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Bio 10
Lecture Notes 7: Plant Diversity, Structure and Function
SRJC
Physiology – study of the adaptations by which organisms function in their environ.
1.) Plants, Tissues and Function
 Plant types and their evolution
 Terrestrial plants evolved from aquatic green algae
 There are three main types:
 Bryophytes- mosses and hornwarts
 “Leaves” have a cuticle to conserve water
 A rudimentary root system anchors them to substratum and allows for
absorption
 Need to live in moist environment
 Have no vascular system
 Produce spores and free swimming sperm need water
 Most can survive drying out by going dormant
 Ferns, Lycophytes and horsetails
 Share features with Bryophytes
 Have rudimentary root and vascular system
 Seed producing plants (Gymnosperms and angiosperms)
 Gymnosperms (naked seed) includes conifers
 Produce cone-like structure
 Wind pollinated- pollen reach exposed reproductive structure
 Have true leaves, roots, vascular tissues, etc
 Do not need water to reproduce
 Angiosperms (vessel seed) Flowering Plants
 Include all adaptations for living on land found in gymnosperms plus
flowers, with some adaptations to extreme environments ( e.g. cacti)
 Three types:
 Monocots (one cotyledon)- grasses, bamboo, etc
 Emerging shoots open into blade-like leaves
 Three floral parts (or multiple of three)
 Veins run parallel to each other
 Vascular bundles distributed throughout shoot
 Magnoliids- effectively ancestral dicots
 Eudicots (two cotyledons)- dominate plant kingdom
 Emerging shoots and leateral buds open into two leaves
 Four of five floral parts (or multiple of four or five)
 Veins are net-like
 Vascular bundles organized into ring (in shoots)
 Plant body is divided into shoots and roots
 Plant organ and tissue systems
 Shoots
 Produce food by photosynthesis
 Carry out reproductive functions
 Roots
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Bio 10
Lecture Notes 7: Plant Diversity, Structure and Function
SRJC
 Anchor the plant
 Penetrate the soil and absorb water and dissolved minerals
 Store food
 Plant Body Plan
 Meristems
 Regions where cell divisions produce plant growth
 Apical meristems
 Lengthen stems and roots
 Responsible for primary growth
 Lateral meristems
 Increase width of stems
 Responsible for secondary growth
 Simple Tissues
 Made up of one type of cell
 Parenchyma – alive
 Found in soft photosynthetic tissues
 Collenchyma – alive
 Provides support
 Sclerenchyma – dead at maturity
 Provides even more support
 Complex Tissues
 Composed of mixed cell types
 Vascular Tissues
 Xylem
 Conducts water and dissolved minerals
 Conducting cells are dead and hollow at maturity
 Phloem
 Transports sugars
 Main conducting cells are sieve-tube members
 Companion cells assist in the loading of sugars
 Epidermis
 Covers and protects plant surfaces
 Secretes a waxy, waterproof cuticle
 Contains stomata
 In woody plants, periderm replaces epidermis
 Stem Growth and Development
 Cells at tip of apical meristem divide
 Their descendents divide and differentiate, giving rise to specialized tissues
 Lateral buds are undeveloped meristematic tissue that gives rise to stems, leaves,
and flowers
 Root Systems, Growth and Development
 Root Structure
 Fibrous root system- typical of monocots, just a mass of small roots
 Tap root- typical of dicots, a single main root that reaches deep into soil
 Root cap covers tip, protects against abrasion
 Apical meristem produces the cap
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Bio 10
Lecture Notes 7: Plant Diversity, Structure and Function
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SRJC
Cell divisions at the apical meristem cause the root to lengthen
Farther up, cells differentiate and mature
 Root hairs
 Provide large surface area for water and mineral absorption
 Internal Structure of a Root
 Outermost layer is epidermis
 Root cortex is beneath the epidermis
 Vascular cylinder contains vascular tissues, surrounded by endodermis
 Xylem conducts water, forms an X in some plant roots
 Phloem conducts nutrients and sugars, forms P’s around xylem in some plants
 Endodermis
 Endodermis, then pericycle surround the vascular cylinder
 In some plants, there is a central pith
 Secondary Growth- increases girth
 Occurs in woody plants
 A ring of vascular cambium produces secondary xylem and phloem
 Xylem grows in phloem grows out
 Wood is the accumulation of these secondary tissues, especially xylem
 Tree Rings
 Form as a result of xylem tubes with different diameters
 Wide tubes develop during wet season (winter or spring)
 Narrow tubes develop during dry months
 Different diameters create discernable pattern of year’s growth
2.) Plant Nutrition, Transport and Gas Exchange
 Soil
 Minerals mixed with humus
 Minerals come from weathering of rock
 Humus is decomposing organic material
 Composition of soil varies
 Suitability for plant growth depends largely on proportions of soil particles
 Macronutrients
 Mineral elements that are required in amounts above 0.5% of the plant’s dry
weight
Carbon
Nitrogen
Magnesium
Hydrogen
Potassium
Phosphorus
Oxygen
Calcium
Sulfur
 Micronutrients
 Elements that are required in trace amounts for normal plant growth
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Chlorine
Iron
Copper
Boron
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 Manganese
 Zinc
 Molybdenum
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Bio 10
Lecture Notes 7: Plant Diversity, Structure and Function
SRJC
 Leaching
 Removal of nutrients from soil by water that percolates through it
 Most pronounced in sandy soils
 Clays are best at holding onto nutrients
 Soil Erosion
 Loss of soil to wind and water
 Often the result of deforestation
 Nutrient loss affects entire food chain
 Root Hairs
 Extensions from the root epidermis
 Greatly increase the surface area available for absorption
 Root Nodules
 Swelling on roots of some plants
 Contain nitrogen-fixing bacteria
 Bacteria convert nitrogen gas to forms plants can use
 Mycorrhizae
 Symbiosis between young plant root and fungus
 Fungal filaments may cover or penetrate root
 Fungus absorbs sugars and nitrogen from plant
 Roots obtain minerals absorbed from soil by fungus
 Root Structure and Absorption
 Roots of most flowering plants have:
 Endodermis (innermost skin): surrounds vascular cylinder
 Exodermis (outer skin): just below surface
 Both layers contain a Casparian strip
 Controls the flow of water and nutrients
 Plant Gas Exchange
 Simple Diffusion- passive transport or movement of substances along
concentration gradients
 Osmosis- movement of water across a semi-permeable membrane, along a
concentration gradient
 Active Transport- uses ATP to move substances across a membrane
 ATP - high energy molecule
 Small Cells – Simple diffusion is adequate
 Larger Cells – Cytoplasmic Streaming
 Transpiration-water is transpired from leaves creates transport through plant
 Water moves through xylem
 Xylem cells are tracheids or vessel members
 Both are dead at maturity
 Cohesion-Tension- Theory of Water Transport
 Transpiration creates negative tension in xylem
 Tension extends downward from leaves to roots
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Bio 10
Lecture Notes 7: Plant Diversity, Structure and Function
SRJC
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Hydrogen-bonded water molecules are pulled upward through xylem as
continuous columns
 Replacement water is drawn in through roots
 Hydrogen bonds hold water molecules together in conducting tubes of xylem
 Weak bonds still allow water to evaporate through stomata during
transpiration
Wilting
 Water regulation maintains turgor
Cuticle
 Translucent coating secreted by epidermal cells
 Consists of waxes in cutin
 Allows light to pass through but restricts water loss
Stomata
 Openings across the cuticle and epidermis; allow gases in and out
 Guard cells on either side of a stoma
 Turgor pressure in guard cells affects opening and closing of stomata
 CAM Plants
 Most plants stomata open during day and photosynthesis proceeds
 CAM plants are better at water conservation
 Stomata open at night and carbon dioxide is fixed
 Next day, stomata remain closed while carbon dioxide is used
Nutrient Transport
 Pressure Flow Theory
 Transport through phloem driven by pressure (concentration) gradients
 Phloem
 Carry transportable organic compounds
 Conducting tubes are sieve tubes
 Consist of living sieve-tube members
 Companion cells lie next to sieve tubes
 A type of parenchyma
 Help load organic compounds into sieve tubes
 Transportable organic compounds
 Carbohydrates are stored as starches
 Starches, proteins, and fats are too large or insoluble for transport
 Cells break them down to smaller molecules for transport
 Sucrose is main carbohydrate transported
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