CFCs seemed safe at first. But 40 years after they had been developed, scientists discovered the terrible truth.
CHLOROFLUOROCARBONS (CFCs) are covalent compounds whose chlorine, fluorine and carbon atoms are bounded by covalent bonds.
During the 1930s, E.I. duPont de Nemours & Company trademarked varies CFCs under the name Freon.
Initially, everyone thought Freons were fantastic. Freons are colourless, odourless, non-flammable and non-corrosive. It is a non-toxic to breathe in small amounts of Freon too.
As they have a low boiling point, Freons are ideal for systems that require cooling. Thus, Freons became widely used in fridges, air conditioning units and other chilling appliances.
When manufactures learnt that Freons were excellent aerosol-spray propellents, a myriad of products, from hair spray to oven cleaners, ensued. Freons were also used in fire estinguishers since they were great foamblowing agents, as well.
It was in the 1970s that scientists discovered Freons were not as safe as everyone had thought. They found that once let into open air, Freons reacted with the ozone in the atmosphere.
The earth's ozone layer is band of air with a high ozone content, which lies 32km to 48km above the planet's surface. It is very important part of the atmosphere because it protects us from solar ultraviolet radiation, which can cause skin cancer.
At the time, companies refused to believe that Freons were destroying the ozone layer. However, when more and more studied proved freons were dangerous, laws were made to ban their use.
By 1996, most countries had banned the use of Freons and other CFCs.
Thomas Midgley Jr and Charles Kettering were the American scientists who invented Freons.
We can tell which chemical compounds Freons are made of by their number. For example, Freon-11 is trichlorofluoromethane.
In 1986, the global consumption of CFCs was about 1.1 million tonnes. In 1997, it dropped to about 146,000 tonnes.
In the laboratory, you have learned how to prepare a microscope slide of human cheek cells as well as the epidermal cells of onions.
a) The differences you can observe between the two types of cells in term of the following:
Shape Onion cells have a regular shape while cheek cells have an irregular shape.
Presence or absence of cell wall Onion cells have a cell wall while cheek cells do not.
Presence or absence of vacuoles Onion cells have a large vacuole while vacuoles in cheek cells, if present, are small.
b) Can you observe chloroplasts in the epidermal cells of onions? Explain your answer. No chloroplasts can be observed in the epidermal cells of onions because epidermal cells do not carry out photosynthesis.
A pie chart can be used to represent statistical data. It is easy to remember the pie chart because, just like the most pies, it is in the shape of circle.
A pie chart is divided into sectors, whose angles at the center of circle are proportional to the frequency of a certain category of the data. The angles can also be represented as percentages in a pie chart.
To interpret the data in a pie chart, you have to:
i) Determine the angles at the center of each sector. The angle of each sector can be calculated by using the following formula:
Angle of sector = (Quantity represented by sector X 360o ) / Total quantity
ii) Note that the bigger an angle, the larger is the frequency or quantity represented
To convert the angle of a sector into a percentage, use the following formula:
Percentage = ( Angle of sector X 100% ) / 360o
The pie chart on the right represent the number of students who play basketball, football, tennis, hockey and netball in the third form of secondary school.
Basketball = 90o Football = 100o Tennis = 20o Netball = 30o Hockey = x o
a) Find the value of x. Solution: x = 360o - 90o - 100o - 20o - 30o = 120o [Sum of angles at the center = 360o]
b) If the number of students who play netball is 45, calculate the total number of students in the third form. Solution:
30o (the number of students who play netball) represent 45 students.
1o would represent (45/30) students
Hence the total number of students (represented by 360o) will be
= (45/30) X 360o = 540 students
c) How much percentage of the total number of students in the third form play basketball? Solution: The percentage of students who play basketball
= (90/360) X 100%
Body coordination is important to help us avoid injuries as well as adapt to changes around us. As the parts of our body communicate in unison with each other, a series of movements occurs in response to a stimulus.
There are two types of body coordination; nervous coordination and hormonal coordination.
The nervous system generates fast responses while the hormonal system generates slow and long responses.
Nervous Coordination The centrel nervous sytem is the control centre of the body, where impulses are received and interpreted, and response impulses are sent to the relevant parts of the body for the appropriate responses.
The central nervous system communicates through electrical impulses, which are transmitted through interconnecting nerve cells.
Hormonal Coordination The hormonal system consists of the endocrine glands, which secrete hormones. The blood system is involved in ensuring that hormones reach the target areas. The responses are usually projected in the form of growth, which is a slow response.
To round off number to an appropriate number of significant figures, you may use the following steps:
Identify digit x that is to be rounded off.
Is the digit after x greater than, or equal to, 5?
If it is either greater than, or equal to, 5, add 1 to x.
If it isn't, then x remains unchanged.
Do the digits after x lie before or after the decimal point?
If before, replace each digit with a zero.
If after, drop the digits.
Let's try the steps on a few examples.
Suppose we have to round off the following numbers:
a) 34,782 to 1 significant figure Solution: 34,782 The digit to be rounded off is 3. The digit after 3 is 4. 4 is less than 5. Therefore, 3 remains unchanged and each digit to the right of 3 (4, 7, 8, 2) is to be replaced with zero.
34,782 = 30,000 (1 significant figure)
b) 54.78 to 3 significant figures Solution: 54.78 The digit to be rounded off is 7. The digit after 7 is 8. 8 > 5. Therefore, add 1 to 7 and drop the digit 8 because it lies after the decimal point.
54.78 = 54.8 (3 significant figure)
c) 0.0050327 to 2 significant figures Solution: 0.0050327 The digit to be rounded off is 0. The digit after 0 is 3. 3 is less than 5, so leave 0 unchanged. Digit 2 and 7 are after the decimal point, so drop the digits.
0.0050327 = 0.0050 (2 significant figure)
7245.9 to be rounded off to 2 significant figure (sf) is 7,200.
0.0011056 to be rounded off to 3 significant figure (sf) is 0.00111.
986,468 to be rounded off to 1 significant figure (sf) is 1,000,000.
5.00402 to be rounded off to 5 significant figure (sf) is 5.0040.
67.9081 to be rounded off to 4 significant figure (sf) is 67.91.
Atomic structure of the 50S Subunit from Haloarcula marismortui. Proteins are shown in blue and the two RNA strands in orange and yellow. The small patch of green in the center of the subunit is the active site.
MITOCHONDRION Function: A site for cellular respiration and the synthesis of ATP
Simplified structure of mitochondrion
********************* CHLOROPLAST Function: Enables the plant cell to carry out photosynthesis
Chloroplast ultrastructure: 1. outer membrane 2. intermembrane space 3. inner membrane (1+2+3: envelope) 4. stroma (aqueous fluid) 5. thylakoid lumen (inside of thylakoid) 6. thylakoid membrane 7. granum (stack of thylakoids) 8. thylakoid (lamella) 9. starch 10. ribosome 11. plastidial DNA 12. plastoglobule (drop of lipids)
CENTRIOLES Function: Help to form spindle fibres during cell division
3-dimensional view of a centriole
SMOOTH ENDOPLASMIC RETICULUM Function: A site for synthesis of lipids and steroids
GOLGI BODY Function: Processes, packages and transport carbohydrates, proteins and phospholipids
Diagram of secretory process from endoplasmic reticulum (orange) to Golgi apparatus (pink). Please click for full labels.Secretory pathway diagram, including nucleus, endoplasmic reticulum and golgi apparatus. 1. Nuclear membrane2. Nuclear pore3. Rough endoplasmic reticulum (rER)4. Smooth endoplasmic reticulum (sER)5. Ribosome attached to rER6. Macromolecules7. Transport vesicles8. Golgi apparatus9. Cis face of Golgi apparatus10. Trans face of Golgi apparatus11. Cisternae of Golgi apparatus
PUTRAJAYA: SPM school leavers who have requested for entry into the Education Ministry’s matriculation programme will know the results of their application this Friday.
The ministry’s Media and Corporate Communication Unit announced that the official results will be made available to school leavers who have submitted their application to the ministry between July 1 and Oct 10 last year.
Applicants may acquire the results from the ministry’s website at www.moe.gov.my by entering their identity card number and SPM candidate number.
They may also request for the results via SMS. Those interested in using this service are required to type MATIC NO and send it to 15888.
Alternatively, applicants may also call the Matriculation Department at 03-8884 4100 from 8.30am to 4pm on Friday.
Applicants who meet entrance requirements but fail to receive a placement may appeal before April 30 for their application to be reconsidered. Results of appeals will be released on May 22 on the same website.
When selecting a device to measure a quantity, factors like the
type of quantity to be measured
estimated size of the quantity
sensitivity of the device
accuracy of the device
need to be taken into account because sensitivity, precision and accuracy are the three important properties of a measurement.
Sensitivity is the ability of a measuring device to detect small changes in the physical quantity measured.
Eg: A miliammeter is more sensitive than an ammeter. This is because a ammeter is able to measure a smaller magnitude of electric current in the order of mA, in contrast to an ammeter, which measures a larger current in the order of A.
Precision is the ability of a measuring device to give consistent reading after several repeated measurements. The smaller the relative deviation of a set of readings, the higher is the precision level of the measurements.
Accuracy is the ability of a measuring device to provide readings that are exactly the same as, or close to, the actual value of measurement. the closer a measurement is to its actual value, the higher is its accuracy level.
In scientific or technical studies, very large or very small numbers are used sometimes.
Eg: The speed of light is approximately 300,000,000 m/s.
The mass of one oxygen atom is approximately 0.000000000000000000027 g.
That's quite a number of zeros, isn't it? Imagine the amount of space they would take up in your exercise books.
To manage these extremely large or small numbers more easily, we use significant figures and the standard form.
The accuracy level of a measurement in scientific work is indicated by the number of significant figures it has.
Here are some rules to follow when dealing with significant figures;
Rule 1: All non-zero digits are significant. Eg: 6.78 has 3 significant figures 97.122 has 5 significant figures
Rule 2: Zeros between non-zero digits are significant figures. Eg: 1,007 (4 significant figure) 3.0002 (5 significant figure)
Rule 3: A zero after the decimal point of a decimal number is a significant figure. Eg: 6.0 (2 significant figure) 18.00 (4 significant figure)
Rule 4: In a decimal, zeros before the first non-zero digit are not significant. Eg: 0.00865 (3 significant figure) [the first three zeros are not significant] 0.06 (1 significant figure) [the first two zeros are not significant]
Rule 5: In a whole number, zeros after the last non-zero digit may or may not be significant, depending on the level of accuracy specified. Eg: 74,000 has 2 significant figure when rounded off to the nearest thousand. 74,000 has 3 significant figure when rounded off to the nearest hundred.
Antibiotics can cure many disease. Penincilin was one of the first antibiotics discovered by Sir Alexander Fleming in 1928. It is produced by a species of the fungi Penicillium notatum, and has only been widely used from the 1940s.
During the Second World War, penicillin was dubbed a wonder drug; It was widely used to prevent death and amputations due to infected wounds.
Penicillin work buy inhibiting the formation of strong peptidoglycan cross-links in the bacterial cell wall. In other words, it weaken the cell wall of the bacterium. The bacterium then bursts due to pressure on its cell wall.
How Do Bacteria Die?
Microorganisms are sensitive to many physical or chemical agents. These agents are said to have a "bacteriostatic action" when they stop the growth of bacteria, and a "bactericidal action" when they kill them.
The sun, with its ultraviolet rays, is doubtless the oldest bactericidal agent, and one of the most efficient. Ultraviolet rays bring about mutations in bacteria, that is to say, changes in their genetic makeup, which prove to be deadly in most cases.
In general, bacteria are unable to develop in highly concentrated solutions of substances like sugar or salt. In such conditions, the water contained in the microorganisms is released through the cell wall in an attempt to dilute the medium outside (osmosis). The result is that the bacteria dehydrate and stop growing or die. This is what occurs when meat or fish is salted. Similarly, the presence of a large quantity of sugar in fruit jellies or jams helps to preserve them.
Heat is bacteria's mortal enemy. A temperature of 50 to 60 degrees Celsius (122 to 140 degrees Fahrenheit) for half an hour is sufficient to neutralize most bacteria, but those that can form spores require more stringent measures. It takes 20 minutes in a steam sterilizer to kill such germs. For this reason a surgeon's gown and the drapes over his patient are sterilized in such a manner.
Bacteria also are sensitive to many chemical substances. Knowledge of this can be put to good use in various ways, for example, in food preservation. The oldest and best-known chemical preservatives doubtless are alcohol and vinegar. More recently the chemical industry has created a wide variety of products acting either on bacteria or on fungi, and preventing their growth. Some of these chemical agents seem to be harmless, but unfortunately the long-term secondary effects of many of them are not known.
Prime Minister Datuk Seri Najib Tun Razak's new Cabinet will have 28 members. Two ministries have been abolished.
New Cabinet line-up:
Prime Minister and Finance Minister 1 - Datuk Seri Najib Tun Razak
Deputy Prime Minister and Education Minister - Tan Sri Muhyiddin Yassin
Finance Minister 2 - Datuk Ahmad Husni Hanadzlah
Ministers in PM dept - Datuk Seri Mohammed Nazri, Tan Sri Nor Mohamed Yakcop, Tan Sri Dr Koh Tsu Koon and Rtd Brigadier General Datuk Jamil Khir Baharum
Transport - Datuk Seri Ong Tee Keat
Science and Technology - Datuk Dr Maximus Ongkili
Defence - Datuk Ahmad Zahid Hamidi
Home - Datuk Seri Hishammuddin Tun Hussein
Rural and Regional Development - Datuk Seri Shafie Apdal
Housing and Local Government - Datuk Kong Cho Ha
Health - Datuk Seri Liow Tiong Lai
Tourism - Datuk Dr Ng Yen Yen
Human Resources - Datuk Dr S. Subramaniam
Natural Resources and Environment - Datuk Douglas Uggah Embas
Women, Family and Community Development - Datuk Seri Shahrizat Abdul Jalil
International Trade and Industry - Datuk Mustapa Mohamed
Higher Education - Datuk Seri Khaled Nordin
Energy, Green Technology and Water - Datuk Peter Chin
Information, Unity, Culture and Arts - Datuk Seri Dr Rais Yatim
Agriculture - Datuk Noh Omar
Works - Datuk Shaziman Abu Mansor
Domestic Trade - Datuk Ismail Sabri Yaakob
Sports - Datuk Ahmad Shabery Cheek
Foreign - Datuk Anifah Aman
Federal Territories - Datuk Raja Nong Chik Raja Zainal Abidin
Earlier Najib left Istana Terengganu at about 11.25am after a 30-min audience with King regarding the new Cabinet line-up expected to be announced 3pm Thursday.
Najib arrived at the palace 10.57am to submit the list to Tuanku Mizan and left about 30 minutes later without stopping to speak to the media representatives waiting outside the gate.
He is scheduled to announce the new cabinet lineup in Putrajaya at 3pm. The new ministers and deputy ministers will take their oath of office at Istana Negara at 9.30am Friday.
Umno sources earlier said that Najib had spent the last five days juggling names and positions to take into consideration the requests and views of various Barisan Nasional component parties.
It is speculated that there could be as many as seven new faces in the line-up – most of them from Umno, while the party itself may give up a few ministerial posts.
Up till Wednesday evening, several Barisan component leaders had met with Najib and Umno deputy president Tan Sri Muhyiddin Yassin, who will be named Deputy Prime Minister Thursday.
The message Najib had for all of them was the same – that Umno was giving up quite a number of posts and that they should also be willing to make sacrifices.
Najib is expected to downsize his Cabinet, which now has 27 ministries and 31 ministers.
At present, Umno has 22 ministers, the MCA four, and the MIC, Upko, SUPP, PBB and PBS one each.
The new Cabinet is expected to have between 20 and 24 ministries, with no more than 27 ministers. Several ministries are expected to be merged.
Insiders said the ministries which could be merged are Tourism with Unity, Culture, Arts and Heritage; Education with Higher Education; Domestic Trade and Consumer Affairs with International Trade and Industry; and Agriculture and Agro-Based Industries with Plantation Industries and Commodities.
There have also been suggestions that the Federal Territories Ministry be merged with the Housing and Local Government portfolio.
Three ministries – Works; Energy, Water and Communications and Science, Technology and Innovation – could also be merged into two ministries.
This means that seven new ministries will be created from 13 merged ones.
Matter is made up of small and discrete particles, which are constantly in motion and contain kinetic energy.
Solid particles are held by strong forces of attraction, which packed them closely in an orderly manner. Thus, solid has a fixed volume and shape. Solid particles have limited motion; they can only rotate and move about a fixed position.
Forces of attraction between liquid particles are weaker than those in solid particles. Thus, the particles are arranged less compact and less orderly. Liquids have a fixed volume but not a fixed shape. The particles can vibrate, rotate and move throughout the liquids.
Particles in gas are held by very weak forces of attraction. The particles are very far apart from each other and are in constant motion. The particles vibrate, rotate and move randomly. Gas does not have a fixed shape or volume and can be compressed easily.
1. Why are units important in the measurement of a quantity? They provide the exact size of the quantity measured; they provide information about the type of quantity measured; they allow for comparisons between two measurements of the same quantity.
2. State the SI units of the following quantities: electric current, velocity, acceleration, mass, time, energy, pressure, work, momentum and weight. Electric current: A Velocity: ms-1 Acceleration: ms-2 Mass: kg Time: s Energy: J Pressure: Pa Work: J Momentum: kgms-1 Weight: N
3. Differentiate between the SI unit and the SI base unit of force. The SI unit of force is N (Newton) while the SI base unit of force is kgms-2
4. Are cm and m base unit? Differentiate them. Yes, both are base units of length, a base quantity. However cm is not the SI unit of length while m is.
5. State the value equivalent of 1m2 and 1cm3 , respectively. 1m2= 1 x 104cm2 1cm3= 1 x 10-6m3
6. How fast is a car moving in ms-1if its speed is 72kmh-1? 72kmh-1= 72km / 1h = (72 x 103m) / (3.6 x 103 s) = 20ms-1