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.

HaploidDiploid MEIOSIS

FERTILIZATION

Gametophyte Plant (N)

Sporophyte Plant (2N)

B. Life Cycle of Gymnosperms - Reproduction in gymnosperms

takes place in cones, which are produced by a mature sporophyte plant.

1. Pollen conesa. Also called male cones.b. Produces the male

gametophytes, which are called pollen grains.

2. Seed Conesa. Produce female gametophytesb. Much larger than pollen conesc. 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. Fertilizationa. 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.

5. Developmenta. Fertilization produces a

zygote which grows into an

embryob. The embryo becomes

enclosed in a seed

ANGIOSPERMC. 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

OvuleSepal

Stamen Pistil

1. Sepalsa. 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. Petalsa. Brightly colored and found

just inside the sepalsb. Attract insects and other

pollinators to the flower

3. Stamensa. Produce male

gametophytes – pollen grains

b. Consists of anther and filament

4. Carpelsa. Also called pistilsb. produce female

gametophytes – eggsc. Consists of ovary, style,

and stigma

D. Life Cycle of Angiosperms1. Reproduction in angiosperms

takes place within the flower2. Following pollination and

fertilization, the seeds develop inside protective structures

E. Pollination1. 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 Angiosperms1. Double Fertilization – Inside the

embryo sac, two distinct fertilizations take placea. 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 Development1. 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 Dispersal1. 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 Dormancy1. 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