IB Biology B3.3 Notes

So far you have learned about the transport and respiratory systems of organisms for them to live. Next, you need to know about their locomotion (movement), which begins with understanding the two types of species in this context:

1. Sessile species - species that are fixed in one place. As a result, they respond to their environment by changing their growth or development. An example is the phototropism of plants.
2. Motile species - species that are able to move around.  As a result, they respond to their environment by changing their position. An example is the movement of crocodiles into the light to raise their body temperature.

Most sessile species evolved before muscles developed and therefore do not contain muscle. However, many organisms on the plant do contain muscle, and you need to know more detail about how muscles and related structures contribute to the movement of motile species.

However, movement is still very important as it is required to forage for food, escape from danger, search for a mate, and migrate at the least. Examples for each are expected but should be easy to mention from experience (a duck will perform all four).