[Science Form 4] The Endocrine System

• Insulin
  
  • Convert glucose to glycogen.
  
  
• Pituitary
  
  • Found at the base of the brain.
  
  
• Pancreas
  
  • When the cells that produce insulin in one's pancreas are destroyed, he/she gets diabetes.
  
  
• Testosterone
  
  • Causes the development of men's secondary sex characteristics.
  
  
• Glucagon
  
  • Break down glycogen to release glucose.
  
  
• Adrenal
  
  • This gland secretes hormones when one is scared.
  
  
• Ovary
  
  • Controls the mentrual cycle.

In animal anatomy the endocrine system is a system of glands, each of which secretes a type of hormone into the bloodstream to regulate the body.

The endocrine system is an information signal system like the nervous system.

Hormones regulate many functions of an organism, including mood, growth and development, tissue function, and metabolism.

The field of study that deals with disorders of endocrine glands is endocrinology, a branch of internal medicine.

The endocrine system is made up of a series of ductless glands that produce chemicals called hormones.

A number of glands that signal each other in sequence is usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis.

Typical endocrine glands are the pituitary, thyroid, and adrenal glands. Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones.

In contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract, tend to be much less vascular and have ducts or a hollow lumen.

In addition to the specialised endocrine organs mentioned above, many other organs that are part of other body systems, such as the kidney, liver, heart and gonads, have secondary endocrine functions.

For example the kidney secretes endocrine hormones such as erythropoietin and renin.

[Science Form 4] Molecular Or Ionic?

When one or more electrons are transferred from one atom to another, the atom that gains the electron or electrons becomes negatively charged whereas the atom that loses the electron or electrons becomes positively charged.

These atoms with their positive or negative charges are called ions.

The number of protons and electrons differ in an ion. There are more protons than electrons in a positively-charged ion.

In contrast, there are more electrons than protons in a negatively-charged ion.

Some atoms like sodium atoms, potassium atoms and fluorine atoms are very reactive as they can easily turn into ions by losing or gaining electrons.

Meanwhile, two or more elements can bond together to form compounds. The bond can either be molecular or ionic. When atoms share electrons in covalent bonds, molecular or covalent compounds are formed.

In contrast, ionic compounds are made up of positive and negative ions in ionic bonds.

Physical properties of molecular and ionic compounds

[Science Form 4] Numbers In Symbols

An atom, which is the smallest unit of all matter, consists of a nucleus and an outer region.

The nucleus at the centre of an atom contains nucleons (protons and neutrons), and is surrounded by electrons orbiting in the outer region.

A neutral or stable atom has an equal number of protons and electrons.

The number of protons, also called the atomic number, is written as a subscript to the left of the element symbol.

In contrast, the total number of protons and neutrons, also called the nucleon number or mass number, is written as a superscript to the left of the element symbol.

[Science Form 4] Differences Between The Nervous & Endocrine Systems

Nervous sysytem	Different	Endocrine system
Nerve cells	Transmission	Blood
Fast and immediate	Speed of transmission	Slow
Short	Duration of response	Slow and long
Specific	Target areas	Wide

[Science Form 4] Organised & Systematic

Science enables us to learn about the world we live in. To do that, data need to be collected in an organized way - through systematic investigation.

Below is the steps of carrying out a systematic investigation in the correct order.

1. Identify the problem.
   
   
2. Make a hypothesis.
   
   
3. Identify the variables.
   
   
4. Plan the experiment.
   
   
5. Determine the apparatus and materials.
   
   
6. Determine the procedures.
   
   
7. Carry out the experiment.
   
   
8. Collect the data.
   
   
9. Analyze the data.
   
   
10. Interpret the data.
    
    
11. Draw conclusions.

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Example:
Select a reported incident from newspaper. Based on the article, make a hypothesis. Then, plan an experiment to test the hypothesis. The point from (a) to (i) , should be included.
Eg: pollution

a) Problem statement: Location A and B are polluted.

b) Objective: To find out the level of pollution in location A and B.

c) Hypothesis: Location A is more polluted than location B.

d) Variables:

• Manipulated: Area selected.
• Responding: Level of pollution.
• Fixed: The time the papers are exposed.

e) Material and apparatus: Filter paper, gum, and cardboard A and B.

f) Procedure:

1. Stick a filter paper of equal size each on cardboards A and B.
2. Place cardboard A at location A (by a road side) and cardboard B at location B (in a garden).
3. After two hours, check the filter papers.

g) Result: Location A is more polluted than location B.

h) Discussion:

• The passing cars emit a lot of carbon particles from their exhausts. These carbon particles rest on the white filter paper. Hence, the filter paper turns greyish. The other filter paper at location B has only a few black dots on it. This means that fewer pollutants rest on it. So location B is less polluted.

i) Conclusion: Location B is less polluted than location A.

***
Note:
Always remember to be truthful when conducting and reporting investigations. Report only the actual facts and never let your opinions and emotions influence your findings.

[Science Form 4] Responding Rightly

Voluntary actions are acts we are aware of and intend to do, while involuntary actions are acts that our body carries out automatically.

Many picture in newspaper show people in the process of carrying out voluntary actions. Pick any picture you like. Then, based on the picture, write out the reactions that his/her body experiences before responding to the stimulus.

If the picture shows a footballer kicking a ball, your answer should read like the following.

The footballer's receptor organs - his eyes - receive an environmental stimulus, which is the ball. Next, his eyes send electrical impulses through the sensory neurons to his brain. At the sight centre, the approaching ball is being interpreted, and impulses to kick the ball are generated. Impulses are sent through the effector neurons to his leg muscles. The footballer's leg then kicks the ball.

[Science Form 4] Fission & Fusion

Nuclear Fission
When a high energy neutron hits a uranium-235 nucleus, the U-235 nucleus becomes uranium-236, which is highly unstable. The unstable uranium nucleus then splits into two smaller and more stable nuclei - barium-141 and krypton-92.

Three neutrons and a great amount of energy are released during the fission. Along with the energy, light and heat are released. Gamma rays are emitted during the process, which is carried out in a nuclear reactor where energy is produced. This form of energy supplies 16% of the world's supply of electrical energy.

Nuclear Fusion
In nuclear fusion, the tritium nucleus and the deuterium nucleus are combined to form a heavier nucleus. During the process, an alpha particle and a neutron is released, together with a large amount of energy, though less than that produced from nuclear fission. The nuclear fusion activity can be seen from sun flares, which give us light and heat.

[Science Form 4] X-rays

X-RAYS are form of electromagnetic radiation, just like visible light but its short wavelength makes it invisible.

The x-ray particle is a photon that cannot penetrate bone mass. Thus, bone structures appear white on an x-ray film.

A plain radiograph of the elbow.

In hospitals, x-ray machines are used to detect broken bones or deformities in bone structures. Dentist use x-ray radiation to see cavities in teeth.

Six radioactive subtances:

1. Radium
2. Uranium
3. Carbon-14
4. Polonium
5. Cobalt-60
6. Iodine-131

[Science Form 4] Emissions That Stabilise

A radioactive substance with an unstable nucleus gains stability by emitting rays. This process is known as disintegration or radioactive decay.



The rays emitted can be in three forms: alpha rays, beta rays and gamma rays. All three rays may not be emitted at the same time for each disintegration.



In the process of decay, energy is lost and the decayed atom forms a new stable atom.



Alpha (α) decay:

An α-particle consists of two protons and two neutrons, or a helium nucleus. When a substance undergoes decay and emits α rays, the rays cannot penetrate even a piece of paper.

An example of an α decay: Pu-239 -> U-235 + α



Beta (β)^- decay:

A β-particle has the same mass and charge as an electron. In a β decay, a neutron is converted to a proton and a negative charge called β-particle is released. The β-particle can be stopped by a sheet of aluminium.



Gamma (γ) decay:

Gamma rays are high-power electromagnetic waves whose penetration power is high and can only be blocked by a thick lead or concrete.



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nuclear fission - pembelahan nukleus

nuclear fusion - pelakuran nukleus

nuclear reactor - reaktor nuklear

penetration power - kuasa penembusan

radioactive decay - pereputan radioaktif

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[Science Form 4] Twins

Identical Twins

• Formation: The fertilisation of an ovum by a sperm forms a zygote, which divides into half and produces two embryos.
  
  
• Placenta: Share the same placenta in the mother's uterus.
  
  
• Genetic make-up: Have the same chromosome make-up.
  
  
• Physical appearance: Usually have similar physical appearances.
  
  
• Sex: Are of the same sex.

Non-identical Twins

• Formation: The fertilisation of two ova by two sperms, separately.
  
  
• Placenta: Have separate placentas in the mother's uterus.
  
  
• Genetic make-up: Have separate sets of chromosome make-up.
  
  
• Physical appearance: Usually have different physical appearances.
  
  
• Sex: May be of different sexes or the same sex.

[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.