Chapter 2A: Cell Structure Flashcards
What is the formula for magnification?
=image size/actual size
What is magnification?
it is how much bigger a sample appears to be under the microscope than it is in real life
What is resolution?
it is the ability to distinguish between two parts of an image (the amount of detail)
What are artefacts?
they are things that you can see down a microscope that are NOT part of the cell/specimen. They are bad because they can be misinterpreted by someone for a part of the cell (inaccurate description of cell)
What are some examples of artefacts?
dust
air bubbles
fingerprints
problems with staining
Where are artefacts most common?
in electron micrographs
because specimens need a lot of preparation before being used in an E.M. so more chance of a mistake
also have higher resolution, so more likely to pick up artefacts
When are artefacts most likely to be made?
during the preparation of the slide
How could artefacts be distinguished from organelles for early scientists?
they do this by repeatedly preparing specimens in different ways and using different microscopes. If an object was seen regularly was more likely to be an organelle than an artefact
What are the three steps to separate a cell? (to study specific organelles)
- homogenisation
- filtration
- ultracentrifugation
What is homogenisation?
breaking the cell plasma membrane and releases the organelles into a solution
this can be done by putting it in a homogeniser (blender) or vibrating the cells
What conditions must the homogenate have and what effect does it have?
- must be kept ice-cold (to slow down enzyme activity)
- sol. must be isotonic (with cell) to avoid OSMOTIC damage to the organelles (NOT CELLS)
- a buffer sol. is added to maintain pH and prevent denaturation of proteins
Why must the conditions of a homogenised solution be so specific?
this is so that the specimen does not change (or broken down by enzymes and osmotic damage)
What is filtration?
the homogenised cell solution is filtered through a gauze to remove large cell or tissue debris, the organelles are small enough to pass through the gauze
get rid of the large, unnecessary parts of the cell
What is a homogenate?
the homogenised cell solution
What is ultracentrifugation?
the filtered sol. is poured in a tube and spun in a centrifuge at a LOW speed
the heaviest organelles are flung to the bottom and form a pellet, other organelles remain suspended in fluid, called the supernatant
process is repeated at higher speeds each time
What is the order of mass of organelles?
nuclei heaviest
chloroplast
mitochondria
lysosomes
endoplasmic reticulum
ribosomes lightest
What is the difference between a light and electron microscope?
Light / Electron microscope
- Uses light / -uses an electron beam
- Takes few mins to prepare /-longer to prepare (day)
- live or dead specimen / -only dead specimen
- inexpensive / -expensive
mag. - x1500 / -mag.- x1,500,000
Why does an electron microscope have a higher resolving power?
this is because the wavelength of an electron beam is a lot shorter than the wavelength of light so its better for resolution
What are the two types of electron microscopes?
TEM=transmission electron microscope
SEM= scanning electron microscope
How does a SEM work?
it scans a beam of electrons across the specimen, it knocks electrons off the specimen which are gathered in a cathode ray tube to form an image.
it only shows only the surface of the specimen
makes a 3D image of SURFACE
(lower resolution that TEM)
Hows does a TEM work?
they focus a beam of electrons on the cell which travels THROUGH the cell
on the image, denser parts of cell absorb more electrons so show up darker
whiter parts are less dense (less resistance of the electrons)
can see inside the cells
What are eukaryotic cells and 4 examples?
- make up uni-cellular organisms
- more complex, larger
- most organelles are membrane bound
- genetic material is enclosed in the nucleus
- e.g-animal, plant, fungal and algal
How do algal and fungal cells compare to plant cells?
algal cells are very similar to plant cells
so are fungal cells but they have no chloroplasts and their cell walls are made of chitin, not cellulose
What is the cell surface membrane made up of?
a phospholipid bilayer,
also includes lipids and proteins
What is the structure of the nucleus?
a large organelle, surrounded by a nuclear envelope which contains many pores
also contains a nucleolus at centre of nucleus
chromatin= DNA when its not heavily coiled into a chromosome
What is the function of the nucleus and the nucleolus?
nucleus= control’s cells activities and DNA contains instructions to make proteins
nucleolus makes ribosomes
What is the structure of mitochondria?
have an inner membrane and an outer membrane
the inner is folded to form cristae
inside it is the MATRIX, which contains enzymes for respiration
contains 70s ribosomes
What is the function of mitochondria?
site of AEROBIC respiration, aerobic respiration produces ATP
What is the structure of chloroplasts?
has a double membrane
contains many thylakoid membranes which form stacks called grana
grana are linked by lamellae
stroma is the liquid inside the inner membrane
What is the function of the golgi apparatus?
it modifies and repackages proteins and lipids for specific destinations inside/outside the cell
vesicles fuse with the golgi apparatus membrane
also produces lysosomes
What is the structure of the golgi apparatus?
a group of fluid filled membrane bound flattened sacs
vesicles can fuse and leave golgi apparatus
What is a vesicle?
they are small, fluid filled sacs surrounded by membrane that carry proteins and lipids
that are transported from one organelle to another
they are formed as a ripped off piece of membrane from the SER or golgi apparatus
What is the function of a lysosome?
membrane-bound sac---its a type of transport vesicle contains enzymes (lysozymes) that break down biological molecules or infectious bacteria
What is exocytosis?
its the process of moving materials from within a cell to the exterior of the cell. This process requires energy and is therefore a type of active transport
What is the structure of the rough endoplasmic reticulum?
RER is a system of membranes enclosing a fluid-filled space
the surface of it is covered with ribosomes
the folded part of the membrane is called the cisternae
What is the folded part of the E.R?
called the cisternae
What is the function of the RER?
holds ribosomes in place right outside the nucleus so outcoming RNA is much more likely to hit it
it then folds and processes the proteins that have been made at the ribosomes
What is the function of the smooth endoplasmic reticulum?
no ribosomes
proteins move through SER to get ready to be transported
-can synthesise and process lipids
What is a centriole?
they produce spindle fibres (which are used in mitosis to pull chromosomes apart)
In what type of cells do permanent vacuoles exist?
permanent vacuoles only exist in plant cells
animal cells can contain a temporary vacuole
What is inside the vacuole?
cell sap
which is a watery solution of sugars, enzymes and pigments
What is the name of the membrane of a vacuole?
vacuole membrane——-> tonoplast
What feature must cell walls have to allow things in and out?
permeability- they let everything in because the role of the membrane is to choose what can enter and leave so the cell wall just allows everything
What are the pores in the cell wall called?
plasmodesmata- they connect two cells together by their cytoplasm, enabling exchange and transport of substances
What is the function of the cell membrane?
to regulate what can enter and leave the cell
and has receptors to enable cellular communication
What is the definition of a specialised cell?
a cell that is adapted and has special FEATUREs that allow it to carry out a particular function
How is a muscle cell adapted for its function? (2)
mitochondria- carry out respiration that releases energy for muscle contraction
protein filaments- can slide over each other, allowing cell to become smaller, enabling muscle contraction
What is the difference between villi and microvilli?
villi- multicellular structures that are covered by epithelial cells
microvilli- structures found on the cell membrane of each individual epithelial cell
What is the size of a eukaryotic cell and a prokaryotic cell?
eukaryotic: 10-100µm
prokaryotic: 0.5-5µm
Why is a stage micrometer used as well as an eyepiece graticule?
size of the units on the eyepiece graticule depend on the magnification so the micrometer is used to calibrate the graticule
What are two conventions that must be followed to draw a biological drawing?
no sketching
no shading
use a sharp pencil
label lines should no cross
What is the procedure for preparing a plant cell slide?
- place the specimen on a slide
- add a few drops of iodine solution onto the slide to stain the specimen
- carefully place a coverslip over the specimen, making sure there are no air bubbles
What is the function of a palisade cell and how is it specialised to carry out its function?
it produces carbohydrates by carrying out photosynthesis. it contains many chloroplasts to so can absorb maximum light energy
What are the two main groups of prokaryotes?
bacteria
archaea
How is DNA presented in a prokaryotic cell?
DNA is a CLOSED loop that floats freely in the cytoplasm
What is a nucleoid?
an irregular shape region in a prokaryotic cell that comprises most of the genetic material
not membrane enclosed
What is the size of a ribosome in a prokaryote and in a eukaryotic cell?
prokaryotic: 70s
eukaryotic: 80s
What is the cytoplasm made up of in a prokaryotic cell?
cytosol
What is the cell membrane composed of in a prokaryotic cell?
same as a eukaryotic cell
made of a phospholipid bilayer which also contains proteins and lipids embedded in it
What is the cell wall in a prokaryote made up of?
peptidoglycan (or can also be called murein)
-a polymer of amino acids and sugars
What is a mesosome and their predicted function?
they are infoldings of the cell membrane of a prokaryotic cell
function: could be to increase SA for respiration or for secretion
What is the slime capsule and its function?
many pathogenic bacteria are surrounded by a slime capsule, a protective outer layer
-it protects the bacteria from viruses or a host’s immune system by hiding the antigens on the cell’s surface
What is the slime capsule made up of and what does is contain?
made up of polysaccharides and contains water to protect against dessication
What is dessication?
drying out
the water in the slime capsule is there to prevent the slime capsule form drying out
What are flagella?
long, helical tubes that extend out of the cell walls which rotate to allow for movement, that are powered by protein motors
What are pili?
they are hollow protein structures that are used in protein conjugation
What is bacterial conjugation?
the transfer of genetic material from one bacterium to another (through physical contact)
plasmids replicated independently
the plasmid is replicated and transferred to the other bacterium because the membranes will fuse
What is a plasmid?
a small loop of DNA
a copy from the main loop of DNA
What is the function of the thylakoid membrane?
they are membrane bound compartments where the light dependent reactions for photosynthesis occur
What is the function of a chloroplast?
location of where light dependent reactions occur to perform photosynthesis to produce carbohydrates/sugars
Why can mitochondria have different shapes in an electron micrograph?
this is because the electron micrograph is only a cross section and the mitochondria is actually a 3D structure so it can be orientated differently
Why are there many mitochondria in the epithelial cells lining the small intestine?
many mitochondria to provide more energy for a higher rate of respiration to carry out active transport and absorb digested food molecules
What structures of a eukaryotic cell cannot be seen by a light microscope?
ribosomes
mitochondria
lysosomes
endoplasmic reticulum
Why are thylakoid membranes advantageous in the chloroplasts?
they increase the surface are so maximum light can be absorbed
What is this organelle:
‘has membranes arranged in stacks and contains DNA?
a chloroplast
What is the content and function of the mitochondrial matrix?
contents: ribosomes, DNA, proteins
function: to synthesis proteins required for the mitochondrion
- to store substrates of respiration
Why can structures such as mitochondria and ribosomes not be seen through a light microscope?
this is because it has a lower resolving power (because wavelength of light is longer), so less detail can be seen, reduced ability to distinguish between two objects
What are the disadvantages of using TEM?
has to be a very thin specimen
cannot look at living cells
no colour image produced
preparation may cause artefacts
Compare TEMs and SEMs?
TEMs- give high resolution images -can only be used on very thin specimens -only dead specimens SEMs- can be used on thick specimens -gives a 3D image -also can only be used on a non-living specimen
