7.4 Homeostasis and Cells

Homeostasis• Cells need to maintain a constant internal chemistry, size, shape, etc…. even though the

surrounding environmental conditions change.

• Homeostasis is the maintenance of a stable level of internal conditions, size, shape, etc….

and it requires cellular transportation.

Unicellular Organisms

Living organisms made up of only one cell

Multicellular OrganismsLiving organisms made up of many cells

Cell SpecializationThe cells of multicellular organisms are specialized

for particular tasks and communicate with one another to maintain homeostasis.

Stem Cells

Levels of Multicellular Organization

• Cells• Tissues• Organs• Organ Systems• Organisms

Cells are Organized into Tissues

A tissue is a group of cells alike in structure and function.

Skeletal muscle tissue

Cardiac (heart) muscle tissue

Tissues are Organized into Organs

An organ is a group of tissues which work together to perform a specific function.

Kidneys Heart

Organs make up Organ SystemsAn organ system is a group of organs working together to perform a specific

function.

Circulatory System Digestive System

Organ Systems make up Organisms

Cell Communication

The cells of multicellular can communicate using chemical signals, such as hormones.

Receptors and CommunicationIn order to respond to a chemical signal a cell

must have receptors the signal molecule can “plug” into.