SC F1 CHAPTER 2

2.1 What is a Cell?

1. All living things whether they are plants or animals are made up of cells.
2. Cells are the basic units of all living things.
3. Cells are microscopic and can only be seen through a microscope.

Microscope

Technique in Using a Microscope

A microscope is used to examine specimens which are too small to be seen with the naked eye.

It is a very delicate and expensive instrument. It must be used with great care so as not to damage it.

Do

1. Use both hands when carrying a microscope-one hand to hold the limb and the other to support the base.
2. Place the microscope down gently on a table in an upright position.
3. Always keep the stage and other parts of the microscope dry.
4. Always clean the lenses with tissue paper only to avoid scratching them.
5. Always start viewing a specimen with the low power objective lens. Change to the high power lens if necessary.
6. Use the fine adjustment knob for focusing when viewing with the high power objective lens.

Don’t

1. Don’t repair the microscope; report any damage to your teacher.
2. Don’t view slides which are wet; wipe the slides with tissue paper.
3. Don’t use the high power objective lens without covering the specimen with a cover slip.
4. Don’t squint down the microscope; view the specimen with both eyes open.

Technique in mounting a Slide on a Microscope for Viewing

1. Place the microscope in a well-lit place such as in front of the window.
2. Fit the eyepiece for the microscope.
3. Fit the low power objective lens and turn it to position.
4. Look down the eyepiece and adjust the mirror so that a bright view is obtained.                            (Make sure the diaphragm is open if there is one.)
5. Place the prepared slide on the stage so that the specimen to be viewed is in the middle of the hole on the stage.
6. Placing your eye level with the stage, slowly lower the objective lens until it is very close to the slide.
7. Looking down the eyepiece, turn the coarse adjustment knob towards you (raising the objective lens) until the specimen is in focus.
8. Change the objective lens to a medium or high power if necessary. Use the fine adjustment for the high power objective lens.

Technique in Mounting a Specimen on a Slid

1. Place the specimen in the middle of a clean slide.
2. Place a drop of water on the specimen,
3. With the help of your fingers and a long needle, gently lower a cover slip on the specimen. Do not trap any air bubbles!
4. Use a piece of filter paper to wipe away any water around the cover slip. The slide is now ready for viewing.
5. If you wish to stain the specimen: (a) place a drop of iodine solution or methylene blue solution at one end of the cover slip (b) use a strip of filter paper at the other end of the cover slip to draw the solution across the specimen, using irrigation technique.

Animal cells

Generally, each animal cell is made up of cell protoplasm (cytoplasm and nucleus) and cell membrane.

Nucleus	Controls all the cell activities
Cytoplasm	Place where chemical processes occur/ Store food and waste products
Cell Membrane	Controls the movement of substance in and out of the cell

Plant cells

Typical plant cells are rectangular in shape. The plant cell has a rigid cell wall. A cell wall is made up of cellulose, which is a form of carbohydrate.

Nucleus	Controls all the cell activities
Cytoplasm	Place where chemical processes occur/ Store food and waste products
Cell Membrane	Controls the movement of substance in and out of the cell
Cell Wall	Supports and maintains the shape of the cell
Vacuoles	Store water and maintains the shape of the cell
Chloroplast	Chlorophyll absorbs sunlight that is used in photosynthesis. Photosynthesis is the process by which plants make food.

2.2 Unicellular and Multicellular Organisms

Living things are also known as organisms. All living things that are very tiny and can only be seen under a microscope are called microorganisms.

  

Animal cell	Similarities	Plant cell
Has protoplasm (cytoplasm and nucleus)
Has cell membrane
Able to carry out life activities like excretion
	Differences
Not fixed	Shape	Fixed
Absent	Cell wall	Present
Absent except in lower level organisms like Amoeba	Vacuole	Present
Absent	Chloroplast	Present
Glycogen	Food reserves	Starch

Unicellular Organisms

1. Unicellular organisms are living things that have only one cell.
2. Unicellular organisms have a very small body size which can only be seen                                    through a microscope.
3. Unicellular organisms usually live in water or in wet place.
4. There are two type of unicellular organisms: (a)Unicellular animals: Amoeba, Paramecium, Plasmodium (b)Unicellular plants: Chlamydomonas, Yeast, Euglena, Pleurococcus
5. Unicellular organisms carry out all of the life process such as moving, feeding, reproducing, breathing, and excreting.

Multicellular Organisms

1. Multicellular organisms are living things that have more than one cell.
2. Multicellular organisms are made up of various types of cells
3. Each cell has a different structure and carries out certain body functions.
4. There are two type of multicellular organisms: (a) Multicellular animals: Hydra, bird, fish        (b)Multicellular plants: Spirogyra, Mucor, Grass
5. In multicellular organisms, all cells perform their own specialized functions

 

2.3 Cells in the Human Body

The human body is made up of different kinds of cells that perform specialized functions as                 shown as below:

Organizations of cells

The ladder of hierarchy, which shows the organization of cells:

Cells-The basic unit of life

ex.: nerve cell, reproductive cells

Tissues-A group of similar cells performing the same function

ex: muscle tissue, ciliated epithelial tissue

Organ-A group of different types of tissues that perform a particular type of work

ex: ear, stomach

System-A group of organs working together to perform a specific function

ex: respiratory system, blood circulation system

Organism-Made up of several systems that work together

ex: human