Flowers, Seeds, and Technology

Plant structure and function

Flower Types• Complete flowers have all organs.• Incomplete flowers don’t• Depends on what pollinators they are trying to

attract.

Pollen• In anthers:• Microsporocytes undergo meiosis to make 4

microspores. Each becomes a pollen grain.• Pollen grain- gametophyte with a spore wall,

generative cell (divides into 2 sperm), and tube cell (grows into pollen tube).

Embryo Sacs• In ovules :• Megasporocytes undergo meiosis to form 4

megaspores. One survives• Embryo sac – gametophyte with an integument,

egg cell, and two polar nuclei in a central cell

Pollination• Transfer of pollen to the stigma• Pollen germinates and extends a pollen tube• Pollen tube sends two sperm to the embryo sac

(double fertilization)• One sperm fertilizes the egg forming a zygote• One sperm fertilizes the polar cell and in

becomes triploid nutritive tissue called endosperm.

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Pollination Strategies• Colors of flowers- bright, white (night moths),

UV• Scents- sweet (bees), stinky (flies)• Nectar- bats, birds, bees• Mimicry- fake mates (wasps)

Oops...Preventing Self Pollination• Dioecious plants have either male or female flowers• Staminate flowers only contain stamen• Carpellate flowers only contain carpels• Some plants plants stagger their organs• Thrums- flowers with long stamens and short styles• Pin- have short stamens and long styles• Self incompatibility -most plants reject its own pollen

Fruit Development• Ovaries become fruit to protect and disperse

seeds• Ovary wall becomes the thickened wall of the

fruit called the pericarp. Other organs fall off (depends on fruit)

Fruit Types• Simple- from one carpel or carpels fused into one (pea

pod)• Aggregate – from multiple carpels on one flower

(strawberry, blackberry)• Multiple- carpels from many flowers come together

(pineapple, figs)• Accessory- made from tissues besides the ovary

usually the fleshy tissue in the ovary called the receptacle. (apple)

• Usually ripen when seeds are fully developed

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Seed Development• Seed coat- covering from integument• Cotyledon- seed leafs, used for nutrient• Epicotyl- just below the cotyledons, holds mini

leafs and apical meristem• Hypocotyl- just below the epicotyl attached to

the radicle• Radicle – embryonic root.

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Dispersing SeedsSeed Dispersal• Eaten by animals & passed thru digestive tract• Carried by wind• Float in water• Some have hooks to catch fur or feathers

Germination• Imbibition- uptake of water by seed • Radicle breaks through first• The hypocotyle then straightens out raising the

cotyledons and epicotyl• The epicotyl spreads the mini leaves

Asexual Reproduction• Plants can grow through fragmentation a callus

(group of undifferentiated dividing cells) will grow where a plant is clipped.

• Apomixis- asexual seed production

Grafting• Two related plants can be combined or grafted.Usually a shoot is placed on a root. The root is

the stock and the shoot is the scion.Ex. Wine grapes American stock French shoots.

GMO’s• Transgenic- plants having genes inserted to

promote new phenotypes. Ex. bacterium DNA that makes a chemical toxic to insects but theoretically harmless to people, or inserting Daffodil genes into rice to increase beta carotene.

Bio Fuels• Plant biomass could by broken down into sugar

polymers and fermented to create alcohol to use as bio fuel.

(switch grass species, poplar, corn)