Plant Reproduction In Angiosperms Flowering Plants I Introduction

Plant Reproduction In Angiosperms (Flowering Plants)

I. Introduction A. Seed Plants • Adaptations for terrestrial seed plant reproduction: Ø flowers or cones Ø transfer of sperm by pollination Ø protection of embryos in seeds 1. Gymnosperms: 2. Angiosperms: Seed plants that bear unprotected seeds within the slots of cones Flowering plants that bear coated seeds within ovaries (fruit)

II. Structure of Flowers Stigma • Sticky to collect pollen Style Stamen Anther • Site of meiosis to produce sperm in pollen grains Filament • Supports the anther Sepals • Outermost circle of floral parts • Enclose the bud before it opens • Protects the flower while it develops Ovary Pistil • Supports the stigma • Contains one or more ovules (Produces embryo sac, which contains the egg) Petals • Located just inside the sepals • Often brightly colored to attract pollinators

Sepals Immature Flower Parts

Petal Sepal

Stamen Filament Anther

Stigma Style Ovary Pistil

Ovule Ovary

3 Sepals 3 Petals 1 Pistil 6 Stamen

III. Life Cycle of Angiosperms A. Meiosis occurs in the anthers and ovaries to produce pollen grains and embryo sacs. 1. Pollen Grain contains: a. Tube nucleus (n) b. Generative nucleus (n)

2. Embryo Sac contains: a. Egg (n) b. 2 polar nuclei (n)

B. Pollination: pollen released from anther lands on stigma 1. Self- Pollination: pollen lands on a stigma of the same plant 2. Cross- Pollination: pollen lands on a stigma of a different plant * Pollen carried by gravity, wind, insects, birds, small animals, etc.

C. Fertilization 1. Pollen grain’s tube nucleus releases enzymes to “dig” a pollen tube through the style to the ovule

2. Pollen grain’s generative nucleus divides once to produce 2 sperm, which travel down the pollen tube

3. Double Fertilization: a) One sperm fertilizes the egg to produce a diploid embryo b) The other sperm fuses with the 2 polar nuclei to produce triploid (3 n) endosperm.

4. Endosperm = food supply for embryo a) Cotyledons: “seed leaves” that absorb some of the nutrients in endosperm to nourish the seedling during germination *Monocot: plant with one cotyledon *Dicot: plant with two cotyledons

D. Seeds: form from the ovule containing the fertilized embryo sac. 1. Plant embryo surrounded by a food supply ex. bean 2. Seed Coat: surrounds and protects the embryo and keeps the seed contents from drying out

Angiosperm

E. Fruit & Seed Dispersal: 1. After fertilization, ovary walls thicken to form fruit.

2. Seeds dispersed by vectors ex. animals, wind, water * Seed coats cannot be digested. * Animals eat fruit and egest seeds elsewhere

F. Dormancy: Period when embryo is alive but not growing. G. Germination: When conditions are suitable, young plant sprouts from seed