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Biology - AS Level > Cell Structure > Flashcards

Cell Structure Flashcards

1
Q

what is the formula for finding the size of a cell

A

magnification=size of image/size of real object

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2
Q

what is the comman unit of cell study

A

micrometer

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3
Q

micrometer is

A

x10-6

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4
Q

how do you convert between units

A

1mm x1000 = 1000 micrometers
1000 micrometers x1000= 1000000 nano
1mm x1000000= 1000000 nm

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5
Q

magnification

A

how many times bigger the image is compared to the object

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6
Q

resolution

A

the ability to distinguish between two separate points

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7
Q

the resolution depends on

A

the wavelength of the radiation source

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8
Q

2 examples of radiation

A

-light ray
-electron beam

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9
Q

what makes the image clearer

A

being hit by two waves of radiation

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10
Q

what makes up a light microscope

A
  • condenser lens- focuses light up onto the stage
  • the specimen - the thing you want to view
  • objective lens - magnifies the specimen
  • eyepiece lens - magnifies image further
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11
Q

how is total magnification achieved

A

by multiplying mag of both lenses together

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12
Q

how are different shades produced

A

different parts of specimen have different densities
therefore parts of the specimen absorbs different amounts of wavelength

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13
Q

what is the total magnification of a light microscope

A

x1500

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14
Q

what is the total resolution of a light microscope

A

0.2 micrometers

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15
Q

advantages of light

A

-cheap and easy to maintain
- easy to prepare specimens, can use a stain
- living specimens can be used

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16
Q

disadvantages of light

A

-limited magnification
-low resolution

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17
Q

when were electron microscopes invented

A

1930 , not used until 1950

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18
Q

when was the light microscope invented

A

1667 - robert hooke

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19
Q

types of microscope

A

transmission electron microscope
scanning “”

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20
Q

advantages of electron

A

-high resolution
-high magnification

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21
Q

what is the magnification of an electron

A

x250000

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22
Q

disadvantages of electron

A

-only dead specimens can be viewed
-cannot use harsh stains
- expensive
-have to have special training

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23
Q

what is an artefact

A

features that are caused by preparation and do not really exist in the cell

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24
Q

how do you combat artefacts

A

ask other scientists to see if they see what you see

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25
Q

why do electron microscopes have to be in a vacuum

A

the electrons are too small and can scatter easily

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26
Q

how do you prepare specimens for electron

A

cut extremely thin using a diamond knife

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27
Q

how do TEMs work

A

-electron beams are emitted by an electron gun
-they are then narrowed by electromagnetic lenses onto the specimen
-electrons penetrate through the specimen
-different areas appear dark and light due to the levels of electrons that they absorb (electron densities)

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28
Q

how do SEMs work

A

-electrons fired out of a gun
-narrowed by electromagnetic lenses
-scan over the top ad under the specimen, instead of going through

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29
Q

what is an advantage of scanning

A

3D images can be produced

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30
Q

how do you measure cells

A

using an eyepiece graticule and stage micrometer

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31
Q

what is an eyepiece graticule

A

-small glass disc that is placed in the eyepiece lens
-usually divided into 100 units

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32
Q

how do you chose the correct setting for the eyepiece

A

calibrate it against a known length

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33
Q

how do you calibrate it

A

using the stage micrometer

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34
Q

what is the typical length of stage micrometer

A

1mm divided into 100 divisions therefore each one is usually 10 micrometers

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35
Q

example

A

each division is 10 micrometers
24 divisions line up with 90 on the eyepiece graticule
24x10= 240 micrometers
240=90
240/90 = each eyepiece division is 2.67 micrometers

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36
Q

what do you have to do each time you change the magnification

A

you have to re-calibrate it

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37
Q

what do you have to do before each calculation

A

line both EPG and SM up to closet lines and count distance between

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38
Q

what to do when measuring a picture of a cell

A

count how many cells and that equal the number of units

39
Q

to find mean when calculating cell size

A

count up all and get average
OR divide by total number of cells

40
Q

how do you differentiate with the two types of cell

A

the word ‘karyo’ means to do with the nucleus

41
Q

what is a prokaryotic cell

A

bacterial cells- they do not contain a true membrane-bound nucleus or any membrane bound organelles

42
Q

what is a eukaryotic cell

A

true membrane bound nucleus and contain membrane bound organelles
animal, fungal, plant and protoctist cells

43
Q

what is an organelle

A

something that performs a specific role inside a cell

44
Q

what is compartmentalisation

A

when organelles are bound by a membrane and thus a particular job is carried out in a specific area of the cell

45
Q

what is the internal structure of a cell called

A

the ultra-structure

46
Q

what does the nucleus do

A

contains the genetic code which is used to produce genes for protein synthesis

47
Q

what are some features of the nucleus

A

Present in all eukaryotic cells, the nucleus is relatively large (10-20um) and separated from the cytoplasm by a double membrane (the nuclear envelope) which has many pores
Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in- communication
The nucleus contains chromatin (the material from which chromosomes are made)
Chromosomes are made of sections of linear DNA tightly wound around proteins called histones
Usually, at least one or more darkly stained regions(denser electron region) can be observed – these regions are individually termed ‘nucleolus’ and are the sites of ribosome production and RNA

48
Q

what is the role of the mitochondria

A

the site of aerobic respiration and production of ATP

49
Q

what are some features of the mitochondria

A

Surrounded by double-membrane with the inner membrane folded to form cristae which provide a large surface area for efficient enzyme reaction
cristae contain the electron transport chain
The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP and produces its own proteins
Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)

50
Q

what is the role of the ribosomes

A

site of protein synthesis

51
Q

what are some features of ribosomes

A

Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
Each ribosome is a complex of ribosomal RNA (rRNA) and proteins
80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells
they contain two sub-units made of RNA-l manufactured in nucleolus and leave nucleus through pores

52
Q

what is the endoplasmic reticulum (ER)

A

series of membranes in the outer cell membrane
series of interconnected tubes and sacs called cisternae

53
Q

what are some features of (ER)

A

-Rough Endoplasmic Reticulum (RER)
Surface covered in ribosomes
Formed from continuous folds of membrane continuous with the nuclear envelope
Processes proteins made by the ribosomes- and these pass through pores from mebrane into the lumen and are then transported around the cell

-Smooth Endoplasmic Reticulum (ER)
Does not have ribosomes on the surface, its function is distinct to the RER
Involved in the production, processing and storage of lipids, carbohydrates and steroid

54
Q

what is the role of the golgi apparatus(body)

A

modify and package proteins

55
Q

what are some features of the golgi body

A

Flattened sacs of membrane similar to the smooth endoplasmic reticulum- cisternae
Modifies proteins and lipids before packaging them into Golgi vesicles
The vesicles then transport the proteins and lipids to their required destination
Proteins that go through the Golgi apparatus are usually exported (e.g. hormones such as insulin), put into lysosomes (such as hydrolytic enzymes) or delivered to membrane-bound organelles

56
Q

what are lysosomes

A

digestive enzymes

57
Q

what is the role of lysosomes

A

-fuse with cell surface mem and release enzymes outside of the cell
-fuse with phagocytic vacuoles containing foreign material which has been taken in by the cell
-may destroy old worn out organelles

58
Q

what is the cell surface membrane

A

-phospholipid bilayer
-folded into microvilli- increases surface area for absorption
-controls what comes in to and out of the cell

59
Q

what is the role cytosol

A

liquid material containing dissolved material eg nutrients

60
Q

what is the cytoskeleton

A

a system of protien microtubules and microfilaments which give the cell support

61
Q

what is the cellulose cell wall

A

only in plant cells and made of polysaccharide cellulose
Cell walls are formed outside of the cell membrane and offer structural support to cell
Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells
permeable to water

62
Q

permanent central vacuole

A

fluid filled sac surrounded by a single layer of membrane
exerts turgor pressure and helps support cell and plant
can also function as a storage area - contains dissolved nutrients eg amino acids

63
Q

what is the role of the chloroplasts

A

site of photosynthesis

64
Q

what are some features of the
Chloroplasts

A

Larger than mitochondria (2-10um), also surrounded by a double-membrane
Membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana
Grana are joined together by lamellae (thin and flat thylakoid membranes)- chemical reactions happen here
granum contain chloroplasts
Chloroplasts are the site of photosynthesis:
The light-dependent stage takes place in the thylakoids
The light-independent stage (Calvin Cycle) takes place in the stroma
Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
also can contain starch granules- insoluble so not affected by osmotic water potential

65
Q

how can you investigate cell components

A

by using cell fractionation

66
Q

what does the 1st stage do

A

breaks up the cell to release the various components

67
Q

what are the cells first suspended in

A

an
-ice cold- reduce enzyme activity
-isotonic-prevent osmotic damage to the cell-shrinking/bursting
-buffer-same pH concentration as proteins sensitive to change in pH

68
Q

what is homogenisation

A

Homogenisation is the biological term used to describe the breaking up of cell

69
Q

why do you filter the homogenate

A

to remove debris and unbroken organelles
This is a blender-like machine that grinds the cells up

70
Q

what is the next stage of fractionation

A

Ultracentrifugation

71
Q

what is the process of ultracentrifugation

A

-The filtrate is placed into a tube and the tube is placed in a centrifuge
-A centrifuge is a machine that separates materials by spinning
-The filtrate is first spun at a low speed
-This causes the largest, heaviest organelles (such as the nuclei) to settle at the bottom of the tube, where they form a thick sediment known as a pellet-pick the pellet that you want
-The rest of the organelles stay suspended in the solution above the pellet
-This solution is known as the supernatant
-The supernatant is drained off and placed into another tube, which is spun at a higher speed
-Once again, this causes the heavier organelles (such as the mitochondria) to settle at the bottom of the tube, forming a new pellet and leaving a new supernatant
-The new supernatant is drained off and placed into another tube, which is spun at an even higher speed
-This process is repeated at increasing speeds until all the different types of organelle present are separated out (or just until the desired organelle is separated out)

72
Q

what is the order in which the organelles are collected

A

Nuclei
Chloroplasts (if carrying out cell fractionation of plant tissue)
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes

73
Q

what are the levels of organisation

A

-tissue- group of similar cells aggregated and working together to perform a specific function
-organ- a group of organs working together to provide one overall function
-organ system- organs working together to perform an overall function

74
Q

how does cell specialisation occur

A

differentiation

75
Q

why is specialisation advantageous

A

wide range of functions can be carried out at the same time making cells very diverse and adaptable

76
Q

what is a prokaryot cell

A

cells that do not have a true membrane bound nucleus

77
Q

what is a comman example of a prokaryot cell

A

bacteria

78
Q

what is the size of a bacteria cell

A

0.1-10 micrometers

79
Q

where is the genetic material stored in a bacterium

A

in strands in the centre that forms a structure called a nucleoid

80
Q

what is another store of DNA in a bacterium

A

a ring of DNA known as a plasmid

81
Q

what is the bacterium surrounded by

A

a cell wall made of murein- only found in bacteria
and is the target for antibiotics eg penicillin
these prevent cell wall from forming and thus bacteria burst due to high pressure

82
Q

what do some cells also contain- bacteria

A

a slime capsule - makes them smooth

83
Q

what do bacterial cells not have

A

membrane bound organelles
-ER
-glogi
lysosomes

84
Q

how do the bacterium increase their surface area

A

by creating folds in the membrane that are known as meosomes

85
Q

what are the ribosomes like in bacteria

A

smaller than in eukaryotic cells

86
Q

what is the role of the flagellum

A

Flagellum-e long, tail-like structure that rotate, enabling the prokaryote to move (a bit like a propeller)
some have more than one

87
Q

what is a virus

A

non-cellular infectious particles

88
Q

what is their size- bacteria

A

200-300nm

89
Q

what are some common features of a virus

A

A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
A protein coat called a ‘capsid’
Some viruses have an outer layer called an envelope formed usually from the membrane-phospholipids of a cell they were made in
All viruses are parasitic in that they can only reproduce by infecting living cells and using their protein-building machinery (ribosomes) to produce new viral particles

90
Q

what is a bacteriophage

A

viruses that infect bacteria

91
Q

what does HIV stand for

A

human immunodeficiency virus

92
Q

what enzyme is in HIV

A

reverse transcriptase enzyme
this turns the RNA back to DNA for transcription and translation

93
Q
A

Biology - AS Level (13 decks)

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