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Ocr A Level Biology > Cell structure > Flashcards

Cell structure Flashcards

1
Q

Define magnification

A

How many times larger the image is compared to the actual size of the specimen

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2
Q

Define resolution

A

ability to distinguish between 2 points that are close together

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3
Q

What is the equation for magnification

A

magnification=image size/real size

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4
Q

Light microscopes

A

Max magnification:1500x
Max resolution:200nm
-resolution is poor due to long wavelength
-use visible light to form an image
-wavelength of visible light is around 500-650nm
-impossible to distinguish between 2 objects that are closer together than half the wavelength of light
-can view tissues and cells. Eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts
-cannot observe smaller organelles

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5
Q

Advantages of Optical(Light) microscope

A

-cheap to buy and easy to use
-you don’t need to kill the specimen

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6
Q

disadvantages of optical(light microscope

A

-lower magnification
-lower resolution
-can’t see the organelles

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7
Q

Electron microscopes

A

-use electrons to form an image
-a beam of electrons have a smaller wavelength compared to light so it has a higher resolution
-maximum resolution of 0.2nm(can be used to observe small organelles such as ribosomes, endoplasmic reticulum or lysosomes)
-maximum magnification of electron microscope is about 1,500,000

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8
Q

Transmission electron microscopes(TEM)

A

-electrons are fired at the specimen and pass through the material. It is transmitted through the specimen
-denser parts of the specimen absorb more electrons which makes them appear more darker-produces contrast between different parts of the object being observed

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9
Q

Advantages of TEM

A

-can see transparent organelles
-high resolution and magnification
-internal structures can be seen

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10
Q

Disadvantages of TEM

A

-specimen must be dead
-image will be in black and white
-expensive

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11
Q

Scanning electron microscope(SEM)

A

-electrons are fired at the specimen and the beam bounces off the surface of the material and electrons are detected to create a 3D image

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12
Q

Advantages of SEM

A

-can be used on thick or 3D specimen
-allows 3D structure of specimen to be observed

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13
Q

Disadvantages of SEM

A

-specimen must die
-image is in black and white
-expensive

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14
Q

Laser scanning confocal microscope

A

-thick section of tissue or small living organisms are scanned with a laser beam which is reflected by fluorescent dyes
-computer then assembles an image

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15
Q

advantages of Laser scanning confocal microscope

A

-specimen can live
-high resolution
-3D image is produced

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16
Q

disadvantages of Laser scanning confocal microscope

A

-slow process
-laser can cause photodamage to the cells
-very expensive

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17
Q

What is an eyepiece graticule?

A

-An eyepiece graticule is a disc within the eyepiece lens that has a cm ruler. Full length is always shown and length is fixed

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18
Q

What is a stage micrometre?

A

It is a glass disc with a measurement

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19
Q

How to calibrate an eyepiece graticule:

A

-identify a region where the divisions of the eyepiece graticule and stage micrometre line up well
-count divisions of eyepiece graticule and SM in that region
-in 2 columns, write down the eyepiece graticule unit and the length of SM in that region
-divide length of SM by the number of EGU and that gives the length that represents 1 EGU

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20
Q

Magnification

A

-size of cell is usually measured in micrometres(Um) and cellular structures are usually measured in nanometres or micrometres
-all measurements must be the exact same when doing calculations
magnification=eyepiece lens magnification x objective lens magnification

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21
Q

Resolution

A

-if 2 separate points cannot be resolved, they will be observed as one point
-resolution of light microscope is limited as wavelength of light is too long
-longer the wavelength of light, the more it is diffracted
-electron microscopes have a higher resolution due to smaller wavelength of beam of electrons compared to light

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22
Q

Light microscope extra

A

-shine light through specimen which is passed through an objective lens and an eyepiece lens which magnify the specimen

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23
Q

electron microscope extra

A

-fire a beam of electrons
-shorter wavelength-high resolution
-useful for looking at organelles, viruses and DNA
-requires dead specimen

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24
Q

Eukaryotic cells

A

-all cells are surrounded by a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment
-membrane is ‘partially permeable’
-cell membrane is formed from a phospholipid bilayer

25
Cell walls
-found in plant cells and bacterial cells. Not animal cells though -formed outside the cell membrane and offer structural support to the cell -structural support is provided by the polysaccharide cellulose in plants and peptidoglycan in most bacterial cells
26
Nucleus
-present in all eukaryotic cells(except red blood cells) -nucleus is the largest organelle in the cell and separated by the cytoplasm via a double membrane->nuclear envelope which has many pores -nuclear pores allow mRNA and ribosomes to travel out of the nucleus and letting enzymes travelling in -nucleus contains chromatin(material from which chromosomes are made) -chromosomes are made of sections of linear DNA tightly wound around proteins called histones
27
Example of exchange in nuclear pores
DNA is too large of a molecule to leave the nucleus to the site of protein synthesis so it is transcribed into smaller RNA molecules which is exported via the nuclear pores
28
Nucleolus
-produces ribosomes which move out of the nucleus and latch onto the outside of the rough ER where they produce proteins -composed of proteins and RNA. RNA is used to produce ribosomal RNA which is combined with proteins to from ribosomes for protein synthesis.
29
Nuclear envelope
-made of a double membrane -contains nuclear pores to allow molecules to move in and out of the nucleus
30
Mitochondria-present in plant and animal cells
-energy generating organelle -site for final stage of cellular respiration where energy stored in the bonds of complex organic molecules is made available for cell to use by production of molecule ATP -has an inner and outer membrane(double membrane) -inner membrane folds inwards to form cristae which projects into a fluid called the matrix -inner membrane has enzymes to catalyse reactions of aerobic respiration to form ATP
31
Smooth Endoplasmic reticulum -found in plant and animal cells
-formed from continuous folds of membrane which continues off from the nuclear envelope -fluid filled cavities -no ribosomes latched onto surface -involved in the production, processing and storage of lipids, carbohydrates and steroids
32
Rough Endoplasmic reticulum -found in plant and animal cells
-formed from continuous folds of membrane which is continued from the nuclear envelope -coated with ribosomes -fluid filled cavities -processes proteins made from the ribosomes
33
Golgi apparatus -found in plant and animal cells
-stack on membrane bound flattened sacs -modifies proteins and lipids before packaging them into Golgi vesicles which transport them to required destination
34
Lysosomes -found in animal cells but not in plant cells
-forms of vesicles -small bags near a Golgi apparatus -contains hydrolytic enzymes which break biological molecules down -break down waste materials such as worn out organelles -used by cells of the immune system and in apoptosis(programmed cell death)
35
Ribosomes -found in all cells
-spheres with ribosome DNA bound to RER -sites of protein synthesis -made of rRNA and protein
36
Centrioles -only animal cell
-hollow fibres made of microtubules -2 centrioles at right angles form a centrosome which organise the spindle fibres during cell division -made of the protein, tubulin
37
Microtubules -found in all eukaryotic cells
-makes up the cytoskeleton of the cell -made of Alpha and Beta tubulin combined to form dimers which join to make protofilaments -13 protofilaments in a cylinder make a microtubule
38
Cilia -found in plant and animal cells
-hair like projections made from microtubules -protrusions from the cell surface membrane -when mobile, they help move substances in a sweeping motion -when stationary, they have an important function in sensory organs
39
flagella -found in specialised cells
-enables cell mobility -sensory organelles detect chemical changes in an environment
40
chloroplasts -found in plant cells
-surrounded by double membrane -found in green parts of the plant-green colour is the result of the photosynthetic pigment chlorophyll -chlorophyll traps sunlight
41
Large permanent vacuole -found in plant cells
-maintains cell stability especially when it is turgid -provides rigid framework for the cell -contents of cell push against the cell wall. -membrane is called tonoplast -selectively permeable so some molecules can pass through and some cannot -if vacuole does appear in animal cells, it is not large and permanent
42
What are organelles?
-specialised parts of the cell that carry out a particular function -some organelles are membrane bound -nucleus stores DNA which codes for production of proteins-also contains nucleolus which manufactures ribosomes.
43
Stages of production of protein
-DNA from nucleus is copied into the molecule mRNA via transcription -mRNA leaves the nucleus through the nuclear pore and attaches to a ribosome on the rough endoplasmic reticulum -ribosome reads instructions contained within the mRNA and uses this code to synthesise a protein via translation -protein passes into the lumen of the rough ER to be folded and processed --processed proteins are transported to the Golgi apparatus in vesicles which fuse with the Golgi apparatus, releasing the proteins via the transport system of the cytoskeleton -Golgi apparatus modifies the proteins, preparing them for secretion. -proteins are put into secretory vesicles and fuse with the cell surface membrane which releases contents via exocytosis -some are put as lysosomes or delivered to other organelles
44
The cytoskeleton
-network of protein fibres -made of 2 protein fibres which are microfilaments and microtubules -organelles and other cell contents are moved along these fibres using ATP to drive this movement -provides the cell with mechanical strength, forming a kind of 'scaffolding' that helps to maintain the shape of the cell -it aids transport within cells by forming 'tracks' along which organelles can move along -enables cell movement via cilia and flagella which contain microtubules
45
microtubules
-solid strands made from the protein actin -fibres can cause some cell movement and movement of organelles within the cells
46
microfilaments
-hollow strands made from the protein tublin
47
Intermediate filaments
-give mechanical strength to the cells and help maintain their integrity
48
Examples of organelles using the movement feature of the cytoskeleton (intracellular movement)
-movement of vesicles or movement of chromosomes to opposite ends of a cell during cell division
49
Prokaryotic and eukaryotic cells
Eukaryotic cells-plant and animal cells prokaryotic cells-bacterial cells
50
How are prokaryotic cells different to eukaryotic cells?
-smaller than eukaryotic cells -they have a cytoplasm that lacks membrane bound organelles -ribosomes are smaller(70s) compared to those in eukaryotic cells(80s) -no nucleus as they have a single circular DNA molecule free in cytoplasm and is not associated with proteins -cell wall contains murein( a glycoprotein) -have plasmids, capsules and flagellum
51
What are plasmids?
-small loops of DNA which are separate from the main circular DNA molecule -contain Genes that can be passed between prokaryotes
52
Capsules in prokaryotic cells
-some prokaryotes are surrounded by a final outer layer called a capsule which is known as a slime capsule which helps bacteria from drying out and from attack by cells of the immune system of the host organism
53
Flagellum
-long tail like structure that rotate enabling prokaryote to move
54
Dry mount -cover slip is necessary to flatten the specimen
-specimen viewed whole sectioned with a sharp blade -cover slip added e.g. hair, pollen, dust, sections of plant and muscle
55
wet mount
-drop of water/oil added to specimen -cover slip added at an angle, slowly to avoid bubbles e.g. aquatic organisms
56
squash slides
-prepare wet mount -squash specimen with a cover slip/another slide e.g. soft samples-root tips
57
smear slides
-drop of liquid specimen is smeared across the slide using another slide-thin sample e.g. blood
58
Why is staining so important in microscopy?
-some organelles are transparent so staining allows us to identify them and they have different degrees of affinity to dye

Ocr A Level Biology (6 decks)

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