topic 9: plant structure part ii
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Topic 9: Plant Structure Part II. Biology HL Mrs. Ragsdale. Structure and Function of Flowers. Flowers are typically the site of external sexual organs in plants for reproduction Most flowers have both male/female anatomy Female gametes – contained in ovules located in the ovaries - PowerPoint PPT PresentationTRANSCRIPT
Biology HLMrs. Ragsdale
Flowers are typically the site of external sexual organs in plants for reproduction
Most flowers have both male/female anatomy◦ Female gametes – contained in
ovules located in the ovaries◦ Male gametes – contained in
pollen grains produced by the anthers
◦ A fertilized zygote formed by pollen fusing with the ovules
http://www.webquest.hawaii.edu/kahihi/sciencedictionary/P/perfectflower.php
Transfer of pollen from an anther to a stigma
Since plants themselves do not move, an outside agent is typically required for successful cross pollination to occur◦ Wind dispersal◦ Insect/Bee dispersal◦ Animal dispersal
Flower structure typically adapted to method for pollination◦ Bees – flowers are
typically equipped with “landing platforms” and has strategically placed anthers to catch pollen
◦ Birds – sweet nectars for attraction
http://www.mrac.ca/story/protecting-against-pests
Tricking nature to do its bidding!
Pollen grains germinate on the stigma of the flower
Pollen tube with the male gametes travels down the style to the ovary
Fusion of male and female gametes
Ovaries with fertilized ovules develop into fruits
The fertilized ovules develop into seeds
Ultimate job of a fruit is seed dispersal
http://www.motherearthnews.com/organic-gardening/self-pollinating-apples.aspx
Testa -Seed Coat protective layer
Micropyle – opening for the pollen
Plumule – (embryo shoot)
Radicle – embryo root
Cotyledon - food storing seed leaf
http://www.cmg.colostate.edu/gardennotes/137.html
Cotyledons provide energy and nutrients for germination!
First foliage leaves are about to open!
Bend in the stem protects the leaves as the shoot pushes up through the soil
Stem between the cotyledons and the first foliage leaves has grown
Branches of the main root increase the surface area for absorption
Main root growing downward into the soil
Must have adequate water, oxygen and temperatures
Water ◦ Dry tissues must be rehydrated
Oxygen◦ Needed for aerobic cellular respiration
Temperature◦ Germination involves enzymes!◦ Extreme high temps and low temps are not conducive
to germination
Stage One◦ Absorption of water – leads to the rehydration of
living tissues inside the seed Stage Two
◦ Gibberellin is a plant hormone that is produced in the cotyledon of the seed. Production begins after rehydration.
Stage Three◦ Gibberellin stimulates the production of amylase◦ Amylase catalyses the digestion of starches into
maltose
Stage Four◦ Maltose is transported from food storage to the
places that are growing like the embryo root and embryo shoot
Stage Five◦ Maltose is finally converted into glucose◦ Glucose is used in aerobic cell respiration OR it is
used to synthesize cellulose Stage Six
◦ The seedling leaves will finally reach light and begin photosynthesis
Phototropism – plants grow towards light and will literally bend and contort towards it
Auxin – a plant hormone that acts as a growth promoter
Research has shown that auxin redistributes itself in the shoot tips from the lighter side to the darker.◦ Additional growth on the shadier
side causes the plant to bend towards the light
Pumps in plasma membrane = auxin efflux carriers
Pumps distributed unevenly ◦ Auxin is able to be redistributed as needed in
tissues Auxin works by binding to auxin receptors
in plant cells◦ Once auxin binds to the receptor, transcription of
specific genes is promoted◦ This affects the growth of the cells
Why do certain plants only bloom at specific times of the year?
Studies show that it’s not the length of day but the length of night that controls flowering◦ Short-day plants ◦ Long-day plants
http://www.flowersgrowing.com/chrysanthemum/
Plants have the ability to sense day and night light/dark with extreme accuracy
Phytochrome is a pigment in the leaves that exists in two interconvertible forms◦ Pr – absorbs red light with a wavelength of 600nm
Inactive form of phytochrome◦ Once the red light is absorbed it is rapidly
converted into Pfr Active form of phytochrome
◦ As soon as light disappears Pfr is gradually converted back into Pr
The reversion of Pfr is most likely what is used as a darkness “timer”
Pfr in short day plants acts an inhibitor to flowering. Once all of the Pfr has been converted to Pr then flowering will begin
In long day plants, Pfr binds to proteins which then trigger genes involved in flowering to switch on