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:

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 (