[Biology Form 4] Being Multicellular

A multicellular organism is made up of millions of cells, all of which carry out specific and different functions depending on their shapes and structures, and the organelles contained in them.

In multicellular organisms, cells make up tissues, tissues make up organs and organs make up systems.

In an entity, they cooperate with one another and ensure the organism carry out its seven main living processes.

The kind of organisation is extremely necessary to allow different systems to carry out specific functions and to enable the organism to be a complete and functional individual.

Cell organisation

1. To gauge whether you know how multicellular organisms from the plant and animal kingdoms are organised, as the following table.
   

   Plant kingdom	Level of organisation	Animal kingdom
   Hibiscus plant	Organism	Man
   Shoot system	System	Circulatory system
   Leaf	Organ	Skin
   Vascular tissue	Tissue	Connective tissue
   Mesophyll palisade cell	Cell	Epithelial cell

   
   
   
2. Another example of how two other multicellular organisms are organised.
   

   Plant kingdom	Level of organisation	Animal kingdom
   Maze	Organism	Rat
   Root system	System	Circulatory system
   Root	Organ	Lungs
   Ground tissue	Tissue	Connective tissue
   Parenchyma	Cell	Red blood cell

   
   

[Chemistry SPM] Exam Pointers I

Essay
Shown (below) are the proton numbers of sodium and chlorine atoms.

• Element: Sodium, Na
  Proton Number: 11
  
  
• Element: Chlorine, Cl
  Proton Number: 17
  

a) The atomic radius of a chlorine atom is smaller than that of a sodium atom. Explain. [4_marks]

• Answer: The electron arrangements of sodium, Na, and chlorine, Cl, are 2.8.1 and 2.8.7, respectively. Since both of them have three electron-filled shells, they are found in the third period of the periodic table. However, the positive charge in the nucleus of chlorine is higher than that of the sodium atom. This is because a chlorine atom has more protons than a sodium atom. This leads to a stronger force of attraction between the nucleus and the electrons of the chlorine atom. Hence, the shells filled with electrons are pulled nearer to the nucleus, thus reducing the atomic radius of the chlorine atom.

b) Chlorine reacts with sodium to form a compound.

i) Explain the formation of the compound. [6_marks]

• Answer: The electron arrangements of sodium, Na, and chlorine, Cl, are 2.8.1 and 2.8.7, respectively. To form a sodium ion, a sodium atom donates one valence electron to achieve the stable octet electron arrangement, 2.8.
  
  Na --> Na⁺ + e^-
  To form a Cl^- ion, one atom of Cl receives one electron to achieve the stable octet electron arrangement, 2.8.8.
  
  Cl + e^- --> Cl^-
  The Na⁺ and Cl^- ions then forms an ionic bond as they are attracted to each other by a strong electrostatic force. Hence, an ionic compound of NaCl is formed.

ii) The compound conducts electricity is molten state but not in solid state. Explain. [2_marks]

• Answer: In solid state, no free moving ions are available to conduct electricity since strong electrostatic forces hold the ions together. In molten state or aqueous solution, however, the charged ions can move freely to conduct electricity.

[Chemistry Form 4] Two-way Conversion

Electrochemistry is the science that studies the relation between electricity and chemical changes. So how are they related?

An electric current can bring about an otherwise non-spontaneous chemical reaction, such as the recovery of metals from their ores and electroplating of surfaces.

In the process called electrolysis, electrical energy is converted into chemical energy, which is stored in the products of the reaction.

Aluminium and copper are some examples of the products of electrolysis.

Conversely, chemical energy can be converted into electrical energy.

This process can be seen in spontaneous chemical reactions and forms the basis for batteries and fuel cells in supplying electrical power.

An electrolyte is an electrically conductive substance that contains positively- and negatively- charged particles called ions.

The following are electrolytes and non-electrolytes;

• Electrolytes
  
  1. Copper (II) chloride
  2. Molten aluminium oxide
  3. Sodium hydroxide solution
  4. Silver nitrate solution
  
  
• Non-electrolytes
  
  1. Aqueous ammonia
  2. Copper (II) sulphate crystal
  3. Glucose solution
  4. Ethanol
  5. Solid sodium chloride
  6. Molten naphthalene
  7. Acetamide
  8. Tetrachloromethane

Did You Know?

• A battery is a device that converts chemical energy into electrical energy. In 1800, Italian physicist Alessandro Volta developed the first electric battery that generated a steady stream of electricity. His invention was called the Voltaic pile.
  
  Since then, the principles applied to the Voltaic pile have been used in batteries. In 1881, the volt (V), an electrical unit, was named after him.

[Science Form 1] Uses of Carbon Dioxide

Carbon dioxide is used in many consumer products that require pressurized gas because it is inexpensive an nonflammable.

Liquid and solid carbon dioxide are important refrigerants, especially in the food industry, where they are employed during the transportation and storage of ice cream and other frozen foods.

Solid carbon dioxide is called "dry ice" and is used for small shipments where refrigeration equipment is not practical.

Carbon dioxide is also used in the drinks and food that we consume everyday.


Activity

• Can you name a few types of food that contain carbon dioxide?

[Science Form 3] Electricity

Electrical energy

• Definition: Energy produced when an electric current flows.
  
  
• The source of electrical energy is any device that produces electric charges or electric current.

Electricity

• Definition: The flow of electric charges through a conductor.
  
  
• Electrons flow in the direction opposite to the electric current. The electric current is the rate of flow of electric charges passing through a conductor.
  
  
• The unit of electric current (I) is ampere.
  
  
• The unit of voltage (V) is volt.
  
  
• The unit of resistance (R) is ohm.
  
  
• Different materials have different resistance to electricity.
  
  
• The resistance of a conductor is affected by its length, diameter and temperature.
  
  
• A very high resistance allows only a very small amount of current to flow.

Van De Graaff generator

The Van De Graaff generator is a device that can produce electric charges of very high voltage. When the motor is turned on, the lower roller (charger) begin turning the belt.

As the belt is made of rubber and the lower roller is covered in silicon tape, the lower roller will begin to build a negative charge while the belt builds a positive charge.

The negative charge on the lower roller is built up by capturing electrons from the belt as it passes over the roller. This occurs as silicon is more negative than rubber in the triboelectric series.

[Science PMR] Exam Overview

The PMR science exam consists of two papers:

Paper 1 (40 marks)

• 40 objective questions.
  
  
• One hour to complete the paper.
  
  
• Cover all 27 Science topics from Form One to Form Three.
  
  
• There will be at least one question from each topic.
  
  
• The questions are broken down into:
  
  • 50% easy questions; that is about 20 questions.
  • 30% moderate questions; that is about 12 questions.
  • 20% difficult question; that is about eight questions.

Paper 2 (60 marks)

• Section A consists of six questions for 40 marks.
  
  
• Section B consists of two questions for 20 marks.
  
  
• Only questions from selected topics will be asked.
  
  
• Answers can be written all in English or all in Bahasa Melayu or a combination of both language [Please do not combine both languages in the same sentence!]
  
  
• You may answer part of the question in one language and the other part in the other language.
  
  
• The questions are broken down into:
  
  • 50% easy questions; that is about 30 marks.
  • 30% moderate questions; that is about 18 marks.
  • 20% difficult questions; that is about 12 marks.
    
    
• The type of questions commonly asked in Paper 2 are:
  
  • Labelling questions
  • Classification
  • Questions based on experiments
  • Chemical tests
  • Calculation
  • Principles of science
  • Drawing
  • Structured questions
  • General questions

[Science Form 3] Units of Electricity

Volts (V)

• Voltage can be compared to the pressure of water in a hose. The higher the pressure, the faster the water will flow through the hose.
  
  Similarly, the higher the voltage of electricity, the faster it will flow from the source of the electricity to an end user.
  
  A volt, or the unit of voltage, is a common electrical measurement. It is used, for example, to discuss the transmission of electricity from power plants to end users.
  
  

Ohms

• Ohm measure resistance and can be compared to the diameter measurement of a hose. A smaller diameter hose will allow less water to flow through than a larger diameter hose.
  
  Similarly, a thinner wire increases resistance, causing a lesser amount of electricity to be transmitted because it is encountering resistance in the wire.
  
  To reduce resistance, certain metals, such as copper, which allows electrons to flow easily, are used to conduct electricity.
  
  

Amperes (A)

• Amperes can be compared to the volume of water that flows through a hose. The volume of water that flows past a certain point in a specific amount of time can be measured.
  
  Similarly, amperes measure the number of electrons that pass a specific point within a certain amount of time (rate of current) in a circuit.
  
  One ampere is equivalent to approximately 6.25 X 10¹⁸ electrons passing by a specific point in one second.
  
  The rate of the electric current is dependent upon the voltage and resistance. A circuit with high voltage and low resistance will have more amperes (greater number of electrons passing through the circuit) than a circuit with low voltage and higher resistance. The former example has more power than the latter.
  
  It is important to measure the amount of amperes in a circuit because it can help calculate the amount of power consumption or output of a circuit.
  
  

Ohm's Law

1. Ohm's Law is used to describe the mathematical relationship between electric current, voltage and resistance.
   
   
2. We can arrange Ohm's Law depending on which component we are trying to find out.
   
   • I = V/R
   • V = I x R
   • R = V/I
     
     
3. All these variations of Ohm's Law are mathematically equal to one another...
   Measuring of;
   
   • Current (I)
     
     • Method: Ammeter
       Unit= Amperes (A)
       # The ammeter is connected in series to a circuit. The movement of the ammeter needle shows that current is flowing in the circuit.
       
       
   • Voltage (V)
     
     • Method: Voltmeter
       Unit: Volts (V)
       # The voltmeter is connected in parallel to a circuit when measuring voltage.
       
       
   • Resistance
     
     • Method: Resistor
       Unit: Ohm
       # The higher the resistance, the bigger the ohm value in a resistor.

[Science PMR] The Experiment Question

The last question in Paper 2 is usually question number 8, which carries 12 marks. This question will be based on an experiment where you have to write down:

• Readings [Make sure the unit of measurement you use is correct]
  
  
• Variables
  
  • Constant variable [This is the fixed variable]
    
    
  • Manipulated variable [This is the factor that is changed in the experiment to get the specific result. ie: Length of wire (cm)]
    
    
  • Responding variable [This comes from the readings or the results of the experiment. ie: Ammeter reading]
    
    
• Aim of experiment
  
  • Example: To study/investigate the relationship between the manipulated and the responding variable.
    
    
• Hypothesis
  
  • This shows the relationship between the manipulated and the responding variable.
  • Writing format: "When the manipulated variable increases/decreases, the responding variable will increase/decrease."
    
    
• Observation
  
  • What can be observed or what you can see.
    
    
• Plot a line or bar chart
  
  
• Prediction
  
  • This will be based on your graph, where you have to predict a reading for the responding variable when given a value for the manipulated variable.
  • Example of a question: From the graph, find out the value of T when the mass is 10g.
    
    
• Inference
  
  • This is the early conclusion based on your observations.
  • Example: The change in the responding variable depends on the manipulated variable.
    
    
• Conclusion
  This is the same as the hypothesis.

Note: It is very important to get your manipulated variable and the responding variable correct!