🌱 Study the Plant Population Density by Quadrat Method | Class 12 Biology Practical

          The quadrat method is one of the most important ecological techniques used in Class 12 Biology Practicals. It helps students understand how to calculate plant population density in a given area. This method is simple, accurate, and widely used by ecologists to study vegetation.

 AIM:

To determine the population density of plants by quadrat method

REQUIREMENTS:

Thread, nails, hammer, metre scale, paper, pencil

PROCEDURE:

1. In the selected site of study, hammer the nails firmly without damaging the vegetation

2. Fix four nails to make a square

3. Tie each end of the nails using a thread, to make a 1 m X 1 m quadrat.

4. Similarly make nine more quadrats randomly in the site of study.

5. Count the number of individuals of a species "A" present in the first quadrat.

6. Record the data in the table

7. Repeat the same procedure for species B,C and record the data in the table.

8. We can calculate the density of plant population by this equation:

9. Density =Total number of individuals of the species in all the sampling unit (S)

Total number of sampling units studied (Q)

The density value thus obtained is then expressed as number of individuals per unit area.

CONCLUSION:

The population density is the highest for species A and the lowest for species C. The density value is expressed as the number of individuals per unit area.

PRECAUSTION:

• Count the individuals of one plant species at a time.
• Field chosen should have uniform distribution of species.

The Class 12 Biology Practical on “Study of Plant Population Frequency by Quadrat Method” is an important experiment that helps students understand how plant species are distributed in a given area. This practical is commonly included in school field studies because it is simple, reliable, and provides valuable ecological insights.

 AIM: Study the plant population frequency by quadrat method.

REQUIREMENTS:

Thread, nails, hammer, metre scale, paper, pencil

PROCEDURE:

1. In the selected site of study, hammer the nails firmly in the soil without damaging the

vegetation.

2. Fix four nails to make a square.

3. Tie each end of the nails using a thread, to make a 1 m X 1m quadrat.

4. Similarly, make nine more quadrats randomly in the site of study.

5. Select the plant species for study of the population frequency.

6. Observe the presence of species "A" in the first quadrat and mark it in the table

7. Similarly, check for the presence of species "A" in other quadrats respectively and

record the data in the table.

8. Observe the presence of species "B" in all quadrats and mark it in the table.

9. Repeat the same procedure for species C and record the data in the table.

10. We can calculate the frequency of plant populations by this equation:

11. Percentage Frequency=(Number of sampling units in which the species occurs)/(Total

number of sampling units employed for the study)* 100

OBSERVATION:

of sample quadrats.

CONCLUSION:

The plant population frequency is the highest in species C and the least in species A. It shows how many times a plant species is present in the provided number of sample quadrats.

PRECAUSTION:

1. Measure the quadrat accurately,

2. Quadrats should be studied from one area only, with uniform distribution of plants

Class 12 Biology Lab Manual – Final Practical's | 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 

micrograph.

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

Preparing a temporary mount of an onion root tip to study mitosis is an important Class 12 Biology practical that helps students observe cell division stages clearly under a microscope. Onion root tips are ideal because they contain actively dividing meristematic cells. In this practical, students soften the root tip, stain it using safranin, and gently squash it to create a thin, transparent slide. Under the microscope, stages like prophase, metaphase, anaphase, and telophase become visible. This experiment strengthens understanding of the cell cycle, mitosis, and chromosomal behaviour, making it a key part of Class 12 Biology practical exams and lab learning.

AIM:- Prepare a temporary mount of onion root tip to study mitosis

 REQUIREMENTS

Onion bulbs, conical flasks/glass bottles, corked vial/tube, petri dishes, scissors, forceps, methyl alcohol, acetic acid, hydrochloric acid, acetocarmine, distilled water, spirit lamp, microscope. slides coverslips blotting paper etc.

PROCEDURE

1. Take medium sized bulb of onion and trim off the old roots from its base by means of a sharp blade,

Place the onion on a conical flask/ glass bottle full of water, with its base touching the water.

Keep it for a week to grow the roots.

Cut 5 mm off the tips of roots and put them into a vial containing a mixture of 1 : 3 acetic acid and methanol. Keep for one hour. This process is called fixation. (Cutting of root tips should be done in the morning between 7.00 a.m. to 8.00 a.m. during the summer and between 9.30 a.m.to 11.30 a.m. during the winter).

Remove 2 or 3 root tips and hydrolyse them by warming to 60⁰C in 1 N hydrochloric acid for 15 minutes

5. Remove the root tips and wash them thoroughly in water.

6. Place a drop of acetocarmine on a slide. Put one hydrolyse root tip in a drop and place a coverslip on the root.

7. Gently squash the root by tapping the coverslip with the blunt end of a pencil or needle until the cells separate and spread out into a very thin layer.

Make sure that there are no air bubbles under the coverslip.

8 Gently warm the slide over a flame for a few seconds.

9. Observe first under the low power of the microscope to locate the dividing cells. Examine the different stages of mitosis under the high power of the microscope.

OBSERVATIONS

Under low power of the microscope, rectangular cells with Pink nucleus are seen scattered. Under high power of the microscope following stages become distinct:

1. Interphase

(i)It is a non-dividing phase of the cell cycle between two successive cell divisions.

(ii) Chromatin fibres appear in the form of a network within the nucleus.

(iii) Nuclear envelop and nucleolus are distinct.

2. Prophase

(i) Chromatin material shortens and condenses into thread like structures called chromosomes

(ii) Each chromosome consists of two chromatids, jointed at a point called centromere.

(iii) Nuclear membrane and nucleolus start disintegration and disappear at the end of prophase. 

3. Metaphase

(I) A bipolar spindle develops in the cell Chromosomes become thick and two chromatids of each chromosome become clear.

(ii) Chromosomes become arranged at the equator of the spindle

(i) Each chromosome get attached to the spindle fibres at its centromere.

4. Anaphase

(i) The two sister chromatids of each chromosome separate from the centromere and move towards the opposite poles.

(ii) The daughter chromosomes (separated chromatids) appear V.J L and I shapes, depending upon the position of centromere,

5. Telophase

(i) The spindle disappears and the daughter chromosomes uncoil to form chromatin fibres at the two poles,

(ii) Nuclear membrane and nucleolus reappears and two daughter nuclei appear at opposite poles,

(iii) Cytokinesis occurs by cell plate formation between the two daughter nuclei.

PRECAUTIONS

1. The base of the onion bulb should be in contact of water while growing the roots.

2. Root tips should be fixed in the morning between 8 to 10 A.M

3. The slide should be warmed gently much above the flame of the spirit lamp.

Class 12 Biology Lab Manual – Final Practicals | 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 

micrograph.

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

Class 12 Biology Practical: To Perform Emasculation, Bagging and Tagging for Controlled Pollination | Practical File

Aim: To perform emasculation, bagging and tagging for controlled pollination

Principle: Conventional plant breeding programmes involve bringing under human control reproductive processes that lead to seed and fruit formation. For this controlled pollination is desirable using male and female parent having desired traits. One of the process that can be easily brought under human control is emasculation. For this the knowledge of flower structure, mechanism of pollination, fertilisation and physiology of flowering is essential for this. In emasculation technique the stamens are removed before anthesis to obtain female parent and pollen from the desired male parent is transferred on to its stigma.

Requirement: Ornamental plants/ wild plants bearing large bisexual flower, magnifying lens, tweezers, small sharp scissors, brush, alcohol, rubber bands, paper bags, paper clips and tags

Procedure

(i) Select a flower in bud condition where antheses has not occurred. Open the bud carefully and remove the stamens. Mark this as female parent plant.

(ii) Cover the emasculated flower with a plastic bag to protect it from undesired pollen (Bagging) (Fig. 12.2). The bag should be held securely in place with a paper clip/ string/thread. Select the size of bag in accordance with the flower size. Bags must be transparent with minute pores. 

(iii) Bring into physical contact anthers of a desired male plant containing mature pollen grains with the stigmatic surface of emasculated female flower. Use tweezers/brush if necessary to dust the stigmatic surface with pollen.

(iv) Cover the pollinated flower again with the bag immediately. For identification, label the female parent (Tagging). Each pollinated flower should bear a label containing the name of the seed parent, the letter X (to signify a cross), the name of the pollen parent, and the date on which the cross was effected.

OBSERVATION

Afier controlled pollination . the plant is kept undisturbed and under observation till seed setting and harvesting, This leads to the success of the experiment.

RESULT

By the process of controlled pollination, the female parent Plant will produce seeds of the desired characteristics.

Precautions

• A good variety of parent plant should be selected.
• Care should be taken while doing emasculation.
• After controlled pollination. proper care of experimental plant should be done till seed setting

This Class 12 Biology Practical aims to help students understand Mendelian inheritance by studying the colour and size of seeds from any plant, such as pea or bean. Mendel’s laws—Law of Dominance, Law of Segregation, and Law of Independent Assortment—explain how traits pass from parents to offspring. In this experiment, students observe dominant and recessive characters like yellow vs. green seeds or round vs. wrinkled seeds.

To perform this practical, collect seeds of two contrasting traits, mix them, and classify them based on appearance. Record the number of each phenotype and compare your ratio with Mendel’s expected 3:1 ratio for monohybrid crosses or 9:3:3:1 for dihybrid crosses.

This practical helps students clearly understand genetic patterns, Punnett squares, and real-life applications of heredity. It is an important experiment for CBSE Class 12 exam preparation and biology project work.

AIM: To study Mendelian inheritance using seeds of different colour/size of any plant.

REQUIREMENTS

Pea seed sample, enamel tray, petri dishes, notebook pencil/pen,

PROCEDURE

1. Take a lot of about 100 pea seeds in an enamel tray.

2 Separate out round and wrinkled seeds and put them in separate Petri dishes.

3. Note down the number of round and wrinkled seeds and calculate their approximate ratio.

4. Repeat the process for the other contrasting trait of the seed i.e. yellow and green colour.

OBSERVATIONS

Present your findings in the form of a table given below, Data related to two finding is given in the table, record your finding in the same way.

CONCLUSION

The contrasting forms in both the traits of pea seed (i.e., seed shape pue seed colour) show as approximate ratio of 3:1 This ratio is exactly the same as obtained by Mendel for monohybrid crosses and indicate that the dominant and recessive forms of seed shape and seed colour exist in the ratio of 3:1 in the population of pea seeds.

PRECAUTIONS

L Take a sufficiently large number of seed lot for analysis to minimise the error.

2. Observe the contrasting form of the trait carefully,

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.