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Yeast Culture Lab: Background Information

Paper Type: Free Essay Subject: Biology
Wordcount: 1661 words Published: 7th Aug 2018

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In the laboratory, yeasts are stored, maintained & cultivated with the help of few elementary methods. Yeasts, being a group of unicellular organisms taken care of similar to those of most bacteria except that their nutritional & environmental requirements vary.


These are microorganisms having cells with membrane-bound nuclei .Yeasts are unicellular and its size may vary greatly depending on the species. Yeasts have asexual and sexual reproductive cycles and most of them reproduce asexually by budding.

Yeast culture:

Yeast culture composes yeast in the form of dry product over a media & dried over in order to safeguard the fermenting activity of the yeast. The process of fermentation creates metabolites, which is in fact an advantage of yeast culture. The bacterial activity gets stimulated resulting in an increase in digestion of feeds by the bacteria as their number grew. This increase in numbers can result in more nutrients from the feed being available acting as a source of energy.



The natural process supports life as it produces new “progeny” individual organisms from their “parents”. Each individual organism exists due to this biological process. The process involves two methods of the following types: sexual and asexual.

Sexual reproduction requires two individuals of opposite sex to involve during the sexual course. However, the asexual reproduction do not any requires involvement of another individual as it can reproduce with the division of a bacterial cell into two daughter cells.



It is simply the process of taking food into the body through the mouth.

However, reproduction is a function of consumption. When an organism goes under reproduction, its consumption must be adequate to provide the supplementary nutritional support because this biological process needs additional resources for future survival.


Death in Population:

The processes that change the size of populations are birth, death and movement into and out of that population. The science of ecology is not just about understanding nature but often also about predicting or controlling it. In the life history of the unitary organism, as time passes and the post reproductive phase arrives death happens due to senescence which is the organic process of growing older. The individual of different ages do contribute to births in population. As per the static life table, we assume the rates of birth and death to be constant. However, the fecundity of individuals also changes with their age & contribute to births in the population as per age-specific fecundity schedules. Further, understanding the cohort life table for annuals tracks a single cohort from the first birth to the death of last survivor.


Aim of the Experiment:

Let us understand the process of manufacturing Baker’s Yeast by implying fed-batch culture in order to reduce the contamination.


The production of Baker’s yeast involves a series of aerobic stages for the development of inoculums. The process involves eight stages. The first three stages are aseptic as the pure culture for initial inoculums are used. However, open vessels are used to carry rest of the stages.

Pumping of yeast from one stage to the other as well as the seed cultures being centrifuge and washed before transfer reduces the level of contamination. During the later stages, which involves fed-batch systems, ensures better yield.

The development of inoculums for the commercial production of Baker’s yeast involves PC 1, 2, 3 as pure culture batch fermentations. F 1 & 2 is non-aseptic batch fermentations. F 3 & 4 is fed-batch fermentation & F5 is final fed-batch fermentation leading to yield of Baker’s yeast with minimal contamination.



The purpose of this experiment is to understand the process of producing Baker’s yeast with the removal of contamination to its minimalism. It involved the fed-batch culture to describe batch cultures fed with a medium without the elimination of culture fluid.

Materials and Methods:

Molasses, Chemicals like sulfuric acid Ammonium Sulphate, Ammonium Phosphate, Ammonia, Sodium Chloride, Antifoaming, Potato Starch, Emulsifying agent and Sodium Hydroxide etc.

Profile on productions of Baker’s Yeast Retrieved from http://www.southinvest.gov.et/Publications/SSNPR%20draft%20Profile/B/%20Bakers%20Yeast.pdf

The fed-batch fermentation system follows as shown in the figure below.

The Vitaminpros website, diagram retrieved from (http://www.vitaminpros.com/beta-1-3-d-glucan.htm)


The diagrams of different population dynamics inclusive of:

  • Phases of population growth after disaster
  • Limitations of environmental carrying capacity (while it is high)
  • Limitations of environmental carrying capacity (while it is low)
  • Habitable site dominated by population decay

We could easily figure out that factors, which regulate the size of a population, may not determine its size for most of the time instead; responses may change over changing levels of resources.


Population growth cycle:

As we have studied, the density-dependent birth & mortality rates lead to the regulation of popular size. When both are density dependent or either of them, then, the two curves cross. The density at which they do is “carrying capacity”.


The population graph involves four phases:

Lag Phase:

Here, the yeast settles in the environment.

Logarithmic Phase:

Until this phase, they wait for the favorable conditions to grow, consume & reproduce. As they find the proper consequences, they grow exponentially.

Stationary Phase:

This phase is only temporary as reproduction begins to cause their environment to deteriorate to where the death rate begins to overtake the birth rate.

Death Phase:

During this phase, the environment becomes very toxic with their excrement results in their death.

Carrying Capacity: its effect

Carrying capacity is the population level of an organism that persists given the quantity of life supporting infrastructure available to it. In a situation where numbers of an organism are below the carrying capacity of its environment, its birth rate will amplify. If the population exceeds the carrying capacity, the death rate will increase until the population numbers are stable. Carrying capacity increased by the discovery and exploitation of new resources (such as metals, oil or fertile uninhabited land) and decreased by resource exhaustion and waste buildup, for example declining soil fertility and water pollution. The ecological concept of carrying capacity helps to determine a sustainable population level.

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The Energy flow in Biogeochemical Cycle:

We must understand the pattern of energy flow for forest, grassland, plankton community in sea & small ponds. It helps us to understand relative roles of live consumer and decomposer systems. We will observe that the decomposer system is responsible for majority of secondary production and the live consumers have greater role in open-water aquatic communities.


If we discuss the flux of energy & matter through ecosystems, we will come across various cycles:

  • The phosphorus cycle
  • The nitrogen cycle
  • The sulfur cycle
  • The carbon cycle

They act as global pathways of nutrients between the abiotic reservoirs of atmosphere, hydrosphere & lithosphere and the biotic reservoirs consist of terrestrial & aquatic communities.


In general, the snapshot of the entire process goes like this.

The figure Retrieved from http://www.britannica.com/EBchecked/topic/65875/biogeochemical-cycle


The natural processes works in harmony and any effect or changes in the functionality or behavior of one process will have a direct or indirect influence on other natural phenomenon. The Hypothesis accepted as per the successful completion of the experiment mentioned above, as the amount of contamination in the Baker’s yeast produced was minimal.


Coleman, B. (1996). Additives for Horse Feeds. Retrieved from Website: http://www1.agric.gov.ab.ca  

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition), Individuals, Populations, Communities & Ecosystems Retrieved from (Chap. 5, pp. 145-153)

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition), Individuals, Populations, Communities & Ecosystems Retrieved from (Chap. 5, pp. 145-163)

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition), Individuals, Populations, Communities & Ecosystems Retrieved from (Chap. 5, pp. 145-163)

Stanbury, P.F.,Whitaker,A.(1995).Principles of fermentation technology,2nd edition Retrieved from (chapter 6, figure 6.2)

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition), Individuals, Retrieved from Populations, Communities & Ecosystems (Chap. 9, pp. 288)

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition) Retrieved from Individuals, Populations, Communities & Ecosystems, (Chap. 5, pp. 170, fig. 5.21)

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition) Retrieved from Individuals, Populations, Communities & Ecosystems, (Chap. 11, pp. 368, fig. 11.7)

Townsend, C.R. (2008). Essentials of Ecology (3rd Edition) Retrieved from Individuals, Populations, Communities & Ecosystems, (Chap. 11, pp. 381, fig. 11.16)


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