This is sometimes referred to as an Organizational Hierarchy

Transcription

1 Chapter 11 Plant Structure and Function Introduction: Cell Specialization 1. Life in general In order to carry out the basic processes of life: Food production (photosynthesis) Intake of water and nutrients Exchange (CO 2 and O 2 ) gases Distribute and store food Reproduction each organism is made up of Specialized systems Which are composed of Specialized organs Which are composed of Specialized tissues Which are composed of Specialized cells This is sometimes referred to as an Organizational Hierarchy 1

2 2. Plants in particular In plants growth (cell division) occurs only in three places: Root apical meristem at the tip of the root Shoot apical meristem at the tip of the shoot Lateral meristem an area arranged in a ring in the stem Immediately after division, the daughter cells are undifferentiated that is, their fate hasn t been decided about what kind of cell it will become. At some point it will receive chemical messages which will initiate differentiation. Once that has happened, its fate is determined. (Sorta like stem cells) Diagram SILENT READING p Seed Growth and Development Every seed is made up of embryo - dormant, primitive plant cotyledons - storage endosperm - storage testa - seed coat 2

3 In each pollen grain contains two sperm to accommodate two fusion events: 1) fertilization of egg to produce zygote 2) fusion with the polar nuclei to produce endosperm Following fertilization, the zygote germinates rapidly but halts and becomes dormant at some point in its embryonic stage. Meanwhile, the cotyledons and endosperm have grown and the seed has produced a tough, protective coat (testa). This dormancy can last many years, with growth restarting once conditions are favourable and the testa has softened (water presence). The embryo uses the nutrient supply in the cotyledons/endosperm to fuel its renewed growth. It emerges from the testa by pushing through a primary root and shoot. The nutrient reserves continue to be used until the shoot has pushed its way through the soil surface. Two criteria must be met before the plant is able to start producing food on its own. leaves must have enough chlorophyll to trap light. roots must have enough root hairs to absorb water and nutrients. Diagram of germinating bean. 3

4 Plant Tissues There are three basic kinds of plant tissues ground tissues vascular tissues dermal tissues Ground tissues there are three types of ground tissues: Picture Cell Description Function Distribution Parenchyma Living healing Throughout plant: Large, thin-walled regeneration of most common type parts photosynthesis in primary plants storage (food/h 2 O) Collenchyma Living Flexible support Stalks Long, thickened walls Moderately flexible Sclerenchyma Dead Strength and support Long, fibrous, rigid Stalks and testa Ground tissue distribution in the roots and stem 4

5 Vascular tissues there are two systems which conduct water, nutrients and food throughout the plant XYLEM PHLOEM - water conduction - sugars and other dissolved substances - dead at maturity - living cells - tracheids and vessels - seive tubes Tracheids Vessels Seive Tubes Dermal Tissue epidermis - the outermost layer of cells; is similar to skin cells often has specialized cells embedded in it root hair cells guard cells (gas exchange) above ground is coated with cuticle (a waxy coat which prevents water loss) 5

6 Roots taproots - large central core which grows downward with lateral roots fibrous roots - surface roots arising from adventitious roots (roots that grow from unusual places) Root Growth Figure 11.7 Nelson 6

7 Root Structure Figure 11.8 Nelson Shoots The shoot system is made up of: stems leaves Stems Functions of stems: support - to hold the leaves in order to get maximum exposure to sunlight transport - trafficking of chemicals (and water) between roots and leaves storage - of food for later use. Herbaceous stems - soft, green, flexible plants under 1 meter tall 7

8 Woody stems hard, rigid trees Vascular Bundle Distribution Monocot Dicot Stem Structure Figure 1.14 Hopkins 8

9 Stem Development -The Terminal Bud Stem Development - Trees primary growth - increase in height by elongation at the root and shoot apical meristems. secondary growth - increase in stem thickness by addition at the lateral meristem. (a.k.a. vascular cambium) Figure: Hayden s Mock-up 9

10 Leaf Figure 1.16 Hopkins Guard cell function Osmosis (again) Start Finish 100% water Salt solution 100% water Salt solution Start Finish 100% water Salt solution 100% water Salt solution 10

11 Photosynthesis (Again) CO 2 + H 2 O + sunlight C 6 H 12 O 6 + O 2 carbon dioxide + water + sunlight glucose (sugar) + oxygen Terrestrial plant leaves are faced with a huge problem. They must be able to bring carbon dioxide into the leaf without loosing so much water in the process that they shrivel up and die. On the underside of leaves are specialised cells which are located on either side of tiny holes. The holes are called stomata and these specialised cells are guard cells. In sunlight two things happen 1.) CO 2 and H 2 O are converted into sugar SO the concentrations of those tend to decrease within all photosynthetic cells including the guard cells, but because the guard cells have more chlorophyll, they tend to run out of water faster than the rest of the leaf. 2.) Blue light from the sun causes potassium ions ( K + ) to be pumped into the guard cells. This causes an osmotic imbalance and H 2 O follows the K + into the sausage shape guard cells causing them to swell. This swelling causes the guard cells to open. At night the plant cells respire (producing CO 2 ) which causes K + to leave the guard cells and again H 2 O leaves as well. Guard cells shrink and close. Figure 11

12 Leaf Adaptations Environmental Condition Shade Adaptation Dry Need for storage Pollination Bud protection Transportation Water can be transported against the force of gravity to great heights (100 m +) This incredible feat is accomplished by a combination of three processes. 1.) Transpiration - 90% of plant water loss is through stomatal openings. Water is lost from leaf cells and causes an osmotic imbalance (low water) this is replaced by the next cell, and the next, 12

13 and the next A negative internal root pressure (vacuum-like) occurs. This produces an effect quite like sucking on a straw. 2.) Capillary action - the attraction of water to surfaces. This is caused by water tends to travel up fine tubes under this force. 3.) Cohesion - the attraction of water molecules to other water molecules. Together called transpiration - cohesion theory. Food can be translocated from the leaf cells through the phloem to the roots or any other part via osmotic imbalance. Although poorly understood it is believed that food travels from source (where it is made) to sink (where it is used) by the pressure - flow theory. As food is produced at the source, there is an increase in osmotic pressure. As food is used up at the sink, there is a drop in osmotic pressure. Flow between the two points is due to this imbalance. 13

14 Plant Responses Hormonal Hormones are powerful chemicals which are produced in one part of an organism but cause a change in another part. The most common plant hormones are: auxins Hormone inhibit/stimulate plant growth cell elongation apical bud growth fruit ripening Response gibberellins stem elongation and 'bolting' cytokinins promotes cell division especially in leaves, endosperm and fruit abscissic acid stomatal closure regulates seed and bud dormancy resistance to water stress ethylene fruit ripening conversion of starches and acids to sugars Tropism Tropism - growth or movement of a plant in response to an environmental stimulus Tropisms are easy to remember and understand if you remember the following definitions and word parts: 14

15 positive - toward the stimulus negative - away from nastic - neither; a response that is independent of stimulus direction photoperiodism - day length vernalization - some seeds have to go through a freeze cycle before they can germinate. photo - light geo - gravity thigmo - touch (like vines) chemo chemical hydro - water 15