BFI Midterm Microbial

• Biologists use microscopes and tools of biochemistry to study cells.
• Eukaryotic cells have internal membranes that compartmentalize their functions.
• Mitochondria and chloroplasts change energy from one form to another, and have an interesting prokaryotic evolutionary origin.
• Some groups survived and adapted using cellular respiration to harvest energy.
• Most atmospheric oxygen (O2) is of biological origin.
• O2 produced by oxygenic photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations.
• By about 2.7 billion years ago, O2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks, a process known as the "oxygen revolution".
• The initial rise in O2 was likely caused by ancient cyanobacteria.
• The "oxygen revolution" caused extinction of many prokaryotic groups.
• Later increases in atmospheric O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts.
• In a light microscope (LM), visible light is passed through a specimen and then through glass lenses, which refract (bend) the light, so that the image is magnified.
• The size range of cells can be explored using microscopy.
• Three important parameters of microscopy are magnification, resolution, and contrast.
• Magnification is the ratio of an object’s image size to its real size, making something appear bigger.
• Resolution is the measure of clarity of the image, determining if two separate points on the image can be distinguished.
• Contrast is the visibility of differences in parts of the sample, determining if a feature can be distinguished from the background.
• The endosymbiotic theory suggests that an early ancestor of eukaryotes engulfed an aerobic (oxygen-using) nonphotosynthetic prokaryote.
• Peroxisomes are oxidative organelles, using oxygen for some molecular breakdown, forming peroxides but also converting those peroxides into water, protecting other cellular components.
• Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago.
• A second endosymbiotic event involved a photosynthetic prokaryote being engulfed by a eukaryote containing mitochondria.
• The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic.
• Chloroplasts, found in plants and algae, are the site of photosynthesis, a metabolic process that uses the energy from sunlight to fix carbon (from CO2) and uses it to generate energy-rich organic molecules such as glucose.
• The Phanerozoic includes the last half billion years, and encompasses multicellular eukaryotic life.
• The engulfed prokaryote was maintained within the host cell and became an endosymbiont, eventually evolving into a mitochondrion.
• Mitochondria are the site of cellular respiration, a metabolic process that uses oxygen to generate ATP.
• This endosymbiont evolved into a chloroplast.
• Energy-transducing mitochondria and chloroplasts are not part of the endomembrane system, and are derived from prokaryotes.
• Stromatolites date back 3.5 billion years ago.
• The oldest known fossils are stromatolites, rocks formed by the accumulation of sedimentary layers on bacterial mats.
• Mitochondria and chloroplasts change energy from one form to another.
• Light Microscopy (LM) magnifies effectively to about 1,000 times the size of the actual specimen.
• Various techniques enhance contrast and enable cell components to be stained or labelled in Light Microscopy.
• Most subcellular structures, like organelles, are too small to be resolved by standard Light Microscopy.
• In Brightfield (Unstained) Light Microscopy, light directly passes through the specimen, resulting in little contrast, unless the cells are pigmented or stained.
• In Brightfield (Stained) Light Microscopy, staining enhances contrast and cells are fixed and stained (and therefore killed) in most staining procedures.
• Recent advances in light microscopy include confocal microscopy and deconvolution microscopy, which provide sharper images of 3-D tissues and cells.
• Both types of electron microscopes focus a beam of electrons using electromagnets rather than lenses.
• Confocal microscopy uses a laser to produce sharper images and allows 3-D image reconstruction by 'optical sectioning' and reconstructing images from different planes.
• The surface of SEM specimens is usually covered in a thin film of gold, and the electron beam excites the surface electrons.
• Most SEMs are artificially coloured.