Cell Structure Flashcards
it contains the ocular lens
What magnification does the eye piece have? Why?
Has 10x magnification because it contains ocular lens
What can you add/take away from a light microscope that is inserted in the eye piece?
Eye piece graticule can be inserted or taken out (ruler)
What is a turret on a light microscope?
-Contains multiple objective lenses- can be rotated to different lenses
-also known as the revolving nose piece
What is the purpose of the objective lenses on light microscope?
- can be clicked into place by rotating the turret
- contains 4 different lenses= 4 possibilities of magnification to view specimen with
Where is the specimen located on light microscope?
On stage- ensure slide fits in 90* angle
What is the purpose of the stage?
-Specimen is placed onto the stage
- Clips are spring loaded- easily be opened using a lever
What is a condenser in microscopes?
Converges the light rays together to make a beam of focused light
-to pass through aperture in stage
-and then the sample on the slide
What is the iris diaphragm
Underneath the stage above the condenser- size of aperture through which light can pass can be controlled by moving a lever
- by controlling amount of light which passes through slide the specimen can be illuminated but with enough contrast to see details
What is the upper control
Stage clips can be moved backwards+ forwards to position sample
What is the lower control
Stage clips can be moved from side to side to position sample
What is the function of the course focus knob
Bigger/ rough adjustments in height of stage- so sample appears in field of view
What is the function of the fine focus knob
Smaller adjustments- to fine focus the image and view different parts of the same e.g. if 3 dimensions you can focus on each layer
What is the light source in light microscope
Light bulb or mirror
What image does the light microscope form/ produce
2D coloured images
Explain how image is magnified in light microscope
Rays of light pass through sample to form an image—- image is magnified by passing through objective lens times by ocular lens= observer sees magnified image of sample
What is the total magnification in a light microscope
Objective lense times ocular lens equals total magnification
Define microscopic
Items that are too small to be seen with the naked human eye
Define macroscopic
Items that are large enough to be seen with the naked human eye
What is the purpose of microscopes
-Produces a magnified, of the object
-allows biologists to make more accurate descriptions of structures
-give comparisons with other structures
-so we can examine organelles in more details
Advantages of light microscope
-uses light rays to observe object
-can observe living organisms
-does not use harsh chemicals e.g. for staining
-easy to set up and use
-cheap and portable
-colored image
Disadvantages of Light microscope
-low magnification up to 2000 x
-low resolution due to long wavelength of light (200nm)
How to use a light microscope
1) Take a thin slice of specimen- use tweezers to place it in middle of a clean slide
2) Stain the specimen (e.g. eosin to see cytoplasm of cell)
3) Place a cover slip on top of specimen using a mounted needle at a 90* angle
4) Use the arms to clip the slide onto the stage and position so that it sits over the hole
5)Rotate the turret so that lowest objective lens power is in place
6) Use course focus knob to adjust the stage so that it sits underneath the objective lens and look through eye piece to ensure image is roughly in focus
7) Turn fine focus knob to adjust the focus of image until a clear image can be viewed from eye piece lens
8) Rotate the objective lens and select 10 x power and focus image into place using the course and fine adjustment knobs
Define Magnification
refers to how many times larger the image is compared to the object
Define resolution
minimum distance between two objects in which they can still be viewed as separate
-higher resolution= more detail can be distinguished
What determines low resolution in a light microscope
long wavelength of light=low resolution
What determines low resolution in a electron microscope
the wavelength of the beam of electrons
What does TEM stand for
Transmission electron microscope
How is an image created in TEM
-using an electromagnet to focus beam of negatively charged electrons that are fired from the electron gun to pass through sample or specimen
What must be the case for an image to be viewed in a TEM
-specimen must be ultra thin- electrons need to be able to pass through it
- specimen must be dead as it must be viewed in a vacuum
Why are specimens in TEM viewed in a vacuum
Because electrons are absorbed by the air so wont be passed through specimen
How does a TEM function
-extremely thin specimen are stained and placed in a vacuum
-electron gun produces beam of electrons that pass through the specimen
-some parts of specimen absorb electrons- makes them appear darker
-2d image produced showing in detail internal structures of cell
What image does TEM produce
2D and Black and White images
Advantages of TEM
-high magnification (up to 5 million x)
-high resolution
-can see details inside the cell
Disadvantages of TEM
-can only see dead material
-harsh chemicals used in preparation which can cause artefacts
-expensive
-B&W images
-requires skilled, trained individual to complete and prepare specimen
What is the formula involving magnification, image size and actual size
I AM
how to do you go from M to mm
times by 1000
how do you go from mm to M
divide by 1000
how do you go from mm to micrometers
times by 1000
how do you go from micrometers to mm
divide by 1000
how do you go from micrometers to nanometers
times by 1000
how do you go from nanometers to micrometers
divide by 1000
What does SEM stand for
Scanning Electron Microscope
How does a SEM function
-stream of electrons are sent across surface and reflected back to capture image - electrons scatter in different ways depending on the contours of the image
-electrons rebound (bounce off to fluorescent screen- instead of eye piece)
-observed in a vacuum-specimen must be dead
Why does the specimen in SEM not have to be ultra thin
Electrons are not transmitting through they bounce off of image to fluorescent screen
SEM produces what type of image
3D surface image + B&W
Advantages of SEM
-high magnification up to 5 million times
-high resolution
-can see details of the surfaces of structures
Disadvantages of SEM
-can only see dead material
-harsh chemicals used in preparation which can cause artefacts
-expensive
How does a Laser scanning confocal microscope function
-image created using very high light intensity (laser beam of light) to illuminate the specimen stained with a fluorescent dye- these then fluoresce
-image is created as microscope scans the specimen point by point using a focused laser beam to create a 2D or 3D image in different focal planes
Advantages of Laser scanning confocal microscope
-enables scientists to view sections of tiny structures that would be challenging to physically section e.g. embryos- 3D images created
-combines the benefit of high resolution optical imaging with depth selectivity
-can observe cell processes by tracking molecules
-higher magnification + resolution than light microscope
Disadvantages of Laser Scanning Confocal Microscope
-more expensive than light microscope
-more complex than light microscope
Why do we stain things
-to see things much easier and we can differentiate between different parts of the cell
What is dry mount
-sample is cut into a thin slice using a blade- sectioning
-it is covered with a cover slip then is ready to be viewed e.g. hair, pollen, insects
What is a wet mount
-specimen is covered with a drop of liquid e.g. oil or stain or water
-cover slip is placed from an angle using a mounted needle on the sample before viewing it- to avoid bubbles
What is a squash slide
sample is squashed between slide and coverslip- to ensure you have a thin layer of specimen so light can pass through it
- a type of wet mount
-use for soft tissue e.g. root tips squash sample to view chromosomes in mitosis
What is a smear slide
-using another slides edge you smear the sample across a slide- to create a smooth, thin, even coated specimen
- a cover slip is placed on top after smearing
-useful for a thin layer of a liquid e.g. blood sample to view RBC
What is differential staining
-various chemical stains used to stain different parts of a cell in different colors
- used to differentiate between different types of cells that otherwise can not be distinguished
What is an example of a common use of differential staining
Gram staining
What is Gram staining
2 stains used= crystal violet+ safranin
-gram positive bacteria appear blue or purple- stain is retained by thick peptidoglycan cell wall absorbing dye
-gram negative bacteria cannot absorb crystal violet- peptidoglycan cell wall is too thin and do not retain the stain
What is nigrosin and congo red used for
negatively charged- attracted to outside of cell- can’t enter cell as cystol repel them- stained background so unstained cell stands out- can be seen
What is crystal violet and Methylene blue
positively charged so attracted to negatively charged components e.g. organelles
What are the 2 pairs of commonly used stains
1) Nigrosin and Congo red
2) Crystal violet and Methylene blue
What organelles are found in an animal cell
-Nucleolus
-Nucleoplasm
-Nuclear membrane
-Nuclear pores
-Nucleus
- Smooth endoplasmic reticulum
-Rough endoplasmic reticulum
-Secretory Vesicles
-Cytoskeleton
-Cytosol
-Cell surface membrane
-Mitochondria
-Ribosomes
-Golgi Apparatus
-Vesicles
-Centrioles
- Microtubule network
-Lysosomes
-Chromatin
Organelles found in plant cells
-Chloroplast
-Vacuole containing cell sap
-cellulose cell wall
What is the function of nucleus
-contains linear DNA tightly wounded around histone proteins to form thread like structures called chromosomes
What is the function of the Nuclear Envelope
-double membrane that surrounds the nucleus and has nuclear pores
What is the function of the nuclear pores
holes in the nuclear envelope that allow mRNA to leave the nucleus
What is the function of the nucleoplasm
granular, jelly like material contains nucleolus and chromosomes
What is the nucleolus
-largest structure within nucleus
-where rRNA (ribosomal RNA- a single stranded polynucleotide is synthesised at high speed
Define transcription in terms of how a ribosome is formed
process of making RNA copy of a genes DNA sequence- after the rRNA associate with ribosomal proteins they form ribosomal subunits that later assemble to form functioning ribosome
What is the structure of a ribosome
-small+ spherical
-made up of 2 sub-units of proteins and rRNA
What type of ribosomes are found in prokaryotes and eukaryotes
Eukaryotes= 80s (large) found in cytoplasm of cells
Prokaryotes= 70s (small) found in cells- site of protein synthesis
How are ribosomes found in cells
-some are free in cytoplasm (singly or clusters)- site for assembly of proteins that will be used inside the cell
-some ribosomes are bound to exterior of another cell structure (which is membrane bound)- ribosomes mainly for synthesis of proteins that will be exported outside of cell
How do you know ribosomes are not just found in eukaryotes
Because they are not membrane bound meaning they must be present in prokaryotes as well
What is the rough endoplasmic reticulum
-continuous with outer nuclear membrane, it is a system of flattened membrane discs containing fluid filled cavities known as cisternae and are coated with ribosomes
Why are ribosomes present of the surface of RER
-It is a site of translation whereby amino acids are joined together to form peptide bonds
-these are assembled into proteins- occurs during reactions catalysed by peptidyl transferase
- these proteins actively pass through membrane and cisternae then act as intracellular transport system
-areas of RER that are not coated in ribosomes are known as the ER exit sites
- vesicles bud from this region to carry proteins to Golgi apparatus in another area of cell
What is the function of RER and SER
Rough endoplasmic reticulum= protein synthesis
Smooth endoplasmic reticulum= lipids and carbs synthesis and storage
What structures contain cisternae
RER and Golgi
What is the structure of a cisternae
fattened membrane enclosed discs
Structure of Golgi apparatus
collection of fused cisternae is broken down into compartments that make up the cis Golgi and trans Golgi network
Function of Golgi Apparatus
modify, package, label substances e.g. proteins before sending them in Golgi vesicles to different parts of cell or out into extracellular space
Structure of lysosomes
sphere in shape+ type of Golgi vesicle
Function of lysosome
-contains hydrolytic/ digestive enzymes known as lysozymes
-these hydrolyse phagocytic cells, complete breakdown of dead cells (autolysis) and exocytosis
-they release enzymes to outside of cell to destroy material, digest worn out organelles for reuse of materials
How many different types of lysosomes are there
50
What is the function of a mitochondria
Why do cells carry a lot of energy and where do they get this from
-cells that carry out a lot of energy have an abundance of mitochondria to hydrolyse ATP and release energy
-e.g. plant cells use energy to absorb mineral ions from soil by active transport
What enzymes are found in the mitochondria
Enzymes that catalyse each individual reaction in aerobic respiration
What does the inner membrane of a mitochondria consist of?
Inner membrane which is made up of cristae consists of a chain of electron carriers
- which leads to creation of ATP in a complete system (oxidative phosphorylation)
How are mitochondrial proteins and electron carriers made
code on mitochondrial DNA (mtDNA) is transcribed and then amino acids are assembled at mitochondrial ribosome to form mitochondrial proteins and electron carriers
Compare in terms of size the ribosomes found in cytoplasm and the ribosomes found in mitochondria.
ribosomes found in cytoplasm= 70s
ribosomes found in mitochondria= 80s
What is the name of the fluid filled centre in mitochondria and what is its function
fluid filled centre= mitochondrial matrix
-contains DNA to code for enzymes needed in respiration
Describe how proteins are made in eukaryotic cells
1) proteins are packaged into vesicles that bud from specialised regions of endoplasmic reticulum known as the ER exit sites
2) motor proteins walk along the micro-tubule track, dragging vesicles from the RER to the cis face of the Golgi
3) the vesicles fuse with the membrane of the apparatus and empty their contents in the lumen of the cisternae
4) the protein is moved through the different compartments of the cisternae where it is modified
5) the modified proteins reaches the trans face
6) the membrane surrounds the product completely and pinches off to form a Golgi vesicle
7)The Golgi vesicle leaves from the trans face and is dragged by the motor proteins to the cell surface membrane
Give an example and name of a reaction that is catalysed in the Golgi apparatus
-when reactions are catalysed by glycosylation enzymes- within Golgi Apparatus these enzymes attach sugar monomers to proteins as they move through compartments= resulting in formation of glycoproteins and also glycolipids
Where are glycolipids found?
Glycolipids are a component of plasma membrane
8 bullet points
Describe the purpose of the Golgi apparatus in bullet points
-small+ compact
- modifies+ packages protiens into vesicles
- adds carbohydrates to proteins to form glycoproteins
- produces secretory enzymes
- produces or secretes carbohydrates
- transports+ modies+stores lipids
- forms lysosomes
- molecules ‘labelled’ with their destination
What is the purpose of the plasma membrane
it acts as a boundary / barrier separating the conditions of the environment to the interior of the cell
What is the structure of plasma membrane and how does this support it to carry out its function?
-made up of phospholipids arranged into a bilayer and cholesterol sits between phospholipids to regulate fluidity of membrane
-partially permeable+ made up of proteins ( glycoproteins- control the entrance and exit of molecules of cell or organelle and transmembrane proteins)
-molecules are embedded within and attracted to the outside (proteins, carbohydrates, cholesterol)+ carrier proteins and channel proteins etc. which act as a receptor
What is the function and structure of the cytoplasm?
-thick solution that fills each cell- mainly composed of water, salt, proteins in eukaryotes
-within cytoplasm the cellular activities occur including metabolic pathways, glycolysis and processes such as cell division
What is considered as the cytoplasm
all materials outside the nucleus and inside the cell
What is endoplasm and ectoplasm
Endoplasm= the concentrated inner area of the cytoplasm
Cell cortex/Ectoplasm= outer layer of cytoplasm
What is the function of chloroplast
-surrounded by double membrane
-contains the thylakoids which are stacked to make grana and contain a photosynthesizing green pigment- chlorophyll
-fluid filled stroma contains enzymes for photosynthesis
What are the thylakoids
internal membrane made up of flattened sacs
What are grana
stacked up thylakoids
What is the purpose of the cell wall in plants
-made up of cellulose (polymer made up of microfibrils)
-fully permeable to contents of the cell that push against it allowing it to support cell:
stop cell from collapsing if too little water
-stop cell lysis if too much water
What is the purpose of cell wall in fungi
-made up of chitin (a nitrogen containing polysaccharide)
-provides structural support + strength
What are the pits in cell wall
pits are gaps in cell where lignification was not complete and these allow water to pass between vessels
What is the purpose of the middle lamella in a plant cell
-has a pectin layer which cements two adjoining plant cells together
What is the flagella/ flagellum and its purpose?
-whip like structure for mobility and sometimes a sensory organelle for chemical stimuli
What are cilia ?
-hairlike projections out of cell= can be mobile or stationary
What is the function of mobile cilia?
-helps move substances in a sweeping motion e.g. moving mucus from trachea to prevent lung infection
What is the function of stationary cilia?
important in sensory organs e.g. nose -traps pathogens
What is a centriole?
-made up of microtubules
-occur in pairs to form centrosome
-involved in production of spindle fiber and organization of chromosomes in cell division (mitosis/ meiosis)
What is the cytoskeleton?
-network of fibers found within cytoplasm
-consists of microfilaments, microtubules and intermediate fibers
Where are cytoskeleton found
all over the cell
Function of cytoskeleton
-provides mechanical strength to cells and helps to maintain the shape and stability of a cell
-many organelles are bound to cytoskeleton
What is the function of microtubules in the cytoskeleton?
responsible for creating scaffold like structure
What is the function of microfilaments in the cytoskeleton?
responsible for cell movement
What is the function of intermediate in the cytoskeleton?
provides mechanical strength
Key differences between prokaryotic cells and eukaryotic cells
Prokaryotic cells are:
- much smaller
-no membrane bound organelles
-smaller ribosomes
-DNA is not contained within a nucleus
- a cell wall made of murein
They may also contain:
-plasmids
-a capsule around the cell
-flagella
Where do prokaryotes get their energy from
get energy from chemiosmosis ATP
Compare prokaryotes and eukaryotes in terms of membrane bound organelles
Prokaryotes:
-circular DNA in cytosol, no nucleus, no membrane bound organelles
Eukaryotes:
-mitochondria, chloroplast, ER, Golgi- all membrane bound organelles
Compare prokaryotes and eukaryotes in terms of ribosomes
Prokaryotes:
-70s- smaller ribosomes found in prokaryotic cells, mitochondria and chloroplast
Eukaryotes:
-80s- large ribosomes found in eukaryotic cell
Both have ribosomes in gel like cytoplasm
Compare prokaryotes and eukaryotes in terms of nucleus
Prokaryotes:
-no nucleus- instead there is a single circular DNA molecule free in the cytoplasm which is not protein bound
Eukaryotes:
-Nuclear Envelope= double membrane contains nuclear pores
-Nuclearplasm= granular, jelly-like material
-Chromosomes= protein bound, linear, DNA
-Nucleolus= smaller sphere, inside which is site of rRNA- production of ribosomes
Compare prokaryotes and eukaryotes in terms of plasmids
Prokaryotes:
-small loops of DNA which only carry a few genes- occur in varying numbers
Eukaryotes- no plasmids, nucleus contains DNA
Compare prokaryotes and eukaryotes in terms of cell wall
Prokaryotes:
-contains murein, a glycoprotein also known as a petidoglycan
Eukaryotes:
- plants made of microfibrils of cellulose polymer
-fungi- made up of chitin and nitrogen containing polysaccharide
Compare prokaryotes and eukaryotes in terms of capsule
Prokaryotes:
- slimy layer of proteins prevents bacteria from desiccating (dying out)
-protects bacteria against hosts immune system + covers antigens to make it harder for hosts immune system to detect bacteria
Compare prokaryotes and eukaryotes in terms of flagellum
Prokaryotes:
-rotates to enable bacteria to move
How long is a mitochondria compared to it being wide
- a mitochondria is measured and found to be 7 x longer than it is wide
Describe the diameter of of mitochondrion compared to a ribosome
- diameter of typical mitochondrion is about 50 x that of a ribosome
Outline the importance of microscopes in the study of living organisms
They help us magnify or enlarge images by 100s of 1000s of times =help us see minute species and microorganisms, e.g. bacteria, protists, fungi etc.
-enables scientists to investigate the structure of cells and each organelle + their function, which can ultimately aide scientists to discover new drugs or design them to treat new microbes or diseases
-cells are too small and cannot seen by the naked human eye
Suggest the reason why cell theory was not fully developed before the 19th century
One reason was the lack of understanding of microscope technology so no correct observations were made e.g. when Hooke was unable to see or understand organelles within cells. He did not understand the structures within the cells whilst observing them
Do summary questions 1, 2, 3 in Kerboodle textbook page 14
Answers are in the back- make flashcards
Do summary questions 4 a and b in Kerboodle textbook page 14
Answers are in the back- make flashcards
Go on page 16 and 17 of kerboodle textbook and make flashcards on eye piece graticule
Do Summary questions o page 18 in Kerboodle text book
Answers are at the back
Do summary questions on page 25 of Kerboodle textbook year 1
Answers are at the back + make flashcards
There are many different types of cells in the human body. Describe where epithelial cells are found in the human body.
Surface of stomach
What’s the function of ribosomes
Protein synthesis
Bacterial cells can cause cholera. After an earthquake there can be a rapid spread of cholera. Explain 2 reasons why.
- Damns can break down
2 Sewage leakage
Yeast cells are used in the production of alcohol. During tis process, conditions are controlled so that the yeast grows at an optimum rate. One condition that is controlled is temperature. Write down two other ways to optimise the growth rate of yeast.
- pH
- remove waste products
Unit conversions, m, mm, micrometers, nm
Look in bio book green cover
Label an animal cell
Green cover book
Label a plant cell
Green cover book
Staining is a process often used in microscopy. Describe the advantages of staining specimens to be viewed under a microscope.
Staining helps to highlight and distinguish between organelles and it increases contrast.
Fill in the blanks:
Microscopes allow us to_________ objects and, therefore, study organisms at ______ level ands learn about unicellular organisms
Magnify
Cellular
Which type of microscope was the first to be developed?
light microscope
List 3 advantages of using a light microscope
- relatively cheap
-easy to use
-can be used for dead and living samples
-relatively easy to stain and section
Why would an electron microscope be preferred over a light microscope?
Greeter magnification and resolution so more detailed images
What is the main benefit of using a scanning electron microscope?
Produces 3D images
How does a laser scanning confocal microscope differ from conventional light microscope?
-Uses a laser rather than a visible light
-sharply focused images, meaning high resolution
-can focus various depths to produce a 3D images
Why is it important to cut sections thinly when reviewing under a microscope?
Light needs to be able to pass through specimen and for clarity we want to be able to see only a single layer of cells
What equipment would you use to measure actual length of an object under magnification?
Eye piece graticule
Stage micrometer
A lot of biological tissue is transparent, why is this a problem and how can the problem be overcome?
Transparent samples would not show up clearly under the light microscope so staining is used to provide sufficient contrast between structures
Sometimes multiple stains are used on specimens, this is referred to as differential staining. Explain why this is carried out.
-Differential staining allows different parts of a cell or different cell types to be distinguished
-Some stains bind to a specific structure within a cell so they can be easily picked out on a specimen
A light microscope has a eye pice lens magnification of x7 and three objective lenses at magnification at x 5, x10 and x 40
What is the maximum total magnification
What is the lowest total magnification possible?
max= 7x40= 280
min= 7x5= 35
Total magnification=eyepiece magnification x objective lens magnification
Complete the definition. Magnification is…
the number of times bigger an image is compared to the actual object
Define resolution
a measure of the clarity of an image, it refers to the ability to distinguish between 2 adjacent objects as separate
What is the magnification and resolution for a light microscope
Magnification= x2000
Resolution= 200nm
What is the magnification and resolution for a scanning electron microscope
Magnification= 100,000
Resolution= 10 nm
What is the magnification and resolution for a transmission electron microscope microscope
Magnification= 1000,000
Resolution= 0.2 nm
What is the structure and function of a nucleus?
Structure= The largest organelle surrounded by a nuclear envelope wirth nuclear pores, contains the nucleolus
Function=
-contains the genetic material of the cell
- chromatin consist of DNA and protein
- when cells divide, chromatin condenses into invisible chromosomes
-nucleolus makes RNA and ribosomes
Structure and Function of Golgi Apparatus
Structure= a stack of membrane bound flattened sacks, vesicles can be found to the side of golgi apparatus
Function=
-receives proteins from the ER and modifies them e.g. by adding sugar molecules
-then packages the modified proteins into vesicles
- for storage and in the cell or for export
Structure and function of lysosomes
Structure= spherical sacks surrounded by a single membrane
Function= contains hydrolytic enzymes to breakdown pathogens or old organelles
Describe how we can distinguish between smooth and rough endoplasmic reticulum
RER= has ribosomes on the surface
What carbohydrates are plant cell walls made up of
Cellulose
Describe the structure of centrioles
Form the spindle during cell division
Structure and function of cytoskeleton
Structure= a series of protein threads made up of microfilaments, microtubules and intermediate fibres
Function= provides mechanical strength to cells, including maintaining the shape of the cell and facilitates the movement of organelles within the cells
True or false.
The cytoskeleton is found on the outside of the cell.
False
True or false
Prokaryotic cells contain nucleoli
False
True or False
Ribosomes are the site of protein synthesis
True
True or False. Chloroplasts have a double membrane
True
True or False
Centrioles are found in plant cells
False
True or False
Lysosomes contain digestive enzymes
True
What is a stain
used to differentiate between different microscopic structures
What is a Eukaryotic cell
Complex cell which contains many membrane organelles
What is an organelle
Structures found within cells that carry out specific function
