chapter 2: cell as the basic unit of life

2.1 What  is     a     cell?

1.      Cells are the basic units of life.

2.     All living thing are made up of cells

3.     Cells are the smallest living parts in a living thing.

Examples :

A flat is the basic unit of  block of flat. A brick is the basic unit of wall.

4.     Some living things are very simple.  
        They are made up of only one cell.

5.     Some living things are very complex.  
        The human body is made up of 50 to 60 trillion cells.

2.2 Microscope

1.   Cells are very small. We cannot see them with the naked eye.

2.   We need the help of a microscope to see cells.

3.   A microscope is a tool that enables us to look at small things which cannot be seen with the naked eye.

4.   A microscope is very expensive. It must be handled with care.

5.   Always keep the microscope clean and dry.

6.   Use the low power objective lens first before you use the high power objective lens.

7.   Turn the focus knob slowly and carefully so that you do not break   the slide.

2.3 How  To  Use  A          Microscope.

1.   Put the microscope on the table with the arm towards you.

2.   Turn the low power objective lens until you hear the ‘ click’ sound.

3.   Make sure that the low objective lens is above the hole in the 
      stage

4.   Open the diaphragm to the maximum opening.

5.   Look through the eyepiece. Adjust the mirror until you see the bright, circular area.

6.   Put a specimen slide over the hole of a stage. Fix the slide‘s position with the clips.

7.   Turn the coarse focus knob to lower objective lens to about 10 mm above the slide.

8.   Look through the eyepiece. Turn the coarse focus knob to move the objective lens upwards until you see a clear image.

9.   Turn the fine focus knob to get a sharp image.

10. Turn the high power objective lens until you hear the ‘click’ sound.  Repeat step 9.

2.7 Unicellular            and             multicellular             organisms

Unicellular  PMR 03, 07, 08

1.      Some living things or organisms are made up of one cell.

2.     These are:

•  Amoeba- animal  
•   Paramecium-animal
•  euglena-animal (contains chloroplast)
• chlmydonas-plant 
•  yeast-plant 
• pleurococus-plant

3.     They are unicellular organisms `uni’ means `one’

Multicellular     PMR 06

1. Multicellular organisms are made up of more than one cell.

2. Animals and most plants are also multicellular organisms. (mammal, bird, reptile, amphibian, fish)

3. Examples of multicellular organisms:

•  Hydra - animal 
•  Spirogyra – plant (contains chloroplast)
• mosses  
• ferns
• flowering plant

2.3 General          Structures         Of        animal  Cells          and    Plant       Cells.

1.	A cell is made of many different parts or structures.
2.	The animal cell and the plant cell have three common structure membrane, the nucleus and the cytoplasm
3.	Protoplasm         refers  to     both      the   cytoplasm       and  the     nucleus.

4.   The cell membrane  and cytoplasm are structures present in all 
       types of cells 

5.   However,  not every cell has a nucleus. The human red blood cell does not have a nucleus.

6.   The plant cell has three structures which are not found in the
       animal cells: the cell wall, the vacuole and the chloroplasts.

7.   The cell wall is a border that surrounds a plant cell. The cell wall is present in every plant cell.

8.   The vacuole is a large sac that takes up a great part of a plant cell. A plant cell  has only one vacuole.

9.   Chloroplasts contain chlorophyll, which is a green pigment that gives a plant its green colour.

10. Chloroplasts are found  in the green parts of a plant, for example the leaves.

11. The cells in the roots of a plant do not have chloroplasts.

2.4    Functions   Of        Cell       Structures.

1.      Every cell structure performs a function for the cell.

2.      The function of a chloroplast is to carry out photosynthesis to make food for the plant.

3.      Only cells that contain chloroplasts can carry out  photosynthesis.  The cells in a plant root for example, cannot carry out photosynthesis.

4.      The  nucleus can control all activities of the cell because it contains chromosomes.  Chromosomes carry genetic  information that control the cell’s activities.

5.      The cell membrane is the structure that controls what substances move into or out of the cell.

6.      Food passes through the cell membrane before it enters the cell.

7.      Waste materials pass through the cell membrane  before they leave the cell.

8.      The cell wall is  a strong structure that gives the plant cell a regular shape .   The animal cell does not have a regular shape because it does not have a cell wall.

2.5       Cells          In        The    Human    Body.

1.   The human body is made up of trillion of cells.

2.   There are about 200 types of cells in the human body.

3.   Each type of human cell is responsible for doing a specific job for  
      the bodys

Examples :

i.   Fat cells                 -   store fat for the body

ii.   Human sperm cell   -  the male reproductive cell

iii.   Human egg cell       -  the female reproductive cell

iv.   Red blood cell         -  carry oxygen to different parts of the body

v.  White blood cell      -  kill bacteria and protect the body from 
                                       dicease
vi.   Bone  cells PMR 06, 07  -form bones that protect and support
                                              the body  
viii.   Muscles cells - form muscle tissues which enable 
                                 movements

   xi.   Epithelial cells  -  join together to form the skin that 
                                   covers body and lines the inner surface of the   
                                   body. 
    x.   Nerve cells        -carry massages in the form of electrical
                                       signals (impulses) between different parts of
                                     the body.

2.6    Organization      Of       Cells      In     The       Human        Body

1.   The cells in the human body do not work  individually.

2.   They are organised  to work together to perform various functions of body.

3.   The organization of cells in the human body from simple to complex is shown below :

i.    Cell    - The basic unit that makes up the body. 
                  Example : red blood cell, white blood cell.

           ii.    Tissue PMR 08   -Made up of the same type of cells that work

Together to perform a function.  
Examples:epithelial tissue PMR 06, muscle tissue,  bone tissue and nerve tissue.

iii.Organ     -  Made up of different tissues that work together to perform a function. Examples  :  brain, eyes,   nose, ears,   lungs,   heart  and skin.

iv.     System - Made up of different organs that work together to perform a  function. There are ten systems in the human body.

Examples

Skeletal system

1. Excretory system

2. Muscular system

3. Respiratory system

4. Blood circulatory

System

1. Digestive system

2. Lymphatic system

3. Endocrine system

4. Nervous system

5. Reproductive system

2.6 The        Body   System.

Name Of System	Organs In System	Function Of System
Skeletal System	Skull,   Rib,    Pelvic girdle, Back bone.	-       Forms the skeleton -       Support the weight of the body. -        Protects internal organs, for examples, the heart  and lungs. ( It supports or holds up the body)
Excretory  System	Kidney,   Ureter,  Liver, Skin,  Urinary Bladder, Lungs.	-       Removes waste materials. For example, water vapour,  carbon dioxide and urine from the body.
Muscular System	Skeletal  Muscles,   Smooth Muscles,   Cardiac Muscles.	-     Enables body movement. -     Enables the heart  to beat. -     Enables food to move from     the mouth to the intestines. -     Enables breathing.
Respiratory System	Nose,  Trachea,  Lungs	-     Takes in oxygen from the atmosphere. -      Removes carbon dioxide and water vapour from the body. (It supplies oxygen and removes carbon dioxide)
Blood Circulatory System	Heart,  Blood vessels	-     Carries oxygen and food to every part of the body. -      Carries waste materials to the kidney. -      Carries carbon dioxide to the lungs. (It transports blood throughout the body)
Digestive System	Mouth,  aesophagus, Stomach,  Liver, Pancreas, Gall bladder,  Small intestine,  large intestine.	-       Breaks food down into simpler substances which the body can absorb. (  It digests food  )
Lymphatic system	Lymph nodes,  Lymphatic vessels.	-      Defends the body against infection with the help of lymphocytes  (a type of white blood ).
Endocrine System	Thyroid gland,  Pituitary gland,  Adrenal gland, Testis,  Ovary,  Pancreas.	-     Makes  and secretes hormones to control the activities of the body. -     Controls mental development, growth  and reproduction.
Nervous System	Brain.  Nerves,  Spinal Cord.	-     Responds to changes inside and outside the body. (  It coordinates the activities of the body).
Reproductive System	Female      -       Ovary Male         -        Testis	-     Produces  egg cells. -     Produces sperm cells. (It produces young ones for the next generation)