Exploring Levels of Biological Organization

1. The Biosphere
As soon as we are near enough to Earth to make out its continents and oceans, we begin to see signs of life-in the green mosaic of planet's forest, for example. This is our first views of biosphere, which consists of all the environments on Earth that are inhabited by life. The biosphere includes most regions of land, most bodies of water, and the atmosphere to an altitude of several kilometers.



2. Ecosystems
As we approach Earth's surface for an imaginary landing in Ontario, we can begin to make out a forest with the abundance of deciduous trees (tree that lose their leaves in one season and grew new ones in another). Such a deciduous forest in an example of an ecosystem. Grasslands, deserts, and the ocean's coral reef are other types of ecosystems. An ecosystems consist of all the living things in a particular area, along with all the nonliving components of the environment with which life interacts, such as soil, water, atmospheric gases, and light. All of Earth's ecosystems combined make up the biosphere.


3. Communities
The entire array of organisms inhabiting a particular ecosystems is called a biological community. The community in our forest ecosystems includes many kinds of trees and other plants, a diversity of animals, various mushrooms and other fungi, and enormous numbers of diverse microorganisms, which are living forms, such as bacteria,that are too small to see without a microscope. Each of this forms of life is called a species.

4. Populations
A population consists of all the individuals of a species living within the bounds of a specified area. For Example, our Ontario forest includes a population of sugar maple trees and a population of white-tailed deer. We can now refine our definition of a community as the set of populations that inhibit a particular area.



5. Organisms
Individual living things are called organisms, Each of the maple trees and other plants in the forest is an organisms, and so is each forest animal, such as a frog, squirrel, deer, and insect. The soil teems with microorganisms such as bacteria.








6.Organs and organ systems
The structural hierarchy of life continues to unfold as we explore the architectures of the more complex organisms. A maple leaves in an example of an organ, a body part consisting of two or more tissues (which we'll see upon our next scale change). An organ carries out a particular function in the body. Stems and root are the other major organs of plants. Examples of humans are the brain, heart, and kidney. The organs of humans, other complex animals, and plants are organized into organ systems, each a team of organs that cooperate in a specific function. For example, the human digestive system includes such organs as the tongue, stomach, and intestines.


7.Tissues
Our next scale change-to see a leaf's tissues-requires a microscope. The leaf shown here has been cut on an angle. The honeycombed tissue in the interior of the leaf (left portion of photo) is the main location of photosynthesis, the process that converts light energy to the chemical energy of sugar and other food, We are viewing the sliced leaf from a perspective that also enables us to see the jigsaw puzzle=like tissue called epidermis, the "skin" on the surface of the leaf. The pores through the epidermis allow the gas carbon dioxide, a raw material for sugar production, to reach the photosynthetic tissue inside the leaf. At this scale, we can also see that each tissue has a cellular structure. In face, each kind of tissue is a group of similar cells.


8.Cells
The cell is life's fundamental unit of structure and function. Some organisms, such as amoebas and most bacterias, are single cells. Other organisms, including plants and animals, are multicellular. Instead of single cell performing all the functions of life, a multicellular organism has a division of labor among specialized cells. A human body consist of trillions of microscopic cells of many different kinds, such as muscle cells, which are organized into the various specialized tissues. For example, muscle tissues consists of bundles of muscle cells. In the photo below, we see a more highly magnified view of some of the cells in a leaf tissue. each of the cells is only about 25 micrometers across. It would take more than 700 of these cells to reach across a penny. As small as these cells are, you can see that each contains numerous green structures called chloroplasts, which are responsible for photosynthesis.

9.Organelles
Chloroplasts are examples of organelles, the various functional components that make up cells. In this image, a very powerful tool called an electron microscope brings a single chloroplast into sharp focus.







10.Molecules
Our last scale vaults us into a chloroplast for a view of life at the molecular level. A molecule is a chemical structure consisting of two or more small chemical units called atoms, which are represented as balls in this computer graphic of chlorophyll molecule. Chlorophyll is the pigment molecule that makes the maple leaf green. One of the most important molecules on Earth, chlorophyll absorbs sunlight during the first step of photosynthesis. Within each chloroplast millions of chlorophylls and other molecules are organized into the equipment that converts light energy to the chemical energy on food.