CELL STRUCTURE

What are the 3 principles of cell theory?

- cells are the basic unit of all life

- both plant & animal tissue are composed of cells

- cells only develop from existing cells

define magnification

how many times larger the image is compared to the actual size of the object (specimen) being viewed

define resolution

The ability to distinguish two separate points as distinct objects.

fill in the gaps: A high resolution will produce an image that's shows all the ____ ______ of the specimen

A high resolution will produce an image that's shows all the fine detail of the specimen

define microscopy

use of microscopes to study small objects/organisms

name the 4 types of microscopes

- compound optical (light) microscope

- laser scanning confocal microscope

- transmission electron microscope

- scanning electron microscope

define eukaryotic

cells that have a true nucleus

fill in the gap: All living things, apart from ________, are eukaryotic

All living things, apart from bacteria, are eukaryotic

how many lenses does a compound optical (light) microscope have and what are they called?

2 lenses; objective lens and eyepiece lens

The objective lens and eyepiece lens in a compound optical (light) microscope work to increase the _____ of the image

magnification

the best quality compound optical (light) microscopes will allow a maximum magnification and resolution of what?

max magnification = x1500 (up to x2000)

max resolution = 200nm (0.2µm)

fill in the gaps: Any structures that are closer than ____ ___ __________ of light can't be seen separately (can't be resolved)

Any structures that are closer than half the wavelength of light can't be seen separately (can't be resolved)

what is the shortest wavelength of visible light and what is maximum resolution as a result?

shortest wavelength of visible light = 400nm

∴ max resolution = 200nm

(therefore a ribosome that has a diameter of 20nm won't be visible using a light microscope)

what are the advantages of using a compound optical (light) microscope?

- easily available

- relatively cheap

- can be used outside (needs light source)

- can be used to observe living organisms & dead, prepared specimens

what are the disadvantages of using light microscopes?

- can't see very small objects

- low resolution

- can't magnify much above x1500 and still get a clear image

how does a laser scanning confocal microscope work?

- uses laser beams (intense beams of light) to scan a specimen that's being treated with fluorescent dyes

- the laser light scans the specimen point by point

- a computer is used to assemble the pixel information into one image, displayed on a screen

define fluorescence

The absorption and re-radiation of light

fill in the gap: Images produced from a laser scanning confocal microscope are high __________ and have high contrast.

Images produced from a laser scanning confocal microscope are high resolution and have high contrast.

a laser scanning confocal microscope can focus at different depths with a specimen. what does this mean?

whole living specimens, as well as cells can be seen

what is an example of when a laser scanning confocal microscope may be used?

used in the medical profession (e.g. to observe fungal corneal infections of the eye at a much earlier stage) & many areas of biological research.

how do electron microscope work?

a beam of electrons in an electron microscope is focussed by electromagnets to a screen/photographic plate

what are the 2 main advantages of using an electron microscope compared to a compound optical (light) microscope?

- much greater resolution because the wavelength of an electron is 0.004nm, ∴ clear & detailed images can be produced

- much greater magnification can be used (e.g. x500 000)

what are the 2 different types of electron microscopes called?

- transmission electron microscope (TEM)

- scanning electron microscope (SEM)

how does a transmission electron microscope (TEM) work?

the electron beam is transmitted through the specimen before viewing

what is a photo taken with an electron microscope called?

electron micrograph

what is the best resolution of a transmission electron microscope (TEM)?

0.5nm (0.0005µm)

what is the best magnification of a transmission electron microscope (SEM)?

x2 million

how does a scanning electron microscope work (SEM)?

- an electron beam is scanned to and fro across the surface of the specimen

- the electrons that reflect off the surface of the specimen are collected

- these electrons are used to form a TV-like image on a screen

what is the best resolution of a scanning electron microscope (SEM)?

3-10nm (0.003-0.01µm)

what is the best magnification of a scanning electron microscope (SEM)?

x 200 000

what are the added benefits of using a SEM microscope?

- surface structures are shown

- 3D effect is produced

fill in the gap: The inside of an electron microscope is a ______ to ensure electron beams travel in straight directions, therefore samples need to be processed in a specific way.

The inside of an electron microscope is a vacuum to ensure electron beams travel in straight directions, therefore samples need to be processed in a specific way.

what are the 4 methods of specimen preparation for electron microscopes?

- fixation using chemicals/freezing to prevent sample breaking down

- staining with heavy metals; creates a contrast that helps with viewing image

- dehydration with solvents; prevents water boiling in vacuum that would damage sample

- embedded in resin (TEM samples); allows thin slices to be obtained

compare compound optical (light) microscopes with electron microscopes

LIGHT:

- inexpensive to buy & operate

- small & portable

- simple sample preparation

- sample preparation doesn't usually lead to distortion

- vacuum isn't required

- natural colour of sample is seen (or stains are used)

*- up to x2000 magnification

*- maximum resolution = 200nm (0.2µm)

- specimens can be dead or alive

ELECTRON:

- expensive to buy & operate

- large & needs to be installed

- complex sample prep

- sample prep often distorts material

- vacuum is required

- black & white images are produced (can be coloured digitally)

*- over x500 000 magnification

*- maximum resolution for TEM is 0.5nm (0.0005µm)

*- maximum resolution for SEM is 3-10nm (0.003 - 0.01µm)

- specimens are dead

how do we convert millimetres (mm) to micrometres (µm)?

x 1000

how do we convert micrometres (µm) to nanometres (nm)?

x 1000

how do we convert from nanometres (nm) to micrometres (µm)?

➗ 1000

how do we convert from micrometres (µm) to millimetres (mm)

➗ 1000

what is the total magnification of a low power lens?

x40

how many micrometres (µm) is 4 EPU equal to and ∴ how many micrometres (µm) is 1 EPU equal to for a low power lens?

4 EPU = 100 µm

1 EPU = 25 µm

what is the total magnification of a medium power lens?

x100

how many micrometres (µm) is 10 EPU equal to and ∴ how many micrometers (µm) is 1 EPU equal to for a medium power lens?

10 EPU = 100 µm

1 EPU = 10 µm

What is the equation linking total magnification, eyepiece lens, and objective lens?

total mag = eyepiece x objective

how many micrometers (µm) is 40 EPU equal to and ∴ how many micrometers (µm) is 1 EPU equal to for a high power lens?

40 EPU = 100 µm

1 EPU = 2.5 µm

what is the equation linking magnification, image size, and actual size?

image size

magnification = ---------------

actual size

what is the formula triangle for the magnification, image size, and actual size equation?

describe the structure of the plasma (cell surface) membrane

- consists of a bilayer; 2 layers of phospholipids and proteins molecules

what is the width of the plasma (cell surface) membrane?

7nm

what is the function of the plasma (cell surface) membrane?

a selectively permeable membrane controlling what goes into and out of a cell

describe the structure of the nucleus

- largest cell organelle (typically 10µm in diameter)

- enclosed by an envelope of 2 membranes that is perforated by nuclear pores

- contains chromosomes

- contains nucleolus

what are chromatin?

long tangles of chromosomes & protein

what is the typical diameter of the nucleus?

10µm

what is the function of the nucleus?

- chromosomes contain DNA, which is organised into genes

- genes control all activities of a cell

- DNA carries the code for making proteins

- nucleolus manufactures ribosomes

what are the two types of endoplasmic reticulum (ER)?

- rough endoplasmic reticulum (RER)

- smooth endoplasmic reticulum (SER)

describe the structure of the endoplasmic reticulum (ER)?

- system of flattened sacs called cisternae, forming tubes and sheets

- RER is continuous with the outer membrane of the nuclear envelope

what is the function of the rough endoplasmic reticulum (RER)?

transports proteins made by ribosomes through the cisternae

what is the function of the smooth endoplasmic reticulum (SER)?

- synthesises fats and steroids (e.g. SER will synthesise oestrogen in the cells in the ovaries)

- in liver cells, SER is involved in detoxification

describe the structure of ribosomes

- very small organelles (20nm)

- consist of a large and small sub-unit

- made of protein and RNA

where are ribosomes typically found? what happens to the proteins made in these areas?

either on the RER (proteins made leave the cell) or lie free in the cytoplasm (proteins made stay in the cell)

what is the function of the ribosomes?

protein synthesis

describe the structure of the Golgi apparatus

- stack of flattened, membrane-bound sacs, called cisternae, continuously being formed at one end of the stack and budded off as vesicles at the other

what is the function of the Golgi apparatus?

- internal processing and transport system (e.g. proteins from ER (protein changes shape, carbohydrates added))

- Golgi vesicles transport materials to other parts of the cell or to the cell surface (plasma) membrane

- makes lysosomes

Describe the structure of mitochondria

- surrounded by a double membrane, the inner being folded to form cristae

- contains a matrix, few ribosomes, circular loop of DNA and phosphate granules

what is the length and diameter of the mitochondria?

1-10 µm in length

diameter doesn't exceed 1 µm

What is the function of the mitochondria?

- aerobic respiration > breakdown of organic molecules in the presence of oxygen to make ATP (energy currency of the cell)

describe the structure of lysosomes?

- simple spherical sac surrounded by a single membrane

- contains digestive (hydrolytic) enzymes

what is the diameter of lysosomes?

0.2-0.5µm

what is the function of lysosomes?

- join with other vesicles in a cell that contain either molecules/structures to be digested (e.g. bacteria taken in by endocytosis or unwanted organelles

describe the structure of centrioles

- small hollow cylinders

- occur in pairs

- each contain 9 triplets of microtubules made of protein called tubulin

what is the length and diameter of a centrioles?

- length = 0.3-0.5µm

- diameter = 0.2µm

what is the function of centrioles?

- cell division (animal cells only)

- microtubules form spindle and are needed for movement of chromosomes around the cell

Clilia and flagella are identical in structure, but flagella are longer. Describe the structure of cilia and flagella

- flagella are longer

- contain microtubules, arranged in 9 and 2 arrangement: 2 microtubules in the centre surrounded by a ring made up of 9 pairs of microtubules

- movement is produced when the microtubules slide against each other

What is the function of cilia and flagella?

- outgrowths of cells which can beat either in one direction (cilia) or like a wave (flagella)

- used in locomotion of single cells (sperm) or to move fluids over the surface of cells (cilia moving mucus through the respiratory tract)

describe the structure of chloroplasts

- surrounded by a double membrane (envelope)

- contains a gel-like storm through which runs a system of membranes (grana) that are stacked in places to form thylakoids

- stroma also contains ribosomes, circular loop of DNA and lipid droplets

what is the function of chloroplasts?

- the grand contain chlorophyll which is needed in the light-dependent reaction of photosynthesis

describe the structure of the cell wall

- plant cell walls are made up of long strands of cellulose

- these fibres are very strong and are arranged in a mesh-like way, which are held together by a matrix that contains pectin

what is the function of the cell wall?

- provides mechanical strength and support

- prevents cells from bursting if the cells take up a lot of water

describe the structure of the cytoskeleton

- complex structure containing microfilaments, intermediate filaments, and microtubules

what is the function of the cytoskeleton?

- maintains cell shape and provides mechanical strength

- directs movement of organelles within the cells

- provides "tracks" along which organelles can be moved

- causes movement of whole cell too

what protein subunit do microfilaments have?

actin

what protein subunit do intermediate filaments have?

keratin

what protein subunit do microtubules have?

tubulin

describe the structure of microfilaments

2 twisted strands of actin

Describe the structure of intermediate filaments

fibres that wind into thick cables

Describe the structure of microtubules

hollow tubes

what is the function of microfilaments?

- maintains cell shape

- motility/movement (pseudopodia)

- contraction (muscle) (flexible plasma membrane)

- cytokinesis of cell division

what is the function of intermediate filaments?

- maintains cell shapes

- anchors nucleus and organelles

what is the function of microtubules?

- maintains cell shape

- move chromosomes (spindle)

- move organelles ('tracks")

- mobility: (e.g. cilia: moves fluids/cell past the cell its attached to and flagella: moves a cell that it is attached to (e.g. sperm))

Is the plasma membrane present in animal cells?

always present

Is the plasma membrane present in plant cells?

always present

is the cell wall present in animal cells?

not present

is the cell wall present in plant cells?

always present

are the nucleus, nucleolus, and nuclear envelope present in animal cells?

almost always present

are the nucleus, nucleolus, and nuclear envelope present in plant cells?

almost always present

is the endoplasmic reticulum present in animal cells?

both RER and SER are present

is the endoplasmic reticulum present in plant cells?

both RER and SER are present

Is Golgi Apparatus present in animal cells?

usually present

Is Golgi Apparatus present in plant cells?

usually present

are lysosomes present in animal cells?

often present

are lysosomes present in plant cells?

sometimes present