Question

12. How is radial symmetry an advantage to sessile or planktonic animals? Text 13. The embryo becomes layered during gastrulation, and these germ layers form the various tissues and organs of the body. The names of the germ layers describe where they are found in the early embryo: Text 14. Each germ layer forms specific tissue types. For example, where is the ectoderm, and what does it give rise to? Text 15 What are throa fiinctions of the hody cavity? Thou provide space for development

Answer 1

12.

Radial symmetry is advantageous to sessile organisms as sense organs are distributed around the whole body surface instead of concentrating in one particular region. This gives them the ability to sense danger from their prey from any direction.

Sessile animals can get food from any direction..

13.single layered blastula is converted into multilayered gastrula. Gastrula is triploblastic having three layers , outer ectoderm, middle mesoderm and inner endoderm.

Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers.Each layer gives rise to specific tissues and organs in the developing embryo.

The ectoderm gives rise to epidermis, the nervous system, and to the neural crest in vertebrates.

The endoderm gives rise to the epithelium of the digestive system and respiratory system, and organs associated with the digestive system, such as the liver and pancreas.

The mesoderm gives rise to many cell types such as muscle, bone, and connective tissue.

14.. The ectoderm originates from the outer layer of germ cells.. it is most outer layer of embryo.

ectoderm differentiates to form the

nervous system (spine, peripheral nerves and brain)

tooth enamel and the epidermis (the outer part of integument).

It also forms the lining of mouth, anus, nostrils, sweat glands, hair and nails.

15.The function of the body cavities is to provide space for development, expansion and movement of organs such as heart, lungs and liver.