1. Subatomic and Atomic Level:
2. Molecular level:
3. Organelle and Cell level:
4. Tissue level:
5. Organ and Organ system level:
6. Individual level:
7. Population Level:
8. Community level:

Biologists study biological organization at different levels. The list goes from simpler to complex levels.

1. Subatomic and Atomic Level: All types of matter are made up of elements and there are about 92 kinds of elements, found in nature. Each element is made up of a single kind of atom (a": not, tom: cut).

These atoms are the structures formed by many subatomic particles. The most stable subatomic particles are electrons, protons, and neutrons. Each of these is found in a definite number, in a specific atom.

Bio elements:

Out of the 92 kinds of elements that occur in nature, 16 are called bioelements. These take part in making the body mass of a living organism.

Out of these elements; only six (O. C, H, N, Ca, & P) make up 99% of the total mass. The other ten (K, S, CI, Na, Mg, Fe, Cu, Mn, Zn, & I) collectively make 0.1% of the total mass.

2. Molecular level:

In organisms, bioelements usually do not occur in isolated forms. Rather, atoms of different bioelements combine through ionic or covalent bonding. The stable particle formed by the bonding between different elements is called a molecule. Bioelements share their atoms in making biomolecules or molecules of life.

3. Organelle and Cell level:

An enormous number of biomolecules become associated in a particular way and form organelles. The organelles are sub-cellular structures and when they assemble, cells are formed. Each type of organelle is specialized to perform a specific function. For example; mitochondria are specialized for cellular respiration and ribosomes are specialized for protein synthesis. In this way, the functions of the cell are accomplished by structures. It is an example of the division of labor within the cell.

4. Tissue level:

In multicellular organisms, similar cells (performing similar functions) are organized into groups, called tissues. We can define tissue as a group of similar cells specialized for the performance of a common function. Each cell in a tissue carries on its life processes (like cellular respiration, and protein synthesis), but it also carries on some special processes related to the function of the tissue There are four major types of animal tissues i.e. epithelial, connective, nervous and muscular tissues. Epithelial tissue acts as the covering and glandular tissue. Connective tissue acts as the connecting and supporting tissue. Nervous tissue conducts messages and muscular tissue acts as the contracting tissue.

There are four major types of animal tissues i.e. epithelial, connective, nervous, and muscular tissues. Epithelial tissue acts as the covering and glandular tissue. Connective tissue acts as the connecting and supporting tissue. Nervous tissue conducts messages and muscular tissue acts as the contracting tissue.

5. Organ and Organ system level:

In higher multicellular organisms, particularly in animals, more than one type of tissue having related functions are organized together and make a unit, called an organ. Different tissues of an organ perform their specific functions and these functions collectively become the function/s of that organ.

For example, the stomach is an organ specialized for the digestion of proteins and for storing food. Two major types of tissue are organized in their structure. Epithelial (glandular) tissue secretes the gastric juice and muscular tissue performs contractions of stomach walls for grinding of food, mixing enzymes with food, and moving food to the posterior end. So, two tissues perform their specific functions, which collectively become the function of the stomach.

Note:

The organ system level is less definite in plants as compared to animals. The complexity of organ and organ system levels in animals is associated with a far greater range of functions and activities than in plants.

6. Individual level:

Different organs (in plants) and organ systems (in animals) are organized together to form an individual/organism. In organisms, various organs and organ systems are organized in such a way that all the functions, processes, and activities are coordinated. For example, when a man is engaged in continuous and hard exercise, not only his muscles are working but also there is an increase in the rate of heartbeat. This accelerated rate of respiration and heartbeat supplies more oxygen and food to the muscles which they need for continuous work.

Note:

In animals, regulation of activities (coordination) is achieved by the nervous system and hormones while in plants, coordination is brought about only by hormones.

7. Population Level:

Biologists extend their studies to the population level where they study interactions among members of the same species living in the same habitat. A population is defined as a group of organisms of the same species located in the same place, at the same time. For example, the number of rats in a field of rice in 2002, the number of students in biology class in the semester of 2008, etc. Similarly, the human population comprises the number of human beings in a particular city or country at a particular time.

Note:

At the population level, biologists study life in several new parameters, which cannot be considered at the individual (organism) level. For example gene frequency gene flow, age distribution, population density, and population pressure.

8. Community level:

A community is an assemblage of different populations, interacting with one another within the same environment. A forest may be considered a community It includes different plant species e.g. oak trees, ash trees grasses, bushes, etc; different species of microorganisms and fungi, and different animal species. Communities are collections of organisms, in which one population may increase and others may decrease. Usually, populations change due to fluctuations in abiotic factors and changes in the size of other populations.

Complex Communities:

Some communities are complex e.g. a forest community, a pond community, etc. Other communities may be simple e.g. a fallen log with various populations under it.

Simple Community:

In a simple community number and size of populations is limited so any change in biotic or abiotic factors may have drastic and long-lasting effects.