An Organization Of Life And The Photosynthesis.


There are four levels or organization of life in organisms. These are: Cells, Tissues, Organs and System. The simplest of all these levels is the cell.


The cell is defined as the smallest unit of living organisms. It is the first level of organization of life. All plant and animals are made up of cells. Some of these plant and animals are made of only one cell Unicellular while others are made up of many cells and are therefore called Multi-cellular.

Example of unicellular are: Amoeba, Euglena, Paramecium, Plasmodium; Trypanosome, Chlamydomonas e.t.c.

Example of multi-cellularare: in plant are Phloem cells, xylem vessels e.t.c in animals are Eyes, ova or eggs, spermatozoa, nerve cells red blood cells, white blood cells, epidermal cell, nerve cells e.t.c.


Tissue is a group of similar cells forming a layer in an organism which performs a particular function. In other words, a tissue consists of two or more different types of cells aggregating together to perform a specific function. Examples are:

In Plant are: Mesophyll layer in leaves, epidermal tissue, clerenchyma tissue, xylem tissue, parenchyma tissues in stem e.t.c

In Animal are: Muscles, Bone, Cartilages and Blood (liquid tissue)

In Organism are: Hydra, Algae, Sponges and Fungi


Organ is a group of similar tissues forming a layer in an organism which performs a specific function. Examples are:

In Plant are: Leaves, Flowers, Roots, Steams, Seed e.t.c.

In Animals are: Skin, Eyes, Ears, Stomach, Brain, Hearth, Liver, Kidney e.t.c.


System is a group of similar organs which work together to perform specific functions. Examples are: Root and Shoot system in Plant.

In Animal are: Digestive Reproductive, Respiratory, Skeletal, Nervous, Excretory and Circulatory system.


Photosynthesis is defined as the process by which green plants manufactures their food (organic compounds) making use of carbon dioxide and water in the presence of sunlight.

6CO2 > + > 6H2O > Sunlight > C6H12O6 > + > 6O2

Carbon dioxide + Water Chlorophyll Glucose + Oxygen


Light Reaction stage: light reaction occurs during the day or in the presence of sunlight. The light energy or solar energy is captured by the chlorophyll and electrons are excited. The energy trapped is used to split water into hydrogen ion (H+) and hydroxyl ion (OH ). This splitting of water into hydrogen ion and hydroxyl ion is called Photolysis of Water.

4H2O Light H+ + H

Water Chloroplast Hydrogen ion Hydroxyl ion

During the process, oxygen is given out as by-product as shown in the chemical equation above.

At the same, a compound, co-enzyme or NADP is reduced by hydrogen ion to NADP and ATP (Adenosine Triphosphate) is formed.

Dark Reaction stage: dark occurs at night or in the absent of light. Together with energy provided by ATP, reduced compound Nicotinamide Adenine Dinucleotide (NADP) then lead to the assimilation of carbon dioxide through series of steps, each control by a specific enzymes, a three carboncompound (CH2O) or sugar is formed.

The formation is represented by equation below:

4H+ + CO2 Enzyme CH20 + H20

H2O is the carbon structure from which simple sugar, fat and oil, protein and so on, is formed during the dark reaction.


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