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A-level AQA Biology > Chapter 2A: Cell Structure > Flashcards

Chapter 2A: Cell Structure Flashcards

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1
Q

What is the formula for magnification?

A

=image size/actual size

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2
Q

What is magnification?

A

it is how much bigger a sample appears to be under the microscope than it is in real life

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3
Q

What is resolution?

A

it is the ability to distinguish between two parts of an image (the amount of detail)

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4
Q

What are artefacts?

A

they are things that you can see down a microscope that are NOT part of the cell/specimen. They are bad because they can be misinterpreted by someone for a part of the cell (inaccurate description of cell)

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5
Q

What are some examples of artefacts?

A

dust
air bubbles
fingerprints
problems with staining

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6
Q

Where are artefacts most common?

A

in electron micrographs
because specimens need a lot of preparation before being used in an E.M. so more chance of a mistake
also have higher resolution, so more likely to pick up artefacts

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7
Q

When are artefacts most likely to be made?

A

during the preparation of the slide

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8
Q

How could artefacts be distinguished from organelles for early scientists?

A

they do this by repeatedly preparing specimens in different ways and using different microscopes. If an object was seen regularly was more likely to be an organelle than an artefact

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9
Q

What are the three steps to separate a cell? (to study specific organelles)

A
  1. homogenisation
  2. filtration
  3. ultracentrifugation
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10
Q

What is homogenisation?

A

breaking the cell plasma membrane and releases the organelles into a solution
this can be done by putting it in a homogeniser (blender) or vibrating the cells

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11
Q

What conditions must the homogenate have and what effect does it have?

A
  1. must be kept ice-cold (to slow down enzyme activity)
  2. sol. must be isotonic (with cell) to avoid OSMOTIC damage to the organelles (NOT CELLS)
  3. a buffer sol. is added to maintain pH and prevent denaturation of proteins
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12
Q

Why must the conditions of a homogenised solution be so specific?

A

this is so that the specimen does not change (or broken down by enzymes and osmotic damage)

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13
Q

What is filtration?

A

the homogenised cell solution is filtered through a gauze to remove large cell or tissue debris, the organelles are small enough to pass through the gauze
get rid of the large, unnecessary parts of the cell

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14
Q

What is a homogenate?

A

the homogenised cell solution

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15
Q

What is ultracentrifugation?

A

the filtered sol. is poured in a tube and spun in a centrifuge at a LOW speed
the heaviest organelles are flung to the bottom and form a pellet, other organelles remain suspended in fluid, called the supernatant
process is repeated at higher speeds each time

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16
Q

What is the order of mass of organelles?

A

nuclei heaviest
chloroplast
mitochondria
lysosomes
endoplasmic reticulum
ribosomes lightest

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17
Q

What is the difference between a light and electron microscope?

A

Light / Electron microscope

  • Uses light / -uses an electron beam
  • Takes few mins to prepare /-longer to prepare (day)
  • live or dead specimen / -only dead specimen
  • inexpensive / -expensive
    mag. - x1500 / -mag.- x1,500,000
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18
Q

Why does an electron microscope have a higher resolving power?

A

this is because the wavelength of an electron beam is a lot shorter than the wavelength of light so its better for resolution

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19
Q

What are the two types of electron microscopes?

A

TEM=transmission electron microscope

SEM= scanning electron microscope

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20
Q

How does a SEM work?

A

it scans a beam of electrons across the specimen, it knocks electrons off the specimen which are gathered in a cathode ray tube to form an image.
it only shows only the surface of the specimen
makes a 3D image of SURFACE
(lower resolution that TEM)

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21
Q

Hows does a TEM work?

A

they focus a beam of electrons on the cell which travels THROUGH the cell
on the image, denser parts of cell absorb more electrons so show up darker
whiter parts are less dense (less resistance of the electrons)
can see inside the cells

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22
Q

What are eukaryotic cells and 4 examples?

A
  • make up uni-cellular organisms
  • more complex, larger
  • most organelles are membrane bound
  • genetic material is enclosed in the nucleus
  • e.g-animal, plant, fungal and algal
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23
Q

How do algal and fungal cells compare to plant cells?

A

algal cells are very similar to plant cells

so are fungal cells but they have no chloroplasts and their cell walls are made of chitin, not cellulose

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24
Q

What is the cell surface membrane made up of?

A

a phospholipid bilayer,

also includes lipids and proteins

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25
Q

What is the structure of the nucleus?

A

a large organelle, surrounded by a nuclear envelope which contains many pores
also contains a nucleolus at centre of nucleus
chromatin= DNA when its not heavily coiled into a chromosome

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26
Q

What is the function of the nucleus and the nucleolus?

A

nucleus= control’s cells activities and DNA contains instructions to make proteins
nucleolus makes ribosomes

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27
Q

What is the structure of mitochondria?

A

have an inner membrane and an outer membrane
the inner is folded to form cristae
inside it is the MATRIX, which contains enzymes for respiration
contains 70s ribosomes

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28
Q

What is the function of mitochondria?

A

site of AEROBIC respiration, aerobic respiration produces ATP

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29
Q

What is the structure of chloroplasts?

A

has a double membrane
contains many thylakoid membranes which form stacks called grana
grana are linked by lamellae
stroma is the liquid inside the inner membrane

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30
Q

What is the function of the golgi apparatus?

A

it modifies and repackages proteins and lipids for specific destinations inside/outside the cell
vesicles fuse with the golgi apparatus membrane
also produces lysosomes

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31
Q

What is the structure of the golgi apparatus?

A

a group of fluid filled membrane bound flattened sacs

vesicles can fuse and leave golgi apparatus

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32
Q

What is a vesicle?

A

they are small, fluid filled sacs surrounded by membrane that carry proteins and lipids
that are transported from one organelle to another
they are formed as a ripped off piece of membrane from the SER or golgi apparatus

33
Q

What is the function of a lysosome?

A 
membrane-bound sac---its a type of transport vesicle
contains enzymes (lysozymes) that break down biological molecules or infectious bacteria
34
Q

What is exocytosis?

A

its the process of moving materials from within a cell to the exterior of the cell. This process requires energy and is therefore a type of active transport

35
Q

What is the structure of the rough endoplasmic reticulum?

A

RER is a system of membranes enclosing a fluid-filled space
the surface of it is covered with ribosomes
the folded part of the membrane is called the cisternae

36
Q

What is the folded part of the E.R?

A

called the cisternae

37
Q

What is the function of the RER?

A

holds ribosomes in place right outside the nucleus so outcoming RNA is much more likely to hit it
it then folds and processes the proteins that have been made at the ribosomes

38
Q

What is the function of the smooth endoplasmic reticulum?

A

no ribosomes
proteins move through SER to get ready to be transported
-can synthesise and process lipids

39
Q

What is a centriole?

A

they produce spindle fibres (which are used in mitosis to pull chromosomes apart)

40
Q

In what type of cells do permanent vacuoles exist?

A

permanent vacuoles only exist in plant cells

animal cells can contain a temporary vacuole

41
Q

What is inside the vacuole?

A

cell sap

which is a watery solution of sugars, enzymes and pigments

42
Q

What is the name of the membrane of a vacuole?

A

vacuole membrane——-> tonoplast

43
Q

What feature must cell walls have to allow things in and out?

A

permeability- they let everything in because the role of the membrane is to choose what can enter and leave so the cell wall just allows everything

44
Q

What are the pores in the cell wall called?

A

plasmodesmata- they connect two cells together by their cytoplasm, enabling exchange and transport of substances

45
Q

What is the function of the cell membrane?

A

to regulate what can enter and leave the cell

and has receptors to enable cellular communication

46
Q

What is the definition of a specialised cell?

A

a cell that is adapted and has special FEATUREs that allow it to carry out a particular function

47
Q

How is a muscle cell adapted for its function? (2)

A

mitochondria- carry out respiration that releases energy for muscle contraction
protein filaments- can slide over each other, allowing cell to become smaller, enabling muscle contraction

48
Q

What is the difference between villi and microvilli?

A

villi- multicellular structures that are covered by epithelial cells
microvilli- structures found on the cell membrane of each individual epithelial cell

49
Q

What is the size of a eukaryotic cell and a prokaryotic cell?

A

eukaryotic: 10-100µm
prokaryotic: 0.5-5µm

50
Q

Why is a stage micrometer used as well as an eyepiece graticule?

A

size of the units on the eyepiece graticule depend on the magnification so the micrometer is used to calibrate the graticule

51
Q

What are two conventions that must be followed to draw a biological drawing?

A

no sketching
no shading
use a sharp pencil
label lines should no cross

52
Q

What is the procedure for preparing a plant cell slide?

A
  • place the specimen on a slide
  • add a few drops of iodine solution onto the slide to stain the specimen
  • carefully place a coverslip over the specimen, making sure there are no air bubbles
53
Q

What is the function of a palisade cell and how is it specialised to carry out its function?

A

it produces carbohydrates by carrying out photosynthesis. it contains many chloroplasts to so can absorb maximum light energy

54
Q

What are the two main groups of prokaryotes?

A

bacteria

archaea

55
Q

How is DNA presented in a prokaryotic cell?

A

DNA is a CLOSED loop that floats freely in the cytoplasm

56
Q

What is a nucleoid?

A

an irregular shape region in a prokaryotic cell that comprises most of the genetic material
not membrane enclosed

57
Q

What is the size of a ribosome in a prokaryote and in a eukaryotic cell?

A

prokaryotic: 70s
eukaryotic: 80s

58
Q

What is the cytoplasm made up of in a prokaryotic cell?

A

cytosol

59
Q

What is the cell membrane composed of in a prokaryotic cell?

A

same as a eukaryotic cell

made of a phospholipid bilayer which also contains proteins and lipids embedded in it

60
Q

What is the cell wall in a prokaryote made up of?

A

peptidoglycan (or can also be called murein)

-a polymer of amino acids and sugars

61
Q

What is a mesosome and their predicted function?

A

they are infoldings of the cell membrane of a prokaryotic cell
function: could be to increase SA for respiration or for secretion

62
Q

What is the slime capsule and its function?

A

many pathogenic bacteria are surrounded by a slime capsule, a protective outer layer
-it protects the bacteria from viruses or a host’s immune system by hiding the antigens on the cell’s surface

63
Q

What is the slime capsule made up of and what does is contain?

A

made up of polysaccharides and contains water to protect against dessication

64
Q

What is dessication?

A

drying out

the water in the slime capsule is there to prevent the slime capsule form drying out

65
Q

What are flagella?

A

long, helical tubes that extend out of the cell walls which rotate to allow for movement, that are powered by protein motors

66
Q

What are pili?

A

they are hollow protein structures that are used in protein conjugation

67
Q

What is bacterial conjugation?

A

the transfer of genetic material from one bacterium to another (through physical contact)
plasmids replicated independently
the plasmid is replicated and transferred to the other bacterium because the membranes will fuse

68
Q

What is a plasmid?

A

a small loop of DNA

a copy from the main loop of DNA

69
Q

What is the function of the thylakoid membrane?

A

they are membrane bound compartments where the light dependent reactions for photosynthesis occur

70
Q

What is the function of a chloroplast?

A

location of where light dependent reactions occur to perform photosynthesis to produce carbohydrates/sugars

71
Q

Why can mitochondria have different shapes in an electron micrograph?

A

this is because the electron micrograph is only a cross section and the mitochondria is actually a 3D structure so it can be orientated differently

72
Q

Why are there many mitochondria in the epithelial cells lining the small intestine?

A

many mitochondria to provide more energy for a higher rate of respiration to carry out active transport and absorb digested food molecules

73
Q

What structures of a eukaryotic cell cannot be seen by a light microscope?

A

ribosomes
mitochondria
lysosomes
endoplasmic reticulum

74
Q

Why are thylakoid membranes advantageous in the chloroplasts?

A

they increase the surface are so maximum light can be absorbed

75
Q

What is this organelle:

‘has membranes arranged in stacks and contains DNA?

A

a chloroplast

76
Q

What is the content and function of the mitochondrial matrix?

A

contents: ribosomes, DNA, proteins
function: to synthesis proteins required for the mitochondrion
- to store substrates of respiration

77
Q

Why can structures such as mitochondria and ribosomes not be seen through a light microscope?

A

this is because it has a lower resolving power (because wavelength of light is longer), so less detail can be seen, reduced ability to distinguish between two objects

78
Q

What are the disadvantages of using TEM?

A

has to be a very thin specimen
cannot look at living cells
no colour image produced
preparation may cause artefacts

79
Q

Compare TEMs and SEMs?

A 
TEMs- give high resolution images
-can only be used on very thin specimens
-only dead specimens
SEMs- can be used on thick specimens
-gives a 3D image
-also can only be used on a non-living specimen

A-level AQA Biology (6 decks)

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