NDA (II) 2023 General Ability Test · Question 95 of 146

Correct — A, Egg → zygote → embryo → seed. The chain runs in the only order the biology allows. The egg cell waits inside the embryo sac of the ovule; a male gamete delivered by the pollen tube fuses with it, and that fusion produces the zygote. The zygote then divides repeatedly and differentiates into the embryo, with its radicle, plumule and cotyledons. Meanwhile the ovule that houses all of this matures into the seed, so the seed is the finished package that carries the embryo away from the parent. Each item in the sequence is therefore the direct product of the one before it.

• (b)Embryo → egg → zygote → seed — It puts the embryo first, before the egg has even been fertilised. The embryo is a late product of the process, not its starting point, so this reverses the beginning of the sequence.
• (c)Egg → embryo → zygote → seed — It swaps the zygote and the embryo. Fertilisation of the egg gives the single-celled zygote first, and the embryo is what that zygote grows into, so the embryo can never precede the zygote.
• (d)Egg → seed → zygote → embryo — It places the seed second, before fertilisation has happened at all. The seed is the ripened ovule and forms only after the zygote and the embryo have developed inside it, so it belongs at the end of the chain.

Sexual reproduction in a flowering plant begins with pollination and ends with a seed. Pollen lands on the stigma, germinates, and sends a pollen tube down the style into the ovule, where it releases two male gametes. One fuses with the egg to give the zygote and one fuses with the polar nuclei to give the endosperm, which is why the process is called double fertilisation. The zygote becomes the embryo, the ovule becomes the seed, and the ovary around it becomes the fruit.

Sequence questions of this kind are marked wrong far more often than they are misunderstood — the biology is familiar, but three of the four options are simply the same four words shuffled. The reliable method is to fix one relationship you are certain about and use it to strike out options. Here the safest is that the zygote must come before the embryo, since the embryo is what the zygote develops into; that alone removes option (c). Then note that the seed is the last stage, being the matured ovule with the embryo already inside, which removes option (d). Option (b) fails on the plain fact that the embryo cannot precede the egg. Only option (a) survives.

• Fertilisation of the egg by a male gamete produces the zygote, which then develops into the embryo.
• The ovule matures into the seed and the ovary matures into the fruit.
• Angiosperms show double fertilisation — one male gamete fuses with the egg and the other with the polar nuclei to form the endosperm.
• The pollen tube carries the male gametes from the stigma through the style to the ovule.

• Reading the options too quickly — three of them are the same four terms in a different order.
• Treating the embryo and the zygote as interchangeable; the zygote is one cell and always comes first.
• Thinking the seed forms early, as a container that then fills; it is the matured ovule and comes last.

Asked as a sequence item — arrange four familiar stages of plant reproduction in developmental order.

• practice — not a real PYQ

  In a flowering plant, the zygote is formed by the fusion of a male gamete with the

  • (a)polar nuclei
  • (b)egg cell
  • (c)synergid
  • (d)nucellus

  Answer(b) egg cell — the second male gamete fuses with the polar nuclei instead, giving the endosperm.

• practice — not a real PYQ

  In angiosperms, the seed develops from the

  • (a)ovary
  • (b)ovule
  • (c)stigma
  • (d)receptacle

  Answer(b) ovule — the surrounding ovary matures into the fruit.