Friday, February 24th PLANTS!

Classification All plants fall into three major groups: – Nonvascular (bryophytes) – Seedless Vascular (tracheophytes) – Seeded Vascular (tracheophytes)

Bryophytes Lack of true stems and leaves Mosses and liverworts

Tracheophytes Have vascular tissue Xylem (water) and Phloem (food)

The Seeded Plants (2 types) Gymnosperms – woody plants, evolutionarily the oldest plants around. Ex: spruces, hemlocks, and firs. Perennials, live year after year. Can find the age by counting number of tree rings (which are dead xylem!)

This is actually dead xylem!

The Seeded Plants (2 types) Angiosperms – “flowering plants” Most varied and widespread Enclosed seeds within a fruit or nut Ex: oak, cherry, walnut Can be further divided into Monocots and Dicots

Monocots Single Cotyledon (embryonic seed leaf) Leaves with parallel veins Flower parts in multiples of three (3, 6, 9) Scattered vascular bundles (xylem and phloem) Fibrous root system Orchids and lilies

Dicots Two cotyledons (embryonic seed leaf) Broad leaves with netted veins Flower parts in multiples of 4 or 5 Vascular bundles (xylem and phloem) in a circle Taproot System Geraniums and Snapdragons

Monocot vs. Dicot

Alternation of Generation The plant will spend time as a diploid (2n) and a haploid (1n) Sporophyte – “spore plant” – the diploid generation (2n) Gametophyte – “gamete plant” - the haploid generation (1n)

Alternation of Generation STEP 1: Diploid Sporophyte produces haploid spores by meiosis – occurs in sporangia Spores are the first cells of the gametophyte generation. They divide by MITOSIS STEP 2: Gametes fuse, producing a diploid zygote (2n). This is the first stage of the sporophyte generation. Diploid zygote grows into a Sporophyte, which produces sprangia, which split into spores in meiosis…

Moss (bryophyte) life cycle Dominated by gametophyte (1n) stage

In Vascular Plants (tracheophytes) Dominated by sporophyte (2n) stage, gametophyte generation is reduced in size

The Cycle

Flowering Plants (angiosperms) Sepals – Green, leaf-like structures that enclose the flower and protect it when closed Petals – Colorful structures that attract pollinators to the flower Stamens – Male organs, at the ends of the stamen are anthers (site of meiosis and pollen development Carpel – Female organ, made up of the – (1) stigma, a sticky or feathery surface that receives pollen grains during pollination – (2) Ovary – site of the reproductive ovules – (3) Ovule – holds the developing egg

Parts of the Flower

Pollination in 8 Steps 1. Formation of pollen grains in anther (male) 2. Formation of embryo sac in the ovary (female) 3. Pollination –pollen grains are transferred from the anther of one plant to the stigma on the carpel of another. Pollen grain germinates, pollen tube grows down the stigma to the ovary, within the pollen grain, mitosis produces 2 sperm cells 4. Double Fertilization – pollen tube reaches ovary, one sperm fertilizes the egg to produce a zygote; the other sperm combines with haploid nuclei to produce 3n cell

Pollination in 8 Steps 5. Seed Development – Ovule develops into a seed. Zygote into an embryo and 3n cell into an endosperm (will provide seed with nourishment). Seed Coat protects everything. 6. Dormancy – seed lies dormant until outside conditions are favorable 7. Fruit Development – The plant’s flower loses its pedals, ovary walls increase thickness creating a fruit around the fertilized seeds. Fruit & Seeds are dispersed 8. Germination – When seed reaches soil with water & good conditions. Root grows downward and Shoots grow upward, using endosperm for fuel

Early Seedling Development As the embryo germinates, the plant begins to develop Cotyledons – first embryo leaves to appear

What triggers sexual reproduction in plants? Plants flower in response to changes in amounts of daylight and darkness (photoperiodism) – – more specifically  lengths of darkness Short-Day Plants – require long periods of darkness Long-Day Plants –require short periods of darkness Day-Neutral plants – flower in response to changes in water or temperature

Life Cycles of Plants Annuals – complete life cycle within one year or growing season (corn, wheat, soybeans). Growth can be rapid in good conditions. Die after they flower. Biennials – uncommon, complete their life cycle within two years. Store up food during 1 st year, produce flowers 2 nd year. Die after flowering. Perennials – includes most vascular plants such as trees & shrubs – continue to grow over the course of many years. Flowering and seed production occurs continually.

Tropisms Phototropism – how plants response to sunlight (move towards the sun) Gravitropsim – how plants respond to gravity (shoots grow up, roots grow down) Thigmotropism – how plants respond to touch (ivy grows around a post or trellis

Plant Hormones Plant HormoneSite of ProductionResulting Activity AuxinRoots, shoots, and young leaves Promote cell elongation, general growth, and phototropism GibberellinsApical Meristem, seeds, young leaves Promote germination of seeds and are involved in the growth of fruit CytokininsRootsPromote cell division and differentiation EthyleneMost plant tissuesInduces leaf abscission and promotes fruit ripening Abscisic Acid Leaves, roots, fruitInhibits leaf abscission, regulates stomata opening / closing

Practice Question 1 All of the following are major characteristics of dicots EXCEPT (A)They contain vascular tissue (B)The leaves have netted veins (C)They have 2 cotyledon (D)The flower parts are in multiples of three (E)The cotyledon provides food for the germinating embryo

Practice Question 2 Which of the following structures is NOT part of the pistol? (A)Ovule (B)Ovary (C)Style (D)Anther (E)Stigma

Practice Question 3 The plant hormone responsible for the ripening of fruit is (A)Auxin (B)Cytokinin (C)Gibberellin (D)Ethylene (E)Abscisci acid

Practice Question #4 All of the following are examples of tracheophytes EXCEPT (A)Trees (B)Moss (C)Grass (D)Corn (E)Beans HINT: tracheophyts = vascular plants