2.3 Sexual Reproduction in Plants

1. 2.3 Sexual Reproduction in Plants

2. How Plants Meet the Challenge of Sexual Reproduction • Plants can also reproduce by sexual reproduction. The offspring have the genes from two parents - their genes are different, so the offspring will not be identical. There is variety in the species. • Movie • Sexual Reproduction cross-word

3. How Plants Meet the Challenge of Sexual Reproduction • Seeds are the products of sexual reproduction in most plants. • A seed is a complete reproductive package that contains an embryo, a food supply, and a seed coat, which protects it from drying out. • Angiosperms – flowering plants • Gymnosperms – seeds inside cones

4. Angiosperms • Flowering plants contain the most diverse and widespread members of the plant kingdom: monocots dicots • The greatest contribution to the success of the angiosperms was the evolution of the flower, which greatly improved its reproductive efficiency.

5. Angiosperms • Sexual Reproduction Angiosperms • The angiospermstook it one step further. They not only have seeds, but they also have flowers. • What kind of an advantage is that? Well what if you didn't need to rely on the wind to spread your pollen around anymore? What if someone could do it for you? Maybe an insect? Sounds like a new advantage. That's right, those specialized flowers are able to attract organisms to help pollinate and distribute seeds. Another cool advantage it the fruit/seed packaging. Would you rather eat a pine cone or an apple? So would a lot of animals. When they do, they are able to spread the seeds across wide areas. After the animal poops the seeds out of course.

6. Reproductive organs in flowering plants. The stamens are the male parts of the plant. Each consists of a stalklike filament topped by an anther. The anther contains four pollen sacs which burst to release tiny grains of pollen, the male sex cells. The carpels are the female reproductive parts. Each carpel has a stigma which catches the pollen grain. The style connects the stigma to the ovary. The ovary contains one or more ovules, the female sex cells. Buttercups have many ovaries; the lupin has only one.

7. Flowers in Angiosperms • The flower is the main reproductive organ that holds the sexual organs of the plant. Each part of the flower has a specific function during the different stages of sexual reproduction; namely pollination, fertilisation and fruit formation with seeds. The flower is arranged in whorls (rings) of modified leaves each performing a specific function. These whorls are arranged on an enlarged base of the flower stalk called the receptacle. • See diagram of flower

8. Pollination and Fertilization in Angiosperms • Pollination occurs when pollen is transferred from the ripe anther to the ripe stigma. Minute pollen grains become exposed when the anther splits open and are carried away by insects, birds, the wind and sometimes water. Flowers must be pollinated to ensure that the egg cells in the ovary can be fertilised. • If the pollen reaches the ripe stigma of the same flower it is called self-pollination. If the pollen reaches the ripe stigma of a different flower of the same species, then it is called cross-pollination. The latter method of pollination produces stronger and healthier seeds and therefore plants. • Do the following activity to differentiate between self and cross – pollination.

9. Seed Development in Angiosperms A seed consists of an embryo, food storage tissue, and a seed coat. The embryo contains the parts that form a new plant. It also has one or more cotyledons, which absorb and digest food from the food storage tissue. The seed coat protects the seed from injury, insects, and loss of water.

10. Gymnosperms • Were the first of the two groups of seed plants to appear in the fossil record. • Almost all conifers are evergreens with needle-shaped leaves and are among the tallest, largest, and oldest living organisms. • The cone is the distinguishing feature of conifers; in the pine, two different types of cones produce male and female gametophytes on the sporophyte tree

11. Pollen grains released as immature male gametophytes land on female cones housing immature females gametophytes inside complex ovules. • After a period of gametophyte maturation, fertilization occurs. • The zygote develops into an embryo, which is packaged into a winged seed that disperses by the wind from exposed scales of the mature female cone.

12. Gymnosperms • Seeds let you send you offspring out into the world. Seeds provide a protective coat so that the embryo plant can develop when it finds a nice piece of soil. But remember this... no flowers. Flowers are an evolutionary advancement after seeds. So if you have a vascular system, seeds and no flowers what are you? A GYMNOSPERM!

13. Seed Dispersal in Angiosperms Mechanism of dispersal

14. Seed Dispersal • Seeds have adapted so as to prevent them falling close to the parent plant. Failure to disperse would result in overcrowding and competition for the same resources. The role of the fruit is to help scatter or disperse the seed far and wide so that they can grow in turn into healthy new plants. The main agents of dispersal are wind, water and animals. • Try this activity to see to better understand the different methods of seed dispersal.

15. Wind Dispersal Examples: poppy, dandelion, sycamore, tumble weed, agapanthus, pine tree, maple, orchid, oats • The seeds are light and small so that they can be blown along by a light breeze. • They are also smooth so they can roll along the ground easily. • Some seeds have papery wings, parachutes or long hairs to carry them on air currents. • Some plants are able break off when dry; the wind then rolls them along the ground scattering the seeds as they roll. Try this activity to check your understanding

16. Animal Dispersal Examples: many berries, many fleshy fruits and vegetables, protea, mistletoe • Some seeds have hooked fruits that catch in the fur of passing mammals or in people's clothing. They then fall off some distance from the parent plant. Succulent and brightly coloured fruits attract birds, insects and animals that eat the fleshy part, while the seed passes undigested through the alimentary canal, to be dropped some distance from the parent plant. • Other seeds in large fruits may be carried away from the parent tree by animals that eat the flesh and discard the seed. Try this activity to check your understanding