Lecture 20 Angiosperm Life Cycle

Question 1

1st stage of angiosperm pollen development

Answer 1

endosporic development 1 round of mitotic division tube cell and generative cell

2-celled endsporic microgametophyte (pollen grain)

no prothalial cell is produced

Question 2

why are angiosperm microgametophytes so reduced?

Answer 2

no prothalial cell is produced sperm nuclei produced directly by generative cell

Question 3

2nd stage of angiosperm pollen development

Answer 3

after pollination, the pollen grain germinates

exosporic growth of pollen tube occurs before reaching the ovule

generative cell–>mitosis–>2 non-motile sperm nuclei

Question 4

monosporic megagametophyte development

Answer 4

megasporophyte undergoes meiosis and cytokinesis–>linear tetrad of 4 megaspores

3 degenerate-> 1 functional megaspore undergoes 3 rounds of free nuclear division

->8-nucleate megagametophyte

all haploid

Question 5

egg apparatus

Answer 5

thin cell walls form around 3 nuclei at the micropylar end of the megagametophyte. it is 3-celled, 1 egg cell and 2 synergids

Question 6

chalazal

Answer 6

the end opposite the micropylar end

Question 7

antipodal cells

Answer 7

cell walls form around 3 nuclei at chalazal end of the megagametophyte this is opposite the egg apparatus

Question 8

polar nuclei

Answer 8

the 2 nuclei not involved in the egg apparatus or the antipodal cells from the 8-nucleate megagametophyte form these.

they migrate to the large central cell

cell walls do not separate the polar nuceli,

8-nucleate megagametophyte has 7 cells, with a bi-nucleate central cell

Question 9

tetrasporic megagametophyte development

Answer 9

meiosis w/o cytokinesis–>4-nucleate cell, non-identical nuclei.

1 megaspore is produced w/ 4 haploid nuclei, products of meiosis

1 haploid nucleus at micropylar end produces egg cell

3 haploid nuclei fuse to form a triploid nucleus at chalazal end

2 rounds of free nuclear division–> 8-nucleate megagametophyte with 4 haploid nuclei and 4 triploid nuclei

Question 10

why is double fertilization in angiosperms more efficient?

Answer 10

1. nutritive tissue for the developing embyonic sporophyte is produced only after fertilization occurs
2. reduced megagametophytes, and additional resources are invested only after successful fertilization.

unfertilized ovules are aborted

Question 11

Angiosperm double fertilization

Answer 11

chemo-attractant is released to guide pollen tube to megagametophyte

pollen tube penetrates ovule through micropyle

pollen tube grows in between cells (Instead of digesting the cells like gymnosperms)

1 of the 2 synergids in the egg apparatus is entered, then the tube nucleus and 2 sperm nuclei are discharged

1 sperm nuclei fuses with egg nucleus–>zygote

1 sperm nuclei fuses with 2 polar nuclei–>primary endosperm nucleus

Question 12

Seed development in angiosperms

what happens to the zygote and primary endosperm

Answer 12

zygote–>mitosis and cytokinesis->multicellular embryonic sporophyte with shoot apical meristem, 1-2 cotyledons, hypocotyl, radicle

primary endosperm nucleus–> mitosis–>endosperm tissue

Question 13

embryo of wheat seed

Answer 13

germ

Question 14

seed coat of wheat seed

Answer 14

bran

Question 15

Endosperm of wheat seed

Answer 15

flour

Question 16

Seed dispersal in angiosperms

Answer 16

fertilized ovule->seed ovary–>fruit

sometimes the fruit is the unit of dispersal, and is not fleshy, like helicopters

Question 17

Seed germination in angiosperms

Answer 17

root grows, anchoring seedling

hypocotyl elongates

raises cotyledons and apical shoot meristem into air

sometimes the cotyledons remain below ground.

Question 18

monosporic/tetrasporic megagametophyte development

Answer 18

monosproic: meiosis AND cytokinesis produce 4 nuclei,

3 degenerate, leaving 1 functional megaspore

only haploid nuclei

then undergoes 3 rounds of nuclear division

tetrasporic:

meiosis WITHOUT cytokinesis,

not genetically identical

NO DEGENERATION

there are triploid nuclei formed at chalazal end through karygamy

finally, 2 rounds of free nuclear division