cell structure Flashcards

Question

how to unblur images

Answer 1

Switch to the lower power objective lens and try using the coarse focus to get a clearer image Consider whether the specimen sample is thin enough for light to pass through to see the structures clearly There could be cross-contamination with foreign cells or bodies

Answer 2

A graticule is a small disc that has an engraved ruler It can be placed into the eyepiece of a microscope to act as a ruler in the field of view As a graticule has no fixed units it must be calibrated for the objective lens that is in use. This is done by using a scale engraved on a microscope slide (a stage micrometer) By using the two scales together the number of micrometers each graticule unit is worth can be worked out After this is known the graticule can be used as a ruler in the field of view

Answer 3

The size of cells or structures of tissues may appear inconsistent in different specimen slides Cell structures are 3D and the different tissue samples will have been cut at different planes resulting in this inconsistencies when viewed on a 2D slide Optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that can not be seen The treatment of specimens when preparing slides could alter the structure of cells

Answer 4

Many tissues that are used in microscopy are naturally transparent, they let both light and electrons pass through them This makes it very difficult to see any detail in the tissue when using a microscope Stains are often used to make the tissue coloured/visible Coloured dyes are used when staining specimens The dyes used absorb specific colours of light while reflecting others; this makes the structures within the specimen that have absorbed the dye visible Certain tissues absorb certain dyes, which dye they absorb depends on their chemical nature Specimens or sections are sometimes stained with multiple dyes to ensure the different tissues within the specimen show up - this is known as differential staining

Answer 5

methylene blue is positively charged dye which is attracted to negatively charge materials in the cytoplasm dyes such as congo red is negatively charged and are repelled by the negatively charged cytosol so this dye stays outside the cell leaving it unstained but it creates a contrast between the stained background Toluidine blue and phloroglucinol are common stains used Toluidine blue turns cells blue Phloroglucinol turns cells red/pink

Answer 6

When using Transmission electron microscopes (TEMs) the specimen must be stained in order to absorb the electrons Unlike light, electrons have no colour The dyes used for staining cause the tissues to show up black or different shades of grey Heavy-metal compounds are commonly used as dyes because they absorb electrons well Osmium tetroxide and ruthenium tetroxide are examples Any of the colour present in electron micrographs is not natural and it is also not a result of the staining Colours are added to the image using an image-processing software

Answer 7

used to separate bacteria into two groups gram-positive and gram-negative (differential staining) crystal violet is applied to the bacteria, then iodine and then the slide is washed with alcohol. the gram positive bacteria retain the stain and appear blue-purple but gram negative bacteria have thinner cell walls and therefore lose the stain. they are then counter stained with safranin dye and appear red.

Answer 8

The drawing must have a title The magnification under which the observations shown by the drawing are made must be recorded A sharp HB pencil should be used (and a good eraser!) Drawings should be on plain white paper Lines should be clear, single lines (no thick shading) No shading The drawing should take up as much of the space on the page as possible Well-defined structures should be drawn The drawing should be made with proper proportions Label lines should not cross or have arrowheads and should connect directly to the part of the drawing being labelled Label lines should be kept to one side of the drawing (in parallel to the top of the page) and drawn with a ruler plan drawings- lower magnification

Answer 9

magnification is how many times bigger the image is to the real life object actual size= image size/magnification

Answer 10

A light microscope has two types of lens: An eyepiece lens, which often has a magnification of x10 A series of (usually 3) objective lenses, each with a different magnification To calculate the total magnification the magnification of the eyepiece lens and the objective lens are multiplied together: eyepiece lens magnification x objective lens magnification = total magnification

Answer 11

Resolution is the ability to distinguish between two separate points If two separate points cannot be resolved, they will be observed as one point The resolution of a light microscope is limited by the wavelength of light As light passes through the specimen, it will be diffracted The longer the wavelength of light, the more it is diffracted and the more that this diffraction will overlap as the points get closer together Electron microscopes have a much higher resolution and magnification than a light microscope as electrons have a much smaller wavelength than visible light This means that they can be much closer before the diffracted beams overlap

Answer 12

Light microscopes are used for specimens above 200 nm Light microscopes shine light through the specimen, this light is then passed through an objective lens (which can be changed) and an eyepiece lens (x10) which magnify the specimen to give an image that can be seen by the naked eye The specimens can be living (and therefore can be moving), or dead Light microscopes are useful for looking at whole cells, small plant and animal organisms, tissues within organs such as in leaves or skin Electron microscopes, both scanning and transmission, are used for specimens above 0.5 nm Electron microscopes fire a beam of electrons at the specimen either a broad static beam (transmission) or a small beam that moves across the specimen (scanning) The electrons are picked up by an electromagnetic lens which then shows the image Due to the higher frequency of electron waves (a much shorter wavelength) compared to visible light, the magnification and resolution of an electron microscope is much better than a light microscope Electron microscopes are useful for looking at organelles, viruses and DNA as well as looking at whole cells in more detail Electron microscopy requires the specimen to be dead however this can provide a snapshot in time of what is occurring in a cell eg. DNA can be seen replicating and chromosome position within the stages of mitosis are visible

Answer 13

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

Answer 14

found in plants and not in animal cells cell was is formed outside the cell membrane of the cell and offers structural support to the cell this structural support is provided by the polysaccharide cellulose in plants cell wall is freely permeable

Answer 15

the nucleus contains chromatin (complex of linear dna tightly wound around histone proteins) which is what makes chromosomes present in all eukaryotic cells except erythrocytes the nucleus is large and separated from the cytoplasm by a double membrane (the nucleus envelope) which has many pores the nucleus pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus as well as allowing enzymes and signalling molecules to travel in

Answer 16

area within the nucleus that is responsible for producing ribosomes. it is composed of proteins and RNA. RNA is used to produce ribosomal RNA (rRNA) which is then combined with proteins to form the ribosomes necessary for protein synthesis

Answer 17

site of aerobic respiration within all eukaryotic cells surrounded by a double membrane with the inner membrane folded to form cristae the matrix formed by the cristae contains enzymes needed for aerobic respiration producing ATP small circular pieces of DNA and ribosomes are also found in the matrix needed for replication

Answer 18

found in plant cells larger than mitochondria also surrounded by a double membrane membrane bound compartments called thylakoids containing chlorophyll stack to form structures called grana grana are joined together by lamella (thin and flat thylakoid membranes) chloroplasts are the site of photosynthesis: the light-dependant stage takes place in the thylakoids the light-independent stage takes place in the stroma

Answer 19

Ribosomes are formed in the nucleolus and are composed of almost equal amounts of RNA and protein Not membrane bound Found in all cells Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells Each ribosome is a complex of ribosomal RNA (rRNA) and proteins 80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells 70S ribosomes (composed of 50S and 30S subunits) in prokaryotes, mitochondria and chloroplasts Site of translation (protein synthesis)

Answer 20

Rough Endoplasmic Reticulum (RER) stacks of membrane bound sacs which form sheets called cisternae Found in plant and animal cells Surface covered in ribosomes Formed from continuous folds of membrane continuous with the nuclear envelope Processes proteins made by the ribosomes Smooth Endoplasmic Reticulum (ER) Found in plant and animal cells Does not have ribosomes on the surface, its function is distinct to the RER Involved in the production, processing and storage of lipids, carbohydrates and steroids

Answer 21

Found in plant and animal cells Flattened sacs of membrane similar to the smooth endoplasmic reticulum Modifies proteins and lipids before packaging them into Golgi vesicles The vesicles then transport the proteins and lipids to their required destination Proteins that go through the Golgi apparatus are usually exported (e.g. hormones such as insulin), put into lysosomes (such as hydrolytic enzymes) or delivered to membrane-bound organelles folds in the apparatus are called cisternae

Answer 22

A sac in plant cells surrounded by the tonoplast, selectively permeable membrane Vacuoles in animal cells are not permanent and small

Answer 23

Found in plant and animal cells A membrane-bound sac for transport and storage

Answer 24

Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down) Break down waste materials such as worn-out organelles Used extensively by cells of the immune system and in apoptosis (programmed cell death)

Answer 25

Hollow fibres made of microtubules Two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division Each centriole contains an outer membrane with a ring of 9 protein microtubules inside with 2 microtubules in the middle (9+2 arrangement ) allows movement for locomotion

Answer 26

formed by the globular protein tubulin they polymerise to form tubes that determine the shape of the cell they can also act as tracks for organelles moving around the cell

Answer 27

Found in specialised animal cells Cell membrane projections Used to increase the surface area of the cell surface membrane in order to increase the rate of exchange of substances

Answer 28

Hair-like projections made from microtubules Allows the movement of substances over the cell surface

Answer 29

Hair-like projections made from microtubules Allows the movement of substances over the cell surface

Answer 30

fibres made from the protein actin responsible for the movement of the cell an cytoplasm during cytokinesis

Answer 31

gives strength to cells and helps maintain integrity

Answer 32

made up of microtubules microfilaments and intermediate fibres Strengthening and support: The cytoskeleton provides the cell with mechanical strength, forming a kind of 'scaffolding' that helps to maintain the shape of the cell It also supports the organelles, keeping them in position Intracellular (within cell) movement: The cytoskeleton aids transport within cells by forming 'tracks' along which organelles can move Examples of this include the movement of vesicles and the movement of chromosomes to opposite ends of a cell during cell division Cellular movement: The cytoskeleton enables cell movement via cilia and flagella These structures are both hair-like extensions that protrude from the cell surface and contain microtubules that are responsible for moving them

Answer 33

The DNA from the nucleus is copied into a molecule of mRNA via a process known as transcription The mRNA strand leaves the nucleus through a nuclear pore and attaches to a ribosome on the rough endoplasmic reticulum The ribosome 'reads' the genetic instructions contained within the mRNA and uses this code to synthesise a protein via a process known as translation This protein then passes into the lumen (the inside space) of the rough endoplasmic reticulum to be folded and processed Cells that produce a large number of proteins, e.g. enzyme- or hormone-producing cells have an extensive rough endoplasmic reticulum The processed proteins are then transported to the Golgi apparatus (also known as the Golgi body or Golgi complex) in vesicles which fuse with the Golgi apparatus, releasing the proteins The Golgi apparatus modifies the proteins, preparing them for secretion Proteins that go through the Golgi apparatus are usually exported (e.g. hormones such as insulin), put into lysosomes (e.g. hydrolytic enzymes) or delivered to other organelles The modified proteins then leave the Golgi apparatus in vesicles Finally, these vesicles (containing the final proteins) fuse with the cell surface membrane, releasing the proteins by the process of exocytosis