Recognizing Living Things – SS1 Biology Lesson Note (First Term)

Living things are organisms that show characteristics such as movement, respiration, nutrition, irritability, growth, excretion, reproduction, life span, competition and adaptation. These characteristics separate them from non-living things. Plants and animals are the two main groups of living things, and they differ in features such as movement, nutrition, growth and response to stimuli.

Behavioural objectives

By the end of the lesson, students should be able to:

• state the characteristics of living things;
• define respiration, nutrition, irritability, growth, excretion and reproduction;
• name the five main stages in the life span of an organism;
• explain the differences between plants and animals.

What are the characteristics of living things?

Everything in nature can be classified into two groups: living and non-living things.

Living things can be distinguished from their non-living counterparts through the following characteristics, which are observable in all living things:

1. Movement: Animals can move from place to place on their own in search of food. Higher plants move certain parts of their body in response to growth or external stimuli.
2. Respiration: To perform the numerous life processes, living things need a lot of energy. The energy can only be obtained when the organism respires. Respiration is the oxidation of food substances in the presence of oxygen to produce energy, with carbon(IV) oxide and water released as by-products.
3. Nutrition: The act of feeding is called nutrition. All organisms need food to carry out their biological activities. Green plants can manufacture their food, so they are autotrophs. Animals depend on plants for their food, so they are heterotrophs.
4. Irritability: This is the ability of living things to respond to external and internal stimuli to survive. External stimuli may be light, heat, water, sound or chemical substances.
5. Growth: This is the tendency of organisms to increase irreversibly and rapidly in length, size and mass. The essence of growth is to enable organisms to repair or replace damaged or old tissues in their bodies. The food eaten by an organism provides the basis for growth.
6. Excretion: Toxic waste products of metabolism and other unwanted materials have to be eliminated to ensure the proper functioning of the bodies of organisms. Such wastes include water and carbon(IV) oxide.
7. Reproduction: This is the ability of a living organism to give birth to young ones (offspring). The essence is to ensure the continuity of life. Reproduction can be sexual (involving two organisms) or asexual (involving one organism).
8. Life span and death: Every organism has a definite and limited period of existence. Life, for all organisms, has five main stages: origin (birth), growth, maturity, decline and death.
9. Competition: Living things struggle for the basic things of life in order to survive. They compete for food, water, light, mates and space.
10. Adaptation: To survive, every organism has the ability to get used to changes in its environment.

What are the differences between plants and animals?

All living organisms can be generally classified as plants or animals. However, plants can be distinguished from animals in the following ways:

Evaluation

1. List the ten characteristics of living things.
2. What is the difference between an autotroph and a heterotroph?
3. Name the five main stages in the life span of an organism.
4. State three differences between plants and animals.

Assignment

1. Explain the differences between growth in plants and animals.
2. Define the following characteristics of living things:
   • (a) respiration
   • (b) irritability
   • (c) excretion
3. What are the similarities between living and non-living things?
4. What are the similarities between plants and animals?