gymnosperms. gymnosperms are vascular plants that produce cones
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Gymnosperms
Gymnosperms are vascular plants that produce cones.
Their seeds have a protective seed coat and a food supply for the embryo.
Seeds are also “Naked” – the seeds are exposed and not enclosed in a fruit
Unlike the mosses and ferns, Gymnosperm sporophytes grow within the gametophyte structures and not independently.
1. Division Ginkgophyta – Ginkgo Only one species is still living. The
Maidenhair tree. (Also known as the silver apricot or ginkgo)
Leaves are fan-shaped. They are Dioecious – male and female
cones are produced on different plants. (females have seeds that stink but are edible)
2. Division Cycadophyta - Cycads Grow to be about 15 feet tall, with an un-
branched stem. They are pollinated by beetles instead of
wind, because their pollen is to large to travel in the air.
They are dioecious. Male and Female cones are huge, with
some species measuring up to 3’ 3” and weighing over 100 pounds. The female cone is covered in wooly hair.
3. Division Gnetophyta Have vessels in their xylem, which is
unique to gnetophytes.3 Genera:
A. Ephedra – Theyooze a sticky fluid to catch pollen. The leavesturn brown shortly afterappearing. They haveribbed stems.
B. Gnetum – Vine-like broad leaves found in South America, Africa and Southeast Asia.
C. Welwitschia - only one species, found in Southwest Africa. Only two leaves per lifetime. Can grow for 100 years, by surviving off of the dew and condensation from fog.
4. Division Pinophyta Also called Conifers, because they produce
cones Ex.: Pine, Cedar,
Fir, Spruce The largest genus
of conifers is Pinus, with over 100
species.
Leaves are needle-like and in clusters called fascicles. These fascicles usually have between 2 and 5 leaves.
Pinophytes can survive harsh environments, including low temperatures and high wind areas.
The fascicles absciss (fall off) within 2 to 5 years of maturity.
They are “evergreen” because there is always some leaves on a evergreen tree.
They have resin canals, which are tubes lined with special cells that secrete resin/sap. The resin is used to protect the tree from bacteria and fungus. It is also produced in response to injury.
Pines are considered softwoods because they do not have a thick cell wall.
Have large growth rings, due to rapid growth each season.
Bark is relatively thick. Redwoods have bark that is 2 feet thick.
They produce two kinds of Strobilior cone.1. Pollen cones – “ Male Strobili” –
are produced only in the spring They produce microsporangia at the
base of the cone that will develop into four microspores. These microspores develop into pollen grains.
Pollen grains are made of four cell with air space so that they can be transported by wind
2. Seed Cones – “ female Strobili” – these are the large, woody cones. The megasporangia are located within
the ovules and the megaspores are Produced at the base of the cone from the megasporangia.
The megasporangia, also, helps to create the nucellus which surrounds and encloses the integument which helps to form the seed coat. Within the integument there is a pore called the micropyle that helps to direct sperm to the egg.
The megasporangia produces 4 large megaspores produced by each cone. 3 of which quickly die off.
The remaining megaspore develops into the female gametophyte
As the female gametophyte develops it produces 2 to 6 archegonia.
Each archegonia contains one single large egg.
It takes several seasons for the seed cone to mature, but an immature cone can spread apart to allow pollen to enter.
When the pollen enters it sticks to the pollen drops which is a sticky fluid that will evaporate to pull the pollen to the micropyle.
After Pollination, the scales close-up to protect the ovules.
It takes about a month after pollination for the megaspores to mature and up to a year for the archegonia to develop.
The pollen grains are immature male gametophytes.
They produce a pollen tube that will grow and digest it’s way through the nucellus.
While the pollen tube grows, 2 of the 4 original cells enter the tube.
One of the 2 cells, generative cells, divides to form a spermatogenious and a sterile cell.
The spermatogenious cell then divides to form 2 sperm cells.
A mature male gametophyte is made of the pollen grain, the pollen tube, and the 2 sperm.
About 15 months after pollination, the pollen tube arrives at the egg to discharge all the contents.
1 sperm unites with the egg to form a zygote, the other sperm dies.
The zygote turns into a embryo that is nourished by the female gametophyte.
The embryo forms seeds with thin wings from the cone scales, that help the seed disperse.
When the seed is buried it forms a new young sporophyte or seedling.
Angiosperms
Angiosperms- Vascular plants that produce flowers
Angiosperm literally means “Vessel Seed.” The vessel is the carpel/pistils which is an enrolled leaf with seeds along the margins. These carpels are the female reproductive structure of the flower.
Seeds develop from the ovule and the ovary makes the fruit.
All Angiosperms are in Division Magnoliophyta.
Only 2 Classes:1. Magnoliopsidia – Dicots – 2 Cotyledons
2. Liliopsidia – Monocots – 1 Cotyledons
(Cotyledons are the seed leaves of the embryo, which store and help to make food.)
The members of the angiosperm group are very diverse. They include grasses, shrubs, trees, parasitic plants(live off of other organisms) and saprophytic plants ( live off of dead organisms).
The sporophyte stage is once again the dominant life cycle stage, just as in the gymnosperm
Heterospory- They produce two types of spores.
FEMALE: Female gametophytes are formed in the ovule
which is a part of the ovary that will develop into the seed. ( The ovary is found at the base of the pistil/carpel in a flower)
The megasporocyte undergoes meiosis within the ovule to form four megaspores, three quickly die.
The megaspore divides by mitosis until there are 8 nuclei, without any cell walls dividing the nuclei and the cell now becoming very large.
As the cell grows, the outer two layers form the integument which becomes the seed coat and a pore called the micropyle
The 8 nuclei form 2 groups on opposite ends of the cell.
Two nuclei fuse together in the middle to form the Central Cell Nuclei and cell walls form around the remaining nuclei.
On the end closest to the micropyle there is an egg and 2 synergids that are later destroyed.
The other end contains three antipodals, that have no known function and are also later destroyed.
The Female Gametophyte is made of a large sac of seven cells with 8 nuclei and is now called a megagametophyte
MALE: The male gametophyte is found in the
anther of the flower. There are four patches of tissue containing
the microsporocytes that each undergo meiosis to form a quartet of microspores.
These spores end up forming four pollen sacs in the anther, and as the anther matures the walls between the pollen sacs break down forming two larger sacs.
After undergoing meiosis, these two pollen sacs must undergo the following 3 things to develop into a pollen grain:1. The nucleus divides by mitosis once.
2. The members of each quartet separate.3. A two-layered wall develops around each microspore.
Once the pollen grain has formed, it contains an outer layer, exine, that contains chemicals that allow it to only pollinate the correct species.
Each pollen grain has a thin pore-like area called the aperature and two nuclei One of which, the spermatogenious nuclei, divides to form two sperm nuclei.
The mature male gametophyte is made up of the pollen grain and three nuclei, two sperm and one tube nuclei.
Pollination- Transfer of pollen from the Anther (male) to the Pistil (female)
Self-Pollination- Pollen is transferred to the pistil from the anther on the same plant.
Cross-Pollination - Pollen is transferred to the pistil from the anther on a different plant.
Fertilization- the combining of sperm and egg.
5 Main Pollinators:1. Bees2. Birds3. Bats4. Butterflies5. Beetles
Fertilization takes place after pollination and pollen has landed on the pistil.
The pollen grain absorbs part of the stigma, which is the top portion of the pistil, and the pollen tube comes out of one of the aperatures.
Once the tube reaches the micropyle, the pollen grain, which includes two sperm nuclei, discharges it’s contents into the tube.
The pollen tube grows until it reaches the female gametophyte, where it enters into the gametophyte, destroying the synergids and releasing it’s contents.
Pollen Tubes
Then Double Fertilization occurs. This process is unique to angiosperms and is also called double fusion.
During double fertilization two things occur:1. One sperm unites with the egg to form the zygote2. One sperm unites with the Central Cell Nuclei to form a 3N (3 sets of chromosomes) nutritive tissue, called the endosperm
In monocots, the endosperm forms the part of the seed in dicots, the endosperm provides nutrients to the embryo.
In both monocots and dicots the integument hardens and becomesthe seed coat
All the remaining nuclei are destroyed the ovule becomes the seed and the ovary matures into a fruit.
Embryo
Angiosperm Families
There are more than 300 angiosperm families.
Each family is distinguished from each other based on flower and fruit structures.
1. Buttercup- There are 1500 different species, their flowers have numerous stamens (male) and pistils (female) reproductive organs. Most are found in northern temperate and arctic regions.Ex. Buttercup, Columbine
2. Laurel - Made of 1000 species, without petals It is made of mostly tropical shrubs and trees.Ex. Bay Tree, Sassafras, Avocados
3. Poppy – Found North of the equator, are usually planted as ornamental plants and they all produce an alkaloidial drug.Ex. Bloodroot, Opium
Columbine Buttercup
Laurel
Avocado
Bloodroot
Opium
4. Mustard- They have four petals that are arranged to form a cross. Ex. Cabbage, Broccoli
5. Rose – Contains more than 3000 species. The non-reproductive parts of the flower are fused to form a cup.Ex. Fruits.
6. Legume – This is the third largest class with 13000 species.Ex. Peas, nuts, beans
Mustard
Rose
Legume
7. Spurge – Found in temperate regions. They are unisexual. They produce a milky latex and most are poisonousEx. Poinsettia
8. Cactus – They are native only to North America and are found in drier subtropical regions. Ex. cactus
9. Mint – Most produce an aromatic leaf and stem. Ex. Rosemary, thyme, sage, oregano
Spurge PoinsettiaChristmas Cactus Cacti
MintOregano Rosemary
Sage
10. Nightshade – Have over 3000 species that are herbs, shrubs, trees and vinesEx. Tomato, potato, eggplant
11. Carrot – Found all over the Northern hemisphere. Flowers tend to be small and numerousEx. Carrot
12. Pumpkin – found in tropical and subtropical regions. They are unisexual edible plants.Ex. Squash, pumpkin, watermelon
13. Sunflower – The 2nd largest family, with 20,000 species.Ex. Sunflower, Marigold, Lettuce
Nightshade Tomato Carrot Pumpkins & Squash Sunflower
1. Grass- The largest family in terms of individual plants. And the most widely distributedEx. Wheat, rye, barley
2. Lily – Have large flowers that usually have parts in multiples of 3Ex. Lily, daffodil
3. Orchid – The largest family in terms of individual species with over 35,000 species. Ex. Orchids
Wheat Rye Barley
Lily Calla Lily
Orchid