Week 1 Lecture Notes on Characteristics of Living Organisms

WEEK 1

Lecture 1: Characteristics of Living Organisms

  • Cellular: All organisms are composed of membrane-bound units known as cells.

  • Process Information: Organisms process hereditary information encoded in genes, as well as information from their environments.

  • Acquire and Use Energy: All organisms have metabolic processes to acquire and utilize energy.

  • Replication/Reproduction: Organisms have the capability to produce offspring.

  • Evolution: Populations undergo continuous evolutionary changes over time.

Theories Forming the Framework of Modern Biological Science

  1. Cell Theory: What are organisms made of?

  2. Chromosome Theory of Inheritance: How is hereditary information transmitted from parent to offspring?

  3. Theory of Evolution by Natural Selection: Where do organisms come from?

Life is Cellular

  • Late 1660s: Observations by Robert Hooke and Anton van Leeuwenhoek led to the knowledge that cells are the fundamental units of life.

  • A cell is described as a compartmentalized structure containing a membrane and chemicals in an aqueous solution.

Definition of a Theory

  • A theory is an explanation of a broad range of phenomena or observations that can be supported by empirical data.

Anatomy of the Scientific Method

  • Hypothesis: A testable statement providing an explanation (model/mechanism) of phenomena.

  • Prediction: An empirically testable and measurable expectation that must be accurate for a hypothesis to be valid.

  • Experiment: A method to test the effect of one or more variables on a certain phenomenon, while directly testing the predictions of a hypothesis.

  • Predictions must be empirically verifiable and based on the proposed mechanisms in the hypothesis. A hypothesis is considered valid only if it can be empirically verified.

Theories on the Origin of Cells

Two Hypotheses About Cell Origin

  1. Cell Theory (Rudolph Virchow, 1858): New cells arise from preexisting cells.

  2. Spontaneous Generation Theory: Cells (particularly microbial cells) arise spontaneously in nutrient-rich environments, such as spoiled food.

Louis Pasteur’s Experiment (1870s-1880s)

  • Tested the spontaneous generation hypothesis by using sterilized broth in two types of flasks:

    1. Straight-neck Flask: Allowed microbes from the air to contaminate the broth.

    2. Swan-neck Flask: Prevented contaminants from entering the broth.

  • Results showed microbial growth only occurred in the straight-neck flask, leading to rejection of spontaneous generation. Conclusion: Microbial growth requires exposure to preexisting microorganisms.

Lecture 2: Abiogenesis

  • Currently, the exact conditions leading to the emergence of life on Earth remain unclear.

  • "Bounded ignorance" refers to our understanding of generating hypotheses and predictions regarding life's origins.

Life Processes Information

  • Chromosomal Theory of Inheritance: Proposed in 1902 by Walter Sutton and Theodor Boveri, indicating that genetic information is encoded in genes located on chromosomes.

  • Structure of DNA: DNA comprises a double helix formed from four building blocks: A, T, C, and G.

  • **Central Dogma of Molecular Biology:

    1. DNA is transcribed to RNA, which is then translated into proteins.

    2. Each gene corresponds to a specific protein product.**

  • DNA replication is crucial for transferring genetic information from cell to cell and between generations.

  • Occasional mistakes in DNA replication can induce changes in proteins, impacting the organism's outward appearance.

Evolution Concepts

  • Evolution refers to changes in the traits of populations over time, involving both phenotype and genotype changes. It implies that species are interconnected through common ancestry and constantly evolve.

  • A population is defined as a group of individuals of the same species living in the same area during the same period.

  • Historical perspectives on species included notions of special creation, which asserted species were independently created and unchanging.

Challenges to Special Creation Theory

  • Evidence against static species concepts emerged as paleontologists discovered fossil records indicating extinct life forms, thereby challenging the notion of unchangeable species.

  • Prior to Darwin and Wallace, early scientists had proposed evolutionary change but lacked a mechanism to explain these changes. The contributions of Darwin and Wallace solidified the framework for understanding evolution through mechanisms of natural selection.

Natural Selection and Evolution

The evolutionary mechanisms leading to changes include:

  1. Adaptive Evolution: Through natural selection.

  2. Nonadaptive Evolution: Including genetic drift, gene flow, mutation, and non-random mating.

The Concept of Natural Selection

  • Natural selection acts on populations, not individuals.

  • Three conditions must be met for natural selection to occur:

    1. Trait Variation: Individuals in the population exhibit trait variability.

    2. Heritability: Variation in traits is at least partly heritable, allowing for traits to be passed from parents to offspring.

    3. Reproductive Success: In specific environments, particular heritable traits enhance reproductive success more than other traits.

Consequences of Natural Selection

  • Traits favoring increased reproductive success become more common over time within populations.

  • Natural selection results in adaptation, with leads to speciation when populations diverge sufficiently.

Example of Natural Selection

  • Case of Galapagos Finches: Variations in beak size influenced by seed availability—demonstrating adaptive evolution driven by changes in environmental conditions.

Concepts in Experimental Biology

  1. Good Experimental Design Characteristics:

    • Inclusion of control groups.

    • Controlled experimental conditions.

    • Similar treatment for experimental and control groups.

    • Replication of experiments to ensure reliability of results.

  2. Angler Fish Adaptations:

    • Camouflage aiding predation.

    • Specialized lure attractions and variations affecting mating success.

  3. Mutation Events:

    • Mutations occur randomly and are not always adaptive, leading to a diverse range of effects on populations.

Conclusion

The first weeks of lectures outline the characteristics of living organisms, the foundational theories of biology, the early hypotheses about cell origins, and the principles of evolutionary change through natural selection. Each concept interlinks to provide a systemic understanding of life processes, cellular structures, and the overarching framework guiding the biological sciences today.