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