Biology (Theory)

Emasculation means removing the anthers from a bisexual flower before they shed pollen, so that self-pollination cannot happen.
Papaya is dioecious – male and female flowers are on separate plants – so its female flowers have no anthers to remove. Only bagging of the female flower is needed.
Rice, wheat and pea have bisexual flowers, so emasculation is required in them.

The immune system consists of lymphoid organs (bone marrow, thymus, spleen, lymph nodes etc.), lymphocytes and other leucocytes, and soluble molecules such as antibodies and complement (plasma proteins).
Red blood cells carry oxygen; they have no role in recognising or fighting pathogens, so they are not a component of the immune system.

(i) True – after ovulation the ruptured follicle becomes the corpus luteum, which secretes large amounts of progesterone.
(ii) False – both LH and FSH peak around mid-cycle (LH much more sharply).
(iii) True – the mid-cycle LH surge induces rupture of the Graafian follicle, i.e. ovulation.
(iv) False – the follicular phase is the proliferative phase; the luteal phase is the secretory phase.

India has more than 50,000 genetically different strains of rice (and about 1000 varieties of mango), so 'fewer than 1000' is wrong.
The other pairs are correct: there are 12 mega-diversity countries; Robert May estimated about 7 million species globally; zoos protect animals outside their natural habitat, i.e. ex situ.

Pomato is a somatic hybrid: protoplasts (cells with the cell wall removed) of tomato and potato were fused and the hybrid cell was grown into a plant. It did not combine the useful features of both parents for commercial use.

Vertical distribution of different species occupying different levels (e.g. trees on top, shrubs, then herbs and grasses at the bottom of a forest) is called stratification. It is a structural feature of an ecosystem.

Sacred groves in India: Khasi and Jaintia hills – Meghalaya; Aravalli hills – Rajasthan; Western Ghats – Karnataka and Maharashtra; Sarguja, Chanda and Bastar – Madhya Pradesh / Chhattisgarh region.
So the Meghalaya grove is in the Jaintia hills.

The orientation of one homologous pair at the metaphase I plate does not depend on the orientation of the other pair. So alleles of genes on different chromosomes separate independently, giving four kinds of gametes (AB, ab, Ab, aB) in equal proportion. This is Mendel's law of independent assortment explained at chromosome level.
Linkage would keep A with B together, which is not shown here.

a. Biolistic (gene) gun – shoots DNA-coated gold/tungsten particles into plant cells → v.
b. Chitinase – enzyme used to break the chitin cell wall of fungal cells → iv.
c. Ti plasmid – the tumour-inducing plasmid of Agrobacterium tumefaciens → ii.
d. Ca²⁺ ions – used to make bacterial cells competent to take up DNA → i.

Lamarck said that organs which are used more get stronger and those not used degenerate, and that such acquired characters are passed on (e.g. the long neck of giraffes). Darwin proposed natural selection, Malthus wrote on population, and de Vries proposed mutation theory.

Plasmids are autonomously replicating, circular, extra-chromosomal DNA. They have their own origin of replication (ori), so their replication is independent of the chromosomal DNA. Hence (B) is the wrong statement. They often carry antibiotic-resistance genes, which is why they are useful as cloning vectors.

Each ovary is held in place by ligaments that connect it to the pelvic wall and to the uterus. Tendons join muscle to bone, so they are not the answer.

Industrial melanism: pollution killed lichens and darkened tree trunks with soot. Dark moths resting on dark trunks were hidden from predatory birds, while white moths were easily seen and eaten. So natural selection increased the dark moth population. R directly explains A.

Rosie (1997) produced milk containing human alpha-lactalbumin (2.4 g per litre), which made it more balanced for human babies – so A is true.
R names the wrong protein ('alpha-lactaglobulin'); the protein is alpha-lactalbumin, so R is false.

In the aeration tank of secondary (biological) treatment, aerobic bacteria associated with fungal filaments form mesh-like flocs – A is true.
These microbes consume organic matter aerobically (that is why air is pumped in and BOD falls). Anaerobic digestion happens later in the sludge digester by other bacteria. So R is false.

In terrestrial ecosystems most energy flows through the detritus food chain, not the grazing food chain (the grazing chain carries the major share only in aquatic ecosystems). So A is false.
R is true: some organisms of the detritus chain are eaten by animals of the grazing chain, so the two chains are connected at some levels.

(a) Humoral immune response is the antibody-mediated response: B-lymphocytes produce large numbers of antibodies (proteins) that are released into the blood (humor) to fight pathogens.
(b) Any two: IgG, IgA, IgM, IgE (also IgD).

(i) Because mature seeds are dehydrated and dormant, the farmer can store them safely for a long time and use them to raise the crop in the next season (or sell them / use them as food).
(ii) Pea is a non-endospermic (non-albuminous) seed – the endosperm is used up completely during embryo development and food is stored in the cotyledons. Castor is an endospermic (albuminous) seed – part of the endosperm remains in the mature seed.

The primary oocyte inside the tertiary follicle (in the ovary) grows and completes meiosis I.
The division is unequal and gives a large haploid secondary oocyte and a tiny first polar body.
Tip: do not say 'ovum' – meiosis II is completed only after the sperm enters.

(a) The sequence reads the same on both strands when read in the same direction (5'→3'), so it is a palindromic sequence. It is recognised by a restriction endonuclease – here EcoRI.
(b) The enzyme binds to the recognition site and cuts each strand of the sugar-phosphate backbone a little away from the centre of the palindrome, between the same two bases on both strands (for EcoRI, between G and A). This leaves single-stranded overhangs called sticky ends, which can join with complementary ends cut by the same enzyme.

The sex that makes two kinds of gametes is the heterogametic sex.
Case I: XO males produce sperms with X and without X, so it is male heterogamety – e.g. grasshopper (many insects).
Case II: ZW females produce eggs with Z or W, so it is female heterogamety – e.g. birds (hen).

(i) A DNA nucleotide has deoxyribose sugar (and one of A, G, C, T), while an RNA nucleotide has ribose sugar (and one of A, G, C, U).
(ii) The nitrogenous base is joined to the 1' C of the pentose by an N-glycosidic linkage; the phosphate is joined to the 5' C of the sugar by a phosphoester linkage.

(i) Standing crop = biomass, and the consumer bar is larger than the producer bar, so it is an inverted pyramid of biomass. It occurs in the sea: phytoplankton have a small standing crop at any time but reproduce very fast, so they support a larger standing crop of zooplankton or fish.
(ii) Any two:
• It does not account for one species belonging to two or more trophic levels.
• It assumes a simple food chain and cannot show a food web.
• Saprophytes/decomposers are given no place though they are vital.

(i) Any two effects of biodiversity loss in a region:
• Decline in plant production.
• Lowered resistance to environmental disturbances such as drought.
• Increased variability in ecosystem processes like water use and pest/disease cycles.
(ii) Any two of the 'Evil Quartet': habitat loss and fragmentation; over-exploitation; invasion of alien species; co-extinctions.

(a) No. Viability depends on the species and on temperature and humidity.
• In rice and wheat, pollen grains lose viability within about 30 minutes of release.
• In some members of Rosaceae, Leguminosae and Solanaceae, pollen remain viable for months.
(b) Pollen grains can be stored for years in liquid nitrogen at −196 °C (cryopreservation) in pollen banks, for later use in crop-breeding programmes.

(a) Pedigree analysis is the study of how a trait is inherited over several generations of a family, using a family tree.
Importance: it helps trace the inheritance of a trait, abnormality or disease; it helps predict the chance of a disorder in future children (genetic counselling).
(b)(i) Two unaffected parents have affected children, so the trait is recessive and the parents are carriers. An affected daughter has an unaffected father – this is impossible for an X-linked recessive trait – so the trait is autosomal recessive.
(ii) Sickle-cell anaemia (also thalassemia or phenylketonuria).

(a) Take a gene with two alleles, A (frequency p) and a (frequency q). Since these are the only alleles, p + q = 1.
In a diploid, random mating combines gametes at random:
• Chance of AA = p × p = p²
• Chance of aa = q × q = q²
• Chance of Aa = pq + qp = 2pq
The genotype frequencies must add to 1, so p² + 2pq + q² = (p + q)² = 1.
(b) Any two: gene migration (gene flow), genetic drift, mutation, genetic recombination, natural selection.

Draw an inverted (anatropous) ovule attached to the placenta by a stalk.
Labels that must be shown (any six):
• Funicle – the stalk joining the ovule to the placenta
• Hilum – junction of ovule and funicle
• Micropyle – small opening at the tip of the integuments
• Outer integument and inner integument
• Nucellus – mass of cells inside the integuments
• Embryo sac (female gametophyte) inside the nucellus, with egg apparatus (egg + 2 synergids) at the micropylar end, 3 antipodals at the chalazal end and 2 polar nuclei in the centre
• Chalaza – basal part opposite the micropyle
Common mistake: drawing the micropyle and the chalaza on the same side.

(a) Opioids come from the poppy plant Papaver somniferum; they are extracted from the latex (milky juice) of the unripe fruit/capsule.
(b) Heroin (smack) is diacetylmorphine – it is obtained by acetylation of morphine.
Morphine is a very effective sedative and painkiller, useful for patients after surgery.
Heroin is a depressant that slows down body functions.

(a) cry IAb – the gene for the Bt toxin that controls corn borer.
(b) The spores (mixed with water) are sprayed on the plants and eaten by the insect larvae. The Bt toxin crystals are an inactive protoxin; in the alkaline pH of the insect gut they dissolve and become active. The active toxin binds to the epithelial cells of the midgut, makes pores, the cells swell and burst, and the larva dies.
(c) The corn of field B is Bt corn: the cry IAb gene from Bacillus thuringiensis was inserted into it, so the plant itself makes the Bt toxin. Any borer feeding on it is killed, so no spraying is needed.

(a) DNA is negatively charged (phosphate groups) and moves towards the anode (+). In the first set-up the wells are already at the anode, so the DNA does not move into the gel. After staining, no separated bands are seen in the gel (DNA remains at the wells).
(b) The positions of the anode and the cathode were interchanged, so the wells are now at the cathode and DNA moves through the gel towards the anode.
Agarose acts as a sieve: smaller fragments move faster and farther. The 100 bp fragment is the smallest, so it travels the farthest – to position X.

(a) Competitive release: a species whose distribution is restricted by a competitively superior species expands its range when the superior competitor is removed. Here Chthamalus spreads once Balanus is removed.
(b) In some shallow South American lakes, visiting flamingos and resident fishes compete for the same food – zooplankton. (Any correct example.)
(c) By resource partitioning – species use the resource differently, e.g. by feeding at different times or using different foraging patterns. Example: MacArthur showed that five closely related warbler species living on the same tree avoid competition and coexist because they forage in different parts of the tree.

(a) Cross I: all 500 progeny are tall, so at least one parent is homozygous tall – TT × tt, TT × Tt or TT × TT.
Cross II: 375 : 125 = 3 : 1 tall : dwarf, which is obtained only from Tt × Tt.
(b) Cross III gives 250 : 250 = 1 : 1. This is a test cross (Tt × tt) – crossing a dominant-phenotype plant with the recessive parent. It is used to find whether a plant showing the dominant trait is homozygous (TT) or heterozygous (Tt).
(c) In both crosses only the tall character appears in heterozygotes and dwarf appears only when homozygous, so tall is dominant over dwarf. This illustrates Mendel's Law of Dominance.

1. Fertilisation: a sperm contacts the zona pellucida of the secondary oocyte; changes in the membrane block entry of other sperms.
2. Entry of the sperm induces completion of meiosis II in the secondary oocyte, giving a haploid ovum (ootid) and a second polar body.
3. The haploid nuclei of the sperm and the ovum fuse to form a diploid zygote.
4. Cleavage: the zygote divides by mitosis as it moves through the isthmus of the oviduct towards the uterus, forming blastomeres.
5. The embryo with 8–16 blastomeres is called a morula.
6. The morula continues to divide and becomes a blastocyst – an outer layer of trophoblast and an inner cell mass (which later forms the embryo).
7. Implantation: in the uterus, the trophoblast attaches to the endometrium; uterine cells divide rapidly and cover the blastocyst, which becomes embedded in the endometrium. This leads to pregnancy.
Site of fertilisation: the ampullary region (ampullary–isthmic junction) of the fallopian tube.

(i) Case I: sperms are normal but cannot reach the ejaculate. Sperms can be collected and used for in vitro fertilisation followed by embryo transfer (ZIFT or IUT); IUI/artificial insemination with the collected sperms is also accepted.
Case II: eggs cannot travel through the blocked tubes, so in vitro fertilisation is done in the lab and the embryo (more than 8 blastomeres) is placed directly in the uterus – IVF followed by IUT (intra-uterine transfer).
Case III: low count and poor motility – ICSI (intra-cytoplasmic sperm injection, a sperm injected directly into the ovum) or artificial insemination/IUI with the husband's concentrated semen.
(ii) Copper-releasing IUDs: CuT, Cu7, Multiload 375 (any two).
Why effective: they increase phagocytosis of sperms inside the uterus; the Cu ions released suppress sperm motility and the fertilising capacity of sperms.

(i) • X-ray diffraction studies of DNA by Maurice Wilkins and Rosalind Franklin.
• Base-pairing rules of Erwin Chargaff: in double-stranded DNA, A/T = 1 and G/C = 1.
(ii) Any three:
• DNA has two polynucleotide chains; the sugar–phosphate backbone is outside and the bases project inside.
• The two chains have antiparallel polarity (5'→3' and 3'→5').
• Bases of the two strands pair by hydrogen bonds: A=T with two H-bonds and G≡C with three H-bonds (purine opposite pyrimidine, so the distance between strands is uniform).
• The two chains are coiled in a right-handed manner; pitch 3.4 nm, about 10 bp per turn, 0.34 nm between adjacent base pairs.
• The plane of one base pair stacks over the next, which adds stability.

(i) Template strand is complementary and antiparallel to the coding strand:
3' – TAC TGG CAT AAA AGA CAT CAC GGG CAT GAA GTC CGT AAT – 5'
mRNA has the same sequence as the coding strand with U in place of T:
5' – AUG ACC GUA UUU UCU GUA GUG CCC GUA CUU CAG GCA UUA – 3'
(ii)(1) Bacteria have no split genes and no splicing, so the mRNA stays the same:
5' – AUG ACC GUA UUU UCU GUA GUG CCC GUA CUU CAG GCA UUA – 3'
(2) In humans the hnRNA is spliced (all three GUA introns removed), capped at the 5' end and tailed at the 3' end:
5' – m⁷Gppp – AUG ACC UUU UCU GUG CCC CUU CAG GCA UUA – poly(A) tail – 3'
(iii) The mature mRNA has 10 codons (no stop codon in the given stretch), so the polypeptide has 10 amino acids.

(i) Plasmodium falciparum (causes malignant malaria).
(ii) The sexual stages are completed in the female Anopheles mosquito:
• the mosquito sucks blood of an infected person and takes up gametocytes;
• gametes form, fertilisation occurs and development takes place in the mosquito's gut (stomach wall);
• sporozoites formed move to the salivary glands, ready to be injected at the next bite.
(iii) Sporozoites reach the liver and multiply asexually there; then they attack red blood cells, multiply inside them and cause the RBCs to rupture. This releases a toxic substance, haemozoin, which causes chills and high fever recurring every 3–4 days.
(iv) Any two: avoid stagnant water around houses; clean coolers regularly; use mosquito nets and wire mesh on doors/windows; introduce larva-eating fish such as Gambusia into ponds; spray insecticides in ditches and drains.

(i) Biofertilisers are living organisms that enrich the nutrient quality of the soil. Main sources: bacteria, fungi and cyanobacteria.
(ii) • Bacteria: Rhizobium lives symbiotically in root nodules of legumes and fixes atmospheric nitrogen into organic forms used by the plant; Azotobacter and Azospirillum fix nitrogen while free-living in the soil.
• Fungi: Glomus forms mycorrhiza with plant roots; the fungus absorbs phosphorus from the soil and passes it to the plant. Such plants also resist root-borne pathogens, tolerate salinity and drought and grow better.
• Cyanobacteria: autotrophic microbes such as Anabaena, Nostoc and Oscillatoria fix atmospheric nitrogen; they are important in paddy fields and also add organic matter.
(iii) Any two: they do not pollute soil or ground water; they conserve beneficial soil microbes and soil health; they do not harm human health; they reduce dependence on costly chemical fertilisers.