2 CELLS AND TISSUES Cells A cell is the basic living structure of an organism. It can be divided into four main parts: cell membrane cytoplasm mitochondrion nucleus DNA endoplasmatic reticulum lysosome ribosome Golgi apparatus Types of cells There are trillions of cells in a human body; they belong to hundreds of different types, and they have different structures and functions. Despite their differences, they depend on one another, either directly or indirectly, to keep the body functioning as one unit. These are the most common types of cells: stem, bone, blood , muscle, fat, skin, nerve, endothelial, sex, pancreatic, and cancer cells. Tissues Tissues are groups of similar cells that work together. The following are the four main types of tissues. Epithelial tissues cover the surface of the body and some internal organs. The first studies of cells were conducted on dead cork cells in 1665. Can you name some of the cells mentioned in a blood test? lining: rivestimento to nourish: nutrire organelle: organulo citoplastico stem cell: cellula staminale 16 BODY AND MIND plasma (cell) membrane, the outer lining membrane which separates the cell from the external environment; cytoplasm, the substance between the nucleus and the plasma which surrounds organelles; organelles, permanent structures specialised in a specific cellular activity. They include: the nucleus, containing hereditary factors; ribosomes, very small granules; the endoplasmic reticulum, responsible for many different functions; the Golgi apparatus, which processes proteins; the mitochondria, which generate energy; the lysosomes which contain digestive enzymes; inclusions, secretions, and storage products of cells like melanin, glycogen, and lipids. The science which studies the cells is called Cytology. Connective tissues can be classified into: embryonic connective tissues, made of mucosa and located under the foetus s skin and developing bones; adult connective tissues, which include cartilage, bone, and blood tissues. Nervous tissues contain two main types of cells: neurons, which are sensitive to stimuli that they convert into impulses; neuroglia, which nourish and support neurons. Muscle tissues consist of highly specialised cells which provide motion, maintenance of posture, and heat production. Histology is the science that studies the different types of tissue.