1. NOTES: CH 38 – Plant Reproduction

2. *Modifications in reproduction were key adaptations enabling plants to spread into a variety of terrestrial habitats.

3. **Our focus in this chapter:
* Water has been replaced by wind and animals as a means for spreading gametes.
* Embryos are protected in SEEDS.
Vegetative (asexual) reproduction is used for propagation of some plants
in a variety of environments.
**Our focus in this chapter:
SEXUAL REPRODUCTION!

4.  GAMETOPHYTE: reproductive structure of plants
-where haploid GAMETES (n) are produced (sperm and egg cells)
-gametes fuse to form a ZYGOTE (2n) that develops into a multicellular plant

5. …ALTERNATION OF GENERATIONS!

6. FLOWERS: -the reproductive structure of angiosperms
-four sets of modified leaves:
1) Sepals
2) Petals
3) Stamens:
-anther, filament
4) Carpel (a.k.a. pistil):
-stigma, style, ovary

8. FLOWERS:
 STAMENS and CARPELS (PISTILS) are the reproductive parts of the flower.

9. FLOWERS:
 Female gametes develop in EMBRYO SACS, which contain the EGG CELLS
 this occurs at the base of the carpel /pistil, inside the OVARY

10.  Male gametes develop in the stamen inside POLLEN GRAINS
 this occurs at the stamen tips within chambers of the ANTHERS

11. FLOWER VARIATIONS:
 Complete flower = flower with sepals, petals, stamens, carpels
 Incomplete flower = flower missing one or more of these parts
(e.g. most grasses do not have petals on their flowers)

12. FLOWER VARIATIONS:
 Perfect flower = flower having both stamens and carpels (a.k.a. bisexual)
 Imperfect flower = flower that is either STAMINATE (male) or CARPELLATE (female) – a unisex flower. (a.k.a. unisexual)

13.  Monoecious = “one house”; plants with either perfect flowers or with both staminate (male) and carpellate (female) flowers on the same plant
(ex: star lily, rose, dandelion)
Dioecious = “two houses”;
plants having staminate and
carpellate flowers on separate
plants (ex: willow, juniper)

14. Development of the Male Gametophyte (POLLEN):
POLLEN GRAIN = the immature male gametophyte; develops within the anthers of stamens in an angiosperm
 extremely durable;
tough coat to
prevent
biodegradation

15.  At the time of pollination:
A pollen gain consists of 2 cells (both haploid):
-GENERATIVE CELL: divides to form 2 sperm cells
-TUBE CELL: produces the pollen tube; contains the generative cell

17. Development of the Female Gametophyte (EMBRYO SAC)
● Female gametes are contained in the EMBRYO SAC

18. Embryo Sac:
egg cell (OVUM) at one end
ovum flanked by 2 syngerids (help to attract sperm cells)
 two nuclei in center (“polar nuclei”)

20. POLLINATION:
-occurs when wind- or animal-born pollen released from the anthers lands on the STIGMA at the tip of the carpel

23. POLLINATION
POLLINATION = the placement of pollen onto the stigma of a carpel
Methods of Pollination / spread of pollen:
• wind
• animals / insects
• self-pollinate
(most plants
cross-pollinate)

26. To prevent self-pollination (and thus ensuring sperm and egg from different plants meet), some plants:
-have stamens and carpels that mature at different times;
-have structural arrangement of flower parts that reduces the chance of pollen getting transferred from stamen to carpel;
-are SELF-INCOMPATIBLE (a biochemical block that prevents the pollen grain from developing and fertilizing the egg)

27.  SELF-INCOMPATIBILITY: the rejection of pollen from the same, or closely related, plant by the stigma

28. after POLLINATION… -pollination is followed by this sequence:
1) a pollen tube grows from the pollen grain, down the carpel, into the embryo sac;
2) sperm are discharged from the pollen grain resulting in fertilization of the egg;
3) the zygote develops into an embryo;
4) as the embryo grows, the ovule surrounding it develops into a SEED;
5) while seed formation is taking place, the entire ovary is developing into a FRUIT, which will contain one or more seeds.

30. DOUBLE FERTILIZATION:
 When a compatible pollen grain lands on a stigma of an angiosperm, double fertilization occurs.
DOUBLE FERTILIZATION = the union of two sperm cells with two cells of the embryo sac

31. DOUBLE FERTILIZATION:
Steps:
1) pollen grain adheres to stigma, germinates, and extends a pollen tube toward the ovary;
2) generative cell divides (mitosis) to form 2 sperm;
3) directed by a chemical attractant, pollen tube enters and discharges its 2 sperm nuclei into the embryo sac;
4) 1 sperm unites with the egg  ZYGOTE;
5) other sperm combines with the 2 polar nuclei to form a 3n (triploid) nucleus in the large central cell of the embryo sac.

34. this central cell will give rise to the ENDOSPERM (a food storing tissue for the seed/embryo)
**after double fertilization, each ovule develops into a seed and the ovary into a fruit surrounding the seed(s).

35. ENDOSPERM:
• rich in nutrients (which it provides to the developing embryo)

36. Structure of the mature seed:
in mature seeds, the embryo is quiescent (dormant) until germination
• the seed dehydrates until its water content is only 5-15% by weight.
• the embryo is surrounded by endosperm, enlarged cotyledons, or both.
• the seed coat is formed from the outer layers / integuments of the ovule.

37. Dicot seed structures:
-cotyledons = embryonic leaves
-hypocotyl = embryonic axis below cotyledons
-radicle = embryonic root
-epicotyl = embryonic axis above cotyledons

39. *Seeds are dispersed from the source plant when fruits are moved about by the wind or animals.
*Seeds deposited in soil of the proper conditions (moisture, nutrients), will GERMINATE.

43. FRUITS:
-ovary develops into fruit (adapted for seed dispersal)

45. *Fruits ripen about the time seeds are becoming fully developed
Ripening fruits are characterized by:
1) fruit becomes softer as a result of enzymes digesting the cell wall components;
2) colors usually change and fruit becomes sweeter as organic acids or starch are converted to sugar;
3) these changes produce an edible fruit which entices animals to
feed, thus dispersing the seeds!