Human Blood

Blood is a connective tissue in liquid form. It is made up of 55% plasma and 45% blood cells.

There are three types of blood cells:

1. Erythrocyte - Erythrocytes transport oxygen.
   
2. Leucocytes - Leucocytes defend the body against diseases.
   
3. Platelet - Platelets help in blood clotting.

Blood Clotting

A cut cause a wound on the blood vessel.

Once blood is exposed to air, the platelets release thrombokinase (blood clotting factor), which converts prothrombin (inactive enzyme) into thrombin (active enzyme) in the presence of calcium ions.

Thrombin catalyses the conversion of soluble fibrinogens into insoluble fibrins.

Fibrins form a fibrous network over the wounded area of the blood vessel.

This fibrous network traps the blood cells and forms a blood clot to stop the bleeding.

DNA Fingerprinting

DNA fingerprinting is a technique used to differentiate organisms.

As each individual has a unique set of DNA (except in identical twins), scientists use this method in criminal identification an forensics, and also to establish paternity/maternity.

There are many ways to obtain a DNA fingerprint. One example is as follows:

1. A sample of DNA is extracted and cut into fragments using restriction enzymes.
   
2. The DNA fragments are placed on a gel in a device. This device uses electric current to separate the fragments according to their sizes. The smaller pieces travel faster therefore they are closest to the bottom of the gel. The larger pieces travel slower and are closer to the top.
   
3. This process results in unique DNA-banding patterns known as DNA fingerprints.

How to Study Science?

Before you enrol into a science class, you need to know that the knowledge of most science courses is accumulative, that is, new knowledge builds on old one. You therefore should also understand today's science concepts before tomorrow's class.

Before we begin, ask ourselves these question:

• How often do I sit down with my science book to read ahead before we cover material in class?
• Do I take note while I read?
• Do I seek help whenever I don't understand something?
• Do I review my notes and read the chapter under study often?
• Do I do extra problems in the book that are not assigned?

To study and understand science successfully, we suggest you to do the following:

Before Class

Get an overview of the study scope by quickly skimming through the sections of the chapter to be discussed in the class. Then, formulate possible questions for your teacher from your quick reading.

During Class

Ask for things that you do not understand during the class. It is proven that interactions in the class enhance the learning experience, as opposed of just taking notes and study later. If you miss something, write what you can (keywords for example) and clarify with your teacher right after class. Take note on any concepts or principles that your teacher emphasises during class.

After Class

After every class, you need to summarise, review and complete your notes using reference book. Then, build relationships between concepts in the current chapter and the previous ones, show similarities and differences. Try to solve problems related to the sections covered in class.

A Note to Remember...

Your teacher cannot make you learn. You have to take responsibility for your own education, stay actively engaged with your study material, and ask for help in understanding. Your teacher can help, but they cannot tell when you need help unless you tell them.

Reflex Action

A reflex action is an automatic response that occurs spontaneously and without conscious control. It acts as a protection against injuries and dangerous situations.

For example, a little child may not know how the needle-shaped spike on the cactus may hurt, however the child's body will know.

This reflex action involves three types of neurones: 

1. Afferent neurone.
2. Efferent neurone.
3. Interneurone.

When a child's hand touches the cactus's needle shaped spike, the sensory receptors in the child's finger are triggered to send a nerve impulse through the afferent neurone.

The nerve impulse travels along the afferent neurone and passes through the synapse to an interneurone (which is located in the grey matter of the spinal cord). The nerve impulse the passes another synapse to the efferent neurone.

The nerve impulse travels along the efferent neurone to the muscles (or the effectors) in the child's hand. The muscles contract and the child moves his/her hand away from the cactus's spike.