Studying for bio test. Oh, what a joy.
I am sick and delirious right now, so if this seems silly, forgive me.
This is the most memorizing-dependent unit, it seems. Have fun. -____-
So an animal is composed of many levels of structure. Here they are, ascending in size:
Atoms - yeah: carbon hydrogen oxygen
Molcules - groups of atoms: carbon dioxide, water, glucose
Organelles - tiny structures inside the cell: mitochondrion, nucleus, chloroplast
Cells - smallest unit of life: blood cells, skin cells, nerve cells
Tissues - groups of cells that perform specific limited functions: epithelial, cardiac muscle tissue
Organs - groups of tissues that perform specific function; may contain several types of tissues: the heart contains nerve, cardiac muscle, epithelial, connective tissues
Organ System - group of organs that work together to perform a major function: circulatory system contains heart, blood, spleen
Just like a multi-cell organism usually has organs, a cell has organelles. They are small structures within the cell that carry out the functions of the cell.