10.2 4.2.3 cambrian explosion

What does this mean?

Cambrian explosion refers to the tremendous increase in the number and type of multicellular organisms at the start of the Cambrian period of the Paleozoicera. Ancestral forms of all organisms emerged then, which have gradually changed to become the life forms we see today.

Cambrian explosion: explanation http://www.fossilmuseum.net/Paleobiology/CambrianExplosion.htm

Significant changes have taken place in all groups of plants and animals.

Plants:

From being purely aquatic, plants gradually colonized land and had to cope with life in a completely different medium. They had to develop several structuralchanges, such as:

• They developed true roots, stems and leaves with different tissues in these organs. Some plants developed flowers and fruit.
• They developed supporting tissue like xylem and thick secondary walls with lignin.
• They developed a means of protecting themselves against dehydration, such as the development of a cuticle and sunken stomata.
• They became less dependent on water for fertilization, using wind and or animals to transfer pollen grains with sperm nuclei.

Animals:

Animals also became more complex than their primitive ancestors. Some colonized land and had to make further changes.

• They developed a head with a brain and limbs on both sides of the body.
• The digestive system became more complex, developing a gut with two openings and various glands associated with digestion.
• They had to protect themselves against dehydration, so many developed internal breathing systems, protecting the delicate lungs.
• Birds and mammals became endothermic, i.e. able to keep their body temperatures constant despite changes in environmental temperature.

See: http:www.khanacademy.org/video/introducti-to-evolution-and-natural- election?playlist=Biology