Question

Consider the following:

A. One of the basic chordate characteristics is a tendency toward cephalization. How do the presence and the location of the eyespot and otocyst in a tunicate larva relate to this characteristic?

B. In addition to lacking a nucleus, mammalian red blood cells lack mitochondria. How might this impact oxygen utilization of the cell itself? Could that have an impact on how much oxygen can be delivered to the tissues?

C. Frogs are ectothermic, which means their body temperature is determined by external environmental conditions. Humans are endothermic, which means they regulate their body temperature internally. Given the differences in metabolism do the differences in the red blood cells of the two species make sense from a functional perspective?

D. Which chordate characteristics do tunicates retain as adults?

Answer 1

A. Tunicates are the organisms which are sedentary and reduced body structure. The larval form is more advanced than the adult tunicate. It has head which has the sense organs like eyes and the otocysts. Cephalization is head formation. Head is the region where most of the nerve tissue is concentrated. Because the nerve tissue is concentrated in the head region, sense organs are also located near by which give input to the brain. All sense organs give information to brain which processes the information and respond. SO presence of eyes and other sense organs in the anterior end of body where most of nerve tissue is concentrated is the process of cephalization seen in Tunicate larva.

B. RBC s do not have nucleus and mitochondria in humans. Nucleus occupies 10- 30% space in the RBC. Lack of mitochondria is to prevent the the RBC cell itself using the O2 that they carry. The number of RBCs present in the body is too huge. If all these RBcs start using the O2, there will not be enough O2 left for the tissues. AS the RBCs do not utilize the O2 that they are carrying , maximum O2 that they carry is transfered to tissues. RBCs get energy by anaerobic respiration in the absence of mitochondria.

C. Forg's RBCs are having nucleus . Because of this , they are living cells. NUcleus present in RBcs will occupy 10 - 30% of the space leaving less space for hemoglobin. Because of this tissues are getting less O2. This results in the metabolism of the tissues is low and the animal is sluggish. Because the metabolism is low, it produces less heat or energy to keep the body warm That is why frogs are ectothermic. In mammals, RBCs (human) have no nulceus, giving more space for hemoglobin allowing larger concentration of hemoglobin transported to tissues. Tissue produce more energy, which is used in keeping their body temperature constant and makes then endotherms.

D. Chordate characters are presence of Notochord, hollow tubular nerve cord, post anal tail and pharyneal gill slits.

Of all these characters, tunicates have only pharyngeal gill slits.