1. Reproduction in Angiospermophytes
Topic 9.3

2. Assessment Statements
9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower Distinguish between pollination, fertilization and seed dispersal Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed Explain the conditions needed for the germination of a typical seed Outline the metabolic processes during germination of a starchy seed Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.

3. Flowers Reproductive structures of angiospermophytes
Dependent upon animals for pollination
Can grow as large as 3 feet in diameter and weigh as much as 14.5 lbs.
Rafflesia arnoldii
When mature, this flower smells like rotting meat thus attracting flies that transfer pollen from the male reproductive structures to the female structures

4. Flower structure and function
Flower part
Function
Sepals
Protect the developing flower while in the bud
Petals
Often are colorful to attract pollinators
Anther
Part of stamen which produces the male sex cells, pollen
Filament
Stalk of stamen that holds up the anther
Stigma
Sticky top of carpel on which pollen lands
Style
Structure of the carpel that supports the stigma
Ovary
Base of carpel in which the female sex cells develop

5. Carpel (entire female part)
Stamen (entire male part)
Complete – contain sepals, petals, stamen, and carpal
Incomplete – lack at least one part
Staminate – have only stamens
Carpellate – have only carpels

6. Alternation of generations
All plants show two different generations in their life cycle:
Gametophyte generation which is haploid
Sporophyte generation which is diploid
Gametophyte generation produces plant gametes by mitosis
Sporophyte generation produces spores by meiosis
For example, a cherry tree is in the sporophyte form (it grew from a zygote and produces new cells by mitosis). When the cherry tree produces flowers, haploid spores are formed and develop into haploid bodies referred to as gametophytes. Sperm form within the male gametophytes, and eggs form within the female gametophytes.

7. Pollination
Process by which pollen (containing male sex cells) is placed on a female stigma
First step towards fertilization and the production of seeds
Common vectors: wind, insects, birds, water, and other animals
Means of attraction
Red flowers are conspicuous to birds
Yellow and orange flowers are noticed by bees
Heavily scented flowers are easily found by nocturnal animals
Plants that rely on wind have inconspicuous, odorless flowers

8. Types of pollination Self-pollination Cross-pollination
Pollen from the anther of the same plant falls onto its own stigma
Form of inbreeding and results in less genetic variation within a species
Pollen is carried from the anther of one plant to the stigma of a different plant
Increases variation and may result in offspring with better fitness
Problem: distance

9. Fertilization
Pollen grain adheres to the stigma, which is covered by a sticky, sugary substance
Pollen germinates to produce a pollen tube
Pollen tube grows down the style of the carpel
Within the growing pollen tube is the nucleus that will produce the sperm
Pollen tube completes its growth by entering an opening at the bottom of the ovary
Sperm moves from the tube to combine with the egg of the ovule to form a zygote
Zygote develops with the surrounding tissue into the seed
As the seed is developing, the ovary around the ovule matures into a fruit
The fruit encloses and helps to protect the seed

11. The seed (means by which an embryo can be dispersed to distant locations)
Seed part
Function
Testa
Tough, protective outer coat
Cotyledons
Seed leaves that function as nutrient storage structures
Micropyle
Scar of the opening where the pollen tube entered the ovule
Embryo root (radicle) and embryo shoot (epicotyl)
Become the new plant when germination occurs
Plumule will become first leaves.
Hilum is where the seed was attached to the ovary.
Endosperm provides nutrition for growing embryo.

12. Maturation
Dehydration until water content of the seed is about 10% - 15% of its weight
Seed enters dormancy (low metabolism, not growth or development)
Adaptation to overcome harsh environmental conditions
Conditions needed for germination:
Water
Oxygen for aerobic respiration
Appropriate temperature for enzyme action
Other (testa disrupted, fire exposure)
Most will not become a functional plant so plants produce large numbers of seeds

14. Seed metabolism during germination
Uptake of water
Gibberellin is released
Gibberellin (growth hormone) triggers the production of the enzyme amylase
Amylase causes the hydrolysis of starch into maltose. The starch is present in the seed’s endosperm
Maltose is further hydrolyzed into glucose that can be used for cellular respiration or may be converted into cellulose by condensation reactions.
Cellulose is then used to produce the cell walls of new cells being produced

15. Control of flowering in angiosperms
Photoperiodism – plant’s response to light involving the relative lengths of day and night (a very important factor in the control of flowering)
A plant must flower when pollinators are available and when necessary resources are plentiful.
Plant-type
Flowering and light
Examples
Long-day plants
Bloom when days are longest and nights shortest (midsummer)
Radishes, spinach, lettuce
Short-day plants
Bloom in spring, late summer, and autumn when days are shorter
Poinsettias, chrysanthemums, asters
Day-neutral plants
Flower without regard to day length
Roses, dandelions, tomatoes

16. Phytochrome
Phytochrome is a photoreceptor, a pigment that plants use to detect light.
There are two forms: Inactive (Pr) and active (Pfr)
When red light (wavelength of 660 nm) is present in available light, the inactive form Pr is converted into the active form Pfr which has the ability to absorb far-red light (wavelength of 730 nm).
This Pfr is rapidly converted back to the inactive form in daylight.
However, in darkness, the conversion is very slow.
It is thought that this slow conversion of Pfr back to Pr allows the plant to time the dark period.

17. In long-day plants, the remaining Pfr at the end of a short night stimulates the plant to flower. In this case, Pfr acts as a promoter
In short-day plants Pfr appears to act as an inhibitor of flowering. For these short-day plants, enough Pfr has been converted to Pr to allow flowering to occur.
Even though the names refer to day length, it is actually the length of night that controls the flowering process.