Plants are multicellular autotrophs that can be classified as a angiosperm or gymnosperm.
- A Vascular Plant: Contains a vascular system (xylem and phloem)
- Contains a well-protected seed package
- Are tall in height
- Performs alternation of generations
- Reproduction no longer requires water
- Fertilization occurs through air and or animals vectors
Examples of Gymnosperms
- Cycads (Cycadophyta)-Palmlike plants of the tropics. Very Tall (15-25 meters)
- Gnetophytes (Gnetophyta)- Desert plant that has two strap like leaves.
- Conifers (Coniferophyta)- Most abundant. Needle like leaves (Pine Trees)
- Ginko (Ginkgophyta)- Maidenhair tree. Contain sex linked chromosomes
Reproduction of Gymnosperms
I am going to use a tree for this example (conifera). During this conifer’s life span it will undergo alternation of generations which is the changing of sex from male to female.
Gymnosperm produces seeds that are called heterosporous, meaning that the seed produces two type of spores. One becoming a male gametophyte and one becoming a female gametophyte.
The plant/tree contains both pollen and eggs. (male and female)
Now let’s go over some terms…
Sporophyte- A multicelluar diploid plant that undergoes alternation of generation to produce haploid spores.
Microsporophyll- Houses the microsporangia.
Microsporangium- Spores of a heterosporous plants that undergoes mitosis to produce male gametophytes
Microgametophytes- The pollen grains that were process through meiosis in the microsporangium.
Megasporophyll- Houses the megasporangium.
Megasporangium- Spores of a heterosporous plants that undergoes mitosis to produce female gametophytes (megaspores).
Megagametophyte- The female gametophyte that arises from a megaspore of a heterosporous plant
1. The gymnosperm and in this case the conifer, produces a ovulate cone (megasporophyll) and a pollen cone (microsporophyll).
- The megasporophyll (ovulate cone) contains the megasporangium which is surrounded by layers of sporophyte tissues called integument. In side the megasporangium are the ovules.
- The microsporophyll (pollen cone) contains the microsporangium which contains the pollen.
2. Meiosis occurs in the microsporangium which then produces pollen grains (micro gametophytes)
- The microgametophytes are protected with in the tough exterior of the pollen cone
3. The entire microgametophyte reaches the mega gametophyte by the help of animals or wind.
4. When the microgametophytes (pollen) reaches the megasporophyll, micro gametophyte produces an elongate structure (pollen tube) that grows to the megaspore (female egg). Sperm are transferred directly through this tube to the megaspore. The advantage of this process is that sperm do not have to swim long distances and they do not need water.
5. Now the two haploid cells are now a diploid or a zygote. Now the seed is protected by the exterior coat and has nourishment of an embryo. When Conditions are favorable, the seed will germinate.
Here is an overview of this…
Diploid/Sporophytic (2 sets of chromosomes)-> Meiosis (# of sets of chromosomes cut in half)-> Haploid/Gametophytic-> Fertilization-> Zygote-> Diploid
Characteristics-Reproduction of Angiosperms
Angiosperms are vascular plants that has seed bearing fruit ovaries.
So.. When you think of a angiosperm, think of a flower.
Female Parts: Pistil
The Pistil contains: Stigma- The superior knoblike structure on the stigma
Style- The tube like structure that connects the stigma to the ovary
Ovary- Usually inferior, contains the ovules, the female eggs
Male Parts: Stamen
The Stamen contains: Anther- Is the tip of the filament that produces pollen
Filament- Is the slender structure that supports the anther
How Fertilization Occurs
- Pollen from the anther travels to the stigma. This can be done by either cross fertilization or self fertilization. Cross Fertilization- This may be done by wind, water, or animals (more specifically insects). Self fertilization- which is the fertilization of the organism with itself. The organism’s pollen being transfer on its own stigma.
- Pollen grows a tube structure down into style. The pollen actually germinates and develops into a pollen tube. This tube will attach to the ovaries and fertilize it.
- The pollen tube carries several nuclei that travel down the pollen tube.
- Pollen nuclei joins with ovaries and fertilization has occurred
- When conditions are favorable, germination will occur
Insect fertilization of Angiosperms:
Pollen is “accidentally” transfer from the insect’s body to the stigma.
- Bees: Guides towards nectar, main target is nectar.
- Butterflies: Attracted to the sweet smell of flowers
- Flies: Attracted to flowers that have a smell of rotten flesh
- Moth: Attracted to white and a Fragrance
- Bats: Copious of nectar, smells like fruit.
- Birds: Attracted towards red and a tubular corolla
Gymnosperm Fertilization Angiosperm Fertilization
1. Pollination: Wind born 1. Pollination: Carried by animals
2. Seed Protection: On the surface of
the leaf 2. Seed Protection: Inside a chamber
3. Seed Dispersal: Mostly by Wind 3. Seed Dispersal: Varies
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