What is a cell? | Cells: Cells are the smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane. Plant Cell: All animal cells are multicellular. They are eukaryotic cells surrounded by plasma membrane and it contains the nucleus and organelles. Animal cells are of various sizes and have irregular shapes. Most of the cells size range between 1 and 100 micrometers and are visible only with help of microscope. Trillions of cells are found in the human body. There are many different types of cells, approximately 210 distinct cell types in adult human body. Human Cell: The interior of the cell is divided into the nucleus and the cytoplasm. The nucleus is a spherical or oval shaped structure at the center of the cell. The cytoplasm is the region outside the nucleus that contains cell organelles and cytosol, or cytoplasmic solution. |
What are the roles of various organelles such as the nucleus, endoplasmic reticulum, ribosomes, cell wall, cell membrane, chloroplasts, mitochondria, Golgi apparatus, lysosomes and centromeres?
- The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle.
- The endoplasmic reticulum serves many general functions, including the folding of protein molecules in sacs called cisternae and the transport of synthesised proteins in vesicles to the Golgi apparatus.
- The ribosomes plays a very important role in protein synthesis, which is the process by which proteins are made from individual amino acids.
- The cell wall is a tough, flexible layer that surrounds some cells. It is located outside the cell membrane and provides these cells with structural support and protection, in addition to acting as a filtering mechanism.
- The cell membrane controls the movement of substances in and out of cells. The basic function of the cell membrane is to protect the cell from its surroundings.
- Their main role is to conduct photosynthesis, where the photosynthetic pigment captures the energy from sunlight, and stores it in the energy storage molecules.
- The roles of the mitochondria are to produce the energy currency of the cell through respiration, and to regulate cellular metabolism.
- The function is the modifying, sorting and packaging of proteins for secretion. It is also involved in the transport of lipids around the cell, and the creation of lysosomes. The sacs or folds of the Golgi apparatus are called cisternae.
- Lysosomes are cellular organelles that contain acid hydrolase enzymes that break down waste materials and cellular debris. They can be described as the stomach of the cell.
- Without centromeres, cells cannot divide properly and the overall process of mitosis fails
References:
http://en.wikipedia.org/wiki/Cell_(biology)
http://biology.tutorvista.com/animal-and-plant-cells/animal-cell.html
http://www.enchantedlearning.com/subjects/animals/cell/