01_LifeCycles - Life Cycles page 1.01 RR Lew Growth...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Life Cycles – page 1.01 – RR Lew Biological organisms normally exhibit some type of life cycle –growth, development and reproduction– which has evolved to enhance survivability and adaptability. Sur- vival implies successful reproduction to continue the species; adaptability implies the ability of the organisms to adapt to environmental (and other) challenges during its reproductive lifetime. One of the simplest life cycles is that of a prokaryote. Prokaryotes usually divide by binary fission: The lifecycle, from one to two to four cells, etc., is usually described by the generation time (the doubling time –the time required for a cell division to occur). The doubling time depends on nutrient supply, tempera- ture and other conditions. Under optimal conditions, doubling is about 20–80 min- utes. In the absence of any constraints on continued growth — ad infinitum — popula- tion growth will follow the relation: N T = N 0 • 2 (T/g) N T is the number of cells at time T N 0 is the number of cells at time T = 0 g is the generation time 0 50 100 150 200 250 300 350 400 0 50 100 150 200 g(20) g(40) g(80) N T T Implicit in the process of binary fission is the concept that DNA will be duplicated and passed on from the ‘mother’ cell to the two ‘daugh- ter’ cells. Mutations can occur during DNA replication. Mutations will increase genomic variability through the many bacterial genera- tions. The age of the bacteria is remarkable: The progenitor of any bacteria existing now appeared 3 to 4 billion years ago. as time increases, t/g = 1, 2, 3 ..., thus 2 1 , 2 2 , 2 3 , etc. Growth
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
It is important to emphasize the complexity of growth. The simple exponential growth process can and does occur under some conditions, but constraints on growth are many. Growth of the individual may or may not be determinant (stopping at a well- defined endpoint, a good example is human (animal) development). Growth of a population will decline as resources are exhausted (humanity may become a good example ...). Below is just one example of population growth over time: These are population growth curves for the organism Moina macrocopa . The data are from Terao, A. and T. Tanaka (1928) Population growth of the water- flea, Moina macrocopa Strauss. Proc. Imper. Acad. Jpn. Vol. 4, pp. 550–552. It’s an example of how temperature affects the doubling time (fastest at 33.5 degrees) and the population size (maximal at 24.8 degrees [1] . [1] Data were redrawn by Seiichi Sakanoue in a recent publication: Sakanoue, S. (2007) Extended logistic model for growth of single-species populations. Ecological Modelling 205(1-2):159-168. The article describes the multitude of equations which are used to predict not only the sigmoidal characteristic of growth of organisms and populations, but also many economic processes. The complexity of the mathematical models can be daunting, especially when the multi-variate nature of carrying capacity must be considered. Even more complex is the challenge of incorporating predator-prey relations. The Lotka-Volterra model describing predator-prey effects on predator (x) -
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern