Showing posts with label Laboratory practicals. Show all posts
Showing posts with label Laboratory practicals. Show all posts

Sunday, 6 March 2022

Biology class 12 practical term 2
March 06, 2022

Biology class 12 practical term 2

 List of Biology Experiments for Term II

1. Prepare a temporary mount of the onion root tip to study mitosis.




General Guidelines
1.The practical examination will be of one-hour duration.
2.The written examination in practicals for these students will be conducted at the time of practical examination of all other students.
3. The written test will be of 30 minutes duration.
4. The question paper given to the students should be legibly typed. It should contain a total of 8 practical skill based very short answer type questions. A student would be required to answer any 5 questions.
5. A writer may be allowed to such students as per CBSE examination rules.
6. All questions included in the question paper should be related to the listed practicals. Every question should require about two minutes to be answered.
7. These students are also required to maintain a practical file. A student is expected to record the listed experiments Term -wise as per the specific instructions for each subject. These practicals should be duly checked and signed by the internal examiner.
8. The format of writing any experiment in the practical file should include aim, apparatus required, simple theory, procedure, related practical skills, precautions etc.
9. Questions may be generated jointly by the external/internal examiners and used for
assessment.
10. The viva questions may include questions based on basic theory/principle/concept,
apparatus/materials/chemicals required, procedure, precautions, sources of error etc.

Class XII
Practicals should be conducted alongside the concepts taught in theory classes.
A. Items for Identification/ familiarity with the apparatus for assessment in practicals (All
experiments)

TERM -II:
1. Soil from different sites- sandy, clayey, loamy; Small potted plants, Cactus/Opuntia (model), Large flowers, Maize inflorescence.
2. Model of Ascaris
B. List of Practicals
TERM -I:
1. Study of flowers adapted to pollination by different agencies (wind, insects).
2. Identification of T.S of morula or blastula of frog (model).
3. Preparation of pedigree charts of genetic traits such as rolling of tongue, colour blindness.
TERM -II:
4. Study of the soil obtained from at least two different sites for their texture.
5. Identify common disease-causing organisms like Ascaris (Model) and learn some
common symptoms of the disease that they cause.
6. Comment upon the morphological adaptations of plants found in xerophytic conditions.
Note: The above practicals may be carried out in an experiential manner rather than recording observations.

Prescribed Books:
1. Biology, Class-XII, Published by NCERT
2. Other related books and manuals brought out by NCERT (including multimedia)
3. Biology Supplementary Material (Revised). Available on CBSE website. 

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March 06, 2022

To observe the images of two plants and two animals on the basis of their morphological adaptations.

Aim

To observe the images of two plants and two animals on the basis of their morphological adaptations.

Requirements

Models or virtual images of two plants and two animals found in aquatic conditions.

Observations

Two Aquatic Plants

• Lotus

• Water Hyacinth





Morphological Adaptations:

• Aquatic plants have very thin cuticle or no cuticle at all because the cuticle prevents water loss.

• There are a number of stomata on either side of the leaves. The stomata are always open.

• They are less rigid in structure.

• They have specialized roots to take in oxygen.

• The leaves on the surface are flat to facilitate floating. Also, the presence of air sacs helps them to float.

• The roots are very small.

Two Aquatic Animals

• Fish

• Turtle





Morphological Adaptations:

• They inhale oxygen through their gills or skin. Marine mammals have lungs and have to come to the surface to breathe.

• They are cold-blooded, i.e., their body temperature is the same as the surrounding environment.

• The collapsible lungs and rib cages help them to withstand very high water pressures.

• The aquatic animals at great depths are bioluminescent, i.e., they emit light to attract preys and mates.

• They have the property of osmoregulation, i.e., the fish can maintain an internal environment of salt and water.

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March 06, 2022

To study the morphological adaptations of two plants and two animals (models/virtual images) found in xeric conditions.

Aim

To study the morphological adaptations of two plants and two animals (models/virtual images) found in xeric conditions.

Requirements

Virtual images or models of two plants and two animals found in xeric conditions.

Observations

Two Xeric Plants

Cacti

Pineapple





Morphological Features:

• Succulence: These plants have special cells with water holding capacity in low moisture conditions.

• Reduced Leaves: The leaves are reduced to spines that help in reducing excess loss of water through transpiration.

• Stomata: In these plants, the stomata are either few on in sunken pits below the surface of the leaves.

• Waxy, hairy and spiny outer surfaces: The hair and spines scatter light to reduce sun’s effect. The waxy covering holds in water.

• Roots near the surface: These have the capacity of holding water quickly and can regenerate easily after rain.

Two Xeric Animals

Camel

Sandfish





Morphological Features:

• The desert animals are poikilotherms, i.e., they can match their internal temperature to the external.

• They excrete nitrogenous waste in the form of uric acid.

• They undergo hibernation.

• The animals stay in burrows to avoid water loss from the body and excrete highly concentrated urine.

• The body temperature of camels increases by 7℃ during the late afternoon that decreases the heat flow from the environment. The fur reduces the heat gain from the environment.

Thus these adaptations help them to conserve water as much as possible and prepare them to live without water if required.


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March 06, 2022

To observe the disease-causing organisms like Ascaris, Entamoeba, Plasmodium and Ringworm through permanent slides.

 Aim 

To observe the disease-causing organisms like Ascaris, Entamoeba, Plasmodium and Ringworm through permanent slides. 

Materials Required 

    Preserved slides or specimens of disease-causing organisms like Ascaris, Entamoeba, Plasmodium and Ringworm. 

Procedure 

   Observe the specimens or slides and identify the organism on the basis of its features. 

Observations 

Ascaris 

Phylum: Aschelminthes 

Class: Nematoda 

Type: Ascaris lumbricoides 


Ascaris exhibits the following characteristic features: 

• It has a long, cylindrical and unsegmented body. 

• The male and female organisms are separate. 

• It bears a mouth at the anterior end surrounded by three lips. 

• There is an excretory pore on the ventral surface slightly behind the anterior end. 

• A pair of penial spicules are present in the male worms close to the cloacal opening. 

• The female genitals are present at about one-third distance from the anterior end. 


Ascariasis is the disease caused by Ascaris lumbricoides or roundworm. 


Symptoms: 

• Abdominal cramping 

• Abdominal swelling 

• Nausea 

• Vomiting 

• Fever 



Entamoeba 

Phylum: Protozoa 

Class: Rhizopoda 

Type: Entamoeba hystolytica 

Following are the characteristic features of Entamoeba: 

• It is a unicellular organism with an irregular shape. 

• It consists of a few food vacuoles. The contractile vacuole is absent. 

• Cysts with four nuclei are present. 

• It consists of a nucleus located eccentrically in the cell. 


Entamoeba histolytica is an organism found in the intestines of humans that is responsible for causing amoebic dysentery. 


Symptoms: 

• Abdominal pain 

• Watery diarrhoea with mucus, blood and pus 

• Fatigue 

• Fever 

• Nausea 

• Vomiting 


Plasmodium 

Phylum: Protozoa 

Class: Sporozoa 

Type: Plasmodium vivax 

Plasmodium can be identified by the following characteristic features: 

• It is a unicellular endoparasite found within the red blood cells of the diseased person. 

• The parasite is mostly diagnosed at the “signet ring” stage where the parasite appears as a round body. 

• There is a big vacuole present inside the cell. The cytoplasm is accumulated at one place and contains the nucleus. 


Plasmodium vivax is a protozoan parasite that causes malaria in humans. The infected female anopheles bites a healthy person and transmits the sporozoite into the peripheral blood vessels of humans, thereby, causing malaria. 

Symptoms: 

• High fever 

• Shaking chills from moderate to severe. 

• Headache 

• Vomiting 

• Nausea 


Ringworm 

Kingdom: Fungi 

Class: Deuteromycetes 

Type: Trichophyton rubrum 


Trichophyton or ringworm fungus has the following characteristic features: 

• This fungus feeds on the keratin of the skin of human beings. 

• The hyphae are waxy and can be smooth or cotton-like. 

• Hyphae that are not stained are yellowish-brown, reddish-brown or white in colour. 


Ringworm is a communicable fungal infection of the skin. 

Symptoms: 

• Scaly, itchy skin 

• Red and raised patches 

• They are redder at the periphery than at the centre and forms a ring-like appearance.


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March 06, 2022

To study pH level, clarity and presence of microbes and other living organisms from two different water bodies.

 Aim

To study pH level, clarity and presence of microbes and other living organisms from two different water bodies.

Required Materials and Apparatus

• Tile.

• Tape.

• Pins.

• Beaker.

• Needles.

• Dropper.

• Test tube.

• pH paper.

• Glass slides.

• Cover slips.

• Filter paper.

• Secchi’s Disk.

• Compound microscope.

• Universal Indicator solution.

Procedure

To study pH levels:

• Take two clean and dried test tubes.

• Add the collected two different water samples into the two test tubes.

• For a safer side, label the test tubes as A and B.

• Dip the individual pH paper strips into the two different water samples.

• Keep the strips on the tile and wait for the strips to dry.

• Alternatively, pH levels of the water sample can also be found using the universal indicator solution.

• Now, with the help of a dropper, add five drops of universal Indicator solution into both the test tubes.

• Observe the change in colour in both the test tubes and compare the same with the colour chart.

Observation

Note the change in colour and associate the same with a broad range indicator paper to get a rough idea of the pH level.

Precaution 
1. Take clean and dried test tube.
2. Dry the pH paper before comparing the clour with the colour scale.
3. Match the colour carefully and determine pH carefully.

To study the clarity of the water sample:

From a scientific perspective, the number of particles present in a liquid may make it cloudy or hazy. This property is called turbidity. The procedure for finding turbidity of a water body is as follows:

• Reach the centre of a pond in a boat.

• Immerse Secchi’s disc into the water, lowering it eventually until the black and white segments are no longer visible.

• Mark the length on the rope, where the disk is not visible with a pin.

• Name this position as “A”.

• Carefully, bring the disc back up and mark the length of rope where the disc becomes visible again.

• Name this position as “B”.

• Use a meter tape to measure the length of section A to B.

• Next, find the mean length of the rope by using X= (A+B)/2.

Observation

The value of X tells us the depth of the photic zone. Below this level, enough light does not penetrate, hence, photosynthesis does not take place.

Precaution 
1. The holes in the cardboard box should not be large.
2. The light source should be of sufficient intensity.

To study the presence of living organisms

• Take a clean dried test tube.

• Add the collected water sample, preferably from a pond, into the test tube.

• Leave the sample undisturbed, until the sediment settles at the bottom of the test tube.

• Transfer a drop from the test tube on to a glass slide.

• Gently place a coverslip on the slide using a needle.

• Observe the entire slide under a compound microscope.

Observation

Pond samples have large numbers of microscopic organisms.

Conclusion 
Presence of large number of organisms indicates the presence of organic pollutants in water.

Precaution

Ensure safety measures are in place when travelling to the centre of the pond.


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Saturday, 5 March 2022

March 05, 2022

To study soil samples from two different sites and analyse their properties such as texture, moisture content, water-retaining capacity and pH. Also, the study aims to correlate the plants found in such soil.

Aim:-  To study soil samples from two different sites and analyse their properties such as texture, moisture content, water-retaining capacity and pH. Also, the study aims to correlate the plants found in such soil.

Procedure 

The following are the steps taken to prepare the soil samples for experiments to analyse various properties. 

Aim:- To study the pH of the Soil Samples 

• Take the collected roadside soil and garden soil into two different beakers containing water. 

• Mix the test tubes with the soil solution slowly 

• Now into a clean and dried two test-tube, arrange a funnel spread covered with a filter paper. 

• Now gently pour the soil solutions into the test tubes separately. 

• Let the water to completely filter off from the filter paper. 

• Take the collected filtrates (soil) into the two different test tubes for testing the pH values. 

• With the help of a dropper, add a few drops of universal indicator solution to both the test tubes. 

• Observe the changes. 


Observation 

When the universal pH indicator is added to the test tube containing the soil solution, the colour changes. These colour changes can be tracked using the pH colour chart. Roadside soil has a pH level of 7 while garden soil has a pH level of 6. Most crops grow between pH levels of 6.0 and 7.0. 



Aim:- To study the texture of Soil Samples 

• Collect 50 gm of any soil sample in a beaker. 

• Take a clean and moisture-free measuring cylinder and the collected soil sample into it. 

• Now pour little water into the same measuring cylinder and shake well. 

• Keep the apparatus undisturbed for a few minuted and wait for the particles to settle down. 

• After a while, observe the changes in the measuring cylinder. 

• The soil particles in the measuring cylinder will start to settle down in layers. 

• Record the thickness of these layers. 


Observation 

Using a soil textural triangle, draw the corresponding percentage of the soil components (silt, clay & sand). The resultant lines which, intersect indicate the type of soil. 



Aim:- To study the Moisture Content of Soil Samples 

• Collect two different soil sample in two different crucibles. 

• Weight the soil samples using a weighing balance. 

• Make a note of the reading. 

• Place the two crucibles over the bunsen burner and heat it until it becomes dry. 

• Now again weigh the soil samples and record the weight of the dry soil samples. 

• The samples are now ready to be used to determine the moisture content of the soil. 

• Calculate the two different readings to know the moisture content of soil samples. 


Observation 

The sample where the initial and final weight is the larger indicates a higher moisture content. Lower values mean the moisture content is quite low. 



Aim:- To study the Water Holding Capacity of Soil Samples 

• Collect a  garden soil sample in a beaker. 

• To a clean and dried mortar pestle add the collected soil sample. 

• Now slowly grind the soil sample into a fine powder using a pestle. 

• Place a filter paper at the bottom of the tin box. 

• Weigh the entire contents of the tin box. 

• Now, add the powered soil into the tin box. 

• Use the glass rod to press and tap the box, so that the soil is uniformly layered. 

• Now, the weight of the tin box is measured and to be recorded. 

• Next, take two glass rods and place them parallel to each other. Ensure that the distance between the two is not long. 

• Position the tin on the two glass rods in such a way that the bottom is in contact with the water. 

• The complete setup should be left undisturbed until the water seeps through the upper surface of the soil. 

• Now, remove the tin and allow all the water to flow out from the bottom. 

• Wait until no more water percolates from the tin. 

•  Now wipe the bottom dry and use the weighing machine to note down the weight. 

• Calculate the two different readings to know the water holding capacity of the given soil samples. 


Observation 

The water holding capacity of the soil is determined by the quantity of water held by the soil sample versus the dry weight of the soil sample.



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March 05, 2022

Preparation and study of mitosis in onion root tips

Aim: Preparation and study of mitosis in onion root tips


Principle: Somatic growth in plants and animals takes place by the increase in the number of cells. A cell divides mitotically to form two daughter cells wherein the number of chromosomes remains the same (i.e., unchanged) as in the mother cell. In plants, such divisions rapidly take place in meristematic tissues of root and shoot apices, where the stages of mitosis can be easily observed. In animals, mitotically dividing cells can be easily viewed in the bone marrow tissue of a vertebrate, epithelial cells from gills in fishes and the tail of growing tadpole larvae of frog.


Requirement: Onion bulbs, wide mouth glass tubes/jar/bottle, glacial acetic acid, ethanol 2-4% acetocarmine/acetoorcein stain, N/10 HCl, spirit lamp/hot plate, slide, cover slips, blotting paper, molten wax/nail polish and compound microscope

Procedure

Growing of root tips

1. Select a few medium-sized onion bulbs. Carefully remove the dry roots present.
2. Grow root tips by placing the bulbs on glass tubes (of about 3-4 cm. diameter) filled with water. Care should be taken so that the stem portion of the bulb (basal part) just touches the water. 
3. A few drops of water may be added periodically to compensate evaporation losses. New roots may take 3-6 days to grow.
4. Cut 2-3 cm long freshly grown roots and transfer them to freshly prepared fixative, i.e., aceto-alcohol (1:3:: glacial acetic acid: ethanol). Keep the root tips in the fixative for 24 hours and then transfer them to 70% ethanol (for preservation and use in future). 
5. Onion root-tip cells have a cell cycle of approximately 24-hour duration, i.e., they divide once in 24 hours. and this division usually takes place about two hours after sunrise. 
6. Therefore, roots grown on water should be cut only at that time to score maximum number of dividing cells.


Preparation of slide
Take one or two preserved roots, wash them in water on a clean and grease- free slide. Place one drop of N/10 HCl on the root tip followed by 2–3 drops of aceto-carmine or aceto-orcein stain on it. Leave the slide for 5–10 minutes on a hot plate (or warm it slightly on spirit lamp). Care should be taken that the stain is not dried up. Carefully blot the excess stain using blotting paper.
Now cut the comparatively more stained (2–3 mm) tip portion of the root and retain it on the slide and discard the remaining portion. After
(10–20 seconds) put one or two drops of water and blot them carefully using blotting paper. Again put a drop of water on the root tip and mount a cover slip on it avoiding air bubbles. Place the slide in between the folds of blotting
paper using the fingers in such a way that the cover slip mounted on the slide is properly held. Now slowly tap the cover slip using the blunt end of a pencil so that the meristematic tissue of the root tip below the cover slip is properly squashed and spread as a thin layer of cells. Carefully seal the margins of the cover slip using molten paraffin wax or nail polish. This
preparation of onion root tips cells is now ready for the study of mitosis.

Study of slide
Place the slide on the stage of a good quality compound microscope. First observe it under the lower magnification (10 X objective) to search for the area having a few dividing cells. Examine the dividing cells under higher magnification of the microscope to observe the detailed features of mitosis.



Observation 

The stages of mitosis can be broadly categorised into two parts: karyokinesis (division of nucleus) followed by cytokinesis (division of cytoplasm, and ultimately of the cell). Those cells, which are not in the phases of cell division are considered to be in interphase. You may observe that most of the cells in a microscope field are in interphase 

Interphase 
The cells are mostly rectangular, oval or even circular in shape, with almost centrally situated densely stained nucleus. The chromatic (coloured) material of the nucleus is homogeneous and looks granular. The boundary of the nucleus is distinct. One or few nucleoli (sing: nucleolus) can also be observed inside the nucleus 

Stages of Mitosis
(a) Prophase
Intact nuclear outline is seen. The chromatin (seen as a homogeneous material in the nucleus at interphase) appears as a network of fine threads (chromosomes). Nucleoli may or may not be visible.

(b) Metaphase
The nuclear membrane disappears. Chromosomes are thick and are seen
arranged at the equatorial plane of the cell. Each chromosome at
this stage has two chromatids joined together at the centromere, which can
be seen by changing the resolution of the microscope. Nucleolus is not
observed during metaphase.

(c) Anaphase
This stage shows the separation of the chromatids of each chromosome. The
chromatids separate due to the splitting of the centromere. Each chromatid now represents a separate chromosome as it has its own centromere. The chromosomes are found as if they have moved towards the two poles of the
cell. The chromosomes at this stage may look like the shape of alphabets 'V', 'J' or 'I' depending upon the position of centromere in them. Different anaphase cells show different stages of movement of chromosomes to opposite poles,
and they are designated to represent early, mid and late anaphase 

(d) Telophase
Chromosomes reach the opposite poles, lose their individuality, and look like a mass of chromatin (Fig. 6.1e). Nuclear membrane appears to form the nuclei of the two future daughter cells.

Cytokinesis
In plants, a cell plate is formed in the middle after telophase. The plate can be seen to extend outwards to ultimately reach the margin of the cell and divide the cell into two. Such cell plates are characteristic of plant cells. However, in an animal cell, the two sides of the cell show inpushings or constrictions formed from the peripheral region in the middle of the cell,
which grow inward and meet to divide the cell into two daughter cells. 


Precautions 
1. Root tip should be taken early in morning hours.
2. Slide should be neat and clean.


















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