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Plant Structures Roots, Stems, and Leaves

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Presentation on theme: "Plant Structures Roots, Stems, and Leaves"— Presentation transcript:

1 Plant Structures Roots, Stems, and Leaves
Chapter 23

2 23-1 Specialized Tissues in Plants
Plants are as successful if not more successful than animals Seed plants have three main structures: Roots Stems Leaves Linked together by various means

3 23-1 Specialized Tissues in Plants
Roots Absorbs water and nutrients Anchor plant to the ground Hold soil in place and prevent erosion Protect from soil bacteria Transport water and nutrients Provide upright support

4 23-1 Specialized Tissues in Plants
Stems Support for the plant body Carries nutrients throughout plant Defense system to protect against predators and infection Few millimeters to 100 meters

5 23-1 Specialized Tissues in Plants
Leaves Main photosynthetic systems Suseptable to extreme drying Sight of oxygen/carbon dioxide intake and release

6 23-1 Specialized Tissues in Plants
Plant tissue systems Exist within the root, stems, and leaves Dermal tissue Vascular tissue Ground tissue

7 23-1 Specialized Tissues in Plants
Dermal Tissue Outer covering Single layer of cells Cuticle – waxy coating Trichomes – Spiny projections on the leaf Roots have dermal tissue Root hairs Guard Cells

8 23-1 Specialized Tissues in Plants
Vascular Tissue Transport System Subsystems Xylem Phloem Subsystems are used to carry fluids throughout plant

9 23-1 Specialized Tissues in Plants
Xylem Two types Seed plants Angiosperms Tracheid – long narrow cells Walls are connected to neighboring cells Will eventually die Vessel Element – wider that tracheids

10 23-1 Specialized Tissues in Plants
Phloem Sieve Tube Elements Cells arranged end to end Pump sugars and other foods Companion Cells Surround sieve tube elements Support phloem cells

11 23-1 Specialized Tissues in Plants
Ground Tissue Cells between dermal and vascular tissue Parenchyma Thin cell walls, large vacuoules Collenchyma Strong, flexible cell walls Sclerenchyma Extremely thick, rigid cell walls

12 23-1 Specialized Tissues in Plants
Plant Growth Meristems – tissues responsible for growth Undifferentiated cells Apical Meristem Produce growth increased length Differentiation Cells will assume roles in the plant Flower Development Starts in the meristem

13 23-2 Roots Types of Roots Taproots Fibrous roots Found in dicots
Long, thick root Hickory and oak trees Fibrous roots Found in monocots No single root larger than any other Many thin roots Help prevent erosion

14 Root Structure and Growth
Outside layer = epidermis Central cylinder = vascular tissue Between these two = ground tissue Roots important in water and mineral transport 14

15 23-2 Roots Root Structure Epidermis – outside layer
Root hairs Cortex – spongy layer of ground tissue inside epidermis Endodermis – layer inside cortex Vascular cylinder – central vascular system Root Cap – the tip, cellular production

16 Root Growth Roots grow by producing new cells near the tip!
Root lubricates its path New cells are added at the root cap Behind the meristematic tissue, cells grow longer These cells specialize and take on different functions (process of differentiation)

17 Root Functions Anchor a plant in the ground
Absorb water and dissolved nutrients from the soil Water and nutrients do not just soak into the root from the soil The plant requires energy to absorb water 17

18 23-2 Roots Plant Nutrient Uptake Plant requirements
Soil includes sand, silt, clay, air, bits of decaying organic matter Soil type determines plant type! Plant requirements - Oxygen, CO2 - Nitrogen - Magnesium - Phosphorus - Calcium - Postassium - Trace elements

19 Types of soil Sandy soil is made up of mostly grains of sand. Water passes through this type of soil quickly. Clay soil is mostly made of fine clay particles. Water poured on clay soil sinks slowly. Loamy soil contains decaying plant and animal matter along with clay and sand.

20 Essential Nutrients Nitrogen is important for leaf growth and color. A plant that lacks nitrogen will have yellow leaves. Phosphorous is needed for roots, stems and flower growth as well as seeds. A plant lacking phosphorous will have stunted growth and few flowers.

21 Potassium is important in root, stem and flower development as well
Potassium is important in root, stem and flower development as well. It helps the plants live in the cold and fight disease. Plants with too little potassium have stunted roots. Potassium is sometimes called potash. Calcium is needed for cell growth and for strong cell walls. Magnesium is needed to make chlorophyll. Plants will die without chlorophyll.

22 Plants also need very small amounts of what are called trace elements
Plants also need very small amounts of what are called trace elements. The plant will not grow well if these trace elements are not present, but if there is too much of the trace elements in the soil they are poisonous to the plant.

23 23-2 Roots Active Transport in Plants Vascular Cylinder
Root hairs use ATP Pump minerals from soil Causes water molecules to follow by osmosis Vascular Cylinder Casparian Strip – waterproof strip surrounding endodermal cells: H20 retention

24 Osmosis and Root Pressure
Water moves into the vascular cylinder by osmosis (diffusion through semipermeable membrane) Water and minerals can’t pass through the Casparian strip, so they’re trapped once inside the vascular cylinder! Root Pressure One-way movement creates pressure Forces water up into the plant If pressure didn’t build up, roots would swell up!

25 23-3 Stems Stem Structure Essential part of transport system
Produce leaves, branches, and flowers Hold leaves up to sunlight Transport substance between roots and leaves Essential part of transport system Function in storage and photosynthesis Like other plant parts, stems have vascular, dermal, and ground tissue!

26 23-3 Stems Xylem and phloem – major tubule systems
Transport water and nutrients Composed of 3 tissue layers Contain nodes – attachment for leaves Internodes – regions between the nodes Buds – undeveloped tissue

27 23-3 Stem Types Monocot – vascular bundles are scattered throughout
- Distinct epidermis Dicot – vascular tissue arranged in a cylinder - Pith – parenchyma cells inside the ring (ground tissue with thin cell wall, large vacuole) Monocot – vascular bundles are scattered throughout Distinct epidermis Dicot – vascular tissue arranged in a cylinder Pith – parenchyma cells inside the ring (ground tissue with thin cell wall, large vacuole)

28 23-3 Stem Growth Primary growth – new cells produced at the root tips and shoots Increases the length Secondary growth – increase in stem width Vascular cambium – meristematic tissue that produces vascular tissue and increases thickness Cork cambium – produces outer covering of stems

29 23-3 Stems Formation of Vascular Cambium
Xylem and phloem bundles present in a ring Secondary growth initiates production of a thin layer The vascular cambium divides Produces new xylem and phloem

30 23-3 Stems Formation of wood Wood – layers of xylem
Produced year after year Results from the older xylem not conducting water – heartwood Becomes darker with age Sapwood – surrounds heartwood

31 Annual Rings In spring, growth happens quickly, producing light-colored xylem cells with thin cell walls At the end of the season, the cells become darker with thicker cell walls (late wood) Each season, a ring with light and dark is produced By counting rings in a tree, you can estimate age!

32 23-3 Roots Formation of Bark
All the tissues outside the vascular cambium Consists of outermost layers of dead cork Water proof

33 23-4 Leaves Main site of photosynthesis Consist of:
Blade – thin flattened section Petiole – stalk that attaches stem to blade Covered by epidermis and cuticle (waxy covering) Create water proof barrier

34 23-4 Leaves Leaf Functions
Photosynthesis – occurs in the mesophyll (specialized ground tissue in leaf) Palisade mesophyll – absorb light Spongy mesophyll – beneath palisade level

35 Stomata Stomata – pores in the underside of the leaf Singular: stoma
Guard Cells – epidermal cells surrounding the stomata, specialized to open and close

36 23-4 Leaves Transpiration Loss of water through its leaves
Replaced by water drawn into the leaf through xylem

37 Gas Exchange Take in CO2 and release O2
Can do the opposite – when using food, take in oxygen and release CO2 Gas exchange takes place at the stomata Not open all the time Stomata is controlled by water pressure in guard cells

38 Gas Exchange & Homeostasis
Plants keep stomata open just enough to allow photosynthesis to occur, but not to lose too much water! When water pressure is high, guard cells pulled away and stoma opens! When water pressure is low, inner walls pull together and stoma closes! Usually: stomata open in daytime, closed at night… why?

39 23-5 Transport in Plants Water Transport
Active transport and root pressure Cause water to move from soil to roots Capillary action Combined with active transport and root pressure, moves materials throughout the plant

40 23-5 Transport in Plants Capillary Transport
Capillary transport results from both cohesive and adhesive forces Water molecules attracted to one another Water is also attracted to the xylem tubes in the plant Causes water to move from roots to the stem and upward

41 23-5 Transport in Plants Transpiration
Evaporation is the major moving force As water is lost, osmotic pressure moves water out of vascular tissue This pulls water up from the stem to the leaves Affected by heat, humidity, and wind

42 23-5 Transport in Plants Controlling Transpiration
Open the stomata – increase water loss Close the stomata – decrease water loss

43 23-5 Transport in Plants Transpiration and Wilting
Osmotic pressure – keeps plants semi-rigid Wilting is a result of high transpiration rates Loss of water causes a drop in osmotic pressure Loss of rigidity Conserves water

44 23-5 Transport in Plants Nutrient Transport Source to Sink
Most nutrients are pushed through plant Nutrient movement takes place in phloem Source to Sink Source – any cell that produces sugars Sink – any cell where sugars are used Pressure-flow Hypothesis

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