Chromosomes

For my students =)

Those of you who still have problems on understanding What is a CHROMOSOME, this post is for you. Do read and try to understand. Enjoy!

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-A chromosome is found in the nucleus of all cells (except RBC, since they do not have nucleus)

-Chromosomes are made up of a long, linear DNA molecule which in turn is made up of many sets of genes : it is the genetic material that all organisms inherit from their parents

-A DNA molecule is usually very long & consists of hundreds & thousands of genes

-G1 phase : cell does its normal everyday job. Each chromosome contains only a single molecule of DNA where it is not condensed & appear like thread-like structures called chromatin

-S phase : synthesis of DNA occurs. Replication of DNA in nucleus. Duplication will result in sister chromatids

-Within a sister chromatid, it contains a DNA double helix

-G2 phase : cell gets ready for mitosis

-When cell division begins, chromatins will condense, coil up, compact & thicken, thus making them easily seen under the light microscope. In the middle, it has a narrow region called the centromere

-DUring mitosis, this 2 sister chromatids will finally separate during anaphase & each will become an independent daughter chromosome

Science : CHAPTER 5 - Acids & Alkalis (II)

Dear students of 7 Aqua & Aer,

** Do read through everything before you start to do anything. **

Please do a revision by reading up on the link Module 5 – Acids & alkalis again.

Once you have finished reading, I require every one of you to write a report by writing some short notes as a report on these few questions that I will list below. Please be advised that you are allowed to use the search engines on the internet to help you write your report. However, do read through the facts and only choose the relevant ones.

Guiding questions:

1) The characteristics of acids.

2) The characteristics of alkalis

3) Neutral substances

4) Everyday uses of acids and alkalis (make sure you state appropriate examples)

5) The common hazard symbols which are associated with acids and alkalis

You are to hand in the report at the end of the class.

For those of you who are able to finish up early, you might want to try out this activity of The Virtual Kitchen.Good luck and have fun – in Science! Please remember to hand in your report. I’ll see you tomorrow. ^_^

Chapter 5 : Acids & Alkalis - Indicators

Dear students,

Today we will be learning about INDICATORS. What are indicators actually? If you search from the dictionary, indicators means "to point out" or "to specify something". Those are very general definitons of what the word indicator is. However, in Science, when you mention an indicator, it gives a whole different meaning to it.

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Indicators

There is a device called a pH meter which you can dip into a liquid and which will measure its pH. However, it is easier to use an indicator.

An indicator is a chemical that changes colour. Indicators are liquids, but they can be soaked into a type of paper similar to blotting-paper to form strips of indicator paper.

Just dip the indicator paper into the unknown liquid and it will change colour to show the pH.

The simplest indicator is Litmus (from the Litmus plant). It goes red in acids, blue in alkalis.

pH = less than 7	pH = more than 7

Universal indicator is a better indicator than litmus because it can show a greater range of colours. The chart below shows the approximate colour that universal indicator goes when put into liquids of different pH values.

pH = 3 or less	pH = 4 or 5	pH = 6	pH = 7 (neutral)	pH = 8 or 9	pH = 10 or more

Universal indicator is available as a liquid or soaked into absorbing paper. It is often used to work out the pH of soil samples to see which plants can be grown in a certain patch of ground.

There are other indicators, for example, methyl orange (which changes colour from colourless to orange at pH of about 3). They all have different pH values where they change colour, and each has its own uses.

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If you want to find out more on indicators, click on this website What are some natural acid/base indicators?

Remember, if you have fun learning about Science, you will learn about Science!

Science: CHAPTER 5 - Acids & Alkalis (I)

Dear students of 7 Aer, Aqua & Terra,

Please google up "Acids and alkalis Year 7" and find out more on what exactly are they. Or you can go to Module 5 -Acids and alkalis.

Once you have done that, go to the link under "For My Students" for Alien Juice Bar. Try every component under that, only then proceed to The pH factor.

As you are playing those educational games, please be reminded that you are to read all the pop-ups that give you facts from time to time. From there you can gather on the whole on what acids and alkalis are like, what are their characteristics and identify certain examples.

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For revision, please try out Acids & Alkalis - Matching game and also read up on Acids & Alkalis - terms you need to know.

Meiosis (For my dear students ^_^ )

Why do we look like our parents?

Each parent donates genes to their offspring via sexual reproduction. The genes combine to give different but similar looking offspring.

Homologous chromosomes

a) Humans have 46 chromosomes consisting of 23 homologous pairs. Each parent donates one chromosome to each of the 23 homologous pairs. That means, half of an individual’s chromosomes comes from the female parent while the other half comes from the male parent.

b) Homologous chromosomes are the same length and carry the same genes in the same location. Those genes could be different versions. E.g., imagine the homologous chromosomes carry the eye color gene but one produces blue eyes while the other produces brown.

c) The exception is the sex chromosomes. For these, females have a homologous pair (XX) while males do not (Xy).

d) The other chromosomes are called autosomes (non-sex chromosomes).

Two types of cells in general

a) Somatic – diploid (2n) body cells. Contain a complete set of chromosomes.

b) Reproductive cells – haploid (n) sex cells. These cells are called gametes and contain only half the number of chromosomes. If one somatic cell (2n) is fertilized by another (2n), the resulting zygote would contain twice the number of chromosomes (4n). I.e., the chromosome number would double each generation (4n, 8n, 16n etc.). For this reason, the chromosome number must be reduced during the production of gametes. This way, one haploid (n) gamete is fertilized by another (n) and the resulting zygote is diploid (2n).

c) The zygote carries a complete set of chromosomes. Half from the the female parent and half from the male.

d) Every cell in the resulting organism is diploid and arises by mitotic division of the original zygote.


The main stages of meiosis are the same as those in mitosis

a) Meiosis happens in two stages: Meiosis I and Meiosis II. The two cell divisions result in 4 haploid daughter cells.

b) During Meiosis I (the reduction division) homologous chromosomes are separated.

c) In Meiosis II, sister chromatids are separated.

d) After the chromosomes are replicated, sister chromatids remain attached at the centromere. Also, homologous pairs (each consisting of two sister chromatids) remain close together. The four sister chromatids are called a tetrad and the process is called synapsis.

e) During synapsis, the arms of chromosomes in a homologous pair become intertwined. Pieces of the homologous chromosomes break off and switch places. This phenomenon is called crossing over. This increases genetic diversity which results from sexual reproduction.

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MEIOSIS I

Interphase - duplication of DNA

Prophase I - similar to mitosis except for synapsis
1. Synapsis - pairing of homologous chromosomes
2. Chromatin shortens & thickens to become chromosomes
3. Nuclear envelope disappears
4. Nucleolus disappears

Metaphase I
1. Homologous chromosomes line up in pairs across the equator
2. Spindle fibers attach to the centromeres of the chromosomes

Anaphase I - separation of homologous chromosomes

Telophase I
1. Chromosomes arrive at spindle poles
2. Nuclear envelope reforms in some cells
3. Each cell has one each homologous chromosome, cytokinesis occurs to split cells

No Interphase

Prophase II
1. Chromosomes shorten and thicken
2. Nuclear envelope disappears
3. No duplication occurs

Metaphase II
1. Chromosomes line up along the equator
2. Spindle fibers attach to the centromeres

Anaphase II
1. Centromeres divide
2. Sister chromatids separate, become chromosomes

Telophase II
1. Nuclear envelope forms around each set of chromosomes
2. Nucleolus appears in each nucleus
3. Chromosomes lengthen and become indistinct

---> Cytokinesis occurs forming 4 cells

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For further illustration/information, please check out these links:

1) http://www-users.york.ac.uk/~mal503/common/thesis/jpegimages/meiosis.jpg

2) http://www.sfu.ca/~fankbone/biol/meiosis.jpg

3) http://tutor.lscf.ucsb.edu/mcdb/tutorial/meiosis/

Also do check out the link under "For My Students" for Animations on Meiosis, Click and Clone, Meiosis = double cell division and Meiosis tutorial.

Mitosis (For my dear students ^_^ )

For my Biology students, hope the notes below will help you guys somewhat. ^_^ Happy reading! If you still find yourself quite unsure, try cliking on the Mitosis (Flash) link under "For My Students". For further understanding, do try out the quiz, crossword puzzle and interactive tutorials under mitosis. Gambatte and all the best!!


What is (and is not) mitosis?

Mitosis is nuclear division plus cytokinesis, and produces two identical daughter cells during prophase, prometaphase, metaphase, anaphase, and telophase. Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell cycle.

* daughter cells - When a cell divides, it copies its DNA and produces two new daughter cells that have identical DNA


Interphase

The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules.

• G1 - Gap 1 phase, cell enters mitosis, 2N
• S - DNA synthesis occurs, 4N
• G2 - Gap 2 phase, time before metaphase, 4N

M Phase

Prophase
Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.


















Prometaphase
The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving.





















Metaphase
Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.





















Anaphase
The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.





















Telophase
Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.















Cytokinesis

In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus. In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.

** All pictures are taken from HOPES, Huntington's Outreach Project for Education, at Stanford & Mitosis

Uniforms - "Aye" or "Nay" ?

"Some people believe that requiring students in school settings to conform to a dress code improves student behavior, reduces differences among socioeconomic levels, and enhances students' self-confidence. Others say that policies stipulating dress codes or requiring school uniforms infringe upon students' First Amendment rights, stifle individuality, and impose unnecessary means of control."

This was a quote taken from a website on Educational Management which was discussing about uniforms implemented in schools that I was reading from. I do really wonder why are these people even bringing up the issue about school uniforms. I mean, if the government implemented the policy that all students attending public schools must wear uniforms, then what is the big deal?

When I read this part..."infringe upon students' First Amendment rights, stifle individuality, and impose unnecessary means of control", I instantly thought of one thing. How on Earth can your uniform stifle your individuality?!! If you have style, you HAVE style. If you stand out, you WILL stand out - be it in jeans and t-shirt or the ever controversial school uniform. Granted, if you are dressed in branded clothes and have cool accessories (or even weird ones) - you will definitely attract attention. When the quote of "stifling individuality" comes up, I think its just that those who are fashion freaks a.k.a Mr/Ms Vain Pot's way of saying that "I want to stand out and attract as much attention as I can get. So just get off my case!" Thus, I would like to say it again - if you're cool, you're COOL. Accept the fact if you're not, and stop whining, giving lame excuses and blaming anything or anyone else. Grow up, mature and show TRUE INDIVIDUALITY!

And the part of "imposing unnecessary means of control", I really think its no issue at all! How is it that wearing school uniform reflects the school's control over an individual? Try remembering the times when you were (or are still) in school which required you to wear uniform. Did it even managed to control you in anyway? Okay, I'll admit...with the school uniform on, it will be a nuisance if you were to be outside of school when it is still in session. Therefore, the control that it puts will be on those who plans to play truant. However, are you even supposed to be doing that when you are in school for a reason? If asked the question, "Why are you in school?" The answer would be, "To learn and study" of course! Then when playing truant is not supposed to happen when school is in session, can you honestly say that the control is unnecessary? Isn't it just one tiny, simple way of dealing with one of the many discipline problems that the schools/Education Ministry are worried about?

Okay, I know that this comment..."reduces differences among socioeconomic levels, and enhances students' self-confidence" does not ring 100% true. But it does make sense to a certain degree. The uniform policy was implemented, in hopes that the disparity among students can be lessened if not totally diminished. But it definitely exist, the disparity in SES (socioeconomic status) between students in schools. Even with the implementation of uniforms, there is undeniably still an obvious difference between students from the middle-income earning group compared to those from the high-income earners. Still, I do think its good that whatever little disparity that can be lessened, it'll go a long way in encouraging wholesome friendships and reducing cliquing. The part about self-confidence...I really do not know how can school uniforms encourage the building of it. I myself had my uniformed days in school, and I can't really say that it did encourage self-confidence. Perhaps if looked from another viewpoint - uniforms keep the other students from being overly fashionable and dripping with brand names from head-to-toe. Thus, keeping the other less fortunate students from looking mousy and sooooo unfashionable.....then, maybe there is a point there.

This opinionated post is available for further discussion. Please feel free to comment as you feel appropriate about this issue. ;) Looking forward to any comments. Thx a bunch!!