MORPHOLOGICAL DIFFERENCES BETWEEN CARTILAGINOUS AND BONY FISH

Cartilaginous and bony fishes falls under the kingdom animalia. Vertebrates are organism that contains a back bone and all fishes contains a back bone which means that they are all vertebrates. The morphological structure of the two fishes is totally different. They are both very rough but catilaginous is more rougher.


Cartilaginous fishes are so called because of their lack of the real bone even though their bodies consist of a cartilage. The cartilaginous fishes have strong jaws. The mouth of the cartilaginous fish is found underside of the head, while the eyes are found on top of the head. Cartilaginous fishes also possess the two nostrils which are used for smelling. They can not see food as it enters their mouth. Some Shark solve this problem by touching their food with their nose before they eat. Some use powerful electro sensory system. Sharks, Skates and rays have rough skin. Sharks have five to seven gills slits on each side of their head. But bony fishes have 1 gill on each side. Chimaeras or Gost shark have skins that are very smooth and have only one pair of external gill openings. Cartilage fish give live birth through their bodies, they prefer internal reproduction whereas bony fishes reproduce by laying eggs. Cartilages prefer water with high salt quantity only while bony fishes survive in all types of salt.


Bony fishes are very common and their example include gurnard and snapper. Bony fish are classified into Lobe finned and the Ray –finned. Lobe-finned bone fish includes fish such as lungfish and coelacanth’s, where as Ray-fins includes the goldfish, tuna, and trout. They contains a tail fin which is equal in both the proportion bottom and top. They have a bony skeleton and single pairs of external gill openings. The mouth is generally at the front of the body. It has relatively short tube. Bony fish reproduce by external fertilisation of eggs and releases them into water. The male releases sperm called Milt into water. Milt combines with the eggs and fertilisation takes place.


Their liver is filled with oils which keep them from sinking. They have internal fertilisation. The bones of fish are made mostly by calcium but Shark does not have any bones. Shark skeleton is made of cartilage, and have no bladder, but bony fish have a gas filled swim bladder which enables them to float in the water. Bony fish have movable parts were as shark does not have. Shark can turn around in a smaller space than bony fish.The brain of the ghost sharks is closely related to that of the birds and mammals. As compared to that of the bony fish, the brain of the cartilaginous is ten times to that of the bony fish. While the brain size of the bony fish is thought to closely relate to that of the human beings, the reason of having such a big brain because they use a lot of energy.



Reference

1. Studios, A.R. 1997 Biology for kids vertebrates fish [Internet]. [Cited 2006 May 16] Available from:http://www.biology4kids.com/files/vert_fish.html[2006

2. The wikipedia contributor, the free encyclopaedia [internet] [Cited 2006 May 16] Available from: [http://en.wikipedia.org/wiki/Cartilaginous]

3. Wikipedia contributors, the free encyclopaedia, [Internet] [Cited 2006 May 16] Available from:http://en.wikipedia.org.wiki/Bony
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HOW THE FIRST PLANTS AND ANIMALS EVOLVED AND BECAME DEPENDANT ON EACH OTHER

Mutualism is the living together of two species whereby they both benefit from this way of life. The interaction between plants and insects during the process of co-evolution has been beneficial to both of them. Co-evolution between interactions started in aquatic environment b before they evolved on the land. The first species to evolve was the eukaryote. This was discovered through the process of fossilisation and it was found that the eukaryote is multi-cellular animal. These first animals were called eukaryotic because they contain nucleus.


Through the process of photosynthesis some plant species can generate their own food. Single cell plants and blue or green algae are the species that co-evolved and these are the same species that produced their own food. These plants help the herbivore animals to depend on them for food. Plants also help them with oxygen. This is where animals depend mostly on plants for their survival because they are gaining both food and oxygen. So finally plants were considered producers because they use the sun as their source of energy, carbon dioxide from the animals and water to produce food. This is mostly where the food chain begins.


The production of oxygen by algae helps the animal species to evolve on land. The most part of the O-zone layer is formed by oxygen which blocks the dangerous ultraviolet rays of the sun. If there is no oxygen supplied the rays make it impossible for animal species to live out of the water. In case of the plant the rays help them in food production. The relationship between plants and animals is very broad. Beside food and oxygen animals still depend on plants for shelter. Many animals use the trees as their habitat, mostly birds because that’s where they also lay their eggs for reproduction. During reproduction plants depend on animals mostly insects like bees to transport pollen grains to the female flowers. This is far better than wind on increasing plant population.

There are some plants which depend on insects for dispersing their pollen grains. Such insects transport pollen for the same plant and in most cases they end up building their habitat in that plant. Acadia plants also depend on arcadia trees for food and in return they end up protecting this tree from herbivores because they can’t always use that tree for food because of the ants which sting them.


References

1. Kazlev.A.M. 2002, Plants, (Land plants) [Internet] 2003 April 28 [cited 2006 May 08].Available from: http://www.palaeos.com/Plants/default.htm

2. Sean, B. Carroll. 2005, (Endless Form Most Beautiful) [Internet] [cited 2006 May 09] Available from: http://en.wikipedia.org/wiki/Segmentation_(biology)

3. Kohler, S. Plants, [Internet] 2006 May 8, 14:30. UTC [cited 2006 May 07]. Available from:
http://www.blueplanetbiomes.org/plants.htm

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FOSSILISATION AS A PROCESS AND ITS SIGNIFICANCE IN INTERPRETATION OF EVOLUTIONARY EVENTS

The term fossilisation refers to the deposit of inorganic processes which allow the remains of a past living creature to be after its death. This word is derived from the Latin word meaning dug up. On the beginning of ancient Greeks it was used to describe different objects or materials found underneath the ground or found lying on the surface of the earth including mineral ores, rocks, stone implements and organic remains.


Fossils are formed when a living organism dies and the body or part of the body is preserved in a different way but usually by being buried rapidly in sediments. Burial prevents destruction of organisms by scavengers, bacteria or weathering. In most cases burial can occur in different places like on the bottom of the sea, in rivers or in Lakes. Shells bones, teeth, husk and skeleton are the only hard parts which are preserved usually and they are can survive even if subjected to traumas such as impact fracture, disintegration or dispersal caused by atmospheric phenomena . In some instances soft parts such as mammoths are also preserved but it is hard for them to survive because they are vulnerable to predation and decomposition.


The importance of fossils is in interpreting the evolutionary events, like in the case of dinosaurs. If it was not of fossils the generation of today would not even have a clue on how it use to look like. Fossilisation as a process can only take place when certain conditions are present. This process depends on the chemistry of an environment and on the biochemical make-up of the organisms. There are different processes through which fossils can be preserved:Pertrification is the crystallization of minerals inside cells. One of the best known forms of Pertrification is silicification, a process in which silica-fluids enter the plant’s cell and crystallize, making the cells appear to have turned to stone. Pertrification can also occur in animals when minerals such as calcite or silica fill the pores and cavities of fossil shells and bones. Carbonization plants are mostly fossilised through this process. The mobile oils in the plant’s organic matter are leached out and the remaining matter is reduced to a carbon film. Plants have an inner structure of rigid organic walls that maybe preserved in this manner, revealing the framework of the original cells. Animal soft tissue has a less rigid cellular structure and is rarely preserved through carbonisation. Recrystallization animal shells are composed of mineral aragonite, a form of calcium carbonate that breaks down over millions of years to form the more stable mineral calcite. This method of preservation destroys the microscopic details of the shell but does not change the overall shape.


Mummification may occur in hot arid climates which can dehydrate organisms before their soft tissue are fully decayed. The skin itself is preserved for only a short time but the impressions of the skin in the surrounding sediment turns to rock.There are other different methods for preserving but they all perform different functions. Everything which happened in the past is discovered through fossilisation and it is compared to the present evidence if such species still exist.

Reference List

1. Wikipedia contributors, the free encyclopedia [internet] [cited 2006- May- 02] Available from: http://palaeo.gly.bris.ac.uk/communication/harrison/fossil.html

2. Wikipedia contributors, the free encyclopedia [internet] [cited 2006- May- 02] Available from: http://www.musei.unina.it/Paleontologia/eng/3.2.4.1.htm

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GENERAL ADAPTATIONS BIRDS HAVE EVOLVED FOR FLIGHT

Birds belongs to a class called aves. They are the only group of animals to posess feathers and they are best known for their ability to fly. These warm blooded vertebrates have feathers covering their skin and their forelimbs. The taxanomic point of view shows that there are about 8.800-10.200 living bird species and their size range from the tiny hummingbirds to the huge ostrich.


Fossilisation shows that dinosaur and reptile are the only great ancestors of the birds. According to the skeletal bones it was found that bone the close ancestor of the birds were arboreal or evolve flight from the trees nor they were physiologically intermediate between typical reptiles and living birds, nor that their feathers evolved for flight. The ancestors of birds were terrestrial,fast growing and active animals.


Feathers are made of a protein called keratin. They are made of thousands of branches called barbs. Feathers grow in specific areas called feather tracks. Between the feathers tracks there are down feathers which are used to keep the body weight. The spine down the middle, called the shaft, is hollow. The vanes are on the two halves of the feather. They are made of thousands of branches called barbs. Because there are many spaces between these barbs, a feather has as much air as matter. They grow from a bump of skin. Growth starts by a tip of a feather. After the bird hatches then the tip separates and looks like fuzz on the baby bird. Pin feathers are rolled inside the sheath. For a bird to survive it depends on the condition of its further. They take a lot of time caring for their feathers and this is called preening. Their feet and beaks are used to arrange and to clean their feathers. They chew each feather from the base to the tip meaning that they bath a lot. Feathers protect the skin of the bird, during winter they can be fluffed up and in summer they can be squeezed down. They also help in making the nest.


Different birds have different types of feathers but all birds have feather on their wings. The wing on a bird serves as the basic structure for flight. The shape of the wing allows the bird to fly. During the flight the tail of the bird also plays an important role, it acts as the rudder balancing and steering the bird. If the tail is turned downward it acts like a brake, helping the bird to stop. Everything about the bird is made perfectly for flying. The entire body inside and outside is designed for flight. Every part must give maximum power with a minimum of weight. The heavier the bird the bigger its wings need to be and the bigger the wings, the more muscles are needed to move them.


The easiest way to fly is to be light. Birds have feathers that are very light in weight. The bones that birds have are made for lightness. Birds have fewer bones than most animals. The bones they have are hard but thin. The biggest bones in flying birds are the breast bone and the shoulder bones. The shape of the wing is called the airfoil. When the wing moves the air goes above and below. The air moving over the upper surface has to be faster than the air on the lower part of the wing. The shape of a wing is called an airfoil. As the airfoil moves through the air, air goes above and below. The air flow over the upper surface has to move farther than the lower part of the wing. In order for the air flows to make it to the edge of the wing at the same time, the top air must go faster.

Reference


1. Wikipedia contributors, the free encyclopedia [Internet] [Cited 2006 May 12] Available From: http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Anials/intermediate/birds-01.html
2. Wikipedia contributors, the free encyclopedia [Internet] [Cited 2006 May 12] Available From: http://animals.about.com/z/js/o.htm?k=birds&d=Birds&r=http%3A//animals.about.com/od/birdsastudyguide/a/introtobirds.htm
3. Wikipedia contributors, the free encyclopaedia [Internet] [Cited 2006 May 12]
http://animals.about.com/od/birdsastudyguide/a/introtobirds.htm


Dianah Nangammbi
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Email: dnangammbi@csir.co.za
http://wwwdianah.blogspot.com/

MORPHOLOGICAL DIFFERENCES BETWEEN CARTILAGINOUS AND BONY FISH

Cartilaginous and bony fishes falls under the kingdom animalia. Vertebrates are organism that contains a back bone and all fishes contains a back bone which means that they are all vertebrates. The morphological structure of the two fishes is totally different. They are both very rough but catilaginous is more rougher.


Cartilaginous fishes are so called because of their lack of the real bone even though their bodies consist of a cartilage. The cartilaginous fishes have strong jaws. The mouth of the cartilaginous fish is found underside of the head, while the eyes are found on top of the head. Cartilaginous fishes also possess the two nostrils which are used for smelling. They can not see food as it enters their mouth. Some Shark solve this problem by touching their food with their nose before they eat. Some use powerful electro sensory system. Sharks, Skates and rays have rough skin. Sharks have five to seven gills slits on each side of their head. But bony fishes have 1 gill on each side. Chimaeras or Gost shark have skins that are very smooth and have only one pair of external gill openings. Cartilage fish give live birth through their bodies, they prefer internal reproduction whereas bony fishes reproduce by laying eggs. Cartilages prefer water with high salt quantity only while bony fishes survive in all types of salt.


Bony fishes are very common and their example include gurnard and snapper. Bony fish are classified into Lobe finned and the Ray –finned. Lobe-finned bone fish includes fish such as lungfish and coelacanth’s, where as Ray-fins includes the goldfish, tuna, and trout. They contains a tail fin which is equal in both the proportion bottom and top. They have a bony skeleton and single pairs of external gill openings. The mouth is generally at the front of the body. It has relatively short tube. Bony fish reproduce by external fertilisation of eggs and releases them into water. The male releases sperm called Milt into water. Milt combines with the eggs and fertilisation takes place.


Their liver is filled with oils which keep them from sinking. They have internal fertilisation. The bones of fish are made mostly by calcium but Shark does not have any bones. Shark skeleton is made of cartilage, and have no bladder, but bony fish have a gas filled swim bladder which enables them to float in the water. Bony fish have movable parts were as shark does not have. Shark can turn around in a smaller space than bony fish.The brain of the ghost sharks is closely related to that of the birds and mammals. As compared to that of the bony fish, the brain of the cartilaginous is ten times to that of the bony fish. While the brain size of the bony fish is thought to closely relate to that of the human beings, the reason of having such a big brain because they use a lot of energy.



Reference

1. Studios, A.R. 1997 Biology for kids vertebrates fish [Internet]. [Cited 2006 May 16] Available from:http://www.biology4kids.com/files/vert_fish.html[2006
2. The wikipedia contributor, the free encyclopaedia [internet] [Cited 2006 May 16] Available from: [http://en.wikipedia.org/wiki/Cartilaginous]
3. Wikipedia contributors, the free encyclopaedia, [Internet] [Cited 2006 May 16] Available from:http://en.wikipedia.org.wiki/Bony


Dianah Nangammbi
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VARIATION IN SHELL STRUCTURE THAT OCCUR IN PHYLUM MOLUSCA

Macology, which is the study of molluscs, defines molluscs generally as soft-bodied animal that usually produces exoskeleton. This external skeleton is called a Shell. A Shell is made up of calcium carbonate (CaCO3). The shell serves both for protection and supporting functions. The one feature common to all molluscs is the presence of a fleshy mantle. This is a fold or lobe (or a pair of them) of fleshy material, which secretes, modifies and lines the shell. These animals need moisture to survive so they live in all parts of the world from deep water oceans to high upon the mountains. There are seven different classes of molluscs which are recognized.


The Gastropoda, this class is composed of 60,000 species. This is where we find species like Snail and Slugs. They have a well developed head with tentacles, often highly developed foot for crawling. Shells can only be formed in fresh waters that are non-acidic, and in the ocean at depths above the level where the water becomes under saturated with Calcium Carbonate. Gastropods show different shapes, colours, patterns and sculpturing of their shell. In some gastropods, the shell is only conspicuously coiled in the early stages when it is still young. The coiling will disappear when the species grows and when it is an adult it will develop a single whorl shell which will be largely expanded. In many other gastropods, the shell has become more reduced or it is completely absent. In other cases the foot and mantle are very large and the mantle has reflexed backwards over the shell so that it becomes totally covered. These animals are no longer able to pull their bodies completely into their shells.


The Bivalves comprise about 10,000 living species. They have two valves made of calcium carbonate. Bivalves are mollusks in which the mantle cavity has been greatly enlarged in size, and whose gills, in addition to their respiratory function, act as a food sorting organ. In some clams, the gills also serve as a brood chamber for developing young. The edges of the mantle in a clam are partly fused to form a pair of siphon that pump and circulate huge quantities of water through the mantle cavity.


The shell and mantle have become enlarged to cover the foot and mantle cavity completely. The head region has atrophied, the radula is totally absent, and the body is flattened laterally. A clam shell consists of two halves or valves usually equal in size and shape, which are connected above by a flexible ligament whose resilience keeps them slightly open at the bottom. The valves of the shell can be shut by the contraction of one or two large muscles. The spring like ligament tends to hold the shell open, while the muscles enable the clam to shut its shell. The molluscan foot has been altered into either a digging organ or a secretor of holdfast fibres, since different kinds of clams can be free-living burrowers, remain fastened to one spot during most of their life, or bore into rocks and wood.

The Scaphopoda have about 350 living species. Tooth shells are occasionally called tusk shells; they are a member of the class Scaphopoda. The shell, which looks like a miniature elephant tusk, is open at both ends. The narrow end often protrudes above the mud or sand in which the animal lives. Water currents enter a long mantle cavity that is lined with simple folds instead of gills.


A combination of ciliary actions and muscular contractions of the foot circulates water and expels waste materials from the narrow end of the shell. Both head and foot can be extended from the broad end of the shell. The foot is modified to serve both in burrowing and feeding, it is used firrt to raise or lower the animal in the substrate to the point where food is available
The Polyplacophora are often considered by scientists to be the most primitive of all existing molluscs. Strictly marine, the majority of the chiton species inhabit rocky seashore environments where their low dome-shaped shells are well suited to withstanding the violent serge of ocean waves. They have a very broad creeping foot and a flattened visceral hump. These organs are protected by an articulated shell of eight calcareous plates whose edges are formed by and embedded in a flexible part of the mantle called girdle.


The Aplacophora are about 250 described species, mostly found in deeper waters. The class Aplacophora, animals also known as Solenogasters consists mostly of small worm-like molluscs that or feed upon the cnidarians. They have no shell, but have calcareous spicules in the body surface. The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body. Aplacophorans have a radula and a posterior mantle cavity. Some are detritus feeders, others are predators.


The Cephalopoda have only about 400 species in existence now. Only the tetrabranchs produce an external shell in this class of molluscs. Externally, the shell of the nautilus is creamy white with broad reddish-brown stripes. Inside it is brilliant, iridescent mother-of-pearl. The nautaloid shell is very complex, chambered and spiraled over the head of the animal. Even though coiled, it is radically different than that of the gastropods, being divided by transverse septa creating internal chambers.


The Monoplacophora are the limpet-shaped molluscs which are segmented like worms. The internal vital organs are duplicated in each segment of this animal.
Monoplacophorans have a single, large, bilateral shell. The shell is a simple depressed limpet or disk -shaped valve, less than 25 millimetres across usually and is often thin and fragile. The outer surface of the adult is covered with a protective sheath. On the inner surface of the shell, there are significant paired muscle scars, suggesting segmentation.


Reference List


1. Wikipedia contributors. Monoplacophora [Internet]. Wikipedia, The Free Encyclopaedia; 2006 April 22, 20:03 [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Monoplacophora


2. Wikipedia contributors. Scaphopoda [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 04, 20:07 [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Scaphopoda

3. Wikipedia contributors. Caudoveata [Internet]. Wikipedia, The Free Encyclopaedia; 2006 April 9, 09:01 [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Caudofoveata

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EVOLUTION CAUSES AMPHIBIANS TO BE LIMBLESS

Almost all aquatic species, mostly marine evolved some 40-50 million years ago from terrestrial tetrapod ancestors during some past ten to twelve million years. All living whales lack hind limbs and have forelimbs modified as flippers. Their limbed ancestors such as the Eocene Ambulocetus natans use paraxial locomotion powered by limbs. When this species are inside the water, locomotion is facilitated by a combination of tail undulation and paddling, which use the pelvic limbs. But now modern cetaceans use oscillatory locomotion. Aquatic mammals rely much less on vision and olfactory senses than terrestrial mammals. A major selective pressure during the transition to the aquatic environment was adaptation to underwater hearing. Some species such as whales, dolphins and others use acoustics for communication, orientation and detecting, recognizing and localizing companions, competitors, mates, predators and prey. The external ears have been lost and thus reducing hydrodynamic resistance during swimming.


Different approaches from paleontology, morphology, development, genetics and molecular biology has tried seek an integrated explanation for whether highly specialized phenotypes such as vertebrates that are not closely related, could result from similar genetic or developmental mechanisms. The origin and evolution of whales was addressed concerning the series of morphological changes that facilitates the progressive reduction and ultimate loss of hind limbs. Genetic evaluation was done on limb loss in snakes and to legs-less lizards, to see whether similar mechanisms which have driven the loss of hind limbs in whales could have been used. Also to see to which degree has such mechanisms diverged in the evolution of similar evolutionary trends shown by limb loss.


Limb loss and concurrent morphological and physiological changes is associated with the transition from land to water are discussed within the context of the current whale phylogeny. This is mostly emphasized concerning the fore and hind limb development, how the fore limbs are transformed into flippers and how the hind limbs are regressed leaving no elements or vestigial skeletal elements. Hind limbs started regressing after the ancestor of whales entered the aquatic environment. Elongation of the body during transition from land to water causes the loss of hind limbs.


In most snakes limbliness was associated with adoption of new lifestyle and was driven by developmental changes associated with elongation of the body. Adaptation to burrowing between the parallel reflect structural and functional changes associated with the switch of locomotion to axial. However, selective pressures acting on a wide range of developmental processes and adult traits other than the limbs could have driven the loss of hind limbs in whales. All limbs less tetrapod are descended from limbed ancestors. Most possess limb buds at some stage during their development. Limbless ness represents arrest of limb bud development rather than absence of limb initiation or regression of a fully formed limb.

Reference

Andrews, R. C. 1921. [A remarkable case of external hind limb in a hump-back whale] [Cited on 2006 05 10] Available from:
http://whitelab.biology.dal.ca/lb/Bejder%20and%20Hall.pdf


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SIGNALS USED BY INSECTS TO ATTRACT A MATE FOR SEXUAL REPRODUCTION

Insects have both male and female species that mate and reproduce sexually. Some insects reproduce by lying eggs while in some the egg hatches inside the female and are born after a short time. During other seasons of the year the males are not available to mate with the female but species like aphids still reproduced.


Different insects use different semiochemicals to attract their mating partners. Semiochemicals are chemicals that mediate interactions between organisms. These chemicals are divided into allelochemicals and pheromones depending on the nature of interactions if it was interspecific or intraspecific. Allelochemicals are those chemicals that important to individuals of a species that are different from the source species. These chemicals are also subdivided into different groups depending on whether the respond of the receiver is comfortable with the emitter not the receiver or the chemical is favourable with the receiver not the emitter or is favourable to both emitter and the receiver. Both allelochemicals and pheromones it is always useful to refer to chemicals as arrestants, attractants, repellents, deterrents, stimulants or other descriptive terms. These terms can indicate what behaviour is involved in the response such as a feeding stimulant or flight arrestant. Pheromones are released by a certain species with the effect of having the attraction to the same kind of species.


Insects have different ways they use to attract each other like in the case of the moths. The female moths have scent glands on the abdomen that secrete pheromones. These chemicals are secreted to attract the male moth. The male moth can detect these chemicals at a distance of four to eleven kilometres. Sometimes the males secrete pheromone just to induce the females so that they mate. Insects like butterflies use colour and movement. The males will be attracted by the coloured imitations of females and in the same time they will be chasing the other male away. Male flies also form a compact swarms that attracts the female.


Sound is also used as a way to attract each other sexually. The male mosquitoes are attracted to the note or sound produced by the wing vibration of the wing. Female grasshoppers, crickets and cicadas are attracted by the sound produced by their males. Crickets use the burrows to resonate the sound, the cicadas use their large empty space in their abdomen and the substrate vibration helps the leafhoppers to communicate. After mating the males have different methods they use to protect their sperm from other males. Some guard the mated female preventing her from mating with other males. Extended copulation is also used which also prevents other male to mate with her for that period. Some produce accessory glands which produce chemicals that plug the vagina after mating thus giving her an opportunity only to mate once. Other males use genital apparatus that push the new arriving sperms back out of the way in the female spermathecae. If the female has already mated, other male have scoops which remove sperms of the previous males from the females systems.

Reference

1. Insects and bugs Information [Internet] [cited 2006 05 08] Available from: http://www.ivyhall.district96.k12.il.us/4th/KKhp/1insects/buginfo.html

2. Neuroendocrine control of reproduction in insects [Internet] [cited 2006 05 08] Available: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7186527&dopt=Abstract

3. How do the sexes find each other [Internet] [cited 2006 05 08] Available: http://bugs.bio.usyd.edu.au/Entomology/InternalAnatomy/reproduction.html

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HOW PLACENTA MAMMALS HAVE COLONIZED LAND, WATER AND AIR

The placental mammals are very diverse species and range from elephants, whales, shrews, and armadillos. They also include pets such as dogs and cats, as well as many other animals such as sheep, cattle, and horses. It is also recognised that human being are also the placental mammals. They form a very diverse group of species and their young’s are born at relatively advanced stage as compared to other mammals.


The placentals mammals include about 4300 species, making it by far the largest of all three mammal groups. Young placental mammals spend a relatively long time developing inside the body of their mother before birth. They are protected within the womb, which is nourished by a spongy organ called the placenta. This serves to absorb nutrients from the blood of the mother and transfers them to the developing animal. By the time a young placental mammal is born, it is usually fully developed, although it may not yet have fur, functioning eyes or teeth.


Some placental mammals have adapted to survive in the water, land and air. They have developed different body shapes and sizes, which act as the driving forces behind colonising water, land or air. They have wings to survive in air, feet to survive in land and gills to survive in the water. Species such as Seal, sea lions and walruses as for example, have adapted to live in both land and in the water. These species do sleep and feed in the ocean but they return to land in order to reproduce. However, manatees and dugongs are large, plant-eating mammals that spend their entire lives in the water.


In the same manner, whales and dolphins are well adapted as fast, open-ocean predators. Most aquatic animals still need to breathe because they can drown, but whales and dolphins are truly pelagic, meaning that they wander far out into open water. These marine placentals mammals colonize areas where food is abundant and where the water temperatures is low. They survive the cold temperature in two different ways; firstly -Others such as sea otters and fur seals have a double coat of fur, with extremely dense under fur hairs that are so closely packed that the skin never gets wet. Secondly -whales have very sparse hair, and keep warm with a thick layer of fat called blubber. Such characteristics enable this species to survive even in low temperature.


In addition, dolphins have adapted for an aquatic lifestyle, by having flippers that help them glide through the water. The manatees and dugongs are large, plant-eating mammals that spend their entire lives in the water. Contrary, the jaguar, a terrestrial carnivore has explosive running power, which enables them to survive on land. This species colonise the land and most of its prey lived on land. Other species such as bat have evolved limbs into wings that enable them to inhabit the skies. Generally, mammals have adapted to some of the most extreme habitats on earth. They are warm-blooded, or endothermic, meaning that they maintain their body temperature within a narrow range despite changes in the environment.

Reference


1. Wikipedia contributors, Whales [Internet] The Free Encyclopedia, [ Cited 2006 May 12]
Available From:
http://encarta.msn.com/encyclopedia_761565254_2/Whale.html

2. Mammal, [Internet] [Cited 2006 May 12] Available From:
http://encarta.msn.com/encyclopedia_761561349/Mammal.html


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REVISION SHOWING THAT DINOSAURS WERE WARM-BLOODED ANIMALS

The dinosaur fossils are dated about 230 million years ago. The oldest dinosaur known in the world was found in Madagascar, which is a place situated on the South East coast of Africa. The first dinosaurs that were found were slightly built and their height was about 3 to 3.5 metres long. They have very different diets, some were carnivores, herbivores, omnivores and others were insectivores.


There has been a great confusion going on about whether dinosaurs were warm-blooded or cold-blood. Scientists have conflicting opinions on this matter. Paleoanthropologists think that all dinosaurs were warm-blooded as modern mammals and birds because they have the same metabolic rate. Other scientists think that the biggest dinosaurs could have warm bodies because of their large body size. Generally if all the animals were examined at a proper time they will all appear to be warm blooded because their internal bodies are the same.


The mechanism by which the body temperature is maintained is more important. This can be explained simply by using two terms which are ectothermic and endothermic. Ectothermic animals rely on heat from the outside environment to maintain their body temperature while endothermic animals use the heat generated from inside their own bodies by the metabolic process, they are composed of bodies with a higher metabolic rate.Once it was believed that all dinosaurs were cold blooded but now much evidence proves that at least some were warm blooded. All creatures whether warm-or cold-blooded use the same biochemical processes, enzymes and substrate to produce energy. All chemical reactions involved have a particular optimal temperature. If there is a drop of temperature then the process will be very slow.


There is no definite answer about whether dinosaurs are warm- or cold- blooded but in the 1970s scientists began to look at some evidence showing that dinosaurs were maybe warm-blooded. Recent studies are showing that dinosaurs were neither warm-blooded like mammals nor cold-blooded like reptiles but in between.


The isotope of their bones shows that they are warm-blooded. Warm-blooded animals grow more quickly than cold blooded ones. Dinosaurs grew very fast; this was proved by Jack Horner through the bones of a tiny baby dinosaur found in hadrosaur nests. The bones show that baby dinosaurs reach a considerable size while still in the nest. Additional evidence about the growth was found in the microscopic structure of the bones where it was observed that dinosaur bones are rich in the passage ways called Halversian canals which transport nutrient-laden blood to the cells that lay down new bones. This conflict will never end because recent studies also show that the heart of a herbivore dinosaur was studied and it consisted of four chambers instead of three which is common in a warm-blooded animal.


If dinosaurs were warm-blooded then we could expect that their lives were more like mammals than reptiles, because reptiles are like snakes and lizards spend most of their time moving from one place to another looking for a warm area just as they do during winter when they hibernate.


Reference


1. Feduccia, A. 1974. Dinosaurs and Archaeopteryx [Internet] [Cited 2006 May 10] Available From:
http://www.isgs.uiuc.edu/dinos/de_4/5c51d90.htm

2. Bakker, R. 1972. Anatomical and Ecological Evidence of Endothermy in Dinosaurs [Internet] [Cited2006 May 10] Available From:
http://www.dinoruss.com/de_4/5c51d90.htm

Dianah Nangammbi
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DIFFERENCES BETWEEN NEW WORLD MONKEYS AND OLD WORLD MONKEYS

Monkeys grow well in the subtropical and tropical regions of South and Central America, Asia and Africa where they are mostly dominated. "New world monkeys belong to order Platyrrhini they are limited to tropical environments and they are mostly herbivores. They feed on fruits, nuts and gums some also prey small insects. There are about 53 species of new world monkeys and they are divided into three families and sixteen genera these families include Callithricidae, Cebidae and Atelidae. The old world monkeys belong to the order Catarrhini which consists of two superfamilies. The platyrrhini evolved from the ocean"(1).

The new and old world monkeys look similar if you are observing them from a distance but if you take a close look you can see some unique and distinctive difference between them. These two monkeys can be easily differentiated looking at faces. "The new world monkeys have a flat face and their nostrils are far apart and open on the side. They have three molars which are very large but in most cases the last molar is smaller and in some monkeys they are not there. The ear of the new world monkey has a trampanic membrane connected to the external ear by a bony ring"(2).
They have different tails, but some species like howlers and spiders are composed of prehensile tails. The thumb orientation of their hands lies in the line with other digits while opposing the next digit in a scissor like grip. Some species like spider monkeys have lost their thumbs. Male species contribute a lot when it comes to infant care.

The old world monkeys have a down facing nose with nostrils that are closer together and open down ward and sometimes forward. "They have two premolars, premolar found in the mandible is sectorial meaning that it is specialised for sharpening the upper canine and their molars have sharply connected cusps. The tympanic membrane is connected to the external ear by the bony tube which is visible on the outside of the skull. Old world monkeys have tails all of them but they lack prehensive feature. These tails are considered as the sitting pads as the monkeys sit on trees"(2).

"The thumbs are more like of modern people, they are rotated and more opposed. In some monkeys the thumbs are reduced or absent. The fingernails and toenails are present at all types of monkeys. The old world male monkeys do not have a close relationship with their infants except the gibbons and the siamangs. They tolerate wide range of habitats, including rainforest, through savanna fringe or open savannah to semiarid regions. Many spend most of their day underground"(2).

Reference

1. Wikipedia contributors. Monkeys [Internet]. Wikipedia, The Free Encyclopedia; [Cited 2006 May 15], Available from: http://en.wikipedia.org/wiki/Monkeys

2. Anthropology 1, new world (America) and old world (Africa and Asia) monkey: A comparison, [internet] [cited 2006 May 11] Available form:
http://www.cabrillo.edu/~crsmith/monkeycomparisons.html

Dianah Nangammbi
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Tel: +27 12 841 2133
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COMPARISON BETWEEN PLACENTAL AND MARSUPIAL MODES OF REPRODUCTION

Marsupials are animals that belong to the order Marsupiala and an infraclass Metatheria. Other members of the class include kangaroo, koala, Tasmanian devil and the Virginia opossum. Marsupials are also defined by biologists as a subdivision of mammals with several characteristics. They have more incisor teeth and in most of them the first toe of the hind foot is opposed to the other four and it also lack a claw. Their brain size is very small. They are generally accepted as non-placental mammal whose female carries her young in a pouch or marsupium, where young ones are provided with a proper environment, warmth, possess a placenta, although that placenta is non-invasive and functions in the transferring of nutrient and waste for a short period of time.



Placenta mammals are given this name because the placenta connects the growing embryo within the uterus to the circulatory system of the mother. It is the pathway provider for the nourishment of the fetus. This enables the fetus to reach a higher level of maturity of the body and brain before birth, most of the placenta mammals invest most of their time in the stage of growth.



The major difference between the marsupial and placental mammals is the rate of gestation, or the time the offspring has taken in the uterus. Mating system vary in marsupials throughout the year. Some species are solitary and they only come together to mate and this pattern of social behaviour reflect promiscuous mating systems. Male of some species defend their access to several females. In marsupials the developing embryo is separated from the body of its mother by amniotic membrane. After fertilisation the embryo will become a new organism and the immune system will attack it. The amniotic protects the embryo from this attack by isolating it from all biological interactions with the parent. The Marsupial embryo depends on the egg yolk for nutrients so it is limited to the quality of nutrients contained in the egg. The shortness of the gestation period is due to the type of yolk-type reproduction. Birth in marsupials occur very fast compared in placental mammals including the helpless fetus journeys to the pouch where it becomes attached there for weeks or months depending on the species. The longest days a marsupial can spend in a reproductive tract are only twelve.



Placental mammals have a longer gestation period and this result in offspring that are born being fully developed. The extended maturation of placental is caused by the placenta which, which allows nutrients to travel from the mother's system to the embryo and waste to be carried away. The embryo and the mother do not share the same blood supply, but instead the placenta is composed of several layers which are richly supplied with blood vessels, and acts as a preferential immigration barrier letting nutrients and metabolites pass through, and preventing the transfer of immunity system components.



If marsupials are pregnant it does not stop the oestrus cycle to take place but in placentals the oestrus cycle stop until the whole period of pregnancy is over and it will then re-start again. In marsupials the ovarian inhibition is mediated by lactation or suckling stimulus. These regulatory modifications are important because the baby will no longer be carried internally so negative feedback stimulus from the presence of the babies must come from nursing activity.


Reference



1. Oppossaum Reproduction and Life Cycle [Internet] [Cited 2006 05 11] Available From:
http://www.opossumsocietyus.org/opossum_reproduction_and_life_cycle.htm



2. Andrienne, L. 2001. The Human Evolution Coloring Book [Internet] [Cited 2006 05 11] Available From:
http://www.pbs.org/wgbh/evolution/library/01/4/pdf/l_014_02.pdf


3. Culp, G. Richard. 1998. The Geographical Distribution of Animals and Plants [Internet] [Cited 2006 05 11] Available From:
http://www.nwcreation.net/marsupials.html


Dianah Nangammbi
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Tel: +27 12 841 2133
Cell: +27 73 121 3589
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