ix. reproductive structures of flowering plants

IX. Reproductive Structures of Flowering Plants

A. Sporophyte1. Growth

• Mitotic division of a fertilized egg

2. Flowers

• Gametophytes

– Sperm

– Eggs

Carpel

X.

A. A New Generation Begins

1. Cells in pollen sacs

undergo meiosis to

form microspores

2. Mitosis forms male

gametophyte

(pollen grains)

3. Cells in ovule undergo

meiosis to form

megaspores

4. Mitosis without

cytoplasmic division

forms female

gametophyte

B. Pollination to Fertilization

1. Pollination– Pollen grains to stigma

2. Pollen tube grows to and penetrates embryo sac, releases two sperm

3. Double fertilization– One sperm fuses with egg nucleus (2n)– One sperm fuses with nuclei of endosperm

mother cell (3n)

C. How do plants get pollen from one plant to another? (plants are rooted in the ground)

A. Wind 1. Gymnosperms and some flowering plants (grasses & many trees)2. Hit or miss affair (very chancy)

B. Many flowering plants rely on animals for cross-pollination 1. 3 main animal pollinators- insects, birds, and mammals

a. Insect pollinators- beetles, bees, wasps, flies, butterflies, and mothsb. Bird pollinators- hummingbirds, honey creepers, and honeyeatersc. Mammals- bats

2. Many plants have evolved relationships with animals that are their pollinators (co-evolution)

D. Seed Structure (a mature ovule)

1. Seed coat

2. Radicle – embryonic root

3. Plumule – embryonic leaves

4. Epicotyl and hypocotyl – shoot

5. Cotyledons (seed leaves) derived from endosperm

E. Fruit = a mature ovary which usually contains a seed

See Table on pg 537

F. Seed Dispersal1. Wind Dispersal – Maple Tree, Dandelion

- goal is to land far enough away so they do not have to compete with parent plants

2. Animalsa. seed adheres to animal w/ hooks, hairs, and sticky surfacesb. Seed survives digestion due to thick seed coat

3. Water Dispersala. Waxy coat to avoid water penetration (coconut fruit)b. Sacs of air to help them float

4. Humans – imports and exotic species5. Explosives - Impatiens

XI. Asexual Reproduction in Plants (See Table pg 540)

XII. Growth and Development Overview (Chp 32: pgs 546-547)

XIII. Plant hormonesA. Definition – an organic compounds produced in

one part of a plant, transported to another part, where it stimulates a physiological response

B. Five major types

1. Auxins a. Stimulates cell elongation in the

stem and thereby phototropism of the plant

b. Produces apical dominance by inhibiting lateral bud growth

c. Transported through parenchyma

2. Cytokininsa. Produced in rootsb. Stimulate lateral budsc. Delay plant aging

3. Ethylene (a gas)a. Triggers ripening in fruitsb. Produced in nodes, fruit, and aging tissue

4. Gibberellinsa. Promote stem elongationb. Promote seed germination

5. Abscisic acida. Closes stomata under water stressb. Delays germination of seeds in cold (high

levels in seeds)

XIV. Rate and Direction of Growth

A. Gravitropism – growth response to Earth’s gravity

B. Phototropism – leaves adjust rate and direction of growth in response to light

C. Thigmotropism – plant shifts direction of growth when in contact with solid object

XV. PhotoperiodismA. Processes by which plants control their cycles

using periods of lightness and darknessB. Types of plants affected by photoperiods

1. Long-day plants - plants affected by a critical period of darkness or lessa. Flower in spring and early summerb. Clover, black-eyed Susan, spinach (14

hrs.)2. Short-day plants - plants affected by a

critical period of darkness or morea. Flower in late summer or fallb. Chrysanthemum, poinsettia

C. Phytochromes - light-absorbing pigments that affect a plant’s photoperiod

1. In short-day plants Pfr inhibits flowering. A long night means more Pr and therefore lower Pfr levels. Result is flowering

2. In long day plants Pfr induces flowering. A short night means more Pfr. Result is flowering

XVI. Leaf abscission (leaf drop)A. Purpose - to prevent plant dehydration due to transpiration

when ground water is locked up in a frozen state

B. Process

1. In the fall woody parts of plant reabsorb valuable minerals from the leaves

2. Chlorophyll breaks down leaving and revealing accessory pigments (carotenoids and xanthophylls)

3. Changes occur in abscission zone, which has few fibers and is mostly parenchyma

a. Protective layer of cork cells forms

b. Enzymes digest cell walls in the zone

c. With connection weakened some mechanical force (wind) knocks leaf off tree

PetioleTwig

Abscission zone