Download Structure and Evolution of Flowers

Structure and Evolution of
Flowers
42.3
Learning Objectives
1. List the parts of a flower
2. Distinguish between bilateral and radial
symmetry
3. Differentiate between microgametophytes
and megagametophytes
Flower Evolution
● Flowers evolved in Angiosperms
● Flowers evolved from leaves
● Floral diversity is result of natural selection
of pollination strategies
● Flowers and pollinators have co-evolved
Flower Morphology
4 parts (whorls)
1. Calyx
● outermost whorl
● made of sepals
● protect the bud
2. Corolla
● 2nd whorl
● made up of petals
● petals attract pollinators
3. Androecium (Male Parts)
● 3rd whorl
● Stamen
○ male portion of the flower
○ 2 parts
■ Filament
●
stalk that bears the anther
■ Anther
●
●
group of 4 microsporangia
produce pollen (sperm spores)
4. Gynoecium (Female Structures)
● 4th innermost whorl
● known as the Carpel
○ composed of:
■ stigma
■ style
■ ovary
■ ovule
Function of the Carpel Parts
Stigma
● sticky structure that attaches pollen
Style
● slender tube that connects stigma and ovary
Ovary
● contains ovules and develops into the fruit
Ovule
● eggs that will develop into seeds when fertilized
Floral Specialization
Complete Flower
● has all 4 whorls present in the flower
Incomplete Flower
● lacks 1 or more whorls
Or
● whorls have fused together
Monocot vs. Dicot
MONOCOTS
DICOTS
Embryo with single cotyledon
Embryo with two cotyledons
Pollen with single furrow or pore
Pollen with three furrows or pores
Flower parts in multiples of three
Flower parts in multiples of four or five
Floral Symmetry
1. Radial Symmetry
● primitive flowers
● can divide the flower in half by drawing a
line through the center anywhere
2. Bilateral Symmetry
● more advanced flower groups
○ flowers with precise pollination
systems
● can only be divided along 1 line
Alternation of generations
Microgametophyte= male gametophyte
● pollen grains
Megagametophyte = female gametophyte
● embryo sac
Sporophyte = fertilized egg (seed)
Process of Pollination
Steps:
1. pollen is transferred from anther to the
stigma (pollination)
2. pollen tube grows down into ovule
3. sperm fertilizes the egg (fertilization)
4. ovule develops into seed
5. ovary develops into fruit
Self-pollination