Biology (Theory)

Maize is monoecious – male (tassel) and female (cob) flowers are on the same plant. Pollen can reach a female flower of the same plant (geitonogamy) or of another plant (xenogamy); self-pollination within one flower (autogamy) is impossible because the flowers are unisexual.
Papaya, date palm and spinach are dioecious (male and female flowers on separate plants), so only xenogamy is possible in them.

hCG from the placenta keeps the corpus luteum alive in early pregnancy, so progesterone keeps being secreted and the endometrium is maintained.
Oxytocin is from the posterior pituitary (it causes uterine contractions at birth). hPL and relaxin are also produced during pregnancy, but the hormone whose key role is maintaining pregnancy is hCG (as accepted in the marking scheme).

Ovulation usually happens around day 14 of a 28-day cycle. The fertile period, when conception is most likely, is taken as day 10 to day 17. Avoiding coitus in this window is the periodic abstinence (natural) method.

44 + XXY is Klinefelter's syndrome: the person is male with overall MASCULINE development, though some feminine features (gynaecomastia) appear, and is sterile. So pairing (B) is wrong.
45 + XX (trisomy 21 in a female) = Down's syndrome – broad palm with palm crease: correct.
44 + XO = Turner's syndrome – sterile female, rudimentary ovaries: correct.
44 + XY = normal male: correct.

With n kinds of bases and codon length k, the number of different codons = nᵏ. We need nᵏ ≥ number of amino acids.
Real case: 4² = 16 < 20, 4³ = 64 ≥ 20 → triplet code.
Hypothetical case: 12¹ = 12 < 96, 12² = 144 ≥ 96 → a codon of 2 bases is enough.
Common mistake: dividing 96 by 12 (= 8); the count of codons grows as a power, not a product.

The nitrogenous base is joined to the 1′ carbon of the pentose sugar through an N-glycosidic linkage, forming a nucleoside.
The P–S links along the backbone are 3′–5′ phosphodiester bonds; hydrogen bonds join bases of opposite strands; peptide bonds occur in proteins.

In an allergy, IgE antibodies are produced against an allergen; the allergen then makes mast cells release histamine and serotonin, causing sneezing, watery eyes, running nose etc. So mast-cell activity rises sharply in allergy.

Lactobacillus (a lactic acid bacterium) cannot make its own food; it uses the lactose of milk and converts it to lactic acid, which coagulates milk proteins into curd. It is therefore a heterotrophic bacterium (Eubacteria).

Transgenic mice are being developed and used to test the safety of vaccines (e.g. polio vaccine) before they are used on humans; if successful this can replace the use of monkeys for such testing.

Hind II, the first restriction endonuclease isolated, always cuts DNA at a particular point by recognising a specific sequence of six base pairs – its recognition sequence.

Golden rice is engineered to make β-carotene (provitamin A) in the grain, giving it a golden colour; it is rich in vitamin A and is meant to fight vitamin-A deficiency.

Rate of formation of new organic matter by consumers = secondary productivity.
NPP = GPP − respiration losses; this is the biomass available to herbivores and decomposers.

A is true – legal adoption is allowed and is a good option for childless couples.
R is false – in India, emotional, religious and social factors are in fact deterrents to adoption; that is why many couples do not choose it.

The 9 : 3 : 3 : 1 ratio depends on independent assortment of two genes. Genes lying close together on the same chromosome tend to be inherited together (linkage), so parental combinations appear far more often than recombinants and the ratio deviates. R is the cause of A.

A is false – Agrobacterium tumefaciens is a pathogen of several DICOT plants (causes crown gall).
R is true – its Ti plasmid carries T-DNA, which it delivers into plant cells, turning them into tumour cells; a disarmed Ti plasmid is therefore used as a cloning vector.

A is true – GEAC (Genetic Engineering Appraisal Committee) judges the validity of GM research and the safety of introducing GM organisms for public services.
R is false – GM organisms CAN have unpredictable effects when released into an ecosystem; that is exactly why such a regulatory body is needed.

A: Pericarp is the wall of the fruit, formed from the wall of the ripened ovary.
B: In grasses (monocots) the single cotyledon is called the scutellum.
C: The embryonal axis is the part that bears the radicle (root tip) and plumule (shoot tip) – epicotyl/hypocotyl portions.
D: Persistent remains of the nucellus in a seed are called perisperm (e.g. black pepper, beet).

Naturalist: Jean-Baptiste Lamarck.
Explanation: evolution is driven by use and disuse of organs.
Ancestors of giraffes, trying to eat leaves on tall trees, kept stretching their necks, so the neck elongated a little in their lifetime.
This acquired character (longer neck) was passed on to the offspring; over many generations giraffes came to have very long necks (inheritance of acquired characters).

Steps (IVF–ET):
1. Ova are collected from the wife or a female donor, and sperm from the husband or a male donor.
2. They are made to fuse under simulated conditions in the laboratory (in vitro) to form a zygote.
3. The zygote/early embryo is transferred into the female's fallopian tube or uterus (ZIFT/IUT) for further development.
Test tube baby: the first part – fertilisation and early development – takes place outside the body, in laboratory glassware, hence the name.

(i) The doctor injected antivenom (anti-snake venom), i.e. ready-made antibodies/antitoxins against the venom. Snake venom acts fast; the body cannot make its own antibodies in time, so preformed antibodies are given to neutralise the toxin immediately.
(ii) Since the antibodies are supplied from outside and not made by the patient's own body, it is passive immunity (artificially acquired).

1. Organic farmers believe complete eradication of pests is not only nearly impossible but also undesirable.
2. Many beneficial predatory and parasitic insects (biocontrol agents such as ladybirds, dragonflies) feed on or live in the pests; if all pests are destroyed, these useful organisms will not survive.
3. Their key belief is that biodiversity furthers health – a more diverse farm ecosystem is more stable and sustainable; pests are kept at manageable levels by natural checks.

A (primary consumers): zooplankton / small herbivorous fish.
B (producers): phytoplankton.
Type: inverted pyramid of biomass – the producer biomass at a given time is less than the consumer biomass.
Ecosystem: sea (aquatic). Phytoplankton have small standing crop but reproduce very fast, so they can support a larger biomass of consumers.

Composition: progestogens alone or a progestogen–estrogen combination.
Mode of action:
1. Inhibit ovulation.
2. Inhibit implantation.
3. Alter the quality of cervical mucus so that entry of sperm is prevented or retarded.
Schedule:
1. One pill daily for 21 days, starting within the first five days of the menstrual cycle.
2. After a gap of 7 days (during which menstruation occurs), the course is repeated in the same way as long as the woman wishes to avoid conception.
(Saheli, a once-a-week non-steroidal pill, is another example.)

(a) Repetitive DNA – satellite DNA (e.g. VNTRs, variable number of tandem repeats).
Features (any two):
• It does not code for any protein.
• It forms a large portion of the human genome.
• It shows a high degree of polymorphism – the number of repeats differs from person to person, and this is inheritable.
(b) Applications (any two): forensic science (identifying criminals), paternity/maternity testing, finding population and genetic diversity, studying evolution, tracing hereditary diseases.

(a) In 1953 Miller sealed CH₄, H₂, NH₃ and water vapour in a closed flask, kept at about 800 °C and passed electric sparks through it (to mimic the early earth's atmosphere and lightning).
After some days amino acids were formed.
Significance: organic molecules can form from inorganic molecules under such conditions – experimental support for the theory of chemical evolution of life.
The hypothesis was proposed by Oparin (Russia) and Haldane (England).
(b) Analysis of meteorite content has revealed similar organic compounds, showing that similar processes are taking place elsewhere in space – this supports the idea.

A (pneumonia, Streptococcus pneumoniae/Haemophilus): fever, chills, cough, headache; in severe cases lips and finger nails turn grey to bluish (alveoli fill with fluid).
B: Salmonella typhi (confirmed by Widal test).
C (common cold): nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness.
D (ringworm): fungi Microsporum, Trichophyton, Epidermophyton.
E (ascariasis): internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage.
F: Amoebiasis (amoebic dysentery), caused by the protozoan Entamoeba histolytica.

Colour blindness is an X-linked recessive trait. Let Xᶜ = allele for colour blindness, X = normal.
Father (colour blind): XᶜY. Mother (normal vision) must be a carrier: XXᶜ – otherwise the son could not be colour blind.
Cross: XXᶜ (carrier mother) × XᶜY (colour-blind father)
Gametes: mother – X, Xᶜ; father – Xᶜ, Y
Offspring: XXᶜ – carrier daughter; XᶜXᶜ – colour-blind daughter; XY – normal son; XᶜY – colour-blind son.
Conclusion: NO for the son – a son gets only the Y chromosome from his father, so his Xᶜ came from his mother. The daughter (XᶜXᶜ) received one Xᶜ from the father and one from the mother.

(i) Transgenic animals are animals whose DNA has been manipulated so that they possess and express an extra (foreign) gene.
(ii) The first transgenic cow was Rosie (1997).
Importance: she produced milk enriched with human protein – about 2.4 g of human alpha-lactalbumin per litre. Such milk is nutritionally more balanced for human babies than natural cow milk.

(i) EcoRI comes from Escherichia coli RY13:
• E – first letter of the genus Escherichia
• co – first two letters of the species coli
• R – the strain RY13
• I (Roman numeral) – the order in which the enzyme was isolated from that strain (first).
(ii) Illustration: EcoRI recognises the palindrome
5′ – G A A T T C – 3′
3′ – C T T A A G – 5′
It cuts each strand between G and A:
5′ – G A A T T C – 3′
3′ – C T T A A G – 5′
This leaves single-stranded overhangs (AATT) called sticky ends, which can pair with complementary ends of other DNA cut by the same enzyme.

(a) Ophrys uses 'sexual deceit':
1. One petal of its flower resembles the female of a particular bee species in size, colour and markings.
2. The male bee is attracted to what it takes to be a female and 'pseudocopulates' with the flower; pollen is dusted on its body.
3. When the same bee pseudocopulates with another Ophrys flower, it transfers the pollen, causing pollination. Only that bee species is fooled, so pollination is species-specific.
(b) Co-evolution: if the colour pattern of the female bee changes even slightly during evolution, pollination success falls unless the orchid flower also evolves to keep the resemblance. Thus the plant and its pollinator evolve together – co-evolution (an example of mutualism-like interaction).

(a) Region III represents tropical latitudes, where diversity is highest because (any one):
• tropics remained relatively undisturbed for millions of years (no frequent glaciation), giving long evolutionary time for species diversification;
• the environment is less seasonal, more constant and predictable, favouring niche specialisation;
• more solar energy is available → higher productivity → greater diversity.
(b) Latitudinal gradient in diversity – species diversity decreases from the equator towards the poles.
(c) 1. Conventional taxonomic methods (based on morphology) are not suitable for identifying microbial species.
2. Many microbial species cannot be cultured under laboratory conditions, so they cannot be studied and counted. (Biochemical/molecular methods suggest their diversity may run into millions.)

(a) Colony 4. It grows on Plate M but not on Plate N (which has tetracycline). The foreign DNA was ligated into the tetracycline-resistance gene, so that gene was inactivated; the bacteria still resist ampicillin but not tetracycline. Colonies that grow on both antibiotics carry the non-recombinant plasmid.
(b) The ampR and tetR genes are selectable markers, and the points within them where foreign DNA is joined are restriction (recognition) sites (e.g. BamHI/SalI in tetR, PstI/PvuI in ampR of pBR322).
Role: selectable markers help to identify and select transformants and eliminate non-transformants; insertion of alien DNA at a site within one marker inactivates it (insertional inactivation), so recombinants can be told apart from non-recombinants.
(Note: the marking scheme awarded full marks for this part to all candidates.)
(c) Restriction endonuclease (molecular scissors) and DNA ligase (molecular glue); Taq DNA polymerase is also acceptable.

(i) 1. In the young anther, the sporogenous tissue forms microspore mother cells (2n).
2. Each microspore mother cell undergoes meiosis (microsporogenesis), producing a cluster of four haploid cells – the microspore tetrad.
3. As the anther matures and dries, the microspores separate and develop into pollen grains.
4. Each mature pollen grain divides by unequal (asymmetric) mitosis into a large vegetative cell (with food reserve and irregular nucleus) and a small spindle-shaped generative cell that floats in its cytoplasm – the 2-celled stage.
5. In some plants the generative cell divides mitotically to form two male gametes before shedding, giving the 3-celled stage (in others this happens in the pollen tube).
(ii) Diagram – a round pollen grain with a thick two-layered wall. Labels to show:
• Exine (outer, sporopollenin layer)
• Intine (inner, cellulose–pectin layer)
• Germ pore (gap in the exine)
• Vegetative cell with its nucleus
• Two male gametes (sperm cells)
• Cytoplasm.

(i) Diagram – an oval section of the ovary showing follicles at various stages in the stroma. Labels that must be shown: (1) blood vessels entering the stroma; (2) primary follicle – a primary oocyte surrounded by a single layer of granulosa cells; (3) tertiary follicle – larger follicle with a fluid-filled cavity (antrum) and theca layers; (4) ovum (secondary oocyte released/inside Graafian follicle). Other parts often shown: secondary follicle, Graafian follicle, corpus luteum.
(ii) Primary follicles are formed during the embryonic (foetal) stage; no new oogonia are formed after birth.
(iii) 1. LH and FSH reach a peak in the middle of the cycle (about day 14); the rapid rise of LH (LH surge) causes rupture of the Graafian follicle and release of the ovum – ovulation.
2. Luteal phase: the remaining parts of the Graafian follicle change into the corpus luteum.
3. The corpus luteum secretes large amounts of progesterone, which maintains the endometrium for implantation.
4. If fertilisation does not occur, the corpus luteum degenerates and progesterone level falls.
5. This causes disintegration of the endometrium, leading to menstruation – the start of the next cycle.

Scientist: Frederick Griffith (1928), working with Streptococcus pneumoniae.
Strains: S strain – smooth, shiny colonies, has a polysaccharide (mucous) coat, virulent; R strain – rough colonies, no coat, non-virulent.
Experiment:
1. Live S strain injected into mice → mice died.
2. Live R strain → mice lived.
3. Heat-killed S strain → mice lived.
4. Heat-killed S + live R → mice died, and live S bacteria were recovered from the dead mice.
Conclusion:
• The R-strain bacteria had been transformed by the heat-killed S strain.
• Some 'transforming principle' passed from heat-killed S to R bacteria and enabled them to make the smooth polysaccharide coat and become virulent – this must be due to transfer of genetic material.
• Heat that killed the bacteria did not destroy the properties of the genetic material – showing its stability.
(Later Avery, MacLeod and McCarty showed the transforming principle is DNA.)

Tall (T) and violet (V) are dominant, so the plant can be TTVV, TTVv, TtVV or TtVv. Self it and observe the progeny.
Case 1: TTVV × TTVV → gametes TV only → all TTVV.
Phenotype: all tall violet; genotype: all TTVV (pure for both traits).
Case 2: TTVv × TTVv → gametes TV, Tv → TTVV : TTVv : TTvv = 1 : 2 : 1.
Phenotype: tall violet : tall white = 3 : 1.
Case 3: TtVV × TtVV → gametes TV, tV → TTVV : TtVV : ttVV = 1 : 2 : 1.
Phenotype: tall violet : dwarf violet = 3 : 1.
Case 4: TtVv × TtVv → gametes TV, Tv, tV, tv (4 × 4 Punnett square).
Phenotype: tall violet : tall white : dwarf violet : dwarf white = 9 : 3 : 3 : 1.
Genotype: TTVV 1 : TTVv 2 : TtVV 2 : TtVv 4 : TTvv 1 : Ttvv 2 : ttVV 1 : ttVv 2 : ttvv 1.
Inference: no segregation → TTVV; only white appears → TTVv; only dwarf appears → TtVV; both appear in 9:3:3:1 → TtVv.
(Any three crosses with both ratios earn full marks.)

(i) Contact inhibition. In normal cells, contact with neighbouring cells stops their further growth and division. Cancer cells lose this property, so they keep dividing, forming masses of cells (tumours).
(ii) Proto-oncogenes (cellular oncogenes, c-onc). They are normal genes in all cells; when activated under certain conditions (mutation, carcinogens, viral oncogenes) they cause oncogenic transformation of cells, i.e. uncontrolled division.
(iii) (1) Biopsy and histopathology: a piece of suspected tissue is cut into thin sections, stained and examined under a microscope by a pathologist for abnormal/increased cell counts – confirms cancer.
(2) MRI: uses strong magnetic fields and non-ionising radiation to detect pathological and physiological changes in living tissue; useful for detecting cancers of internal organs without surgery and without harmful ionising radiation.

(i)(1) In the aeration tanks the effluent is constantly agitated and air is pumped in. This allows vigorous growth of useful aerobic bacteria, which with fungal filaments form mesh-like 'flocs'. They consume the major part of the organic matter, greatly reducing the BOD of the effluent.
(2) The sediment is called activated sludge. Its significance: a small part of it is pumped back into the aeration tank to serve as inoculum (supply of microbes); the rest is used in anaerobic sludge digesters.
(3) Once BOD is reduced sufficiently, the effluent is passed into the settling tank where the bacterial flocs are allowed to settle (forming activated sludge). The clear supernatant – the secondary/treated effluent – is then released into rivers and streams. (The major part of sludge goes to anaerobic digesters, where anaerobic bacteria digest it and produce biogas – CH₄, H₂S, CO₂.)
(ii) Any two from different kingdoms:
• Rhizobium (bacterium, Monera) – lives symbiotically in root nodules of leguminous plants and fixes atmospheric nitrogen into organic form usable by the plant.
• Glomus (fungus) – forms mycorrhiza with roots; absorbs phosphorus from the soil and passes it to the plant (also gives resistance to root pathogens, drought tolerance).
• Cyanobacteria such as Anabaena, Nostoc, Oscillatoria (Monera) – fix atmospheric nitrogen and add organic matter, increasing soil fertility (e.g. paddy fields).