Bio 2

.Living Organisms and Homeostasis

  • Living organisms possess the capability to maintain an internal constancy, also known as homeostasis.

    • Homeostasis refers to the processes that keep bodily functions stable despite external environmental changes.

    • A common example of homeostasis is temperature regulation.

  • Body Temperature Regulation:

    • In cold conditions (e.g., winter), if unprotected, the body can respond by shivering, a primary mechanism to generate heat.

    • In warm conditions (e.g., summer), the body produces sweat through sweat glands to cool down.

    • Different animals exhibit varying methods of temperature regulation:

    • Mammals and Birds (Homeotherms):

      • Can maintain a stable internal body temperature due to their internal mechanisms.

    • Ectotherms (Cold-Blooded Animals):

      • Include fish, insects, reptiles, and amphibians and do not have the ability to regulate their internal temperature. They rely on external temperatures to function.

      • Ectotherms may enter a dormant phase (hibernation) in cold weather, where metabolism slows down significantly.

      • For example, turtles bask in sunlight to warm themselves, as their body temperature relies on external heat sources.

    • Unique Case: The Leatherback turtle is noted for displaying slight homeothermic traits, capable of maintaining a warmer internal temperature by shivering.

Characteristics of Living Organisms

  • Living organisms must reproduce, grow, and develop, which are key characteristics:

Reproduction:

  • Types of Reproduction:

    • Asexual Reproduction:

    • Results in offspring that are genetically identical to a single parent.

    • Offspring are essentially clones.

    • Common methods include:

      • Fragmentation: Parts of a parent organism (e.g., strawberry plants) break off and develop into new individuals.

      • Regeneration: An organism regrows lost body parts (e.g., starfish regrowing an arm).

    • Sexual Reproduction:

    • Involves two parents contributing genetic material to produce unique offspring.

    • The offspring exhibit a combination of DNA from both parents and do not look identical to either parent.

    • Key aspects:

      • Involves gametes (male sperm and female egg) fusing to create a zygote which develops into a new organism.

  • Advantages of Asexual vs. Sexual Reproduction:

    • Asexual reproduction allows rapid population growth without needing a mate, but genetic variability is limited.

    • Sexual reproduction introduces genetic diversity, enhancing adaptability to environmental changes.

  • Echinoderms and Invertebrates: Some organisms, like certain starfish and flatworms, can reproduce both sexually and asexually.

  • Bacteria: Reproduce asexually through binary fission, splitting into two identical cells.

    • They can also exchange genetic material in primitive ways through structures like pili, although they do not form zygotes.

Growth and Development:

  • Organisms undergo stages from zygote to fully formed individuals, displaying growth and development:

    • For example, a fertilized egg develops into an embryo, then into a fetus, and ultimately into a mature organism.

    • Plants follow a similar pattern from seed to fully developed flowering plants.

Response to the Environment

  • All living organisms respond to environmental stimuli, which is crucial for survival. Responses can include:

    • Changes in behavior (e.g., deer freezing when spotting a predator).

    • Physiological adjustments (e.g., shivering or sweating in response to temperature changes).

    • Plants may shed leaves in response to colder temperatures.

Genetic Information Transfer

  • Another hallmark of living organisms is the ability to pass genetic information to offspring through DNA.

    • DNA Structure:

    • Higher organisms possess a double helix structure of DNA, while bacteria and archaeans have circular DNA.

  • Bacteria, while primarily asexual, can still exchange genetic material, contributing to antibiotic resistance and evolution.

Evolution

  • Evolution is the gradual change in living organisms over time at the genetic level, often resulting from natural selection.

    • Natural Selection:

    • Mechanism whereby organisms better adapted to their environment tend to survive and produce more offspring.

    • Example: Bacteria in an antibiotic-rich environment can develop traits that confer resistance, leading to a higher survival rate of resistant bacteria and altering the population.

  • Typically, evolution is observable in populations over extensive periods rather than individual organisms.

  • Bacterial Evolution: Due to their rapid reproduction rates, bacteria can evolve more quickly than higher organisms.

Classification of Organisms

  • Taxonomy is the science of grouping and classifying living organisms based on evolutionary relationships and shared features:

    • Types of classifications:

    • Domains: Archaea (prokaryotic, often extremophiles) and Eukarya (includes animals, plants, and fungi, with nucleated cells).

    • Phylogenetic Tree: Represents evolutionary relationships among species, demonstrating common ancestry.

Viruses and Their Classification

  • Viruses present a classification challenge as they exhibit characteristics of living and non-living entities:

    • Cannot reproduce independently; they require host cells to replicate.

    • They possess genetic material (DNA or RNA) and can evolve but do not fit traditional definitions of life due to their dependency on host organisms.

    • Their classification can vary as they do not neatly fit into living or non-living categories.