Overview of Plants & Plant Structure Botany: Part I Overview of Plants & Plant Structure This is the first in a series of four PowerPoints for the AP Biology Redesign Botany Unit.

The Study Of Botany Derives Components From Each Of The Four Big Ideas In Biology Big Idea 1: The process of evolution drives the diversity and unity of life Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow to reproduce & to maintain dynamic homeostasis Big Idea 3: Living systems store, retrieve, transmit, and respond to information essential to life processes Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties. Big Idea 1: Land plants evolved from algae. The selective pressures of living and reproducing on land drove the evolution of plants from simple nonvascular plants to modern flowering plants. Big Idea 2: Many examples of plant concepts reside here: photosynthesis; C and N cycles; role of cell walls; respond to changes in environment; homeostasis; immune responses; timing of seed germination; phototropism; photoperiodism Big Idea 3: Communication between plant cells via plasmodesmata and/or plant hormones; sexual reproduction in plants (details of each cycle not required) Big Idea 4: Organelles interact, including plant specific ones – chloroplasts, central vacuoles; interactions between organ systems (root, stem and leaf); food chains and webs; primary productivity; plants as invasive species; affect of diseases on plants, especially on native species vs. invasive ones.

Characteristics of Land Plants Eukaryotic Autotrophs Cell Wall - cellulose Alternation of Generations Embryophytes – protected embryo Review the meaning of both eukaryotic and autotrophs, relating plants to photosynthetic organisms with chloroplasts. The cell wall composed of cellulose is specific to plants. Alternation of generations will be explained further, but is essentially the alternation between a haploid (gametophyte) and a diploid (sporophyte) generation. All land plants have a protected embryo at some stage in their life cycle.

Photosynthetic Autotrophs Students should have some prior knowledge of photosynthesis. This is a good time to see what they recall about the process.

Alternation of Generations Alternation of Generations is not specifically mentioned in the new Curriculum Framework, but it is clearly important to understanding how plants function and how they differ from other organisms. This is a generic slide representing a complex life cycle. It is important that students recognize where mitosis and meiosis occur and that gametophytes produce gametes and sporophytes produce spores. It is very helpful to have students draw their own representations of the alternation of generations in plants. It is also helpful to explicitly point out that plants do not produce gametes by meiosis, but rather use meiosis to produce haploid spores for the diploid sporophyte. Their haploid gametes are produced by mitosis within a haploid generation of the plant. It is also a good time to have students discuss, again, the importance of meiosis in producing genetic variety and its importance in evolution.

Alternation of Generations Key Haploid (n) Diploid (2n) Spore dispersal MEIOSIS Sporangium Mature sporophyte (2n) Sporangium Sorus Here we use the fern life cycle as a specific example of alternation of generations in plants. No specific plant life cycles are required knowledge on the AP exam, so do not feel you have to teach life cycles for mosses, ferns, gymnosperms and angiosperms. Feel free to insert a different example here if you prefer. Talk through the next three slides of the life cycle of a fern and allow the students to explain the sequence of the cycle to their neighbor. Here we start with a mature sporophyte (diploid) with sori (plural for sorus which is a cluster of sporangia) on the underside of its reproductive leaves. (You may want to have samples of sori on fern leaves to show your students.) In the sporangium, cells undergo meiosis and become haploid spores. When the sporangium matures it ruptures and the spores are released. A review of the meaning of diploid and haploid may be appropriate for your students. Fiddlehead (young leaf)

Alternation of Generations Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Rhizoid Underside of mature gametophyte (n) Sporangium Sperm Archegonium Mature sporophyte (2n) Egg Sporangium FERTILIZATION Sorus The released spores develop into photosynthetic gametophytes (n). Each gametophyte develops sperm-producing organs called antheridia and egg-producing organs called archegonia. Notice that only mitosis is occurring as these structures develop and produce gametes. The sperm use flagella to swim to eggs in the archegonia (challenge students to explain how this limits the range of habitats for ferns). When the egg and sperm unite upon fertilization, the diploid condition is restored. Fiddlehead (young leaf)

Alternation of Generations Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Rhizoid Underside of mature gametophyte (n) Sporangium Sperm Archegonium Mature sporophyte (2n) Egg New sporophyte Sporangium Zygote (2n) FERTILIZATION Sorus The zygote (2n) develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. Whether you are discussing fern, moss, roses, or pecan trees the general theme of alternation of generations remains the same. Gametophyte Fiddlehead (young leaf)

Four Groups Bryophytes Ferns Gymnosperms Angiosperms From the simplified phylogenetic tree, students should recognize that these four groups of plants are monophyletic, meaning there is a unique common ancestor that all four groups share amongst themselves that they do not share with any other organisms. They also show four evolutionary steps as plants moved from water onto land. (great examples of evolution producing adaptations to local environments; also examples of adaptive radiation)

Adaptations for Moving on To Land Prevention from dehydration-Evolution of waxy cuticle Method of gas exchange for photosynthesis-Evolution of stomata and lenticels. Method to obtain water and minerals-Evolution of roots Increase in size and support-Evolution of xylem fortified with lignin Method of reproduction without water-Evolution of pollen and pollination strategies. Method of protecting embryo from dehydration-Evolution of the seed Nonvascular land plants must live where water is readily available and will not be very tall due to the lack of vascular tissue. In these plants the sporophyte is nutritionally dependent on the gametophyte and remains attached.

Adaptations for Moving on To Land Prevention from dehydration-Evolution of waxy cuticle Method of gas exchange for photosynthesis-Evolution of stomata and lenticels. Method to obtain water and minerals-Evolution of roots Nonvascular land plants must live where water is readily available and will not be very tall due to a lack of vascular tissue. In these plants the sporophyte is nutritionally dependent on the gametophyte and remains attached. Graphics: http://www.squidoo.com/plants-lessons, http://en.wikipedia.org/wiki/Stoma, http://utsa.edu/sombrilla/fall2009/story/plastic-surgery-plants.html