Pollination:
the transfer of pollen from an anther to a stigma.
 |
What is a monoecious plant? |
Review pollination
Alternation of generations: the alternation between diploid and haploid cells or organisms. In most lower plants, up to and including ferns, the gametophyte (haploid) and sporophyte (diploid) generations are separate, independent, free-living plants. In flowering plants, through evolution, the gametophyte generation has become reduced to just a small group of haploid cells, enclosed within the flower and completely supported by the diploid parent plant. In Angiosperms, the male gametophyte generation takes place in the anther. The final product of this generation is the pollen grain.
Formation of pollen grains
Angiosperms form sperm cells in the anthers of the flower.
The process is:
- The diploid microspore mother cells undergo meiosis to produce 4 haploid microspores.
- The nucleus in each of these microspores divides once by mitosis to produce a pollen grain
with two haploid cells. This pollen grain is the male gametophyte.
- One of the cells of the pollen grain contains the tube nucleus which enables the pollen tube to grow down the style of the flower to the ovule. The other cell of the pollen grain, the generative cell, divides mitotically to form 2 haploid sperm.
During pollination, a pollen grain lands on the stigma where the pollen is stimulated to germinate, producing a pollen tube that grows through the style to the egg in the ovule. While pollination and fertilization are different processes, the two are very closely related.
Self-pollination vs Cross-pollination: 
While it is possible for some plants to pollinate their own flowers, this is not ideal because the inbreeding limits them genetically. Many plants will have some factor that promotes cross-pollination between individuals of the same species.
- Dioecious plants achieve cross-pollination by the very nature of their structure. No self-pollination is possible because an individual plant will produce pollen only or carpels only.
- Monoecious plants have staminate and carpelate flowers on the same plant. Cross-pollination can be achieved by having the stamens or carpels mature prior to the reciprocal structure maturing in perfect flowers.
- Protandrous flowers produce pollen prior to the carpel of the same flower becoming able to receive pollen.
- Protogynous is the reverse situation where the carpel receives pollen from stamens of different flowers because the stamens of that flower have not produced mature pollen.
- Physical separation of stamens from stigmas can help prevent self-pollination when the structures mature at the same time.
- Some species are genetically designed so that pollen from the same flower, or from other flowers on the same plant, cannot cause fertilization. This design, known as self-incompatibility, ensures that seed production results only from cross-pollination.
- Heterostyly is a genetically determined combination of morphological and physiological mechanisms promoting cross-pollination in some insect-pollinated plant families. The two types of flowers have a complementary form: each tends to deposit pollen on the part of the pollinator's body that comes in contact with the stigma of the opposite type of flower. The two types are cross-compatible, but pollen of each type is usually unable to fertilize other individuals of that type. The situation is somewhat analogous to separate sexes, except that each individual is capable of producing offspring.
In some species self-pollination is the norm despite the genetic benefits of cross-pollination. This situation may be desirable where a given genotype is particularly
adapted to an environment. Another advantage is the lack of dependence for pollination agents.
Day 3
|
How do plants get animals to pollinate their flowers? |
Types of pollen:
Pollen grains have species specific shapes. The shapes usually have a function in the way the pollen is distributed. These websites have pictures of pollen identified.
Botanical Society of America
Tulsa Pollen HomePage
pollen . com
Pollen distribution:
- Wind pollination: is a good strategy when many plants are close together. The grasses and most temperate zone deciduous trees are pollinated by wind. Wind pollination is a much less efficient method than pollination by animals. Therefore, in order to reproduce successfully, wind-pollinated plants must produce a great deal more pollen than animal-pollinated plants.
- Flowers are usually small and do not produce nectar.
- Pollen is simple and light weight.
- Corn pollination is accomplished by wind.
- Animal pollination: depends on animal "vectors" being attracted to the flower. In general, animals are attracted to a flower by some reward. Nectar provides a carbohydrate energy source and pollen is rich in protein.
- Flowers are usually large and showy, and produce a fragrant nectar to attract animal pollinators.
- Pollen is large and often has a complex shape.
- Flower characteristics help determine the type of animal vector.
- Bees tend to visit flowers whose petals form a wide surface for landing.
- Butterflies tend to visit flowers whose petals form a protective cup or tube.
- Moths are pollinators of flowers that are open at night. They tend to find flowers that are light colored and have a strong, sweet scent.
- Beetles are attracted to dull colored flowers with a spicy smell.
- Flies are pollinators for some specialized flowers that may be dull, green, and have a foul odor.
- Hummingbirds perfer red and orange flowers that are tube shaped.
Day 4
|
What is the scientific name of a honey bee? |
On your own:
- Learn more about honey.
- How much honey does a bee make in their lifetime?
- How many flowers must be visited to make a pound of honey?
- How many flowers does a honey bee visit during one collection trip?
- How many sides does each honeycomb cell have?
- Honey as a food.
- How many grams of water are in 100 grams of honey?
- What vitamin is found in the highest amount in honey?
- What mineral is found in the highest amount in honey?
- There are several types of sugar in honey. Which sugar is found in the highest percentage?
- Learn about honeybees.
- What is the scientific name of a honey bee?
- What is the average lifespan of a queen bee?
- How long do worker bees live in the summer?
- Melittin makes up 50% of the venom in a bee sting. What does melittin do to the human body?
- Melittin is not the major source of pain from a bee sting. What chemical in the venom is responsible for most of the pain?
Research Links:
Monoecious plants have both male and female flowers on the same plant.
Plants must provide an incentive to get animals to pollinate their flowers.
This incentive is usually in the form of foods such as nector.
The scientific name of a honey bee is Apismellifera scutellata.
with two haploid cells. This pollen grain is the male gametophyte.
to grow down the style of the flower to the ovule. The other cell of the pollen grain, the generative cell, divides mitotically to form 2 haploid sperm.