SSS 1 Biology - Living things | Organization of life

BEHAVIOURAL OBJECTIVES:

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

i. State four(4) levels of organization of life.
ii. Explain complexity of organization in higher organisms.
iii. State five(5) advantages of complexity in higher organisms.
iv. State five(5) disadvantages of complexity in higher organisms.

INTRODUCTION: Life existed in an organized form so as to carry out efficiently the characteristics of living things. 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 and so on.

Levels of organization of life

There are four(4) levels of organization of life in organism. These are:

1. Cells (First level of organization): A Cell is the structural and functional unit of life. All plants and animals are made up of cells. Organisms with only one cell are called Unicellular organisms e.g. Amoeba, Euglena, Paramecium, Chlamydomonas, Plasmodium, Trypanosome, etc. organisms with many cells are called Multicellular organisms e.g. Spirogyra, Earthworm, Fish, Toad, Bird, etc. and they are capable of carrying out life processes such as movement, respiration, nutrition, reproduction, etc. Examples of cells in higher plants are Phloem cells, Xylem vessels, etc. Examples of cells in higher animals include Egg cell, Sperm cell, Nerve cell, Red and White blood cell, Epidermal cell, etc.
2. Tissue (Second level of organization): A Tissue is the collection of cells which have similar structure and functions. Examples of tissues in higher plants are Mesophyll layer in leaves, Epidermal tissues, Sclerenchyma, Parenchyma, Collenchyma, Phloem and Xylem tissues. Examples of tissues in higher animals include Muscles, Bone, Cartilages, Connective tissues, etc. Examples of organisms which exist at tissue level are Hydra, Algae, Sponges and Fungi.
3. Organs (Third level of organization): An Organ is a collection of different tissues that performs a specific function. Examples of organs in plants are Leaf, Flower, Root, Stem, Seed, etc. Examples of organs in animals are Skin, Nose, Ear, Kidney, Heart, Liver, etc.
4. System (Fourth level of organization): A System is a collection of different organs which work together to perform specific functions. Examples of systems in plants are the Shoot and Root system. Examples of systems in animals are Digestive, Excretory, Transport, Skeletal system, etc.

Complexity of organization in higher organisms

There is an increase in complexity from unicellular to multicellular organisms. Even though unicellular organisms can perform all life processes, they still lack vital tissues, organs or systems that are efficient and capable of ensuring their survival. As a result of this, higher organisms have advantage in complexity over unicellular organisms.

Advantages of complexity in higher organisms

i. It leads to cellular differentiation: As a result of complexity, group of similar cells are differentiated to form tissues that carryout similar functions.
ii. It leads to internal structural specialization: A group of similar cells or tissues become specialized to carryout one or more functions.
iii. Mutual interdependence between component cells: There is division of labour among the component cells.
iv. Complexity leads to efficiency: Complexity makes the higher organism to be efficient in carrying out life processes.
v. Complexity leads to increase in size: This is because there are spaces between cells for growth.
vi. It increases adaptation to environment.

Disadvantages of complexity in higher organisms

i. Inability of the individual cells to exist on their own.
ii. Difficulty in acquisition of oxygen and food materials.
iii. It leads to slower rate of diffusion.
iv. Difficulties in reproduction.
v. Slower expulsion of waste products.
vi. Decrease in ability to regenerate.