Life Science Grade 11

Grade 11 Life Sciences Lesson Plansparts on an animal is balanced• Animals that have an irregular shape are notsymmetrical and are said to be asymmetrical. E.g.sponges• Radially symmetrical animals can be cut through acentral axis to give two mirror images and have morethan one plane of symmetry.• These animals have no heads or tails or left or rightsides and allows the animal to have more contact withtheir environment to obtain food and other usefulsubstances• They can also react to danger coming from anydirection E.g. sea anemones, sea urchins and jelly fish• Bilaterally symmetrical animals can be cut into mirrorimages in one plane only• These animals have a concentration of nerve tissue atthe front end of the body and are usually more activethan animals who are radial symmetrical E.g. earthworm,Gemsbok• Cephalisation refers to the presence of a headcontaining sensory organs that dace in the direction thatthe animal moves. Bilaterally symmetrical animals showcephalisation.• As an embryo develops, it is surrounded either by twoor three layers of cells• Embryos that develop two tissue layers are diploblasticand those that develop three layers of cells aretriploblastic• Diploblastic animals have an outer ectoderm and aninner endoderm• Triploblastic animals also have a middle layer knownas a mesoderm• The ectoderm will give rise to the outer covering of theanimal and sometimes to a central nervous system• The mesoderm forms muscles and most organs that liebetween the digestive tract and the outer bodycovering• The endoderm gives rise to the lining of the digestivetract and some organs such as the liver and lungs invertebratesLearners need to draw the flow chartfrom Understanding Life Sciences p88 Fig1.3.1 showing sexual reproduction, germlayer development and tissuedifferentiation.20 minSolutions for all p93Study and Master p118Understanding Life Sciences p87-882.3 ConclusionDiscuss the definitions as a class10 minTerm 1 Page 63© Gauteng Department of Education (CAPS version)