nota sains bab 2

CHAPTER 2 ( CELL AS A UNIT OF LIFE ) 

 2.1 What is a cell

1.Cell is a basic unit of life.
2. The cells structure can be observed by using microscope.
3. Steps using a microscope:
    a. Place the microscope with its mirror facing a light source.
    b. Adjust the mirror so that enough light enters the microscope.
    c. Place the slide onto the stage and ensure that the specimen is at the centre of the aperture.
    d. Adjust the rough / coarse focus knob and fine focus knob until the specimen can be seen clearly.
 4. The precaution steps when using / handling a microscope:
     a. Use both hands to hold the microscope. One hand holds the body while the other hand supports its                                       base.
      b. Place the microscope in vertical position.
      c. Ensure that the microscope is always dry and clean to avoid fungal growth and rusting. Clean the lenses with tissue paper.
      d. Always rotate the coarse adjustment in an anticlockwise direction.
      e. Open both eyes when viewing through the microscope.
       f. Initially, use an objective lens with low power.
       g. The glass slide with specimen must be closed with a cover slip.
5. Plant and animal cells differ in their shapes and functions.
6. Function of cells structures: Part of the cell Function Nucleus Controls all the activities of the cell Cytoplasm Stores dissolved material and chemical processes take place Cell membrane Protects the cell and controls the movement of substances in and out of the cell. Cell wall Support and maintains the shape of the cell Chloroplast Contains chlorophyll. Chlorophyll absorbs sunlight and changes light energy to chemical energy Vacuole Stored water and dissolved minerals
 7. Comparison of animal cells and plants cell Animal Cell Similarities Plant Cell Has protoplasm ( cytoplasm & nucleus ) Has cell membrane Able to carry out life activities Ex: excretion Animal Cell Differences Plant Cell Not fixed Shape Fixed Absent Cell wall Present Absent Vacuole Present Absent Chloroplast Present Glycogen Food reserves Starch


 2.2 Unicellular and Multicellular Organism 

 Unicellular Organism

• Consist of only one cell. 
• Cannot be seen with eye and can only be seen through the microscope. 
• Carry out all the processes of life such as movement, reproducing, breathing and excretion. 
• Unicellular animal: Amoeba and Paramecium 
• Unicellular plant: Euglena, Chlamydomonas and Yeast 

 Multicellular Organism

• Consist of many cells ( various types of cells ). 
• Carry out all the process of life.
• Each cell has a different structure and carries out certain body functions. 
• Multicellular animal: Fish, Rabbit and Hydra. 
• Multicellular plant: Spirogyra, mucor and fern. 

 2.3 Human Cells

• Human being is a multicellular organism. They have types of cells and their own function. Type of Cell Function Red Blood Cell Transports oxygen throughout the body Muscle cell To allow movements of the body White blood cell Kills germs that invade the body Sperm Fertilizes the ovum in sexual reproduction Nerve cell Conveys messages throughout the body Bone cell Support and protect organs Skin cell Prevent the loss of water from the body 
• The organisation of human body is as follow: Cells → Tissues → Organs → Systems → Organism 
• Cell : Performing a particular type of work are similar in many aspects. Each t type carries out a special function. 
• Tissues: A group of similar cells that performs the same work. Many type of tissue: muscle tissue & nerve tissues 
• Organ : Different tissues group together to perform a particular kind of work. Organ can consists two or more types of tissues to perform its function. 
• System: A few organ works together to perform a certain function in a life p r process to form a system. System Function Digestive Breaks down food materials for absorption by the body Excretory Remove excretory products from the body Nervous Coordinates activities of the body Endocrine Secretes hormones to maintain activities of the body Muscular Controls body movement Respiratory Takes in oxygen and removes carbon dioxide. Oxides food to produce energy Blood circulatory Transports nutrients, oxygen and excretory products Reproductive Produces offspring Skeletal Provides support to the body, maintains the shape of the body, protects internal organs and allows movements of the body 
• Organism: Is made up of many systems. 

2.4 Human Are complex Organism. 
 1. Human beings are considered complex organisms. Human cells are organized into tissues, organs and systems.
2. Each cell performs a specific function only.