Cephalisation, Embryonic tissue layers and Development of a coelom

Question 1

what is Cephalisation

Answer 1

Cephalisationis the evolutionary trend towardconcentrating
nervous tissue, the mouth and other sense organs toward an animal’s front (anterior) end.

Question 2

how does this differ in animals

Answer 2

Fully cephalised organisms have a head and brain, while less cephalised animals display one or more regions of nervous tissue. Cephalisation isassociated withbilateral symmetryand movement. The head of a cephalised animal facesforward.This is an evolutionary adaptation that allows the organism todetectfood, danger and other stimuli and respond quickly.

Question 3

what are diploblastic animals

Answer 3

the embryo’s cellsorganise themselves intotwo body layersof cells. Each layer has itsfunction. The embryo’s outer layer is called theectodermand the inner layer is called theendoderm. A body with only two layers of cellscannot growinto a very large-sized animal. The cells that form the ectodermal origin make theouter surfaceof the organism, while the cells that form the endodermal originline the gut.

Question 4

what are triploblastic animals

Answer 4

In triploblastic animals, the embryo’s cellsorganise themselves intothree body layersof cells. The third layer of cells is called themesodermand is formedbetweentheectodermandendodermof the embryo.Cells of the mesodermal origin can become a thick mass of cells and make up the bulk of the body of most (more complex) animals. The mesodermal cells allow for the development of organs and organ systems. Cells of the ectodermal origin make up the skin surface. Cells of endodermal origin line the gut. Triploblastic animals often havelarger bodies.

Question 5

what is a Coelom

Answer 5

As organisms evolved and becamelarger and more complex, additional structures developed within somemore advancedtriploblastic organisms,such as a morecomplicated gut. In triploblastic organisms, the mesodermal cells allow for the formation of acoelom.

A coelom (pronounced: ‘sea-lom’) is the fluid-filled body cavity between the mesodermal and the ectodermal layers. The coelom separates the gut from the body wall.This allows the outer parts of the body to move independently from the inner parts of the body. Tissues in theouter part of the mesoderm form muscle layers of the body, andtissue on the inner layer of the mesoderm formsthe muscles of the gut. Separating these two muscle layers with a coelom allows the muscles of the gut to contract without affecting the movement of the rest of the body. This aids

digestion. Organisms with a coelom can essentially multi-task. For example, the organism can independently move while independently digesting its food. The movements of the various tissues work independently.

An organism with a coelom is referred to as a coelomate organism.An organism without a coelom is called an acoelomate organism.