Tuesday, June 30, 2009

[Science Form 3] Fertilisation In Plants

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Simple/Quick Note
  1. Stigma becomes sticky -->
  2. Pollen grains are transferred to stigma -->
  3. Pollen tube emerges -->
  4. Pollen tube penetrates the style into the ovule in the ovary -->
  5. Male gamete from pollen tube is released into ovule (female gamete) -->
  6. Male gamete and female gamete fuses to form a zygote -->
  7. Ovule develops into a seed -->
  8. Ovary develops into a fruit.
*******

Flowering plants


After the pistil is pollinated, the pollen grain germinates in a response to a sugary fluid secreted by the mature stigma (mainly sucrose). From each pollen grain, a pollen tube grows out that attempts to travel to the ovary by creating a path through the female tissue.

The vegetative (or tube) and generative nuclei of the pollen grain pass into its respective pollen tube. The growth of the pollen tube is controlled by the vegetative (or tube) cytoplasm.

Hydrolytic enzymes are secreted by the pollen tube that digest the female tissue as the tube grows down the stigma and style; the digested tissue is used as a nutrient source for the pollen tube as it grows.

During pollen tube growth toward the ovary, the generative nucleus divides to produce two separate sperm nuclei(haploid number of chromosomes) - a growing pollen tube therefore contains three separate nuclei.

The pollen tube does not directly reach the ovary in a straight line. It travels near the skin of the style and curls to the bottom of the ovary, then near the receptacle, it breaks through the ovule through the micropyle (an opening in the ovule wall) and the pollen tube "bursts" into the embryo sac.

After this happens the pollen tube nucleus disintegrates, and one male sperm fuses to the female egg cell, whilst the other fuses to two polar nuclei(triploid number of chromosones). This is the point when fertilisation actually occurs.

Note that pollination and fertilisation are two separate processes. After being fertilised, the ovary starts to swell and will develop a fruit. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule.

The process is easy to visualise if one looks at maize silk, which is the female flower of corn. Pollen from the tassel (the male flower) falls on the sticky external portion of the silk, and then pollen tubes grow down the silk to the attached ovule. The dried silk remains inside the husk of the ear as the seeds mature; if one carefully removes the husk, the floral structures may be seen.

In many plants, the development of the flesh of the fruit is proportional to the percentage of fertilised ovules. For example, with watermelon, about a thousand grains of pollen must be delivered and spread evenly on the three lobes of the stigma to make a normal sized and shaped fruit.

Double fertilisation

Double fertilisation is the process in angiosperms (flowering plants) during reproduction, in which two sperm nuclei from each pollen tube fertilise two cells in an ovary.

The pollen grain adheres to the stigma of the carpel (female reproductive structure) and grows a pollen tube that penetrates the ovum through a tiny pore called a micropyle.

Two sperm cells are released into the ovary through this tube. One of the two sperm cells fertilises the egg cell (at the bottom of the ovule near the micropyle), forming a diploid (2n) zygote.

The other sperm cell fuses with two haploid polar nuclei (contained in the central cell) in the centre of the embryo sac (or ovule). The resulting cell is triploid (3n). This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue, inside the seed.

The two central cell maternal nuclei (polar nuclei) that contribute to the endosperm arise by mitosis from a single meiotic product. Therefore, maternal contribution to the genetic constitution of the triploid endosperm is different from that of the embryo.

One primitive species of flowering plant, Nuphar polysepala, has endosperm that is diploid, resulting from the fusion of a pollen nucleus with one, rather than two, maternal nuclei.

It is believed that early in the development of angiosperm linages, there was a duplication in this mode of reproduction, producing seven-celled/eight-nucleate female gametophytes, and triploid endosperms with a 2:1 maternal to paternal genome ratio.

[Science Form 3] Structure of a seed

Testa
Function: Protect the seed

Micropyle
Function: Seed pore that allows air and water to enter the seed during germination

Hilum
Function: Attaches the seed to the ovary wall

Cotyledon
Function: Stores starch

Seed coat
Function: Protect the inside of the seed

Embryo
Function: The beginning of the new plant

Endosperm
Function: Stored food in a monocotyledon

Stored food
Function: A plant uses stored food until it grows leaves that can make food

Monocot
Function: A type of seed that has only one cotyledon

Dicot
Function: A type of seed that has two cotyledons

Germination
Function: The process of growing a new plant from a seed

[Science Form 3] Vegetative Reproduction

Vegetative reproduction is an asexual reproduction that produces a new plant from a certain part of a parent plant without involving seeds.

Rhizome
Stem that grows under the ground; rhizome contains stored food.
Eg: Lalang, tumeric, ginger

Leaf
A small bud is produced at the part of a leaf that is able to develop into a new plant.
Eg: Bryopyllum, begonia, aloe vera

Tuber
Underground stem with a swollen end; tuber contains food.
Eg: Potato

Stem
Some plants reproduce through the stem that has several buds.
Eg: Tapioca, sugar cane, rose plant

Runner
Stem that creeps on the surface of the ground; nodes on the stem will produce buds.
Eg: Grass, sweet potato

Bulb
Consists the layer of swollen fleshy leaves; a bud grows to become a new plant.
Eg: Shallot, lily plant

Corm
A swollen stem with buds that grow upright under the ground.
Eg: Yam

Sucker
A young plant grows from a short stem in the ground.
Eg: Banana tree, bamboo tree

[Mathematic Form 1] Percentages

Percentages
  • A percentage is a fraction with 100 as the denominator
  • It is represented by the symbol %
Eg: 15/100 is 15%

The percentage of increase or decrease

Percentage increase = (Amount increase / Original value) x 100%

Percentage decrease = (Amount decrease / Original value) x 100%

Eg:

a) Find the decrease percentage when RM250 is decreased by RM55

Amount decrease = RM55

Percentage decrease = (RM55 / RM250) x 100% = 22%

b) In February, Aiman sold 560 durians. In March, the number of durians that he sold increased by 15%. How many durians did he sell in March?

Amount increase = Percentage increase x Original value

Amount increase = 15% x 560 = (15/100) x 560 = 84

New value = Original value + Amount increase

New value = 560 + 84 = 644

In March, he sold 644 durians.

Monday, June 29, 2009

Seremban School Closed Till July 5

The Star

SEREMBAN: Chung Hwa High School near here has become the latest school to be ordered closed after a Form Three student tested positive for the influenza A (H1N1) virus yesterday.

The private school will be closed from today and classes will resume on July 6, its headmaster Sua Sin Zang said.

The girl was believed to have been infected by her 22-year-old brother who had returned for his semester break from Australia on Monday.

Meanwhile, health director-general Tan Sri Dr Ismail Merican said a 15-month-old toddler who was under home quarantine has been infected with the H1N1 virus, bringing the total number of cases to 124.

There were 12 new cases as of yesterday morning, of which 11 were imported, including four from Jakarta, which was a first.

Of the 12 cases, six involved children, including the toddler who was the 17th local transmission case.

Dr Ismail expressed concern whether those under the seven-day home quarantine abided by the ministry’s 10 precautionary steps.

The boy, he said, had no overseas travel history but his mother had visited Phuket and became the country’s 86th case.

All passengers and crew on affected flights are advised to contact the ministry or call the current hotline numbers at 03-88810200 or 03-88810300.

On news reports that the SJK (C) Jalan Davidson principal had returned to the school while still on his seven-day home quarantine, Dr Ismail said they would investigate the matter, adding that there had been no cases of people jumping quarantine so far.

In George Town, Pulau Tikus assemblyman Koay Teng Hai, who returned from China on June 19, has been put under home quarantine as a precautionary measure after he complained of headache and sore throat.

State Health, Welfare, Caring Society and Environment Committee chairman Phee Boon Poh said swab samples from Koay have been taken for testing.

Saturday, June 27, 2009

Michael Jackson Dies

NST

LOS ANGELES, Fri: Pop icon Michael Jackson died on Thursday after suffering a cardiac arrest, multiple US media outlets reported, sending shockwaves around the entertainment world.

The Los Angeles Times and TMZ.com celebrity news website reported Jackson, 50, died after suffering an arrest just after 12:00 pm (1900 GMT) local time and paramedics were unable to revive him.

The Times cited multiple city and law enforcement officials as confirming the pop icon’s death.

Jackson’s manager Tohme E. Tohme was not immediately available for comment when contacted by AFP. Officials at UCLA Medical Center where Jackson was treated also could not be reached for comment.

National and local television networks showed hundreds of media gathered at UCLA Medical Center for what appeared to be a briefing. CNN was unable to confirm the death, stating that Jackson was in a coma.

Los Angeles Fire Department spokesman Devin Gales did not confirm Jackson’s identity but said paramedics went to an address corresponding to the star’s home at 12:21 pm (1921 GMT) and the person was taken to UCLA Medical Center.

An unidentified family member earlier told TMZ — the first outlet to report that Jackson had suffered a cardiac arrest — that the star was in “really bad shape.”

Michael’s father Joe Jackson told E! Online he was aware of the emergency but did not know further details.

“I am in Las Vegas, but yes, people in Los Angeles called me and are with Michael and tell me he was taken to the hospital,” he said. “I am not sure what’s wrong. I am waiting to hear back from them.”

The reports came as Jackson prepared to make a keenly anticipated concert comeback in London, his first series of shows in more than a decade and the first since his 2005 acquittal on child molestation charges.

However those concerts — billed as the “final curtain” — had been thrown into doubt after Jackson pushed back the opening dates last month.

Organizers of the concerts at the time stressed the delay was not linked to Jackson’s health.

In a press conference from the United States broadcast over the Internet, AEG Live president Randy Phillips was asked about Jackson’s health and said: “I would trade my body for his tomorrow. He’s in fantastic shape.”

While Jackson reigned as the “King of Pop” in the 1980s, his once-stellar career had been overshadowed by his colorful public behavior, his startling physical transformation and multiple allegations of child abuse.

Jackson lived as a virtual recluse following his 2005 acquittal on charges, including child molestation and plotting to kidnap his young accuser.

Despite his acquittal, the trial was a body blow from which the pop music superstar struggled to recover.

Four years later, Jackson is still worshipped by fans for revolutionising music, dance and music videos at the peak of his success.

The attention however paid to him in recent years has been less flattering, focusing on apparent cosmetic surgery — which he denies — his baby dangling antics and a decade of swirling child abuse allegations.

Born on August 29, 1958, Jackson made his show business debut with four of his older brothers in the Jackson Five pop group, and went on to lead the stage clan with a piping soprano and dazzling dance moves.

By 1969, the group had signed a contract with Motown Records, becoming one of the last great acts to emerge from the legendary label.

The Jacksons produced seven platinum singles for Motown, selling over a million, and three multi-platinum albums, selling more than two million. They moved to CBS’s Epic Records in 1976.

Despite the early success, Jackson was to recall those years as unhappy and lonely ones. Eventually the family act broke up, as Jackson went solo.

In 1979, Quincy Jones produced Jackson’s first solo album for Epic, “Off the Wall,” a huge disco-oriented success that sold 10 million copies.

They teamed up again in 1982 for what would be Jackson’s breakthrough album as a composer and co-producer, “Thriller,” which became the top-selling album of all time, with sales exceeding 41 million.

Wednesday, June 24, 2009

[Biology Form 4] Proteins

Proteins play an important role in the formation of cellular components, cells and tissues in the human body.

They are also needed for growth and development. Without them, we will not grow or be able to repair damaged tissues in our body.

Among the substances made up of proteins in the human body are haemoglobins, antibodies, enzymes, certain hormones, muscle tissues and part of the cell membrane.
  • The basic building block of proteins is the amino acid.

  • There are 20 types of amino acids.

  • Of these, the essential amino acids are the ones that cannot be synthesised by the body and must be obtained from the food we eat.

  • Five example of amino acids are leucine, tryptophan, glutamic acid, valine and serine.

  • If amino acids are known as monomers, proteins are polymers.

  • When two amino acids are joined together, a dipeptide is formed.

  • The bond between two amino acids is called a peptide bond.

  • The process in which polypeptides are formed from amino acids is known as condensation.

  • Protein can be broken down to amino acids in a process called hydrolysis.

  • A molecule that is a protein in nature can be used to speed up the process mentioned above. This molecule is an enzyme.

Resonance structures of the peptide bond that links
individual amino acids to form a protein polymer.



Chemical structure of the peptide bond


A peptide bond between leucine and threonine

Tuesday, June 23, 2009

A(H1N1): Seri Cempaka School Closed As Well

The Star

KUALA LUMPUR: The Seri Cempaka International School in Batu 9, Cheras here has been closed for a week, Health Minister Datuk Seri Liow Tiong Lay said on Tuesday, after a student tested positive for Influenza A(H1N1).

The number of cases nationwide increased to 69 with 10 new cases, he said, with two of them being local transmissions.

SJK (C) Jalan Davidson here and SRK Assunta 2 in Petaling Jaya were closed earlier after students were confirmed with the virus.

SMK Seksyen 9 Shah Alam, SMK Damansara Utama in Petaling Jaya and SM Wangsa Maju in Kuala Lumpur have each had one class stopped from Monday.

Meanwhile, Education Ministry director-general Tan Sri Alimuddin Md Dom says parents with children in the affected schools can keep them at home for the rest of the week if they are worried or the children feel unwell.

"All they would need to do is to inform the school; there is no need for a medical certificate from a doctor," he said.

Math & Science In English: Final Decision In July

The Star

KUALA LUMPUR: The Government will make its decision on the teaching of Science and Mathematics in English (better known by its Malay acronym PPSMI) early next month, Education Minister Tan Sri Muhyiddin Yassin said.

He said the Government’s full analysis and the ministry paper on the PPSMI policy have been completed and will be handed over to the Cabinet for deliberation soon.

“We will make a full announcement by early July.

“Whatever decision that comes out will be for the people’s benefit and goes in line with the Prime Minister’s ‘people first’ vision,” he told Parliament.

He said that a study conducted by the ministry and researchers from local universities revealed that overall, teachers and students achieved only a moderate level of knowledge in English.

“The ministry’s focus then is to improve English knowledge among teachers and students by improving the training programme for teachers and improving the learning of English in schools.

“We are looking into introducing English literature in schools to improve students’ knowledge of the language, and the functions of the school computer laboratories will also be upgraded with better software and equipment for the teaching of English subject.

“The Ministry also wants to resolve the gap between the achievements in English of students in the urban and rural areas since the PPSMI policy was introduced in phases in 2003.

“The final decision in the implementation of the PPSMI policy will also look into the policy’s effect on students in both urban and rural areas,” he said in reply to Dr Tan Seng Giaw (DAP-Kepong).

Battery Biohazard

Throwing your batteries in the dustbin can harm the environment.

You've probably got a dozen things that are powered by batteries. Just check your mobile phone, calculator, television remote control, camera and torchlight.

Batteries are incredibly useful but they run on poisonous chemicals and metals like mercury, lead, cadmium and nickel. That is why you mustn't throw old and damaged batteries in the dustbin.

When batteries are thrown into a rubbish heap or a landfill, the chemicals they run on leak into the soil and groundwater. Nobody wants that in their food or water!

If you throw a battery into incinerator, heavy metals like mercury can vapourise and be released into the air. When it rains, they fall back to the earth, poisoning soil, rivers and oceans.

Burning batteries leave ashes with concentrated cadmium and lead. When these are dumped, the poison leaks into the environment.

You can reduce the amount of batteries you use by buying rechargeable products. They cost a little more, but you can use them many times.

You can also buy batteries with fewer dangerous chemicals. Modern alkaline batteries have up to 90% less mercury than those used 20 years ago. Some are completely mercury free. Just read the label!

When your batteries dies, take it to a recycle centre. The recycle centre disposes of any leftover chemicals in such a way that they can't harm the environment.

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Info:
  1. Batteries are electrochemical devices that convert chemical energy to electrical energy.
  2. The modern battery was invented by Italian physicist Alessandro Volta in 1800.
  3. A typical lead-acid car battery today is now made up of about 70% recycled lead and plastic.
  4. Malaysians produce enough rubbish every day to fill up the Petronas Twin Towers in less than 10 days.
*******

[Biology Form 4] Class Of Chemicals

Cells need various types of organic and inorganic compounds to enable them to carry out their functions, as well as build their cellular components. While organic compounds contain the element carbon, inorganic compounds do not.

Below is the classified descriptions of chemical compound.

Carbohydrate
  • Starch made up of long chain of glucose
  • The ratio of C:H:O in it is 1:2:1
  • Cellulose that strengthens the cell walls of plants
  • Maltose can be converted into glucose by hydrolysis
  • Its glucose molecules can be converted into glycogen

Lipid
  • Cholesterol is an example of it
  • Fats have the triglyceride molecules in them
  • Fatty acids can be saturated and unsaturated
  • The hormone testosterone is an example of it

Nucleic Acid
  • An example is the DNA found in the nucleus of a cell
  • Genetic material that directs protein synthesis
  • Contain pentose sugars and phosphate groups

Protein
  • Amino acids are its building blocks
  • Nearly all enzymes are examples of it
  • The haemoglobin molecules in the red blood cells
  • Builds muscles and aids growth

Water
  • An inorganic compound with no carbon in it
  • A polar molecule with two H atoms and one O atom
  • A universal solvent
  • Acts as a medium for reactions in one's body

Monday, June 22, 2009

A(H1N1): First School In Malaysia Closed

The Star

KUALA LUMPUR: SJK (C) Jalan Davidson is the first school in Malaysia to be closed after an 11-year-old student testing positive on Friday for the Influeza A(H1N1) was found to have transmitted the virus to two classmates.

Health Minister Datuk Seri Liow Tiong Lai said the National Security Council agreed to close the school until June 26 and its students and staff numbering some 2,100 were home quarantined.

Making the announcement after meeting with the school staff and Parent-Teacher Association here Sunday, Liow said Deputy Prime Minister Tan Sri Muhyiddin Yassin who chairs the National Security Council agreed to close the school for a week.

He added that the other two schools with infected students in Petaling Jaya and Shah Alam would be closed only if the authorities discovers a local transmission of the virus.

Earlier when opening a A(H1N1) awareness campaign in Batu 11, Cheras organised by the Serdang MCA division, Liow had said that he had proposed for the closure of the school with the council after the local transmission was detected.

“It is our opinion that we should close the school. As long as there is even one case of local transmission, we must take precaution and close the school,” he had said.

Another eight new cases were reported Sunday bringing the total to 50 cases.

It included five school children - an 11-year-old from SRK Assunta 2, a 16-year-old from SM Shah Alam, and the three at Class 5 I of SJK(C) Jalan Davidson.

He said the Ministry had to look at all eventualities and take necessary steps to ensure the virus does not spread further in the school.

“We don’t want to have any problems in that school so we have to make sure the safety of the children come first,” he said, adding that the Health Ministry’s guidelines recommended schools to be closed if a local transmission is detected.

[Science Form 4] Genes

The human body is made up of cells, and in every cell, there is a nucleus that contains chromosomes.

Genes in the chromosomes provide instructions for cell growth and function.

Specific genes also determine hereditary traits in an individual.

Eg: There is a gene for hair colour and a gene for eye colour. Variations of a specific gene are called alleles.

During sexual reproduction, the genes for certain traits are passed down from parents to their offspring.

A child the carries two genes for each trait - one from the father's sperm and the other from the mother's ovum.

The genes can either be dominant or recessive. If the child inherits one dominant gene and one recessive gene, the dominant will overpower the recessive.

Eg: Given that T represents a father's dominant height gene and t represents a mother's recessive height gene, their child whose height gene is represented by TT or Tt will be tall. On the othe hand, their child whose height gene is represented by tt will be short.

Saturday, June 20, 2009

Program Merakyatkan Seni Budaya

Source: Flier

PROGRAM MERAKYATKAN SENI BUDAYA

Tempat:
Padang Sekolah Kebangsaan Sri Serdang
, 43300 Seri Kembangan, Selangor

Tarikh:
21hb JUN 2009 (AHAD)

Masa:
7.30 pagi - 2.00 petang

Atur Cara Dan Pertandingan
  • Anyam Rotan
  • Batu Seremban
  • Congkak
  • Mewarna Batik
  • Kanak-kanak: Mewarna (4-6 Tahun & 7-9 Tahun)
  • Senam Seni Malaysia
  • Sepak Raga Ratus
  • Pemeriksaan Kesihatan (BMI & Mamogram)
  • Untai Gelang Getah

Penyertaan Walk-in Dan Hadiah Disediakan

DATANGLAH BERAMAI-RAMAI SAMBIL BERSANTAI

Pameran, Persembahan Kebudayaan Dan Kenduri Rakyat Sambil Bersantai Bersama Keluarga

Cabutan Pengunjung Bertuah... Siapa Punya???
40 Pack+++ Hadiah

Friday, June 19, 2009

It Is Now Datuk Sudirman Arshad

The Star

PEKAN: One of Malaysia’s greatest singing sensations, the late Sudirman Arshad, was awarded a posthumous Datukship by the Sultan of Pahang, Sultan Ahmad Shah, at Istana Abu Bakar here Thursday.

Sudirman (1954-1992), burst onto the local entertainment scene when he won the local talent contest Bintang RTM in 1976 before going on to establish a lucrative chart-topping career.

He was known as the “Singing Lawyer” and the “Elvis of Malaysia,” recording hits not only in Malaysia but also in other countries around the region.

His performances brought him standing ovations in Australia, Japan, Kuwait and the United States.

He was named a “Singing Ambassador” by the Malaysia Tourism Development Board and his rendition of the To know Malaysia is to love Malaysia is still played in promotions.

One of the many high points in his career was on April 15, 1986, when he held an open air concert at Chow Kit Road in Kuala Lumpur, believed to have been the country’s first ever “street concert.”

A crowd of more than 100,000 jammed the streets, leading The Star then to report that “KL came to a standstill and it had nothing to do with the recession but with one man, Malaysia’s top entertainer,” adding that it was “an electrifying performance and a most memorable night.”

He won the title of “Best Performer” at the Asia Music Awards 1989 held at the Royal Albert Hall in London.

He died at the age of 37 on Feb 22 in 1992 after suffering a stroke as a result of a cerebrovascular disease.

Thursday, June 18, 2009

[Chemistry Form 5] Collision Theory

  • The collision theory is based on the kinetic theory, which states that molecules are in constant random motion.

  • In order for a reaction to occur, the reactant molecules must collide in the correct orientation, and with enough energy to form products.

  • Collision between particles that produce a chemical change are called "effective collisions". This is when the reactant molecules collide with enough kinetic energy to break their original bonds and then form new bonds in the product molecules.

  • Effective collision frequency is the number of effective collisions per unit time.

  • The activation energy Ea, is the minimum energy the colliding reactant particles must have before any collision between them can result in a chemical reaction.

The Collision theory, proposed by Max Trautz and William Lewis in 1916 and 1918, qualitatively explains how chemical reactions occur and why reaction rates differ for different reactions.

This theory is based on the idea that reactant particles must collide for a reaction to occur, but only a certain fraction of the total collisions have the energy to connect effectively and cause the reactants to transform into products.

This is because only a portion of the molecules have enough energy and the right orientation (or "angle") at the moment of impact to break any existing bonds and form new ones. The minimal amount of energy needed for this to occur is known as activation energy.

Particles from different elements react with each other by releasing activation energy as they hit each other.

If the elements react with each other, the collision is called successful, but if the concentration of at least one of the elements is too low, there will be fewer particles for the other elements to react with and the reaction will happen much more slowly.

As temperature increases, the average kinetic energy and speed of the molecules increases but this only slightly increases the number of collisions.

The rate of the reaction increases with temperature increase because a higher fraction of the collisions overcome the activation energy.

Collision theory is closely related to chemical kinetics.

Reaction rate tends to increase with concentration -
a phenomenon explained by collision theory

Wednesday, June 17, 2009

[Mathematic Form 3] Factorising Expressions

Factorising is the reverse process of expansion.

When you factorise an expression, you write it as a product of two or more common factors.

Tip: You may have to find the Highest Common Factor (HCF) for the terms first in order to arrive at an answer.

Eg:

Factorise each of the following:
i) 3p + 6
ii) 8a2 - 6ab
iii) ab + ac + bd + cd

Solution:

i) 3p + 6 ( 3 is the HCF)
= 3(p + 2)

ii) 8a2 - 6ab (2a is the HCF)
= 2a(4a - 3b)

iii) ab + ac + bd + cd
= a(b + c) + d(b + c)
= (b + c) (a + d)

Factorisation is also done by using the difference of two squares:

(a2 - b2) = (a + b) (a - b)

or by your knowledge of perfect squares:

a2 + 2ab + b2 = (a + b)2
a2 - 2ab + b2 = (a - b)2

Eg:

Factorise 4p2 - 25q2

Solution:

4p2 - 25q2
= (2p + 5q) (2p - 5q)

*********************
Factorise the following:

a. 10a + 15 = 5(2a + 3)

b. 12ab - 18b2 = 6b(2a - 3b)

c. 4mn + 12mn2 = 4mn(1 + 3n)

d. 9x2 - 64y2 = (3x + 8y) (3x - 8y)

e. 4p2 - 100q2 = 4(p + 5q) (p - 5q)

f. 12a2 - 48b2 = 12(a + 2b) (a - 2b)

g. x2 + 6xy + 9y2 = (x + 3y)2

h. 3p2 + 6pq + 3q2 = 3(p + q)2

i. a2 + ab + 3a + 3b = (a + 3) (a + b)

j. mk - m2 + 4k - 4m = (m + 4) (k - m)

k. (a - 7)2 - 100 = (a + 3) (a - 17)

*********************

Tuesday, June 16, 2009

[Biology Form 4] Meiosis In Humans

In females, meiosis occurs in cells known as oogonia (singular: oogonium). Each oogonium that initiates meiosis will divide twice to form a single oocyte and two polar bodies.

However, before these divisions occur, these cells stop at the diplotene stage of meiosis I and lay dormant within a protective shell of somatic cells called the follicle.

Follicles begin growth at a steady pace in a process known as folliculogenesis, and a small number enter the menstrual cycle. Menstruated oocytes continue meiosis I and arrest at meiosis II until fertilization.

The process of meiosis in females occurs during oogenesis, and differs from the typical meiosis in that it features a long period of meiotic arrest known as the Dictyate stage and lacks the assistance of centrosomes.

In males, meiosis occurs in precursor cells known as spermatogonia that divide twice to become sperm. These cells continuously divide without arrest in the seminiferous tubules of the testicles. Sperm is produced at a steady pace.

The process of meiosis in males occurs during spermatogenesis.

[Biology Form 4] Meiosis - The Significance & Nondisjunction

Meiosis facilitates stable sexual reproduction. Without the halving of ploidy, or chromosome count, fertilization would result in zygotes that have twice the number of chromosomes as the zygotes from the previous generation. Successive generations would have an exponential increase in chromosome count.

In organisms that are normally diploid, polyploidy, the state of having three or more sets of chromosomes, results in extreme developmental abnormalities or lethality. Polyploidy is poorly tolerated in most animal species. Plants, however, regularly produce fertile, viable polyploids. Polyploidy has been implicated as an important mechanism in plant speciation.

Most importantly, recombination and independent assortment of homologous chromosomes allow for a greater diversity of genotypes in the population. This produces genetic variation in gametes that promote genetic and phenotypic variation in a population of offspring.

The normal separation of chromosomes in meiosis I or sister chromatids in meiosis II is termed disjunction. When the separation is not normal, it is called nondisjunction. This results in the production of gametes which have either too many of too few of a particular chromosome, and is a common mechanism for trisomy or monosomy. Nondisjunction can occur in the meiosis I or meiosis II, phases of cellular reproduction, or during mitosis.

This is a cause of several medical conditions in humans (such as):

  • Down Syndrome - trisomy of chromosome 21
  • Patau Syndrome - trisomy of chromosome 13
  • Edward Syndrome - trisomy of chromosome 18
  • Klinefelter Syndrome - extra X chromosomes in males - ie XXY, XXXY, XXXXY
  • Turner Syndrome - lacking of one X chromosome in females - ie XO
  • Triple X syndrome - an extra X chromosome in females
  • XYY Syndrome - an extra Y chromosome in males

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