Living Things

Living Things - Characteristics and Classification of Living Things

The term living things refers to any organism or a living form that possess the characteristics of life or being alive.
The world is made up of many different non-living and living things. Some of the things are living and non-living. Living things eat, grow, breathe, move, reproduce, and have senses. Example of the living thing is a dog. The dog is an animal; it needs food, water, space, and shelter. It is a living thing. Likewise, a tree is a plant, and trees and flowers need air, nutrients, water, and sunlight. These are also living things. Living things also have senses such as seeing, hearing, smelling, tasting, and feeling.
One more illustration of a living thing is a bird. A bird eats seeds and worms. It breathes in air. It comes from eggs and grows. It moves by flying. It lays eggs and reproduces. It smells and sees because it has senses. A bird is a living thing. 



Characteristics of living things:

A living thing is that it refers to any organism that shows the characteristics of being alive. The following are the points that separate living things with that of Non-living things.

  • • A living thing is an organized structure. It may be single-celled such as a bacterial cell, or multi-cellular such as animals and plants that are made up of several cells. A cell is the fundamental biological unit of an organism or life. Various cellular processes are carried out by the cell in a systemized manner. A cell consists of protoplasm enclosed by a plasma membrane.

  • • A living thing requires energy for survival. Energy is essential as it fuels various metabolic activities of a cell. The way the organisms synthesize energy is by photosynthesis where light energy is converted into chemical energy. Another way to synthesize the energy is by cellular respiration wherein biochemical energy is harvested from an organic substance and then stored in energy-carrying molecule such as ATP for later use.

  • • A living thing is capable of reproducing. There are two ways by which living things can reproduce-sexual reproduction and asexual reproduction. In sexual reproduction, male and female cells of the two parents unite and form a zygote that will develop eventually into a being of its kind. In asexual reproduction, it does not involve the sex cells. The off-spring comes only from one parent. Examples are binary fission, vegetative propagation, budding etc.

  • • A living thing grows. At the cellular level, the growth may refer to an increase in number or increase in size. The increase in the number of cells is through cell division. The stem cells of animals and meristematic cells of the plants divide to give rise to new cells. As of increase in cell size, it is often attributed to the increase in cytoplasmic mass.

  • • The cell undergoes a series of phases in the cell cycle. Most of the time, the new cell produced by mitosis goes through interphase. It is the phase in the cell cycle where the cell grows in size. Unless differentiated the cell could replicate its DNA to prepare for the next cell division. In plants, new cells inflate in volume by taking in and storing water inside a vacuole. Some of the plant cellsgrow a secondary cell wall between the primary cell wall and plasma membrane.

  • • At the tissue level, growth in vascular plants are divided into two types: primary and secondary. Primary growth involves vertical growth as primary xylem from procambium. While the secondary growth is associated with lateral growth by the formation of secondary xylem from the vascular cambium.

  • • A living thing metabolizes. Metabolism refers to the various processes that are accountable for the keeping up of the living state of an organism or a cell. Examples of those involved in cell growth, respiration, reproduction, response to stimuli, bimolecular synthesis, waste elimination etc. Metabolism consist of two types: Catabolism and Anabolism.

  • • In catabolism, the living things carry our degradative chemical reactions that lead to the breaking down of complex molecules into smaller units and obtain energy that is released from the process. In anabolism, energy driven chemical reactions boost the molecules from smaller units.

  • • A living thing responds to stimuli and adjuststo environmental changes. It can detect modifications in the environment, especially by cells that function as receptors. Humans have five fundamental senses: hearing, sight, smell, touch, and taste. The other senses include vestibular sense which detects the body movement, acceleration, and direction and the sense for thermoception, by which an organism recognize body temperature.A living thing moves. Since a living thing detects stimuli from its surroundings, it can respond accordingly. For example, animals move to forage, seek a potential mate, and escape predators. While animals can move at will, plants have a rather limited form of movement referred to as Nastic Movement.

  • • A living thing always dies. A living thing has a life to live and this life ends eventually. Senescence refers to biological aging. It is when a living thing gradually deteriorates over a period of time. The organism gradually loses its ability to function and further it dies.



  • Classification of living things:

    Living things were initially classified as a plant or an animal. While both plants and animals are eukaryotic, they are distinguished based on their defining characteristics. For example, mode of nutrition, cellular features etc.

    Animals are basically living organisms that are motile and heterotrophic whereas plants are those that are non-motile, photosynthetic, and have a cell wall. However, bacteria are neither plants nor animals mainly because they are prokaryotes.

    The bacteria and archaea contain only single-celled organism. Both archaea and bacteria have cell walls, but their cell walls are made up of different materials. They lack a nucleus.

    The classification of living things includes 7 levels namely: kingdom, phylum, classes, order, families, genes, and species.

    Kingdoms:

    The most fundamental classification of living things is kingdoms. There are five kingdoms currently. The living things are placed into certain kingdom based on how they acquire their food, types of cells they make the body, and the number of cells they contain.

    Phylum:

    The phylum is the next level in the classification of living things followed by the kingdom. It is an attempt to find some kind of physical resemblance among organisms within a kingdom. These physical similarities suggest that there is a common ancestry among the organisms in a particular phylum.

    Classes:

    Classes are the way to further subdivide organisms of a phylum. The organisms of a class have even more in common than those in an entire phylum. Humans belong to the mammal class because they drink milk as a baby.

    Order:

    Orders in each class are further broken down into order. A taxonomy key is used to determine to which the organism belong to. A taxonomy key is nothing but a checklist of the characteristics that determine how the organisms are grouped together.

    Families:

    Orders are divided into families. Organisms within a family have more in common than with organisms in any classification level about it. Because offamiliarity, the organisms of a family are said to be related to each other. Humans are in the Hominidae family.

    Genus:

    Genus is a way to characterize the generic name for an organism. The genus classification is very specific so there are lesser organisms within each one. For this reason there are a lot of different genera among both animals and plants. When using taxonomy to name an organism, the genus is used to complete the first part of its two-part name.

    Species:

    Species are as specific as you can get. It is the lowest and most exacting level of classification of living things. The main pattern for an organism to be placed in a particular species is theability to breed with other organisms of that same species. The species of an organism regulate the second part of its two-part name.



    Properties of the five kingdoms:

    The properties of the five kingdoms are as follows:

    Monera:

    The cell type is prokaryotic. The cell wall is present and it is non-cellulosic. The nuclear membrane is absent. It is a unicellular organism and the mode of nutrition is autotrophic and heterotrophic. Bacteria are an example of an organism in themonera kingdom.

    Protista:

    The cell type is eukaryotic. The cell wall is present. The nuclear membrane is also present. It is a unicellular organism and the mode of nutrition is autotrophic.

    Fungi:
    The cell type is eukaryotic. The cell wall is present. The nuclear membrane is also present and it is a multicellular organism and the mode of nutrition is heterotrophic. Example mushroom is a fungus. They cannot make their own food.

    Plantae:

    The cell type is eukaryotic. The cell wall is non-cellulosic. The nuclear membrane is present. The organism is tissue or organ. The mode of nutrition is autotrophic. Examples are plants, trees, and a bush.

    Animalia:

    The cell type is eukaryotic. The cell wall is absent. The nuclear membrane is present. The organism is a tissue or organ or organ system. The mode of nutrition is heterotrophic.