Question

1. Explain and give an example of negative and positive feedback. Include information on how the endocrine and nervous are involved in response to stimuli.

2. Describe how gas exchange occurs in aquatic animals through gills (include countercurrent exchange), insects through tracheal systems, and mammals through lungs.

Answer 1

Ans 1) NEGATIVE FEEDBACK MECHANISM - shuts off the original stimulus or reduces its intensity . eg - control of blood presure and temperature regulation.

INITIAL STIMULUS -> RESPONSE-> DECREASED STIMULUS

POSITIVE FEEDBACK MECHANISM -increase the original stimulus to maintain homeostasis eg- release of a oxytocin from posterior pitutary gland during childbirth.

INITIAL STIMULUS -> RESPONSE ->INCREASED STIMULUS

ENDOCRINE SYSTEM helps to regulates and maintain body functions by synthesizing and releasing hormones. it is composed of glands located throughout the body that secrete chemical substance called HORMONES .

  + TRH +thyrotropin

HYPOTHALAMUS---+---->PITUTARY HORMONE----+----->THYROID------+----->THYROXINE (Thyroid hormone )

     

Other Brain Centers Hypothalamus TRH Anterior TSH Pituitary Thyroid gland Thyroid Hormones target cells throughout body

Ans 2) Aquatic animals through gills- fish use gills to take up oxygen dissoved in water and diffuse co2 out of bloodstream .fish exchange gases by pullin oxygen rich water through their mouth and pumping it over their gills. In some fish capillary blood flows in the opposite direction to the water , causing counter current exchange . the gills push the oxygen poor water out through openings in the side of pharynx.

Insects through tracheal systems- air enters the respiratory system of insects through a series of external openings called SPIRACLES. these external opening lead to internal respiratory system called TRACHEAE. It is responsible for delivering oxygen to all cells and for removing carbon dioxide that is produced by the waste product of cellular respiration.

Mammals through lungs -air or oxygen is inhaled from external environment enter through nose or mouth.then enter into pharynx then trachea (windpipe) then pass through right and left primary bronchi to alveoli (where exchange of gases takes place between air and blood , oxygen travell across wall of alveoli in blood stream and co2 diffuse back and exhaled as it is a waste product) in lungs .