Multicellular Organisms Unit Six – Organizing Cells

Multicellular Organisms  Multicellular organisms have more cells (working parts) than unicellular organisms  The Douglas fir tree (shown below) is one of the largest organisms on earth  It is 76 metres high and 3 metres in diameter  Consists of many cells which form the trunk, branches and leaves  Together these cells help the tree to survive

Specialization and Differentiation  Multicellular organisms start as a single cell  When the cell divides, the new cells stay close to one another  The number of cells formed determine the size of the organism  As the number of cells increase, each cell becomes able to perform a specific function within the organism

Specialization and Differentiation  How does a town represent the concept of cell specialization?  Mechanic, teacher, doctor, police officer…  Multicellular organisms are specialized to do one job very well  Benefits multicellular organisms – greater efficiency  Ex. Heart vs. Digestive System

Cell Differentiation  Cell specialization takes place early in the development of a multicellular organism  Each cell changes and develops characteristics making it unique  This process is called cell differentiation  Once a cell differentiates, it performs a specific function  Ex. Muscle cells vs. nerve cells

Tissues  Differentiated cells are organized according to the function they perform  Tissue refers to a group of cells similar in shape and function  In animals, there are four basic types of tissue:  Epithelial – line cavities and structures in the body like mouth, heart and liver  Muscle – composes muscle in the body  Connective – connects, supports and binds tissues or other organs  Nervous – composes the nervous system in the body

Tissues continued  In plants, tissues from thin-walled plant cells are typically found in the parts of the plant that carries water and nutrients  Tissues in thick walled plant cells are found in the parts of the plant that provide structure

Organs  Different tissues join together to form larger structures such as the skin, stomach and heart  These structures are called organs  Organs are composed of two or more tissues that work in unison to perform one of more functions within the organism  Ex. Skin is the largest organ in the human body and is composed of all four of the basic tissue types  Skin functions as structural support for the body and acts as a barrier to protect us internally from the external environment  Animal organs – heart, stomach, brain, lungs, eyes…  Plant organs – stems, leaves, flowers, roots…

Organ Systems  Organs do not work independently, and two or more organs working together to perform a related function is known as an organ system  Digestive system – mouth, esophagus, stomach, liver, pancreas, intestines and anus   Organ systems frequently overlap and share organs  Ex. Circulatory system and respiratory system share the lungs  Interdependent – all organ systems need contact with the brain  Animal organ systems also include the circulatory, respiratory, musculoskeletal and nervous system

Organ Systems continued  Plants have two major organ systems:  Root system – network of roots of the plant  Shoot System – stems, leaves, flowers and buds

Check Your Learning  1. Reconstruct Table One (Organ Systems in the Human Body) in your notebook  2. Complete questions 2 – 6 on page 151