WHAT'S A PLANT • Plants are members of the kingdom plantae. Plants are photosynthetic multicellular eukaryotes - or PHOTOAUTOTROPHS. What about the venus flytrap? • Cell walls are made of CELLULOSE - the material that bacteria and protists in our small intestine digest for us. Cellulose is a kind of complex sugar or polysaccharide. • Although cellulose plays an important role in structural support in the cell walls of plants, cellulose is found in other forms - such as cotton. • The green of plants comes from their photosynthetic pigments (chlorophyll a & b)
LIFE CYCLE OF PLANTS • The life cycle of plants has two different phases. This is called; ALTERNATION OF GENERATIONS. In this alternation of generations, the plant takes turns undergoing mitosis and meiosis to produce haploid (n) and diploid (2n) gametes. • The diploid (2n) phase is called the sporophyte- or spore producing plant. The haploid (n) phase is called the gametophyte - or gamete producing plant. • The spores are haploid (n) and produced thru meiosis in the sporophyte plant - each spore can grow into a new plant; the gametophyte! • A gamete is a reproductive cell produced by mitosis and fuses during fertilization with another gamete to produce a new individual - the diploid sporophyte.
WHAT A PLANT NEEDS • SUNLIGHT • WATER & MINERALS • GAS EXCHANGE • MOVEMENT OF WATER & NUTRIENTS
HISTORY • Plants didn't exist for most of the Earth's history. Life was mainly found in the oceans, lakes and streams. • Only after photosynthetic prokaryotes (cyanobacteria) and algae put oxygen in the atmosphere, did the conditions on Earth become favorable for other forms of life to evolve and therefore, to move onto land. • The first plants are thought to have evolved from plantlike-protist, the green algae. "From these pioneers, several major groups of plants evolved." (Miller, 555) • 1. Mosses and their relatives • 2. The other lineage gave rise to all the other plants found today. • Botanists divide plants into four major groups depending on three main characteristics: water-conducting tissue, seeds, & flowers.
BRYOPHYTES • "In the cool forests of the northern woods, the moist ground is carpeted with green. When you walk, this soft carpet feels spongy. Look closely and you will see the structure of this carpet - mosses. • Mosses and their relatives are generally called bryophytes, or nonvascular plants. Unlike all other plants, these organisms do not have vascular tissues, or specialized tissues that conduct water and nutrients." (Levine, 556) • Groups of bryophytes: mosses, liverworts, and hornworts
SEEDLESS VASCULAR PLANTS • Ferns, club mosses, and horsetails • Because bryophytes can only transport water from cell to cell, their height and overall size were limited to a few centimeters. Around 420 m.y.a., something remarkable happened. The little mosses were joined by plants that were up to a meter tall. • The first vascular plants had a new type of cell that was specialized to conduct water. TRACHEIDS. This was a revolutionary adaptation in the plant kingdom. • These cells are key in xylem - a water transport system that carries water up the plant from the root. And phloem - which transports solutions of nutrients and carbohydrates produced by photosynthesis.
SEED PLANTS: Gymnosperms (cones) & Angiosperms (flowering plants) • "Whether they are acorns, pine nuts, dandelion seeds, or kernels of corn, seeds can be found everywhere. Seeds are so common that their importance may be overlooked. Over millions of years, plants with a single trait - the ability to form seeds - became the most dominant group of photosynthetic organisms on land." (Levine, 564) • REPRODUCTION FREE FROM WATER • Like all plants, seed plants have an alteration of generation life cycle. Unlike mosses and ferns, seed plants do not need water for fertilization of gametes. • Adaptations that allow plants to reproduce without water are flowers and cones. • Pollen: male gametophyte / Seed: embryo of a living plant that is encased in a protective covering and surrounded by food.
GYMNOSPERMS - CONE BEARERS • These are the most ancient surviving seed plant. This group includes the gnetophytes, cycads, ginkgoes, and conifers. • These plants all reproduce with seeds that are exposed - gymnosperm means naked seed.
Cycads • Cycads: beautiful palm-like plant that reproduce with large cones. Huge forests of cycads thrived when dinosaurs roamed Earth. Today only nine genera exist.
Ginkgoes • These plants were common when the dinosaurs existed, but today there is only one species left. Carefully cultivated in China.
Conifers • Conifers: more than 500 known species. This group includes the pines, spruces, firs, cedars, sequoias, redwoods, junipers, and yews. Some conifers like the bristlecone, can live for up to 4000 years. Other species like the giant redwoods, can grow to more than 100 meters in height. Most conifers are evergreens - that is, they retain their leaves throughout the year.
ANGIOSPERMS - FLOWERING PLANTS • "...First appeared about 135 m.y.a... Angiosperms develop unique reproductive organs known as flowers. In general, flowers are an evolutionary advantage to plants because they attract animals such as bees, moths, or hummingbirds, which then transport pollen from flower to flower. This is much more efficient than the wind pollination of gymnosperms." (Levine, 569) • Flowers contain ovaries which surround and protect the seeds. The presence of an ovary gives angiosperms their name which mean enclosed seed. • The unique angiosperm fruit - a wall of tissue surrounding the seed - is another reason for the success of these plants. Why?
DIVERSITY: MONOCOTS & DICOTS (number of seed leaves - cotyledons - in plant embryo) • A cotyledon is the first leaf or the first pair of leaves produced by the embryo of a seed plant. • There are other differences. What are they?
WOODY vs. HERBACEOUS • ANNUALS (completion of one life cycle in one season) ~ wheat • BIENNIALS (completion of one life cycle in two seasons) ~ parsley & celery • PERENIALS (live for more than two years) ~ asparagus, grasses, palms, maple trees.