Lab 8 Review PDF

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Lab 8: The Effects of the Environment on Yeast - Major Concepts Ecology Basics  ecology – the scientific study of the ways that living organisms interact with their environment, or the study of the distribution and abundance of organisms and the factors that control distribution and abundance o the main focus of ecology is to gather information about organisms and their habitats  there are three major types of ecology: 1. population ecology is the study of how individuals of a given species interact with their environment 2. community ecology is the study of how members of different species interact within a given environment 3. ecosystem ecology is the study of the ways that different communities interact and how the environment affects community dynamics and structure  these types of ecology form a hierarchy with one field nested in another o groups of individuals make up a population, groups of populations form communities, groups of communities form ecosystems, and all ecosystems together form our biosphere  these three fields have varying levels of focus on organisms and the environment o organisms - biotic factors o the environment – abiotic factors o hint for remembering the difference: in “biotic” – bio means living, and in “abiotic”, abio means non-living o organisms are living species, environmental factors are typically non-living  population ecology and ecosystem ecology focus on the effects that abiotic factors have on the organisms of interest, while community ecology focuses more in interactions among organisms, and therefore focuses on biotic factors o our experiment this week focuses on population ecology, so we will be focusing on abiotic factors (how changes in the yeast’s environment will affect their behavior) Population Ecology  population (biology definition) – a group of interbreeding or potentially interbreeding individuals of any particular species that are isolated from other similar groups  population (population ecology definition) – a group of individuals of the same species inhabiting a given area o the population ecology definition removes the emphasis on interbreeding, and focuses more on population abundance (how many individuals live in a given place and what can affect that number) o the population ecology definition is what is most relevant to us when performing this lab  populations can be defined at various spatial scales o local populations can occupy very small habitats (ex: the bugs feeding on a single plant)

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o a metapopulation is a set of local populations connected by dispersing individuals regardless of scale, population size changes in only four ways: 1. birth 2. death 3. immigration (new individuals arriving at an area) 4. emigration (individuals leaving an area) changes in the availability of resources (ex: food, space, water, etc) can trigger changes in birth, death, immigration, or emigration o a population CANNOT grow (at least, not indefinitely) at a faster pace than the available resources will support o the maximum number of individuals of a given species that a particular habitat will support is known as the carrying capacity o as a population grows and gets closer to its carrying capacity, resources become more limited and the population must respond and grow more slowly – usually by either lowering the birth rate or increasing the death rate ecological models that focus on a single species and the relevant carrying capacity are called single species models o multi-species models focus on more than one species, and are often considered in community ecology

Yeast  yeasts are eukaryotic, unicellular fungi  there are many different species of yeast – approximately 1,500 in total  though all yeasts are unicellular, some may form strings of connected cells, known as pseudohyphae  yeasts are heterotrophic, as are all fungi  some species of yeast require oxygen for aerobic cellular respiration, while others can perform anaerobic respiration (fermentation) in addition to aerobic respiration  yeasts are NOT currently thought of as a monophyletic group, because yeasts are often groups with both Ascomycetes and Basidiomycetes  budding yeasts, often called “true yeasts” ARE classified in a monophyletic group, known as Saccharomycetales, within the Ascomycetes group  the type of yeast used in lab 8 is Saccharomyces cerrevisiae – this type of yeast is commonly used for baking bread and fermenting alcohol  yeasts are a useful model organism for eukaryotes, because they are a relatively simple eukaryotic organism, they have a short generation time (can reproduce quickly), and they are easy to store  yeast grown in a laboratory setting are usually grown on solid growth media, also known as agar, which is a gel that contains the nutrients necessary for microorganisms or cells to survive o in our lab, we will grow yeast on a solid growth media known as YEPD o YEPD contains yeast extract, peptides, proteins, nitrogen, and water o we will add glucose to the growth media in varying amounts (high glucose vs low glucose) to control the amount of sugar available to the yeast *

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yeast show a primitive form of sex differentiation o there are two mating types of yeast: a and a (or alpha) – these are both haploid o the mating type of a specific yeast cell is determined by a gene called MAT o yeast have the ability to switch between mating types (MATa vs MATa) due to a form of genetic recombination (conjugation) o a MATa cell can mate with a MATa cell – this produces a MATa/MATa diploid cell o all types of cells (MATa haploid, MATa haploid, and MATa/a diploid) can reproduce via mitosis o when yeast cells perform mitosis, the daughter cells pinch off of the mother cells – this process is known as budding o diploid cells are unable to mate, but during stressful conditions (ex: not having enough of a nutrient that is necessary for survival), the diploid cells can divide by meiosis, and produce four haploid spores (two MATa cells, and two MATa cells)  these spores will later become individual haploid yeast cells in lab 8, the yeast cells being used are all MATa haploid cells, and the only reproduction that they will undergo is haploid budding

Sterile Technique  when working with microorganisms (and especially when trying to grow microorganisms), it is important to keep all materials involved in the experiment completely sterile to prevent contamination o microorganisms exist on our bodies, as well as on every surface around us, and these microorganisms can easily grow on our agar plates if they come into contact, which will ruin the yeast colonies that we are trying to observe  we will use four aspects of sterile technique in BIO200 lab: o sterilization via autoclaving – a machine known as an autoclave is commonly used to heat lab materials to a high enough pressure/temperature, for a long enough amount of time, in order to kill any microorganisms that are present on the materials o a clean workspace – lab benches should be cleaned before (and after) working with microorganisms – we will wash our benches with 70% alcohol before and after plating the yeast – hands should also always be washed before and after yeast plating o protection from airborne contaminants – sterile cultures/petri dish lids should never be exposed directly to the air or your breath – when removing the petri dish lid, the lid should never be flipped over to expose the inside portion to the external environment, and it should never be placed on the benchtop – the petri dish should be opened just enough to plate the microorganisms, and then the lid should be immediately placed back down o avoiding cross-contamination – always use a new, sterile tool for each microorganism culture (in our case, always use a new toothpick) – never re-use a sterile tool between plates or between species...