A cell is the smallest unit of a living thing. A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Thus, cells are the basic building blocks of all organisms.
Several cells of one kind that interconnect with each other and perform a shared function form tissues, several tissues combine to form an organ (your stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems that function together form an organism (like a human being). Here, we will examine the structure and function of cells.
There are many types of cells, all grouped into one of two broad categories: prokaryotic and eukaryotic. For example, both animal and plant cells are classified as eukaryotic cells, whereas bacterial cells are classified as prokaryotic. Before discussing the criteria for determining whether a cell is prokaryotic or eukaryotic, let’s first examine how biologists study cells.
Structure: Made of a double layer of phospholipids known as the phospholipid bilayer. A phospholipid is a lipid molecule composed of two fatty acid chains and a phosphate group.
Function: It is selectively permeable and controls the movement of substances into and out of the cell. The cell membrane is involved in facilitated diffusion, diffusion, osmosis and active transport.
Structure: Made mostly of water, the cytoplasm is the liquid that fills the cell. Cytosol has a gel-like consistency that the organelles float in. A watery solution containing dissolved substances, enzymes and cell organelles.
Function: The cytoplasm is the site of many chemical reactions and can act as a buffering solution ensuring appropriate conditions for enzyme function. Many metabolic reactions, including protein synthesis, take place in the cytoplasm.
Structure: Surrounded by a membrane made of phospholipids, the nucleus contains the cells genetic material and nucleolus.
Function: Controls and regulates cell activity. Often contains a dense spot of genetic material (DNA) known as the nucleolus where ribosomes are made.
Structure: Surrounded by a double membrane, the inner layer contains cristae- folds that increase the internal surface area. Mitochondria contain their own DNA and ribosomes.
Function: Performs cellular respiration.
Structure: Semi-rigid structure outside the cell membrane made of cellulose in plants and peptidoglycan in bacteria. Cellulose and peptidoglycan are both carbohydrates.
Function: Provides structure and support to the cell. The cell wall controls the volume of the cell by preventing too much water to be absorbed.
Structure: Surrounded by a double membrane, the chloroplast contains a green pigment called chlorophyll, which is bound in a complicated series of proteins. Chloroplasts contain their own DNA and ribosomes.
Function: Performs photosynthesis. Transforms energy from the sun into chemical energy in glucose.
Only found in plants.
Structure: Bound by a single membrane, the vacuole contains water and minerals for the plant.
Function: The vacuole takes up most of the space in the cell. It regulates the amount of water in the rest of the cell. This is important for plants as they cannot control how much water they have access to.
Only found in plants. Animal cells have small vacuoles not a large central vacuole.
Structure: A plasmid is a small ring of circular DNA molecule often found within bacterial cells.
Function: It is physically separated from a chromosomal DNA and can replicate independently. It contains additional genes that may or may not help the bacteria.
Structure: Long hair-like structure protruding the cell membrane.
Function: Assists the cell in movement.
Found in Prokaryotes and some unicellular Eukaryotes. Found in sperm cells.
Structure: Made mostly of protein and nucleic acids. There are to sub-units that fit together to make a ribosome.
Function: Makes polypeptides by "reading" RNA and attaching amino acids to each other. After the polypeptide is properly folded it becomes a protein. Ribosomes make proteins.