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Sexual Reproduction in Flowering Plants — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYSexual Reproduction in Flowering Plants4 Marks
Question
Read the following and answer any four questions from (i) to (v) given below:

Embryo develops at the micropylar end of the embryo sac, where the zygote is situated. Most zygotes divided only after certain amount of endosperm is formed. The early stages of embryo development are similar in both monocotyledons and dicotyledons. The zygote gives rise to the proembryo and subsequently to the globular heart-shaped and mature embryo. A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. Embryo of monocotyledons possess only one cotyledon.

  1. True embryo develops as a result of fusion of:
  1. Two polar nuclei of embryo sac.
  2. An egg cell and a male gamete.
  3. Synergid and male gamete.
  4. A male gamete and antipodals.
  1. Refer to the given diagram of the embryo of an angiospermous plant with parts labelled P, Q and R. Select the correct statement(s) regarding this.

  1. Part 'P' supplies nutrition to the developing embryo.
  2. Part 'Q' is the protective sheath of radicle and root cap.
  3. Part 'R' is the protective sheath of shoot apex and leaf primordia.
  4. The embryo shown in the diagram is present in members of Family Poaceae.
  1. (IV) only.
  2. (II) and (III) only.
  3. (I) and (IV) only.
  4. (I), (II), (III) and (IV).
  1. Which of the given statements are true?
  1. During the development of a dicot embryo, heart-shaped embryo is followed by globular embryo.
  2. The part of embryonal axis above the level of cotyledons is epicotyl, while the part below the level of cotyledons is hypocotyl.
  3. Monocot seeds possess a single cotyledon, represented by scutellum.
  1. (I) and (II).
  2. (II) and (III).
  3. (I) and (III).
  4. (I), (II) and (III).
  1. Consider the following parts of an embryonal axis of a dicot seed.
  1. Hypocotyl.
  2. Epicotyl.
  3. Radicle.
  4. Plumule.

In which of the following the above parts are correctly arranged from top to base?

  1. (III) → (I) → (II) → (IV).
  2. (II) → (I) → (III) → (IV).
  3. (IV) → (II) → (I) → (III).
  4. (III) → (IV) → (II) → (I).
  1. In grass family, the cotyledon, is called:
  1. Epiblast.
  2. Plumule.
  3. Scutellum.
  4. Perisperm.
✓

Answer

  1. (b) An egg cell and a male gamete.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

In double fertilisation, out of the two male gametes, one fuses with egg or oosphere to perform generative fertilisation. Generative fertilisation is also called syngamy or true fertilisation. It gives rise to a diploid zygote or oospore.

  1. (c) (I) and (IV) only.
  2. (b) (II) and (III).

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

During the development of dicot embryo, initially the dicot embryo is globular and undifferentiated. Early embryo with radial symmetry is called proembryo. It is transformed into embryo with the development of radicle, plumule and cotyledons. Two cotyledons differentiate from the sides with a faint plumule in the center. At this time the embryo becomes heart-shaped.

  1. (c) (IV) → (II) → (I) → (III).
  2. (c) Scutellum.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

In the grass family, the cotyledon is called scutellum that is situated towards one side (lateral) of the embryonal axis.

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