Chapter 36 - The Flowering Plant Life Cycle

Front 1

• Each part of the flower has a specific function

Back 1

o Receptacle – tip of the stalk where some or all of the flower parts are borne
o Sepals – are the outermost and lowest whorl on a floral shoot; cover and protect the flower parts when the flower is a bud; collective term is calyx
o Petals – whorl just inside and above the sepals; are broad, flat, and thin; have many different shapes and colors; collective term is corolla
o Stamens – male reproductive organs; each stamen has a thin stalk called a filament; an anther [saclike structure in which pollen grains form] sits on top o the filament
 Each pollen grain consists of two cells surrounded by a tough outer wall. The generative cell divides mitotically to form two non-flagellate male gametes [sperm cells]. The other cell, the tube cell, produces a pollen tube trough which the sperm cells travel through to get to the ovule.
o Carpels – female reproductive organs; bear ovules; may be separate or fused into a single structure; pistil is the female part of the flower and has a stigma [where the pollen grains land], a style [a neck-like structure through which the pollen tube grows], and an ovary [a jug-like structure that contains one or more ovules and can develop into a fruit]

Front 2

• Female gametophytes are produced in the ovary, male gametophytes in the anther

Back 2

o The female gametophyte usually contains seven cells with eight haploid nuclei
 Six contain a single nucleus and the large central nuclei has two nuclei which are called polar nuclei
 The egg and both polar nuclei participate directly in fertilization
o Pollen sacs within the anther contain numerous diploid cells called microsporocytes which undergo meiosis to produce four haploid cells called microspores
 Each divides mitotically to produce a pollen grain that consists of the tube cell and the generative cell
 The pollen grain becomes mature when its generative cell divides to form two non-motile sperm cells

Front 3

Pollination

Back 3

• The transfer of pollen grains from anther to stigma
• Self-pollination – pollination occurs within the same flower or a different flower on the same individual plant
• Cross-pollination – when pollen grains are transferred to a flower on another individual of the same species
• Many plants have mechanisms to prevent self-pollination
o Inbreeding – mating of genetically similar individuals
 Can increase the concentration of harmful genes in the offspring
o Some plants have separate male and female parts
 The male plants have staminate flowers that lack carpels
 The females plants have pistillate flowers that lack stamens
o Outcrossing – mating of dissimilar individuals
o Self-incompatibility – genetic condition in which the pollen is ineffective in fertilizing the same flower or other flowers on the same plant
 Usually inhibit the growth of the pollen tube in the stigma and style

Front 4

• Flowering plants and their animal pollinators have coevolved

Back 4

o Animals
 Showy petals as a visual attractant
 Scent as an olfactory attractant
 Get nectar as a “reward”
 Pollinators carry pollen grains on their body parts
o Insects
 Often have blue or yellow petals
 Can see well only in the violet, blue, and yellow range of visible light
 Do not perceive red as a distinct color thus insects do not generally pollinate red flowers
 Many have dramatic UCV markings that directs the insect to the center of the flower where the pollen grains lie
 Strong scent that may be or may not be pleasant to humans
o Birds
 Usually red, orange, or yellow because most birds see well in this range of visible light
 Bird-pollinated flowers usually do not have a scent because birds cannot smell
o Bats
 Feed at night
 Bat-pollinated flowers usually bloom at night
 Usually have dull white petals
 Strong nighttime output of scent that usually smells like fermented fruit
• A single mutation in a gene for flower color can result in a shift in animal pollinators

Front 5

• Some flowering plants depend on wind to disperse pollen

Back 5

o Wind-pollinated plants produce many small, inconspicuous flowers
o Do not produce large, colorful petals, scent, or nectar
o Some have large, feathery stigmas
o Produce large quantities of pollen grains which increases the likelihood that some pollen grains will land on the appropriate stigma

Front 6

Fertilization and Seed/Fruit Development

Back 6

• A unique double fertilization process occurs in flowering plants
o The egg within the unites with one of the sperm cells forming a zygote.
o The two polar nuclei in the central cell of the ovule fuse with the second sperm cell to form the first cell of the triploid endosperm [the tissue with the nutritive and hormonal functions that surrounds the developing embryonic plant in the seed

Front 7

• Embryonic development in seeds is orderly and predictable

Back 7

o The two cells [basal cell and apical cell] that are formed as a result of the first division of the fertilized egg establish polarity or direction in the embryo
o The large basal cell [located towards the outside of the ovule] typically develops into a suspensor [an embryonic tissue that anchors the developing embryo and aids in nutrient uptake from the endosperm]
o The apical cell [toward the inside of the ovule] develops into the plant embryo
o Proembryo – small cluster of cells
o Globular embryo – sphere of cells that develops during cell division
 Cells begin to develop into specialized tissues during this stage
 When the eudicot embryo starts to develop its two cotyledons, it has two lobes and resembles a heart
o During the torpedo stage, the embryo continues to grow as the cotyledons elongate
o As the embryo enlarges, it often curves back on itself and crushes the suspensor

Front 8

• The mature seed contains an embryonic plant and storage materials

Back 8

o Seed coat – tough and protective that surrounds a mature seed
o Integuments – outermost layer of an ovule
o Radicle – short, embryonic root
o Cotyledons – seed leaves
 Monocots – one
 Eudicots – two
o Hypocotyl – short portion of the embryonic shoot connecting the radicle to one or two cotyledons
o Plumule – shoot apex, or terminal bud, located above the point of attachment of the cotyledons
o Dormancy – temporary state of arrested physiological activity
o Germinate – the plant sprouts and the embryo resumes growth
o Must be nourished during germination until it becomes photosynthetic
o Cotyledons of plants function as storage organs and become large, thick, and fleshy as they absorb the food reserves

Front 9

• Fruits are mature, ripened ovaries

Back 9

o Can contain one or more seeds
o Fruits provide protection for the enclosed seeds and sometimes aid in their dispersal

Front 10

o Simple fruits

Back 10

develop from a single ovary which may consists of a single carpel or several fused carpels
 May be fleshy or dry

Front 11

 Berry

Back 11

simple, fleshy fruit in which the fruit wall is soft throughout [tomato]

Front 12

 Drupe

Back 12

simple, fleshy fruit in which the inner wall of the fruit is a hard stone [peach]

Front 13

 Follicle

Back 13

simple, dry fruit that splits open along one suture to release its seeds; fruit is formed from ovary that consists of a single carpel [milkweed]

Front 14

 Legume

Back 14

simple, dry fruit that splits open along two sutures to release its seeds; fruit is formed from ovary that consists of a single carpel [green bean]

Front 15

 Capsule

Back 15

simple, dry fruit that splits open along two or more sutures or pores to release its seeds; fruit is formed form ovary that consists of two or more carpels [iris]

Front 16

 Caryopsis

Back 16

simple, dry fruit in which the fruit wall is fused to the seed coat [wheat]

Front 17

 Achene

Back 17

simple, dry fruit in which the fruit wall is separate from the seed coat [sunflower]

Front 18

 Nut

Back 18

simple, dry fruit that has a stony wall; is usually large; does not split open at maturity [oak]

Front 19

o Aggregate fruit

Back 19

fruit that develops from a single flower with several to many pistils
 Ex. blackberry

Front 20

o Multiple fruit

Back 20

fruit that develops from the ovaries of a group of flowers
 Ex. mulberry

Front 21

o Accessory fruit

Back 21

fruit composed primarily of nonovarian tissue
 Ex. Apple

Front 22

• Seed dispersal is highly varied

Back 22

o Wind
 Winged fruits
 Light, feathery plumes
o Spines and burrs that attach to the fur of animals and falls off as the animal moves about
o Fleshy, edible fruits that go through the digestive systems of animals unharmed
o Some are dispersed because squirrels and birds bury the seeds for winter use and many are never retrieved
o Ants bury the seeds they harvest while the plant provides food to the ant
o Explosive dehiscence – the fruit bursts open suddenly and quite violently, forcibly discharging its seeds

Front 23

• Germination

Back 23

the process of a seed sprouting
• No seed germinates unless it has absorbed water

Front 24

• Imbibition

Back 24

the absorption of water by a dry seed

Front 25

• Each species has an ideal temperature at which the germination percentage is highest
• Some seeds do not germinate immediately

Back 25

o Many seeds are dormant because certain chemicals are present or absent or because the seed coat restricts germination
o Scarification – the process of scratching or scarring the seed coat before sowing it [passage through the digestive tract of an animal]

Front 26

• Eudicots and monocots exhibit characteristic patterns of early growth

Back 26

o The first part of the plant to emerge from the seed is the radicle [embryonic root]
o The shoot is next to emerge
o Coleoptile – special sheath of cells that surrounds and protects the young shoot

Front 27

• Rhizome

Back 27

horizontal underground stem that may or may not be fleshy
o Fleshiness indicates that the rhizome is used for storing food materials
o Frequently branch in different directions
 Over time, the old portion of the rhizome dies and the two branches separate to become distinct plants
o Some produce tubers [fleshy underground stems enlarged for food storage]

Front 28

• Bulb

Back 28

modified underground bud in which fleshy storage leaves are attached to a short stem
o Frequently forms axillary buds that develop into small daughter cells [bulblets]
o When the parent bulb dies and rots away, each daughter cell can become established as a separate plant

Front 29

• Corm

Back 29

short, erect underground stem that superficially resembles a bulb
o Corm’s storage organ is a thickened underground stem
 Axillary buds frequently give rise to new corms
 The death of the parent corm separates these daughter corms which then become established as separate plants

Front 30

• Stolons/runners

Back 30

horizontal, aboveground stems that grow along the surface and have long internodes
o Buds develop along the stolon and each bud gives rise to a new shoot that roots in the ground
o When the stolon dies, the daughter plants live separately

Front 31

• Suckers

Back 31

aboveground shoots that develop from adventitious buds on roots
o Each sucker grows additional roots and becomes an independent plant when the parent plant dies

Front 32

• Apomixes is the production of seeds without the sexual process

Back 32

o Allows sterile plants to reproduce and therefore survive
o seeds and fruits produced by apomixes can be dispersed by methods associated with sexual reproduction

Front 33

A Comparison of Sexual and Asexual Reproduction

Back 33

• Sexual reproduction results in genetic variation in the offspring
• Asexual reproduction renders identical offspring to the parent
• Sexual reproduction is usually accompanied by high death rates among offspring