Study Notes for Practical Exam in General Biology I PDF

Study Notes for Practical Exam in General Biology I (First Quarter Topics) MICROSCOPY W...

Study Notes for Practical Exam in General Biology I (First Quarter Topics) MICROSCOPY What is a MICROSCOPE? A microscope is an instrument that can be used to observe small objects, even cells. Its lens bends light toward the eye and makes an object appear larger than it actually is. Parts of a Microscope and their Functions BASE: It acts as microscope’s support. It also carries microscopic light source. FINE ADJUSTMENT KNOB: This knob is inside the coarse adjustment knob and is used to bring the specimen into sharp focus under low power and is used for all focusing when using high power lenses. COARSE ADJUSTMENT KNOB: This is used for a rapid control which allows for quick focusing by moving the objective lens or stage up and down. It is used for initial focusing. STAGE: This is the section in which the specimen is placed for viewing. ARM:. It gives support to the head of the microscope and it is also used when carrying the microscope. OCULAR LENS/ EYEPIECE: This is the part used to look through the microscope. It’s found at the top of the microscope. LIGHT SOURCE: Also known as the microscopic illuminator, this is the microscope's light source, located at the base. It is used instead of a mirror. DIAPHRAGM: It’s also known as the iris. It is found under the stage of the microscope and its primary role is to control the amount of light that reaches the specimen. STAGE CLIPS: Stage clips hold the slides in place. OBJECTIVES: These are the major lenses used for specimen visualization. They have a magnification power of 40x-100X. Your microscope has commonly 4 objective lenses: Scanning (4x), Low Power(10x), High Power(40x), and Oil Immersion (100x). In addition to the objective lenses, the ocular lens (eyepiece) has a magnification. The total magnification is determined by multiplying the magnification of the ocular and objective lenses. REVOLVING NOSEPIECE: Or simply known as nosepiece, it holds the objective lenses. It is movable hence it can revolve the objective lenses depending on the magnification power of the lens. BODY TUBE: Also known as the head. It carries the optical parts in the upper part of the microscope. __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez  MITOSIS (Onion Root Tip) Observing the Different Stages of Mitosis in Onion Root Tips Root tip as compared to the leaf tip is the best material to study mitosis. Root tip is a rapidly growing part of a plant body because of the meristematic cells that are situated in the tip of the roots, and thus many cells will be in different stages of mitosis, making it the most desirable and suitable raw material to study the different stages of mitosis. In actively growing onion (Allium cepa) root tips, you usually find at least a few cells at various stages of mitosis. The majority of cells will be in interphase, so it is important to go to 400x magnification to clearly see the mitotic cells. It takes a bit of time to view the cells carefully to start to recognize the different stages. Use the diagram below to help identify the stages of mitosis. Here are more examples showing the different stages of mitosis in different onion (Allium cepa) root tip sample slides: __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez Now, during your practical exam, remember that a sample slide of Allium cepa root tip may contain multiple stages of mitosis. They won’t be singled out or individually focused like the photos above. You may need to carefully examine and identify them one by one. Let’s take a look at actual HPO photos of your Allium cepa root tip, and examine each stages of mitosis. INTERPHASE Just a dark mass. NOTE: In some older microscopes, those cells in interphase may appear like a simple big, black dot/circle. PROPHASE __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez METAPHASE ANAPHASE __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez TELOPHASE Let’s take a look at other examples: __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez PHASES OF MITOSIS: A Simple Recall of Your Past Lesson 1. Prophase The process of mitosis is initiated at this stage wherein coiling and thickening of the chromosomes occurs Shrinking and hence the disappearance of the nucleolus and nuclear membrane takes place The stage reaches its final state when a cluster of fibers organizes to form the spindle fibers 2. Metaphase Chromosomes turn thick in this phase. The two chromatids from each of the chromosomes appear distinct Each of the chromosomes is fastened to the spindle fibers located on its controller Chromosomes align at the center of the cell 3. Anaphase Each of the chromatid pair detaches from the centromere and approaches the other end of the cell through the spindle fiber At this stage, compressing of the cell membrane at the center takes place 4. Telophase Chromatids have reached the other end of the cell The disappearance of the spindles Chromatin fibers are formed as a result of the uncoiling of daughter chromosomes The appearance of two daughter nuclei at the opposing ends due to the reformation of the nucleolus and nuclear membrane At this phase, splitting of the cell or cytokinesis may also occur __________________________________________________________________________________________________ PREPARED BY: Ma. Trisha Nicole B. Valdez