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A Level Biology OCR A > 2.1.1 > Flashcards

2.1.1 Flashcards

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1
Q

How does a light microscope work?

A

2 lenses, The objective magnifies first then eyepiece(ocular) lens. Specimen is illuninated by a light or a mirror. Images brought into focus by the course knob then the fine knob.

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2
Q

What is chromatic abberation?

What type of microscope helps prevent this?

A

The failure of a lens to focus all of the colours of the colour spectrum to one focal point,
A compound microscope prevents this.

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3
Q

What is resolution?

A

The shortest distance between two close points so that they are still seen as seperate objects.

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4
Q

What is resolving power?

A

The ability to distinguish between two close points.

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5
Q

What is magnification and what is its equation?

A

Magnification is how many times the image has been enlarged from its actual size,
magnification=image/actual.

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6
Q

How to prepare a dry mount?

What specimens need a dry mount?

A

Used for solid specimen,

Cut thin slice of specimen using a sharp knife. Place the specimen on the slide and cover with a cover slip.

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7
Q

How to prepare a wet mount?

A

Put solution on a slide with a well, place specimen on and place it at an angle to prevent air bubbles from forming.

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8
Q

How to prepare a squash slide?

Examples of specimens that need it?

A

Prepare a wet mount. Squash specimen under cover slip and inbetween two slides, this dirsupts structures and reveals the inside,
Larger softer structures.

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9
Q

How to prepare a smear slide?

What is is good for?

A

Smear specimen onto the slide with another slide. This leaves an evenly coated slide,
Good for blood cell counts.

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10
Q

Why is it hard to see many structures of an unstained specimen?

A

Unstained specimen are transparent.

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11
Q

Why is staining used?

A

Differential staining creates contrast and allows you to see more structures.

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12
Q

What is fixing(not heat fixing regular fixing)?
When is it used?
Why is it used?

A

Fixing is when the specimen is dryed,
it is used for specimen that can be washed away by the stain,
It is used before staining in dry mount.

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13
Q

What is blotting?

When is it used?

A

The stain is added and cover slip added but then a tissue is used on one side of the cover slip to draw accross the stain,
It is used in a wet mount.

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14
Q

What is heat fixing?

A

The slide is put through a flame to “heat fix” it to the slide.

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15
Q

How are specimen preserved?

Does this method affect the structure of the specimen?

A

Formaldehyde is used to preserve specimen and stop them degrading,
The structure is not affected and the specimen is the same as before.

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16
Q

What is sectioning?
What is it used for?
Why is it used?

A

For tissue or soft samples where structures can be damaged by cutting,
sample is covered in alcohol to dehydrate it-then coveres in a wax or resin mould,
this forms a hard block which is easy to section without damaging structures.

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17
Q

How do positive stains affect the cell?
Examples?
What part do they stain?

A

They are attracted to the negative parts of the cell,
methlene blue-crystal violet,
stain the inside of cells.

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18
Q

How do nagative stains affect the cell?
Examples?
What part do they stain?

A

They are repelled by the negative parts of the cell,
nigrosin-congo red,
stain the outisde of cells.

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19
Q

Stages of gram staining?
How the positive and negative bacteria react to the stain and why?
Why is it important to differentiate between gram positive and gram negative bacteria?

A

1.add crystal violet
2.add iodine to fix the stain
3.wash the slide with alcohol
Gram positive take up the stain because of their thicker cell walls and appear blue/purple, gram negative dont take it up because they have thin cell walls,
For gram negative apply the counterstain sanfranin dye, this is absorbed by gram negative bacteria,
gram positive is sussceptible to antibiotics such as penicillin wheras gram negative isnt.

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20
Q

Eyepiece graticule key info?

A
  • Arbitrary scale
  • Eyepiece lens needs to be replaced by the graticule.
  • The procedure must be repeated for each ocular lens.
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21
Q

Stage micrometer key info?

A
  • Precision scale
  • Each division is 0.1mm
  • Placed on stage
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22
Q

How to callibrate the graticule?

A

Starting on the lowest power objective lens,
Rotate the eyepiece graticule and orientate it until it is lined up with the stage micrometer,
Use the focusing knob to get into focus,
Use the micrometer scale to calibrate the graticule,
Measure specimen,
Reapet the process foreach objective lens.

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23
Q

Why do samples need to be very thin?

A

To allow electrons/light through.

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24
Q

Key information(not stats) on TEM?

A
  • 2D image
  • Uses beam of electrons
  • electrons are transmitted through the specimen and then focused to produce an image.
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25
Q

Key information (not stats) on SEM?

A
  • 3D image
  • Uses beam of electrons
  • electrons hit the specimen and are reflected back to produce an image.
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26
Q

Why do electron microscopes have a better resolution than light microscopes?

A

Electrons have a shorter wavelegnth than light.

27
Q

What is a picture produced by a microscope called?

A

Micrograph.

28
Q

How to prepare specimen in a electron microscope?

A

1.vacuum inside the microscope
2.fixation-using a chemical method or freezing
3.dehydrate-using solvent
4.stain using a heavy metal
In TEM use a thin slice mounted in resin,
In SEM whole specimens can be cracked/broken to expose the inside.

29
Q

What are artefacts?

A

These structures occur in the manipulation of the sample/specimen,
They can be mkistakenly identified as new structures,
eg. mesosomes in bacteria.

30
Q

Compare the resolution and magnification of light microscopes, TEM and SEM?

A

Light- x2,000 magnification 200nm resolution
TEM- x500,000 magnification 0.5nm resolution
SEM- x500,000 magnification 3-10nm resolution.

31
Q

ADV and DIS of light microscopes?

A

Inexpensive, portable, little distortion, no vacuum required, specimens can be alive, natural colours are shown if unstained.

32
Q

ADV and DIS of electron microscopes?

A

Expensive, inportable, artefacts/distortion can occur, vacuum required, specimens must be dead, black and white images, SEM produces 3D images.

33
Q

Laser scanning confocal lens?

A

Cover specimen with fluroescent dye,shine laser on specimen (at one point) and the fluroescence given off is focused on the detector to build up an image through a pinhole aperture(avoids light from parts close to the spot), the spot moves accross the specimen and a 2D or 3D images are produced.

34
Q

Why are laser confocal scanning microscopes usefull?

A

They can be used in situation as they are non-invasive

-They are usefull for detecting eye diseases.

35
Q

What is ultrastructure?

A

The details seen through electron microscopes.

36
Q

What are eukarytic cells?

A

Animal, Plants Fungi

Usually multicellular, exception incude ameba and some fungi.

37
Q

What are prokarytic cells?

A

Unicellular organisms

eg.bacteria.

38
Q

Describe the nucleus including its ultrastructure and their functions?

A
  • Double membrane called the nucleaur envelope, this is to protect the nucleus and contains nucleaur pores to allow molecules to go in and out.
  • Contains genetic code in the form of DNA, this is associated with histone proteins, together forming Chromatin(long uncoiled chromosones) which appear grainy.
  • Nucleoulus, darker region of the nucleus, its function is to produce ribosomes. It contains nucleic acid RNA which will produce ribosomal RNA (rRNA), this then combined with other proteins to form ribosomes.
39
Q

Describe the appearance of chromatin?

A

grainy.

40
Q

Describe the mitochondria including its ultrastructure and their functions?

A
  • Double membrane,inner and outer
  • Inner membrane is folded into cristae, this increases surface area
  • Cristae are embedded with enzymes that catalyse ATP production
  • Main role of Mitochondria is to produce ATP in the final stages of respiration
  • Aerobic respiration occurs in the cristae because of the enzymes enbedded in it
  • The inner area of the mitochondria is called the matrix and is fluid filled
  • Mitochondria also contain mitochondrial DNA (mtDNA), this means they can control enyme production and can make structural proteins or even reproduce themselves.
41
Q

Describe the vesicle including its ultrastructure and their functions?

A
  • Double membrane
  • Inner membrane encloses the fluid filled centre
  • Its role is to transport substances around the cell
  • Often seen around the outskirts of the golgi.
42
Q

Describe the lysosome including its ultrastructure and their functions?

A
  • Specalised vesicles
  • Contain powerful hydrolytic enzymes which catalyse hydrolysis reactions
  • They are good for breaking down waste materials, old organelles, pathogens after phagocytes have englufed them and some worn out cells.
43
Q

What is the cytoskeleton?

A
  • 3D network of fibres which are accross the cytoplasm
  • They give the cell stregnth and stability
  • They also are involved in the movement of organelles, eg. before mitosis.
44
Q

Describe the three main parts of the cytoskeleton?

A

-Microfilaments
they can contract so are contractile
they are made of the protein actin
they help the cell move and divide(cytokinesis)
-Microtubules
they form a tube like structure
they are made of the protein tubulin
they provide shape and integrity to the cell
they act as tracks for organelle movement
-Intermidiate filaments
They give mechanical stregnth to the cell.

45
Q

Describe the centrioles including its ultrastructure and their functions?

A
  • not found in flowering plants or fungi
  • made of microtubules
  • two(a pair of) centrioles make up a centrosome
  • produce and assemble the spindle apparatus for meiosis and mitosis.
46
Q

Describe the flagella and cillia including its ultrastructure and their functions?

A
  • Both are found on the outside of cells
  • Flagella are larger and usually used for locomotion but can also be used for sensory purposes
  • Cillia are smaller and more numerous, they can be stationary and be used in a sensory capacity or can be mobile and waft rythmically to create a current
  • They are both made of microtubules arranged in a 9+2 pattern.
47
Q

What organelles work together in protein synthesis?

A

Smooth endoplasmic reticulum, Rough endoplasmic reticulum and golgi apparatus.

48
Q

Describe the reticulums?

A
  • Basically a network of of membranes flattened into folded discs/sace called cisternae
  • The network is connected to the outer membrane of the nucleaur envelope
  • Two types:smooth and rough
49
Q

What are the main roles of the smooth and rough endoplasmic reticulums?

A 
Smooth:
-lipid and carbohydrate synthesis
-storage of these molecules
Rough:
-protein synthesis
-transport of these molecules
-have ribosomes which are associated with the cisternae.
50
Q

Describe the ribosome?

A
  • Made up of two subunits, a large subunit and a small sub unit, both composed of RNA molecules
  • no membranes
  • site of all protein synthesis
  • can be found freely or attached to rough endoplasmic reticulum
  • mitochondria and chloroplasts have their own ribosomes.
51
Q

Describe the Golgi apparatus(body)?

A
  • Appearance like stacked plates
  • Long sections of cisternae
  • Main role is to modify proteins
  • Cis face small face, trans face large face
  • Proteins are modified then packaged into vesicles(to be secreted) or lysosomes(if hydolytic enzymes are neeeded in the cell).
52
Q

Describe the process of packaging?

A
  1. mRNA takes genetic code to the ribosome on the rough endoplasmic reticulum.
  2. Here the protein is made and then packaged into vesicles.
  3. The vesicles arrive at the cis face of the golgi.
  4. The vesicles fuse to the membrane releasing the protein.
  5. The protein is modified in the golgi.
  6. At the trans face proteins are packaged into vesicles or lysosomes(if hydrolytic enzymes are needed in the cell).
53
Q

Describe the cellulose cell wall of the plant?

A
  • Surround the cell surface membrane
  • Made of cellulose(polysaccharide)
  • Gives the cell stregnth and rigidity
  • Also supports the plant
  • Acts as a barrier to pathogens, preventing cellular invasion
  • Made of chitin in fungi.
54
Q

Describe the vacuole?

A
  • a large bag/sac
  • surrounded by a membrane called tonoplast
  • contains cell sap
  • when filled with cell sap it becomes turgid, applying turgor pressure
  • a permenant vacuole maintains turgor pressure helping the plant keep its shape.
55
Q

Describe the chloroplast?

A
  • Thylakoids, small sacs filled with photosensitive pigment chlorophyll
  • Stack of thylakoids is granam and mulitple granam are grana
  • Grana joined by extensions called lamelae
  • Liquid inner called stroma
  • Main site of photsynthesis
  • Also can contain starch grains
  • The grana and granam and thylakoids mean their is a large surface area so a faster rate of photosynthesis
  • Also contain their own DNA and ribosomes.
56
Q

What are the small gaps inbetween cell walls called

and why are they there?

A

They are called plasmodesmata, they allow substances to travel from one cell to another.

57
Q

What is the role of the pit?

A

Connects the xylem to the cell.

58
Q

Describe the cytoplasm?

A
  • Contains all of the organelles and the cytosol
  • The cytosol is the liquid part of the cell not contained within any organelles, mainly composed of water, organic molecules and salts.
59
Q

Describe how COMPARTMENTALISATION works in eukaryotic cells?

A

Each oganelle is a self contained unit, so carrys out its own processes without imapacting other organelles. Membranes are all selectively permeable so only let cetain molecules in or out.

60
Q

What are extromphiles and which type of cell are these?

A

Can survive extreme enviroments. Prokaryotes.

61
Q

Describe the DNA(nucleoid) in prokaryotes?

A
  • Exists in one large chromosone
  • loosely associated with proteins to form loop structure
  • often has small loops of DNA callled plasmids
  • genes of the large looped DNA are grouped into units called operons, this means that several genes can be switched on/off at the same time
  • plasmid genes often confer antibiotic resistance.
62
Q

Describe the cell wall in prokaryotes?

A

-surrounds the cell surface membrane
-made of peptidoglycan
-used for protection
-gram +ve have more peptidoglycan(thicker walls)
gram-ve have less peptidoglycan(thinner walls)
-Sometimes cell walls can be surrounded by a slime layer, this stops the cell being detected by the immune system.

63
Q

Describe ribosomes in prokaryotes?

A
  • same function as in eukaryotes
  • much smaller and not attached to reticulum
  • prokaryotes have the size 70S, eukaryotes have the size 80S.
64
Q

Describe flagella in prokaryotes?

A

Same function as in eukaryotes(locomotion)

  • no 9+2 arrangement
  • the filament is attached to the basal body and the molecular motor
  • energy from CHEMIOSMOSIS(not directly ATP) is used to power the motor, spinning the hook of the flagella and making a whipping action.

A Level Biology OCR A (2 decks)

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