Key Concepts in Biology

Chapter 1 - Study of Life

Themes in Biology

  1. The process of science

  2. Life’s Hierarchy

  3. Evolution, the core theme in biology

Requirements for Life

  • Organization

  • Cellular composition

  • Metabolism

  • Responsiveness

  • Movement

  • Homeostasis

  • Development

  • Reproduction

  • Evolution

Necessary Life Functions

1. Organization

Living things exhibit a higher level of organization compared to nonliving things.

2. Cellular composition

Living matter is always compartmentalized into one or more cells.

3. Metabolism

Refers to the internal chemical reactions necessary for sustaining life.

4. Responsiveness

The ability to sense and react to stimuli, also referred to as irritability or excitability.

5. Movement

Involves both the movement of the organism as a whole and the movement of substances within the organism.

Necessary Life Functions (cont.)

6. Homeostasis

The ability to maintain relatively stable internal conditions despite changes in external environments.

7. Development

Refers to differentiation and growth of an organism over time.

8. Reproduction

The process of producing copies of themselves and passing genes to offspring.

9. Evolution

The gradual changes in genes and traits passed through generations, affecting the characteristics of organisms.

Levels of Organization of Living Things

  1. Atom: Smallest & most fundamental unit of matter.

  2. Molecule: Consists of at least two atoms held together by one or more chemical bonds.

  3. Macromolecule: Large molecules composed of repeating units.

  4. Organelles: Aggregates of macromolecules surrounded by a membrane.

  5. Cell: The fundamental unit where actual life begins; the smallest unit of life.

  6. Tissues: Groups of similar cells performing related functions.

  7. Organ: A structure composed of two or more tissues performing a common function.

  8. Organ system: A group of organs working collectively.

  9. Organism: An individual living entity.

Structural Organization in Biological Systems

  • Chemical Level: Atoms combine to form molecules.

  • Cellular Level: Cells are constructed from molecules (e.g., smooth muscle cell).

  • Tissue Level: Tissues consist of similar types of cells (e.g., smooth muscle tissue).

  • Organ Level: Organs are made up of different types of tissues (e.g., blood vessel).

  • Organ System Level: Consists of different organs working together (e.g., cardiovascular system).

  • Organismal Level: The complete human organism is made up of several organ systems.

Cell Theory

The Cell Theory consists of three parts:

  1. All living things are made up of one or more cells.

  2. The cell is the basic unit of life.

  3. New cells arise from existing cells.

Types of Cells

(a) Eukaryotic cells: Characterized by having a membrane-bound nucleus.

  • Size: approximately 1 µm.
    (b) Prokaryotic cells: Do not possess a membrane-bound nucleus and are generally smaller.

  • Size: approximately 0.1 µm.

Energy Processing

Metabolism includes all the chemical reactions occurring within an organism and requires energy.

  • Plants: Obtain energy from sunlight and convert it into chemical energy.

  • Animals: Utilize chemical energy found in food consumed.

Regulation and Homeostasis

Regulation includes various mechanisms that coordinate internal functions, respond to stimuli, and manage environmental stress. Examples include:

  • Nutrient transport

  • Blood flow
    Homeostasis is a specific type of regulation where the organism maintains internal conditions within a narrow range despite environmental changes.

  • Example: Humans sweat to cool down in heat and shiver to generate heat when cold.

Survival Needs

Humans require certain factors for survival, which must be in appropriate quantities:

  1. Nutrients

    • Chemicals essential for energy and cell maintenance.

    • Types of nutrients:

      • Carbohydrates: Major energy source.

      • Proteins: Necessary for cell building and processes.

      • Fats: Long-term energy storage.

      • Minerals and vitamins: Essential for chemical reactions and structural functions.

  2. Oxygen

    • Necessary for energy release from food.

    • The body can famously only survive a few minutes without it.

  3. Water

    • Most abundant chemical in the body, forming a watery environment necessary for chemical reactions and functioning as the fluid base for secretions and excretions.

  4. Normal body temperature

    • Essential, as deviations from the range of approximately 37°C impact reaction rates critically.

  5. Appropriate atmospheric pressure

    • Required for procedural breathing and effective gas exchange within the lungs.

Homeostasis

Homeostasis is defined as the maintenance of relatively stable internal conditions despite ongoing changes in the environment.

  • It represents a dynamic state of equilibrium, with constant adjustments as necessary to maintain balance.

  • Failure to maintain homeostasis can lead to a condition known as Homeostatic Imbalance.

Growth and Development

Once a new organism forms via reproduction, it grows and develops from the zygote (the first body cell) into a multicellular organism through the process of mitosis, which is the cell division mechanism for body cells.

Reproduction

Reproduction occurs at both the cellular and organismal levels:

  • In cells, mitosis is utilized to create two identical daughter cells.

  • At the organismal level, meiosis is responsible for the production of egg cells (female ovum) and male sperm cells.

Fertilization of the egg by a sperm cell marks the initiation of a new organism's development.

Evolutionary Adaptation

An adaptation is a heritable trait (for example, color) that enhances an organism's chances for survival and reproductive success in its environment.
Evolution refers to the shift in frequency of these heritable traits within a population (a group of organisms of the same species living in a specific area) over time.

  • In broad terms, evolution signifies the gradual change in inherited traits resulting in the emergence of new species from older ones.

Diversity of Life

Evolution serves as the foundation explaining the great diversity of life on Earth.

  • Taxonomy: The systematic categorization of life’s diversity.

  • There are three primary domains of life:

    1. Bacteria: Unicellular organisms lacking organelles (prokaryotes).

    2. Archaea: Prokaryotes that thrive in extreme environments.

    3. Eukarya: Organisms containing organelles and true nuclei, including:

      • Protista: A diverse group within Eukarya primarily consisting of unicellular organisms, such as Amoeba.

      • Plantae: The plant kingdom, categorized as producers that utilize sunlight to synthesize chemical energy.

      • Fungi: The mushroom kingdom, characterized as heterotrophs, organisms that consume others for energy.

      • Animalia: The animal kingdom, which also includes heterotrophs.