslip if stage is too high

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18
Q

What are two things we want to prevent happening when using a light microscope and how do we prevent them

A

-Dehydration of tissue and blurry or unclear images
-Thin layers dry rapdily, adding a drop of water prevents this
-Switch to lower power and using the course focus
-Consider if the sample is thin enough
-Is there any cross contamination

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19
Q

Tell me about using a gracticule and how we use it for measurements and what is it

A

-A small disc with an engraved ruler that is placed in the eyepeice
-No fixed units so must be calibrated to the objective lens
-This is done by using a scale engraved on the slide, a stage micrometer
-Therefore the gracticule can be used as a ruler

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20
Q

What are the limitations of using an optical microscope to view samples

A

-Structures will be inconsistent due to samples being cut differently
-Optical microscopes do not have same mag power as others
-Treatment of preparing slides could alter the structure

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21
Q

Why is staining needed for light microscopes and how does it work, what are the common dyes used

A

-Tissues are naturally transparent, difficult to see
-Dyes absorb specific colours of light while reflecting others
-Dye absorbtion depends on chemical nature of tissue
-Multiple dyes may be needed, known as differential staining
-Common dyes used are toludine blue and phloroglucinol which turns cells red and pink

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22
Q

How is staining in electron microscopy used and example stains

A

-In TEM samples must be stained to absorb the electrons
-Heavly metal compounds are commonly used as they absorb electrons well
For example osmium tetroixide and ruthenium tetroxide
-Staining in does not cause a colour rather different shades of grey or black

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23
Q

What are the guidelines you should follow when drawing cells

A

-Title
-Magnification must be recorded
-Sharp HB pencil
-On white paper
-Clear lines
-No shading
-Drawing take as much space as possible
-Well defined
-Proper proportions
-No arrowheads on label lines
-Lines should be parrallel

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24
Q

Magnification of an object an be calculated using the formula

A

mag = size of image / size of object

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25
How do the units of measurement relate to each other in um, nm, mm and cm and m
10mm = 1cm 1m = 1000mm 1mm = 1000um 1um = 1000 nm
26
What are the different units used to measure, um, nm, mm, cm
um - actual size of cells nm - internal structures size of images - mm/cm
27
When coverting large units to smaller units we
Multiply
28
When converting small units to larger units we
Divide
29
What are the units for magnifcation
It has none
30
Magnification is defined as
The number of times larger an image is than the actual object
31
How can we calculate the magnification of a light microscope
Multiply the objective lens and eyepeice magnification
32
What is resolution defined as
The ability to distinguish seperate points on an image as two seperate objects
33
Why is the resolution of a light microscope limted
Due to wavelength of light, light is diffracted and light waves spread out, light waves overlap if structures are close together, these points can't be distinguished from each other
34
Why is the resolution of light microscopes so much higher
Electrons have a smaller wavelength than visible light, objects can be must closer together before hte beams diffract and overlap
35
What is the wavelength of visible light compared to electrons
Visible light 400-700nm Electrons 1nm
36
Tell me about the cell surface membrane
-Although structure looks static, the phosphlipids and proteins are actually always in motion -Controls the exchange of materla, described as partially permarble -Formed from phospholipid bilayer, of phospholipids 10nm
37
Tell me about the cell wall
-Freely permable to most substances -Not in animal cells -Structural support Provided by cellulose in plants and peptidoglycan in bacteria -Narrow threads called plasmodestma connect cytoplasm to neighbouring cells
38
Tell me about the nuclues
-In all eukaryotic cells -Large, has a double membrane called nuclear envelope which has pores -Pores allow mRNA and ribosomes to travel out and allowing enzymes in -Chromatin, material from chromosomes are made is contained. Chromosomes are made from sections of linear DNA wound around proteins called histones Has a nucleolus which is the site of ribosome production
39
Tell me about the mitochrondia
-Site of aerobic respiration -Double membrane with inner membrane folded to form cristea -Matrix formed by cristea contains enzymes for respiration, producing ATP -Circular peices of DNA are found and ribosomes for replication -Self replicating -Abundant in high metabolic areas
40
Tell me about chloroplasts
Found in plant cells Large, double membrane Thylakoids containing chloropyll stack to form grana Grana are joined together by lamellae Chloroplast is site of photosynthesis First stage takes place in thylakoids Second stage takes place in stroma Contains circular peices of DNA and ribosomes to synthesise proteins
41
Tell me about ribosomes
Found in all cells Free in cytoplasm or in the rough endoplasmic reticulum Each ribosome is a complex of rRNA and proteins Eukaryotic cells have 80S ribosomes (60s and 40s sununits) Prokaryotic and mito and chloro have 70s ribosomes (50s and 30s subunits) Site of translation
42
Tell me about the rough endoplasmic reticulum
Found in animal and plant cells Surface covered in ribosomes Formed from continuous folds of the nuclear envelope Processes proteins made by ribosomes Intercellular transport system, fluid filled cavaties called cisternae
43
Tell me about the smooth endoplasmic reticulum
Found in plants and animals No ribosomes on surface Involved with production, processing andstorage of lipids, carbs and steriods. Contain enzymes used in metabolic lipid reactions
44
Tell me about the golgi apparatus
Found in plant and animal cells Flatterned sacs of membrane Modifies proteins and lipids before packaging them into vesicles Transport them to destination
45
Tell me about large permant vacuoles
Found in plant cells A sac that is surrounded by the tonoplast, selectively permaeble membrane Vacoules in animal cells are not permant and are small
46
Tell me about vesicles
Found in plant and animal cells Membrane bound sac for transport and storage
47
Tell me about lysosomes
Specilaist vesicles, contain hydrolytic enzymes Break down waste such as worn out organelles Used in the immune system in apoptosis, abundant in phagocytic cells
48
Tell me about centrioles
Hollow fibres made of microtubules Two centrioles at right angles form a centrosome which organises spindle fibres during cell division Not in flowering plants or fungi
49
Tell me about microtubules
Found in eukaryotic cells Makes up the cytoskeleton, made of alpha and beta tubulin combined to form dimers, dimers are joined to prtotfilaments, thirteen protofilaments in a cylinder make a microtubule
50
What is the function of the cytoskeleton
Provide support and help with movement of the cell
51
Tell me about microvilli
Found in specialised aminal cells Cell membrane projections Increase surface area of the cell surface membrane to increase rate of exchange substances
52
Tell me about cilia
Hair like projections made from microtubules Allows movement of substances over the cell surface
53
Tell me about flagella
Found in specialised cells, simialir in structure to cilia made of longer microtubules Contract to rpovide cell movment in sperm
54
What is undulipodia
The long cilia of a sperm cell
55
What organelles are invovled in the production of proteins and how
Nuclues - DNA stored, nucleolus creates ribosomes, transcription occurs and an mRNA copy of DNA is produced Ribosomes - mRNA attaches to a ribosome Translation occurs, chain of amino acids is produced Rough ER - Ribosomes may attach to surface, after translation polypeptides are folded to produce proteins Golgi apparatus - Proteins are modified and prepared Vesicles - Transports from RER to GA and to to other places
56
Tell me about the cytoskeleton
-Made up of two main types of protein fibres, microfilaments and microtubules Microfilaments are solid strands, made out of actin and help movement by moving against each other Microtublues are hollow strands made of tubulin. Organallse move along these fibres Intermediate filaments are also found within the cytoskleleton
57
What is the importance of the cytoskeleton
Intercellular movement Cellular movement, via cilia Provides mechinal stength to cells anda ids with transport and movement
58
What are some differences between eurkaytoic and prokaryotic cells
P are smaller P lacks membrane bound organelles P ribosomes are smaller P has no nuclues, single ciruclar DNA P cell wall has murein
59
What is the difference between the main DNA circle and plasmids
Plasmids are small loops of DNA that can be passed between prokaryotes
60
What is capsule in prokaryotes
Outer layer that protects them from drying out and from attack of immune system cells
61

OCR A Biology A-Level (3 decks)

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