Subphylum spermosida The seed bearing plants
In angiosperms the flowers are the structures that are specialized for sexual reproduction. • Flowers in mature sporophytes produce male and female gametophytes. The angiosperms
Some plants produce male and female gametophytes on separate plants (willow). • Some plants produce male and female gametophytes on different parts of the same plant, some even in the same flower. The angiosperms
Structure of a typical flower The angiosperms
Angraecum sesquipedale • This orchid has a nectar tube that is 25-30 cm in length. • How does it get pollinated? The angiosperms
By this moth! • Xanthopan morgani praedicta
Life Cycle • Step 1 : The flower is the sporophyte. (Diploid generation -2N)
Life Cycle • Step 2: Within the ovary, ovules (2N) are produced. The ovules mature to produce a structure (embryo sac) with several nuclei (meiosis occurs). -This is the female gametophyte. -There are 8 nuclei (N). -2 polar nuclei. -The egg will later be fertilized.
Life Cycle • Step 3: Within the anther, meiosis occurs to produce pollen grains consisting of 2 nuclei. When mature, the pollen grains are released. - Tube nucleus – will later degenerate. - Generative nucleus – will later divide into 2 sperm nuclei.
Life Cycle • Step 4: Pollination occurs – the transfer of pollen from anther to stigma. • Types of pollination: • A)self-pollination: pollen falls from the anther to the stigma of the same plant. • B) cross-pollination: pollen is transferred from the anthers of one plant to the stigma of another plant. • A sticky substance on the stigma stimulates the growth of a pollen tube.
Life Cycle • Step 5: A pollen tube grows down to the stigma, style, ovary into the ovule. The generative nucleus has divided into 2 sperm nuclei. • Now there are 3 nuclei: 2 sperm nuclei and 1 tube nucleus.
Life Cycle • Step 6: Sperm are released into the ovule. 1 sperm fertilizes the egg to produce a zygote which later grows into a multicellular embryo. The other sperm fertilizes the 2 polar nuclei which then becomes triploid (3N). This triploid cell later becomes the endosperm that will be the embryo’s food supply while developing. This is called doublefertilization. • http://www.youtube.com/watch?v=X7uH46X0G5Y
Life Cycle • Step 7: After fertilization, sepals, petals, and stamens wither. The ovary swells, and the ovule grows. The ovary ripens into the fruit. The ovules mature into seeds which are found within the ovules. Seeds are dispersed by insects, animals, wind and rain.