Biology in Society

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Biology in Society-Assignment Two
“The Mother of Us All”- Summarise the six steps required and discuss how different selection pressures may have encouraged this type of evolution and the introduction of various species. “Over time evolution has occurred, a process by which life has developed by stages from single celled organisms into the multiplicity of animal and plant life. It has been hypothesised that six-steps are needed to move from single cells to complex animals.” These six-steps are: STARTING POINT-CHOANOFLAGELLATES

Choanoflagellates are single cellular organisms known as ‘filter feeders’. These organisms are the closest relatives to a multi-cellular organism. Choanoflagellates have a very recognisable morphology. They have a oval like cell body with a flagellum (tail) that is surrounded by micro-villi The Choanoflagellates form colonies, however the cells are found on the outside surface. STEP ONE-MULTICELLULARITY EVOLVED

The Choanoflagellates began to stick closer together and cadherins were found in the separate genomes of singular Choanoflagellates from the specialized molecules that multi cellular organisms, like humans use. Nicole King from the University of California supposes that the Choanoflagellates use the cadherins to find and identify harmful bacteria. Other molecules made it possible for food to be shared between the cells and transport to occur. This process made it possible for the outside cells to feed while the cell on the inside could divide. This division of labour allowed for faster growth. The first multi-cellular organisms were growing larger and as a result some cells began to settle ‘on the bottom’. This gave the cell a larger surface area for feeding, and was called a sponge. Initially, the larval stage of the sponge stayed swimming and became the yolk so the organism did not need to feed. STEP TWO- EXTRACELLULAR DIGESTION AND SEALED EPITHERLIA EVOLVED The sponges’ individual cells began capturing small particles for it to...
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