Recently, in Term 2, since I was taught about Ecology, I started having an interest in sharks, and how they adapt to the environment as the ferocious and hardy creatures they are.
Adaptation of Sharks

Basically, sharks are a type of fish with a full cartilaginous skeleton and a highly skeleton and streamlined body. Did you know the earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs. Scientist has only found 440 species of sharks. Ranging from small-sized dwarf shark to the enormous whale shark, which can grow up to approximately 12 metres and which feeds only on plankton, squid and small fishes by filter feeding. Sharks are found in all seas and are common down to depths of 2,000 metres. Most sharks lived in the ocean but some sharks like the bull shark can live in fresh water too. All sharks breathe through 5 to 7 gill slits and they do not have scales but a toothed-like skin which enable them to shark faster.
 
Firstly, what is adaptation?
- The evolutionary process whereby a population becomes better suited to its habitat. This process takes place over many generations, and is one of the basic phenomena of biology.
- A feature which is especially important for an organism's survival and reproduction.
- Produced in a variable population by the better suited forms reproducing more successfully, that is, by natural selection.

Sharks’ adaptation to Biotic Factors
- Sharks have a large oily liver and light cartilaginous skeleton, unlike fish that have a swim bladder to regulate buoyancy. These adaptations allow the shark to control their buoyancy in water. With an oil filled liver instead of a swim bladder, sharks are able to make fast changes in depth without having to wait for gas pressure to be equalize, which is a necessary adaptation for pursuing preys in the depth of the surface to 100m. Did you know that even though sharks’ cartilage is about half as dense as bone and the liver constitutes up to 30% of their body, sharks still have to keep on swimming or they would sink. To prevent sinking, the sharks employ dynamic lift to maintain depth. Some sharks such as Sand Tiger sharks store air in their stomachs, using it as a form of swim bladder. However, certain shark species, such as the nurse shark, are capable of pumping water across their gills, allowing them to rest on the ocean bottom.
- Most sharks have streamlined body, which are torpedo shape; this will enable the shark to swim faster so as to pursue prey. Also, the shark have a tailfin with a longer lobe, which is necessary as it provides a downward driving force to balance forward lift caused by the pectoral fins and flat ventral surface of the snout.
- All sharks have dermal denticles, which feel like sandpaper. This will channel the surrounding water to produce laminar flow, which lowers friction, making the shark hydrodynamic. With the shark having lesser water resistance, the shark is able to swim much faster, allowing it to hunt for its prey easier.
- Another adaptation of many predatory shark species have a nictitating lower eyelid, such as the Tiger Shark, which slides across the eyeball allowing the shark to protect its most vulnerable organ at the time of the attack. However, some sharks like the great white shark, do not have the nictitating eyelid. Instead of using the eyelid, they roll their eyes backwards, preventing injuries in their eyes from the threshing of prey.
- A sharks’ most important sense is smell. It is so powerful that sharks are able to niff a tea spoon of blood in an Olympic size pool, sharks can smell up to 100m or more. Once the shark identifies the scent, it will start swimming. The sharks’ natural swimming motion of moving its head back and forth provides further assistance in determining where the scent is coming from. With each movement, the snout picks up more water for the shark to analyze, and the shark is able to tell whether it’s coming from the right or left nares. This helps them determine which way to swim. The shark’s nose may work so well because it does not have to do anything else. Shark use their nose just for smelling and the sharks’ sense of smell is not connected to its mouth so sharks often do not know how something is going to taste until they have taken a bite. With this keen form of smell, sharks are able to locate weak, injured and old preys, making it easier for the shark to hunt for its prey.
- Sharks have probably the most efficient teeth in the animal world as they are able to remove tissues/flesh up to 10kg or more from their prey from just a single bite. The teeth are arrange in rows, which moves up when those that are in used are damaged or lost in the struggle with the prey. This process will last a life-span, meaning to say that the sharks will continuously have teeth. It was said by some researchers that sharks can lose up to 5000 teeth per life time. Their teeth also get replaced by bigger teeth as they get bigger. The bite-force of a shark can be enormous, with a large force of 18 tons per square inch. Different teeth have different functions. The Mako’s and Sand Tiger’s have fang-like teeth for seizing and holding their fast moving prey, in which the prey is swallowed whole. In another case, the Great White Shark have large triangular teeth for cutting large cunk of flesh from its prey.
 
Sharks’ adaptation to Abiotic Factors
- Salinity. Sharks tend to live in salty water, however there are still sharks that are able to live in fresh water, such as the bull shark.
- Temperature. For every shark, there is a different amount of temperature for the shark to survive. Great white sharks live in water where the temperature is between 12°C and 25°C (54°F to 78°F), while nurse sharks tend to stay in warm waters.

Habitat
The approximate 500 different shark species can be found in all of the oceans and the vast majority of the seas throughout the world. Because water covers an enormous percentage of the earth’s surface, this implies a significant number of animals inhabiting its depths. There are a small number of shark species that are able to live in freshwater rivers and lakes as well. Most sharks live between the water’s surface and 2000 metres down. It is rare to find sharks living at 3000 metres or more below sea level, but it has been witnessed, such as the goblin shark. Sharks tend to prefer the shallower continental shelf areas. This is because these are the areas at which rivers deposit nutrients into the oceans. These nutrients feed the marine lives in this water from a cellular level, which, in turn, feed larger and larger species. The chain continues until it reaches predators such as sharks and even human beings, who feed off fish, crustaceans and molluscs.

The Carbon Cycle

Recently, in Term 2, under the topic Ecology, I was taught about the Carbon Cycle.
The Carbon Cycle exists in the ecosystem and plays a very important role in it. Carbon is found in every ecosystem, because every living things, whether it is humans, tigers or even plants, are composed of carbon compounds. The atmosphere is the main source of carbon for all ecosystem. The Carbon Cycle also ensures that there is a continuous supply of carbon dioxide for plants to carry out photosynthesis, which in turn produce oxygen and food, which is necessary for living things to survive. With food produce, it enables energy to flow through the ecosystem.
So, how does the process work? The following is the process taken:

Photosynthesis
- Carbon is absorbed in the form of CO2, carbon dioxide and is converted to glucose which may then be used for respiration and for building of protoplasm in plants.
- The plants are then consumed by primary consumers, which carbon and energy is then transferred in to them. With successive feeding, carbon compounds move up to higher tropic levels in the ecosystem.

Respiration
- When plants and animals respire, carbon dioxide is released into the atmosphere.

Decomposition
- As organisms die, they decay and decomposed, which releases carbon dioxide back into the environment.

Destruction of vegetation
- As bush fires occurs, plants are being burnt down by large forests which releases large quantities of carbon dioxide into the environment.

Sedimentation and Mineralization
- In the form of fossils where carbon is stored into organism which did not undergo decomposition when they died.
- Found in shells of organisms in the sea where they are in the form of bicarbonate. When the organisms die, their shells sink to the bottom of the sea and become compacted. Over a long period of time, they become limestone(calcium carbonate) which stores carbon.

Differences between Male and Female Gametes

Recently in Term 2, under the Biology topic of Reproduction in Animals, I learned about the two different animal gametes, the sperm and the egg. I have thus come up with a comparison chart between the two gametes to give myself, as well as others a better understanding of the two gametes of the male (sperm) and female (egg).

Criteria for Comparison	Female Gamete	Male Gamete
Amount of cytoplasm	A lot of cytoplasm to provide nourishment for embryo	Little cytoplasm to decrease weight to enable it to move faster
Shape	Spherical	Streamlined so that there is less resistance in swimming towards ovum
Presence of  tail	No tail, non-motile since it is swept along oviduct by cilia/peristaltic contraction of muscles of oviduct movement not necessary	Has a tail/flagellum/motile to allow it to swim in the egg
Amount per release	Only one is released per month	Released/produced in larger/greater number To ensure survival/ due to high mortality rate in vagina To ensure successful fertilization
Jelly coating	Contains jelly coat that contain receptor for the sperm to bind	Jelly coat/ zona pellucida
Acrosome Level	No Acrosome	Contains Acrosome that contains enzymes that breaks down layers surrounding egg
Mitochondria Level	Contains few mitochondria as it is non-motile, thus requiring less energy	Contains many mitochondria to provide the sperm with energy to swim

Science Graphic Organiser- Reproduction in Animals

Recently, in Term 2, under the topic Reproduction in Animals in Biology, I was tasked to do an optional graphic organiser on the female menstrual cycle. It is indeed a complex topic, but having done adequate research and listening intently to my Science teacher, I have grasped the paramount yardstick to this topic, having understood most of it. To have a closer look at my graphic organiser above, please click on the picture above, or on this link. Thank you!

Science for Fun Enrichment Workshop

Science for Fun Enrichment Workshop Reflections on 12^th April 2011

From today’s Science for Fun enrichment workshop, I have learnt many new and interesting science facts. In the workshop, there were activities such as ‘Moving Air’, ‘Human Battery’, ‘Eye Model’, ‘Tornado Tube’, ‘Top Secret’, ‘Pineapple Gelatin’, ‘Lava Lamp’, ‘Blue Bottle’,  and ‘Absorption of Heavy Metal Ions’. 

For the ‘Moving Air’ activity, the setup consisted of a hair-dryer on a retort stand a ping-pong ball, and a Styrofoam cup with a hole at the bottom. The ping pong ball floated above the hair-dryer when it was turned on, and the Styrofoam cup directed the air from the hair-dryer. The ping-pong ball floated gently above the hair-dryer without falling off. 
For the next activity, the ‘Human Battery’, it consisted of a circuit with two metal plates, copper and aluminum. It was supposed to show a voltage when someone places hands on each plate. For the next activity, the ‘Eye Model’, it was a setup consisting of a plastic eye, and it showed how long sightedness and short sightedness can be cured by using appropriate lenses. Lenses could be slotted into the eye, which was filled with water, and an image from in from of the eye could be seen from a plastic piece inside, which was supposed to be a retina. 
For the following activity, it was a setup consisting of two bottles fixed together by the heads with one bottle nearly filled with water. When shaken upside down, the water formed into a vortex and flowed into the lower bottle. 
The following activity was ‘Top Secret’, which consisted of a magnetic top being spun on a magnetic stand. 
The next activity was ‘Pineapple Gelatin’. It was a setup consisting of pineapple gelatin, pineapple juice, and water. Different mixtures were added into test tubes and the test tubes were cooled in a cooling tray for a few minutes. Two out of the three test tubes filled with some of these mixtures solidified, while the first test tube had its mixture remaining in liquid form. 
For the next activity, it was a demonstrative experiment shown by one of the trainers. Some coloured water was added into a bottle of oil. As oil is lighter than water, the oil rose above the coloured water. Next, an Alka-Seltzer tablet was dropped into the oil and water. It sank to the bottom, being denser than both the liquids. When the tablet started to dissolve in the coloured water, carbon dioxide gas was produced. The gas rose above the oil, carrying some of the coloured water with it. The liquid sank to the bottom after reaching the top, when the gas escapes. 
For the next experiment, the ‘Blue Bottle’, the experiment consisted of glucose solution, sodium hydroxide solution, and Methylene blue solution. First, the sodium hydroxide was mixed with the glucose. Next, the Methylene blue solution was added in. The solution turned blue, and was left to stand for a few minutes. After a while, the solution lost its blue colour and turned colourless. However, when the bottle that the solution was in was capped and shaken, the solution turned blue again. 
For the last activity, it was ‘Absorption of Heavy Metal Ions’. It was about putting samples of copper (II) ion and orange peel, reacting, and the solution was put in a machine to be read. The concentration of the solution was then found. 

Overall, I liked the ‘Eye Model’ activity the most, as I found it very interesting, as it showed how the human eye worked, and how the image seen would be inverted on the retina. I feel that this Science for Fun workshop was an enjoyable experience for me, and I look forward to a similar enriching workshop like this in future.