(i) The tuber has nodes and internodes.
(ii) Leafy shoots appear from the nodes.

Convergent evolution:
It is the evolutionary process in which anatomically different organs in different groups of organisms, evolve towards the same function.
Analogous organs are the result of convergent evolution, e.g. Sweet potato (root modification) and potato (stem modification) are analogous, as they both are tuberous with stored food materials. 
Divergent evolution:
It is the evolutionary process in which the same structure develops in different directions in different groups of organisms as adaptations to different needs.
Homologous organs are the result of divergent evolution, e.g. human hands are homologous to the wings of a bird, as their basic structure (number and types of bones) is similar. 

The male accessory ducts are rete testis, vasa efferentia, epididymis and vas deferens.These ducts store and transport the sperms from the testes to the outside through the urethra. The male accessory glands are paired seminal vesicles, prostate gland and paired Bulbourethral glands. The secretion of these glands forms seminal plasma, which is rich in fructose, calcium and certain enzymes. The secretion of Bulbourethral glands lubricates the glans penis.

(i) Emasculation refers to the practice of removal of anthers/stamens from a bisexual flower before the pollen grains mature.
(ii) It is necessary to prevent the self-pollen from contaminating the stigma.
(iii) Bagging refers to the covering of the emasculated flowers with a suitable bag made of butter paper; it is essential to prevent contamination of the stigma of the emasculated flower with unwanted pollen grains.
(iv) When the stigma becomes receptive, the pollen grains from the selected flowers are dusted on it and the flower is rebagged for the development of fruits and seeds.
(v) If female parent bears unisexual flowers, there is no need for emasculation.
(vi) The female flower buds are bagged before they open.
(vi) When the stigma becomes receptive, pollination is carried out with the desired pollen the flowers are rebagged.

(a) (i) In the mature embryo sac of an angiosperm, two polar nuclei in the central cell fuse to form a diploid secondary nucleus.
(ii) During fertilisation, one of the male gametes fuses with the secondary nucleus to form a triploid primary endosperm nucleus (PEN); the central cell is now called primary endosperm cell (PEC).
(iii) Since, three nuclei triple fusion.
(b)(i) The primary endosperm nucleus of the primary endosperm cell undergoes repeated mitotic divisions, to give rise to a number of free nuclei; at this stage, the endosperm is called free nuclear endosperm.
(ii) Subsequently, cell wall formation starts from the periphery and the endosperm becomes cellular.
(iii) The water in the tender coconut represents the nuclear endosperm, while the white kernel represents the cellular endosperm.

(a) Allele frequencies in a population are stable and constant / gene pool total genes and their allels in a population remain constant from generation to generation and maintain genetic equilibrium.
(b) Factors affecting genetic equilibrium are -
(i) Gene migration / gene flow
(ii) Genetic drift
(iii) Mutation.
(iv) Genetic recombination
(v) Natural selection
(c) Change in allele frequency New genes develop, old genes are lost Migration Drift New species When section of population gets separated due to migration or genetic drift, gene frequencies changed; sometimes this change in allele frequency is different in the new population so that they becomes new species, this is called founder effect.

Where corrective treatments are not available, there are special techniques called Assisted Reproductive Technologies (ART) to help the couple produce children; they are as follows:
1. Test Tube Baby programmes
1. In this method, ovum from the wife or a donor female and the sperms from the husband or a donor are allowed to fuse under simulated conditions (as that of the body) in the laboratory; it is called in vitro fertilisation (IVF).
2. The zygote or early embryo is transferred into the uterus or fallopian tube for further development; this process is called Embryo Transfer (ET) and can be done in the following ways:
(i) The zygote or embryo up to eight blastomeres is transferred into the fallopian tube; it is called Zygote Intra-Fallopian Transfer (ZIFT).
(ii) Embryos with more than eight blastomeres are transferred into the uterus.It is called Intra Uterine Transfer (IUT).
2. Gamete Intra-Fallopian Transfer (GIFT).
This method involves the transfer of an ovum collected from a donor female into another female, who cannot produce ova but can provide suitable conditions for fertilisation and further development of the foetus up to parturition.
3. Intra Cytoplasmic Sperm Injection (ICSI).
In this method, the sperm is directly injected into the ovum to form an embryo in the laboratory and then embryo transfer is carried out.
4. Artificial Insemination
(i) In this method, the semen collected from the husband or a healthy donor is artificially introduced into the vagina or into the uterus (intra uterine insemination).
(ii) This method is used in cases where infertility is due to the inability of the male partner to seminate the female or due to very low sperm counts in the ejaculates.

(a) Hypocotyl and epicotyl. Hypocotyl is part of stem below cotyledons in the embryo of a plant and epicotyl is part of stem above cotyledons.
(b) Coleoptile and coleorhiza. Coleoptile is the sheath around the plumule. Coleorphiza is a sheath enveloping the radicle and root cap in certain plants.
(c) Integument and testa. Any protective covering around ovule is integument and testa is outer integument of seed coat.
(d) Perispern and pericarp. Pericarp is wall of ripened  ovary of fruit and perisperm  is remnant of nucellus in a seed.

Meiosis occurs during sporogenesis.
The structure formed at the end are microspores and megaspores respectively.