Download Lesson 5 - Body Systems (2D)

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A. Cell Differentiation
A unicellular organism contains organelles that perform all required life functions in one
cell. Multicellular organisms are much more complex and are composed of many
different types of cells. A specialized cell has a unique structure that allows it to
perform a specific function.
 Ex. the structure and function of a red blood cell is
much different from that of a fat cell
It is more efficient to have “specialist” cells that perform one
function very well instead of every cell having to perform
every function.
Cell differentiation is the process of creating specialized cells, and is controlled by the
DNA. All multicellular organisms begin as a single cell. In humans this cell is called a
zygote. The zygote goes through a series of cell divisions (mitosis) to form a group of
identical cells called an embryo. At this point, the embryonic cells are called stem
cells because they have the potential to become any type of cell! As the embryo
develops, the cells begin to show differences in their shape, contents, and function.
 Embryonic stem cells – unspecialized cells that can differentiate into any cell
type (this makes them valuable for medical research and treatment)
 Adult stem cells – exist in some tissues, but can only produce specific cell types
(ex. bone marrow stem cells can form red blood cells, white blood cells, and
B. Levels of Organization
Multicellular organisms, such as plants and animals, are made of
many types of specialized cells that are organized in a way that
allows them to work together to keep that organism alive.
There are levels of organization in each multicellular organism that
form a hierarchy (levels of organization of increasing complexity).
Cell – the smallest functional unit of life (ex. muscle cell)
Tissue – a group of similar cells that work together to perform a simple
Organ – a structure composed of different tissues that work together to
perform a more complex function
Organ system – a group of organs that work together to perform a major
body function
Organism – a collection of organ systems that work together to keep the
organism alive
C. Tissues
Animals have 4 main types of tissue. Each tissue contains many types of specialized
cells, and each tissue is found in most organ systems.
1) Epithelial Tissue
Description: thin sheets of tightly packed cells that cover body surfaces and lines
internal organs and body cavities
Ex. skin, lining of the digestive system
Function: protection
These cells divide very quickly to replace lost/damaged cells
2) Connective Tissue
Description: various types of cells and held together by a liquid or solid
substance called a “matrix
Ex. bone, blood, tendons, cartilage
Function: supports protects, connects the body’s organs, insulation
These cells divide slowly so the body structure remains strong (exception: blood
3) Muscle Tissue
Description: bundles of long cells (“muscle fibres”) that can shorten (“contract”)
Ex. biceps, hamstring, heart
Function: movement, organ function
These cells divide very slowly...cardiac and skeletal muscle cells do not divide at
4) Nervous Tissue
Description: long, thin, branching cells that can conduct electrical impulses
Ex. brain tissue, spinal cord, nerves
Function: sends signals from one part of the body to another
These cells never divide. Damage done to any nervous tissue cannot be
D. Animal Organ Systems
All animals accomplish the same basic life functions regardless of their appearance,
behaviour, or habitat. The task of organ systems is to perform these life functions. There
are 11 major organ systems in the human body. Use the provided handout to fill in the
chart below.
Organ System
Organs that are
part of this system
E. Interactions of Body Systems
Organ systems interact to keep the organism functioning. All organ systems interact
with at least one other organ system. In complex animals, the circulatory system acts
as a transport system that connects all other systems.
a) The respiratory and circulatory systems work together to distribute oxygen to all
body cells and to remove carbon dioxide.
 The respiratory system brings oxygen gas into the lungs where it diffuses into the
blood in the circulatory system.
 The circulatory system transports the oxygen to all tissues, where it diffuses into
the cells. Oxygen gas is used in the process of cellular respiration to produce
 Carbon dioxide is a waste product of cellular respiration and it diffuses from the
cells into the blood. The circulatory system transports the carbon dioxide back to
the lungs, where it diffuses from the blood back into the lung airways to be
breathed out.
b) The digestive and circulatory systems work together to distribute nutrients to all
body cells and to remove waste products.
 The digestive system breaks down food into small molecules that diffuse through
the walls of the digestive tract and into the blood. The circulatory system then
transports these nutrients to all tissues in the organism, where they diffuse into the
cells. Any waste products diffuse out of the cells and into the blood and are
transported to the urinary system. The waste products are filtered out of the
blood and end up being expelled from the body in urine.
c) The lymphatic and circulatory systems work together to protect the body from
foreign invaders (ex. viruses and bacteria).
 The lymphatic system filters out any disease-causing organisms that get into the
body’s tissues.
 The lymphatic system also produces white blood cells and antibodies which are
released into the bloodstream to be transported all over the body to fight
invading germs.