9.3 – Reproduction in Angiospermophytes

FlowersFlowers

FlowersFlowers – reproductive structures of – reproductive structures of angiospermophytesangiospermophytes

Flowers evolved from modified leaves and stemsFlowers evolved from modified leaves and stemsNon-Reproductive Floral Structures:Non-Reproductive Floral Structures: Sepals Sepals – “leaves,” at base of flower – enclose – “leaves,” at base of flower – enclose

the flower before it opensthe flower before it opens PetalsPetals – brightly colored structures that aid in – brightly colored structures that aid in

attracting birds and insectsattracting birds and insects Both sepals and petals are not directly involved Both sepals and petals are not directly involved

in reproductionin reproduction

9.3.1

Floral StructureFloral Structure

9.3.1

Reproductive StructuresReproductive StructuresReproductive Floral Structures:Reproductive Floral Structures: StamenStamen – male reproductive structure – male reproductive structure

AntherAnther – sac where pollen in produced – sac where pollen in produced Filament Filament – stalk that supports anther– stalk that supports anther

Carpel (Pistil)Carpel (Pistil) – female reproductive – female reproductive structurestructure StigmaStigma – sticky area on top of carpel that – sticky area on top of carpel that

receives pollenreceives pollen StyleStyle – tube that connects stigma to ovary – tube that connects stigma to ovary OvaryOvary – base of carpel that contains ovule – base of carpel that contains ovule

and egg sacand egg sac 9.3.1

Floral StructureFloral Structure

9.3.1

Control of FloweringControl of Flowering

PhotoperiodismPhotoperiodism – plant response to light – plant response to light involving relative lengths of day and night.involving relative lengths of day and night. Very important factor in flowering – Very important factor in flowering – why?why?

9.3.6

Control of FloweringControl of Flowering

Long-day plantsLong-day plants – bloom when days are – bloom when days are longest and nights are shortest (mid-summer)longest and nights are shortest (mid-summer)

Short-day plantsShort-day plants – bloom in spring, late – bloom in spring, late summer, and autumn when days are shorter and summer, and autumn when days are shorter and nights are longernights are longer

Day-neutral plantsDay-neutral plants – day-length not important – day-length not important for floweringfor flowering

Day length is not as critical as Day length is not as critical as night lengthnight length in in regulation of flowering.regulation of flowering.

9.3.6

Control of FloweringControl of Flowering

Control by light is due to a pigment in Control by light is due to a pigment in plants called plants called phytochromephytochrome..

PhytochromePhytochrome – blue-green pigment that – blue-green pigment that controls various growth responses controls various growth responses (including flowering) in plants(including flowering) in plants

Two forms of phytochrome:Two forms of phytochrome: PPrr – inactive form – inactive form

PPfrfr – active form – active form

9.3.6

Control of FloweringControl of Flowering

Phytochrome is converted from inactive to active Phytochrome is converted from inactive to active forms due to different light wavelengths:forms due to different light wavelengths: In red light (660 nm) inactive PIn red light (660 nm) inactive Prr is rapidly converted to is rapidly converted to

active Pactive Pfrfr..

Active PActive Pfrfr can absorb far-red light (730 nm) can absorb far-red light (730 nm)

In daylight, PIn daylight, Pfrfr is rapidly converted to back to P is rapidly converted to back to Prr

In darkness, PIn darkness, Pfrfr is very slowly converted back to P is very slowly converted back to Prr

The slow conversion of PThe slow conversion of Pfrfr to P to Prr helps plants time the helps plants time the

night length. night length.

9.3.6

Control of FloweringControl of Flowering

9.3.6

Control of FloweringControl of Flowering

In long-day plants, the remaining PIn long-day plants, the remaining Pfrfr at the at the

end of the night stimulates floweringend of the night stimulates flowering PPfrfr remains due to slow conversion at night remains due to slow conversion at night

In short-day plants, the remaining PIn short-day plants, the remaining Pfrfr at the at the

end of the night inhibits floweringend of the night inhibits flowering Short-day plants only flower when enough Pfr Short-day plants only flower when enough Pfr

has been converted to Phas been converted to Prr. (this only occurs . (this only occurs

during long nights)during long nights)

9.3.6

Control of FloweringControl of Flowering

9.3.6

PollinationPollination

Process of moving pollen grains from the Process of moving pollen grains from the anther to the sticky stigma on the carpelanther to the sticky stigma on the carpel

Plants have evolved numerous Plants have evolved numerous adaptations for pollinationadaptations for pollination Wind pollinated plants produce large amounts Wind pollinated plants produce large amounts

of pollen = allergies! of pollen = allergies! Why do they do this?Why do they do this? Different colors and shapes of flowers allow Different colors and shapes of flowers allow

plants to attract different pollinatorsplants to attract different pollinators

9.3.2

PollinationPollination

What we see… What insects see…

PollinationPollination

Most plants have evolved adaptations to Most plants have evolved adaptations to limit self-pollination – limit self-pollination – why is this why is this important?important? Stamens and carpels may mature at different Stamens and carpels may mature at different

timestimes Floral structure makes self pollination difficultFloral structure makes self pollination difficult Flowers are self-incompatible – biochemical Flowers are self-incompatible – biochemical

mechanisms block prevents pollinationmechanisms block prevents pollination

FertilizationFertilization

Process of fusing sperm and egg to produce Process of fusing sperm and egg to produce new embryonew embryo

After pollinationAfter pollination – the pollen grain produces a – the pollen grain produces a tube that extends down the style toward the tube that extends down the style toward the ovaryovary Growth of the tube is directed by a chemical attractant Growth of the tube is directed by a chemical attractant

(usually calcium produced by the ovary)(usually calcium produced by the ovary) Sperm within the pollen grain fertilize the egg Sperm within the pollen grain fertilize the egg

and produce the plant embryoand produce the plant embryo Pollination does not always lead to fertilizationPollination does not always lead to fertilization

9.3.2

Seed StructureSeed Structure

Seed coat (testa)Seed coat (testa) – hard shell that – hard shell that encases and protects embryoencases and protects embryo

Radicle (hypocotyl)Radicle (hypocotyl) – embryonic root – embryonic root Plumule (epicotyl)Plumule (epicotyl) – embryonic shoot – embryonic shoot CotyledonsCotyledons – seed leaves – seed leaves

Dicots have two seed leavesDicots have two seed leaves Monocots have one seed leafMonocots have one seed leaf

9.3.3

Seed StructureSeed Structure

9.3.3

Seed DormancySeed Dormancy

Evolutionary adaptation that germination Evolutionary adaptation that germination (sprouting) will take place when conditions are (sprouting) will take place when conditions are favorablefavorable

For example:For example: Desert plants will only germinate after significant Desert plants will only germinate after significant

rainfallrainfall Many forest species require heat from fire to Many forest species require heat from fire to

germinate – germinate – how is this an advantage?how is this an advantage? In areas with harsh winters – seed require a long In areas with harsh winters – seed require a long

“chilling,” period before germinating – “chilling,” period before germinating – why?why?

9.3.4

GerminationGermination

1.1. Begins with Begins with imbibitionimbibition – the absorption of – the absorption of waterwater

Causes seed coat to rupture and triggers metabolic Causes seed coat to rupture and triggers metabolic changes within embryochanges within embryo

2.2. The embryo begins producing a plant growth The embryo begins producing a plant growth hormone – hormone – gibberellinsgibberellins

3.3. Gibberellins stimulate the production of Gibberellins stimulate the production of amylase in the seedamylase in the seed

4.4. Amylase begins digesting food stores of the Amylase begins digesting food stores of the endosperm (starch) into maltoseendosperm (starch) into maltose

9.3.5

GerminationGermination

5.5. Maltose is transferred to the growing regions of Maltose is transferred to the growing regions of the embryo – the embryonic root (radicle) and the embryo – the embryonic root (radicle) and shoot (plumule)shoot (plumule)

6.6. Maltose is converted to glucose – where it Maltose is converted to glucose – where it used in aerobic respiration for energy or it is used in aerobic respiration for energy or it is used to make cellulose and other materials used to make cellulose and other materials needed for growthneeded for growth

7.7. Once the seedling breaks ground, Once the seedling breaks ground, photosynthesis can begin and the endosperm photosynthesis can begin and the endosperm food stores are not neededfood stores are not needed

9.3.5

GerminationGermination

Factors Affecting GerminationFactors Affecting Germination

WaterWater – must be available for imbibition– must be available for imbibition OxygenOxygen – required for aerobic respiration – required for aerobic respiration

during germinationduring germination TemperatureTemperature – enzyme action (amylase) – enzyme action (amylase)

can be affected by fluctuations in can be affected by fluctuations in temperaturetemperature

9.3.4