Sejt

Sejt, also known as a cell, is the basic unit of life in biology. All living organisms are composed of cells, and a sejt carries out essential processes such as metabolism, growth, response to stimuli, and reproduction. Cells are broadly classified into prokaryotic and eukaryotic forms.

In prokaryotic cells, DNA resides in a nucleoid region, and there are no membrane-bound organelles. They are typically smaller and simpler, with a cell membrane, cell wall, ribosomes, and cytoplasm. Eukaryotic cells contain a true nucleus enclosed by a nuclear membrane and possess numerous membrane-bound organelles, including mitochondria, endoplasmic reticulum, Golgi apparatus, and, in plants and algae, chloroplasts.

All cells share certain features: a plasma membrane that encloses the cell, cytoplasm where metabolism occurs, and genetic material (DNA). Ribosomes carry out protein synthesis. Mitochondria produce energy in many cells; chloroplasts capture light energy in photosynthetic organisms; vesicles and vacuoles transport and store substances. The cytoskeleton provides structure and enables movement.

Cell replication occurs through the cell cycle. In multicellular organisms, somatic cells divide by mitosis, producing two genetically identical daughter cells. Reproductive cells divide by meiosis, reducing the chromosome number to create gametes. Prokaryotes divide by binary fission.

Cell theory summarizes these ideas: all living things are composed of cells; the cell is the basic unit of life; and new cells arise from preexisting cells. Modern cell biology uses microscopy and molecular techniques to study structure and function.