General Instructions:
- This question paper contains 33 questions. All questions are compulsory.
- The question paper is divided into five sections – Sections A, B, C, D, and E.
- Section A – Questions number 1 to 16 are multiple choice type questions. Each question carries 1 mark.
- Section B – Questions number 17 to 21 are very short answer type questions. Each question carries 2 marks.
- Section C – Questions number 22 to 28 are short answer type questions. Each question carries 3 marks.
- Section D – Questions number 29 and 30 are case-based questions. Each question carries 4 marks. Each question has subparts with internal choice in one of the subparts.
- Section E – Questions number 31 to 33 are long answer type questions. Each question carries 5 marks.
- There is no overall choice. However, an internal choice has been provided in Sections B, C, and D of the question paper. A candidate has to write an answer for only one of the alternatives in such questions.
- Kindly note that there is a separate question paper for Visually Impaired candidates.
- Wherever necessary, neat and properly labelled diagrams should be drawn.
SECTION A
1. Long ribbon-like pollen grains are seen in some:
- (A) Aquatic plants
- (B) Wind-pollinated grasses
- (C) Gymnosperms
- (D) Bird-pollinated flowers
Answer: (B) Wind-pollinated grasses
Explanation:
Wind-pollinated grasses produce long, ribbon-like pollen grains that are lightweight and easily carried by the wind. This helps them reach other plants for fertilization.
2. Estrogen is secreted by:
- (A) Corpus luteum
- (B) Membrane granulosa of Graafian follicle
- (C) Pituitary gland
- (D) Germinal epithelium
Answer: (B) Membrane granulosa of Graafian follicle
Explanation:
Estrogen is primarily secreted by the granulosa cells of the Graafian follicle in females. It plays a critical role in the development of female secondary sexual characteristics and the regulation of the menstrual cycle.
3. Amniocentesis is a technique that is used to:
- (A) determine any disease of the heart
- (B) determine any genetic disorder of the foetus
- (C) determine any disorder of the brain
- (D) detect any abnormality in the bone formation
Answer: (B) determine any genetic disorder of the foetus
Explanation:
Amniocentesis is a medical procedure used during pregnancy to extract a small amount of amniotic fluid, which contains fetal cells. The fluid is analyzed for genetic disorders such as Down’s syndrome, cystic fibrosis, and other genetic conditions. It is typically done around the 15th to 20th week of pregnancy.
4. In humans, non-disjunction of the 21st pair of chromosomes leads to:
- (A) Acquired Immune Deficiency Syndrome
- (B) Klinefelter’s Syndrome
- (C) Turner’s Syndrome
- (D) Down’s Syndrome
Answer: (D) Down’s Syndrome
Explanation:
Down’s syndrome, also known as trisomy 21, occurs when there is a non-disjunction (failure to separate) of the 21st pair of chromosomes during cell division. This results in a child having three copies of chromosome 21 instead of the usual two, leading to developmental delays and certain physical features.
5. Which one of the following codons has dual function?
- (A) AUG
- (B) AUC
- (C) ACU
- (D) ACA
Answer: (A) AUG
Explanation:
The codon AUG serves as both the start codon and also codes for the amino acid methionine. It is the initiation signal for translation in protein synthesis and the first amino acid to be incorporated into a growing polypeptide chain.
6. Which one of the following options gives the correct temperature condition and the mixture of the gaseous components that were used by S.L. Miller in 1953 to prove abiogenesis of life?
- (A) CH4, H2, NO2 and water vapour at 1800°C
- (B) CH4, H2, NH3 and water vapour at 1800°C
- (C) CO2, H2, NH3 and water vapour at 800°C
- (D) CH4, H2, NH3 and water vapour at 800°C
Answer: (D) CH4, H2, NH3 and water vapour at 800°C
Explanation:
In 1953, Stanley Miller conducted an experiment to simulate the conditions thought to be present on early Earth. He used a mixture of methane (CH4), hydrogen (H2), ammonia (NH3), and water vapor in a closed apparatus and subjected it to electrical sparks to simulate lightning. This experiment demonstrated the synthesis of organic molecules like amino acids, providing evidence for the theory of abiogenesis (the origin of life from non-living matter).
Here are the answers with explanations for the questions you asked:
7. The mosquito-borne disease in humans causing chronic inflammation of the lymphatic vessels is:
- (A) Elephantiasis
- (B) Ascariasis
- (C) Ringworm
- (D) Amoebiasis
Answer: (A) Elephantiasis
Explanation:
Elephantiasis, also known as lymphatic filariasis, is a disease caused by infection with filarial worms (such as Wuchereria bancrofti), which are transmitted by mosquitoes. The worms block the lymphatic system, causing severe swelling and chronic inflammation of the limbs, leading to the characteristic “elephant-like” appearance.
8. In plants, which one of the following helps in the absorption of phosphorus from the soil?
- (A) Glomus
- (B) Rhizobium
- (C) Frankia
- (D) Anabaena
Answer: (A) Glomus
Explanation:
Glomus is a genus of fungi that forms mycorrhizal associations with plant roots. These fungi help plants absorb phosphorus from the soil, which is otherwise difficult to take up in large amounts. Mycorrhizal fungi form a symbiotic relationship with plants, enhancing nutrient uptake, especially phosphorus.
9. The most primitive ancestor of humans is:
- (A) Homo habilis
- (B) Australopithecus
- (C) Ramapithecus
- (D) Homo neanderthalensis
Answer: (C) Ramapithecus
Explanation:
Ramapithecus is considered one of the earliest ancestors of humans, believed to have lived about 14 to 10 million years ago. It is often linked to the evolution of the human lineage. Australopithecus (option B) is another important early hominid but is considered slightly more evolved than Ramapithecus.
10. The sequence that controls the copy number of linked DNA in the vector is termed:
- (A) Selectable marker
- (B) Ori site
- (C) Palindromic sequence
- (D) Recognition site
Answer: (B) Ori site
Explanation:
The Ori site (Origin of Replication) is the DNA sequence that controls the replication of the plasmid or vector. It determines the number of copies of the plasmid that are maintained in a cell. This is crucial for cloning experiments, as the vector needs to replicate within the host cell to produce multiple copies of the inserted DNA.
11. Crystals of Bt toxin produced by some bacteria, do not kill the bacteria producing them because:
- (A) bacteria are resistant to the toxin
- (B) toxin is immature
- (C) toxin is inactive
- (D) bacteria encloses ‘toxin’ in a special capsule
Answer: (C) toxin is inactive
Explanation:
Bt toxin (produced by Bacillus thuringiensis) is produced as an inactive protoxin in the bacteria. It is only activated in the alkaline environment of the insect’s gut. The bacteria do not produce the active form of the toxin to avoid self-damage. The toxin becomes active only when ingested by certain insects, causing their death.
12. The population interaction where one species is harmed and the other is unaffected is:
- (A) Amensalism
- (B) Commensalism
- (C) Parasitism
- (D) Predation
Answer: (A) Amensalism
Explanation:
Amensalism is a type of interaction in which one species is harmed, while the other remains unaffected. This can occur, for example, when one organism produces toxins that harm another species but the first organism is not affected. An example is the growth of penicillin-producing molds, which inhibit bacterial growth without benefiting themselves.
Here are the answers for the given question format, based on the Assertion and Reason provided:
13. Assertion (A): The pH of a solution increases when sodium hydroxide is added to water.
Reason (R): Sodium hydroxide is a strong base and dissociates completely in water, releasing hydroxide ions (OH⁻).
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
When sodium hydroxide (NaOH) is dissolved in water, it dissociates completely into sodium ions (Na⁺) and hydroxide ions (OH⁻). These hydroxide ions increase the pH of the solution, making it alkaline, which explains why the pH increases.
14. Assertion (A): In a plant cell, the nucleus is surrounded by a double membrane.
Reason (R): The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
The nucleus in plant cells is indeed surrounded by a double membrane known as the nuclear envelope. The outer membrane is continuous with the endoplasmic reticulum, and this structural relationship is essential for the transport of molecules between the nucleus and the cytoplasm.
15. Assertion (A): Water is a good solvent for ionic compounds.
Reason (R): Water molecules are polar and can separate the positive and negative ions of ionic compounds.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
Water is indeed a good solvent for ionic compounds due to its polarity. The polar nature of water molecules allows them to surround and separate the positive and negative ions in ionic compounds, leading to their dissolution.
16. Assertion (A): Green light is not absorbed by chlorophyll.
Reason (R): Chlorophyll reflects green light, which is why plants appear green.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
Chlorophyll absorbs most wavelengths of light except green, which is reflected. This is why plants appear green to the human eye. The green light is not absorbed by chlorophyll, hence it is reflected, leading to the characteristic color of plants.
Here are the questions along with answers and explanations:
SECTION B
13. Assertion (A): Periodic abstinence is a method in which couples avoid coitus from day 10 to 17 of the menstrual cycle.
Reason (R): Periodic abstinence has limited effectiveness because menstrual cycles are not always regular.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
Periodic abstinence involves avoiding intercourse during the fertile period of a woman’s menstrual cycle, typically days 10-17. This method relies on regularity in the menstrual cycle to be effective, but since cycles are not always regular, its effectiveness can be limited, as mentioned in Reason (R).
14. Assertion (A): Streptococcus pneumoniae and Haemophilus influenzae are responsible for causing infectious diseases in human beings.
Reason (R): A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
Streptococcus pneumoniae and Haemophilus influenzae are known to cause respiratory infections, among others. These bacteria are transmitted through droplets or aerosols when an infected person coughs or sneezes, making Reason (R) a valid explanation of Assertion (A).
15. Assertion (A): Biotechnology produces transgenic microorganisms that act as microfactories for proteins.
Reason (R): To produce proteins for human use like insulin, transgenic microorganisms can be developed.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
Biotechnology involves the use of genetically modified organisms, such as transgenic microorganisms, to produce valuable proteins. For example, bacteria can be engineered to produce human insulin, which is used in diabetes treatment. Reason (R) explains how transgenic organisms are developed for this purpose.
16. Assertion (A): Gross primary productivity is always less than net primary productivity.
Reason (R): Rate of synthesis of organic matter by consumers is known as secondary productivity.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer: (C) Assertion (A) is true, but Reason (R) is false.
Explanation:
Gross primary productivity (GPP) refers to the total energy captured by producers through photosynthesis, while net primary productivity (NPP) is the energy left after producers use some of this energy for their own metabolic processes (respiration). Hence, NPP is always less than GPP. However, Reason (R) is incorrect because secondary productivity refers to the production of organic matter by consumers, not by producers, and it does not explain the difference between GPP and NPP.
Here are the questions from Section B along with their answers:
17. State the cellular nature and functions of myometrium and endometrium. (2 marks)
Answer:
- Myometrium: It is the thick muscular layer of the uterus. Its primary function is to contract during labor, helping to expel the fetus from the uterus. It also aids in the menstrual flow.
- Endometrium: The inner lining of the uterus, composed of epithelial and connective tissue. It undergoes cyclic changes during the menstrual cycle, thickening to prepare for implantation of a fertilized egg. If fertilization does not occur, it sheds during menstruation.
18. How do ‘implants’ act as an effective method of contraception in human females? Mention their one advantage over contraceptive pills. (2 marks)
Answer:
Implants are small rods or devices placed under the skin of a female’s arm, releasing hormones like progestin that prevent ovulation, thicken cervical mucus, and make the endometrium inhospitable for implantation.
- Advantage over contraceptive pills: Implants provide long-term contraception (3 to 5 years) without the need for daily administration, whereas contraceptive pills require daily intake.
19. (a) Given below is a representation of the “Central dogma”:
‘A’ DNA → ‘B’ mRNA → ‘C’ protein.
Identify ‘A’, ‘B’, and ‘C’ in the above representation. (1 mark)
Answer:
- A = DNA
- B = mRNA
- C = Protein
19. (b) What does the Central Dogma state in molecular biology? Write an example where it is not applicable. (1 mark)
Answer:
The Central Dogma states that genetic information flows from DNA → RNA → Protein, meaning that DNA is transcribed into mRNA, which is then translated into protein.
- Example where not applicable: In retroviruses (like HIV), RNA is reverse-transcribed into DNA by the enzyme reverse transcriptase, which contradicts the Central Dogma’s flow of information from DNA to RNA.
20. Why is making host cells ‘competent’ essential for rDNA technology? Mention any two ways by which this can be achieved. (2 marks)
Answer:
Making host cells “competent” is essential for rDNA technology because competent cells are able to take up foreign DNA, allowing for the insertion of recombinant DNA into their genome.
- Ways to achieve competence:
- Chemical method: Treating the cells with calcium chloride to make their cell membranes more permeable to DNA.
- Electroporation: Using an electric shock to open the cell membrane and allow DNA to enter.
21. (a) Comment on the interaction between a fig tree and wasp. Mention the phenomenon that operates in their relationship. (2 marks)
Answer:
The interaction between a fig tree and fig wasp is an example of mutualism. The female wasp enters the fig’s syconium (a fig’s flower cluster) to lay her eggs. In the process, she pollinates the fig flowers. The larvae develop inside the fig, and the new female wasps leave the fig to find a new fig tree in which to lay their eggs. The fig tree benefits from pollination, while the wasp benefits by using the fig as a breeding ground.
21. (b) Explain “brood parasitism” with the help of an example. (2 marks)
Answer:
Brood parasitism is a reproductive strategy where one species lays its eggs in the nest of another species, relying on the host to raise its young.
- Example: The cuckoo is a well-known brood parasite. The female cuckoo lays her eggs in the nests of other bird species, like the reed warbler. When the cuckoo chick hatches, it often pushes the host’s eggs or chicks out of the nest, ensuring it gets all the food and care from the host parents.
SECTION C
24. (b) Draw a labelled diagram of an initiator tRNA charged with its respective amino acid. (2 marks)
Answer:
(Here is a textual representation of the diagram, as I cannot draw images.)
- The tRNA molecule has three main parts:
- Anticodon loop: Contains the anticodon sequence that is complementary to the mRNA codon.
- Amino acid attachment site: Located at the 3′ end of the tRNA, where the amino acid is attached (for the initiator tRNA, this is usually Methionine).
- Amino acid: The amino acid attached to the tRNA molecule.
24. (c) Explain the role of the initiator tRNA in the initiation of protein synthesis. (3 marks)
Answer: The initiator tRNA plays a crucial role in the initiation phase of protein synthesis:
- The initiator tRNA carries the amino acid methionine (in eukaryotes) or formylmethionine (in prokaryotes), which is the first amino acid incorporated into a nascent polypeptide.
- The initiator tRNA binds to the start codon (AUG) on the mRNA. This codon signals the beginning of the protein coding sequence.
- The small ribosomal subunit binds to the mRNA and aligns the initiator tRNA with the start codon. The large ribosomal subunit then binds to form the complete ribosome, allowing for the continuation of protein synthesis.
25. Differentiate between the explanations given by Darwin and de Vries respectively on the mechanism of evolution. Write any three differences. (3 marks)
Answer:
| Darwin’s Explanation | De Vries’ Explanation |
|---|---|
| Darwin proposed natural selection as the mechanism of evolution, where organisms with favorable traits survive and reproduce. | De Vries proposed mutation theory, stating that evolution occurs through sudden, large mutations, rather than gradual changes. |
| Darwin believed that traits evolve gradually over generations. | De Vries suggested that evolution can happen in single generations due to mutations. |
| Darwin’s theory involves variations that arise through recombination and sexual reproduction. | De Vries emphasized mutations as the primary source of variations in evolution. |
26. (a) What is gene therapy? (1 mark)
Answer:
Gene therapy is a technique used to treat or prevent diseases by introducing, removing, or altering genetic material within a person’s cells. The goal is to correct faulty genes responsible for disease development.
26. (b) Describe the procedure of such a therapy that could be a permanent cure for a genetic disease. Name the genetic disease. (2 marks)
Answer:
Gene therapy procedure:
- Gene Identification: Identify the faulty gene responsible for the disease.
- Gene Insertion: The healthy gene is inserted into the patient’s cells using vectors (usually modified viruses).
- Gene Expression: The inserted gene is expressed in the patient’s cells, producing the functional protein needed for normal cellular function.
Example of genetic disease:
- Cystic fibrosis can be treated with gene therapy by inserting a correct copy of the CFTR gene into the patient’s lung cells, enabling them to produce the functional CFTR protein and alleviate symptoms.
27. (a) Differentiate between Grazing food chain and Detritus food chain. (Any three differences) (3 marks)
Answer:
| Grazing Food Chain | Detritus Food Chain |
|---|---|
| It starts with producers (plants/algae). | It starts with dead organic matter (detritus). |
| Primary consumers are herbivores. | Primary consumers are decomposers (bacteria, fungi). |
| The energy flow is direct from plants to herbivores to carnivores. | The energy flow is indirect, starting with the breakdown of dead organic material. |
27. (b) Differentiate between Upright pyramid and Inverted pyramid. (Any three differences) (3 marks)
Answer:
| Upright Pyramid | Inverted Pyramid |
|---|---|
| Producer biomass is at the base, and the biomass decreases at higher trophic levels. | Producer biomass is at the top, and the biomass increases at higher trophic levels. |
| Common in terrestrial ecosystems. | Common in aquatic ecosystems. |
| The number of organisms decreases as you move up the pyramid. | The number of organisms increases as you move up the pyramid. |
28. (a) (i) What are “biodiversity hotspots” regions? Mention any two criteria used for determining any region as a “hotspot.” (3 marks)
Answer:
- Biodiversity hotspots are regions that are both rich in endemic species (species found nowhere else) and have experienced significant habitat loss.
Criteria used to determine hotspots:
- The region must contain at least 1,500 species of vascular plants as endemics.
- The region must have lost at least 70% of its original habitat.
Example of biodiversity hotspots:
- The Western Ghats and Sundaland in India.
28. (ii) Name any two hotspots of India. (1 mark)
Answer:
- The Western Ghats
- The Indo-Burma region
OR
28. (b) Explain, giving three reasons, why tropics show the greatest level of species diversity. (3 marks)
Answer: The tropics show the greatest level of species diversity because:
- Stable Climate: Tropical regions have a relatively stable climate throughout the year, providing consistent environmental conditions for species to thrive.
- High Primary Productivity: The abundance of sunlight and water leads to high rates of photosynthesis and primary production, supporting a large number of species at all trophic levels.
- Ecological Complexity: Tropics have a wide range of habitats, including forests, wetlands, and coastal ecosystems, which provide niches for a large number of species to evolve and coexist.
SECTION D – Case-based Questions
29. Read the following passage and answer the questions that follow. (4 marks)
Passage: Restriction endonuclease was isolated for the first time by W. Arber in 1962, in bacteria. DNA, the genetic material, can be manipulated by addition or substitution of the desired gene by using a specific restriction endonuclease, resulting in recombinant DNA (rDNA). This is one of the major steps in biotechnology.
(a) Name the first isolated restriction endonuclease. Why are restriction endonucleases so called? (1 mark)
Answer:
- The first isolated restriction endonuclease is EcoRI.
- Restriction endonucleases are so called because they restrict or cut the foreign DNA at specific sequences, and they are enzymes that cut the DNA internally (endonucleases) at specific sequences known as recognition sites.
(b) Write the palindrome recognised by EcoRI. (1 mark)
Answer:
- The palindrome sequence recognized by EcoRI is:
- GAATTC
- The sequence is read the same in both directions when read in a 5′ to 3′ direction on both strands.
(c) (i) How does restriction endonuclease function? Explain. (2 marks)
Answer:
- Restriction endonucleases function by scanning a DNA molecule for a specific palindromic sequence (usually 4-8 base pairs long). When the enzyme finds the matching sequence, it cuts the DNA at a specific point within or near this sequence.
- The enzyme cleaves the phosphodiester bonds between nucleotides, resulting in two separate fragments of DNA. This is useful in biotechnology for manipulating DNA, such as inserting a gene into a plasmid vector.
OR
(c) (ii) Write the convention for naming a restriction endonuclease with the help of an example. (2 marks)
Answer:
- The naming convention for restriction endonucleases involves:
- The first letter of the genus of the bacteria in uppercase.
- The first two letters of the species name in lowercase.
- The strain of the bacterium (if applicable) is indicated by a single letter.
- A Roman numeral is used to denote the enzyme from that species.
Example:
- EcoRI:
- E = Escherichia (genus)
- co = coli (species)
- R = strain R
- I = first enzyme isolated from this strain.
30. Read the following passage and answer the questions that follow. (4 marks)
Passage: A senior student, sneezing very badly, with watery eyes and having difficulty in breathing was brought to the school medical room by his fellow friends. The medical room nurse enquired as to what had happened. One of the students said, “After the football match we all were sweating profusely, and one of our friends sprayed deodorant on us. Soon after the deodorant was sprayed on the senior boy, the symptoms appeared.”
(a) What are the symptoms seen in the student indicative of? Elaborate. (1 mark)
Answer:
- The symptoms seen in the student, such as sneezing, watery eyes, and difficulty in breathing, are indicative of a hypersensitivity reaction or allergic reaction.
- The reaction is likely triggered by an allergen in the deodorant spray, which caused an immune response in the body. This type of allergic response can lead to the release of histamines, causing inflammation in the airways and eyes.
(b) State how the cause of such responses can be confirmed. (1 mark)
Answer:
- The cause of the allergic response can be confirmed by conducting an allergy test such as:
- Skin prick test: Small amounts of allergens (like deodorant chemicals) are applied to the skin to observe for a reaction.
- Blood test: Measure the levels of IgE antibodies, which are often elevated during an allergic reaction.
(c) (i) Name the cells in our body and the chemicals produced by them that are responsible for such reactions. Name any two drugs used to reduce these symptoms. (2 marks)
Answer:
- The cells responsible for allergic reactions are mast cells and basophils.
- These cells release histamine and other chemicals (like leukotrienes and prostaglandins) that cause symptoms like sneezing, watery eyes, and difficulty in breathing.
- Two drugs used to reduce these symptoms are:
- Antihistamines (e.g., cetirizine, loratadine) that block histamine receptors.
- Corticosteroids (e.g., prednisolone, hydrocortisone) that reduce inflammation.
OR
(c) (ii) ‘In recent times, there is a rise in such reactions amongst the urban human population.’ Do you agree? Give three reasons in support of your answer. (3 marks)
Answer:
- Yes, I agree that there is a rise in allergic reactions in the urban population. The reasons are:
- Increased Exposure to Pollutants: Urban areas have higher levels of air pollutants (like car exhaust, smoke) and chemicals, which can trigger allergies.
- Use of Artificial Fragrances and Chemicals: Products like deodorants, perfumes, cleaning agents, and cosmetics often contain chemicals that can cause allergic reactions.
- Urban Lifestyles: People in urban areas often live in environments with higher levels of dust, mold, and allergens, and may also have weakened immune systems due to stress, poor diet, and lack of outdoor exposure.
SECTION E – Long Answer Type Questions
31. (a) (i) Draw a labelled diagram of a fertilised embryo sac of an angiosperm. (label any four parts) (5 marks)
Answer:
The fertilised embryo sac of an angiosperm consists of several important parts. A labelled diagram of the fertilised embryo sac is as follows:
Diagram Description:
- Embryo sac contains the egg cell, synergids, central cell, antipodal cells, and polar nuclei.
Key parts to label:
- Egg cell – The cell that fuses with the male gamete (sperm).
- Synergids – Two cells near the egg that help guide the pollen tube.
- Central cell – Contains two polar nuclei that fuse with one sperm to form the triploid endosperm.
- Antipodal cells – Cells located at the opposite end of the embryo sac that do not play a significant role in fertilisation.
- Micropyle – The opening through which the pollen tube enters the embryo sac.
(ii) Explain double fertilisation in angiospermic plant. (5 marks)
Answer:
- Double fertilisation is a unique process in angiosperms (flowering plants) where two fertilisation events occur:
- Fusion of male gamete (sperm) with the egg cell: The sperm cell enters the egg cell and fertilises it, forming the zygote (2n). This zygote will later develop into the embryo.
- Fusion of the second male gamete with the two polar nuclei: The second sperm cell fuses with the two polar nuclei present in the central cell to form the triploid endosperm (3n). The endosperm provides nourishment to the developing embryo.
Thus, double fertilisation results in the formation of the zygote (embryo) and endosperm, which are critical for seed development.
OR
(b) (i) Draw a labelled diagram of a cross-section of human seminiferous tubule. (label any four parts) (5 marks)
Answer:
A cross-section of the human seminiferous tubule is as follows:
Key parts to label:
- Lumen – The central cavity of the seminiferous tubule where sperm cells are released.
- Sertoli cells – These are large, columnar cells that provide nourishment to the developing sperm.
- Spermatogenic cells – These cells are involved in the process of spermatogenesis, including spermatogonia, spermatocytes, and spermatids.
- Basal membrane – The outermost layer that separates the seminiferous tubule from the surrounding connective tissue.
The seminiferous tubules are the site of spermatogenesis, where sperm cells are produced.
(ii) Explain the hormonal regulation of spermatogenesis. (5 marks)
Answer: The process of spermatogenesis is regulated by various hormones:
- Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the anterior pituitary gland to release:
- Follicle-stimulating hormone (FSH): This hormone acts on Sertoli cells in the seminiferous tubules to stimulate spermatogenesis (production of sperm).
- Luteinizing hormone (LH): LH acts on the Leydig cells (interstitial cells between the seminiferous tubules) to produce testosterone.
- Testosterone:
- Stimulates spermatogenesis and promotes the development of male secondary sexual characteristics.
- It also exerts negative feedback on the hypothalamus and anterior pituitary, inhibiting the release of GnRH, FSH, and LH to maintain hormonal balance.
Thus, FSH, LH, and testosterone work together to regulate spermatogenesis.
32. (a) (i) Absence of lactose in the culture medium affects the expression of lac operon in E. coli. Why and how? Explain. (5 marks)
Answer:
- The lac operon in E. coli is responsible for the breakdown of lactose into glucose and galactose. It consists of three genes: lacZ, lacY, and lacA, which code for enzymes that help metabolize lactose.
- The operon is regulated by the lac repressor protein. When lactose is absent in the culture medium, the lac repressor binds to the operator region of the operon, blocking the RNA polymerase from transcribing the genes. As a result, the operon is not expressed.
- When lactose is present, it binds to the repressor protein, causing a conformational change that releases the repressor from the operator. This allows RNA polymerase to transcribe the genes and produce the enzymes necessary for lactose metabolism.
Thus, absence of lactose prevents expression of the lac operon, while presence of lactose induces the expression of the operon.
(ii) Write any two ways in which gene expression is regulated in eukaryotes. (5 marks)
Answer:
- Chromatin Remodeling: In eukaryotes, chromatin (the material that makes up chromosomes) can be modified through acetylation or methylation. Acetylation of histones promotes transcription by loosening the chromatin structure, making DNA more accessible for transcription. Methylation of DNA, on the other hand, often leads to gene silencing.
- Transcription Factors: The binding of transcription factors to the promoter region of a gene is necessary for RNA polymerase to initiate transcription. These factors can be activators, which enhance gene expression, or repressors, which inhibit transcription.
OR
(b) (i) By taking two suitable traits in a pea plant, work out a dihybrid cross up to F2 generation. (5 marks)
Answer: Let’s consider two traits in pea plants:
- Seed color: Yellow (Y) is dominant over green (y).
- Seed shape: Round (R) is dominant over wrinkled (r).
- The parental generation is YYRR × yyrr.
F1 generation (All heterozygous):
- YyRr (All F1 plants have yellow, round seeds).
Now, for the dihybrid cross between F1 individuals (YyRr × YyRr):
| Gametes | YR | Yr | yR | yr |
|---|---|---|---|---|
| YR | YYRR | YYRr | YyRR | YyRr |
| Yr | YYRr | YYrr | YyRr | Yyrr |
| yR | YyRR | YyRr | yyRR | yyRr |
| yr | YyRr | Yyrr | yyRr | yyrr |
F2 Phenotypic Ratio:
- 9 Yellow, Round (YYRR, YYRr, YyRR, YyRr):
- 3 Yellow, Wrinkled (YYrr, Yyrr):
- 3 Green, Round (yyRR, yyRr):
- 1 Green, Wrinkled (yyrr).
Mendel’s law derived from this dihybrid cross is:
- Law of Independent Assortment: Genes for different traits assort independently during the formation of gametes.
(ii) State Mendel’s law derived from such a cross only. (5 marks)
Answer:
- Mendel’s Law of Independent Assortment: During gamete formation, the alleles for different traits assort independently of each other, leading to the formation of different combinations of traits in offspring.
33. (a) Describe the process of wastewater (sewage) treatment under the following heads: (5 marks)
- Primary Treatment:
- In this stage, physical filtration is done to remove large debris and particles. The wastewater is passed through grates or screens to remove larger objects like plastics, paper, and food waste.
- The wastewater is then sent to sedimentation tanks, where heavy solids settle down as sludge, and lighter materials, like oil and grease, float on the surface and are skimmed off.
- Secondary Treatment:
- In this stage, biological treatment is used to remove dissolved and suspended organic matter. The wastewater is treated with bacteria and other microorganisms that consume the organic matter and convert it into simpler substances.
- This can be done through activated sludge processes or trickling filters, where microorganisms break down the organic pollutants in the
water.
OR
(b) (i) Explain the sequence of events occurring in a biogas plant. (5 marks)
Answer:
- Collection of organic waste: Organic waste such as cow dung, food waste, and agricultural residue is collected and placed in the biogas digester.
- Anaerobic Digestion: The organic waste is broken down by microorganisms in the absence of oxygen (anaerobic conditions). This process produces methane (CH₄), carbon dioxide (CO₂), and small amounts of other gases.
- Production of biogas: Methane is the main component of biogas, which is collected and stored in a gas holder.
- Sludge formation: The remaining organic material, known as digested slurry, is separated and can be used as organic fertilizer.
(ii) Write the components of biogas. (5 marks)
Answer:
- The primary components of biogas are:
- Methane (CH₄): 50-70% – The main component responsible for energy production.
- Carbon dioxide (CO₂): 30-40%.
- Nitrogen (N₂): 1-2%.
- Hydrogen sulfide (H₂S): Trace amounts, which are removed for safety reasons.
- Water vapor: Present in small amounts.
(iii) Write any three advantages of using cow dung as the raw material. (5 marks)
Answer:
- Renewable Source: Cow dung is an abundant and renewable resource that can be continuously supplied.
- Efficient Waste Management: Using cow dung in biogas plants helps in managing animal waste effectively, reducing pollution.
- Nutrient-Rich Sludge: The digested slurry from biogas production is rich in nutrients and can be used as organic fertilizer for crops, improving soil fertility.
Let me know if you need further clarification or additional questions!