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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:
1) Stem cutting – in water or soil where new roots will form
2) Grafting - branch from plant with desirable features is attached to stem of other plant (common
in orchards)
3) 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
pollen tube
ovary containing ovule
towards the ovary, which contains the ovule and egg cell (female gamete).
Fertilisation takes place when the ‘sperm’ nucleus from the pollen grain enters the egg cell. The resulting zygote eventually turns into a seed.
Fertilization9Ad
pollen tube with pollen grain nucleus
ovuleEmbryo grows inside the ovule.
egg cell
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 coat
food supply (cotyledon)
embryo
seed
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
Reproductive PartsMale 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
stigmapollen
on the stigma of another plant. This is called pollination.
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
size
Selective breeding in plants
colourtaste
texture
Selective breeding and cross-breeding are carried out on plants to produce flowers and crops with desirable characteristics…
9Ad
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?
She puts the bag over the flower again. Later she collects the seeds and grows them to produce the new plant.
female parent
anthers removed
collected pollen
The other plant is the male parent. Its anthers develop as normal.
Anne collects its pollen and brushes it onto the female 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
Plant• 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
Human• 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