Life Science Grade 11

Grade 11 Life Sciences Lesson Plansanemones and corals, which are all living animals• They are marine (live in salt water) and freshwater animals thatare sedentary(attached to submerged objects such as rocks)animals or free-swimming, living in open seas• The sedentary or sessile stage is known as a polyp while thefree-swimming stage is known as a medusa• Both of these organisms are radially symmetrical• This means that their body parts are arranged in a circularplan so that cutting the animal in any vertical plane throughthe central axis of the animal will give two mirror images• Polyps are cylindrical in shape and have one digestiveopening and one closed end that is attached to a substrate• The mouth may be surrounded by six to eight tentacles andleads to a large gastrovascular cavity known as thecoelenterons• This cavity is filled with water and serves as a hydrostaticskeleton• The medusa is similar but is not attached to a substrate andhave their digestive openings underneath• They are flattened from top to bottom• The Cnidarians are diploblastic having both an outerectoderm and an inner endoderm with a jelly-like non-cellularmesoglea in between• These are considered true tissues• The many types of ectodermal cells are responsible fordetecting stimuli in the environment• Undigested food is egested through the mouth opening• Although Cnidarians have a gastrovascular cavity they areconsidered acoelomatePlatyhelminthes• The phylum Platyhelminthes is made up offlatworms such asthe liver fluke, planarian and tapeworm• They may be free-living and may be found in fresh-water ormarine environment• Some live in damp terrestrial environments• Others such as the tapeworm, are parasitic and live mainly onvertebrates (the parasitic tapeworm will be discussed later inanother lesson)• Both free-living and parasitic flatworms are similar to eachother in that they have a definite anterior end where anaccumulation of sense organs occur (known as cephalisation)• Their bodies are flattened from top to bottom (dorso-ventrallyflattened)• As a result of cephalisation and dorso-ventral differentiation,flatworms are bilaterally symmetrical (can be cut into mirrorimages in one plane only along a central longitudinal plane)Term 1 Page 72© Gauteng Department of Education (CAPS version)