Characteristics of Living Things

Basic Characteristics of Living Things

The basic characteristics of living things are the fundamental processes, features and traits that distinguish animate (living) organisms such as animals, plants, fungi, protists and other microorganisms from non-living matter.

The basic characteristics of living organisms are summarized under the acronym 'MR NIGER DAC', where 'M' stands for movement, 'R' for respiration, 'N' for nutrition, 'I' for irritability, 'G' for growth, 'E' for excretion, 'R' for reproduction, 'D' for death, 'A' for adaptation and 'C' for competition. These characteristics of living things are explained below:

• Movement

This is the ability to change direction or position. A living organism is able to move its whole body or parts of its body. Movement in living organisms also occurs internally. For example, food and oxygen are transported from one point to another within the organism.

Organisms moves via a variety of ways. These will include walking, running, swimming, flying, slithering, and crawling. Movement can occur via various structures; for example, through the contraction and relaxation of muscle cells; through pseudopodia in amoeba; cilia in paramecium (alongside cells of the human respiratory tract and fallopian tube); through flagella in various bacteria, euglena and the sperm cell.

Please read on protists explained with their characteristics here.

Movement in plants are generally slower than animal movement. Plants can move towards light (phototropism), towards water (hydrotropism), towards gravity (geotropism or gravitropism), and touch (thigmotropism).

• Respiration

This is the breakdown of digested food to release energy for work. Respiration can be aerobic or anaerobic.

In aerobic respiration, organisms break down digested food in the presence of oxygen to produce energy (in the form of ATP), alongside CO₂ and H₂0 as waste products. Below is an equation for aerobic cellular respiration:

C6CH12O6 + 6O2 -> ATP + 6CO2 + 6H2O

Anaerobic respiration takes place in the absence of oxygen. The end products of anaerobic respiration are (2 ATP molecules) and lactic acid (in animal muscle cells) or ethanol, carbon dioxide, and energy (in yeast and plant cells). 

Please read more on cellular respiration here.

• Nutrition

This is the ability to take in food in order to provide energy for work, growth, repair of worn out tissues and to stay healthy.

Living organisms which produces their own food are termed autotrophs. Examples include all green plants, certain bacteria and protists. Organisms incapable of producing their own food are called heterotrophs. Examples include all animals, fungi and some protists and bacteria.

Autotrophic organisms are further divided into two groups. These are:

• Photoautotrophs: These are autotrophic organisms that manufacture their food through sunlight via a process termed photosynthesis

• Chemoautotrophs: These are autotrophic organisms that manufacture their food through chemicals, via a process termed chemosynthesis.

Please read more on autotrophic nutrition here.

• Irritability (Sensitivity)

This is the ability of living organisms to detect and respond to both external and internal stimuli within their environment.

Irritability ensures survival by triggering essential actions, such as movement toward food, light, water, or away from danger; thus maintaining stability, and allowing for adaptation and survival.

Examples of irritability is seen when we immediately remove our hands after touching hot objects, zebras running away from lions, the shoot of plants growing towards light, the root of plants growing towards water, and so on.

Irritability connects an organism's nervous or physiological systems to its environment. 

Please read on homeostasis and internal environment here.

• Growth

This is an irreversible increase in size, mass or number of cells of living organisms. Growth in living organisms result from a type of cell division termed mitosis.

Living things grow because they consume food, and carry out metabolic processes. Most plants exhibit continuous growth throughout their lives, and such growth are generally restricted to specific regions called meristems; for examples, the tips of roots and shoots.

Please read on the classification of plants and differences between plants and animals here.

Most animals undergo diffuse growth which occurs throughout the body; and these animals stop growing when they reach maturity. However, certain animals like coral, lobsters, crocodiles, sharks, and tortoises grow throughout their lives.

• Excretion

This is the removal of metabolic waste and toxic substances from an organism's body in order to maintain homeostasis. These excreted metabolic wastes include urine, mineral salts, urea, uric acid, excess water, salts, electrolytes, etc.

Egestion should not be mistaken for excretion. Egestion simply refers to the discharge or removal of undigested materials from the body through the anus.

The organs of excretion in vertebrates include the kidneys (excretes urea), lungs (excretes CO₂ and water vapor) and the skin (excretes sweat). Amoeba and some other unicellular organisms excrete waste product through contractile vacuoles. Insects excrete nitrogenous wastes through malpighian tubules while earthworm eliminates waste products via the nephridia. Platyhelminthes like tapewoworm uses flame cells, while plants excrete gases via stomata within their leaves. They can also store waste in leaves which eventually falls off, or as resin and gums.

Please read on the classification of living things here.

• Reproduction

This is the process through which all living organisms give birth to young ones of the same kind. There are two types of reproduction; these are: sexual and asexual reproduction.

Asexual reproduction involves only one parent which produces genetically identical offspring (called clones), without the fusion of sperm and ova. Examples are binary fission in amoeba and bacteria, budding in hydra and yeast, spore formation in fungi and pteridophytes, fragmentation (or regeneration) in planaria, and vegetative propagation from vegetative parts (roots, stems, leaves) of the parent plant.

Please read more on asexual (vegetative) propagation in plants here.

Sexual reproduction involves the fusion of nuclei or male and female gametes (sperm and egg) through a process termed fertilization to form a zygote, thus, bringing about genetic variation.

Fertilization can be internal, (as present in mammals) or external, (as seen in fishes and amphibians).

In flowering plants, sexual reproduction occurs through a process termed pollination.

Please read on the male accessory sex organs here.

• Death

Death is defined as an irreversible cessation of all biological functions that sustain a living organism, marking the end of the organism's life. In simple terms, it is said to occur when living organisms cannot carry out other basic characteristics of life.

The death of cells can occur in different ways. These are:

Apoptosis: This is a programmed cell death. It is a natural, controlled process used for removing unhealthy cells so that they become easily replaced by new cells.

Necrosis: This is an unprogrammed cell death which may result from trauma, injury, or lack of blood supply, causing damage to nearby tissue.

Autophagy: This is a process whereby cells digest themselves in order to recycle their components under stress.

Please read on cell here.

Note: Death is a natural, essential process allowing for ecological nutrient recycling and population control. 

• Adaption

This is the process of evolution whereby species of different organisms become better suited to their environment through a process of natural selection, and also as a result of the organism's structural, physiological, and behavioral changes, ultimately enhancing survival and reproduction. Simply put, adaptation refers to how living things adjust to unfavorable conditions imposed on them in their environment.

Examples of structural adaptation include the long neck of giraffes (for eating from tall trees, and scanning for predators ), sharp teeth and claws in wild cats (for killing preys), feathers in birds (for flight), streamline bodies in fishes (for swimming), webbed feet in ducks (for swimming), and so on.

Example of physiological adaptation include the production of venoms in snakes, (for killing prey), production of sweat by the skin under sunny environment (for regulating body temperature), conservation of water by desert plants and animals, etc.

Please read on the types of habitat here.

Examples of behavioral adaptation include mimicry, nocturnal hunting, seasonal migration and so on.

• Competition

This refers to the interaction among species of living organisms vying for limited resources, such as food, water, light, space, mate or territory. Simply put, competition is the ability of living things to struggle for all the necessities of life in order to survive in their environment. It brings about evolution, natural selection, and population dynamics. 

There are generally two types of competition. These are intraspecific and interspecific competition respectively.

Please read more on the characteristics of living organisms here.

Intraspecific competition occurs between members of the same species. It is often intense because individuals have very similar needs. Example include similar trees in a forest competing for sunlight.

Interspecific competition occurs between different species that share a limited resource. Examples include lions and hyenas competing for the same prey in the savanna.

Please read the continuation of this topic here (Importance of plants and animals to humans)

Please read Len Academy scheme of work for JSS1 first term here.