Reproduction in Flowering Plants

Types of reproduction Asexual – the production of clones; no other plant necessary (« I can do it own my own, thanks! ») Sexual – gametophytes formed; pollination is necessary

Asexual reproduction Also called vegetative reproduction Asexual reproduction occurs in various ways: - production of rhizomes (modified stems); could be ‘eyes’ on potatoes - from fragments of roots or shoots (e.g dandelions, quack grass)

Costs and benefits Benefits? Advantageous traits will be passed on Less energy than sexual reproduction Faster Only one plant needed Young plantelets are more robust and survive better

One big cost….. No diversity in genetic clones – if the environment changes quickly or if there is a disease or insect outbreak, the entire population will die….

Human uses of asexual plant reproduction Gardeners, nurseries Reproducing copies of plants with desirable characteristics using methods such as: Stem cutting – in water or soil where new roots will form Grafting - branch from plant with desirable features is attached to stem of other plant (common in orchards) Tissue culture – piece of plant in test tube with growth media

Sexual reproduction The product of sexual reproduction (in flowering plants) is a seed. Seed function: - to protect and nourish the embryo - to move the embryo to a new location

Costs and benefits Benefits: High level of genetic diversity Seeds are dispersed; less competition for resources Seeds can remains dormant for a long time Cost? - Lots of energy – specialized structures

Sexual reproduction Similar in angiosperms and gymnosperms Meiosis forms gametophytes – pollen grain and ovule Pollen grain is carried to ovule (in the process of pollination) where fertilization occurs Embryo grows by mitosis Germination occurs

It starts with pollination Pollination happens by wind only in gymnosperms and both wind & animals in angiosperms (pollinators) Conifers have both male and female cones on the same tree Pollen grain must land close to an ovule on a female cone (most don’t), then fertilization occurs (can take about 13 months)

Angiosperm pollination Animal-pollinated flowers are very showy and colourful while wind-pollinated flowers can barely be noticeable (maple tree) Some plants can have both female and male parts (e.g. corn), can self-pollinate Some plants only have male or female flowers (must cross-pollinate)

From Pollen to Ovary The pollen grain grows a pollen tube towards the ovary, which contains the ovule and egg cell (female gamete). pollen tube ovary containing ovule 12

9Ad Fertilization Fertilisation takes place when the ‘sperm’ nucleus from the pollen grain enters the egg cell. The resulting zygote eventually turns into a seed. pollen tube with pollen grain nucleus ovule Embryo grows inside the ovule. egg cell 13

Zygote to Embryo The zygote will grow through the process of mitosis to form an embryo (The ovule is now called a seed and is covered by a protective seed coat.) seed seed coat food supply (cotyledon) embryo

Fruit Formation Some plants produce fruit containing seeds. Fruit: Mature ovary Tissue surrounding the embryo develops into fruit. When the fruit is fully developed it drops off the plant, or is carried away by an animal. When fruit decomposes it releases the seed and germination can occur.

Germination A seed requires moisture (water) to germinate. The as the embryo grows, the root and shoot break through the seed coat. Nutrients stored in the cotyledon provide nourishment and support early development

Sexual reproduction in gymnosperms Conifers (e.g pines and cedars) produce both male and female cones Male gametophytes (haploid) produced and stored in pollen grain Wind pollination gets pollen grain to female gametophyte (haploid) in ovule One sperm nuclei fertilizes the egg after a pollen tube grows into ovule (13 months)

Sexual reproduction in angiosperms Seeds are contained inside a fruit – a mature ovary This fruit is an important part of the diet for many animals including humans. Sexual structure is the flower…….

Parts of a flower 20

Reproductive Parts Male reproductive organs (stamen): Anther: produces pollen grains Filament: supports anther above female reproductive organs Female reproductive organs (carpel): Stigma: sticky landing site for pollen grains Style: tube that leads down to ovary Ovary: contains ovules that develop into seeds

Reproductive Mechanisms Pollen (male gamete) from one plant lands on the stigma of another plant. This is called pollination. pollen stigma 22

Monocot and dicot flowers Monocot: Petals and stamens are always in multiples of three. Dicot: Petals and stamens are in multiples of four or five.

Pollination and fertilization in angiosperms Cross – pollination: by wind or animals between flowers of different plants of the same or closely related species(pollinators) – like? Self-pollination: pollen transfer from flowers on the same plant

Sexual reproduction

Selective breeding in plants 9Ad Selective breeding in plants texture size Selective breeding and cross-breeding are carried out on plants to produce flowers and crops with desirable characteristics… taste colour 27

9A Plant-breeding techniques Anne the plant breeder chooses two parent plants with useful characteristics. One plant will be the female parent. Anne removes the anthers and covers the flower with a bag. Why? female parent The other plant is the male parent. Its anthers develop as normal. Anne collects its pollen and brushes it onto the female plant. collected pollen anthers removed She puts the bag over the flower again. Later she collects the seeds and grows them to produce the new plant.

Fruit formation A fruit – a mature ovary that helps protect and disperse the seed Fruit – can be sweet and fleshy (e.g. plums and strawberries) or dry like walnuts and wheat or vegetables (e.g. peppers, peas and squash)

Importance of seeds Grain crops (like wheat) are staples around the world Greenhouses Seed collection for breeding Survival of other species on earth

Comparing Plant and Human Reproductive Systems Male and Female organs Male Gamete is pollen Female Gamete is egg produced in ovule Pollen nuclei fuses with egg nuclei (fertiliation) Diploid zygote Zygote grows into embryo Embryo grows inside protective seed coat Cotyledons provide nourishment Male or Female organs Male Gamete is sperm Female Gamete is egg produced in ovary Sperm nuclei fuses with egg nuclei (fertilization) Diploid zygote Zygote grows into embryo Embryo grows inside protective womb Placenta provides nourishment