Transcript Reproduction in Flowering Plants

Flowering Plants Reproduction
Chapter 35
Angiosperms
• The largest and most successful group of plants
• Can reproduce both sexually and asexually
• Advantages:
– Sexual – genetic variation
– Asexual – rapid and efficient
• Disadvantages:
– Sexual – requires time and energy
– Asexual – lack of genetic variation
Alternation of Generations
• Diploid sporophyte generation – larger
and nutritionally independent
– Produces haploid spores by meiosis
• Haploid gametophyte generation –
located in the flower; microscopic and
totally dependent on the sporophyte
– Gives rise to the gametes by mitosis
Flower structure
• Complete flowers:
– All four whorls
• Sepals (all together = calyx)
• Petals (all together = corolla)
• Stamen – male flower part
– Filament, anther
• Carpel (a.k.a. pistil) – female flower part
– Stigma, style, ovary
Pollination
• Self-pollination – within the same flower
or another flower on the same plant
• Cross-pollination – pollen grains travel to
another plant
– Insects, birds, small mammals, wind and
water can all serve as agents
Tricks to prevent inbreeding
• Self-pollination reduces genetic variation
and may concentrate ‘bad’ genes
• Incomplete flowers – separate male and
female flowers
• Timing variation – pollen is shed at a time
when stigma is not receptive
• Self-incompatibility – a plant has the
ability to identify and reject its own pollen
Coevolution
• Plants and their animal pollinators are
usually closely adapted to each other
– Colors, scents
• Animals may also have adaptations
– Physical features and even behavior
Fertilization
• Pollen grains lands on stigma
• One cell grows a thin pollen tube through the style to the
ovary
• The 2nd cell in the pollen grain divides to form 2 sperm
cells which travel down the tube to the ovule
• One sperm cell fertilizes the egg and form a zygote
• The other sperm cell joins with 2 polar nuclei and forms
a triploid endosperm which will nourish the embryo
• This process is called double fertilization
Seeds
• Contain an embryonic plant and food
stored in the cotyledons or endosperm
• Surrounded by a protective seed coat
• Germination – seed sprouts and relies on
stored food until leaves are functional
• Fruits are mature, ripened ovaries
Asexual reproduction
• Rhizome – horizontal, underground stem
that can branch in many directions
• Bulb – underground bud with thick leaves
that store food
• Runners – horizontal, aboveground stems
• Suckers – shoots that branch off of
underground roots