All living beings are made up of cells. Life began as simple unicellular organisms that evolved over time into more complex multicellular organisms made up of organized groups of cells. Cells are the basic building blocks of living things and come in different shapes depending on their function. While all cells share basic components like a cell membrane, nucleus, and cytoplasm, plant cells also contain chloroplasts and cell walls not found in animal cells. Groups of cells working together form tissues, organs, and organ systems that carry out essential functions for the organism.
13. Tissues, organs and systems There are several systems in the bodies of living beings that are organized and specialized to do specific tasks . All systems have to work at the same time in a coordinated process.
