Multicellular OrganismsUnit 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 https://www.youtube.com/watch?v=_QYwscALNng

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