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Tissues:
Beyond Cells
• All cells come from previously existing cells.
Mitosis
• One fertilized egg (zygote) undergoes mitosis many,
many times to produce a baby.
• An adult human contains 75 – 100 trillion cells.
• 300 different types of cells in the body.
• How does one fertilized egg develop into all of the
different types of cells found in a human?
fat cells
bone cells
skin cells
muscle
cells
Answer: Cell Specialization
• Specialized cells have physical and chemical
differences that allow them to perform different
functions
• Red blood
cells carry
oxygen in the
blood
• Nerve cells
transmit
electrical
impulses
• Plant leaf cells
perform
photosynthesis
• How did one cell give rise to so many different types
of cells in one organism?
Genes
• Genes (base pair sequences) turn on and off to
control the characteristics and functions of a cell.
• Many factors influence what genes are turned on
and off, including the environment and
neighbouring cells.
Stem Cells
• Stem cells are
undifferentiated
cells that can
divide to form
specialized cells.
Levels of Organization
• Cells in organisms are organized into tissues.
• Tissues are collections of similar cells that perform a
particular function.
• Tissues are organized into organs.
• Organs are organized into organ systems.
• More than one kind of cell or tissue are found in any
organ.
• Different cells, tissues, organs and organ systems are
found in animals and plants.