10 min readPathway sheet1-mark MCQ on coconut endosperm or the scutellum, a 3-mark answer on endosperm development, and dicot vs grass embryo as a 3 or 5-mark question with diagrams; also a NEET favourite

Post-fertilisation: development of endosperm and embryo

The PEN divides first to form the endosperm that feeds the embryo. The zygote passes through proembryo, globular and heart-shaped stages to a mature embryo.

Free-nuclear endospermThe PEN divides many times without cell walls, giving free nuclei; walls form later and the endosperm becomes cellular

CoconutTender coconut water is free-nuclear endosperm; the white kernel is cellular endosperm

Dicot embryoEmbryonal axis + two cotyledons; epicotyl ends in the plumule, hypocotyl ends in the radicle with a root cap

Grass (monocot) embryoOne cotyledon, the scutellum; coleoptile covers the shoot apex, coleorrhiza covers the radicle

Development of endosperm

1
Endosperm development comes before embryo development. This assures food for the young embryo.
2
The primary endosperm cell divides again and again to form triploid endosperm tissue, filled with reserve food.
3
In the most common type, the PEN divides many times without cell walls. The result is free-nuclear endosperm.
4
Cell walls then form and the endosperm becomes cellular. The number of free nuclei before this varies a lot.
5★
In a tender coconut, the water is free-nuclear endosperm with thousands of nuclei; the white kernel around it is cellular endosperm.

★ key step

Endosperm: used up or kept?

Used up before the seed maturesThe growing embryo consumes all of it, as in pea, groundnut and beans. Food is then stored in the cotyledons.

Persists in the mature seedPart of it stays and is used up during germination, as in castor and coconut.

Draw it: stages of embryo development

The early stages are similar in monocots and dicots.

Dicot embryo vs grass (monocot) embryo

Feature	Dicot embryo	Grass (monocot) embryo
Cotyledons	Two	One, called the scutellum, on one side of the embryonal axis
Part above the cotyledon	Epicotyl, ending in the plumule (stem tip)	Epicotyl, with the shoot apex and a few leaf primordia, covered by a hollow sheath, the coleoptile
Part below the cotyledon	Hypocotyl, ending in the radicle (root tip) covered by a root cap	Radicle and root cap, covered by a sheath, the coleorrhiza
Examples	Pea, bean, groundnut	Wheat, maize, rice

How to draw dicot and grass embryos

Dicot: draw a vertical embryonal axis with two large cotyledons attached near its upper end, one on each side, with the plumule between them.
Label the top of the axis plumule and the part just above the cotyledons epicotyl. Label the part below them hypocotyl, and the bottom radicle with a root cap.
Grass: draw a long axis with a shield-shaped scutellum on one side. Label the axis above the scutellum epicotyl.
Draw a sheath over the top around the shoot apex; label it coleoptile. Draw a sheath over the bottom around the radicle and root cap; label it coleorrhiza.
Titles: (a) A typical dicot embryo; (b) L.S. of an embryo of grass.

In real life

Tender coconut water (elaneer, nariyal pani) sold on Indian streets is liquid free-nuclear endosperm, and its soft white malai is cellular endosperm. In groundnut and peas you eat food-filled cotyledons instead.

Exam angle

2 marks: “The water of a tender coconut and its white kernel are both endosperm. How do they differ?” Coconut water is free-nuclear endosperm (thousands of free nuclei without walls); the kernel is cellular endosperm, formed after walls are laid down.

3 marks: “Give three differences between the embryo of a dicot and the embryo of a grass.” Dicot: two cotyledons; plumule not sheathed; radicle not sheathed. Grass: one cotyledon (scutellum) on one side; shoot apex in a coleoptile; radicle and root cap in a coleorrhiza.

1 marks: “Why does endosperm development come before embryo development?” It assures a supply of food for the developing embryo.

Remember it

Embryo stages: Please Give Her Mangoes: Proembryo, Globular, Heart-shaped, Mature.