A-level Biology > 2.1.1 - Cell structure > Flashcards

2.1.1 - Cell structure Flashcards

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1
Q

Name the different types of microscopes ?

A
  • Light microscope
  • Transmission electron microscope ( TEM )
  • Scanning electron microscope ( SEM )
  • Laser scanning confocal microscope
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2
Q

What are the features of a light microscope ?

A
  • Uses light to form an image
  • Resolution of 0.2 µm
  • Maximum magnification of x 1500
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3
Q

What are light microscope used to observe ?

A

Large structures like :
- Entire cells
- Nuclei
- Mitochondria and chloroplasts

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4
Q

What are the advantages of light microscopes ?

A
  • They are small/ relatively cheap
  • Specimen preparation can be straightforward enough to perform in a school laboratory
  • Produce colour images
  • Allow the observation of living specimens
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5
Q

Explain how a light microscope produces an image ?

A
  • The specimen is placed on a glass slide on the stage
  • Visible light ( from light bulb/ mirror ) passes through the specimen
  • The objective lens produces a magnified image which is magnified again by the eye piece lens
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6
Q

Explain how to prepare sample for light microscope ?

A
  • Place stain at edge of sample
  • Lower cover slip at an angle/ use mounted needle
  • Use blotting paper to pull stain through/ remove excess stain
  • Use more than one stain to increase contrast
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7
Q

What are the features of an electron microscope ?

A
  • Uses a beam of electrons to form image which are focused using elecromagnets
  • Have a resolution of 0.2 nm
  • Have a maximum magnification of x 1,000,000
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8
Q

What are electron microscope used to observe ?

A

Small structures inside cells like :
- Cell membranes
- Ribosomes
- Endoplasmic reticulum
- Lysosomes

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9
Q

What are the disadvantages of an electron microscope ?

A
  • They are very large and expensive
  • Complex sample/specimen preparation process
  • Specimens must be dead/ not-living a viewed in a vacuum
  • Images are always black and white
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10
Q

Explain how a transmission electron microscope produces an image ?

A
  • TEMs use electromagnets to transmit a beam of electrons through a very thin specimen to produce high resolution 2D image
  • Denser parts of the specimen absorb more electrons, meaning that denser parts appear darker on the final image
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11
Q

Explain how a scanning electron microscope produces an image ?

A
  • SEMs pass a beam of electrons which are bounced/ reflected off the surface of a specimen
  • They then detect the rate at which the electrons bounce back forming a 3D image of the surface of the specimen
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12
Q

What is the difference between images produced by TEM’s and SEM’s ?

A
  • TEM’s produce 2D images that allow the internal structures within cells, and within organelles to be seen
  • SEM’s produce 3D images of the surface of a specimen
  • TEM’s produce high resolution images ( 0.5 nm ) while SEM’s have a lower maximum resolution than TEM’s
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13
Q

What are the features of a laser scanning conical microscope ?

A
  • A higher light intensity is used to view specimen
  • Uses a laser to focus light/ magnify the specimen
  • The specimen is treated with a fluorescent chemical/ dye
  • Light is absorbed and re-emitted by the specimen
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14
Q

Explain how a laser scanning cofocal microscope produces a magnified image ?

A
  • Light is directed through the thin layer of biological material that is supported on a glass slide
  • This light is focused through several lenses so that an image is visible through the eyepiece
  • The magnifying power of the microscope can be increased by rotating the higher power objective lens into place
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15
Q

Explain how you use an eyepiece graticule and micrometer to measure length of cell ?

A
  • Use eyepiece graticule
  • Calibrate graticule using micrometer
  • Align two scales and record number of divisions per graticule unit
  • Measure the diameter of the nucleus in graticule units/ epu
  • Take repeated measurements and calculate the mean diameter
  • Use calibrated epu to calculate diameter
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16
Q

What is staining ?

A

The process of dyeing specimen to increase contrast and identify specific components

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17
Q

Why is staining used during light microscopy ?

A
  • Staining increases contrast
  • This allows organelles to become more easily visible by binding to stain
  • This results in a more clear image being produced
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18
Q

What is differential staining ?

A

The process of distinguishing between two types of organism or organelles of an organism ( that would otherwise be hard to identify ) by using more than one dye

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19
Q

How do you represent cell structures seen under a light microscope ?

A
  • Draw solid continuous lines
  • Line should not overlap
  • Draw proper proportions
  • No shading
  • Label or identifiable organelles visible ( label lines should not cross or have arrowheads and should connect directly )
  • Title drawing
  • State magnification
  • Use at least 50% of space available
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20
Q

What is the equation for magnification ?

A

magnification = ( image size ) / ( object size )

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21
Q

Do you know how to do magnification calculations ?

A

Yes

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22
Q

Define the term ‘magnification’ ?

A

Magnification - How many times larger the image in comparison to the size of the object

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23
Q

Define the term ‘resolution’ ?

A

Resolution - The ability to see individual objects as separate entities instead of as one

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24
Q

List the differences between a light and electron microscope ?

A
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25
Label the cell ?
26
What is the function of the nucleus ?
- 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
27
What is the nucleolus ?
An area within the nucleus that is the site of ribosome production
28
What is the function of the nucleolus ?
Ribosome production
29
What is the nuclear envelope ?
A double membrane that surrounds the nucleus
30
What is the function of the nuclear envelope ?
It protects the nucleus from damage in the cytoplasm
31
What are nuclear pores ?
They are gaps/ holes in the nuclear envelope
32
What is the function of nuclear pores ?
- Allow for the movement of substances in and out of nucleus - Allow mRNA and ribosomes to travel out of the nucleus - Allow enzymes (eg. DNA polymerases) and signalling molecules to travel in
33
What is the rough and smooth endoplasmic reticulum ?
- Flattened sac of membrane - The SER has no ribosomes attached to its surface - The RER has ribosomes bound to its surface
34
What are the features of the rough endoplasmic reticulum ( RER ) ?
- Found in plant and animal cells - Surface covered in ribosomes - Formed from continuous folds of membrane continuous from nuclear envelope - Responsible for the synthesis, processing and transport of proteins
35
What are the features of the smooth endoplasmic reticulum ( SER ) ?
- Found in plant and animal cells - Does not have ribosomes on its surface - Involved in the production, processing and storage of lipids, carbohydrates and steroids
36
What are the features of the Golgi apparatus ?
- Found in plant and animal cells - Flattened sacs of membrane - Modifies proteins and lipids before packaging them into Golgi/ secretory vesicles
37
What are the features of ribosomes ?
- Each ribosome is a complex/ made of ribosomal RNA (rRNA) and proteins - 80S ribosomes are found in eukaryotic cells - 70S ribosomes in prokaryotes, mitochondria and chloroplasts - Site of translation/ protein synthesis
38
Where are ribosomes found in a cell ?
- Free-floating in the cytoplasm - Bound to the surface of the rough endoplasmic reticulum in eukaryotic cells
39
What is the function of ribosomes ?
They are the site of translation/ protein synthesis
40
Label the mitochondrion ?
41
What is the function of the mitochondria ?
The site of aerobic cellular respiration
42
Explain the structure of the mitochondria ?
- Mitochondria have a double membrane, an inner and outer membrane - The foldings of the inner membrane are called cristae and the fluid interior the mitochondrial matrix - Mitochondrial matrix contains enzymes needed for aerobic respiration, producing ATP - Mitochondrial matrix contain mitochondrial DNA and ribosomes - This allows mitochondria to produce they own enzymes and proteins required for replication/ aerobic respiration
43
What are vesicles ?
A membrane-bound sac for transport and storage
44
What are lysosomes ?
Specialist forms of vesicles which contain hydrolytic enzymes ( lysozymes )
45
What is the function of lysosomes ?
- They are responsible for breaking down waste material in cells ( eg. Worn out organelles ) - They are responsible for breaking down pathogens ingested by phagocytic cells/ apoptosis
46
What is the cytoskeleton ?
A network of protein fibres
47
What is the function of the cytoskeleton ?
- Mechanical strength : Provides mechanical strength to maintain the shape of the cell and supports organelles by keeping them in position - Involved in organisation of spindle fibres during cellular division - Intracellular movement : AIDS TRANSPORT of organelles/ molecules in the cell - Extra cellular movement : The cytoskeleton enables cell movement via cilia and flagella which contain microtubules
48
What are the main components of the cytoskeleton ?
- Microfilaments - Microtubules
49
What are microfilaments and what is their function ?
- Microfilaments are solid strands that are mostly made of the protein actin - Responsible for cell movement/ movement of some organelles within cells by contracting
50
What are microtubules and what are their function ?
- Microtubules are tubular/ hollow strands that are mostly made of the protein tubulin - Organelles/ other cell contents are moved along these fibres using ATP
51
What are the features of centrioles ?
- Hollow fibres made of microtubules - Two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division - Not found in flowering plants and fungi
52
What are the main differences between Animalia and plant cells in terms of structure ?
- Animal cells: centrioles and microvilli - Plant cells: the cellulose cell wall, large permanent vacuoles and chloroplasts
53
Explain how the various organelles work together to produce and secrete proteins ?
- Nucleolus synthesises ribsosomes for protein synthesis in the rough endoplasmic reticulum - Nucleus synthesises mRNA via transcription which leaves nucleus and binds to ribosome for translation - Proteins are synthesised by ribosomes bound to RER - Proteins pass into RER's cisternae and are folded/ processed - Proteins are packaged into TRANSPORT vesicles and move from RER to Golgi apparatus via microtubules - Vesicles fuse with CIS FACE of Golgi apparatus and proteins are modified and packaged into secretory/ Golgi vesicles - Secretory vesicles fuse with the cell surface membrane and secrete proteins via exocytosis
54
Label the cell ?
55
How do prokaryotic cells differ from eukaryotic notes ?
- A cytoplasm that lacks membrane-bound organelles - Their ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S) - No nucleus (instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins) - A cell wall that contains murein (a glycoprotein)
56
What extra structures do prokaryotic cells contain ?
- Plasmids - Capsules - Flagellum
57
What are the features of plasmids ?
- Plasmids are small loops of DNA that are separate from the main circular DNA molecule - Plasmids contain genes that can be passed between prokaryotes (e.g. genes for antibiotic resistance)
58
What are features of the capsule of prokaryotic cells ?
- A final out layer/ slime capsule - It helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism
59
What is the cell wall made up of for different organisms ?
- Cellulose in plants - Chitin in fungi - Peptidoglycan in prokaryotic organsims
60
What is the function of the cell wall ?
- It is freely permeable so allows for the passing of substances to and away from cell membrane - It provides mechanical strength and offers structural support to cell - It acts as a defence mechanism and protects the cell against invading pathogens
61
What are features of the permanent vacuole ?
- A sac in plant cells surrounded by the tonoplast, selectively permeable membrane - Vacuoles in animal cells are not permanent and small
62
What is the function of the permanent vacuole ?
- It is responsible for maintaining turgor pressure within the cell and keeping it rigid - It is selectively permeable and allows for the passage of small molecules in and out of the vacuole
63
What is the membrane of the permanent vacuole made of ?
Tonoplast
64
Label the chloroplast ?
65
What is the function of chloroplasts ?
It is the site of photosynthesis
66
Explain the structure of chloroplasts ?
- Chlorplasts have a double membrane, an inner and outer membrane - The fluid enclosed within is called the storma - Grana are stacks of disc-shaped sacs called thylakoids - Grana are joined by lamellae - Grana contain chlorophyll-pigments where light-dependant reactions occur during photosnyethsis - Chlroplasts contain small amounts of DNA and ribosomes so can make their own enzymes and proteins required for photosynthesis/ replication
67
What are features of flagella ?
- They are tail-like structures made of longer Microtubules which ROTATE - Contract to enable cell mobility/ locomotion
68
What are the features of cilia ?
- Hair-like projections made from microtubules - Allows the movement of substances over the cell surface
69
Lis the similarities and differences between prokaryotic and eukaryotic cells ?
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