cells and microscopy

• an instrument used to magnify an object
• first developed in the 16th to 17th century
• allowed scientists to develop the cell theory
• inexpensive to buy and operate
• sample preparation is simple and does not usually lead to distortion
• a vacuum is not required
• the natural colour of the sample can be seen
• up to 2000x magnification 
• a resolving power of 200nm
• specimens can be living or dead

• both plant and animal tissues are comprised of cells 
• cells are the basic unit of all life
• cells only develop from existing cells

• had two lenses
• the objective lens is placed near the specimen
• the objective lens produces a magnified image
• the eyepiece lens then magnifies that image
• illumination is provided by light underneath the sample

• how many times larger the image is than the actual size of the object being viewed
• simply magnifying an object does not increase the amount of detail that can be seen

• ability to see individual objects as separate entities
• limited by the diffraction of light as it passes through the sample and lenses

magnification = size of image / actual size of object

• a beam of electrons (with a wavelength less than 1nm) is used to illuminate a specimen
• produces images up to x500,000
• very expensive
• hard to use
• specimens can be damaged
• complex sample preparation
• a vacuum is required
• artifacts are common
• black and white images are produced
• specimens must be dead
• a resolving power from 0.5 - 10nm, depending on type

• an electron beam is transmitted through the specimen
• the best resolving power is 0.5nm
• similar to light microscopy

• a beam of electrons is sent across the surface of the specimen and reflected electrons are collected
• resolving power of 3 - 5nm
• 3D images of surfaces of specimens

• artifact - visible structural detail caused by the processing of the sample that is not a feature of the specimen

• moves a single spot of focused light across a specimen
• causes fluorescence from components labelled with a dye
• the emitted light is filtered through a pinhole
• only light radiated from very close to the focal plane (distance giving the sharpest focus) is emitted
• spot illuminating the specimen is moved to produce 2D images
• 3D images can also be produced by using different focal planes to produce images
• non-invasive

• can make up multicellular organisms

• contains coded genetic information in DNA form
• DNA directs the synthesis of all proteins required by the cell 
• often the biggest single organelle
• contained within a double membrane (nuclear envelope)
• nuclear pores in the nuclear envelope allow molecules to move in and out of the nucleus
• DNA is associated with histones to form chromatin
• chromatin coils and condenses to form chromosomes

• an area within the nucleus 
• comprised of proteins and RNA
• produces ribosomes

• the site of the final stages of respiration
• the number of mitochondria usually indicates the amount of energy the cell uses
• more mitochondria = more energy
• have a double membrane structure
• the inner membrane is tightly folded and called cristae
• the fluid interior is called the matrix
• they contain a small amount of their own DNA
• the can produce their own enzymes
• the can reproduce themselves

• membranes are membranous sacs
• they have storage and transport roles
• they have a single membrane with fluid inside
• lysosomes contain hydrolytic enzymes
• they break down waste material in cells
• they break down pathogens ingested by phagocytes
• they have a role in apoptosis (cell death)

• is present throughout the cytoplasm
• they have a network of fibres
• they have microfilaments
• they have contractible fibres
• they are responsible for cell movement
• they are also responsible for cell contraction during cytokinesis

• a scaffold-like structure
• they determine the shape of the cell
• control the movement of organelles around the cell
• as spindle fibres, they move chromosomes during cell division
• they are intermediate fibres
• they give mechanical strength to cells

• they are a component of the cytoskeleton
• they are comprised of microtubules
• two associated centrioles make a centrosome
• they are responsible for assembly and organisation of the spindle fibres during cell division

• they have a whip-like structure
• they enable cell mobility
• are used as a sensory organelle to detect chemical changes
• longer than cilia
• less abundant than cilia

• they are hair-like projections
• they are present in greater numbers than flagella 
• can be mobile or stationary
• mobile cilia beat in a rhythmic manner to enable movement of substances near to the cells
• each cilium has 2 central microtubules surrounded by 9 pairs or microtubules arranged as a wheel 
• this is the 9 + 2 arrangement

• a network of membranes enclosing flat sacs 

• lipid and carbohydrate synthesis and storage
• no ribosomes

• has ribosomes bound to the surface 
• responsible for the synthesis and transport of proteins

• can be free-floating or attached to ER
• non-membrane bound
• constructed of RNA
• made in the nucleolus
• site of protein synthesis
• mitochondria and chloroplasts contain ribosomes

• a compact structure
• formed of cisternae
• modifies and packages proteins into vesicles
• may package into secretory vesicles or lysosomes

• proteins are synthesised on ribosomes bound to rough ER
• proteins pass into cisternae and are packaged into transport vesicles
• vesicles move towards Golgi apparatus via the cytoskeleton
• vesicles fuse with the cis face of the Golgi apparatus and the proteins enter
• proteins are structurally modified
• proteins leave the Golgi apparatus in vesicles from the trans face

• freely permeable
• gives the cell its shape
• the contents of the cell push against it making it rigid
• supports individual cells and plants themselves
• a defense mechanism against invading pathogens

• a membrane-lined sac
• contains cell sap
• many plant cells have large permanent vacuoles
• the membrane of the vacuole is the tonoplast
• it is selectively permeable
• helps maintain turgor

• the organelle responsible for photosynthesis
• found in the green parts of the plant
• the fluid interior is stroma
• an internal network of membranes for sacs called thylakoids
• several thylakoids are called a granum
• grana are joined by membranes called lamellae
• grana contain chlorophyll for photosynthesis
• contain DNA and ribosomes
• starch produced in photosynthesis is present as starch grains

• first appeared 3.5 billion years ago
• always unicellular 
• DNA is not contained within a nucleus
• organelles are not membrane-bound 
• reproduce by binary fission

• single chromosome
• supercoiled to be compact
• genes are often grouped into operons so a number can be switched on or off at the same time

• smaller (70S)
• size is determined by the rate they settle in a solution

• made of peptidoglycan

• thinner than in eukaryotes
• does not have a 9 + 2 structure
• energy to rotate comes from chemiosmosis, not ATP
• attached to the cell by the basal body and rotated by molecular motor