Question

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Embryogenesis and plant life cycle

Plant life cycle shows both similarities and also major differences from animal life cycle. In both cases ……….. (haploid/diploid) (1N/2N) organism goes through to ……….. (mitosis/ meiosis) to produce gametes, but plant life cycle has an extra step in which it produces a ……….. (diploid/haploid) plant before it produces gametes. Thus, plant life cycle ………… between diploid and haploid plants. Plant life cycle consists of three distinct phases, embryogenesis, vegetative phase and reproductive phase. During ………….. (vegetative phase/embryogenesis), the fertilized egg (or …….. (embryo/zygote)) cell develops into a multicellular embryo with limited number of tissues. In vegetative phase mature ……….. (egg/embryo) germinates and developed into a mature plant and then enters into the reproductive phase in which plant produces flowers and haploid spores, which give rise to ………… (sporophyte ans spores/gametophytes and gametes).

The female reproductive structure of a plant is known as ……….. (stamen/pistil), which is made up of three parts, stigma, style and the ovary. Inside the ovary, small structure called ………. (seed/ovule) (that will become the future ……… (fruit/seed)). All the cells in the ovule as well as pistil are ……. (diploid/haploid) cells. One cell inside the …….. (seed/ovule) will become ……………… (microspore/megaspore) mother cell, which will undergo ………… (mitosis/meiosis) to produce 4 ………….. (microspores/megaspores), which are haploid. Similar to animal system, ….. (2/3) of these haploid cells will disintegrate leaving one haploid …………. (microspore/megaspore) (In animal system, this would become the ……. (sperm/egg)). The haploid nucleus of the ………. (microspore/megaspore) will divide through ………… (meiosis/mitosis) to produce …… (7/8) haploid nuclei from which the egg cell, two synergids, 3 antipodal cells and a central cell with … (2/3) haploid nuclei are formed. This structure with haploid cells is called …….. (seed/embryo sac) (or female gametophyte). Thus, unlike in evolutionary lower plants (e.g. moss), gametophyte in angiosperms is reduced to a small tissue (consists of …. (8/7) cells) that depends on the sporophyte for nutrients. The male reproductive organ of the sporophyte is called the ……… (stamen/anther), which consists of filament and the …… (stigma/anther). Anther has 4 pollen sacs in which diploid microspore mother cells divide by ……….. (mitosis/meiosis) to produce ….. (2/4) ……… (diploid/ haploid) microspores (similar to animal sperm formation). However, in angiosperms (flowering plants), nucleus of each microspore cell divides to produce …… (2/4) haploid nuclei, named generative nucleus and the tube nucleus. Generative nucleus produce it’s own cell membrane to produce a cell. This two cell structure is called the pollen (which consists of two haploid cells). It is actually the male …………… (sporophyte/gametophyte). Similar to female gametophyte, angiosperm male gametophyte is also reduced to a tissue (but with only …… (seven/two) cells).

After pollination (deposition of pollen on the stigma), pollen (male gametophyte) will germinate to produce a long pollen tube, which will enter the female gametophyte through the micropyle (small opening) in the ovule. During this process, haploid ……… (tube/generative) nucleus will divide ……… (meiotically/mitotically) to produce two sperm nuclei, one of which will fertilize the egg cell (to produce 2N zygote) and the other will fertilize the central cell with two haploid nuclei to produce 3N nucleus. While 2N zygote will mitotically divide to produce …….. (endosperm/embryo), 3N nucleus divides mitotically to produce large number of 3N cells that cover the entire embryo sac area, which is now called …………. (endosperm/gametophyte). Endosperm cells accumulate starch in the growing seed, which is necessary as the initial food source for the germinating seed.

The 2N zygote first divides acentrically to produce upper apical daughter cell (which will eventually divide by ……. … (meiosis/mitosis) to produce entire embryo (except the root), and lower basal daughter cell, which will divide mitotically to produce lower suspensor cells and the uppermost “hypophysis” cell. Hypophysis will then divide to produce the ……. (shoot/root) of the embryo. Unlike in animal embryo, which will have all the organs at the time of birth, plant embryo only has minimum tissues such as SAM, RAM , hypocotyl, and cotyledons etc. Most of the plant’s organs (e.g. leaves, stem, roots) are developed after the germination of embryo. Thus plant development is considered as post- embryonic.

Answer 1

Embryogenesis and plant life cycle

Plant life cycle shows both similarities and also major differences from animal life cycle. In both cases diploid 2N (haploid/diploid) (1N/2N) organism goes through to meiosis (mitosis/ meiosis) to produce gametes, but plant life cycle has an extra step in which it produces a haploid (diploid/haploid) plant before it produces gametes. Thus, plant life cycle cross  between diploid and haploid plants. Plant life cycle consists of three distinct phases, embryogenesis, vegetative phase and reproductive phase. During embryogenesis (vegetative phase/embryogenesis), the fertilized egg (or zygote(embryo/zygote)) cell develops into a multicellular embryo with limited number of tissues. In vegetative phase mature embryo (egg/embryo) germinates and developed into a mature plant and then enters into the reproductive phase in which plant produces flowers and haploid spores, which give rise to gametophytes and gametes (sporophyte ans spores/gametophytes and gametes).

The female reproductive structure of a plant is known as pistil. (stamen/pistil), which is made up of three parts, stigma, style and the ovary. Inside the ovary, small structure called …ovule……. (seed/ovule) (that will become the future …seed…… (fruit/seed)).

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