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Questions and Answers
Which of these options are correct? (Select all that apply)
Which of these options are correct? (Select all that apply)
What is the best explanation for the following: Water is the most abundant compound in cells and a solvent for metabolic reactions; $H_2$, $H_2S$, and $CH_4$ gases are produced and used by bacteria and archaea; $H^+$ ions are the basis for transfers of cellular energy and help maintain the pH of cells.
What is the best explanation for the following: Water is the most abundant compound in cells and a solvent for metabolic reactions; $H_2$, $H_2S$, and $CH_4$ gases are produced and used by bacteria and archaea; $H^+$ ions are the basis for transfers of cellular energy and help maintain the pH of cells.
Which element is a central atom in the chlorophyll molecule; and is also required for the function of membranes, ribosomes, and some enzymes?
Which element is a central atom in the chlorophyll molecule; and is also required for the function of membranes, ribosomes, and some enzymes?
What are the two types of photoautotrophs?
What are the two types of photoautotrophs?
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What are the two categories of heterotrophs?
What are the two categories of heterotrophs?
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What kind of heterotrophs are the majority of heterotrophic organisms?
What kind of heterotrophs are the majority of heterotrophic organisms?
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Facilitated diffusion does not require energy.
Facilitated diffusion does not require energy.
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What is the specific type of transport that utilizes a carrier protein in the cell membrane?
What is the specific type of transport that utilizes a carrier protein in the cell membrane?
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Active transport does not require energy.
Active transport does not require energy.
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Which of the following processes are considered to be active forms of transport?
Which of the following processes are considered to be active forms of transport?
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What is the significance of osmotic pressure in cells?
What is the significance of osmotic pressure in cells?
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What is the optimal growth temperature of most human pathogens?
What is the optimal growth temperature of most human pathogens?
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Which of the following statements is true about obligate aerobes?
Which of the following statements is true about obligate aerobes?
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Facultative anaerobes can grow in the presence or absence of oxygen.
Facultative anaerobes can grow in the presence or absence of oxygen.
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What are the two enzymes that neutralize toxic oxygen byproducts?
What are the two enzymes that neutralize toxic oxygen byproducts?
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What type of organism grows best at higher carbon dioxide tensions than normally present in the atmosphere?
What type of organism grows best at higher carbon dioxide tensions than normally present in the atmosphere?
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Study Notes
Microbial Nutrition
- Microbial nutrition is the process of acquiring chemical compounds (nutrients) from the environment to sustain life.
- Bioelements, such as carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, sodium, chlorine, and magnesium, are essential for life.
- Essential nutrients are substances, either elements or compounds, that an organism must obtain from outside its cells.
- Macronutrients are required in large amounts, playing key roles in cell structure and metabolism, including proteins and carbohydrates.
- Micronutrients, or trace elements, are required in smaller amounts, involved in enzyme function and maintaining protein structure. Examples are manganese, zinc, and nickel.
Organic and Inorganic Nutrients
- Organic nutrients contain carbon and hydrogen atoms and are often products of living things. Examples include methane (CH4), carbohydrates, lipids, proteins, and nucleic acids.
- Inorganic nutrients contain atoms or molecules other than carbon and hydrogen, such as metals (and their salts like magnesium sulfate, ferric nitrate, sodium phosphate), gases (such as oxygen and carbon dioxide), and water.
Chemical Analysis of Cell Contents
- Cells are primarily composed of water (70%), followed by organic compounds (97% of dry cell weight).
- Proteins are the most prevalent organic compounds in cells.
- These organic compounds are built from six elements: carbon, hydrogen, oxygen, phosphorus, sulfur, and nitrogen.
Essential Biological Nutrients
- Different elements/nutrients are presented in different natural forms including gases (CO2), carbonates (CO32-), and organic compounds.
- Examples of sources/reservoirs include air, sediments, soils, and living things.
- The elements/nutrients are crucial to cell function, contributing to various biological processes and structures.
- Carbon (CO2, CO3^2-, organic compounds), crucial in photosynthesis & respiration, cell walls, skeletons, organisms
- Nitrogen (N2 gas, NO3-, NO2-, NH3, organic nitrogen), required for amino acids and nucleic acids, primary source for algae, plants, and most bacteria
- Oxygen (O2, oxides, H20), necessary for aerobic metabolism, a major component of photosynthesis, significant element in organic and inorganic compounds
- Hydrogen (H2, H2O, H2S, CH4, organic compounds), crucial for many biological processes; part of various biomolecules, produces by bacteria and archaea, and part of cellular energy
- Phosphorus (PO4^3- (phosphate) ), component of DNA/RNA, part of ATP, NAD, and phospholipids
- Sulfur (S, SO4^2-, SH), part of certain amino acids, forms disulfide bonds that stabilize proteins.
- Potassium (K+), important in protein synthesis and membrane transport.
- Sodium (Na+), participates in membrane actions and maintaining osmotic pressure
- Calcium (Ca+), stabilizes cell walls and contributes to resistance to bacterial endospores, part of protozoan shells
- Magnesium (Mg+), part of chlorophyll, helps with membrane, ribosome, and enzyme functions
- Chloride (Cl-), involved in membrane transport crucial for obligate halophiles
- Zinc (Zn+), enzyme cofactor, regulates eukaryotic genetics
- Iron (Fe+), part of respiratory proteins such as cytochromes.
- Micronutrients (copper, cobalt, nickel, molybdenum, manganese, iodine) and required in small amounts functioning as cofactors in enzyme systems.
Sources of Essential Nutrients
- Heterotrophs obtain carbon from organic compounds produced by other living organisms.
- Autotrophs obtain carbon from inorganic sources of CO2.
Growth Factors
- Essential organic nutrients—such as certain amino acids, vitamins—cannot be synthesized by an organism and must be provided for survival.
Classification of Nutritional Types
- Main determinants of a nutritional type are the carbon source and energy source.
- Carbon source: Heterotroph (organic carbon), Autotroph (CO2)
- Energy source: Chemotroph (chemical compounds), Phototroph (sunlight)
Nutritional Categories of Microbes
- Nutritional categories are based on how microbes acquire both carbon and energy (e.g., photoautotroph, chemoheterotroph, etc.).
Autotrophs and Their Energy Sources
- Photoautotrophs use sunlight as their energy source and CO2 as their carbon source (e.g., photosynthetic organisms).
- Chemooautotrophs use inorganic substances for both energy and carbon source (e.g., methanogens).
Heterotrophs and Their Energy Sources
- Heterotrophs derive both carbon and energy from organic compounds. Common examples include saprobes (free-living microbes that feed on dead organisms) and symbionts (organims that live on or within another organism)
Transport: Movement of Substances Across the Cell Membrane
- Passive transport does not require energy —molecules move from areas of high concentration to areas of low concentration through simple diffusion, osmosis, or facilitated diffusion.
- Facilitated diffusion requires membrane channels or carriers;
- Active transport does require energy and carrier proteins — molecules move, often against concentration gradients
Diffusion and Molecular Motion
- Molecules move randomly from regions of higher concentration to those of lower concentration. This is how things like gases and liquids move through membranes.
Osmosis
- Osmosis is the diffusion of water across a selectively permeable membrane. Osmosis occurs because there are differences in water concentration between two areas separated by a membrane. This movement of water can change the shape or even cause the rupture of cells.
Effect of Differing Osmotic Content Solutions
- Isotonic: Equal water concentrations inside and outside the cell
- Hypotonic: Lower solute concentration outside the cell; water moves into the cell, possibly causing swelling or bursting
- Hypertonic: Higher solute concentration outside the cell; water moves out of the cell, possibly causing shrinking or plasmolysis
Movement of Solutes: Facilitated Diffusion
- This passive transport uses protein carriers (membranes) for substance movement.
- The transporter or carrier protein exhibits selectivity; therefore, it binds to a specific molecule only, and the saturation rate of the transport is limited on the binding sites in the transport protein.
Carrier Mediated Active Transport
- Specific membrane proteins interact with nearby solute-binding proteins. Energy is required (from ATP) to move the substance across the membrane.
In Group Translocation
- Active transport where a molecule is altered as it crosses the cell membrane.
- Energy is used to chemically change the molecule, making it useable by the cell.
Endocytosis: Eating and Drinking by Cells
- Phagocytosis ingests whole cells or substances. Pseudopods are involved in the engulfing process.
- Pinocytosis ingests dissolved substances, fluids. Microvilli aid in the process.
Method of Analyzing Population Growth
- Turbidometry measures the degree of cloudiness in a liquid culture to estimate population size.
- Viable colony count determines the number of living cells after plating.
- Direct cell count (manually or automated) counts the number of cells microscopically.
Stages in the Population Growth Curve
- Lag phase: initial period of adjustment.
- Exponential/Log phase: rapid growth.
- Stationary phase: growth rate equals death rate.
- Death phase: decreasing population due to exhaustion of resources or buildup of waste.
Other Microbial Relationships: Biofilms
- Results from the attachment of organisms to substrates through extracellular matrix causing complex organized layers.
- Dominate natural environments and cooperate via quorum sensing to develop biofilms.
Interrelationships Between Microbes and Humans
- Humans contain normal microbiota, or microbial flora, which includes bacteria, fungi, and protozoa living in symbiotic relationships.
- These relationships can be commensal, parasitic, or synergistic affecting human physiology, immunity, and genetics.
The Study of Microbial Growth
- Microbial growth involves both cellular enlargement and population increase—mainly by binary fission.
- Binary fission: the parent cell enlarges, replicates its chromosome, and forms a central transverse septum dividing the cell into two daughter cells.
Rate of Population Growth
- Generation time (doubling time) the time required for a microbial population number to double.
- Exponential growth occurs when each cycle causes the population to increase by a factor of two.
- The rate of growth is expressed quantitatively using an equation for calculating population size over time.
Methods of Analyzing Population Growth
- Turbidometry measures the degree of cloudiness in a liquid culture to estimate the population size.
- Enumeration methods: Viable colony count, direct cell count (manual or automated – Coulter counter, flow cytometer) give the total count of population, either living (viable) and dead microbes
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