Recognizing Living Things

Biology SSS1 First Term

WEEK 1

Recognising Living Things

Performance Objectives

Student should be able to:

1. Give the characteristics of living things with examples
2. Differentiate between plant and animals
3. Understand the levels of organization of life and give examples

Content

The earth in which we are living is made up of several things. Everything we can find around us can be classified as either living or non-living things. A cat, birds, soil, dog, mountains, book, pen, stone, cup, flowers and a lot more things make up the ecosystem. Living things include plants and animals that can breathe, move, and reproduce while non-living things include those things that cannot breathe, move, and reproduce.

Characteristics of Living Things

Living things are distinguished from non-living things by several characteristics which include:

A. Movement

Movement is the ability of an organism to move its own whole body or part of its body from one place to another. Most animals can move from one place to another, while plants can only move parts of their bodies in response to external stimuli. Animals can move as they possess specialized locomotory organs, for example – Earthworms move through longitudinal and circular muscles. Plants respond to the movement of the sun. Living things move to look for food, for reproduction and to run away from danger or respond to the environment.

B. Growth

Growth is defined as an irreversible or permanent increase in size, dry mass or weight of an organism. Growth enables organisms to repair or replace damaged or old tissues in their bodies. Living things mature and grow through different stages of development. The food we eat provides the basis for growth of organisms.

C. Respiration

Respiration is a chemical reaction which occurs inside cells to release energy from the food. It involves the exchange of gases between organisms and their environment. The food that is ingested through the process of digestion is broken down to release energy that is utilized by the body to produce water and carbon dioxide as by-products.

D. Nutrition

Nutrition is defined as the ability of living organisms to feed. They acquire and fulfil their nutritional requirements to survive through the process of nutrition and digestion, which involves engulfing and digesting the food. Feeding enables living organisms to live and carry out life processes like growth, respiration and reproduction.

E. Reproduction

One of the important features of living things is that they are capable to produce offspring of their kind through the process of reproduction in which genetic information is passed from the parents to the offspring. Reproduction ensures the continuity of life i.e. it enables life to be passed on from one generation to the next. Reproduction occurs in two forms:

i. Asexual reproduction: Involves only one organism to produce another offspring.

ii. Sexual reproduction: Involves two organisms coming together for reproduction.

F. Excretion

The digested food is eliminated from the body through the process of excretion. Waste products of metabolism such as water and carbon dioxide which are toxic to the body are gotten rid off.

 G. Adaptation

Adaptation is the way living organisms get used to their various environments in such a manner that they would be comfortable. This is done to survive.

H. Irritability or Sensitivity

Living things exhibit sensitivity in other to enable them to survive in their environment. They respond to stimuli such as heat, pain, water, chemicals substances and sound. Living things are sensitive to touch and have the capability to sense changes in their ambience.

I. Competition

Living things struggle for all the necessities of life to survive in their environments. They compete for food, space, water light, mates, etc, to survive and be in continuous existence.

J. Death

All living things die because they have a definite and limited period of existence. All living things pass through five stages of life namely:

Birth          Growth              Maturity             Decline (old age)                Death

Non-Living Things

Non-living things are not alive. They do not possess life. They do not have cells and do not grow. They do not reproduce and do not have a life span. They do not respire as they do not require food for energy and hence do not excrete. Examples of non-living things include book, pen, bottle, plastic, stone, etc.

Differences between Plant and Animals

Plants and animals are living things, but there are still differences between them. Some of these differences are summarized in the table below.

	Plants	Animals
1	They are mostly green i.e. possess chlorophyll therefore carry out photosynthesis.	They cannot carry out photosynthesis but depend on the plant for their food.
2	Growth is restricted to growing or apical movements. They continue to grow throughout life No definite number of parts.	It takes place in all parts of the body regions intercalary. Limited to certain periods of life. Definite numbers of parts.
3	They are not active and have no organ of movement	They are active and have organs of movement
4	Plants have slow response to external stimuli	Animals respond faster to external stimuli
5	Plant cell has a rigid, non-living cellulose cell wall	Animal cell is a thin, flexible living cell membrane
6	They have no fixed number of parts and branching is continuous	They have a fixed number of parts which are usually compact
7	They have no special excretory organs	They have well-developed excretory systems
8	They possess no special sense organ	They possess specialized sense organs

 

Levels of Organization of Life

All living things are highly organized. The scientific study of the different levels of organization of living things helps us gain an insight into the complexities of their structure and functioning. This organization occurs in levels. The simplest structures are found at the lowest levels and they interact to build up more complex structures at the next level. There are four basic levels of organization of life in organisms. These are cells, tissues, organs and systems with cell been the simplest.

Cells

The cell is considered as the basic unit and building block of life. It is the first level of organization of life. It is bound by a cell membrane, and possesses a nucleus which acts as its brain. Other organelles of the cell are mitochondria, ribosome, vacuole, chloroplasts, peroxisomes etc. All plants and animals are made up of cells. Unicellular organisms are those that are made up of only one cell, while multicellular organisms are made up of many cells.

Examples of unicellular organisms are Amoeba, Chlamydomonas, Paramecium, Trypanosome, Euglena, and Plasmodium.

Examples of cells in higher plants and animals are phloem cells, xylem vessels, rod and cone cells in the eyes, spermatozoa, nerve cells, red and white blood cells, etc.

Tissue

This level is a combination of different types of cells which perform specialized functions. A tissue is a group of similar cells forming a later in an organism which performs a particular function. The group of cells that form a tissue need not be identical, but they should have the same origin. Different types are the nervous, muscle, connective and epithelial tissues. Connective tissues are fibrous, and they are made up of cells that are separated by an extracellular matrix. Muscle tissues are actively contractile and useful for producing force and motion. Nervous tissues form organs like the brain and the spinal cord. Epithelial tissues cover the surface of body organs.

Examples of tissues in higher plants are mesophyll layer in leaves, epidermal tissue, sclerenchyma tissue, xylem tissue, parenchyma tissues in the stem. Examples of organisms which exist at this level of organization of life are Hydra, Algae, sponges and Fungi.

Organs

An organ is a group of similar tissues forming a layer in an organism which performs a specific function. It performs certain functions with the help of different tissues. The major organs of animals include lungs, brain, liver, heart, skin, eyes, stomach etc. Examples of organs in plants are leaves, flowers, roots, stems, seeds, etc.

Organs can be classified based on the functions they perform. For example, in the case of animals, the tongue, ears, eyes, skin, and nose are sensory organs. Flowers and seeds are the reproductive parts of plants.

System

Organs working together to perform certain functions form system. A system is a group of similar organs which work together to perform specific functions. Examples are the circulatory, reproductive, skeletal, respiratory, nervous, excretory and digestive systems in animals, and the vascular system in plants. The organs in a system are interdependent, i.e., they work in harmony to carry out various body functions. For example, the digestive system that carries out the process of digestion consists of salivary glands, stomach, oesophagus, gall bladder, liver, intestines, pancreas, rectum, and anus.