Ch. 24- Reproduction of Seed Plants

I. Reproduction With Cones and Flowers A. Alternation of Generations - All plants have a life cycle in which a diploid sporophyte generation alternates with a haploid gametophyte generation. Haploid Diploid MEIOSIS Gametophyte Plant (N) Sporophyte Plant (2N) FERTILIZATION

a. Also called male cones. B. Life Cycle of Gymnosperms - Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant. 1. Pollen cones a. Also called male cones. b. Produces the male gametophytes, which are called pollen grains.

2. Seed Cones a. Produce female gametophytes b. Much larger than pollen cones c. At the base of each cone scale are found 2 ovules in which the female gametophytes develop

3. Pollination – The pollen is carried by the wind and caught on a sticky secretion (pollination drop) on one of the scales of the female cone.

4. Fertilization a. When a pollen grain lands near an ovule, it grows a pollen tube into the ovule. b. A sperm from the pollen tube fertilizes the egg in the ovule.

Development a. Fertilization produces a zygote which grows into an embryo b. The embryo becomes enclosed in a seed

ANGIOSPERM C. Structure of Flowers - Flowers are the reproductive organs that are composed of four kinds of specialized leaves: sepals, petals, stamens, and carpels. (Figure 24-5)

Filament Anther Style Stigma Ovary Petal Ovule Sepal Stamen Pistil

1. Sepals a. The outermost circle of floral parts contains the sepals, which in many plants are green and closely resemble ordinary leaves b. Enclose bud and protect the flower during development

2. Petals a. Brightly colored and found just inside the sepals b. Attract insects and other pollinators to the flower

3. Stamens a. Produce male gametophytes – pollen grains b. Consists of anther and filament

4. Carpels a. Also called pistils b. produce female gametophytes – eggs c. Consists of ovary, style, and stigma

D. Life Cycle of Angiosperms 1. Reproduction in angiosperms takes place within the flower 2. Following pollination and fertilization, the seeds develop inside protective structures

E. Pollination 1. Most gymnosperms and some angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals. 2. Insect pollination is more efficient than wind pollination, giving insect-pollinated plants a greater chance of reproductive success.

F. Fertilization in Angiosperms 1. Double Fertilization – Inside the embryo sac, two distinct fertilizations take place a. First, one of the sperm nuclei fuses with the egg nucleus to produce a diploid zygote, which will grow into the new plant embryo.

b. Second, the other sperm nucleus fuses with two polar nuclei in the embryo sac to form a triploid (3N) cell. This will grow into a food-rich tissue know as endosperm, which nourishes the seedling as it grows.

II. Seed Development and Germination - the development of the seed, which provides protection and nutrition for the embryo, was a major factor in the success of plants on land.

A. Seed and Fruit Development 1. As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seed. 2. The term fruit, biologically speaking, applies to any seed that is enclosed within its embryo wall.

http://www.youtube.com/watch?v=zVNsCW6eiiw

B. Seed Dispersal 1. Dispersal by Animals- Seeds dispersed by animals are typically contained in fleshy, nutritious fruits.

2. Dispersal by Wind and Water- Seeds dispersed by wind or water are typically light weight, allowing them to be carried in the air or to float to the surface of the water.

C. Seed Dormancy 1. Some seeds sprout rapidly while other seeds enter a period of dormancy, during which the embryo is alive but not growing. 2. Environmental factors such as temperature and moisture can cause a seed to end dormancy and germinate.

D. Seed Germination - The early growth stage of the plant embryo