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Characteristics of Living Organisms Flashcards

Characteristics of Living Organisms

The Unifying Characteristics of Living Organisms (MRS C GREN)

  • To be considered 'living', an organism must fulfill specific criteria represented by the acronym MRS C GREN:
    • Movement: An action by an organism causing a change of position or place.
    • Respiration: A chemical reaction releasing energy from glucose.
    • Sensitivity: The ability to detect and respond to stimuli.
    • Control: Maintaining a stable internal environment (homeostasis).
    • Growth: A permanent increase in size.
    • Reproduction: Producing more of the same kind of organism.
    • Excretion: The removal of toxic waste products.
    • Nutrition: Obtaining food to provide energy.
  • If something doesn't carry out all these processes, it's considered dead or non-living.
  • Viruses are non-living because they don't independently carry out all life processes.

Nutrition

  • Organisms need food for energy to carry out life processes.
  • Plants use sunlight, carbon dioxide, and water to produce oxygen and glucose via photosynthesis; they are autotrophic.
    • Autotroph: 'auto' = 'self', 'trophic' = 'feeding'
  • Animals consume other organisms for energy; they are heterotrophic.
    • Heterotroph: 'hetero' = 'different', 'trophic' = 'feeding'
  • Digestion breaks down complex molecules into simpler ones.

Respiration

  • Respiration is a chemical reaction in all living organisms.
  • Energy is released from glucose with (aerobic) or without (anaerobic) oxygen.
  • The products are carbon dioxide and water.
  • Energy is transferred in the form of ATP.
  • Aerobic respiration equation:
    glucose + oxygen \rightarrow carbon dioxide + water

Excretion

  • Metabolic reactions produce waste, some toxic, that must be eliminated.
  • Excretion is the removal of toxic materials from organisms.
  • Excretion in animals:
    • Carbon dioxide from respiration.
    • Water from respiration and other reactions.
    • Urea (nitrogenous waste) from protein breakdown.
      *Gas exchange vs. Respiration:
    • Gas exchange involves getting oxygen into cells and carbon dioxide out.
    • Respiration uses oxygen from gas exchange to release energy (ATP).
  • Excretion in plants:
    • Oxygen from photosynthesis.
    • Carbon dioxide from respiration.
    • Water from respiration and other reactions.

Response to Surroundings (Sensitivity)

  • Sensitivity is the ability to detect and respond to stimuli.
  • Responses increase survival chances.
  • Sensitivity in animals:
    • The nervous system uses receptors, neurons, and effectors with electrical impulses.
    • The endocrine system uses chemical messengers (hormones) in the blood.
  • Sensitivity in plants:
    • Responses are controlled by chemicals and are slower.
      *Excretion vs. Egestion:
    • Excretion removes waste from cell reactions.
    • Egestion removes undigested food remains (faeces).
  • Geotropism: Plants response to gravity, roots grow down.
  • Phototropism: Plants response to light, shoots grow towards sunlight.

Movement

  • Movement is an action that changes position.
  • Locomotion is movement from place to place.
  • Plants can't move from place to place but change orientation (e.g., sunflowers tracking the sun).

Control (Homeostasis)

  • Living organisms control their internal environment to maintain required conditions (homeostasis).
  • Homeostasis in humans:
    • Thermoregulation: Control of body temperature (optimum 37°C).
      • Mechanisms: sweating, vasodilation.
    • Glucoregulation: Control of blood glucose levels.
    • Osmoregulation: Control of water levels.
  • Homeostasis in plants:
    • Transpiration maintains temperature; water evaporates from stomata, causing heat loss.

Reproduction

  • Reproduction produces more of the same organism.
  • Fundamental for population survival.
  • Sexual reproduction:
    • Fusion of male and female gametes.
      • Humans: sperm and egg.
      • Plants: pollen and ovule.
    • Offspring DNA is a combination of maternal and paternal DNA.
  • Asexual reproduction:
    • Involves only one parent; offspring are clones.
    • Mitosis is an example.
    • Plants: tubers, budding, runners.
    • Single-celled organisms: bacteria, amoeba.

Growth

  • Growth is a permanent increase in size.
  • In animals, growth occurs between zygote and adult stages.
  • In plants, growth continues throughout life with new shoots, leaves, and branches forming.

Common Features: Eukaryotic Organisms

  • Living organisms are classified into five kingdoms: Animals, Plants, Fungi, Protoctists, and Prokaryotes.
  • Animals, plants, fungi, and protoctists are eukaryotes.
  • Eukaryotic organisms can be multicellular or single-celled.
  • Eukaryotic cells contain a nucleus with a distinct membrane.

Animals

  • Multicellular.
  • Cells contain a nucleus with a distinct membrane.
  • Cells lack cellulose cell walls.
  • Cells lack chloroplasts; unable to perform photosynthesis.
  • Feed on organic substances made by other living things.
  • Store carbohydrates as glycogen.
  • Usually have nervous coordination.
  • Able to move from place to place.
Animal Cell Structures:
  • Nucleus: Contains DNA, controls cell activities.
  • Cytoplasm: Gel-like substance, supports cell structures, site of chemical reactions (including anaerobic respiration).
  • Cell membrane: Holds the cell together, controls substance entry/exit.
  • Ribosomes: Site of protein synthesis.
  • Mitochondria: Site of aerobic respiration, releases energy.

Plants

  • Multicellular.
  • Cells contain a nucleus with a distinct membrane.
  • Cells have cellulose cell walls.
  • Cells contain chloroplasts.
  • Feed by photosynthesis.
  • Store carbohydrates as starch or sucrose.
  • Lack nervous coordination.
Plant Cell Structures:
  • Cell wall: Made of cellulose, supports cell shape.
  • Chloroplasts: Contain chlorophyll, enable photosynthesis.
  • Permanent vacuole: Contains cell sap (sugars and salts), supports cell shape, storage.

Fungi

  • Usually multicellular (some single-celled, e.g., yeast).
  • Multicellular fungi made of hyphae forming a mycelium network.
  • Cells contain a nucleus with a distinct membrane.
  • Cells have chitinous cell walls.
  • Cells lack chloroplasts; cannot perform photosynthesis.
  • Feed by secreting extracellular digestive enzymes (saprotrophic nutrition).
  • Some are parasitic.
  • Lack nervous coordination.
    *Examples: moulds, mushrooms, yeasts.

Protoctists

  • Diverse kingdom, doesn't fit into other eukaryotic kingdoms.
  • Mainly microscopic and single-celled (some form colonies or filaments).
  • Cells contain a nucleus with a distinct membrane.
  • Some are animal-like (e.g., Plasmodium).
  • Some are plant-like (e.g., green algae like Chlorella).
  • Some photosynthesise, some feed on organic substances.
  • Lack nervous coordination.
    *Examples: amoeba, Paramecium, Plasmodium, Chlorella.

Common Features: Prokaryotic Organisms

Prokaryotes

  • Single-celled.
  • Lack a nucleus; nuclear material in the cytoplasm.
  • Bacteria are prokaryotic organisms.

Bacteria

  • Microscopic, single-celled.
  • Have a cell wall, cell membrane, cytoplasm, and plasmids.
  • Lack a nucleus but contain circular DNA.
  • Lack mitochondria and other membrane-bound organelles.
    *Examples: Lactobacillus, Pneumococcus.
  • Some perform photosynthesis despite lacking chloroplasts.
  • Most feed on other living or dead organisms (saprobionts or decomposers).

Cell Component Comparison:

ComponentEukaryotesProkaryotes
Cell membraneYY
CytoplasmYY
Genetic materialY - in a nucleusY - in the cytoplasm
NucleusYN
Cell wallSome typesY

Pathogens

  • A pathogen is a microorganism that causes disease.

Types of Pathogens:

  • Bacteria
  • Fungi
  • Protoctists
  • Viruses

Pathogenic Bacteria

  • Don't always infect host cells; can remain in body cavities.
    • M. tuberculosis: Causes tuberculosis (TB) in humans.
      • Infects lungs, causing chronic cough and bloody mucus.
      • Associated with poor hygiene and sanitation.
    • M. bovis in cows can transmit to humans.

Pathogenic Fungi

  • More common in plants.
    • Cattle ringworm and athlete's foot are fungal diseases on the skin surface.
    • Black Sigatoka: Fungal disease in bananas.
      • Spreads through leaves, reducing photosynthesis.
      • Causes leaf parts to die; producing black streaks.

Pathogenic Protoctists

  • Plasmodium falciparum: Causes severe malaria in humans.
    • Spread by mosquitoes.
    • Causes fever, chills, and fatigue.

Viruses

  • Not usually classified as living organisms; don't carry out all life processes independently.
  • Only life-process they seem to display is reproduction but even to carry out this process they must take over a host cell’s metabolic pathways in order to make multiple copies of themselves.
  • Small particles.
  • Parasitic.
  • Infect every type of living organism.
  • Lack cellular structure but have a protein coat and contain DNA or RNA.
    • Tobacco mosaic virus (TMV): Discolours tobacco leaves, reduces photosynthesis, spread by direct contact and soil contamination, no treatment.
    • HIV: Leads to AIDS, attacks immune system, spread by sexual contact/bodily fluids/mother to child, controlled by antiretroviral drugs.
    • Influenza virus (