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AS Biology - Module 2 > 2.1 Cell Structure > Flashcards

2.1 Cell Structure Flashcards

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1
Q

What is an electron micrograph?

A

Photograph of an image seen using an electron miscroscope

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2
Q

What is magnification?

A

The number of times larger an image appears, compared with the size of the object

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3
Q

What is an organelle?

A

Small structures within cells, each of which has a specific function

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4
Q

What is a photomicrograph?

A

Photograph of an image seen using an optical microscope

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5
Q

What is resolution?

A

The clarity of an image; the higher the resolution, the clearer the image

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6
Q

What type of magnification do microscopes produce and what does this mean?

A

Linear - if specimen seen magnified x100, it appears 100 times longer and 100 times wider than it really is

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7
Q

What are light microscopes also known as?

A

Optical microscopes

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8
Q

Which type of microscope was the first to be used?

A

Light microscope

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9
Q

Why are optical microscopes still so widely used?

A
  • Relatively cheap
  • Easy to use
  • Portable + able to be used in field + laboratories
  • Can study whole living specimens
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10
Q

How do light microscopes focus light?

A

Lenses

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11
Q

What is the maximum magnification that can be achieved with a light microscope?

A

x1500 (in some cases x2000)

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12
Q

Why are light microscopes limited to the magnification that they have?

A

Their resolution is limited - any closer and you can’t see a clear image

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13
Q

What is the radiation source in light microscopes?

A

Visible light

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14
Q

What is the maximum resolution of light microscopes and why?

A

200nm (0.2 micrometers) as the wavelength of visible light is 400-700nm. Anything closer together than 200nm will appear as one object

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15
Q

What is the equation for calculating magnification?

A

Total magnification = magnifying power of objective lens x magnifying power of eyepiece lens

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16
Q

What is the radiation source in a laser scanning microscope?

A

Laser light

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17
Q

What are laser scanning microscopes also known as?

A

Confocal microscopes

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18
Q

What is the resolution and contrast of a laser scanning microscope like?

A

High resolution and high contrast

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19
Q

In electron microscopes, what is the radiation source?

A

A beam of fast travelling electrons

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20
Q

How do electron microscopes work?

A
  • Electrons fired from a cathode
  • Focussed by magnets onto a screen or photographic plate
  • Wavelength about 0.004nm (125000 times smaller than central part of visible light spectrum) so has a much greater resolution
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21
Q

What are the two types of electron microscope?

A

SEM (scanning electron miscroscope)

TEM (transmission electron microscope)

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22
Q

During microscopy with electron microscopes, what material is used to stain the specimen?

A

Metal and metal salts

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23
Q

How are the specimens prepared for microscopy using a TEM?

A

Has to be chemically fixed/dehydrated and stained

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24
Q

What is different about the specimens used in a light microscope and specimens used in an electron microscope?

A

As electron microscopes have to use a vacuum, the specimen must be dead. In light microscopes, the specimen can be alive as it doesn’t take place in a vacuum

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25
Q

What is the difference in how the electrons form an image in an SEM and a TEM?

A
  • TEM: electrons pass through and are focused onto a screen or photographic plate
  • SEM: electrons cause secondary electrons to bounce of the specimen’s surface onto a screen
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26
Q

What kind of image does a TEM produce?

A

2D black and white (grey scale) image

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27
Q

What kind of image does an SEM produce?

A

A 3DD image (image is black and white but computer can add false colour)

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28
Q

What is the maximum magnification of a transmission electron microscope?

A

x50000000

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29
Q

What is the maximum magnification of a scanning electron microscope?

A

x200000

30
Q

What are the disadvantages of both types of electron microscope?

A
  • Are large and very expensive

- Need lots of skill/training to use

31
Q

What is an eyepiece graticule?

A

A measuring device. It’s placed in the eyepiece of a microscope and acts as a ruler when you view an object under a microscope.

32
Q

What is a stage graticule?

A

A precise measuring device. It is a small scale that is placed on a microscope stage and used to calibrate the value of eyepiece divisons at different magnifications

33
Q

Which organisms have eukaryotic cells?

A

Animal, plant, fungal and protoctist cells

34
Q

What are the features of a eukaryotic cell?

A
  • Nucleus: surrounded by nuclear envelope + containing DNA organised/wound into linear chromosomes
  • Nucleolus: in nucleus, contains RNA, where chromosomes unwind. Involved in making ribosomes
  • Cytoplasm: where organisms are suspended
  • Cytoskeleton: network of protein filaments (actin or microtubules) that move organelles within the cell. Allow some cells to move + allow contraction of the muscles
  • Plasma membrane
  • Other membrane bound organelles: Golgi apparatus, mitochondria, endoplasmic reticulum
  • Small vesicles
  • Ribosomes: organelles without membranes, where proteins are assembled
35
Q

What is division of labour?

A

In cells, each organelle has a particular function so a cell can carry out all its functions efficienctly

36
Q

Which type of cells have membrane bound organelles?

A

Eukaryotic cells

37
Q

What does it mean if an organelle is membrane bound?

A

Covered by a membrane

38
Q

What is the purpose of having membrane bound organelles?

A

Keeps organelles separate from the rest of the cell

39
Q

What is the structure of the nucleus and the nuclear envelope?

A
  • Nucleus surrounded by a double membrane: nuclear envelope
  • Nuclear envelope has pores
  • Nucleus has chromatin in it
40
Q

What is the function of the chromatin?

A
  • Genetic material
  • Consists of DNA wound around histone proteins
  • When cell isn’t dividing, chromatin is spread out/extended
  • When cell is about to divide, chromatin condenses + coils tightly into chromosomes
  • Make up nearly all the organism’s genome
41
Q

What is the function of the nuclear envelope?

A
  • Separates contents of nucleus from rest of cell

- In some regions, outer + inner nuclear membrane fuse so some dissolved substances + ribosomes can pass through

42
Q

What is the function of the nuclear pores?

A
  • Enable larger substances (e.g. messenger RNA) to leave nucleus
  • Some substances, e.g. steroid hormones, enter through pores to cytoplasm
43
Q

What is the function of the nucleolus?

A

Where ribsosomes are made

44
Q

What is the function of the nucleus?

A
  • Control centre of the cell
  • Stores organism’s genome
  • Transmits genetic information
  • Provides instructions for protein synthesis
45
Q

What is the structure of the rough endoplasmic reticulum?

A
  • System of membranes, containing fluid filled cavities (cisternae) continuous with the nuclear membrane
  • Coated with ribosomes
46
Q

What is the function of the rough endoplasmic reticulum?

A
  • Intracellular transport system: cisternae form channels to transport substances from one area of a cell to another
  • Gives large SA for ribosomes (that assemble amino acids into proteins). Proteins actively pass through membrane into cisternae + are transported to Golgi apparatus for modification + packaging
47
Q

What is the structure of the smooth endoplasmic reticulum?

A
  • System of membranes with fluid filled cavities (cisternae) continuous with nuclear membrane
  • No ribosomes on its surface
48
Q

What is the function of the smooth endoplasmic reticulum?

A
  • Contains enzymes to catalyse reactions to do with lipid metabolism, e.g. synthesis of cholesterol, steroid hormones, and lipids/phospholipids needed by the cell
  • Involved with absorption, synthesis + transport of lipids (from the gut)
49
Q

What is the structure of the Golgi apparatus?

A
  • Consists of stacks of membrane bound flattened sacs

- Secretory vesicles bring materials to + from the Golgi apparatus

50
Q

What is the function of the Golgi apparatus?

A
  • Proteins are modified e.g. adding sugar molecules to make glycoproteins or lipids to make lipoproteins and being folded into their 3D shape
  • Proteins are packaged into vesicles that are pinched off then: stored in cell or moved to plasma membrane, either for incorporation to plasma membrane or exported outside the cell
51
Q

What is the structure of a mitochondrion?

A
  • Spherical, rod shaped or branched, 2-5μm long
  • Surrounded by two membranes with fluid filled space between them. Inner membrane is highly folded into cristae
  • Inner part of mitochondrion is a fluid filled matrix
52
Q

What is the function of the mitochondria?

A
  • Site of ATP (energy currency) production during aerobic respiration
  • Self replicating, so more can be made if cell’s energy need increases
  • Abundant in cells with more metabolic activity, e.g. liver cells + at synapses between neurones where neurotransmitter is synthesised/released
53
Q

What is the structure of chloroplasts?

A
  • Large organelles, 4-10μm
  • Only found in plant cells/some protoctists
  • Surrounded by a double membrane/envelope. Inner membrane is continuous with stacks of flattened membrane sacs called thylakoids (looks like piles of plates) that contain chlorophyll. Each stack is called a granum. Fluid filled matrix called a stroma
  • Contain loops of DNA + starch grains
54
Q

What is the function of chloroplasts?

A
  • Site of photosynthesis
  • 1st stage: light energy trapped by chlorophyll + used to make ATP, in grana. Water also split to supply hydrogen ions
  • 2nd stage: hydrogen reduces carbon dioxide with energy from ATP to make carbohydrates, in stroma
  • Abundant in leaf cells, especially palisade mesophyll layer
55
Q

What is the structure of the vacuole?

A
  • Surrounded by a double membrane called the tonoplast

- Contains fluid

56
Q

What is the function of the vacuole?

A
  • Only plant cells have a large, permanent vacuole
  • Filled with water + solutes + maintains cell stability as when full pushes against cell wall, making the cell turgid
  • If all plant cells are turgid then this helps support the plant, especially non-woody plants
57
Q

What is the structure of lysosomes?

A
  • Small bags, formed from the Golgi apparatus. Surrounded by a single membrane
  • Contain powerful hydrolytic (digestive) enzymes
  • Abundant in phagocytic cells, e.g. neutrophils + macrophages (types of WBC) at can ingest + digest invading pathogens e.g. bacteria
58
Q

What is the function of the lysosomes?

A
  • Keep powerful hydrolytic enzymes separate from rest of cell
  • Can engulf old cell organelles + foreign matter, digest them + return digested components to cell for reuse
59
Q

What is the structure of the cilia and undulipodia?

A
  • Protrusions from cell + are surrounded by cell surface membrane
  • Each contain microtubules
  • Formed from centrioles
60
Q

What is the function of the cilia and undulipodia?

A
  • Epithelial cells lining airways each have many cilia that beat + move the band of mucus
  • Almost all cell types in body have one cilium to act as an antenna. Contains receptors + allows cell to detect signals about its immediate environment
  • Only one type of human cell have an undulipodium (longer cilium): spermatozoon (sperm). Enables spermatozoon to move
61
Q

What is the structure of the ribosomes?

A
  • Small, spherical organelles, around 20nm in diameter
  • Made of ribosomal DNA
  • Made in nucleolus as 2 subunits, that pass through nuclear envelope into cell cytoplasm + then combine
  • Some remain free in cytoplasm + some attach to endoplasmic reticulum
62
Q

What is the function of the ribosomes?

A
  • Bound to exterior or RER: mainly for synthesising proteins to be exported outside cell
  • Free in cytoplasm, either singly or in clusters, site of assembly of proteins for use in the cell
63
Q

What is the structure of centrioles?

A
  • Consist of 2 bundles of microtubules at right angles to each other
  • Made of tubular protein subunits + are arranged to form a cylinder
64
Q

What is the function of the centrioles?

A

-Before cell divides, spindle (made of tubulins) forms from centrioles
-Chromosomes attach to middle part of spindle + motor proteins walk along tubulin threads, pulling chromosomes to opposite ends of cell
Help form cilia + undulipodia:
-Before cilia form, centrioles multiply + line up beneath cell surface membrane
-Microtubules sprout outwards from each centriole, forming cilium or undulipodium

65
Q

Which type of plant cells usually have centrioles?

A

They’re absent from cells of higher plants but may be in some unicellular green algae e.g. Chlamydomonas

66
Q

What is the structure of the cytoskeleton?

A
  • Network of protein structures in cytoplasm
  • Rod-like microfilaments made of subunits of protein actin, there’s polymers of actin + each microfilament = abound 7nm (diameter)
  • Intermediate filaments about 10nm diameter
  • Straight, cylindrical microtubules made of protein subunits called tubulin (18-30nm diameter)
  • Consists of cytoskeletal motor proteins, myosins, kinesins + dyneins, that are molecular motors. They’re enzymes + have site that binds to + allows hydrolysis of ATP as their energy source
67
Q

What is the function of the cytoskeleton?

A

-Protein filaments within cytoplasm give support + mechanical strength to keep cell’s shape stable + allow cell movement
-Microtubules provide shape + support to cells, help substances move through cytoplasm within a cell:
•Form track along which motor proteins (dyenein and kinesin) walk + drag organelles from one part of cell to another
•Form spindle before a cell divides. Spindle threads enable chromosomes to be moved within a cell
•Microtubules make up cilia, undulipodia + centrioles
-Intermediate filaments made of a variety of proteins. They:
•Anchor nucleus within cytoplasm
•Extend between cells in some tissues, between special junctions, enabling cell to cell signalling + allows cells to adhere to a basement membrane, therefore stabilising tissues

68
Q

What is the structure of the cellulose cell wall?

A
  • Oustide the plasma membrane in plants

- Made of bundles of cellulose fibres

69
Q

What is the function of the cellulose cell wall?

A
  • Strong + can prevent plant cells bursting when turgid (swollen)
  • Provide strength + support
  • Maintain cell’s shape
  • Contribute to strength + support of whole plant
  • Permeable + allow solutions (solute + solvent) to pass through
70
Q

What is the cell wall of fungi made of?

A

Chitin, not cellulose

AS Biology - Module 2 (3 decks)

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