Unicellular organism – consists of only one cell– That one cell carries out all functions required
to maintain the life of the organism
Multicellular organism – consists of more than one cell– Cells are specialized to perform certain
functions (cell specialization/differentiation)
Examples of Cell Specialization
1. Neuron (nerve cell):– Sends info. from one part of the body to
another– Very long and thin
Examples of Cell Specialization
2. Red blood cells:– Carry oxygen throughout body– Flattened disks so that they can easily flow
through blood vessels
Close-up: Blood cells in capillary
Examples of Cell Specialization3. Sperm cell:
– Fertilizes egg– Strong tail for quick swimming, distinct head
for entering egg cell
Cell Communication• Chemicals released by one cell can
influence the activity of another cell.– Ex: sensory cells to nerve cells to muscle
cells
Cell CommunicationHormones = communication
chemicals that travel
through the blood– Secreted by endocrine
glands– Acts much slower than
nerve impulses but effects last much longer
– Only influence the action of target cells that have specific receptors
– Two mechanisms:
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