chapter 6 learning objectives Flashcards
compare the 4 basic categories of organisms based on their carbon and energy sources
autotrophs- inorganic source of carbon (carbon dioxide) make organic compounds from carbon dioxide, not nutritionally dependent on other living things
heterotrophs- catabolize reduced organic molecules (proteins, carbohydrates, amino acids, and fatty acids), dependent upon other life forms
chemotrophs- acquire energy from redox reactions involving inorganic and organic chemicals
phototrophs- acquire energy from light
distinguish among anaerobes, aerobes, aerotolerant anaerobes, facultative anaerobes, and microaerophiles
anaerobes- undergo anaerobic respiration using a molecule other than oxygen as the final electron acceptor in the ETC
aerobe- undergo aerobic respiration using oxygen as the final electron acceptor in the ETC
aerotolerant anaerobes- do not undergo aerobic respiration but have some enzymes that detoxify oxygen’s poisonous forms
facultative anaerobes- can maintain life via fermentation or anaerobic respiration or by aerobic respiration
microaerophiles- aerobes that require oxygen levels from 2 to 10% and have a limited ability to detoxify hydrogen peroxide and superoxide radicals (atmospheric levels of oxygen are 21%)
explain how oxygen can be fatal to organisms by discussing singlet oxygen, superoxide radical, peroxide anion, and hydroxyl radical and describe how organisms protect themselves from toxic forms of oxygen
singlet oxygen- molecular oxygen with electrons boosted to higher energy state. phagocytic cells use it to oxidize pathogens. phototropic organisms protect themselves through photosynthesis which produces carotenoids that remove the excess energy
superoxide radicals- form during aerobic respiration and anaerobic metabolism occurring in the presence of oxygen. so reactive that aerobes must produce superoxide dismutase to detoxify them. anaerobes lack superoxide dismutase and die as a result
peroxide anion- formed during reactions catalyzed by superoxide dismutase and other reactions. aerobes contain either catalase or peroxidase to detoxify. obligate anaerobes either lack both enzymes or only have a small amount of each.
hydroxyl radical- results from ionizing radiation and from in complete reduction of hydrogen peroxide. the most reactive of the four toxic forms of oxygen. not a threat to aerobes due to action of catalase and peroxidase
explain the importance of nitrogen fixation
the reduction of nitrogen gas to ammonia by certain bacteria is essential to life on earth because nitrogen is made available to living organisms in a usable form
explain how extremes of temperature, pH, and osmotic and hydrostatic pressure limit microbial growth
temp: microbes are unable to control their temp and so their survival is dependent on adapting to the temp of their habitat. temp affects the 3D configurations of proteins and nucleic acids and also affects biological membranes
pH: organisms are sensitive to changes in acidity because H+ ions interfere with hydrogen bonding in proteins and nucleic acids
osmotic pressure: restricts organisms to certain environments (like obligate halophiles and facultative halophiles)
hydrostatic pressure: water exerts pressure in proportion to its depth. for every additional 10 m of depth, water pressure increases 1 atm. barophiles live in deep ocean trenches and rely on the pressure to maintain their 3D functional shape
explain the relationships between organisms living in nature and how they can coordinate and communicate with one another
Antagonistic relationships – one organism harms or even kills another organism
Synergistic relationships – individual members cooperate such that each
receives benefits that exceed those that would result if each lived by itself, even through each could live separately
Symbiotic relationships – organisms live in such close nutritional or physical contact that they become interdependent, such that the members rarely (if ever) live outside the relationship
describe binary fission as a means of reproduction
a process in which a cell grows to twice its normal size and divides in half to produce two daughter cells of equal size.
explain what is meant by the generation time of bacteria
the time required for a bacterial cell (or population of cells) to grow and divide. varies among populations, dependent on chemical and physical conditions
explain logarithmic growth
(number of cells in future) = (number of cells now) x 2^(# of generations)
population sizes double at regular time intervals
describe a bacteria growth curve and explain what occurs at each phase of a population’s growth
lag phase- short. cells are adjusting to their new environment. actively synthesizing enzymes to utilize novel nutrients in the medium
log phase- cells begin to divide and enter steady increasing period of growth.
stationary phase- curve is flat. new cells produced at the same rate old cells are dying. metabolic rate of surviving cells declines. supply or energy and nutrients are exhausted.
death phase- steady decline of cells. number of deaths exceeds number of new cells formed. actual cell lysis may occur. cells can assume unusual shapes.
