foundations in biology - cell structure

magnification

the number of times larger an image appears compared to the size of the object being viewed

resolution

the shortest distance between 2 objects that are still seen as separate objects, higher the resolution the greater the detail

light microscope use

light is passed through a specimen and magnified

light microscope resolution

low resolution of 200nm

light microscope wavelengths used

400-700nm

light microscope conditions required

fixation

staining

thin section onto slide

light microscope examples of specimen

blood samples

cheek cells

light microscope advantages

cheaper

easy to use

portable

light microscope disadvantages

low resolution

cant see key details like mitochondria

check list of when drawing cells

accuracy

labels

no broken lines

no shading

annotations

scale bar

take up over 50% of page

title

cm - mm

x10

mm-micro metres

x1000

micro metres - nm

x1000

nm - micro metres

/1000

micro metres - mm

/1000

mm - cm

/10

image size =

actual size x magnification

overall magnification =

eyepiece magnification x objective magnification

methylene blue stain

all purpose stain

iodine in potassium iodide solution stain

stains cellulose yellow

acetic orcein stain

stains DNA dark red to see chromosomes

eosin stain

stains cytoplasm

why is staining used to view cells under a microscope

makes features or organelles of the cell visible and easier to see by providing a contrast

graticule =

are used to measure the actual size of a specimen

length of eyepiece unit =

total length of eyepiece graticule/ number of eyepiece divisions

why is it important to use the same objective lens throughout the measuring process

the eyepiece graticule remains constant but at different magnifications (due to different objectives being used) each division is worth a different value

how is an image formed in a TEM microscope

the microscope uses a beam of electrons which are controlled by condensation magnets, these pass through the objective and protector lens onto a screen. different thickness of sample creates a contrast

what image is formed in a TEM microscope

2D, black and white image

TEM microscope resolution

high resolution

0.05-1.0nm

TEM microscope magnification

x1000000

TEM microscope wavelengths used

0.004nm

TEM microscope preparations/conditions required

done in a vacuum, stained with metal salts and dried. artefacts of this process may be visible

TEM microscope specimen types

cell ultrastructure - organelles

TEM microscope advantages

see detailed ultrastructure inside cell

superior magnification and resolution

how is an image formed in a SEM microscope

electrons are bounced off the surface of an object and detected. electrons transmitted across surface of gold/ palladium species to detect secondary electrons

what image is formed in a SEM microscope

3D, black and white, can add false colour

SEM microscope resolution

0.4-20nm

SEM microscope magnification

x500000

SEM microscope wavelengths used

0.004nm

SEM microscope preparations/conditions required

gold/ palladium coating of specimen

SEM microscope specimen types

dead sample, often coated in metal

SEM microscope advantages

3D images at high resolution

superior magnification

SEM microscope disadvantages

very expensive

metallic film can be toxic to user

training required

artefact =

‘damage’ caused by preparation process which could be interpreted as part of the structure

organelle

a small structure within a cell which is specialised to carry out a particular function

membrane bound organelles

are organelles which consist of internal membranes e.g. mitochondria

structure of nucleus

largest organelle

membrane bound

chromatin

structure of nucleolus

a darkly stained area within the nucleus

function of nucleolus

responsible for synthesis of ribosomal RNA and formation of ribosomes

structure of nuclear envelope

double membrane

has nuclear pores

function of nuclear envelope

to allow mRNA out of the nucleus for protein synthesis

structure of RER

flattened sacs of membrane called cisternae 

ribosomes on them

function of RER

site of protein synthesis

where the protein falls

structure of SER

same as RER

no ribosomes

function of SER

for the manufacture and processing of lipids

structure of golgi apparatus

stack of membrane bound flattened sacs called cisternae

function of golgi apparatus

responsible for modification of proteins

also transports, modifies and stores lipids

ribosomes structure

small spherical organelles

found in RER in cytoplasm 

ribosomes function

translate genetic info in the form of mRNA into proteins

mitochondria structure

round double membrane bound organelles

mitochondria function

aerobic respiration

ATP production

lysosomes structure

membrane bound spherical sacs

lysosomes function

contain hydrolic digestive enzymes used to break down materials

plasma membrane structure

phospholipid membrane

plasma membrane function

controls what goes in and out of cells

centrioles structure

microtubles found next to nucleus and some protoctists

centrioles function

move chromosomes around by forming fibres

chloroplasts structure

large and has a double membrane

chloroplasts function

absorb light for photosynthesis

cell wall structure

cellulose lattice

cell wall function

gives structure and mechanical strength

vacuole structure

surrounded by membrane called the tonoplast

filled with sap

vacuole function

to store cell sap

provides structure and support

function of cytoskeleton

provides mechanical strength

allows movement of cell

movement within the cell

what is the cytoplasm

complex network of proteins present within the cytoplasm of all cells

what molecules make up the cytoplasm

microfilaments

intermediate filaments

microtubules

motor proteins

function of microfilaments

maintain shape and provide mechanical strength

function of intermediate filaments

hold nucleus in place

join cells together

function of the microtubules

provide shape and support

division of labour

specialised functions of cell organelles that work together to ensure cells survive

production of proteins

1) in the nucleus a gene is transcribed into mRNA

2) the mRNA leaves via the nuclear pore

3) binds to ribosome on the RER

4) ribosome carries out translation

5) polypeptide is folded in the RER and then packaged into a transport vesicle

6) vesicle then fuses with the golgi, which modifies, folds and packages the protein into a secretary vesicle

7) secretery vesicle travels to plasma membrane

8) - exocytosis then takes place   

eukaryotic cells

animals

plants

fungi

protoctists

have nucleus which contains DNA

ribosomes

have membrane bound organelles

flagella with whipping base

prokaryotic cells

bacteria

loose DNA

no nucleus

ribosomes

no membrane bound organelles

flagella with rotating base