9.3 Plant Growth

3 types of plant tissue All plant tissues arise from meristematic tissue The plant version of stem cells During division one cell stays meristematic and the other differentiates Dermal: acts like a skin to the plant protecting against infection prevents water loss Ground tissue Photosynthesis Storage Support Secretion Vascular tissue Phloem and xylem

Apical Meristems Aka primary meristem or shoot apex Occurs at the tips of the stem and roots Responsible for primary growth of the roots and the stems Allows the stem to grow longer

Lateral meristems Form from cambium cells in the center of the vascular bundles Vascular cambium: found in the center of the xylem and phloem Major component of wood Cork cambium Forms cork Occurs in the bark of the tree Causes secondary growth of the plant Results in an increase in the width of the stem

9.1.6: Comparison of growth Growth due to apical meristem Growth due to lateral meristem Occurs at the tips of the roots and stems Position of meristem Occurs laterally between primary phloem and xylem Product of embryonic cells Origin Cambium – meristematic cells left over from primary growth Produces initial tissues Timing of activity Functions in older stems Epidermis, ground tissues, primary phloem and xylem Cell products Secondary phloem and xylem Increases length and height Outcome for stem Increases width and strengthens stem

Role of Auxin in phototropism Plant hormone Produced by cells undergoing repeated cell division Highest concentration found in the stem tips Causes positive phototropism Accumulates on the shade side of the plant causing the plant to grow towards the light (phototropism – growth towards the direction of light)

Other uses for Auxin Auxin changes the pattern of gene expression during cell growth Causes cell division in meristematic cells Causes differentiation of phloem and xylem Stimulates flower growth Causes fruit production without pollination – creates seedless fruit Can develop or suppress lateral bud growth

9.3 Plant Reproduction

Differences between dicot and monocot Example is a sunflower 2 embryo seed leaves (cotyledons) Broad leaves with veins forming a network. Branched roots Parts of the flower in 4’s or 5’s Vascular bundles in a ring in the stem Root system with main taproot Monocot Example is grass 1 embryo seed leaves (cotyledon) Skinny leaves with parallel veins Un-branched roots Parts of the flower occur in groups of 3 Vascular bundles scattered throughout the stem

Flower Structure and Function Part Function Sepal Protection Petals Attract pollinators Anther Produces pollen Filament Supports anther Stigma Sticky part of carpel where pollen lands Style Supports the carpel Ovary Base of carpel where eggs develop Pistil The stigma, style and ovary structure Stamen The filament and anther structure

Pollination Transfer of pollen from a mature anther to a receptive stigma Self-pollination: pollen comes from the same plant or the same flower Limits genetic diversity but easier Cross-pollination: pollen comes from another plant of the same species Increases genetic diversity Done by insects, animals or wind Grasses are wind pollinated and often have small flowers – main cause of allergies Dicots are usually animal pollinated Red: birds Yellow and orange: bees White/scented: nocturnal Insect pollinated plants often produce a sugar called nectar

TOK Moment Why do bees matter? How do we research it? How to do we solve the problem?

Fertilization Fusion of male and female gametes to form a zygote Pollen transfers down the style to the ovule Pollen germinates and makes a pollen tube Tube grows down the style and enters the ovary Nucleus in the pollen tube moves into the egg Two male nuclei are needed One fertilizes the egg The other triggers the formation of food storage for the embryo

The Seed Protective structure that allows for dispersal of the embryo Seed Part Function Testa Protective outer coat Cotyledons Seed leaves Micropyle Scar resulting from the pollen tube Embryo (root and shoot) Becomes the new plant Protective structure that allows for dispersal of the embryo Seed is dehydrated Dormant

Physiology of Seed Germination Dormancy Many seeds do not germinate as soon as they are dispersed Incomplete seed development Embryo is immature and becomes mature during the dormancy period Presence of a plant growth regulator Gibberellic acid (GA) Inhibits development Disappears from the seed over time Impervious seed coat Eventually it is made permeable Can be by abrasion with the soil, fire or action of microorganisms Requirement for pre-chilling Need to over-winter Has to have a certain temperature for a certain amount of time

Germination Germination occurs under the correct conditions Water: seed must take up enough water to be fully hydrated Oxygen: present for aerobic respiration Suitable temperatures: close to optimum for enzymes for aerobic respiration, for translocation of sugars and synthesis of intermediates for growth

Metabolic Processes for Germination Germination is the resumption of growth and development from the seed form Water is needed to activate the enzymes necessary for germination Once enough water has been absorbed the plant produces a growth hormone called gibberellin Amylase breaks down stored starch into maltose Used in cellular respiration Also used to make cellulose for the cell Stored proteins and lipids are hydrolyzed Amino acids are used to make new proteins Fatty acids and glycerol are used in cell membranes and for energy

Control of Flowering The main factor affecting flowering is daylight The response of the plant to changes in the length of the day photo morphogenesis Phytochrome A blue green pigment present in low concentrations Highly reactive Found in two forms PR: Inactive form absorbs mostly red light in the wavelength of 660nm and changes to the active form Changes quickly PFR: Active form absorbs mostly the far red wavelength of 730nm and changes back to the inactive form Changes slowly PFR is responsible for flowering

Short Day Plants Flower only if the period of darkness is longer than a critical point Even a brief flash of light will stop the flowering PFR acts as an inhibitor and only long periods of darkness will allow the levels of PFR to drop to low enough levels to allow flowering Radish Spinach

Long Day Plants Flower only if the period of darkness is shorter than a critical point PFR promotes flowering in these plants A long period of light allows PFR to accumulate