Bio 108 Plant organs: Structure and Function
1. What plant organ might you buy at the grocery store?
2. Structure-Function of various plant organs
3. Leaf arrangements Fig. 3.10
Alternate: 1 leaf at node
Opposite: 2 leaves at node
Whorled: 3 or more leaves at node
4. Simple vs. Compound leaves Fig. 3.10
A simple leaf has a single blade.
A compound leaf has a blade is divided in many little leaflets.
5. Seed plants
Seed plants are the predominant plants covering the land on the planet Earth.
There are two groups of seed plants:
Gymnosperms are naked seed plants. Seeds are NOT enclosed in an ovary
Example: a pine tree with cones. As scales on cones open, seeds drop out
Angiosperms are flowering plants. They are the only plants with flowers and fruits. Seeds are enclosed in an ovary which develops into a fruit. There are about 250,000 known species of angiosperms and thousands more are believed to exist.
6. Flowers Fig. 5.1-5.3
The structure of flowers consists of 4 whorls or rings with the following names, structures and functions. Going from the outside they are:
Sepals-supports the flower, protects unopened bud
Stamens-male part of the plant consisting of filament and anther which produce the sperm-containing pollen
Pistil-female part of the plant consisting of the stigma, style and ovary
Stigma is the top of the pistil to which the pollen sticks
Style is the supporting structure connecting the ovary and stigma
Ovary contains the ovules (eggs). The ovary develops into the fruit. Within the ovary there may be separate compartments called carpels such as the sections of a grapefruit.
a. Complete vs. Incomplete flowers
Complete flowers have all 4 whorls
Incomplete flowers are missing 1 or more whorls. Example: Grass does not have sepals or petals.
b. Perfect flowers vs. Imperfect flowers
Perfect flowers have both male (stamen) and female (pistil) structures within the same flower like a petunia.
An imperfect flower has only stamens or pistils but not both. They could be separately located on the same plant like in corn where the tassel (male structure) is on the top and the ear (female structure) is in the middle of the plant. Alternately, there could be separate male and female plants, for example, persimmon, spinach, asparagus, marijuana.
7. Pollination of flowers Fig. 5.9
Transfer of pollen from anther to stigma is pollination.
Wind vs. animal pollination:
Wind: lots of pollen, non-showy flowers
Animals: insects, birds, bats get sugary liquid called nectar from flowers. Pollen sticks to their body and gets carried to the next flower.
8. What is the benefit of having a specific pollinator vs. a general pollinator?
The benefit of a very specific pollinator like hummingbird is that the bird is more likely to feed on the same species depositing the pollen. The downside is that if the pollinator species declines, no other animal may be able to pollinate that plant.
9. Fertilization of flowers Fig. 5.8
The actual union of egg and sperm is fertilization. Double fertilization occurs in angiosperms. Two sperm cells move out of the pollen grain down a pollen tube to the ovary. One sperm combines with the egg to fertilize it. The second sperm cell combines with a cell in the ovary to form the endosperm. The endosperm is food for the developing fertilized egg.
10. Fruits Fig. 6.1
Fruits are only found in angiosperms. The ovary at the base of the flower develops into a fruit.
A fruit is a ripened ovary containing seed(s).
Function of fruit:
Seeds (fig. 6.2):Seeds contain the embryo (developing plant) and endosperm (food for the embryo) in a seed coat (hard shell)