What Defines Living Organisms? Core Characteristics Explained
Simply put, the living world can be described as the world around us. It comprises all living creatures, plants and microorganisms that we cannot see. It has changed over the course of billions of years but the general composition has remained the same. The main components are still organic and inorganic matter. The organic matter includes amino acids, proteins, lipids etc. whereas inorganic matter includes water and minerals. The following is a brief summary of the world of the living that surrounds us. Living things show a lot of characteristics including growth and the ability to reproduce. Mammals are one of them. Living things live in a space nearer to the surface of the earth. This is because their activities are mostly operated by sunlight, water, carbon dioxide and oxygen. Their temperature range is fixed.
Essentials of the Living World
Basically, the essentials of living are its components. Below is a summary of all the components that are needed to sustain the world of the living.
Water: The water content of the human body is around 70-90%. It plays an integral role in sustaining different biological processes.
Oxygen: The earth’s atmosphere is made of 20% oxygen. It is required during aerobic respiration to produce energy that is important for different metabolic activities.
Sodium Chloride: Sodium chloride in its ionic form plays an important part in the metabolic process of the human body.
Proteins: Proteins are long chains of amino acids connected by peptide bonds. It plays a significant role in forming the structure of the organism. It can be broken down with the release of energy.
Lipids: These are alcohol and fatty acid polymers and they perform several functions.
Taxonomic Categories
To facilitate the study of kinds and diversity of organisms, biologists have developed certain rules and principles for the identification, nomenclature and classification of organisms.The science of naming and classifying organisms into groups is what we understand to be Taxonomy. It is useful in agriculture, forestry, industry and in general for knowing our bio-resources and their diversity. There are many categories/ranks and are generally referred to as taxonomic categories.
Characteristics of Living Organisms / Characteristics of Living Things
Growth - All living organisms grow in number and mass. A multicellular organism replicates by cell division. In plants, growth in the meristematic area continues throughout life and in animals, it occurs till a certain age. Living organisms show internal growth due to addition of important materials and reproduction of cells in the body. Non living organisms like mountains, boulders, crystals also show growth but this is because of the addition of similar materials to their outer surface. Growth is influenced by other factors too: the environment, the food that is being consumed and temperature play an important role too.
Reproduction - It is the formation of new individuals of the similar species. Reproduction is required for population and the survival of a race. In sexual reproduction two parents are involved to produce more or less similar organim, but in asexual reproduction, a single parent is involved and individual is the clone of the parent. Asexual reproduction may carry out by fermentation, fission, regeneration, vegetative propagation etc. In unicellular microorganism, growth and reproduction are the same. Numerous organisms such as mules, sterile worker bees, infertile human couples do not reproduce. Hence, reproduction is not an all-inclusive characteristic of all living organisms. However, no non-living object has the ability to replicate or reproduce.
Metabolism - The sum of all types of chemical reactions taking place in an individual because of specific interactions between different types of molecules in the interior of cells is called metabolism. All activities of an organism including growth, development, movements, reproduction etc. are due to metabolism. Metabolism can be classified into anabolism and catabolism. Anabolism comprises all the building up reactions that increase the mass of an organism like photosynthesis. Catabolism includes breakdown reactions, such as respiration, digestion etc.
Consciousness - It is the awareness of the surroundings and responding to external stimuli. External stimuli may be physical, chemical or biological. Plants also respond to stimuli like light, water, gravitation, pollution etc. All living organisms prokaryotic to eukaryotic respond to different kinds of stimuli. Human being is the only organism who is aware of himself. Consciousness plays an important role in determining behavioral patterns too. Consciousness therefore, becomes a defining property of all living things.
Homeostasis - In the world of living organisms, all living things have to maintain and control their internal states via homeostasis. This would involve balancing, temperature, internal pH levels and water levels. For example, the human body would adjust to the changes in the external weather by wearing a sweater or removing the clothing layers in the body so as to adjust their body temperature.
Life Span - every living organism has a definite life span of birth, growth, maturity, senescence and death. It differs from organism to organism and is related to a lot of external factors too.
Living organisms are therefore self-replicating, evolving and self-regulatory interactive systems capable of responding to external stimuli. Diversity in the living world or biodiversity is the occurrence of a wide range of life forms differing in physical features, size, colour, anatomy, habits and habitats. Each different type of microorganism, plant or animal represents a species. Patterns can be seen in a particular species.
Three-quarters of the land-based environment and roughly 66% of the ocean environment have been significantly altered. More than one third of the world's land surface and nearly more than half of freshwater resources are used for crop or livestock production, Climate change worsens the impact on nature, and our wellbeing. Humans have overfished the oceans, cleared forests, and polluted our water sources. They have created a climate crisis.
FAQs on The Living World: Essentials for Biology Students
1. What are the main characteristics that define a living organism?
Living organisms show several key features that set them apart from non-living things. These include growth (increase in mass and number of cells), reproduction (producing offspring), metabolism (all chemical reactions in the body), cellular organisation, and consciousness (the ability to sense and respond to the environment).
2. What is binomial nomenclature and what are its main rules?
Binomial nomenclature is a formal system for naming organisms with a two-part scientific name, introduced by Carolus Linnaeus. This ensures each organism has a single, unique name recognised worldwide. The key rules are:
- Names are typically in Latin and written in italics.
- The first word identifies the genus and starts with a capital letter.
- The second word identifies the specific epithet (species) and starts with a small letter.
- When handwritten, both parts of the name are underlined separately.
3. What is the taxonomic hierarchy and how does it help classify organisms?
The taxonomic hierarchy is a system where organisms are grouped into successive levels of categories based on their similarities and differences. This method, also called Linnaean hierarchy, makes studying millions of organisms easier. The main ranks, from broadest to most specific, are: Kingdom, Phylum (for animals) or Division (for plants), Class, Order, Family, Genus, and Species.
4. Why is metabolism considered a defining feature of life, but growth is not?
Metabolism, which is the total of all chemical reactions occurring in a living cell, is a defining feature because it only happens inside living systems. No non-living object exhibits metabolism. In contrast, growth (an increase in size) is not a defining feature because non-living things can also 'grow' by accumulating material on their surface, like a sand dune or a crystal. Growth in living things is always intrinsic, meaning it occurs from the inside.
5. What is the difference between taxonomy and systematics?
While they are closely related, they are not the same. Taxonomy is the science of identifying, naming, and classifying organisms into different categories (taxa). Systematics is a much broader field that includes taxonomy but also studies the evolutionary relationships between different organisms to understand their history and lineage.
6. What are the different taxonomic aids used to study organisms?
Taxonomists use several tools and resources to help identify and classify organisms. The main taxonomic aids are:
- Herbarium: A storage place for dried, pressed, and preserved plant specimens.
- Botanical Gardens: Large gardens with collections of living plants for identification and reference.
- Museums: Institutions that have collections of preserved plant and animal specimens for study.
- Zoological Parks (Zoos): Places where wild animals are kept in protected environments, similar to their natural habitats, to study their behaviour.
- Key: An analytical tool that helps identify organisms based on a list of contrasting characteristics.
7. If scientific names are universal, why do we still use common names for plants and animals?
We use common names like 'dog' or 'mango tree' in everyday language because they are simple and easy to remember. However, these names can be confusing as they often change with the region and language. For example, a single bird species might have dozens of different common names. Scientific names are essential for scientists to communicate accurately and universally without any confusion about which organism they are referring to.
8. What is meant by 'biodiversity' in the context of the living world?
Biodiversity, or biological diversity, refers to the vast variety and variability of life on Earth. It encompasses all the different plants, animals, fungi, and microorganisms. It also includes the genetic differences within each species and the variety of ecosystems they are part of, like forests, deserts, and oceans. In simple terms, it is the total richness of life in the living world.
