B 5B Cellular Complexity Approaching Reading level 6.8 – 02

Jinny looked under the microscope at the slide of pond water. “OHHH!! They are moving as if they are alive.” Mrs. Jackson came close to her bench and said, “They are alive, just like us.” That was one of the best days in Jinny’s biology class. She wanted to know more. Over the next few classes Mrs. Jackson explained more. She said that bacteria were the earliest form of life. Today, we divide cells into two separate groups. They are prokaryotes and eukaryotes. Prokaryotes do not have a nucleus. The DNA is found in its cytoplasm. 

Eukaryotes has a membrane bound nucleus. The nucleus contains its genetic material. Although there are differences, all cells are surrounded by plasma membrane, has genetic material, and has ways to produce energy. The next day Mrs. Jackson asked the class about the functions their bodies do. Paul said that the body pumps blood and digests food. “Correct,” said the teacher. She said that the body can do all these things because it is made up of cells. Cells are the basic units of life. The cell is a complex, well-designed structure. A living cell has ways to interact, communicate, and change. A cell exchanges information from its surroundings. It changes, recycles, and creates. It maintains homeostasis through feedback loops. The cell can function if each of its parts work together. Failure of any part results in a nonfunctional cell.

The cell is like a factory. The cell membrane separates the inside of the cell from the outside. Membrane proteins acts as guards, sensing and communicating through chemical and electrical signals. The mitochondria are the power station. They produce energy to power the factory. The DNA acts as a data bank. It contains the blueprint of the organism.

There are transportation systems to carry raw materials. Vesicles carry essential packages. There are organelles that repair and recycle damaged parts.

The next day the lesson continued. Mrs. Jackson said that the cell is a part of a more complex system. It serves as the basis of life. It can grow, differentiate, adapt, and die. The cell cycle is a complex process. There are several stages in cell cycle. As the cell grows and divides it goes through checkpoints at every stage. These points check for damages and repairs when needed. This prevents uncontrolled growth or unwanted changes.

“How did cells become complex?” a student asked. Mrs. Jackson continued with the lesson. Complexity can happen in different ways. One of the simplest ways would be to combine simple cells. One example of this is the mitochondria and the chloroplast. There is evidence to show that they were once primitive bacterial cells. A larger host cell absorbed these bacteria. Overtime they became dependent on each other. Mitochondria and chloroplasts have their own DNA. They also reproduce independently. Over millions of years, mitochondria and chloroplasts have become specialized. They cannot survive outside the cell. As a result, we have a complex cell with specialized organelles.