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Leaving cert Biology Revision: Characteristics of Life

Characteristics of Life 

Biology is the study of life, including the words "bios" (meaning life) and "logos" (meaning knowledge). But what does life mean? 

The process that sustains life is metabolism, which is a function of living things. 


Metabolism is the process by which cells use energy to grow, repair, and create new life. It is not only about obtaining energy. It is what distinguishes living things from non-living entities. 

There are two different reactions in our bodies: 

  1. Anabolic reactions. 

  2. Catabolic reactions.

Like builders, anabolic processes assist in assembling larger molecules from smaller ones. It resembles putting together a masonry home. 

These chemical interactions allow us to develop and heal by combining little components into larger ones.   

However, catabolic processes are similar to breakers in that they disassemble large molecules into smaller ones. It's comparable to when a large building is divided into smaller parts by a bulldozer. 

These processes liberate energy that the body can employ for physical activity like playing and running. Thus, anabolic processes add structure, while catabolic processes demolish it. For our bodies to function properly, both are essential. 

Photosynthesis Chemical Reaction–Anabolic

Anabolic reactions are a part of photosynthesis, a process in which plants combine light and carbon dioxide to create glucose, a sugar. 

Respiration Chemical Reaction–Catabolic

Humans and other organisms break down glucose (sugar) during cellular respiration, a catabolic process that releases energy for cellular functions. 

Continuity of Life 

Because living organisms produce offspring that resemble them, life continues. These infants develop into adults, have more children, and so on. This makes it easier for various species of life to coexist on Earth. 

Characteristics of Life

The characteristics necessary to allow for metabolism and continuity of life are as follows; 

  • Presence of complex molecules like proteins and enzymes. 

  • Access to a constant supply of energy, often from nutrients like glucose. 

  • Ability to reproduce and pass on genetic information to offspring. 

  • Capacity to respond to changes in the environment for adaptation and survival. 


Food is the fuel that keeps living things going. It is the source of their vitality and growth. While some species, like plants, use sunlight to produce their food, other organisms consume the food produced by other living things.   

         Types of Nutrition

Food is obtained by living creatures in a variety of ways. Some create their own, like sunlight-using plants. Some consume vegetation or other creatures. Everybody obtains the energy required for survival in a different way. 


The process by which living things consume food to obtain energy is called respiration. 

Similar to how an automobile runs on petrol. Certain forms of respiration, such as breathing, require oxygen, whereas other forms of respiration don't. It's how our bodies obtain the energy necessary for movement and function. 


Living beings get rid of unnecessary items through excretion. Living creatures dispose of waste in the same way as humans do. It contributes to their internal cleanliness and well-being. 

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