Mechanism of Muscular Contraction : Sliding Filament Theory

Mechanism of Muscular Contraction : Sliding Filament Theory

1. Action potential spreads through T tubules. This stimulates release of Ca2+ ions from sarcoplasmis reticulum.
2. Ca2+ ions binds to troponin & rearrange the troponin-tropomyosin complexes. Tropomyosin movesaway to expose binding sites on actin filaments.
3. ATP attaches to myosin head & is hydrolysed into ADP.
4. High energy myosin head binds to exposed binding site on actin filament, forming cross-bridges (actomysosin bridges).
5. Myosin head bends 45 degrees & pull actin filament towards centre of sarcomere. (ADP is released)
6. ATP attaches to myosin head again. Myosin head detaches from binding site, swings back & reattaches again. This is 'ratchet mechanism'. Actin filaments are pulled closer towards centre of sarcomere.
7. Muscle contracts.

Ornithine Cycle

Chapter Homeostasis : Ornithine Cycle

• NH3 combine with CO2 & H2O to form carbomoyl phosphate.
• Carbomoyl phosphate react with ornithine to form citrulline. This process occurs in matrix of mitochondria in liver cells.
• Citrulline react with aspartate to form argininosuccinate.
• Argininosuccinate breaks down to form fumarate & arginine. Fumarate enters Krebs Cycle.
• Arginine is hydrolysed by H2O to form urea & ornithine.
• Ornithine is released & reused.
• Urea is carried to the kidneys to be excreted in urine.

Munch's Pressure (Mass Flow) Hypothesis

• Leaves are 'sugar source'. Sugar diffuse from mesophyll cells into the sieve tubes of the phloem through symplast route/cytoplasm.
• Concentration of sugar in sieve tube is high, causing water potential in leaves to decrease/low.
• H2O enters sieve tube from the xylem, creating high hydrostatic pressure.
• Growing roots, shoot tips, stems & other parts of the plants are 'sugar sink'.
• Sugar diffuse out of sieve tube/phloem into 'sink tissues'. Water potential in 'sink tissues' decreases.
• As a result, H2O moves into other cells by osmosis, creating low hydrostatic pressure in sieve tubes.
• The hydrostatic pressure gradient formed between 'sugar source' & 'sugar sink' drives mass flow of H2O.

Photosynthesis: Light Reaction & Dark Reaction

Light Reaction

Non-cyclic photophosphorylation : produce ATP & NADPH

• Reaction centre for photosystem II is P680.
• H2O is broken down to provide 2 electrons and O2.
• 2 electrons excited by light energy and achieve high energy potential/energy level, accepted by phaeophytin(primary acceptor).
• 2 electrons flow to/received by plastoquinone, received by cytochrome complex, received by plastocyanin, and received by photosystem I(ADP is used & ATP is produced).
• The flow of electrons provide the energy to pump protons across the thylakoid membrane. This activates ATP synthase to produce ATP.
• From photosystem I, the reaction centre is P700.
• The 2 electron excited by light energy and achieve high energy level, and accepted by FeS.
• 2 electron flow to/received by Ferredoxin and received by NADP reductase.
• Enzyme NADP reductase converts NADP+ to NADPH and H+ ion.

Cyclic photophosphorylation : produce ATP only

• Reaction centre for photosystem I is P700.
• 2 electrons excited by light energy, achieve high energy level, accepted by FeS(primary acceptor).
• The 2 electrons flow to/received by Ferredoxin, received by cytochrome complex, then received by plastocyanin, then received back by photosystem I.(ADP is used & ATP is produced).
• The flow of electrons provide energy to pump protons across thylakoid membrane. This activated ATP synthase to produce ATP.

Dark Reaction

Calvin Cycle

• CO2 combines with 5 carbon compound, RuBP with the help of enzyme rubisco to form unstable 6 carbon compound.------>(CARBON DIOXIDE FIXATION phase)
• 6 carbon compound  split into 2 molecules of 3-phosphoglycerate/phospho-3-glycerate.
• 3-phosphoglycerate undergoes a series of reduction processes to form glycealdehyde-3-phosphate/triose phosphate. ATP & NADPH is used.------>(REDUCTION phase)
• Glyceraldehyde-3-phosphate undergoes regeneration to regenerate RuBP.------>(REGENERATION OF CO2 ACCEPTOR phase)
• Some glyceraldehyde-3-phosphate assimilate to form carbohydrates, lipids, & proteins.------>(PRODUCT SYNTHESIS phase)

DNA Replication Essay

DNA Replication

Using the image above as reference, this is a simple way to memorise the process.

• Enzyme helicase unwind the parental double helix.
• The single strand binding proteins stablise the parental DNA
• The leading strand is synthesised continously in the 5' to 3' direction by DNA polymerase III
• The lagging strand is synthesised discontinuously. Primase synthesises a short RNA primer to form Okazaki fragment
• RNA primer is replaced by DNA polymerase I, then DNA ligase joins the Okazaki fragment to the growing strand.

Argumentative Writing: 'People are becoming more materialistic. They are concerned with making more money and what money can buy. What is your opinion on being materialistic?'

People are becoming more materialistic. They are concerned with making more money and what money can buy. What is your opinion on being materialistic?

          "Life shouldn't be printed on dollar bills". This quote from Clifford Odets tells us that life does not necessarily revolve around money and material wealth. As time proceeds into a modern era, money and materialism have been one of the most influential forces in the world. Some may think that money and wealth is the way of life. They believe that everything luxurious in this world has a price and only by accumulating money and wealth can one enjoy them. In my opinion, I think that people really are becoming more materialistic. This essay will discuss how materialism has affected people, the modern society, and the country's economy.

          Materialism has geared individuals towards the path of making more money. This is so that they can afford life's indulgences like a spacious home and expensive delicacies. They are driven by the want to enjoy a carefree and luxurious lifestyle that seems so popular nowadays. In addition, people work hard to earn more income for the purpose of affording expensive and branded items such as Chanel handbags, IPhones, and tablet personal computers. As people become more focused on wealth and improving living standards, they tend to forget matters that are substantial in life, namely health, family, and friends.
         A materialistic mind-set can drive people to overspend or buy things that they cannot afford yet. This will give a domino effect on the country's economy. Of course, the spending power of the society can help to boost the economy, as they increase sales and business opportunities. However, when people overspend to extreme ends using plastics money or credit cards and take loans that they cannot afford to reimburse them, the country's debt margin will surely rise. For instance, in America, banks are giving loans to individuals who aspire to own big houses that they cannot pay for. Their inability to pay for it became one of the factors that caused the collapse of America's economy.
          Materialism has also affected people's spiritual and moral beliefs. Some people are fortunate enough to have a proper occupation that they can work hard for, but some people who are jobless or have low income can also develop avaricious characteristics. Since they cannot afford the treats in life yet desire it, they can turn to a life of crime for the resolution to satisfy their materialistic needs. This can be observed through the increasing crime rates for theft, break-ins, snatch thefts, frauds, blackmail, kidnapping for ransom, and bank account hacking. Those who commit these crimes are materialistic criminals that lost sight of moral and spiritual values as they are blinded by greed and wealth. Besides that, parents may neglect their children's emotional and spiritual needs because they are fully engrossed in money-making activities. Despite all the comforts and extravagance, the children can become lonely and crave for parental affection, and thus indulge in bad habits like smoking or vandalizing public property as an act to eradicate the loneliness or seek attention.
          In conclusion, materialism is becoming a common quality in the 21st century. People are compelled to work harder to afford indulgences beyond their reach. Even though materialism may spur individuals to strive in life to improve their way of living, the act of overspending can lead to the downfall of the one's well-being and the economy. For me, I believe that money is not everything in life. It is undeniable that without money, one cannot survive in this harsh world, but having money in abundance in meaningless when one is unhappy. As quoted from Virgil, "The greatest wealth is health." I think that there are more significant things in our lives that seem to be overshadowed by our busy daily lives and worldly delights, and they are family, friends, health, and true happiness.

(626 words.)

Band 4

Argumentative Writing: ‘Closed Circuit Television (CCTV) plays a significant role in deterring crime and anti-social behaviour’. Give your opinion.

‘Closed Circuit Television (CCTV) plays a significant role in deterring crime and anti-social behaviour’.

Give your opinion. You should write at least 350 words. Illustrate your opinion with examples.

               Crime prevention has been somewhat a battle that most authorities face as they try to come up with new measures to deter crime and anti-social behaviour among citizens. One of the ways to prevent these problems is by using Closed Circuit Television (CCTV) in places where there are crime risks such as shopping malls and banks. The CCTV can be defined as the use of video cameras to transmit signals or images to a specific place or set of monitors, which allows close monitoring and surveillance. Nowadays, CCTVs are widely used to prevent crimes and some are installed in public areas. I agree that it plays an important role in preventing crime and anti-social behaviour. Since crime and anti-social behaviours such as theft, rape, and other inconsiderate acts can cause damage to our society, measures such as installing CCTVs in certain areas can be used to deter such acts.

                The act of breaking the law or anti-social behaviour such a vandalism of government property are done because the criminals believe that there is no one or no authorized personnel watching their wrongdoings. They believe that they can escape from the law because there is no evidence or witness to the crime. By installing CCTVs in areas where the crime rate is high, for example, parking lots or car parks, crimes like car theft can be reduced. In a survey done by Northeastern University, it was analysed that the surveillance cameras have helped in crime reduction, with a decline of 51% crime rates in parking lots. Recently, more people are installing CCTVs in their private residence to stop break-ins. Criminals become discouraged when they see these devices. This is because the cameras may record the criminal’s actions and their faces. The cameras’ presence in the area can curb the criminals from committing the crime for fear of being recorded on tape. Besides that, the technology of surveillance cameras have improved throughout the years, providing high quality and high definition videos and images that can capture the details of people’s physical appearance with the exact time and place. This may well instil hesitation and fear in the hearts of law-offenders, thus dampening their urge to commit crimes.

                The CCTVs do not only discourage the acts of crime, but it serves as providing critical evidence for certain crimes. For example, CCTVs were substantially useful in the murder of James Bulger in England in the year of 1993. As James’ mother was momentarily distracted in the shopping mall where they were shopping, the surveillance cameras in the shopping mall recorded scenes of how 2-year-old James was abducted by two 10-year-old boys, Jon Venables and Robert Thompson. They brought him out from the shopping mall and to several places before finally murdering him near a cemetery. The video footage documented by the CCTVs of the shopping mall were attained and displayed in national television by the media. A woman who knew Venables and that he had played truant with Thompson that day, saw the video and recognized him. She immediately contacted the police and the two boys were arrested. Clearly, if it had not been for the video, the boys would not have been recognized, and they may have caused other murders or anti-social behaviours which pose a definite threat to people, in this case, small children. The CCTVs have helped to create hard evidence that is unchallenged.

                CCTVs have been a very modern measure in reducing crime rates, but some people argue that it actually displaces crime, rather than deterring it. Easily-available mini CCTVs have been known to be used for criminal activity. It can be install at automatic teller machines (ATM) to steal people’s personal identification number without them knowing it. Apart from the fact that it may violate people’s privacy, the CCTVs’ videos are easily hacked and obtained. Some may use these videos illegally for their own use, usually for artistic purposes. In addition, some people think that the CCTVs cannot prevent crime, because crime prevention can only be done through education or correction of behaviour. They think that the surveillance cameras do nothing to inhibit crime, as in some occasions, crime still occur even though the cameras are present. For instance, a bank can still be robbed even with CCTVs operating for 24 hours. During robbery, the robbers can very well conceal their faces from the recording cameras simply by wearing a mask or cloth to avoid recognition. Their acts may be recorded, but their faces have been hidden. As a result, the videos obtained might prove non-useful. That is why some people believe that the CCTVs actually have no role in preventing crime.

                In conclusion, crime prevention using CCTVs is not the only way to combat crime and anti-social behaviour, but it is one of the practical ways that should be implemented. There are some countries that install CCTVs in public areas for the purpose of deterring crime and anti-social behaviour such as United Kingdom. A survey by University of Cambridge stated that the installations of the cameras have reduced crime and anti-social activity rates in public locations with a drop of 7%. In highways in some countries, CCTVs are fixed to poles or in trees to detect road-bullies and drivers who exceed the speed limits. So, I strongly believe that the CCTVs are particularly useful in both private housing and public places, as it can create the uncomfortable feeling of being closely observed as offenders commit misconduct. This feeling can generate a consciousness in them, making them reluctant to break the law. Looking at the figures, these methods have positive effects in controlling crime. Therefore, the CCTVs have a significant role in preventing crime and anti-social behaviour.

(948 words).

Status: Checked.

Band 4.