This Class 12 Biology practical focuses on observing the transverse section (T.S.) of a mammalian blastula using permanent slides. The blastula is an early embryonic stage formed after repeated mitotic divisions of the zygote. Studying its structure helps students understand the basics of embryonic development.
Under the microscope, students can identify the blastoderm, blastocoel, and the arrangement of cells forming the early embryo. The blastula appears as a hollow, spherical structure with a fluid-filled cavity. Observing these features allows learners to appreciate how complex organisms begin from a single cell.
This practical is essential for CBSE Class 12 Biology exams as it builds a strong foundation in developmental biology. By drawing labelled diagrams and noting key characteristics, students improve their practical record work. This topic is frequently asked in viva questions, making it an important part of Class 12 Biology practical preparation and revision.
AIM: T.S. of blastula through permanent slides (Mammalian)
REQUIREMENTS:
Permanent slide of T.S. of blastula, compound microscope, lens cleaning fluid and paper, pencil eraser.
PROCEDURE:
i. Select a good prepared slide of t. . of blastula and focus under 10x magnification under light microscope.
ii.Now, study the structures and draw the different layers of cells seen.
iii. And finally compare these structures with the labelled diagrams given ahead and identify them accordingly.
OBSERVATIONS:
The transverse section of blastula shows the following features:
i. It is a spherical mass of cells
ii. The outermost layer, i.e. zona pellucida followed by a layer of trophoblasts is clearly seen.
iii. Within the envelope, a fluid filled cavity called blastocoel is commonly found.
iv. Mass of cells inner to the trophoblast is called inner cell mass. Inner mass cells form the embryo.
v. The blastocyst has embryonic or animal pole which is found opposite to the abembryonic pole.
RESULT
The transverse section of blastula clearly shows all the characteristic features of blastula stage of a mammal.
PRECAUTIONS
- Objective and eye lenses should be cleaned before viewing the slide.
- The slide should be centrally placed so that it can be focused properly under the low and high powers of compound microscope in order to enhance the clear visibility of all cells.
Class 12 Biology Lab Manual – Final Practical | Complete Lab Experiment File
A. List of Experiments
1. Prepare a temporary mount to observe pollen germination.
2. Study the plant population density by quadrat method.
3. Study the plant population frequency by quadrat method.
4. Prepare a temporary mount of onion root tip to study mitosis.
5. Isolate DNA from available plant material such as spinach, green
pea seeds, papaya, banana etc.
B. Study and observe the following (Spotting):
1. Flowers adapted to pollination by different agencies (wind, insects, birds).
2. Pollen germination on stigma through a permanent slide or scanning electron
3. Identification of stages of gamete development, i.e., T.S. of testis and T.S. of
ovary through permanent slides (from grasshopper/mice).
4. Meiosis in onion bud cell or grasshopper testis through permanent slides.
5. T.S. of blastula through permanent slides (Mammalian).
6. Mendelian inheritance using seeds of different colour/sizes of any plant.
7. Prepared pedigree charts of any one of the genetic traits such as rolling of tongue,
blood groups, ear lobes, widow's peak and colour blindness.
8. Controlled pollination - emasculation, tagging and bagging.
9. Common disease causing organisms like Ascaris, Entamoeba, Plasmodium, any
fungus causing ringworm through permanent slides, models or virtual images or
specimens. Comment on symptoms of diseases that they cause.
10. Models specimens showing symbiotic association in lichens, root nodules of
leguminous plants, and parasitic mode of nutrition shown by Cuscuta on host.
11. Flash cards / models showing examples of homologous and analogous organs.
Class
Biology
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