All types of microbial growth are heavily impacted by environmental conditions. One of the most critical factors for microbial growth is the availability of nutrients and energy.
Microbes need carbohydrates, fats, proteins, metals, and vitamins to survive, just like animals. The process of using nutrients and converting them into cellular material requires energy. Every microbe has unique nutritional requirements depending on the types of molecules it is capable of making for itself. Most microbes are fairly robust, meaning they can find a way to grow in a variety of nutritional conditions. Nonetheless, microbes grow more slowly when nutrients are limited.
Temperature also impacts microbial growth. Most microbes grow optimally within a certain temperature range dictated by the ability of proteins within the cell to function. In general, at low temperatures, microbes grow slower. At higher temperatures, microbes grow more quickly. For instance, pathogens often grow best at normal body temperature, but slowly at cooler temperatures outside the body or when body temperature increases during a fever.
Extremely high temperatures usually denature the components required for the cells to survive and are lethal for many microbes. Nonetheless, a few exceptional microbes actually prefer to grow at very high temperatures or very low temperatures.
These microbes, known as extremophiles , can grow near hydrothermal vents where the temperature is above boiling or surrounded by solid ice. Even when nutrients are available and the temperature is right, many other environmental factors can influence the growth of microbes.
These include acidity, availability of water, and atmospheric pressure. Each microbe prefers a range of properties for multiple features of the environment. Overall, microbes typically grow best at a specific set of conditions and less well at other conditions Figure 5. Specific preferences for growth are as diverse as the types of microbes.
Decades of research have developed the current understanding of microbial growth to establish the principles outlined above. Establishing common principles allows us to target broad groups of microbes, while unique requirements for growth allows us to target specific microbes.
This knowledge enables the control of microbial growth that facilitates many of our interactions with microbes today. Many methods of control seek to eliminate harmful microbes from foods or equipment.
For example, high temperature is often used to kill microbes during cooking or through processes like pasteurization. In this way, potentially harmful microbes are broadly eliminated from the food product making it safe to consume and store. Similarly, chemicals in disinfectants can damage or kill microbes broadly on surfaces.
Alcohols like ethanol and isopropanol damage the cell membranes. Without this protective structure, microbes cannot control what enters or exits the cell. Subsequently, microbes cannot retain important nutrients and water. Alternatively, hydrogen peroxide damages structures within the cell. As hydrogen peroxide decomposes, it forms molecules known as free radicals that damage proteins and DNA. Meanwhile, we also use soaps to physically remove microbes from surfaces.
The chemical properties of soaps and physical force applied when wiping a surface dislodges the microbes. When microbes cannot be completely eliminated from a material, such as food products that cannot be heated to high temperatures, measures can be taken to mitigate the growth of microbes. Recognizing how temperature impacts growth, supports the importance of refrigeration.
As mentioned, cold temperatures slow the growth of microbes, so refrigeration can delay the growth of microbes in these food products. As described above, microbes can replicate as quickly as every 20 minutes leading to visible growth within only a few hours. At a lower temperature, the cells may divide only once every few hours and it will take multiple days to see visible growth. Alternatively, when we want to take advantage of microbes, we try to optimize the conditions for their growth.
This is why yeasted dough is left at a warm temperature to allow the yeast to grow rapidly. If the dough is refrigerated, it takes much longer to rise. Similarly, to use E. Continuing to better understand microbial growth will help us live safely with the microbes in our community and make use of their unique capabilities.
Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Growth, Development, and Reproduction. NGSS Performance Expectations: MS-LS Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.
The content and activities in this topic will work towards building an understanding of how aquatic plants and algae grow, develop, and reproduce. Chromosomes are duplicated. Meiosis begins in a fashion similar to mitosis with chromosome replication.
Matched sets of chromosomes pair together. Genes are swapped between matched chromosomes. The process of crossing over, or recombination, exchanges genetic information between chromosomes in a cell. The resulting chromosomes are brand new, unique combinations of genetic information. First division separates one of each chromosome pair.
The parent cell divides in half as in mitosis, producing two cells with a complete amount of DNA although they are not identical because of crossing over. Second division separates each chromosome, leaving one copy of each chromosome per cell.
The two new cells divide a second time to produce four new gametes. These gametes contain one-half of the genetic information needed to form a new individual.
Each parent provides one gamete to the process of fertilization, which results in a cell called a zygote with a full compliment of chromosomes. Offspring produced through sexual reproduction are genetically distinct from both parents, since each of their gametes has a unique combination of chromosomes.
Transport substances, defend the body, regulate temperature. Excretory system. Remove waste products and unwanted substances, regulate the water content of the body. Muscular system. Bring about movement. Nervous system. Respond to internal and external stimuli and conditions, carry messages for the body, work as a coordinated whole. Respiratory system. Deliver oxygen for respiration and remove wastes.
Reproductive system. Bring about fertilisation to produce new offspring.
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