Digestive, Excretory, and Reproductive Systems of Porifera, Cnidaria, and Platyhelminthes Coursework

Porifera or sponges do not have true digestive system. They exhibit intracellular digestion and they do not release digestive enzymes in the sponocoel to cause extracellular breakdown of nutrients. Concerning excretory system, they do not have. Porifera reproduce asexually or sexually. The later can take either of this forms; gonochoristic or hermaphroditic. On the other hand, Platyhelminthes have a digestive system that is incomplete and usually much branched. They have mouth but no anus. They exhibit both intracellular and extracellular complementary digestion In terms of reproductive system, Platyhelminthes are monoecious. Fertilization takes place internally (Margulis & Schwartz, 1988).

Eggs are usually microscopic and enclosed in a shell having either direct development or having one or more stages in larva development. Examples include monogenetic trematoda and digenetic trematoda respectively. There are instances that some reproduce asexually. They do have a primitive system used to excrete consisting of a duct pores for excretion and solenocytes. The Cnidaria do not have an excretory system just like the sponges. Cnidaria exhibit both asexual and sexual reproduction. Among the common methods of asexual reproduction include regenerating, splitting horizontally, budding among others

Anatomy of a mollusc

Mollusc have a shell made up of calcium and protects main organs, ligaments aid in enhancing elasticity, umbo is where the shell grows, foot are short and flat located on the ventral surface and allows movement, the mantle is a thick fold tissue enveloping the organic mass as well as secreting shell, the intestine is responsible for absorption of nutrients, the cerebropleural ganglion is the nervous system made up of pedal, cerebropleural and visceral. Molluscs do have anus used to eject faecal matter, kidney is an excretory organ, the heart help in blood circulation, gills are used to take in nutrients from water, and gonad are the reproductive organs producing sperm and egg (Margulis & Schwartz, 1988). Finally the mollusc have mouth which allow food to enter, labial pulp which help in grasping food, digestive glad which produces secretion useful in digestion and stomach which receives food and stores for digestion to take place (Refer to fig. 1)

Life stages of arthropods

Arthropods usually undergo three or four live stages. After mating, eggs are laid and hatched outside the body of the females. This is done on dump places. To attain adulthood, the young ones undergo a series of developmental stages, metamorphosis. The changes are more pronounced towards the end post embryonic development. Moulting or ecdysis then occurs which is a process where the insects shade off the outer parts in order to accommodate the increase in body size. The stages take either of the following, egg-nymph-adult or egg-larvae-pupa-adult. Metamorphosis refers to developmental stages and associated changes that occur in insects (Kardong, 1998).

Incomplete metamorphosis also known as hemimetabolous development is where eggs usually hatch into nymphs that lack various features in adult. The nymph then undergoes a series of stages (instars) to attain attributes exhibited by adults. Complete metamorphosis (holometabolous) is where the hatched egg undergoes the four stages of development; egg-larvae-pupa adult. The larvae are totally different from the adults. Praying mantis, ants, grasshoppers, earwigs and crickets undergoes incomplete metamorphosis while butterfly and ladybugs are examples of insects that undergo complete metamorphosis.

Starfish movement

Starfish usually move by the aid of tubes which are situated under the body. To move about starfish fill the tube with sea water which is brought in via sieve plates located on top of its body. Movement is thus driven by water vascular system. This allows the tubes to contract and elongate. Movement is enhanced by suckers located at the end of the ‘feet’. When the tubes contract they grip substrates via the suckers. They then release their grip and such coordination of contraction and releasing of grip gives starfish the desired movement.

Digestive, excretory, circulatory, respiratory, and nervous systems of a fish

Fish are aquatic and they utilize specialized respiratory organs that have greatly enlarged surfaces and organs having thinner cuticle compared to other parts of the body thus facilitating gaseous exchange. Two main organs use for respiration are gills and lungs. The gills are adapted to extracting oxygen from the waters. However lung fish uses lungs for gaseous exchange. Fish have single circulation. The heart is made of two chambers; atrium and ventricle. Blood vessels are enlarged forming sinus venosus which aid in ensuring that there is continuous flow of blood. On the arterial end, the heart is immediately followed by a thickened muscular ventral aorta. Fish have mouth where food enters the body, oesophagus, fore and midgut and anus where excretory products are got rid of.

Those fish that are carnivorous have a stomach while herbivorous or omnivores do not have stomach. Generally fish have the following organs mouth, pharynx, oesophagus, gizzard, stomach, pyloric caeca, intestine, rectum, pancreas and liver. Fish have a well developed nervous system. They have olfactory bubbles linked to cerebrum responsible for sensing smell. The optic lobes help to process information from eyes. Additionally coordination of body movement and controlling the internal functioning as well as maintain balance are done by cerebellum and medulla respectively. Ideally fish such as salmon have well developed eyes and sense for smell and test. They have ears but not very well in hearing. They have lateral system useful in detecting motion.

Characteristics that have helped reptiles adapt to life on land

Reptile have dry, scaly skin which helps them get protection from adverse environmental conditions, their eggs have a shell and contain all that an embryo need hence ensuring that the off springs will survive, reptiles also have lungs very vital organ to get oxygen and release carbon dioxide, since the habitat do not have enough water, reptiles have kidney well adopted to effective absorption as well as re-absorption of water, although not all of them have legs, those that have can comfortably move about while those who do not have are adopting mechanism to help them move around. Lastly, reptiles are coldblooded and have adopted basking as a technique to help them regulate body temperatures.

Birds are well adapted to avian way of life. The ability to sexually reproduce but to lay eggs is vital in helping reduce the weight hence facilitating flight. As suggested by Berthold, 1993 the skeletal system of birds is a times termed as wishbone and it is a fusion of clavicle bones. This acts as a brace as wings are being flapped. It is the fusion of bones that makes the bird lighter while having a stronger furcula. Birds do have an efficient respiratory system where oxygen moves in one direction thus at all times, the bird will have fresh air moving through vital; for sustaining metabolism at very high altitude. They do also have air sacs extending to the bones which aid in moving oxygen. Birds also have a relatively larger heart to help meet the metabolic demand when in flight. The excretory system of birds entail conversion of nitrogen into uric acid or ammonia is important as it helps in conserving water (Berthold, 1993).

Characteristics of mammals that differentiate them from other vertebrates

Mammals do have fur or hair covering their r bodies. More importantly, the ability to produce milk clearly distinguishes mammals from other vertebrates; they have a diaphragm, non-nucleated red blood cells and a larger brain capacity that enhances comprehension of things within their environment. Additionally, they have sweat glands and are capable of regulating their body temperature. On the same note mammals give birth to off springs who are fully formed.

The lymphatic and endocrine systems

Lymphatic system is made up of organs, nodes as well as duct which help in transporting lymph, a watery and clear fluid. The system has cells which are immune known as lymphocytes that protect the body from antigens. The system plays the following functions; collecting and returning interstitial fluid such as plasma protein to the blood, protecting and defending the body against antigens and absorbing lipids from the intestine and transporting them to the blood stream. Ideally lymph organs include bone marrow, the spleen, lymph nodes, lungs, heart, tonsils, liver, intestines and thymus. The system is not closed and do not have a central pump. Similarly lymph moves despite existence of lower pressure thanks to peristalsis. Lymph vessel forms a network throughout the body and lymph movement is a one way draining from the tissues back to blood.

On the other hand endocrine system includes a system of glands which releases or secretes specific hormones direct into the blood stream so that body functions can be regulated. Ideally the system is an information signalling system that is slow to initiate and have prolonged response that can be experiences for days. Once hormones are released, they are then transported to the target tissue to trigger response. Generally endocrine glands are ductless, vaculine, have intracellular vacuoles or granules that stores hormones. The major endocrine systems operate thanks to feedback loops most of which are mediated through hypothalamus and pituitary. It is worth noting that various human functions such as growth ad development, moods metabolism among others are regulated by hormones.

References

Berthold, P. (1993). Bird Migration: A General Survey. Oxford University: Oxford University Press.

Kardong, K. (1998). Vertebrates: Comparative Anatomy, Function, Evolution. New York: McGraw-Hill.

Margulis, L. & Schwartz, K. (1988). Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth. New York: W.H. Freeman and Company.