Single-celled organisms are organized using specialized cell organelles, while several cells may organize into larger structures, such as tissues and organs. The single-celled organism has all it needs to live independently. Cells organized into more complex structures work together to perform a common function.Know More
An example of a single-celled organism is the amoeba. It is made up of the nucleus, which controls reproduction and growth, a food vacuole that digests food, pseudopods that propel the amoeba, and a contractile vacuole that excretes water and waste. These systems are organized within the cytoplasm, a jelly-like substance. The entire animal is surrounded by the cell membrane. Amoebas reproduce by cell division, a process that is fairly uncomplicated.
Cells that organize in groups to form tissues and organs are remarkably similar to the amoeba. The main difference is that the like cells depend on a trigger, such as a hormone, to allow those cells to work together. One illustration is the reproductive system. The organized cells that make up the pituitary gland generate a hormone called LH, which travels to the cells of the ovary. This causes the cells of the ovary to create progesterone, which controls the thickness of the uterine lining and governs impregnation.Learn more about Cells
Internal respiration takes place in the tissues of the body with the exchange of gases between systemic capillaries and surrounding tissue fluid, according to the McGraw-Hill College Division. In contrast, external respiration is the exchange of gases between air in the alveoli of the lungs and blood in pulmonary capillaries.Full Answer >
Animal cells are eukaryotic cells, or cells that contain a membrane-bound nucleus. The nucleus holds the DNA of the cell that provides the cell with instructions for life.Full Answer >
Eukaryotic cells have organelles, membrane-bound structures that perform different functions in the cell, and prokaryotic cells do not. Some typical eukaryotic organelles include the nucleus, mitochondria, ribosomes, Golgi apparati and chloroplasts.Full Answer >
Rudolf Virchow proposed that all cells arise from pre-existing cells. He was one of the three key figures, along with Theodor Schwann and Matthias Schleiden, who formulated the cell theory.Full Answer >