Levels of organization of plants
Plants have adapted to live on land by:
- developing waxy cuticles to help prevent desiccation.
- developing stomatas which allow for gas exchange through the cuticle
- developing vascular tissue that can move water & nutrients around the plant (xylem & phloem)
- developing seeds that will help protect the embryo from being damaged
Cells
Plants first evolved from algae. The three types of algae are brown algae (Phylum Heterokonphyta), red algae (Phylum Rhodophyta), and green algae (Phylum Chlorophyta). Specifically, plants evolved from multicellular green algae. There are three forms of green algae: unicellular, colonial, and multicellular.
- Unicellular - very common in fresh water. These cells live independently from other cells.
- Colonial - live in long filaments or as colonial spheres. These cells do not depend on other cells, but they live next to them.
- Multicellular - These plants contain the same material in their cell wall as land plants (cellulose), indicating that they have similar DNA and a common ancestor.
Tissue
Pteridophytes were the first group of plants to have vascular tissue. Vascular tissue acts as "transport tubes" which move water and nutrients around the plant. This benefits the plant because it allows them to grow larger and taller, enabling them to out compete other plants for sunlight. Gymnosperm were the first type of plant to develop vascular tissue in their roots, allowing them to survive better without water in cooler and dryer environments.
- Xylem: transports water in the plant from roots to shoots.
- Phloem: transports nutrients from shoots to roots)
Organs
Male gametophyte:
In pteridophytes, gymnosperms and most angiosperm, the male and female gametophytes are located on the same plant (monoecious). The bryophytes are the only plant type that is always going to have two separate plants that have with the antheridium or the archegonium.
When the sperm fertilizes the ovum in the archegonium, the zygote grows inside the archegonium in all of the plant types. The sperm can be transferred to the archegonium from the antheridium by water, wind, or a vector, depending on the plant type.
- antheridium, haploid, produces sperm
- archegonium, haploid, contains the ovum
In pteridophytes, gymnosperms and most angiosperm, the male and female gametophytes are located on the same plant (monoecious). The bryophytes are the only plant type that is always going to have two separate plants that have with the antheridium or the archegonium.
When the sperm fertilizes the ovum in the archegonium, the zygote grows inside the archegonium in all of the plant types. The sperm can be transferred to the archegonium from the antheridium by water, wind, or a vector, depending on the plant type.
Organ Systems
Angiosperms have developed four main organ systems:
- Leaves: leave have stomata, that open when the guard cells absorb water, and close as the guard cells lose water. Stomata open usually happens in the day, but as the water gets used up from photosynthesis, the guard cells become flaccid, closing the stomata. Stomata close is at night, and as the guard cells absorb water throughout the night (because they are not preforming photosynthesis), the guard cells plump up becoming "bean shaped" and opening.
- Stems: Stems move material up and down the plant, can move the leaves of the plant so it gets the most sun, provide structure to the plant, and allow the plant to grow taller and wider.
- Roots: The main function of roots is to absorb nutrients & water from the soil, as well as anchor the plant to the ground.
- Flower: The main purpose of the flower is to attract a pollinator such as a bee. The flower is a modified leaf that has a sepal, petals, stamen (male) and carpel (female).