I can remember when I was in lower form, we learnt 4 of the levels of biological organization only. But, after reading a sub-chapter of Chapter 1, I now know that there are actually 10 levels.
From the smallest level to the biggest level... The smallest level, is of course, molecules. Everything starts with that, even non-living things are made up of molecules. A molecule is a chemical structure consisting of two or small chemical units called atoms. Let me use an example of a organelle. Let's say chloroplast, it has chlorophyll molecules. This chlorophyll molecule plays an important role in the plant, as it absorbs sunlight so that photosynthesis can be carried out.
Moving on the second level, the organelle. Many cells form an organelle. The nucleus is an example of an organelle. You need a powerful microscope to see an organelle.
The third level, is cells. Different organelles make up a cell. A plant cell consists of organelles, for example, chloroplast, nucleus, cell wall, etc... A cell is about 25 micrometers across. It will take 700 cells to reach across a Malaysian 1 sen coin.
A tissue, is made up from a group of similar cells. With a normal microscope, we can see the tissues of a plant. There are many types of tissues even in our human body. Examples are our smooth muscle tissue, our nerve tissues, etc...
From tissues we move on to organ and organ systems, the fifth level in the biological organization. As we all should know now, an organ is made up by many different type of tissues. For example, in our human body, we have many organs. Our heart, kidneys are a few examples of organs. Organs that carry out the same function can be organized into organ systems. For example, our human digestive system includes organs like our tongue, stomach, and intestines.
The next 5 levels will be out soon in "Biology... Exploring Levels of Biological Organization... [Part 2]...". So stay tuned for more info.