Term 4

We learnt about the digestive system and also the respiratory system(further on).
i also learnt these during primary 6 but it was only the basic, so now i learnt the more in depth. For example inside the digestive system, there is alot of different kinds of enzymes, the protease, amylase.

Term 3

We learnt the structure of cells in this term. Although i have learnt it during primary 6 but this is more of a more detailed and "inside: of an animal cell and a plant cell. For example more detailed parts inside parts.

Like ribosomes, which is for the synthesis of proteins. 

Ribosomes

The ribosome is a large complex of RNA and protein which catalyzes protein translation, the formation of proteins from individual amino acids using messenger RNA as a template.This process is known as translation. Ribosomes are found in all living cells.

And also mitochondria, which is for the release of energy.

It helps in respiration, and it releases energy!

     

Mitochondria

In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle found in most eukaryotic cells.These organelles range from 0.5 to 1.0 micrometer (μm) in diameter. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth. Mitochondria have been implicated in several human diseases, including mitochondrial disorders and cardiacdysfunction, and may play a role in the aging process. The word mitochondrion comes from the Greek μίτος mitos, thread, + χονδρίον chondrion, granule.

Several characteristics make mitochondria unique. The number of mitochondria in a cell varies widely by organism and tissue type. Many cells have only a single mitochondrion, whereas others can contain several thousand mitochondria. The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the intermembrane space, the inner membrane, and the cristae and matrix. Mitochondrial proteins vary depending on the tissue and the species. In humans, 615 distinct types of proteins have been identified from cardiac mitochondria, whereas in Murinae (rats), 940 proteins encoded by distinct genes have been reported. The mitochondrial proteome is thought to be dynamically regulated. Although most of a cell's DNA is contained in the cell nucleus, the mitochondrion has its own independent genome. Further, its DNA shows substantial similarity to bacterial genomes.

       

Elements, Compounds and Mixtures

1) Elements
Sodium chloride (salt) is a white solid. If you melt it at a high temperature and then pass an electric current through the molten liquid, it breaks down (decomposes) into a silvery liquid and a yellow­-green gas. The silvery liquid is molten sodium and gas is chlorine. This decomposition reaction is summarised below:


No matter how hard you try, it is impossible to break down sodium or chlorine into simpler substances. Sodium and chlorine are examples of elements.

An element is a substance that cannot be broken down into simpler substances by ordinary chemical methods.

There are about 110 known elements. All substances are made up of these 110 elements. For example, water is made up of two elements called hydrogen and oxygen. Sugar is made up from the elements hydrogen, oxygen and carbon. Common salt is made up from the elements sodium and chlorine. The human body is made up of about 10 main elements and small amounts of many others. The element calcium is found in our bones and the element iron in our blood.

Each element has a name and symbol. The symbol is based on either the element's English name or its name in another language. For example, the symbol for the element iron is Fe - which comes from the Latin name for iron, ferrum. Some examples of common elements and their symbols are given in the table below.





















2) Atoms 

We know that matter is made up of tiny particles. These particles are called atoms. An atom is the smallest particle of any element


Atoms are very small. Each atom has a diameter of about 0.1 nanometre or 0.1 X 10 -9 metre. It would take about 1 000 000 000 000 000 or 1015 atoms to completely cover the head of a pin! We cannot see an atom with our naked eye. But if we look through an electron microscope, an instrument that can magnify objects millions of times, we might be able to see a crude picture of atoms as shown.

Each element consists of a particular type of atom. The atoms of each element are different from the atoms of any other element. For example, all hydrogen atoms are the same (although there can be slight differences between them – e.g. isotopes) and are different from atoms of carbon or iron.
3) Physical and Chemical Changes
In a physical change, no new substance is formed. These changes are easily reversed. An example is the dissolving of salt in water. The solution still consists of salt and water but does not contain any new substance. The change can "easily be reversed by evaporating the water to crystallise the salt. Other examples of physical changes include melting, boiling, mixing two solids or two liquids, and dissolv­ing solids in solvents such as petrol and alcohol.


In a chemical change, a new substance is formed. The new substance has different properties such as different melting points and different chemical reactions. You can often recognise a chemical change from two observations:

1. The new substance has a different appearance, such as a different colour or a different physical state. For example, the rusting of iron is a chemical change. The iron is a shiny grey colour but the rust produced is a brown colour.
2. A lot of heat is often given out in a chemical change. For example, the burning of a candle or cylinder gas in air is a chemical change. These chemical changes produce heat. The heat from such changes is used to provide us with energy.

Chemists call chemical changes chemical reactions.
4) Compounds and Mixtures

Compounds

A compound is a substance containing two or more elements joined together by a chemical reaction. A compound has very different prop­erties from its elements.


Magnesium oxide is a compound made of two elements: magne­sium and oxygen. It is made by burning magnesium in air.

The heat and light show that a chemical reaction took place. The elements are a silvery solid and a colourless gas. The compound has different properties: it is a white solid.


Water is a compound made up of two elements: hydrogen and oxygen. It can be made by applying a lighted splint to a mixture of hydrogen and oxygen.


The heat and light produced by the lighted splint show that a chemical reaction took place. The element hydrogen is a flammable gas. The compound water has very different properties: it is a liquid and does not burn.


The figure below shows the changes in the particles when water is formed from its elements. Each `circle' represents one atom. So the particles of hydrogen, for example, consist of two atoms joined together. In the mixture of hydrogen and oxygen, before reaction, the hydrogen and oxygen atoms are not joined together. When the reaction takes place, the hydrogen and oxygen atoms join together to form the particles of water. Each particle of water consists of two hydrogen atoms and one oxygen atom joined.


A particular compound always contains the same elements. These elements are always present in a fixed proportion in the compound. For example, the percentage composition of hydrogen and oxygen in water is always: 11% hydrogen, 89% oxygen. Water can be obtained from rain, rivers, the sea or a tap. It can be in the solid, liquid orgaseous state. In every case, it has the same percentage composition of hydrogen and oxygen.


When the elements combine together to form a compound, this compound cannot be separated again into its elements by physical means - such as filtering, distillation or dissolving in water. The atoms are firmly joined together. The atoms of different elements in a compound can only be broken apart in chemical reactions.

Mixtures

In a mixture of elements, the atoms of the elements are not joined together (see the mixture of hydrogen and oxygen shown ealier). The percentage of each element in a mixture is not always the same. A mixture does not have a fixed composition. A mixture of oxygen and hydrogen, for example, can have any composition of each element.


Brass is a mixture of two metals, copper and zinc. The percentage of zinc in most brass samples varies between 10% and 60%. Each element in a mixture retains its properties. A mixture can easily be separated by physical means such as filtration, crystallisa­tion or distillation.


A good way of distinguishing a single compound from a mixture of compounds, is from its melting point and its boiling point. A single compound has a fixed melting point and (at sea level) a fixed boiling point. For example, pure water (a single compound) melts at 0°C and boils at 100°C. Butter (a mixture of compounds) melts over the range 30°C to 50°C. This means butter starts melting at 30°C and is com­pletely melted at 50°C. Kerosene fuel used for jet aircraft (also a mixture of compounds) boils over the range of 170°C to 250°C.


Many common substances are mixtures - including air, sea water, concrete and cooking oil. Most metals are used as mixtures because they are stronger than pure metals. That is why brass is used for the pins of electric plugs instead of pure copper. Such mixtures of metals are called alloys.


A comparison of the characteristics of compounds and mixtures is summarised as in the table below.

Periodic Table

We have to memorise some of the periodic table, so as to prepare for our exam...
 Here is a periodic table.(but we do not need to memorise the transition metals)

Research

Below is what i read and watched from the bbc science news:

The three Rocketeers

DURATION: 50 MINUTES

For his entire life, one man has nursed the dream of putting mankind into space. Inspired by the Dan Dare comic strip, Alan Bond first started building rockets as a teenager in his back garden. He started his career working on Britain's Blue Streak rocket, then HOTOL - the world's first attempt to build a 'single-stage-to-orbit' spacecraft. Each time, he was thwarted by lack of funding from the UK government, so, together with two colleagues, Richard Varvill and John Scott-Scott, he decided to go it alone. This documentary tells the story of how the three rocketeers defeated the Official Secrets Act, shrugged off government intransigence and defied all conventional wisdom to build a revolutionary new spacecraft - Skylon.

Source:http://www.bbc.co.uk/programmes/b01mqv45

PS: pls take time to look at the video, it is really interesting, i spent my time watching it and it capture my attention, and make me ponder over it.

1P15:Bouncy egg!

​​​1P15: Bouncy Raw Egg with Moving Waters

​

Purpose: To demonstrate osmosis in living eggs

Step 1: Place a quail's egg in a beaker. Fill the beaker with dilute hydrochloric acid.

​Bubbles of colourless and odourless gas seen with white froth

​Inference:The egg shell is chemically reacting with the dilute hydrochloric acid and a gas was evolved.

Step 2: Soak the egg in the acid for bout 15 minutes, stirring with a glass rod occasionally

Step 3: After about 15 minutes, pour away the acid from the beaker

​Step 4: Carefully rinse the egg with tap water and examine it.

Step 5: Describe how the egg feels to the touch.

Step 6: Measure and record the length of the egg.

​Experimenting with the egg

1. Fill half a beaker with tap water and put the egg into the beaker.

​​2. After 30 minutes, remove the egg from the beaker of water. Describe its hardness and record yourobservation.

3. Put the egg back into the beaker of water. Describe the hardness of the egg and record your observation .​

Inference from observations

​Osmosis has occured. Water has moved from a region of higher water concentration in the beaker to a region of lower concentration in the egg across the partially permeable egg membrane. Thus the egg becomes harder/ turgid.