Organization of organisms is studied at following levels.
1- Subatomic and Atomic level
The most stable subatomic particles are electrons, protons and neutrons. Protons and neutrons are present in the nucleus of atom while electrons orbit around the nucleus in energy levels (electrons shells).
All type of matter is made up of elements and each element contains a single kind of atoms (‘a’: not, ‘tom’: cut). The atoms are actually made up of many subatomic particles.
Bioelements: Out of the 92 kinds of elements 16 elements make body mass of living organisms. These are called bioelements. e.g. O, C, H, Mg, Fe, Cu etc.
2- Molecular level
The stable particle formed by bonding of atoms is called as molecule. e.g. glucose, water etc.
Types of Biomolecules: i) Micromolecules have low molecular weight e.g. glucose, water etc.
ii) Macro molecules have high molecular weights e.g. starch, proteins, lipids etc.
3- Organelle level
Bio molecules assemble and form sub-cellular structures called organelles. For example mitochondrion is an organelle for cellular respiration and ribosome is specialized for protein synthesis.
4- Cell level
Organelles combine to form structural and functional unit of life called cell. In most protists, the entire organism consists of a single cell. In the case of most fungi, animals and plants, the organism consists of up to trillions of cells.
5- Tissue level
A tissue is a group of similar cells which perform common function. It is present in multicellular organisms.
Plant Tissues e.g. epidermal tissue, ground tissue, etc. Animal tissues e.g. nervous tissue, muscular tissues etc.
6- Organ level
In higher multicellular organisms more than one type of tissue having related (same) functions are organized (grouped) together and make a unit, called organ. For example stomach is an organ specialized for the digestion of food. It has
- Epithelial (glandular) tissue to secrete gastric juice for the digestion of proteins.
- Muscular tissue for contractions of stomach walls for grinding of food
7- Organ system level
Different organs performing related functions are organized together to form of an organ system. For example, digestive system is an organ system that carries out the process of digestion. Its Major organs are oral cavity, stomach, small intestine, large intestine, liver, and pancreas. All these organs help in digestion.
Organs system level in plants is less advanced than animals.
8- Individual level
Different organs and organ systems are organized together to form an individual or organism. The functions of organs and organ systems in an individual are coordinated. For example, during continuous and hard exercise, not only muscles worke but also there is an increase in the rate of respiration and heart beat.
A population is defined as a group of organisms of the same species located at the same place, in the same time. For example, human population in Pakistan in 2010 was 173.5 million individuals. Members of species interact with each other.
10- Community level
A community is an assemblage (group) of different populations, interacting with one another within the same environment e.g. a forest is a community.
Types of community I) complex community: It has many populations e.g. a forest community, a pond community etc.
II) Simple community: It has few populations e.g. a fallen log with some populations under it. In simple community any change in biotic or abiotic factors has drastic and long lasting effects.
Area where living organisms interact with the nonliving components of the environment is called ecosystem.
12- Biosphere level
The part of the Earth inhabited by organisms’ communities is known as biosphere. It constitutes (covers) all ecosystems.