lecture 18, Fertilization and seed development

Question 1

Vegetative =

Answer 1

leading to sterile / non-gamete cells

Question 2

Generative =

Answer 2

leading to sperm cells

Question 3

Recap: gymnosperms contain..

Answer 3

• microsporocyte (mother cell)
• tetrad of microspores
• mature pollen grain = 4 cells
  
  • 2x prothallial cell
  • generative cell –> 1 sterile/stalk cell and 1 spermatogenous cell (–> 2 cells)
  • tube cell

Question 4

the difference between an angiosperm and a gymnosperm?

Answer 4

the mature pollen grain contains 3 cells (not 4)
- generative cell –> 2 sperm cells
- tube cell

Question 5

when does pollen grain germination occur?

Answer 5

once the pollen is accepted by the host (female stigma)

Question 6

what does the tube cell develop into?

Answer 6

pollen tube, which will deliver non-motile sperm cells

Question 7

what does the generative cell divide into?

Answer 7

2 sperm cells - only occurs once pollen tube has reached micropyle

Question 8

the ovule structure is made up of

Answer 8

integument
nucellus
female gametophyte

Question 9

unlike a gymnosperm, an angiosperm contains:

Answer 9

• 2-3 integuments (not 1)
• pollen tube enters micropyle

Question 10

definition of coenocytic:

Answer 10

multiple nuclear divisions but no cytokinesis; multinucleate

Question 11

steps of gymnosperm fertilization:

Answer 11

1. 4 megaspores, 1 survives
2. pollination (egg cells have not formed yet)
3. megaspore develops into multicellular megagametophyte
4. archegonia divides into 2 egg cells
5. pollen grain germinates, pollen tube enters micropyle
6. sperm nucleus released
7. one egg cell is fertilized by sperm

Question 12

how many times does a female gametophyte undergo mitosis in angiosperms?

Answer 12

3 times

Question 13

what do 3 rounds of mitosis within a female angiosperm gametophyte produce?

Answer 13

8 nuclei, 7 cells

Question 14

what does double fertilization in angiosperms produce?

Answer 14

A 3N endosperm:
sperm #1 + egg cell
sperm #2 + 2 polar nuclei

Question 15

where is the endosperm from in gymnosperms?

Answer 15

the female megagametophyte (n)

Question 16

5 main components of a seed?

Answer 16

1. seed coat
2. endosperm
3. cotyledons
4. hypocotyl
5. radicle

Question 17

what are the 5 steps in seed development

Answer 17

1. embryogenesis
2. maturation
3. dessication
4. dormancy
5. germination

Question 18

what are the 4 major stages in embryogenesis

Answer 18

1. globular
2. heart
3. torpedo
4. mature

Question 19

what occurs during maturation in seed development?

Answer 19

during the torpedo stage seeds are a carbon sink- endosperm develops and the nutritive tissues are expanded

Question 20

what happens when the embryo reaches full maturity?

Answer 20

it presses against the seed coat ; the endosperm has been consumed from within

Question 21

what occurs during dessication in seed development

Answer 21

loss of water in the seed, metabolic activity is slowed down, shrinkage of size, enters dormancy

Question 22

what are the three steps in seed germination?

Answer 22

1. imbibition
   -rupture of seed coat
2. respiration
   -conversion of sugars in endosperm
3. growth of embryo
   -development of embryonic axis and shoots