Characteristics Of Living Organisms

Characteristics of Living Things

In order to identify living organisms, scientists listed 7 characteristics which all living organisms have:

  1. Nutrition:

    Taking in nutrients which are organic substances and mineral ions, containing raw materials and energy for growth and tissue repair, absorbing and assimilating them.

  2. Excretion:

    Removal from organisms of toxic materials, the waste products of metabolism and substances in excess.

  3. Respiration:

    Chemical reactions that break down nutrient molecules in living cells to release energy.

  4. Sensitivity:

    The ability to detect or sense changes in the environment and to make responses.

  5. Reproduction:

    Progresses that make more of the same kind of organism.

  6. Growth:

    The permanent increase in size and dry mass by an increase in number of cells, cell size, or both.

  7. Movement:

    An action by an organism or part of an organism that changes position or place.

The seven characteristics could be memorized by the term “MRS. GREN”:

M- Movement

R- Respiration

S- Sensitivity

G- Growth

R- Reproduction

E- Excretion

N- Nutrition


The Binomial System:

The Binomial System of scientifically naming organisms was developed by Carolus Linnaeus of Sweden. It consists of the organism’s Genus and species name, and thus it is called as Binomial. It consists of 7 levels:

  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

Now, let’s take up a simple example: Humans

  • Kingdom- Animal
  • Phylum- Vertebrates
  • Class- Mammalia
  • Order- Primate
  • Family- Hominidae
  • Genus- Homo
  • Species- Sapiens

Rules for writing scientific names:

  • The first letter of the genus is ALWAYS capitalised
  • The first letter of the species is NEVER capitalised
  • Scientific names of organisms are always italicized or underlined


The classification of living organisms



Image of Classification and Characteristics of living organisms


Protoctista: are organisms with a nucleus, and many flexible organelles amongst their species (for example, some have chloroplasts and cell walls like plants and some like animal cells without these distinguishing characteristics). Their main characteristics include:

  • unicellular or multi-cellular bodies
  • cells with or without cell wall and chloroplasts
  • some species are autotrophic, rest are heterotrophic
  • all species have cells with nucleus

Examples of Protoctista:

  • Paramecium
  • Chlamydomonas
  • Seaweeds

Fungi: are organisms which do not have chlorophyll, thus are heterotrophic and feed on dead organic matter parasitically. The most common known is the edible mushroom; others include fungi  causing diseases like athlete’s foot, ringworm, panama disease etc.Their characteristics include:

  • Multicellular bodies (very few are unicellular)
  • Have nuclei
  • Reproduce by spore production
  • Are heterotrophic
  • Don’t have chloroplasts
  •  Feed by parasitic or saprophytic means on organic dead matter

Examples include:

  • Saccharomyces cerevisiae
  • Penicillium
  • Mushroom


Phylum Arthropoda:

  • Hard exoskeleton
  • Segmented bodies
  • jointed appendages
  • exoskeleton composed of protein and chitin
  • Open circulatory systems in which heart pumps hemolymph through short arteries into open spaces (sinuses)
  • Aquatic members have gills for gas exchange
  • terrestrial members have tracheal system of branched tubes leading from their surface throughout body



  • More than 4 pairs of jointed legs
  • Breathe through gills
  • Antennae present
  • Mostly marine

Examples of crustaceans: Crabs, lobsters etc.



  • With 4 pairs of jointed legs
  • Breathe through gills and book lungs
  • Mostly terrestrial

Examples of arachnids: Scorpion,spider etc.


Honey Bee

  • Have 3 pairs of jointed legs
  • Have 2 pairs of wings
  • Breathe through trachea
  • Antennae present
  • Mostly terrestrial

Examples of insects: Locust, Moth, House Fly, Grasshopper etc.



  • Body consists of many segments
  • Each segment has jointed legs
  • They can be both herbivores and carnivores
  • Terrestrial

Examples of myriapoda: Centipede, Millipede etc.

Phylum Annelida


  • They are worms
  • Have bodies made up of ring like segments
  • Live in water and moist soil

Example of Annelids: Earthworm

Phylum Mollusca

Tonicella Lineata

  • Soft bodied animals
  • Have unsegmented bodies
  • With or without shell

Examples of Molluscs: Octopus, Jellyfish, Squid etc.

Phylum Nematodes


  • They are worms
  • Bodies are not divided into segments
  • Usually white, long and thin bodied
  • feed by parasitic means

Examples of Nematodes: Hookworm, Roundworm etc.

Phylum Vertebrates

  • Internal skeleton with spine
  • Their nervous system has encephalon (brain) and a spinal cord.
  • The encephalon is placed inside the skull and spinal cord is placed inside the spine.

Class Fish


  • Are cold blooded
  • Have streamlined bodies
  • Aquatic
  • Have scales on their bodies
  • May be Herbivores or Carnivores
  • Lay eggs in water
  • Have fins
  • Breathe through gills

Example of Fish: Mackerel, Pomfret, Tuna, Salmon etc.

Class Amphibians


  • Give birth to offspring by laying eggs
  • Have 4 limbs
  • Their habitat is both terrestrial and aquatic
  • Have moist skin
  • Breathe through gills when young; when mature, breathe through lungs
  • Adult often lives on land

Example of Amphibian: Frog, Salamander etc.

Class Reptiles


  • Have scales on body
  • Are cold blooded
  • Terrestrial
  • Lay eggs to give birth to offsprings
  • Egg shells are rubbery

Examples of Reptiles: Lizard, Snake etc.

Class Birds


  • Don’t have teeth, instead have a beak
  • Have hollow bones
  • Are warm blooded
  • Lay hard shelled eggs
  • Forelimbs replaced by wings
  • Breathe through lungs

Examples of Birds: Flamingo, Eagle, Hawk, Sparrow etc.

Class Mammals


  • Warm blooded
  • Can maintain a constant body temperature
  • Have different types of teeth
  • Have skin covered by Hair
  • Give birth to live young offsprings
  • Have sudoriferous (sweat) glands
  • Females have mammary (milk secreting) glands that produce milk to feed young ones.

Example: Human being

The Plant Kingdom

Phylum Angiosperm:

  • Have root, stem and leaves
  • Have xylem and phloem
  • Reproduce by seed production
  • Seeds are produced inside the ovary of the flower
  • Phloem: Transports sugar
  • Xylem: Transports water and minerals
Plant Part  Monocot  Dicot
 Root System  Adventitious root only  Adventitious root, Taproot or both
 Cotyledons  One  Two
 Stem  Vascular bundles scattered Vascular bundles arranged in a ring
 Leaves  Exhibit parallel venation  Exhibit reticulate venation
 Flower  Either trimerous, tetramerous, seldom pentamerous Either pentamerous, tetramerous, seldom trimerous


  • Entirely microscopic
  • Consisting of a single nucleic acid surrounded by a protein coat
  • Capable of replication only within living cells of bacteria, animals or plants.

Example of Viruses: Human Immunodeficiency Virus, Tuberculosis, etc.


Bacteria are prokaryotic and unicellular. they have cell walls and circular DNA called plasmids. They are Heterotrophs or Autotrophs.

Example: L.bulgaricus 

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