Biology Study Notes: Characteristics of Living Organisms and Varieties

Characteristics of Living Organisms

  • All living organisms exhibit several fundamental functions that can be described using the acronym MRS C GREN:

    • Movement: Ability to change position.

    • Reproduction: Ability to produce offspring, which can occur either sexually (fusion of gametes) or asexually (single organism replication).

    • Sensitivity: Ability to detect stimuli (e.g., light) and respond appropriately.

    • Control (Homeostasis): Ability to regulate internal conditions to maintain a stable internal environment despite external changes.

    • Growth: Capacity to increase in mass and size over time.

    • Respiration: Process of producing energy, which can be either aerobic (using oxygen) or anaerobic (without oxygen).

    • Excretion: Ability to remove toxic substances or waste products resulting from metabolic processes.

    • Nutrition: Ability to absorb nutrients to support growth and repair bodily tissues.

Variety of Living Organisms

Eukaryotes

  • Definition: Organisms that possess a nucleus and organelles, all enclosed within a plasma membrane.

  • Key subcellular structures and their functions:

    • Nucleus:

    • Contains genetic material (DNA) that codes for proteins.

    • Enclosed by a nuclear membrane.

    • Cytoplasm:

    • The fluid substance where chemical reactions take place.

    • Contains enzymes, which are biological catalysts that speed up reactions.

    • Organelles are suspended in the cytoplasm.

    • Cell Membrane:

    • Contains receptor molecules that identify and selectively regulate substances entering or leaving the cell.

    • Mitochondria:

    • Sites of aerobic respiration, providing energy to the cell.

    • Ribosomes:

    • Locations of protein synthesis; can be found on rough endoplasmic reticulum (RER).

Plant Cells

  • Examples: Cereals (e.g., maize) and herbaceous legumes (e.g., peas).

  • Characteristics:

    • Multicellular organisms.

    • Contain chloroplasts (site of photosynthesis with chlorophyll for light absorption).

    • Have cellulose cell walls that provide structural strength.

    • Contain a large permanent vacuole for storing cell sap and maintaining turgidity (rigidity due to stored fluids).

    • Store carbohydrates primarily as starch or sucrose.

Animal Cells

  • Examples: Mammals (e.g., humans) and insects (e.g., flies).

  • Characteristics:

    • Multicellular.

    • Unable to photosynthesize.

    • Lack cell walls.

    • Possess nervous systems that coordinate movement.

    • Store carbohydrates as glycogen.

Fungi

  • Structure:

    • Generally organized into a mycelium made of hyphae (filamentous structures), which may have multiple nuclei. Some fungi are unicellular (e.g., yeast).

  • Examples: Mucor (typical hyphal structure) and yeast (single-celled).

  • Characteristics:

    • Have cell walls composed of chitin.

    • Obtain nutrients through saprotrophic nutrition, which involves secreting digestive enzymes to break down complex food into absorbable units.

    • Store carbohydrates mostly as glycogen.

Protoctists

  • Characteristics:

    • Comprise single-celled organisms.

    • Some exhibit animal-like features (e.g., Amoeba, which inhabits pond water).

    • Others resemble plants and contain chloroplasts (e.g., Chlorella).

Prokaryotes

  • Definition: Organisms that lack a nucleus and membrane-bound organelles.

Bacteria

  • Examples:

    • Lactobacillus bulgaris: A rod-shaped bacterium used in yogurt production.

    • Pneumococcus: A spherical bacterium responsible for pneumonia.

  • Characteristics:

    • Typically single-celled and very small organisms.

    • Contain cell wall, cell membrane, cytoplasm, and plasmids.

    • Lack a true nucleus, possessing instead circular chromosomes of DNA.

    • Some are capable of photosynthesis, but most derive nutrition from other organisms (either dead or alive).

Pathogens

  • Definition: Disease-causing organisms, which can include fungi, bacteria, protoctists, or viruses.

Viruses

  • Examples:

    • Tobacco Mosaic Virus: Interferes with chloroplast formation.

    • Influenza Virus: Causes the flu.

    • HIV Virus: Leads to AIDS.

  • Characteristics:

    • Viruses are much smaller than bacteria and are not classified as living organisms due to their reliance on host cells to reproduce.

    • Parasitic Nature:

    • Can only replicate within living cells.

    • Capable of infecting any type of living organism.

    • Utilize cellular mechanisms of the host to produce multiple copies, often leading to cell bursting.

    • Composed of a nucleic acid (either DNA or RNA) encased in a protein coat.

Bacterial Pathogens

  • Examples:

    • Salmonella: Known for causing food poisoning.

  • Characteristics:

    • Reproduce through a method called binary fission.

    • Secrete toxins that can damage host cells.

Protists

  • Example:

    • Malaria: A disease caused by parasitic protoctists.

  • Characteristics:

    • Use animals as hosts for survival.

Fungal Pathogens

  • Example:

    • Athlete’s Foot: A common fungal infection.

  • Characteristics:

    • Disseminate spores that can be carried by wind or transferred between individuals.

    • Some fungi can be eliminated using antifungal agents (fungicides).