Chapter 38 ~Plant Reproduction and Development

I. Sexual Reproduction n A. Alternation of generations: haploid (n) and diploid (2n) generations take turns producing each other u 1. Sporophyte (2n): F a. produces haploid spores by meiosis; these spores divide by mitosis giving rise to male and female haploid plants called…. F b. Gametophytes (n): develop and produce gametes

Have you labeled a flower lately?

B. Floral variations n 1. Floral organs: sepals, petals, stamens (male ), carpels (female) u a. complete: all 4 floral organs u b. incomplete: lacking 1 or more floral organs u c. perfect: both stamens and carpels on 1 flower

u d.imperfect: lacking either a stamen or carpel u e. monoecious: staminate and carpellate flowers on 1 plant) u f. dioecious: staminate and carpellate flowers on separate plants

C. Gametophyte development u 1. Male gametophyte: microsporocyte (in pollen sacs of anther) divides by meiosis into 4 haploid microspores; F a. mitosis produces a generative cell (sperm) and a tube cell (pollen tube)= a pollen grain u 2. Female gametophyte : megasporocyte (in ovule) divides by meiosis to 4 cells, only 1 survives to a haploid megaspore; F a. 3 mitotic divisions forms the embryo sac; F b. includes: 1 egg cell (female gamete) and 2 polar nuclei (synergids)

D. Pollination – pollen grain lands on stigma n 1. pollen lands on stigma – pollen has 2 sperm cells & a vegetative nucleus n 2. veg. nucleus grows a tube down the style to the ovary n 3. ovule contains 1 egg & 7 accessory cells inside the embryo sac n 4. pollen tube enters embryo sac via micropyle (small opening)

Pollen tube with haploid male gametophyte nuclei.

Allergenic Pollen (poplar, alder, timothy grass, ragweed, sagebrush, scotchbroom)

E. Plant fertilization - sperm combo’s with egg n 1. one sperm fertilizes the egg n 2. nucleus of 2nd sperm fuses w/2 of the accessory cell nuclei forming a triploid nucleus – this grows to form into the endosperm which is the food for the embryo n 3. using 2 sperm for fert. = Double Fertilization n 4. The seed grows from the fertilized ovule…..

n a. mature seed: u 1) seed coat (protection) u 2) cotyledons (seed leaves) u 3) hypocotyl (lower embryonic axis) u 4) radicle (embryonic root) u 5) epicotyl (upper embryonic axis) u 6) plummule (shoot tip) u 7) coleoptile (sheath for embryonic shoot)

The seed

Seeds in a Pod

F. The fruit n 1. Fruit protects seeds and aids in their dispersal n 2. Pericarp (thickened wall of fruit forms from the ovary wall) n 3. Fruit types: u a. simple (1 ovary/1 flower)~ cherry, soybean u b. aggregate (1 flower with many ovaries) blackberry u c. multiple (inflorescence; groups of flowers w/ gps of ovary) ~ pineapple

G. Seed germination – breaking out of seed dormancy – triggers vary in dif species n 1. Seed dormancy (low metabolic rate and growth suspension) – some can stay dormant for thousands of years! n 2. Imbibition (uptake of water) – water instigates the growth process n 3. Radicle grows 1st, then shoot tip (hypocotyl); stimulated by light