Qelizë

Qelizë is the basic unit of life in biology. In Albanian, the term qelizë refers to the cell. The cell theory states that all living organisms are composed of one or more cells, that the cell is the basic unit of structure and function, and that new cells arise from preexisting cells.

Cells vary in size and form, but share common features. Every cell is bounded by a plasma membrane that encloses cytoplasm and genetic material. Prokaryotic cells, found in bacteria and archaea, lack a nucleus and most membrane-bound organelles. Eukaryotic cells, which make up plants, animals, fungi, and protists, have a defined nucleus and a complex system of organelles.

Important organelles: nucleus contains DNA; mitochondria generate energy (ATP); ribosomes synthesize proteins; chloroplasts in plants and algae capture light energy for photosynthesis; the endoplasmic reticulum and Golgi apparatus modify, sort, and ship proteins and lipids. Lysosomes and peroxisomes perform waste processing and metabolism.

Cell functions include metabolism, growth, response to stimuli, and reproduction. Cells divide through mitosis to produce somatic cells, or meiosis to form gametes in sexual reproduction. Transport across membranes occurs by diffusion, osmosis, and active transport, enabling nutrient uptake and waste removal.

Diversity of cells leads to tissues and organs in multicellular organisms, while unicellular organisms consist of a single cell carrying out all life processes. Studying cells, their structure, and function provides insight into biology, medicine, and biotechnology.