Tuesday, April 28, 2009

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Freons & CFCs - From Wonder Chemical To Super Danger


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 breJustify Fullathe 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.

Facts:
  • 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.

Thursday, April 23, 2009

[Chemistry Form 4] Isotopes Identified

Most atoms have several naturally occurring isotopes. An isotope is an atom that contains a different number of neutrons in its nucleus from that of other atoms of the same element.

This means that different isotopes of an element have different masses, since both protons and neutrons contribute about equally to the mass of an atom.

Radioisotopes such as phosphorus-32, carbon-14, sodium-24 and iodine-131 emit radiations. Thus, detectors like Geiger-Müller counter are used to trace the presence of radioactive radiations.

A Geiger-Müller counter

Radioisotopes are used in agricultural, medicinal, archaeological and industrial fields.

Some examples of the various uses of radioisotopes are shown as below, in sector;

NUCLEAR ENERGY
  • Isotope Uranium-235 used to produce nuclear energy.

AGRICULTURE
  • Isotope Phosphorus-32 or Nitrogen-15 used to traces the rate of nutrient absorptions in plants.
  • Gamma Rays used to sterilises pests. Inhibits the sprouting of potatoes, onions and gingers.

INDUSTRY
  • Gamma Rays used to checks wear and tear in engines. Gauges or controls the content level in canned food.
  • Strontium-90 used to gauges or controls the thickness of paper and metal in industries.
  • Cobalt-60 used to detects crack in metal or concrete structures.

Tuesday, April 21, 2009

[Biology Form 4] Animal Cell & Plant Cell

The cell is the basic unit of all organism. It is made up of a cell membrane that encloses the cytoplasm.

Contained within the cytoplasm are not only the
nucleus but also organelles, whose specific functions help the cell perform a range of activities.

While plant and animal cells are similar, the plant cell has, in addition to the cell membrane, another boundary that separates it from its external environment. This is called the
cell wall.

As most plant cells carry out photosynthesis - the synthesis of organic substances - they contain
chloroplasts.

In plant cells,
vacuoles also tend to be larger in size and smaller in number than those found in animal cells.

Onion Skin Cell

Cheek Squamous Epithelial Cells

Typical Plant Cell

Typical Animal Cell


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.

Sunday, April 19, 2009

[Mathematic Form 3] Pie Chart

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

Eg:

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%
= 25%

Saturday, April 18, 2009

N-H Coordination

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.

Friday, April 17, 2009

[Mathematic Form 4] To Round Off Numbers

To round off number to an appropriate number of significant figures, you may use the following steps:
  1. Identify digit x that is to be rounded off.
  2. Is the digit after x greater than, or equal to, 5?
  3. If it is either greater than, or equal to, 5, add 1 to x.
  4. If it isn't, then x remains unchanged.
  5. Do the digits after x lie before or after the decimal point?
  6. If before, replace each digit with a zero.
  7. 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.

[Biology Form 4] Organelles And Its Function

RIBOSOME
Function: A site for the synthesis of proteins

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 membrane 2. Nuclear pore 3. Rough endoplasmic reticulum (rER) 4. Smooth endoplasmic reticulum (sER) 5. Ribosome attached to rER 6. Macromolecules 7. Transport vesicles 8. Golgi apparatus 9. Cis face of Golgi apparatus 10. Trans face of Golgi apparatus 11. Cisternae of Golgi apparatus

Tuesday, April 14, 2009

Matriculation Entrance Results On Friday

The Star

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.

Sunday, April 12, 2009

[Physics Form 4] Measurements Matter

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.

[Mathematic Form 4] Get The Right Figure

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.

Friday, April 10, 2009

[Mathematic Form 3] Mean

The MEAN of a set of data is obtained by adding up all the values of the data and dividing them by the total number of data.

Mean = (Sum of values of data) / (Total number of data)

Eg:

Find the mean of the following sets of data:

a) -8, -5, -3, 0, 0, 1, 2, 8

Solution:

Mean = ( (-8) + (-5) + (-3) + 0 + 0 + 1 + 2 + 8 ) / 8

Mean = - (5/8) or -0.625

Notes - Mathematic PMR

Form 1

Form 2


Form 3

General Knowledge & Science SPM



Science SPM



Penicillin vs Bacteria

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.

Wednesday, April 08, 2009

[Chemistry Form 4] Kinetic Theory Of Matter

  • 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.

[Physics Form 4] Useful Units

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 104 cm2
1cm3 = 1 x 10-6 m3

6. How fast is a car moving in ms-1 if its speed is 72kmh-1 ?
72kmh-1 = 72km / 1h
= (72 x 103 m) / (3.6 x 103 s)
= 20ms-1

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