2.1 Cell Structure Flashcards
(70 cards)
1
Q
What is an electron micrograph?
A
Photograph of an image seen using an electron miscroscope
2
Q
What is magnification?
A
The number of times larger an image appears, compared with the size of the object
3
Q
What is an organelle?
A
Small structures within cells, each of which has a specific function
4
Q
What is a photomicrograph?
A
Photograph of an image seen using an optical microscope
5
Q
What is resolution?
A
The clarity of an image; the higher the resolution, the clearer the image
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
7
Q
What are light microscopes also known as?
A
Optical microscopes
8
Q
Which type of microscope was the first to be used?
A
Light microscope
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
10
Q
How do light microscopes focus light?
A
Lenses
11
Q
What is the maximum magnification that can be achieved with a light microscope?
A
x1500 (in some cases x2000)
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
13
Q
What is the radiation source in light microscopes?
A
Visible light
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
15
Q
What is the equation for calculating magnification?
A
Total magnification = magnifying power of objective lens x magnifying power of eyepiece lens
16
Q
What is the radiation source in a laser scanning microscope?
A
Laser light
17
Q
What are laser scanning microscopes also known as?
A
Confocal microscopes
18
Q
What is the resolution and contrast of a laser scanning microscope like?
A
High resolution and high contrast
19
Q
In electron microscopes, what is the radiation source?
A
A beam of fast travelling electrons
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
21
Q
What are the two types of electron microscope?
A
SEM (scanning electron miscroscope)
TEM (transmission electron microscope)
22
Q
During microscopy with electron microscopes, what material is used to stain the specimen?
A
Metal and metal salts
23
Q
How are the specimens prepared for microscopy using a TEM?
A
Has to be chemically fixed/dehydrated and stained
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
25
What is the difference in how the electrons form an image in an SEM and a TEM?
- 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
26
What kind of image does a TEM produce?
2D black and white (grey scale) image
27
What kind of image does an SEM produce?
A 3DD image (image is black and white but computer can add false colour)
28
What is the maximum magnification of a transmission electron microscope?
x50000000
29
What is the maximum magnification of a scanning electron microscope?
x200000
30
What are the disadvantages of both types of electron microscope?
- Are large and very expensive
| - Need lots of skill/training to use
31
What is an eyepiece graticule?
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
What is a stage graticule?
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
Which organisms have eukaryotic cells?
Animal, plant, fungal and protoctist cells
34
What are the features of a eukaryotic cell?
- 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
What is division of labour?
In cells, each organelle has a particular function so a cell can carry out all its functions efficienctly
36
Which type of cells have membrane bound organelles?
Eukaryotic cells
37
What does it mean if an organelle is membrane bound?
Covered by a membrane
38
What is the purpose of having membrane bound organelles?
Keeps organelles separate from the rest of the cell
39
What is the structure of the nucleus and the nuclear envelope?
- Nucleus surrounded by a double membrane: nuclear envelope
- Nuclear envelope has pores
- Nucleus has chromatin in it
40
What is the function of the chromatin?
- 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
What is the function of the nuclear envelope?
- 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
What is the function of the nuclear pores?
- Enable larger substances (e.g. messenger RNA) to leave nucleus
- Some substances, e.g. steroid hormones, enter through pores to cytoplasm
43
What is the function of the nucleolus?
Where ribsosomes are made
44
What is the function of the nucleus?
- Control centre of the cell
- Stores organism's genome
- Transmits genetic information
- Provides instructions for protein synthesis
45
What is the structure of the rough endoplasmic reticulum?
- System of membranes, containing fluid filled cavities (cisternae) continuous with the nuclear membrane
- Coated with ribosomes
46
What is the function of the rough endoplasmic reticulum?
- 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
What is the structure of the smooth endoplasmic reticulum?
- System of membranes with fluid filled cavities (cisternae) continuous with nuclear membrane
- No ribosomes on its surface
48
What is the function of the smooth endoplasmic reticulum?
- 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
What is the structure of the Golgi apparatus?
- Consists of stacks of membrane bound flattened sacs
| - Secretory vesicles bring materials to + from the Golgi apparatus
50
What is the function of the Golgi apparatus?
- 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
What is the structure of a mitochondrion?
- 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
What is the function of the mitochondria?
- 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
What is the structure of chloroplasts?
- 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
What is the function of chloroplasts?
- 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
What is the structure of the vacuole?
- Surrounded by a double membrane called the tonoplast
| - Contains fluid
56
What is the function of the vacuole?
- 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
What is the structure of lysosomes?
- 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
What is the function of the lysosomes?
- 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
What is the structure of the cilia and undulipodia?
- Protrusions from cell + are surrounded by cell surface membrane
- Each contain microtubules
- Formed from centrioles
60
What is the function of the cilia and undulipodia?
- 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
What is the structure of the ribosomes?
- 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
What is the function of the ribosomes?
- 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
What is the structure of centrioles?
- Consist of 2 bundles of microtubules at right angles to each other
- Made of tubular protein subunits + are arranged to form a cylinder
64
What is the function of the centrioles?
-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
Which type of plant cells usually have centrioles?
They're absent from cells of higher plants but may be in some unicellular green algae e.g. Chlamydomonas
66
What is the structure of the cytoskeleton?
- 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
What is the function of the cytoskeleton?
-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
What is the structure of the cellulose cell wall?
- Oustide the plasma membrane in plants
| - Made of bundles of cellulose fibres
69
What is the function of the cellulose cell wall?
- 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
What is the cell wall of fungi made of?
Chitin, not cellulose
