Aug 2, 2012
Jul 26, 2012
Loss of Cell Cycle Controls in Cancer Cells
Cancer
cells do not respond normally to the body’s control mechanisms. They divide
excessively and invade other tissues. If unchecked, they can kill the organism.
By studying cells growing in culture, researchers have learned that cancer cells do not heed the normal signals that regulate the cell cycle. For example, as the figure above shows, cancer cells do not exhibit density–dependent inhibition when growing in culture; they do not stop dividing when growth factors are depleted. A logical hypothesis to explain this behavior is that cancer cells do not need growth factors in their culture medium in order to grow and divide. They may make a required growth factor themselves, or they may have an abnormality in the signaling pathway that conveys the growth factor’s signal to the cell cycle control system even in the absence of that factor. Another possibility is an abnormal cell cycle control system.
There are other important differences between normal cells and cancer cells that reflect derangements of the cell cycle. If and when they stop dividing, cancer cells do so at random points in the cycle, rather than at the normal checkpoints. Moreover, in culture, cancer cells can go on dividing indefinitely if they are given a continual supply of nutrients; they are said to be “immortal.” A striking example is a cell line that has been reproducing in culture since 1951. Cells of this line are called HeLa cells because their original source was a tumor removed from a woman named Henrietta Lacks. By contrast, nearly all normal mammalian cells growing in culture divide only about 20 to 50 times before they stop dividing, age, and die.
The abnormal behaviour of cancer cells can be catastrophic when it occurs in the body. The problem begins when a single cell in a tissue undergoes transformation , the process that converts a normal cell to a cancer cell. The body’s immune system normally recognises a transformed cell as an insurgent and destroys it. However, if the cell evades destruction, it may proliferate and form a tumour, a mass of abnormal cells within otherwise normal tissue. If the abnormal cells remain at the original site, the lump is called a benign tumour . Most benign tumors do not cause serious problems and can be completely removed by surgery. In contrast, a malignant tumour becomes invasive enough to impair the functions of one or more organs.
By studying cells growing in culture, researchers have learned that cancer cells do not heed the normal signals that regulate the cell cycle. For example, as the figure above shows, cancer cells do not exhibit density–dependent inhibition when growing in culture; they do not stop dividing when growth factors are depleted. A logical hypothesis to explain this behavior is that cancer cells do not need growth factors in their culture medium in order to grow and divide. They may make a required growth factor themselves, or they may have an abnormality in the signaling pathway that conveys the growth factor’s signal to the cell cycle control system even in the absence of that factor. Another possibility is an abnormal cell cycle control system.
There are other important differences between normal cells and cancer cells that reflect derangements of the cell cycle. If and when they stop dividing, cancer cells do so at random points in the cycle, rather than at the normal checkpoints. Moreover, in culture, cancer cells can go on dividing indefinitely if they are given a continual supply of nutrients; they are said to be “immortal.” A striking example is a cell line that has been reproducing in culture since 1951. Cells of this line are called HeLa cells because their original source was a tumor removed from a woman named Henrietta Lacks. By contrast, nearly all normal mammalian cells growing in culture divide only about 20 to 50 times before they stop dividing, age, and die.
The abnormal behaviour of cancer cells can be catastrophic when it occurs in the body. The problem begins when a single cell in a tissue undergoes transformation , the process that converts a normal cell to a cancer cell. The body’s immune system normally recognises a transformed cell as an insurgent and destroys it. However, if the cell evades destruction, it may proliferate and form a tumour, a mass of abnormal cells within otherwise normal tissue. If the abnormal cells remain at the original site, the lump is called a benign tumour . Most benign tumors do not cause serious problems and can be completely removed by surgery. In contrast, a malignant tumour becomes invasive enough to impair the functions of one or more organs.
The cells of malignant tumours are abnormal
in many ways besides their excessive proliferation. They may have unusual
numbers of chromosomes (whether this is a cause or an effect of transformation
is a current topic of debate). Their metabolism may be disabled, and they may
cease to function in any constructive way. Also, owing to abnormal changes on
the cells’ surfaces, they lose or destroy their attachments to neighbouring
cells and the extracellular matrix and can spread into nearby tissues. Cancer
cells may also secrete signal molecules that cause blood vessels to grow toward
the tumour. A few tumour cells may separate from the original tumour, enter blood
vessels and lymph vessels, and travel to other parts of the body. There, they
may proliferate and form a new tumour. This spread of cancer cells to locations
distant from their original site is called metastasis.
A tumour that appears to be localised may be treated with high–energy radiation, which damages DNA in cancer cells much more than it does in normal cells, apparently because cancer cells have lost the ability to repair such damage. To treat known or suspected metastatic tumours, chemotherapy is used, in which drugs that are toxic to actively dividing cells are administered through the circulatory system. As you might expect, chemotherapeutic drugs interfere with specific steps in the cell cycle. For example, the drug Taxol freezes the mitotic spindle by preventing microtubule depolymerisation, which stops actively dividing cells from proceeding past metaphase. The side effects of chemotherapy are due to the drugs’ effects on normal cells. For example, nausea results from chemotherapy’s effects on intestinal cells, hair loss from effects on hair follicle cells, and susceptibility to infection from effects on immune system cells.
Researchers are beginning to understand how a normal cell is transformed into a cancer cell. Though the causes of cancer are diverse, cellular transformation always involves the alteration of genes that somehow influence the cell cycle control system. Our knowledge of how changes in the genome lead to the various abnormalities of cancer cells remains rudimentary, however.
Perhaps the reason we have so many unanswered questions about cancer cells is that there is still so much to learn about how normal cells function. The cell, life’s basic unit of structure and function, holds enough secrets to engage researchers well into the future.
A tumour that appears to be localised may be treated with high–energy radiation, which damages DNA in cancer cells much more than it does in normal cells, apparently because cancer cells have lost the ability to repair such damage. To treat known or suspected metastatic tumours, chemotherapy is used, in which drugs that are toxic to actively dividing cells are administered through the circulatory system. As you might expect, chemotherapeutic drugs interfere with specific steps in the cell cycle. For example, the drug Taxol freezes the mitotic spindle by preventing microtubule depolymerisation, which stops actively dividing cells from proceeding past metaphase. The side effects of chemotherapy are due to the drugs’ effects on normal cells. For example, nausea results from chemotherapy’s effects on intestinal cells, hair loss from effects on hair follicle cells, and susceptibility to infection from effects on immune system cells.
Researchers are beginning to understand how a normal cell is transformed into a cancer cell. Though the causes of cancer are diverse, cellular transformation always involves the alteration of genes that somehow influence the cell cycle control system. Our knowledge of how changes in the genome lead to the various abnormalities of cancer cells remains rudimentary, however.
Perhaps the reason we have so many unanswered questions about cancer cells is that there is still so much to learn about how normal cells function. The cell, life’s basic unit of structure and function, holds enough secrets to engage researchers well into the future.
Jun 24, 2012
Pentaksiran Berasaskan Sekolah (PBS)
On Dec
17, 2010, the Cabinet agreed to introduce School-Based Assessment, or
Pentaksiran Berasaskan Sekolah (PBS), as part of the Education
Transformation Plan to realign the education system from one that
focuses largely on academic excellence to a more holistic assessment.
PBS emphasises assessment for learning and assessment of learning to ensure a more systematic mastery of knowledge.
PBS
assesses each child holistically, taking into account the learner’s
overall well-being (including the intellectual, emotional, spiritual and
physical aspects) in tandem with the National Education Philosophy, as
well as the Standard Curriculum for Primary Schools (KSSR).
PBS
was introduced last year in all government and government-aided primary
schools, and this year in all government and government-aided secondary
schools. Thus Ujian Pencapaian Sekolah Rendah (UPSR) in 2016 and
Penilaian Menengah Rendah (PMR) 2014 will be revamped to accommodate the
transformation.
What is PBS?
PBS is a holistic
form of assessment which assesses the cognitive, affective and
psychomotor domains, encompassing the intellectual, emotional, spiritual
and physical aspects. PBS embraces both academic and non-academic
fields.
Teachers are given due recognition and have the autonomy
to conduct formative assessment during the learning process and also
summative assessment at the conclusion of a learning unit or any other
suitable time during the school year at their own discretion, taking
into account their pupils’ readiness.
There are four components
in the PBS; namely, Central Assessment; School Assessment; Assessment of
Physical, Sports and Co-curricular Activities and Psychometric
Assessment.
Central assessment involves one or more tasks set by
the Examinations Syndicate but administered and graded by teachers based
on scoring rubrics provided by the central body.
School assessment is set, administered, graded and reported by the school based on the requirements of the curriculum.
Learners’
participation and involvement in sports and co-curricular activities
are recorded and reported in Assessment of Physical, Sports and
Co-curricular Activities. Thus co-curricular activities also have a
bearing on a pupil’s overall achievement.
Psychometric assessment is another non-academic component that measures pupils’ innate and acquired abilities.
Why PBS?
The objectives of the PBS are:
·To
enhance the meaningfulness of assessment where the focus is more on
pupils’ development and growth in learning rather than merely on their
achievements in the form of scores or grades;
·To reduce the
over-reliance and over-dependence on data (grades and scores) obtained
through central examinations in getting information about pupils in the
school system;
·To empower the school and teachers to conduct
quality assessment of and for learning, involving their own pupils.
Therefore school assessment will be given its due recognition and
acknowledgement, and a significant place in the overall assessment
system; and,
·To ensure the performance of pupils is comparable
to accepted world standards in various areas of knowledge, skills, and
competence, with the introduction of Standard-Referenced assessment in
PBS.
What subjects are assessed through PBS?
PBS is used to assess all subjects taught in primary and lower secondary schools.
How do teachers implement PBS?
Teachers
conduct formative assessment during the learning process and also
summative assessment, which is normally carried out at the conclusion of
a learning unit or at the end of a semester or at the end of the year.
This
does not mean that teachers have to create test papers or handouts as
instruments every time they wish to assess a pupil’s achievement.
Teachers may carry out creative activities that are fun, to gather
information about their pupils’ learning progress.
Homework,
quizzes, question and answer sessions and even observations are all
examples of activities which teachers could use as instruments to assess
pupils’ development and growth.
The only difference now is that teachers have to record pupils’ learning progress systematically.
In
order to help teachers record and report pupils’ progress, the
Examinations Syndicate has developed the PBS Management System (SPPBS)
which is web-based. SPPBS is also available in the standalone version
for schools which do not have access to the Internet.
How is PBS different?
PBS
concurs with the Standard Referenced Assessment in which pupils’
achievements are measured against a Performance Standard (Standard
Prestasi) which is developed by the Examinations Syndicate and mapped
from the standard curriculum.
Performance Standard explains the
performance or mastery of a pupil in a particular field he undertakes
within a learning period based on an identified benchmark.
Standard
Referenced Assessment allows teachers as well as parents to trace and
measure each pupil’s progress based on his performance measured against a
set of performance indicators.
Thus, a learner’s achievement is
no longer measured by comparing his grades/scores with those of his
peers. In this manner, a learner only competes with himself.
Therefore
a learner’s achievement is no longer gauged by his position in class.
Instead his achievement is ranked with reference to bands One to Six;
One being the lowest and Six the highest.
What are bands?
Learners’ achievements are reported with reference to Bands rather than Grades A,B,C etc, or raw scores, eg. 85%.
Band One shows that a learner tahu or knows. For example, in Mathematics, a Year One learner is able to recognise numbers 1,2,3 ...
Band Two reflects tahu dan faham or
knows and understands, which in Mathematics refers to the ability to
understand the value of numbers; for example, eight is less than nine,
four is more than three etc.
Band Three records that a learner tahu, faham dan boleh buat, which
shows that he is able to apply knowledge acquired. In Mathematics, Band
Three shows that a learner can add, subtract, divide and multiply.
A learner who has attained Band Three is considered to have acquired the basic skills pertaining to the subject.
A learner who attains Band Four (tahu, faham dan boleh buat dengan beradab) shows the ability to solve an elementary mathematical operation using the correct protocol.
A Band Five (tahu, faham dan boleh buat dengan beradab)
reflects the learner’s ability to solve problems. For example, if a
spring chicken costs RM5, how many chickens can Ali buy with RM10?
Finally,
a learner who is awarded a Band Six demonstrates the ability to make a
value judgement and is creative or innovative in solving mathematical
problems. For example, the blue shirt costs RM30 but it is on offer at
50% discount, thus it is better value compared to the same quality shirt
on sale at RM20 nett.
Band Three is equal to a passing grade.
Thus pupils who fail to achieve Band Three will be supported through
remedial work to help them achieve a minimum Band Three.
PBS
makes it possible for teachers to provide immediate feedback to pupils
at each stage of the learning curve. The feedback based on the
Performance Standard will enable teachers and pupils to identify their
strengths and weaknesses during the learning process.
Thus, early
detection of pupils’ inability to master a skill should enable the
teachers to formulate remedial tasks to help them improve their learning
and achievement accordingly.
Again, it is wise to remember that
pupils are assessed against a set of performance indicators and not
compared to the achievements of their peers.
Hence PBS enables learners’ to advance at their own pace in a less stressful learning environment.
Would PBS further burden teachers?
The
main focus of PBS is assessment for and of learning. Assessment should
be integrated in the learning process and be used to enhance pupils’
mastery of learning. If managed and implemented wisely, teachers would
find PBS beneficial and less burdensome.
To ensure the smooth
sailing of PBS, two applications – PBS Management System or SPPBS
(Sistem Pengurusan Pentaksiran Berasakan Sekolah) and PAJSK (Pentaksiran
Aktiviti Jasmani, Sukan dan Kokurikulum) – were developed to ensure
teachers are not further burdened with clerical duties.
The
applications store data pertaining to learners’ achievement which can be
easily retrieved to report learners’ strengths and areas where more
help is needed to parents and other interested parties.
What about teacher bias?
Teacher bias is largely reduced through quality assurance which ensures the reliability and validity of assessment outcomes.
Teachers
are required to file evidence of pupils’ work as proof that the learner
has attained the necessary skills to merit the bands they are awarded.
In this context, quality assurance for PBS implementation is maintained
through the process of mentoring, monitoring, moderation and detection
at various levels.
Mentoring is the process of assisting,
facilitating and guiding teachers to carry out PBS according to the
correct procedures and principles of PBS.
Monitoring ensures that
the correct procedures have been adhered to ensure the reliability and
credibility of the assessment outcome.
Standardisation ensures uniformity of scores with reference to the Performance Standards based on the rubrics of an assignment.
Detection is the process that evaluates the strength, weaknesses and effectiveness of assessment tools.
Is the PBS a new invention?
No,
it is not. Question and answer sessions, quizzes, homework and class
work are all tools of assessment that have been employed by teachers to
gauge their learners’ understanding. Teaching and learning is more fun
and meaningful when assessment is cleverly designed and conducted.
Conclusion
PBS
is being introduced as part of the National Transformation Programme to
produce world-class human capital. It is one of the measures taken by
the Malaysian Education Ministry to enhance pupils’ mastery of learning
through the national assessment system and it is in-line with the
Educational Transformation Plan.
The assessment transformation
introduced by the Education Ministry via the PBS presents the idea that
central examinations like the UPSR and PMR are no longer the sole form
of evaluation in measuring pupils’ achievement.
Through the PBS,
the ministry aims to help pupils’ realise their potential in both
academic as well as non-academic fields within a learning environment
that is more stress-free.
In a nutshell, PBS is an arduous
endeavour that demands total commitment from teachers and school
administrators to help each child reach their full potential.
Jun 10, 2012
A good teacher
Empathy
You have the ability to bond with your students, to understand and resonate with their feelings and emotions. To communicate on their level. To be compassionate with them when they are down and to celebrate with them when they are up.
You have the ability to bond with your students, to understand and resonate with their feelings and emotions. To communicate on their level. To be compassionate with them when they are down and to celebrate with them when they are up.
Positive Mental Attitude
You are able to think more on the positive and a little less on the negative. To keep a smile on your face when things get tough. To see the bright side of things. To seek to find the positives in every negative situation. To be philosophical.
You are able to think more on the positive and a little less on the negative. To keep a smile on your face when things get tough. To see the bright side of things. To seek to find the positives in every negative situation. To be philosophical.
Open to change
You are able to acknowledge that the only real constant in life is change. You know there is a place for tradition but there is also a place for new ways, new ideas, new systems, and new approaches. You don't put obstacles in your way by being blinkered and are always open and willing to listen to others' ideas.
You are able to acknowledge that the only real constant in life is change. You know there is a place for tradition but there is also a place for new ways, new ideas, new systems, and new approaches. You don't put obstacles in your way by being blinkered and are always open and willing to listen to others' ideas.
Role Model
You are the window through which many young people will see their future. Be a fine role model.
You are the window through which many young people will see their future. Be a fine role model.
Creative
You are able to motivate your students by using creative and inspirational methods of teaching. You are different in your approach and that makes you stand out from the crowd. Hence the reason why students enjoy your classes and seek you out for new ideas.
You are able to motivate your students by using creative and inspirational methods of teaching. You are different in your approach and that makes you stand out from the crowd. Hence the reason why students enjoy your classes and seek you out for new ideas.
Sense of Humour
You know that a great sense of humour reduces barriers and lightens the atmosphere especially during heavy periods. An ability to make your students laugh will carry you far and gain you more respect. It also increases your popularity.
You know that a great sense of humour reduces barriers and lightens the atmosphere especially during heavy periods. An ability to make your students laugh will carry you far and gain you more respect. It also increases your popularity.
Presentation Skills
You know that your students are visual, auditory or kinaesthetic learners. You are adept at creating presentation styles for all three. Your body language is your main communicator and you keep it positive at all times. Like a great orator you are passionate when you speak. But at the same time you know that discussion and not lecturing stimulates greater feedback.
You know that your students are visual, auditory or kinaesthetic learners. You are adept at creating presentation styles for all three. Your body language is your main communicator and you keep it positive at all times. Like a great orator you are passionate when you speak. But at the same time you know that discussion and not lecturing stimulates greater feedback.
Calmness
You know that the aggression, negative attitudes and behaviours that you see in some of your students have a root cause. You know that they are really scared young people who have come through some bad experiences in life. This keeps you calm and in control of you, of them and the situation. You are good at helping your students de-stress.
You know that the aggression, negative attitudes and behaviours that you see in some of your students have a root cause. You know that they are really scared young people who have come through some bad experiences in life. This keeps you calm and in control of you, of them and the situation. You are good at helping your students de-stress.
Respectful
You know that no one is more important in the world than anyone else. You know that everyone has a place in the world. You respect your peers and your students. Having that respect for others gets you the respect back from others.
You know that no one is more important in the world than anyone else. You know that everyone has a place in the world. You respect your peers and your students. Having that respect for others gets you the respect back from others.
Inspirational
You know that you can change a young person's life by helping them to realise their potential, helping them to grow, helping them to find their talents, skills and abilities.
You know that you can change a young person's life by helping them to realise their potential, helping them to grow, helping them to find their talents, skills and abilities.
Passion
You are passionate about what you do. Teaching young people is your true vocation in life. Your purpose in life is to make a difference.
You are passionate about what you do. Teaching young people is your true vocation in life. Your purpose in life is to make a difference.
Willing to Learn
You are willing to learn from other teachers AND your students. Although knowledgeable in your subject you know that you never stop learning.
You are willing to learn from other teachers AND your students. Although knowledgeable in your subject you know that you never stop learning.
Acid rain and ozone depletion
Causes
Combustion
of fossil fuels (in power stations, domestic & industrial boilers)
Releases
sulphur dioxide & oxides of nitrogen (NO & NO2)
Both
the gases combine with water vapour formed sulphuric acid & nitric acid
They
fall to earth as acid rain (with pH less than 5)
Effects
The soil becomes very acidic
Thus, unsuitable for cultivation of crops
Causes leaching of minerals (such as potassium, calcium, magnesium)
Affects growth of crops
Photosynthetic tissues are destroyed.
Reduce the producers.
Germination of seed & growth of young seedling is inhibited.
Insoluble aluminium ions accumulate in lakes & rivers (due to leaching)
This can kill aquatic organisms (excessive secretion of mucus by fish gills)
Kill phytoplanktons (that affects the food chain)
Acidic soil releases ions of certain heavy metals (Eg. mercury, lead, cadmium)
This can contaminate supply of drinking water.
Metal railings, steel, cars, bridges, underground pipes corrode
Corrosion of sandstone & limestone.
Ways to overcome
Use scrubbers that clean up emissions from power stations & industrial plants
Use catalytic converters that clean up emissions from vehicle exhaust
Effects
The soil becomes very acidic
Thus, unsuitable for cultivation of crops
Causes leaching of minerals (such as potassium, calcium, magnesium)
Affects growth of crops
Photosynthetic tissues are destroyed.
Reduce the producers.
Germination of seed & growth of young seedling is inhibited.
Insoluble aluminium ions accumulate in lakes & rivers (due to leaching)
This can kill aquatic organisms (excessive secretion of mucus by fish gills)
Kill phytoplanktons (that affects the food chain)
Acidic soil releases ions of certain heavy metals (Eg. mercury, lead, cadmium)
This can contaminate supply of drinking water.
Metal railings, steel, cars, bridges, underground pipes corrode
Corrosion of sandstone & limestone.
Ways to overcome
Use scrubbers that clean up emissions from power stations & industrial plants
Use catalytic converters that clean up emissions from vehicle exhaust
Causes
Increase level of CFCs (chlorofluorocarbons
CFCs used in coolants in air conditioners / refrigerators // propellants is aerosol cans // foaming agents making styrofoam / polystyrene
Increase level of CFCs (chlorofluorocarbons
CFCs used in coolants in air conditioners / refrigerators // propellants is aerosol cans // foaming agents making styrofoam / polystyrene
(Once
in the atmosphere) CFCs are broken down by UV rays into chlorine radicalsChlorine
radicals break down ozone molecules (O3)
Effects
Ozone
depletion causes direct exposure to UV radiation.
Prolong
exposure causes skin cancer, cataracts & sunburns
UV rays also weaken immune system / decreases body resistant against infectious disease
UV rays reduces nutrient contents & crop yields
UV rays also weaken immune system / decreases body resistant against infectious disease
UV rays reduces nutrient contents & crop yields
Leaf
cells & chlorophyll are easily damaged
UV
rays also kill microbes & phytoplankton
Leads
to increase in the earth temperature / global warming
Ways
to overcome
Reduce
/ Stop uses of CFCs
Replace
CFCs with HCFCs or HFCs.
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