Cells and control Study Guide

Growth in multicellular organisms is a complex process involving an increase in size and number of cells. In animals, growth primarily occurs through cell division (mitosis) and subsequent differentiation of these cells into specialised tissues and organs. This process is largely completed by early adulthood, though some cell replacement and repair continue throughout life. In plants, growth is more continuous and localised to specific regions called meristems. Plant growth involves cell division, followed by cell elongation, which significantly increases cell size, and then differentiation into various plant tissues like xylem, phloem, and epidermal cells. The ability of plant cells to elongate contributes significantly to the overall increase in plant size.

Cell differentiation is the process by which a less specialised cell becomes a more specialised cell type. In multicellular organisms, all cells originate from a single zygote through repeated cell divisions (mitosis). Initially, these cells are undifferentiated, meaning they are totipotent or pluripotent and can develop into various cell types. As an organism develops, cells undergo differentiation, where specific genes are activated or deactivated, leading to changes in the cell's structure and function. This specialisation is crucial because it allows different cell types to perform specific roles, contributing to the efficient functioning of tissues, organs, and organ systems. For example, muscle cells develop contractile proteins to facilitate movement, nerve cells form long axons to transmit electrical signals, and red blood cells lose their nucleus to maximise oxygen transport. Without differentiation, a complex organism capable of diverse functions could not develop or survive.