Science of Life

How the living things are organized?

Things In its broadest sense, biology is the study of living things  the science of life. Living things come in an astounding variety of shapes and forms, and biologists study life in many different ways. They live with gorillas, collect fossils, and listen to whales. They read the messages encoded in the long molecules of heredity and count how many times a hummingbird's wings beat each second. 


Properties of Life 

What makes something "alive"? 

Anyone could deduce that a galloping horse is alive and a car is not, but why? We can-not say, "If it moves, it's alive," because a car can move, and gelatin can wiggle in a bowl. They certainly are not alive. What characteristics do define life? All living organisms share a family of basic characteristics: 


I. Cellular organization. All organisms consist of one or more cells. Often we tiny to see, cells carry out the basic activities of living. Each cell is bounded by a membrane that separates it from its surroundings. 
2. Order. MI living things are highly ordered. Your body is composed of many different kinds of cells, each containing many complex molecular structures.

 3. Sensitivity. All organisms respond to stimuli. Plants grow toward a source of light, and your pupils dilate when you walk into a dark room.

 4. Growth, development, and reproduction. All organisms are capable of growing and reproducing, and they all possess hereditary molecules that arc passed to their offspring, ensuring that the offspring are of the same species. 

5. Energy utilization. All organisms take in energy and use it to perform many kinds of work. Every muscle in your body is powered with energy' you obtain from the food you eat.

 6. Evolutionary adaptation. All organisms interact with other organisms and the environment in ways that influence survival, and as a consequence, organisms evolve adaptations to their environments.

 7. Homeostasis. All organisms maintain relatively constant internal conditions, different from their environment, a process called homeostasis. 

Hierarchical Organization 

The organization of the biological world is hierarchical that is, each level builds on the level below it.

The Cellular Level
At the cellular level atoms, the fundamental elements of matter, are joined together into dusters called molecules. Complex biological molecules are assembled into tiny structures called organelles within membrane-bounded units we call cells. The cell is the basic unit of life. Many organisms are composed of single cells. Bacteria are single cells, for example. All animals and plants, as well as most fungi and algae, are multi cellular composed of more than one cell. 

The Organism Level

 Cells are organized into three levels of organization. The most basic level is that of tissues, which are groups of similar cells that act as a functional unit. Tissues, in turn, are grouped into organs, which are body structures composed of several different tissues grouped together in a structural and functional unit. Your brain is an organ composed of nerve cells and a variety of connective tissues that form protective coverings and contribute blood. At the third level of organization, organs are grouped into organ systems. The nervous system, for example, consists of sensory organs, the brain and spinal cord, and neurons that convey signals to and from them. 

The Population Level Individual organisms are organized into several hierarchical levels within the living world. The most basic of these is the population, which is a group of organisms of the same species living in the same place. All the populations of a particular kind of organism together form a species, its members similar in appearance and able to interbreed. At a higher level of biological organization, a biological community consists of all the populations of different species living together in one place. 

At the highest tier of biological organization, a biological community and the physical habitat within which it lives together constitute an ecological system, or ecosystem. For example, the soil and water of a mountain ecosystem interact with the biological community of a mountain meadow in many important ways. 
Emergent Properties At each higher level in the living hierarchy, novel proper-ties emerge. These emergent properties result from the way in which components interact, and often cannot be guessed just by looking at the parts themselves. Examining the cells gives little clue of what the animal is like. You have the same array of cell types as a giraffe. It is because the living world exhibits many emergent properties that it is difficult to define "life." 


All living things share certain key characteristics including: cellular organization, sensitivity, growth, development and reproduction, adaptation, and homeostasis.