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From learning about radioactive wastes and genetics to understanding food production and reproductive health, your Class 12 Science syllabus for Biology introduces you to a wealth of information. On TopperLearning, we have collated the most preferred learning resources for you to study and revise all the chapters in Biology with ease.

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Chapter 2: Sexual Reproduction in Flowering Plants

1. What is the role of tapetum in the pollen grain wall formation? [1]

2.  Fill in the missing words: [1]

Pollen mother cell → Pollen tetrad → Pollen grain → Vegetative cell, ___?____

3.  In the following events, indicate the stages where mitosis and meiosis occur. [1]

Megaspore mother cell →(1)→Megaspores→(2)→Embryo sacs→(3)→Egg

4.  Outer envelope of a pollen grain is made of a highly resistant substance. What is that substance and at which particular point is it absent? [2]

5. A bilobed and dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes can it produce? [2]

6. What is apomixis? Comment on its significance. How can it be commercially used? [3]

7. What are the characteristics of wind, water and insect-pollinated flowers? [5]

8. Explain about the pollination occurring in the chasmogamous flowers. [5]

9.                                                                                                         [5]

(a)  Draw a diagram of a mature embryo sac of an angiosperm and label its following parts:    

  1. Filiform apparatus
  2. Synergids
  3. Central cell
  4. Egg
  5. Polar nuclei
  6. Antipodals

(b) Write the fate of the egg cell and polar nuclei after fertilisation.


Chapter 3: Human Reproduction

1.  Which structure is formed after the release of ova from Graafian follicles? [1]

2.  What happens if pregnancy is not maintained in the human female? [1]

3.  From where do the signals for parturition originate? [1]

4.  Why are male testes located outside the abdominal cavity? [2]

5.  What are the similarities between spermatogenesis and oogenesis? [3]

6.  Differentiate between spermatocytes and oocytes. [3]

7.  Enlist any three functions of a female placenta. [3]

8.  What is spermiogenesis? Write the various changes which occur during this process? [5]

9.  Write the function of the following: [5]

  1. Corpus luteum
  2. Endometrium
  3. Acrosome
  4. Sperm tail
  5. Fimbriae

 

Chapter 4: Reproductive Health

1.  What is the significance of amniocentesis? [1]

2.  How are test tube babies different from the normally produced babies? [2]

3.  What is the advantage of Saheli?  [2]

4.  “Removal of gonads cannot be a contraceptive option”. Why? [3]

5.  What are the different methods of contraception in human beings? [5]

 

Chapter 5: Principles of Inheritance and Variation

1.  Non-disjunction may lead to a zygote containing XXY sex chromosomes, what sex would this produce in Drosophila and in humans? [1]

2.  Assertion: Down’s syndrome is caused due to the presence of an additional copy of the chromosome number 21 (trisomy of 21).[1]

Reason: The affected individual is short statured with small round head, furrowed tongue and partially open mouth.

a. Both assertion and reason are true, and reason is the correct explanation of the assertion.
b. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
c. Assertion is true but reason is false.
d. Both assertion and reason are false.                                                     

3.  Assertion: Sickle-cell anaemia is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). [1]

Reason: Sickle-cell anaemia is caused by a mutation or change, in one of the genes, that provides instructions for making the clotting factor proteins needed to form a blood clot.

a. Both assertion and reason are true, and reason is the correct explanation of the assertion.
b. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
c. Assertion is true but reason is false.
d. Both assertion and reason are false.                                              

4.  What is aneuploidy? Give an example. [2]

5.  A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain. [2]

6.  A pea plant with purple flowers was crossed with a plant with white flowers producing 40 plants with only purple flowers. On selfing, these plants produced 470 plants with purple flowers and 162 with white flowers. What genetic mechanisms account for these results? [3]

7.  Read the following and answer any four questions from (i) to (v) given below: [4]

The chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s), called aneuploidy. Examples of chromosomal disorders include Down’s syndrome and Turner’s syndrome. Failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism and, this phenomenon is known as polyploidy. This condition is often seen in plants.

The total number of chromosomes of a normal human being is 46 (23 pairs). Out of these 22 pairs are autosomes and one pair of chromosomes are sex chromosomes.

Sometimes, though rarely, either an additional copy of a chromosome may be included in an individual or an individual may lack one of any one pair of chromosomes. These situations are known as trisomy or monosomy of a chromosome.

(i)   Down’s syndrome is due to:

  1. Linkage
  2. Sex-linked inheritance
  3. Crossing over
  4. Non-disjunction of chromosome

(ii)   The cause of Down’s syndrome is the presence of an additional copy of the chromosome number:

  1. 21
  2. 15
  3. 16
  4. 8

(iii)   Which of the following is NOT correct symptom of Down’s syndrome?

  1. Short statured
  2. Small round head
  3. Partially open mouth
  4. Rudimentary ovaries

(iv)   _______________ is caused due to the presence of an additional copy of X-chromosome resulting into a karyotype of 47, XXY.

  1. Down’s Syndrome
  2. Klinefelter’s Syndrome
  3. Turner’s Syndrome
  4. Haemophilia

(v)   ______________ is caused due to the absence of one of the X chromosomes.

  1. Down’s Syndrome
  2. Klinefelter’s Syndrome
  3. Turner’s Syndrome
  4. Haemophilia

8. Read the following and answer any four questions from (i) to (v) given below: [4]

Sickle cell anemia is a genetic disorder where the body produces an abnormal hemoglobin called hemoglobin S. Red blood cells are normally flexible and round, but when the hemoglobin is defective, blood cells take on a “sickle” or crescent shape. Sickle cell anemia is caused by mutations in a gene called HBB.

It is an inherited blood disorder that occurs if both the maternal and paternal copies of the HBB gene are defective. In other words, if an individual receives just one copy of the defective HBB gene, either from mother or father, then the individual has no sickle cell anemia but has what is called “sickle cell trait”.

People with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children. There are three inheritance scenarios that can lead to a child having sickle cell anemia:

- Both parents have sickle cell trait

- One parent has sickle cell anemia and the other has sickle cell trait

- Both parents have sickle cell anemia                                                                                                             

(i)   Sickle cell anemia is a/ an ______________________ disease.

  1. X linked
  2. autosomal dominant
  3. autosomal recessive
  4. Y linked

(ii) If both parents have sickle cell trait, then there is _______________of the child having sickle cell anemia.

  1. 25 % risk
  2. 50 % risk
  3. 75% risk
  4. No risk

(iii) If both parents have sickle cell trait, then there is _______________of the child having sickle cell trait.

  1. 25 % risk
  2. 50 % risk
  3. 75% risk
  4. No risk

(iv)   If one parent has sickle cell anemia and the other has sickle cell trait, there is __________that their children will have sickle cell anemia and ___________will have sickle cell trait.

  1. 25 % risk, 75% risk
  2. 50 % risk, 50% risk
  3. 75% risk, 25% risk
  4. No risk

(v)

The following statements are drawn as conclusions from the above data (Kenya).

I. Patients with SCD (Sickle Cell Disease) are less likely to be infected with malaria.

II. Patients with SCD (Sickle Cell Disease) are more likely to be infected with malaria.

III. Over the years the percentage of people infected with malaria has been decreasing.

IV. Year 2000 saw the largest percentage difference between malaria patients with and without SCD.

Choose from below the correct alternative.

  1. Only I is true
  2. I and IV are true
  3. III and II are true
  4. I and III are true


Chapter 6: Molecular Basis of Inheritance

1.  Assertion: Lactose is the substrate for the enzyme beta-galactosidase in lac operon.

Reason: It regulates switching on and off of the operon.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]

2.  Assertion: In Eukaryotes, the nucleosomes in chromatin are seen as ‘beads-on-string’ structure when viewed under electron microscope.

Reason: Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]

3. If the base sequence of one strand of DNA is CAT, TAG, TAC, GAC, what will be the base sequence [2]

  1. Of complementary DNA strand
  2. Of its complementary RNA strand

4.  Mention two functions of the codon AUG. [2]

5.  Describe in brief the process of transcription. [5]

6.  Describe briefly the mechanism of DNA replication. [5]

7.  Write the full names of the different types of RNA. State only how each type is involved in protein synthesis. [5]


Chapter 8: Human Health and Disease

 1.  Mention any two symptoms of AIDS. [2]

2.  Name the infective stage of Plasmodium. Give any two symptoms of the disease caused by this pathogen. [2]

3.  A wife donated one of her kidneys to her husband whose both the kidneys have failed. He has been given immunosuppressive agents/drugs.                       

Now, answer the questions accordingly:

  1. What are immunosuppressive agents?
  2. Why immunosuppressive agents are given to the recipient during an organ transplant?
  3. Name one immunosuppressive agent and its source. [3]

4.  Surveys and statistics show that use of drugs and alcohol has been on the rise especially among the youth which is really a cause of concern as it could result in many harmful effects. Answer the following questions with reference to the above passage:

i. Identify the type of drug obtained from the inflorescence shown in the given figure. 

ii. How are these drugs taken and their effect?

iii. Name any two drugs obtained from these plants. [3]

5.  Read the following and answer any four questions from (i) to (v) given below: [4]

Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually. The mechanisms that underlie development of cancer or oncogenic transformation of cells, its treatment and control have been some of the most intense areas of research in biology and medicine. In our body, cell growth and differentiation is highly controlled and regulated. In cancer cells, there is breakdown of these  regulatory mechanisms. Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appears to have lost this property. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.

(i)   The chemical carcinogens present in tobacco smoke have been identified as a major cause of _______________ cancer.

  1. Lung
  2. Skin
  3. Breast
  4. Prostate

(ii)   In ___________________, a piece of the suspected tissue cut into thin sections is stained and examined under microscope.

  1. X-ray
  2. Biopsy
  3. CT Scan
  4. MRI

(iii)   In which type of cancer treatment, the tumor cells are irradiated lethally?

  1. Immunotherapy
  2. Surgery
  3. Radiotherapy
  4. Chemotherapy

(iv)   Which substances help in activating the immune system and destroying the tumor in cancer patients?

  1. α-interferon
  2. antibiotics
  3. analgesics
  4. Tranquilisers

(v)   Assertion: Several chemotherapeutic drugs are used to kill cancerous cells. Some of these are specific for particular tumors.

Reason: Majority of drugs have side effects like hair loss, anemia, etc.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false.

6.

(a) Name the stage of Plasmodium which gains entry into the human body.

(b) Trace the stages of Plasmodium in the body of female Anopheles after its entry.

(c) Explain the cause of periodic recurrence of chill and high fever during malarial attack in humans. [5]


Chapter 10: Microbes in Human Welfare

1.  Write the scientific name of the microbe used for fermenting malted cereals and fruit juices. [1]

2.  Name the source of cyclosporin-A. How does this bioactive molecule function in our body? [2]

3.  Name any two species of fungus which are used in the production of antibiotics. [2]

4.  Bacillus thuringiensis produces insecticidal protein. Why does this toxin not kill Bacillus? [2]

5.  What is biological control? How Baculoviruses acts as biological control agents? [3]

6.   

  1. What is single cell protein (SCP)?
  2. Name any two organisms which provide SCP.
  3. What is the significance of SCP? [3]

7.  Describe the structure of a biogas plant. Give various steps involved in obtaining biogas. [5]

 

Chapter 11: Biotechnology: Principles and Processes

1.  A restriction enzyme digests DNA into fragments. Name the technique used to check the progression of this enzyme and separate DNA fragments. [1]

2.  Name two commonly used vectors in genetic engineering. [1]

3.  What is the function of gel electrophoresis? [1]

4.  An extra chromosomal segment of circular DNA of a bacterium is used to carry gene of interest into the host cell. What is the name given to it? [1]

5.  Which enzymes are known as “molecular Scissors”? [1]

6.  Assertion: The cut pieces of DNA are linked with plasmid DNA.

Reason: Plasmid DNA fails to act as vectors.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]

7.  Differentiate between plasmid DNA and chromosomal DNA? [2]

8.  What is the role of enzyme “Ligase” in genetic Engineering? [2]

9.  What are sticky ends? Why are they named so? [2]

10.   Name two commonly used bioreactors. State the importance of using a bioreactor. [2]


Chapter 12: Biotechnology And Its Applications

1.  Name the bacterium which produces Bt toxin. [1]

2.  What is the function of ADA? [1]

3.  Expand PCR. List its two uses. [2]

4.  Explain why children eating golden rice are unlikely to suffer from ‘night blindness’? [2]

5.  Bacillus thuringiensis produces insecticidal protein. Why does this toxin not kill Bacillus? [2]

6.  How does the RNA interface help in developing resistance in tobacco plant against nematode infection? [3]

7.  Agrobacterium tumefaciens is used in natural genetic engineering of plants. How is it so? [3]

8.  With the help of an example, explain the role of transgenic animals in

  1. Vaccine safety
  2. Biological products [3]

9.  Describe briefly the structure of insulin. How is genetically engineered insulin synthesised? [3]

 

Chapter 13: Organisms and Population

1.  Why are some organisms called as eurythermals and some other as stenohaline? [1]

2.  Why are green plants not found beyond a certain depth in the ocean? [1]

3.  Name the type of interaction seen between whale and barnacles growing on its back. [1]

4.  State Gause’s ‘Competitive Exclusion Principle’. [1]

5.  Name and explain the type of interaction between big trees and certain species of wasps. [2]

6.  Explain why very small animals are rarely found in polar region. [2]

7.  Construct an age pyramid which reflects an expanding growth status of human population. [2]

8.  How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain. [3]

9.  Define the following terms and give one example for each: [5]

  1. Commensalism
  2. Parasitism
  3. Camouflage
  4. Mutualism
  5. Interspecific competition

10.  Study the population growth curves shown below: [3]

  1. Identity curves A and B.
  2. Mention the conditions responsible for the curves A and B.
  3. Which one of them is considered a more realistic one and why?

 

Chapter 15: Biodiversity and Conservation

1.  Assertion: Habitat loss and fragmentation cause driving animals and plants to extinction.

Reason: The most dramatic examples of habitat loss come from tropical rain forests.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]

2.  Assertion: Species diversity on earth is not uniformly distributed but shows interesting patterns.

Reason: It is generally highest in the tropics and decreases towards the poles.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
3.  Assertion: Sacred forests are protected by tribal communities due to religious sanctity.

Reason: These forests are without any human impact.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
4.  What is IUCN Red List? Give its main aim. [2]
 
5.  A particular species of wild cat is endangered. In order to save them from extinction, which is a desirable approach in situ or ex situ? Justify your answer. [2]

6.  What is the significance of the slope of regression in a species–area relationship? [3]

7.  Identify the levels of biodiversity in India represented by
  1. Diversity among amphibian in Eastern and Western Ghats.
  2. 50,000 strains of rice in India.
  3. Presence of deserts, mangroves and coral reefs of India. [3]

Chapter 2: Sexual Reproduction in Flowering Plants

1. What is the role of tapetum in the pollen grain wall formation? [1]

Solution: It serves as a nutritive tissue for pollen mother cells and microspores.

2.  Fill in the missing words: [1]

Pollen mother cell → Pollen tetrad → Pollen grain → Vegetative cell, ___?____

Solution: Generative cell

3.  In the following events, indicate the stages where mitosis and meiosis occur. [1]

Megaspore mother cell →(1)→Megaspores→(2)→Embryo sacs→(3)→Egg

Solution: 1- Meiosis 2- Mitosis 3- Meiosis

4.  Outer envelope of a pollen grain is made of a highly resistant substance. What is that substance and at which particular point is it absent? [2]

Solution: The outer envelope of a pollen grain is made of a highly resistant substance called sporopollenin. Pollen grain exine has prominent apertures called germ pores where sporopollenin is absent.

5. A bilobed and dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes can it produce? [2]

Solution: Each microsporangium has 100 microspore mother cells which form 400 microspores by meiosis (100 × 4).

In an anther, there are four microsporangia. So, the total number of microspores will be 4 × 400 = 1600.

As each microspore forms one male gametophyte, 1600 male gametophytes can be produced.

6. What is apomixis? Comment on its significance. How can it be commercially used? [3]

Solution: Apomixis is the mode of reproduction which does not involve formation of zygote through gametic fusion.

Significance of apomixis:

  1. Adventives embryos are better clones than cuttings.
  2. Embryos formed through apomixes are generally free from infections.

Hybrid varieties provide higher and better yield. If hybrid seeds are produced every year, they do not maintain hybrid characters because of segregation of traits. Moreover, production of hybrid seeds every year is very costly. This can be avoided by introducing apomixes in hybrid seeds.

7. What are the characteristics of wind, water and insect-pollinated flowers? [5]

Solution: Characteristics of wind-pollinated flowers:

  1. These flowers are not brightly coloured.
  2. They possess no special odours or nectar.
  3. They are small and have no petals.
  4. Their stigma and stamens are exposed to air currents.
  5. The pollen is smooth, light can be blown easily by wind and are in large numbers.
  6. The stigma is feathery and can catch pollen from the wind.

Characteristics of water-pollinated flowers:

  1. They possess small male flowers that are not clearly visible.
  2. A large number of pollens are released in water that is caught by large, feathery stigma of female flowers.
  3. This pollen keeps floating on the water surface until they are caught by female flowers.

Characteristics of insect-pollinated flowers:

  1. They are large with bright-coloured petals to attract insects.
  2. The flowers have nectar and a pleasant fragrance.
  3. The pollen grains are sticky and can easily stick to the insect’s body.

8. Explain about the pollination occurring in the chasmogamous flowers. [5]

Solution: The chasmogamous flowers are open with their anther and stigma exposed for pollination. In these flowers two types of pollinations take place:

Self-Pollination: Self-pollination occurs when both the anther and the stigma mature simultaneously and come in contact with each other.

Cross-Pollination: This type of pollination occurs in self-incompatible plants. In this, the anther and the stigma mature at different times so cannot come in contact with each other. Cross-pollination is of two types:

Geitonogamy– When the pollen grains from the anther transfer to the stigma of a different flower in the same plant, it is known as geitonogamy.

Xenogamy– When the pollen grains from the anther of a flower get transferred to the stigma of a flower in some other plant, it is known as xenogamy. This process carries genetically different pollen to the stigma.

9.                                                                                                         [5]

(a)  Draw a diagram of a mature embryo sac of an angiosperm and label its following parts:    

  1. Filiform apparatus
  2. Synergids
  3. Central cell
  4. Egg
  5. Polar nuclei
  6. Antipodals

(b) Write the fate of the egg cell and polar nuclei after fertilisation.

Solution:

(a)

(b) The filiform apparatus present at the micropylar end of the synergids guides the entry of pollen tubes which carries two male gametes. Of the two gametes, one fuses with the egg cell to form a zygote and the other gamete fuses with two polar nuclei to form the primary endosperm nucleus. This is called triple fusion and such type of fertilisation is called double fertilisation.

 

Chapter 3: Human Reproduction

1.  Which structure is formed after the release of ova from Graafian follicles? [1]

Solution: The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum which secretes large amounts of progesterone essential for maintenance of the endometrium.

2.  What happens if pregnancy is not maintained in the human female? [1]

Solution: Corpus luteum degenerates and estrogen and progesterone levels decline resulting in starting of menstrual flow.

3.  From where do the signals for parturition originate? [1]

Solution: The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.

4.  Why are male testes located outside the abdominal cavity? [2]

Solution: The testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2–2.5o C lower than the normal internal body temperature) necessary for spermatogenesis.

5.  What are the similarities between spermatogenesis and oogenesis? [3]

Solution: Similarities between spermatogenesis and oogenesis:

  1. Both processes occur in three phases—multiplicative phase, growth phase and maturation phase.
  2. Both processes lead to the formation of haploid gametes.
  3. In the multiplicative phase, mitotic division in both processes differentiates the primordial germ cells of the testes and ovaries into gametogonia (spermatogonia and oogonia).

6.  Differentiate between spermatocytes and oocytes. [3]

Solution: Differences between spermatocytes and oocytes:


7.  
Enlist any three functions of a female placenta. [3]

Solution: Function of placenta:

  1. The placenta facilitates the supply of oxygen and nutrients to the embryo and also removal of carbon dioxide and excretory/waste materials produced by the embryo.
  2. The placenta is connected to the embryo through an umbilical cord which helps in the transport of substances to and from the embryo.
  3. Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogen, progestogens, etc.

8.  What is spermiogenesis? Write the various changes which occur during this process? [5]

Solution: Spermiogenesis: It is the process where spermatids undergo a series of complex changes resulting in the development of mature spermatozoa.   

The following changes occur during spermiogenesis:

  1. The spherical nucleus of the spermatid changes to an elongated structure because of the loss of water from it. DNA becomes concentrated; RNA and nucleolus reduce to minimum.
  2. The Golgi apparatus becomes granular and then coalesces into a large globule called the acrosomal vesicle. This vesicle gets attached to the outer portion of the nuclear membrane of the head of the sperm and forms the acrosomal cap.
  3. Centrioles migrate to the opposite end of the spermatid and form the proximal and distal centriole in the neck region of the sperm.
  4. The distal centriole forms the axial filament of the slender tail.
  5. The mitochondria of the spermatid migrate and form the mitochondrial spiral (nebenkern) around the axial filament in the middle piece of sperm.    
  6. The cytoplasm of the spermatid is lost except a thin, condensed sheath around the tail of the sperm (manchette).

After spermatogenesis, sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process called spermiation.

9.  Write the function of the following: [5]

  1. Corpus luteum
  2. Endometrium
  3. Acrosome
  4. Sperm tail
  5. Fimbriae

Solution:

  1. Corpus luteum: It secretes progesterone hormone which inhibits the production of gonadotropin hormone from the pituitary. This prevents the sloughing off of the uterine lining and supports pregnancy.
  2. Endometrium: It provides a place for the implantation of the fertilised ovum. If fertilisation fails to occur, then the endometrium lining sloughs off, leading to menstrual flow.
  3. Acrosome: The acrosome carries the sperm lysin which facilitates the sperm to penetrate the ovum during fertilisation.
  4. Sperm tail: It provides mobility to the sperm with the head forward in the fluid medium.
  5. Fimbriae: It increases the surface area for catching ovum during ovulation.

 

Chapter 4: Reproductive Health

1.  What is the significance of amniocentesis? [1]

Solution: Amniocentesis is a technique by which any chromosomal anomalies in the foetus can be detected.

2.  How are test tube babies different from the normally produced babies? [2]

Solution: Test tube babies are the babies produced by artificial insemination. In this technique, the egg of a woman is removed and fertilized by the father’s sperm outside her body under sterile conditions. The fertilised egg when reaches up to 8-16 celled stage, it is reimplanted to the mother body by a fine plastic tube.

3.  What is the advantage of Saheli?  [2]

Solution: Saheli is the contraception pill for the female which contains a non-steroidal preparation called centchroman. It is to be taken once a week and has very few side effects and high contraceptive value.

4.  “Removal of gonads cannot be a contraceptive option”. Why? [3]

Solution: Removal of gonads cannot be considered as a contraceptive because it will interfere the sexual drive, desire and sexual act of the couple. Also, it will lead to infertility and unavailability of certain hormones that are required for normal functioning of accessory reproductive parts.

5.  What are the different methods of contraception in human beings? [5]

Solution: The prevention of pregnancy in women (by preventing fertilization) is called contraception. There are four methods of contraception: 

  1. Barrier method: In barrier method of contraception, the physical devices such as condoms are used by males and females.
  2. Chemical method: In chemical methods of preventing pregnancy, the females use two types of pills – oral pills and vaginal pills. 
  3. Intra-Uterine Contraceptive Devices – The use of intra-uterine contraceptive devices like Copper-T is very effective in preventing pregnancy.  A Copper-T is placed inside the uterus by a doctor to prevent unwanted pregnancies.
  4. Surgical method: These methods are available for males as well as for females. Vasectomy is done in males and tubectomy is done in females.
a. Vasectomy - In males, a small portion of the sperm duct (vas deferens) is removed by surgical operation and both the cut ends are ligated properly. This prevents the sperms from coming out.
b. Tubectomy - In females, a small portion of the oviducts is removed by surgical operation and the cut ends are ligated. This prevents the ovum from entering into the oviducts.
 

Chapter 5: Principles of Inheritance and Variation

1.  Non-disjunction may lead to a zygote containing XXY sex chromosomes, what sex would this produce in Drosophila and in humans? [1]

Solution: It is female sex in Drosophila and male in humans.

2.  Assertion: Down’s syndrome is caused due to the presence of an additional copy of the chromosome number 21 (trisomy of 21).[1]

Reason: The affected individual is short statured with small round head, furrowed tongue and partially open mouth.

a. Both assertion and reason are true, and reason is the correct explanation of the assertion.
b. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
c. Assertion is true but reason is false.
d. Both assertion and reason are false.   

Solution: B; Down’s syndrome is a genetic disorder caused due to the presence of an additional copy of the chromosome number 21 (trisomy of 21). The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded. Hence, both assertion and reason are true, and reason is not the correct explanation of the assertion.                                          

3.  Assertion: Sickle-cell anaemia is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). [1]

Reason: Sickle-cell anaemia is caused by a mutation or change, in one of the genes, that provides instructions for making the clotting factor proteins needed to form a blood clot.

a. Both assertion and reason are true, and reason is the correct explanation of the assertion.
b. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
c. Assertion is true but reason is false.
d. Both assertion and reason are false. 

Solution: C; Sickle-cell anaemia is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). The disease is controlled by a single pair of allele, HbA and HbS. It is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. Hence, Assertion is true but reason is false.                            

4.  What is aneuploidy? Give an example. [2]

Solution: Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s), called aneuploidy. For example, Down’s syndrome results in the gain of extra copy of chromosome 21.

5.  A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain. [2]

Solution: A pea plant is monoecious, that is, the male and female sex organs are present on the same plant and hence self-pollination is possible and even a single plant produces seeds while papaya is dioecious in which the male and female sex organs are present on different plants and requires cross-pollination so an individual plant does not produce viable seeds.

6.  A pea plant with purple flowers was crossed with a plant with white flowers producing 40 plants with only purple flowers. On selfing, these plants produced 470 plants with purple flowers and 162 with white flowers. What genetic mechanisms account for these results? [3]

Solution: When a pea plant with purple flowers was crossed with a plant with white flowers:

In the F1 generation, only plants producing purple flowers appeared. This means the purple colour is dominant which does not allow the white colour to express itself. In the F2 generation, purple and white-coloured flowers were produced in the ratio of 3:1.

Here, the parental character of white again reappeared in about quarter of the progeny. This occurs because of the segregation of genes during gamete formation. This represents the law of segregation and the monohybrid ratio.

7.  Read the following and answer any four questions from (i) to (v) given below: [4]

The chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s), called aneuploidy. Examples of chromosomal disorders include Down’s syndrome and Turner’s syndrome. Failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism and, this phenomenon is known as polyploidy. This condition is often seen in plants.

The total number of chromosomes of a normal human being is 46 (23 pairs). Out of these 22 pairs are autosomes and one pair of chromosomes are sex chromosomes.

Sometimes, though rarely, either an additional copy of a chromosome may be included in an individual or an individual may lack one of any one pair of chromosomes. These situations are known as trisomy or monosomy of a chromosome.

(i)   Down’s syndrome is due to:

  1. Linkage
  2. Sex-linked inheritance
  3. Crossing over
  4. Non-disjunction of chromosome
Solution: a; Down’s syndrome is due to non-disjunction of chromosome

(ii)   The cause of Down’s syndrome is the presence of an additional copy of the chromosome number:

  1. 21
  2. 15
  3. 16
  4. 8
Solution: a; The cause of Down’s syndrome is the presence of an additional copy of the chromosome number 21 (trisomy of 21).

(iii)   Which of the following is NOT correct symptom of Down’s syndrome?

  1. Short statured
  2. Small round head
  3. Partially open mouth
  4. Rudimentary ovaries
Solution: d; In Down’s syndrome the affected individual is short statured with small round head, furrowed tongue and partially open mouth.

(iv)   _______________ is caused due to the presence of an additional copy of X-chromosome resulting into a karyotype of 47, XXY.

  1. Down’s Syndrome
  2. Klinefelter’s Syndrome
  3. Turner’s Syndrome
  4. Haemophilia
Solution: b; Klinefelter’s Syndrome is caused due to the presence of an additional copy of X-chromosome resulting into a karyotype of 47, XXY.

(v)   ______________ is caused due to the absence of one of the X chromosomes.

  1. Down’s Syndrome
  2. Klinefelter’s Syndrome
  3. Turner’s Syndrome
  4. Haemophilia
Solution: c; Turner’s Syndrome is caused due to the absence of one of the X chromosomes, i.e., 45 with X0.

8. Read the following and answer any four questions from (i) to (v) given below: [4]

Sickle cell anemia is a genetic disorder where the body produces an abnormal hemoglobin called hemoglobin S. Red blood cells are normally flexible and round, but when the hemoglobin is defective, blood cells take on a “sickle” or crescent shape. Sickle cell anemia is caused by mutations in a gene called HBB.

It is an inherited blood disorder that occurs if both the maternal and paternal copies of the HBB gene are defective. In other words, if an individual receives just one copy of the defective HBB gene, either from mother or father, then the individual has no sickle cell anemia but has what is called “sickle cell trait”.

People with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children. There are three inheritance scenarios that can lead to a child having sickle cell anemia:

- Both parents have sickle cell trait

- One parent has sickle cell anemia and the other has sickle cell trait

- Both parents have sickle cell anemia                                                                                                             

(i)   Sickle cell anemia is a/ an ______________________ disease.

  1. X linked
  2. autosomal dominant
  3. autosomal recessive
  4. Y linked
Solution: c. is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous).

(ii) If both parents have sickle cell trait, then there is _______________of the child having sickle cell anemia.

  1. 25 % risk
  2. 50 % risk
  3. 75% risk
  4. No risk
Solution: a. If both parents have sickle cell trait, then there is 25 % risk of the child having sickle cell anemia.

(iii) If both parents have sickle cell trait, then there is _______________of the child having sickle cell trait.

  1. 25 % risk
  2. 50 % risk
  3. 75% risk
  4. No risk
Solution: b. If both parents have sickle cell trait, then there is 50% risk of the child having sickle cell trait.

(iv)   If one parent has sickle cell anemia and the other has sickle cell trait, there is __________that their children will have sickle cell anemia and ___________will have sickle cell trait.

  1. 25 % risk, 75% risk
  2. 50 % risk, 50% risk
  3. 75% risk, 25% risk
  4. No risk
Solution: b. If one parent has sickle cell anemia and the other has sickle cell trait, there is 50 % risk that their children will have sickle cell anemia and 50 % risk will have sickle cell trait.

(v)

The following statements are drawn as conclusions from the above data (Kenya).

I. Patients with SCD (Sickle Cell Disease) are less likely to be infected with malaria.

II. Patients with SCD (Sickle Cell Disease) are more likely to be infected with malaria.

III. Over the years the percentage of people infected with malaria has been decreasing.

IV. Year 2000 saw the largest percentage difference between malaria patients with and without SCD.

Choose from below the correct alternative.

  1. Only I is true
  2. I and IV are true
  3. III and II are true
  4. I and III are true
Solution: d. Patients with SCD (Sickle Cell Disease) are less likely to be infected with malaria due to a faulty copy of genes. It is true that over the years the percentage of people infected with malaria has been decreasing. Hence, both the statements I and III are true.
 

Chapter 6: Molecular Basis of Inheritance

1.  Assertion: Lactose is the substrate for the enzyme beta-galactosidase in lac operon.

Reason: It regulates switching on and off of the operon.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
Solution: A; Lactose acts as an inducer in lac operon. It is the substrate for the enzyme beta-galactosidase and regulates switching on and off of the operon. Hence, both assertion and reason are true, and reason is the correct explanation of the assertion.

2.  Assertion: In Eukaryotes, the nucleosomes in chromatin are seen as ‘beads-on-string’ structure when viewed under electron microscope.

Reason: Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
Solution: A; In Eukaryotes, the nucleosomes in chromatin are seen as ‘beads-on-string’ structure when viewed under electron microscope as the nucleosomes constitute the repeating unit of a structure in nucleus called chromatin, thread-like stained (coloured) bodies seen in nucleus. Hence, both assertion and reason are true, and reason is the correct explanation of the assertion.

3. If the base sequence of one strand of DNA is CAT, TAG, TAC, GAC, what will be the base sequence [2]

  1. Of complementary DNA strand
  2. Of its complementary RNA strand
Solution:
  1. The complementary bases of the DNA strand will be GTA, ATC, ATG, CTG.
  2. The complementary bases of the RNA strand will be GUA, AUC, AUG, CUG.     

4.  Mention two functions of the codon AUG. [2]

Solution: 

  1. AUG is the codon which is known as the initiation codon.
  2. This codon codes for methionine in prokaryotes and formyl methionine in eukaryotes.

5.  Describe in brief the process of transcription. [5]

Solution: Transcription: It is the formation of an mRNA strand on a DNA strand in the nucleus. The mechanism of mRNA synthesis is analogous to DNA replication where only one of the two strands (sense strand) acts as a template. The formation of mRNA takes place in the 5′–3′ direction, so the sequence of nucleotides on the DNA template (sense strand) must be in the 3′–5′ direction.

This process involves unwinding of DNA and transcription starts at a specific point called the promoter region. DNA-dependent RNA polymerase enzyme binds to the ‘Pribnow box’ at the promoter region and starts transcription. RNA polymerase contains a detachable subunit called the sigma () factor. It helps the enzyme to bind firmly to DNA. The RNA core polymerase (minus sigma factor) moves down the DNA at a faster pace and this continues to synthesise a new RNA chain. It requires the building blocks of uracil (U), adenine (A), cytosine (C) and guanine (G). The base sequence in DNA decides the base sequence in mRNA as A pairs with U and G pairs with C. The mRNA is synthesised on the DNA template in the 5′–3′ direction, and so, successive nucleotides are attached at the 3′–OH end of the growing mRNA strand. So, the information of DNA coded in the sequence of bases of the cistron is transcribed to mRNA. This process continues until it reaches the terminator sequence in the sense DNA strand (3′–AAAAAAT–5′). At this point, another protein particle, the rho () factor, forms a complex with RNA polymerase. This causes the enzyme to go off the DNA track, and thus, new mRNA is released. Many mRNA are synthesised in rapid succession along the cistron. The completed mRNA moves away from the nucleus and binds to a group of ribosomes in the cytoplasm. 

6.  Describe briefly the mechanism of DNA replication. [5]

(i)  Origin of replication: It is the start point where DNA replication begins at a specific point where intertwined DNA segments start unwinding. In prokaryotic cells, there is a single origin of replication, whereas in eukaryotic cells, there are numerous origins which merge during replication.
(ii)  Unwinding of two DNA strands: It takes place in the presence of helicases which unwind the helix and topoisomerases which break and reseal one strand of DNA. Unwinding of DNA leads to the formation of a Y-shaped structure of the two strands of the DNA duplex. This is known as the replication fork.
(iii)  Synthesis of primer: It is a stretch of RNA formed on the DNA where synthesis of new DNA starts. The DNA-directed RNA polymerase synthesises the primer strands of RNA for leading and lagging strands. New strands grow from the fork, and as replication proceeds, it appears as if the point of divergence at the fork is moving.

(iv) Synthesis of leading (continuous) strand: The synthesis of the continuous strand (new) of DNA is formed in the 5′–3′ direction on the 3′–5′ DNA template because of the addition of deoxyribonucleotides at the 3′ end of primer RNA. This process occurs in the presence of DNA polymerase and ATP. One new strand is formed in a continuous stretch in the 5′–3′ direction and is called the leading strand.
(v) Formation of lagging (discontinuous) stand: In the second parental strand, the enzyme primase forms the RNA primer. The enzyme DNA polymerase synthesises the DNA in the form of short stretches once again in the 5′–3′ direction starting from a RNA primer. These short DNA segments, consisting of numerous nucleotides, are called Okazaki fragments. The Okazaki short segments are joined by the enzyme DNS ligase. This newly synthesised second DNA strand is called the lagging strand because it is formed later on in reference to the first continuous strand. 

7.  Write the full names of the different types of RNA. State only how each type is involved in protein synthesis. [5]

Solution: The full names of the different types of RNA are (i) r-RNA (ribosomal RNA), (ii) m RNA (messenger RNA) and (iii) t-RNA (transfer RNA). t-RNA has a cloverleaf structure in two dimensions:

(i)    r-RNA: It forms approximately 80% of the total cellular RNA and is a component of the ribosomes. It is a single-stranded molecule but twisted on itself.

Role:  It serves to release mRNA from DNA. The ribosomal proteins and the r-RNA form the functional units of ribosomes during protein synthesis.

(ii)  mRNA: It is formed by the DNA template in the nucleus and moves to the cytoplasm within two subunits of ribosomes. It is a complementary strand to one of the DNA strands formed during transcription. It forms 5–10% of the total RNA in a cell. Its length is almost equivalent to the length of protein to be synthesised in the cytoplasm. It has a cap structure as 5′ end and poly A tail at the 3′ end.

Role: It carries codons which serve as a message tape to be decoded into a protein (amino acids).

(iii)   t-RNA: It is the smallest of all the RNA with molecular weight ranging from 25 to 30 thousand Daltons. It is soluble RNA and constitutes 10–12% of the total RNA in the cytoplasm.

Role: It picks up activated amino acid from the cytoplasm and supplies it to mRNA in the ribosome according to the message expressed by the codon. Each amino acid bears a recognition site, anti-codon site, ribosome attachment site and amino acid attachment site.

 

Chapter 8: Human Health and Disease

1.  Mention any two symptoms of AIDS. [2]

Solution: Symptoms of AIDS:

  1. Swollen lymph nodes and fever                   
  2. Sweating at night and weight loss

2.  Name the infective stage of Plasmodium. Give any two symptoms of the disease caused by this pathogen. [2]

Solution: Infective stage: Sporozoite

Symptoms:

  1. Headache and nausea.
  2. Chill and shivering followed by an outbreak of fever. Fever subsides with profuse sweating.

3.  A wife donated one of her kidneys to her husband whose both the kidneys have failed. He has been given immunosuppressive agents/drugs.                       

Now, answer the questions accordingly:

  1. What are immunosuppressive agents?
  2. Why immunosuppressive agents are given to the recipient during an organ transplant?
  3. Name one immunosuppressive agent and its source. [3]
Solution:
  1. Immunosuppressive agents are the substances used during transplant which suppress the immune system of the recipient.
  2. Immunosuppressive agents are given to the recipient during an organ transplant so that the transplanted organ is not rejected due to incompatibility between donor and recipient.
  3. Cyclosporin A is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma polysporum.

4.  Surveys and statistics show that use of drugs and alcohol has been on the rise especially among the youth which is really a cause of concern as it could result in many harmful effects. Answer the following questions with reference to the above passage:

i. Identify the type of drug obtained from the inflorescence shown in the given figure. 

ii. How are these drugs taken and their effect?

iii. Name any two drugs obtained from these plants. [3]

Solution:

  1. Natural cannabinoids are obtained from the inflorescences of the plant Cannabis sativa.
  2. Generally, cannabinoids are taken by inhalation and oral ingestion and are known for their effects on cardiovascular system of the body.
  3. Charas and ganja are obtained from the flower tops, leaves and the resin of cannabis plant.

5.  Read the following and answer any four questions from (i) to (v) given below: [4]

Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually. The mechanisms that underlie development of cancer or oncogenic transformation of cells, its treatment and control have been some of the most intense areas of research in biology and medicine. In our body, cell growth and differentiation is highly controlled and regulated. In cancer cells, there is breakdown of these  regulatory mechanisms. Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appears to have lost this property. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.

(i)   The chemical carcinogens present in tobacco smoke have been identified as a major cause of _______________ cancer.

  1. Lung
  2. Skin
  3. Breast
  4. Prostate
Solution: a; The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer.

(ii)   In ___________________, a piece of the suspected tissue cut into thin sections is stained and examined under microscope.

  1. X-ray
  2. Biopsy
  3. CT Scan
  4. MRI
Solution: b; In biopsy, a piece of the suspected tissue cut into thin sections is stained and examined under microscope.

(iii)   In which type of cancer treatment, the tumor cells are irradiated lethally?

  1. Immunotherapy
  2. Surgery
  3. Radiotherapy
  4. Chemotherapy
Solution: c; In radiotherapy, tumor cells are irradiated lethally, taking proper care of the normal tissues surrounding the tumor mass.

(iv)   Which substances help in activating the immune system and destroying the tumor in cancer patients?

  1. α-interferon
  2. antibiotics
  3. analgesics
  4. Tranquilisers
Solution: a; The cancer patients are given substances called biological response modifiers such as α-interferon which activate their immune system and help in destroying the tumor.

(v)   Assertion: Several chemotherapeutic drugs are used to kill cancerous cells. Some of these are specific for particular tumors.

Reason: Majority of drugs have side effects like hair loss, anemia, etc.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false.
Solution: b; Several chemotherapeutic drugs are used to kill cancerous cells. Some of these are specific for particular tumors. Majority of drugs have side effects like hair loss, anemia, etc.

6.

(a) Name the stage of Plasmodium which gains entry into the human body.

(b) Trace the stages of Plasmodium in the body of female Anopheles after its entry.

(c) Explain the cause of periodic recurrence of chill and high fever during malarial attack in humans. [5]

Solution: 

(a)  Plasmodium enters a human body at the sporozoite stage through the bite of an infected female Anopheles mosquito.

(b) Life Cycle of Plasmodium:

  1. Plasmodium sporozoites enter the human body through the bite of a female Anopheles mosquito.
  2. First, the parasites undergo asexual reproduction when they enter the liver cells and then attack the RBCs resulting in their rupture.
  3. The rupture of RBCs produces a toxic element called haemozoin which is responsible for the chill and high fever for 3–4 days.
  4. When a female Anopheles mosquito bites an infected person, the parasites enter the mosquito’s body and multiply forming the sporozoites which multiply sexually.
  5. These sporozoites are stored in the salivary glands of the mosquito and are released when a healthy person is bitten by this mosquito.
  6. When these mosquitoes bite a human, the sporozoites are introduced into the body of the human. Thus, plasmodium requires two hosts—man and mosquito—to complete its life cycle. The female Anopheles mosquito acts as the vector.

(c)  Haemozoin is a toxic element released when RBCs get ruptured. This is responsible for the chill and high fever for 3–4 days.

 

Chapter 10: Microbes in Human Welfare

1.  Write the scientific name of the microbe used for fermenting malted cereals and fruit juices. [1]

Solution: Saccharomyces cerevisiae also, commonly called brewer’s yeast is the microbe used for fermenting malted cereals and fruit juices.

2.  Name the source of cyclosporin-A. How does this bioactive molecule function in our body? [2]

Solution: Cyclosporin-A is produced by the fungus Trichoderma polysporum. It is used as an immunosuppressive agent in organ-transplant patients.

3.  Name any two species of fungus which are used in the production of antibiotics. [2]

Solution:

  1. Penicillium notatum.
  2. Trichoderma polysporum.

4.  Bacillus thuringiensis produces insecticidal protein. Why does this toxin not kill Bacillus? [2]

Solution: The insecticidal protein (Bt toxin) exists as an inactive protoxin. When an insect ingests the inactive toxin, it is converted to an active form of toxin because of the alkaline pH of the gut which solubilises the crystals of the protein. Thus, this toxin does not kill Bacillus.

5.  What is biological control? How Baculoviruses acts as biological control agents? [3]

Solution: Biological control is the control of destructive insects with the utilisation of another insects. Baculoviruses are pathogens that attack insects and other arthropods. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications and have negative impacts on plants, mammals, birds, fish or even on non-target insects.

6.   

a. What is single cell protein (SCP)?
b. Name any two organisms which provide SCP.
c. What is the significance of SCP? [3]
Solution:
a. Single Cell Protein (SCP) is a microbial biomass rich in high quality protein.
b. Spirulina and Chlorella.
c. Significance of SCP:
  1. It reduces the pressure on agricultural production systems.
  2. It is a valuable supplement in human diet as it is rich in high quality protein.

7.  Describe the structure of a biogas plant. Give various steps involved in obtaining biogas. [5]

Solution: Biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry which keeps on rising as the gas is produced. The biogas plant has an outlet for supply of biogas and another outlet for removing slurry.

Steps involved in obtaining biogas:

  1. Slurry of animal dung is fed into the digester.
  2. In the digester, microbes break down or decompose the complex compounds of the biomass in the slurry.
  3. The anaerobic microbes do not require oxygen, so the digesters are designed like a sealed chamber.
  4. The process takes a few days and gases like methane, CO2, hydrogen and hydrogen sulphide are produced.


Chapter 11: Biotechnology: Principles and Processes

1.  A restriction enzyme digests DNA into fragments. Name the technique used to check the progression of this enzyme and separate DNA fragments. [1]

Solution: Gel electrophoresis

2.  Name two commonly used vectors in genetic engineering. [1]

Solution: Plasmid and Bacteriophage.

3.  What is the function of gel electrophoresis? [1]

Solution: The main function of gel electrophoresis is to separate the fragments of DNA.

4.  An extra chromosomal segment of circular DNA of a bacterium is used to carry gene of interest into the host cell. What is the name given to it? [1]

Solution: Plasmid.

5.  Which enzymes are known as “molecular Scissors”? [1]

Solution: Restriction Endonuclease.

6.  Assertion: The cut pieces of DNA are linked with plasmid DNA.

Reason: Plasmid DNA fails to act as vectors.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
Solution: c; The restriction enzymes cut the piece of DNA and was then linked with the plasmid DNA. These plasmid DNA act as vectors to transfer the piece of DNA attached to it. Hence, assertion is true but reason is false.

7.  Differentiate between plasmid DNA and chromosomal DNA? [2]

Solution: Plasmid DNA is extranuclear DNA, found in the protoplasm whereas chromosomal DNA is the nuclear or genetic DNA found within the nucleus.

8.  What is the role of enzyme “Ligase” in genetic Engineering? [2]

Solution: Ligase is an enzyme that joins the ends of two strands of nucleic acids so enzyme “Ligase” acts as molecular Suture.

9.  What are sticky ends? Why are they named so? [2]

Solution: Restriction enzymes cut the DNA duplex at specific points. There single-stranded free ends are called sticky ends. These are named so because they can be joined end to end by DNA ligases.

10.   Name two commonly used bioreactors. State the importance of using a bioreactor. [2]

Solution: Two commonly used bioreactors are batch type and stirred tank bioreactors.

The importance of using bioreactors is

  1. It provides large volume for cultures. Thus, products are obtained in high quantity.
  2. It also provides the optimal conditions for achieving the growth of the desired product such as temperature, pH, vitamins and oxygen.


Chapter 12: Biotechnology And Its Applications

1.  Name the bacterium which produces Bt toxin. [1]

Solution: Bacillus thuringiensis.

2.  What is the function of ADA? [1]

Solution: ADA is necessary for the immune system to function.

3.  Expand PCR. List its two uses. [2]

Solution: PCR stands for polymerase chain reaction.

Uses:

  1. It is used to detect HIV in suspected AIDS patients.
  2. It is used to detect mutations in genes in suspected cancer patients.

4.  Explain why children eating golden rice are unlikely to suffer from ‘night blindness’? [2]

Solution: It is because golden rice is genetically engineered with Vitamin A precursor carotenoids. So lack of vitamin A causes night blindness.

5.  Bacillus thuringiensis produces insecticidal protein. Why does this toxin not kill Bacillus? [2]

Solution: The insecticidal protein (Bt toxin) exists as an inactive protoxin. When an insect ingests the inactive toxin, it is converted to an active form of toxin because of the alkaline pH of the gut which solubilises the crystals of the protein. Thus, this toxin does not kill Bacillus. 

6.  How does the RNA interface help in developing resistance in tobacco plant against nematode infection? [3]

Solution: A nematode (Meloidogyne incognita) infects the roots of tobacco plants and affects its yield. So, to prevent this infestation, the RNA interference (RNAi) process is adopted. Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant. The introduction of DNA produces sense and antisense RNA in the host cells. These two RNAs, being complementary to each other, form a double-stranded RNA which binds to and prevents the translation of mRNA (silencing) of the nematode. The parasite will not survive in a transgenic host expressing specific interfering RNA. The transgenic plant therefore gets itself protected from the parasite.

7.  Agrobacterium tumefaciens is used in natural genetic engineering of plants. How is it so? [3]

Solution: Agrobacterium tumefaciens is a plant pathogenic bacterium which can transfer part of its plasmid DNA as it infects host plants. Species of Agrobacterium produce tumours in almost all dicotyledonous plants. These bacteria contain large T1 plasmids which pass on their tumour-causing gene into the genome of the host plant. Gall is formed on the host plant. Therefore, these bacteria are known as ‘natural genetic engineers’ of plants as gene transfer occurs without human interference. T1 plasmid-based vectors are now commonly used for genetic transformation.


8.  With the help of an example, explain the role of transgenic animals in

  1. Vaccine safety
  2. Biological products [3]
Solution: Role of transgenic animals:
  1. Vaccine safety: Transgenic animals are predominantly used for testing of vaccines before they are used on human beings. Example: Transgenic mice are used to test the safety of polio vaccine.
  2. Biological products: Many human diseases are controlled by biological products. The transgenic animals which produce these products are introduced with DNA which codes for a particular product like human protein (α–I–antitrypsin) for treating emphysema. In 1997, the first transgenic cow Rosie was produced which was capable of secreting human protein-enriched milk. The milk contained human alpha-lactalbumin and was nutritionally a more balanced product for human babies than cow milk.       

9.  Describe briefly the structure of insulin. How is genetically engineered insulin synthesised? [3]

Solution: Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges. In mammals, including humans, insulin is synthesised as a prohormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide. This C peptide is not present in the mature insulin and is removed during maturation into insulin. In 1983, Eli Lilly an American company prepared two DNA sequences corresponding to A and B, chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains. Chains A and B were produced separately, extracted and combined by creating disulfide bonds to form human insulin.

Chapter 13: Organisms and Population

1.  Why are some organisms called as eurythermals and some other as stenohaline? [1]

Solution: Some organisms which can tolerate and thrive in a wide range of temperatures are called as eurythermal organisms while the organisms which can tolerate and thrive in a narrow range of salinities are called as stenohaline.

2.  Why are green plants not found beyond a certain depth in the ocean? [1]

Solution: Green plants are not found beyond a certain depth in the ocean as light is unavailable in that zone.

3.  Name the type of interaction seen between whale and barnacles growing on its back. [1]

Solution: The type of interaction observed between whale and barnacles growing on its back is commensalism as the whale do not derive any benefit.

4.  State Gause’s ‘Competitive Exclusion Principle’. [1]

Solution: Gause’s ‘Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.

5.  Name and explain the type of interaction between big trees and certain species of wasps. [2]

Solution: Mutualism exists between big trees and certain species of wasps. Certain wasps pollinate fig by laying eggs in their inflorescence. Fig plants in return offer some of its seeds as food for developing larvae of wasps.

6.  Explain why very small animals are rarely found in polar region. [2]

Solution: Small animals have a larger surface area relative to their volume, and they tend to lose body heat fast when it is cold outside. They have to expend much energy to generate body heat through metabolism. So, small animals are rarely found in polar regions.

7.  Construct an age pyramid which reflects an expanding growth status of human population. [2]

Solution: The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.

8.  How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain. [3]

Solution:

  1. Fungi produce various kinds of thick-walled spores to survive under unfavourable conditions, which germinate during favourable conditions.
  2. Zooplanktons enter diapause stage that is a stage of suspended development under unfavourable conditions.
  3. Bears hibernate during winters to escape the unfavourable conditions.

9.  Define the following terms and give one example for each: [5]

  1. Commensalism
  2. Parasitism
  3. Camouflage
  4. Mutualism
  5. Interspecific competition
Solution:
  1. Commensalism: It is an interspecific interaction between individuals of two species where one species is benefited and other is not affected. Example: Orchid and mango tree.
  2. Parasitism: It is an interspecific interaction between individuals of two species where generally the small species (parasite) is benefited and the large species (host) is affected. Example: Malarial parasite and human beings.
  3. Camouflage: It is the ability of animals to blend with the surroundings or background, and thus, they remain unnoticed for protection or aggression. Example: Stick insect.
  4. Mutualism: It is an interspecific interaction between individuals of two species where both interacting species are benefited in an obligatory way. Example: Pollination in plants by animals.
  5. Interspecific competition: It is an interspecific interaction between individuals of two species where both interacting species are affected. Example: Monarch butterfly and Queen Monarch.

10.  Study the population growth curves shown below: [3]

  1. Identity curves A and B.
  2. Mention the conditions responsible for the curves A and B.
  3. Which one of them is considered a more realistic one and why?
Solution:
  1. A-Exponential growth curve B-Logistic growth curve.
  2. A- Any species growing exponentially under unlimited resource conditions, shows exponential growth curve. B- A population growing in a habitat with limited resources shows an initial lag phase, an accelerated log phase and a decelerated steady phase.
  3. Logistic growth curve B is considered more realistic as the resources are finite and become limiting sooner or later.


Chapter 15: Biodiversity and Conservation

1.  Assertion: Habitat loss and fragmentation cause driving animals and plants to extinction.

Reason: The most dramatic examples of habitat loss come from tropical rain forests.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
Solution: b; Habitat loss and fragmentation is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests as it once covered more than 14 per cent of the earth’s land surface, but now these rain forests cover no more than 6 per cent. Hence, both assertion and reason are true, and reason is not the correct explanation of the assertion.

2.  Assertion: Species diversity on earth is not uniformly distributed but shows interesting patterns.

Reason: It is generally highest in the tropics and decreases towards the poles.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
Solution: a; Species diversity on earth is not uniformly distributed but shows interesting patterns. It is generally highest in the tropics and decreases towards the poles. With the change in the altitudes, there is a change in the species which are found in an area. Hence, both assertion and reason are true, and reason is the correct explanation of the assertion.

3.  Assertion: Sacred forests are protected by tribal communities due to religious sanctity.

Reason: These forests are without any human impact.

  1. Both assertion and reason are true, and reason is the correct explanation of the assertion.
  2. Both assertion and reason are true, and reason is not the correct explanation of the assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false. [1]
Solution: b; Sacred forests are the forest patches of varying dimensions protected by tribal communities due to religious sanctity. These forests are most undisturbed without any human impact and have been free from all human disturbances. Hence, both assertion and reason are true, and reason is not the correct explanation of the assertion.

4.  What is IUCN Red List? Give its main aim. [2]
Solution: IUCN Red List is a catalogue of taxa that are facing the risk of extinction. Its main aim is to give information about the urgency and scale of conservation problems to the public and policy makers.

 

5.  A particular species of wild cat is endangered. In order to save them from extinction, which is a desirable approach in situ or ex situ? Justify your answer. [2]
Solution: Ex situ is a desirable approach to protect the wild cat. The organism is protected outside their natural habitat where special care is taken to protect them.
By using cryopreservation techniques, gametes of threatened species can be preserved under very low temperature.

6.  What is the significance of the slope of regression in a species–area relationship? [3]
Solution: Within a region, the species richness increases with increasing explored area but only up to a limit. The relationship between species richness and area for a wide variety of taxa turns out to be a rectangular hyperbola. On a logarithmic scale, the relationship is a straight line.
log S = log C + Z log A
The value of Z lies in the range of 0.1−0.2 regardless of the taxonomic group or the region. If the species–area relationship is for very large areas like the entire continent, the slope of the line will be much steeper (Z values in the range of 0.6−1.2).

7.  Identify the levels of biodiversity in India represented by
  1. Diversity among amphibian in Eastern and Western Ghats.
  2. 50,000 strains of rice in India.
  3. Presence of deserts, mangroves and coral reefs of India. [3]

Solution:

  1. Western Ghats have a greater amphibian species diversity than the Eastern Ghats, is represented by the species diversity.
  2. India has more than 50,000 genetically different strains of rice. It is represented by genetic diversity.
  3.  Presence of deserts, mangroves and coral reefs in India is greater than in Scandinavian country like Norway. It shows ecological diversity.