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What is cell theory?
Both plant and animal tissues are made of cells
Cells are the basic unit of all life
Cells form from existing cells
What was the importance of microscopes in the study of living organisms?
Disproved the theory of spontaneous generation
Cell theory
Helped to understand genetics and the cause of disease
Why wasn’t cell theory fully developed before the mid -19th century?
Lack of evidence
Didn’t fit existing theories
Lack of good quality microscope lenses
Not enough magnification
Slow spread of ideas (books)
Why does the specimen have to be thin when using a microscope?
So the light can pass through it
What are the 4 ways to prepare samples for a microscope?
Dry mount
Wet mount
Squash slides
Smear slides
What is a dry mount?
Where solid specimens are viewed whole or cut into very thin slices (sectioning) and placed on a slide with a cover slip on top
What is it called when you cut very thin slices off of a specimen?
Sectioning
What are the advantages of dry mount slides?
quick
Little to no preparation needed
Able to view living cells
What are the disadvantages of dry mount slides?
only outer layer visible of the organism
hard to cut very thin sections (especially if opaque)
Some cell types are unsuitable
What is a wet mount slide?
Specimens are suspended in a liquid and a cover slip is placed on an angle on top
Why must the cover slip be placed on an angle when using a wet mount?
To avoid air bubbles
Why must the liquid have the same refractive index as the glass in a wet mount?
If they are not the same it becomes hard to focus as the light changes directions multiple times
What is a squash slide?
A wet mount is first prepared and lens tissue is used to gently press down the cover slip
What are wet mounts good for?
Soft samples
What is the danger of using a wet mount?
Could damage the specimen or distort the image of the specimen
What is a smear slide?
The edge of a slide is used to smear the sample to create a thin even coating on another slide (blood)
Why is a smear slide used for viewing a drop of blood?
Cells in a drop of blood are densely packed together. A smear spreads the cells out so it is easier to view individual cells
What things must you consider when producing slides or microscopes?
specimens must be thin
Refractive index of specimens must be the same as the glass slide
Cover slip is placed to avoid air bubbles (wet mount)
Density of cells (e.g blood)
What is the difference between positive and negative stain technique?
Some dyes are negatively charged so are repelled by the negatively charged cytosol, so the dyes stay outside the cell walls and stain the backgrounds (negative)
Some dyes are positively charged so are attracted to the negatively charged cytosol, so the dyes stain the cell components (positive)
What is differential staining and why is it useful?
Using 2 different stains to distinguish between 2 different organisms/ organelles that would be otherwise hard to identify
What is the difference between gram positive and gram negative bacteria?
Gram positive can retain crystal violet dye when it’s washed away so it appears blue/ violet under a microscope
Gram negative can’t retain crystal violet dye as the walls are too thin so a counter stain is used and it appears red under a microscope
What is magnification?
How many times larger the image is than the actual size of the specimen
What is resolution?
The ability to distinguish between 2 close together objects
What is the limit of the resolution of a light microscope?
No less than half a wavelength of visible light (250 nm)
How is magnification calculated?
Magnification = image size/ actual size
How do you convert between metres to millimetres?
X 1000
How do you convert between micrometers to millimetres?
/ 1000
Which is larger; micrometers or nanometres?
Micrometers
What is the order of units from largest to smallest?
Metres, centimetres, millimetres, micrometers, nanometres
What do you have to do every time you change magnification or microscope when using an eyepiece graticule?
Re-calibrate / re do calculations using scale micrometer
What are the features of an animal cell?
Mitochondria
Ribosome
Cell membrane
Lysosome
Nucleolus
Nucleus
Nuclear envelope
Golgi apparatus
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
What are the features of a plant cell?
Mitochondria
Ribosome
Cell membrane
Nucleolus
Nucleus
Nuclear envelope
Golgi apparatus
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Amyloplast containing starch grains
Permanent vacuole
What is a Eukaryote?
Any organism containing or or more cells that contains DNA in a membrane bound nucleus, separate from the cytoplasm
What is the structure of a nucleus?
Largest organelle
Has pores in the nuclear envelope
Contains chromatin
What is the function of a nucleus?
Protein synthesis
Makes ribosomes
Houses nearly all the genetic material
What is chromatin and why cant it leave the nucleus?
Something that contains DNA and proteins. It makes up chromosomes.
It is too big to fit through the pores so mRNA is transcribed which is small enough to leave the nucleus
What is the structure of the mitochondria?
2 membranes, inner and outer layer
Inner layer folds to form cristae, the cristae project into a liquid called the matrix
Inner membrane is coated in enzymes to catalyse the reactions of aerobic respiration to make ATP
What is the function of the mitochondria?
generates energy
Respiration - large surface area increases rate
What is the structure and function of the lysosome?
spherical sacs surrounded by a single membrane (due to the enzymes)
Specialised vesicles
Contains powerful digestive enzymes
Their role is to break down things (dead cells/ waste/ pathogens)
What is a vesicle?
Membrane bound sac of fluid
What is the Golgi apparatus?
creates lysosomes vesicles
Processes/ modified proteins & lipids before packaging them into Golgi vesicles (for transport)
What 3 things make up the cytoskeleton (and what do they do)?
microfilament (movement)
Microtubules (shape & structure)
Intermediate fibres (mechanical strength)
What are centrioles?
only found in animal cells
Found in pairs
Responsible for spindle fibres in cell division (pulls apart cell components)
Responsible for movement of flagella and cilia
What do flagella and cilia do in a single celled organism?
Essential for locomotion of individual organisms
What do flagella and cilia do in multicellular organism?
Move fluid or materials past immobile objects
What is the structure and function of ribosomes?
tiny organelles in cytoplasm or bound to rough endoplasmic reticulum
Consists of 2 sub-units
Site of protein synthesis
Made of small proteins & mRNA
What is the function and structure of Rough Endoplasmic Reticulum?
Series of flattened membrane bound sacs called cisternae
Studded with ribosomes and transports the proteins made on them
Some proteins are secreted, some placed on surface of the cell
What is the structure and function of Smooth Endoplasmic Reticulum?
Series of flatted membrane bound sacs called cisternae
Involved in the making of lipids that the cells need
What is the structure of the cell wall in a plant cell?
Made of cellulose (polysaccharide) (permeable to water)
Mesh like (made of microfibres - hydrogen bonds between the cellulose particles)
Pores between cells allows for exchange of substances and can connect 2 cells together by their cytoplasm (plasmodesmata)
Lamalae between cells (gap) - acts as glue
What is the functions of a cell wall in a plant cell?
strength & support
Protect from pathogens
Stop cell from bursting when turgid
What other types of cells also have cell walls but what is the difference between these and plant cells?
algae and fungi
Cell walls aren’t made of cellulose
What is the structure of a chloroplast?
double membrane
Thylakoids (membrane bound discs that contains chlorophyll and enzymes) stacked like plates called grana (plural) or granum (single) which are linked together by a flattened membrane to each other. The membrane is the site of photosynthesis
Filled with a liquid called stroma
Starch grains - stored glucose made photosynthesis
Has own loops of DNA & ribosomes to make proteins
What are 2 types of reactions that take place in the chloroplast?
light dependent (chlorophyll harvests sunlight)
Not light dependent ( production of glucose)
What is the structure of a vacuole in a plant cell?
Membrane (called the tonoplast) controls the entry and exit of chemicals
Filled with sap
Important in keeping cell firm
What does sap contain?
water
Sugar
Enzymes
Pigments
What does it mean when a cell is said to be ‘turgid’?
The vacuole is full of sap (swollen)
Why do plants wilt?
The vacuole lacks water and minerals for sap
What is a peptidoglycan?
A material that most bacterial cells walls contain.
Polymers of modified sugars cross linked by a short chained polypeptide
What is a mesosome?
Invaginations formed by the plasma membrane to provide internal membrane surfaces for special purposes
E.g supposedly the site of respiration
What is a plasmid?
Short circular strand of DNA that carry as few genes as possible for special metabolic path ways & resistance to antibiotics
Can transfer between bacteria which makes it important for genetic engineering
What are some differences between prokaryotes and eukaryotes?
P have no membrane bound organelles, E do
P have no nuclear membrane, E do
P have a nuclear mass, E have a nucleus
P have one long chromosome, E have many
P are usually single, E are usually part of an organism
P don’t have mitochondria, E do
P always have a cell wall, E only has them in plant cells (cellulose)
What are some similarities between chloroplasts and mitochondria?
double membrane
Compartmentalisation
Both contain DNA
Both contain ribosomes
Both capable of protein synthesis
Both have readily permeable outer membrane and selectively permeable inner membrane
Permeability is brought about by proteins which span the membrane
Where is the DNA located in prokaryotic cell?
In direct contact with the cytoplasm in a singular continuous thread of DNA located in a region called the nucleoid and plasmids. There is no true nucleus.
What is a systematic error?
An error that will occur every time, due to a mistake in setting up the equipment or the way the particle is ran
What is a random error?
An error that occurs once by random chance. Different amounts every time/ different errors
E.g. human mistakes
What are the microtubules made from?
The protein called tubulin
Made from an alpha tubulin subunit and a beta tubulin subunit join to make a tubulin dimer
25 nm in diameter
What do tubulin diners join to form? (+ how many of these need to join to make a microtubule?)
Protofilaments
13 of these make microtubules
What are the difference between electron and light microscopes?
light are cheaper to buy and operate
Light are small and portable, electron are large and have to be installed
Light have simple sample preparation, electron have complex sample preparation
Electron sample preparation can lead to distortion of materials
Vacuum is not require for light but is for electron
You can see the natural colour using a light microscope but it’s black and white with electron (can be coloured digitally)
Electron has a greater magnification than light (500,000 x compared to 2000 x)
Electron has a higher resolving power (electron can see from 0.5nm or 3-10nm whereas light can see 200nm)
Light microscopes can view living organisms whereas electron cant
What are the advantages and disadvantages of using an electron microscope?
Advantages:
the resolution is 0.2nm
See structured detailed images of organelles inside the cell
SEM (scanning) can produce 3D images of the arrangement of cells
Disadvantages:
electron beams are affected by air molecules so requires a vacuum
Very expensive
Preparing slides and samples requires high level of training and skill (slides have to be very thin)
What is an artefact?
Visible object or distorted cell structure present due to the sample preparation
Why can you see more details using an electron microscope than with a light microscope?
Electron wavelengths are smaller than the half wavelength of light so has a higher resolution and you can see more detailed structures
What are the advantages and disadvantages of a Transmission electron microscope (TEM)?
Advantages:
Greater magnification
Greater resolution
Disadvantages:
smaller samples (more preparation)
What are the advantages and disadvantages of a Scanning electron microscope (SEM)?
Advantages:
3D images
Sample doesn’t need to be thin
Disadvantages:
lower magnification
Lower resolution
What organelles do plant cells not have?
centrioles
Lysosomes
Flagella
Cilia
Glycogen granules
What are the cell wells made from in plant, bacterium and yeast cells?
Plant: cellulose
Bacterium: peptidoglycan
Yeast: chitin
What kind of cell division occurs in plant, animal, bacterium and yeast cells?
Plant: cytokinesis
Animal: cytokinesis
Bacterium: binary fission
Yeast: budding
Do plant, animal, bacterium and yeast cells contain nucleus?
Yes - animal, plant and yeast
No - bacterium
What is an ultra structure?
Detailed structure of cells visible only with electron microscope
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