Course Progress (5%)
13
Multicellular Life Begins
How did life go from a single cell floating alone to millions of cells working together as one body?

For billions of years, life existed as single cells. Then something extraordinary happened: cells learned to stick together and work as teams. In this lesson, your learner will explore the earliest multicellular animals, strange, soft-bodied creatures that lived in ancient oceans. Some looked like pancakes, others pulsed through the water like jellyfish. These simple creatures made of many cells working together led to every animal that has ever lived, including us.

S2S_Lesson13_MULTICELLULAR_LIFE_BEGINS by Selene

Key Ideas

  • After single cells came multicellular life, animals made of many cells working together.
  • Multicellular organization allowed for specialization. Different cells could do different jobs.
  • Early animals like cnidarians (jellyfish ancestors) had simple body plans and lived in the oceans.
  • Some early animals developed radial symmetry (body parts arranged around a center), which was revolutionary. Radial symmetry was a body plan that worked well for floating and drifting creatures.
  • These first animals were soft-bodied with no bones or shells, making them hard to fossilize.

Spines
  • DK's Science as You've Never Seen it Before: Cell Variety pg. 143
  • Mammoth Science: Types of Cells pg. 40
✏️  Notebooking Activity
Red blood cells are designed to carry oxygen, while neurons are designed to carry messages. Compare and contrast their shape and function using a Venn diagram.

Cosmic CalendarWhere we are: December 5
We reach December for the first time. Read the script below before the lesson.

Read aloud: We’ve made it to December on our Cosmic Calendar, and things are about to start moving faster. December 5th marks the appearance of the first multicellular life, organisms made of more than one cell working together. In real years, that’s about 800 million years ago. Look at where we are: December 5th. And look at how much calendar is still left. Everything we think of as complex life, all the animals, the plants, the dinosaurs, the humans, all of it happens in the last 26 days of this calendar year. We spent almost the entire year on single cells. Now in December, the story is going to accelerate. Hold on.

Timeline PageLabel the next page in your timeline “Multicellular Life Begins: 600 Million Years Ago”. The workbook prompt asks learners to draw soft, flat, frond-shaped Ediacaran creatures resting on the seafloor. They had no shells, no eyes, just strange quilted bodies drifting in the dark ocean.

Discussion Questions
  • Why might soft-bodied animals have been hard to find in the fossil record? 
    Sample answer: Soft bodies decay quickly after death and rarely leave impressions in rock. Hard shells, bones, and teeth preserve much better, so soft-bodied creatures like Ediacaran organisms left very few fossils behind.
  • Why was being multicellular helpful in ancient oceans? 
    Sample answer: Having many specialized cells allowed organisms to grow much larger, develop different body parts for different jobs, and compete more effectively for food and space than single-celled organisms ever could.
  • What are some differences between early animals and animals today? 
    Sample answer: Early Ediacaran animals were soft-bodied, slow-moving, and had very simple body plans with no eyes, legs, or mouths as we know them. Today's animals often have hard shells, complex nervous systems, specialized organs, and far more diverse behaviors.
  • How are jellyfish today similar to their ancient ancestors? 
    Sample answer: Modern jellyfish still have radial symmetry, soft bodies, and simple body structures nearly identical to cnidarians from hundreds of millions of years ago. They are one of the oldest animal body plans still alive on Earth today.
 
Vocabulary
  • Multicellular — Made of many cells that work together; multicellular organisms can develop specialized cells for different jobs.
  • Ediacaran — A period of Earth's history (about 635-541 million years ago) when the first multicellular animals appeared.
  • Cnidarian — A group of early animals (including jellyfish and corals) with radial symmetry; among the oldest animal groups.
  • Radial Symmetry — A body plan in which parts are arranged equally around a central point, like a wheel; useful for animals that float or drift.
  • Specialization — The process by which cells in a multicellular organism develop specific shapes and functions for particular jobs.
  • Tissue — A group of similar specialized cells working together to perform a specific function in an organism's body.
  • Evolution — The gradual change in inherited traits of a population over many generations, driven by natural selection.

Species to ResearchThis lesson covers the Ediacaran Period and the first multicellular animals. Here are some species to research:
  • Dickinsonia— A flat, oval, ribbed Ediacaran creature; one of the oldest animals, or possibly a fungus. Scientists still debate it!
  • Charnia— A frond-shaped Ediacaran organism that anchored to the seafloor; one of the first complex multicellular life forms found.
  • Spriggina— A small, segmented Ediacaran animal; may be a very early ancestor of arthropods.
  • Kimberella— An Ediacaran creature that may have grazed on microbial mats, leaving trace fossils of its feeding.
  • Fractofusus— A fractal-branching Ediacaran organism; its body plan is unlike any animal alive today.

Sources

I have completed this lesson Next Lesson