Gen Bio

• Homeostasis


  A dynamic equilibrium that requires a control system in the form of feedback mechanisms
• Feedback mechanisms have the interdependent basic components


  • Receptor
  • Control Center
  • Effector
• Receptor


  Senses the change in the environment
• Control Center


  Relays appropriate signals (Brain)
• Effector


  Causes an appropriate change depending on the information the sensor was sending
• Positive feedback loops


  • Enhance or amplify changes, tend to move a system away from its equilibrium state and make it more unstable
• Negative feedback


  • Tend to dampen or buffer changes, tend to hold a system to some equilibrium state making it more stable
• Negative Feedback Loop


  1. Body temperature increases above normal limits

  2. Nerve cells (sensors) signal the temperature-regulating center in the hypothalamus of the brain (control center)

  3. Activate sweat glands (effectors) to bring the temperature back to the set point

  4. Return to normal temperature signals the sensors and the control center to switch off the effectors
• Positive Feedback Loop


  1. Blood pressure (stimulus) increases

  2. Baroreceptors in the carotid arteries (sensor) send the signal to the brain (integrating center)

  3. Brain sends signals to the heart (effector) to decrease the heart rate

  4. This will lower the blood pressure so that the stimulus is not continued, and the loop stops
• There are some homeostatic mechanisms that change over time, e.g. the respiratory system is found in both aquatic and terrestrial animals in the form of gills (aquatic) and lungs (terrestrial)
• Major Features of Feedback Loops that produce Homeostasis

  • Negative Feedback System
  • Neutralization
  • Thyroid is controlled by the pituitary (TSH) and the hypothalamus (TRH)
  • Oxytocin is a Positive Feedback System
• Neutralization


  Once the chyme moves into the small intestine, the pH needs to be increased to reach the optimal pH (≈ 8) for pancreatic proteases and lipases
• Thyroid hormones


  Are capable of resetting the basal metabolic rate of the body by making energy production more or less efficient, as well as altering the utilization of glucose and fatty acids
• Oxytocin


  Produced by the hypothalamus and stored in the posterior pituitary; its primary function is to stimulate uterine contractions during labor
• Oxytocin


  Secretion stimulated by suckling, which in turn leads to increased milk production is controlled via positive feedback which increases activity for its release
• The key difference between positive and negative feedback is their response to change: positive feedback amplifies change while negative feedback reduces change
• Geologic Time Scale


  Humans subdivide time into useable units such as calendar year, months, weeks, and days; geologists also subdivide time

  
• Eon


  The broadest category of geological time

  
• Homologous structures


  Structures that may perform different functions in the species living in the different environment, or it may have same origin but different functions
• Earth's history eons


  • Hadean
  • Archean
  • Proterozoic
  • Phanerozoic
• Analogous structures


  Structures of unrelated species that may evolve to look alike, have similar function but different origin
• Homoplastic structures


  Structures that look similar, but are derived from convergent evolution, meaning that the two organisms displaying homoplasy do not share a common ancestor
• Hadean Eon


  The earliest part of Earth's history, beginning with the formation of Earth at roughly 4.57 Ga and lasting to 4.1 Ga
• The presence of homologous structure is a strong indicator that the organism evolved from common ancestor. This type of evolution is called DIVERGENT EVOLUTION.
• Hadean Eon


  • Potentially delivering water and organic materials to Earth
• Convergence is an increase similarities among the species derived from different ancestors as a result of similar adaptation to similar environment.
• Archean Eon


  Spanned from 4.0-2.8 Ga, with evidence for simple (single-celled) life including potential microfossils

  
• In convergent evolution, analogous structures of unrelated organisms from different ancestors develop similar function such as butterfly wings and bird wings.
• Archean Eon


  • Remnants of cyanobacteria
  • Methane rapidly disappeared from the atmosphere, reducing the greenhouse effect and cooling the planet
• Embryonic development


  • Includes stages such as blastula, gastrula, and organogenesis
  • The embryo of fishes, salamander, fish, chicken, tortoise and human are similar during the first stage of their embryonic development and have several homologous structures that are not present when the organisms are adults
• Miller-Urrey Experiment
• Jean Baptiste de Lamarck


  A French scientist who developed an alternative theory at the beginning of the 19th century, centred on the law of use and disuse and the law of inheritance of acquired characteristics
• Proterozoic Eon


  Lasts from roughly 2.5-0.63 Ga, characterized by the rise of oxygen on Earth around 2.5 Ga (Great Oxidation Event)
• Law of use and disuse

  Individuals lose characteristics they do not require, or use, and develop characteristics that are useful
• Proterozoic Eon


  • More complex life evolved in the form of protists with nuclei, marking the evolution of eukaryotic life from prokaryotes
• Law of acquired characteristics


  The idea that an organism can pass on characteristics that it has acquired during its lifetime to its offspring (also known as heritability of acquired characteristics or soft inheritance)
• Phanerozoic Eon


  Encompasses the time from 541 Ma to present day

  
• Charles Darwin


  Often cited as the greatest biologist in history, his most famous work, On the Origin of Species, explains the theory of evolution by natural selection, providing numerous supporting examples
• Era


  Eons of geological time are subdivided into eras, which are the second-longest units of geological time

  
• Darwin's theory of evolution and natural selection


  1. Species survived through a process called "natural selection," where those that successfully adapted, or evolved, to meet the changing requirements of their natural habitat thrived, while those that failed to evolve and reproduce died off

  2. Darwin noticed similarities among species all over the globe, along with variations based on specific locations, leading him to believe that the species we know today had gradually evolved from common ancestors

  3. Darwin's theory of evolution and the process of natural selection later became known simply as "Darwinism"