9.1 Plant Organs

• Vegetative Organs– Roots– Stems– Leaves

• Reproductive Structures– Flowers– Seeds– Fruits

Organization of a Plant Body

Organization of a Plant Body

9.1 Plant Organs

• Roots

– Generally, the root system is at least equivalent in size and extent to the shoot system

• Anchors plant in soil

• Absorbs water and minerals

• Produces hormones

– Root hairs:

• Projections from epidermal root hair cells

• Greatly increase absorptive capacity of root

9.1 Plant Organs

• Stems– The main axis of a plant that elongates and produces

leaves

– Nodes occur where leaves are attached to the stem• Internode is region between nodes

– Stems have vascular tissue that transports water and minerals

– In some plants, stems carry on photosynthesis, or

store water and nutrients.

9.1 Plant Organs

• Leaves– Major part of the plant that carries on photosynthesis– Deciduous plants are those that lose their leaves

every year.– Evergreens retain their leaves for two to seven years.– Foliage leaves are usually broad and thin

• Blade - Wide portion of foliage leaf• Petiole - Stalk attaches blade to stem• Leaf Axil - Axillary bud originates

9.1 Plant Organs

• Some Specialized Types of Leaves

– Tendrils - Leaves that attach to objects

– Bulbs - Leaves that store food

– Some leaves are designed to protect buds, and in

some cases leaves capture insects.

9.2 Monocot Versus Eudicot Plants

9.2 Monocot Versus Eudicot Plants

• Cotyledons = seed leaves.– Flowering plants are divided into two groups

dependent upon the number of cotyledons are present in the embryonic plant.

– Monocots (one cotyledon)– Eudicots (two cotyledons)

Structural Differences inMonocots and Dicots

9.3 Plant Tissue

• Meristematic tissue allows plants to grow their entire lives.– Apical meristems are located at or near the tip of

stem and roots, increasing the length of these structures.

9.3 Plant Tissue

• Meristematic tissue gives rise to:

– Epidermal tissue

– Ground tissue

– Vascular tissue

9.3 Plant Tissue

• Epidermal Tissue– Contains closely packed epidermal cells

• Specialized Epidermal Cells– Epidermal cells exposed to air have a waxy cuticle

• Minimizes water loss• Protection from disease

– Root epidermis has root hairs• Absorb water• Anchor the plant

9.3 Plant Tissue

• Specialized Epidermal Cells– Trichomes

• Protect the plant from too much sun• Produce toxic substances

– Stomata• Gas exchange

– Periderm contains cork cells• Protect the plant

Modification of Epidermal Tissue

9.3 Plant Tissue

• Ground Tissue

– Ground tissue forms the bulk of a plant

• Parenchyma cells

• Collenchyma cells

• Sclerenchyma

9.3 Plant Tissue

– Parenchyma cells:

• Least specialized and are found in all organs of plant

• Can divide and give rise to more specialized cells

– Collenchyma cells:

• Have thicker primary walls

• Form bundles underneath epidermis

• Flexible support to immature regions of the plant

9.3 Plant Tissue

• Sclerenchyma cells:– Have thick secondary walls impregnated with lignin– Most are nonliving– Primary function is to support mature regions of the

plant– Two types of sclerenchyma cells

• Fibers• Sclereids

Ground Tissue Cells

9.3 Plant Tissue

• Vascular Tissue– Vascular tissue is for transport

– Xylem transports water and minerals form the roots to the leaves

– Phloem transports sucrose and other organic compounds (including hormones) from the leaves to the roots).

– Xylem and phloem are complex tissues because they are composed of two or more types of cells.

9.3 Plant Tissue

• Xylem has two types of conducting cells

– Vessel Elements• Larger, with perforated plates in their end walls

– Tracheids• Long, with tapered ends

– Pits in end walls

– Vascular rays

– Fibers

Xylem Structure

9.3 Plant Tissue

• Phloem– Sieve-Tube Members

• Are the conducting cells, • Arranged to form a continuous sieve tube• Contain cytoplasm but no nuclei• Have a nucleated companion cell• Plasmodesmata extend from one cell to another

through sieve plates

Phloem Structure

9.4 Organization of Leaves

9.4 Organization of Leaves

9.4 Organization of Leaves

• Leaf Diversity

Classification of Leaves

Leaf Diversity

9.5 Organization of Stems

9.5 Organization of Stems

• Woody twigs provide a good example for

studying stem organization.

– Terminal Buds

– Leaf Scars and Bundle Scars

– Axillary Buds

Stem of a Woody Twig

9.5 Organization of Stems

• Shoot Apical Meristem

– Produces new cells for growth– Protected by leaf primordia

– Primary Meristems• Protoderm• Ground Meristem• Parenchyma tissue

Shoot Tip and Primary Meristems

9.5 Organization of Stems

• Herbaceous Stems– Mature nonwoody stems exhibit only primary growth

– Outermost tissue covered with waxy cuticle

– Stems have distinctive vascular bundles

• Herbaceous eudicots - Vascular bundles arranged in distinct ring

• Monocots - Vascular bundles scattered throughout stem

Herbaceous Stems

9.5 Organization of Stems

• Woody Stems

– Woody plants have both primary and secondary tissues

– Primary tissues formed each year from primary meristems

– Secondary tissues develop during first and subsequent years from lateral meristems

9.5 Organization of Stems

• Woody Stems

– Woody stems have no vascular tissue, and instead have three distinct regions

• Bark

• Wood

• Pith

Secondary Growth of Stems

9.5 Organization of Stems

• Bark– Bark of a tree contains cork, cork cambium,

and phloem• Cork cambium produces tissue that disrupts the

epidermis and replaces it with cork cells.• Cork cells provide waterproofing

– Lenticels are pockets of loosely arranged cork cells that allow gas exchange

• Phloem transports organic nutrients

9.5 Organization of Stems

• Wood

– Wood is secondary xylem that builds up year after

year

– Vascular cambium dormant during winter

– Annual ring is made up of spring wood and summer

wood

– In older trees, inner annual rings no longer function in

water transport

– Annual rings can provide a growth record.

Three-Year-Old Woody Twig

Tree Trunk

9.5 Organization of Stems

• Stem Diversity– Stolons:

• Above-ground horizontal stems• Produce new plants when nodes touch the ground

– Rhizomes:• Underground horizontal stems• Contribute to asexual reproduction• Variations:• Tubers - Enlarged portions functioning in food storage• Corms - Underground stems that produce new plants during

the next season

Stem Diversity

9.6 Organization of Roots

• Root Apical Meristem

– Protected by the root cap

– Three Regions• Zone of Cell Division

• Zone of Elongation

• Zone of Maturation

Eudicot Root Tip

9.6 Organization of Roots

• Tissue of a Eudicot Root– Epidermis– Cortex– Endodermis

• Casparian Strip

– Vascular Tissue• Pericycle

Branching of A Eudicot Root

9.6 Organization of Roots

• Monocot Roots

– Ground tissue of root’s pith is surrounded by vascular

ring

– Have the same growth zones as eudicot roots, but do

not undergo secondary growth

Monocot Root

• Root Diversity

– Primary root (taproot) - Fleshy, long single root, that grows straight down

• Stores food

– Fibrous root system - Slender roots and lateral branches

• Anchors plant to the soil

• Root Diversity– Root Specializations

• Adventitious roots - Roots develop from organs of the shoot system

– Prop roots

• Haustoria:– Rootlike projections that grow into host plant– Make contact with vascular tissue and extract water and

nutrients

• Mycorrhizas:– Associations between roots and fungi– Assist in water and mineral extraction

• Root Nodules - Contain nitrogen-fixing bacteria

Root Diversity

9.7 Uptake and Transport of Nutrients

9.7 Uptake – Water moves into root cells by osmosis; minerals by

diffusion and active transport– Water can enter directly into as cell using symplastic

route OR it can move between the cell walls using the apoplastic route. Minerals cannot not enter the xylem using the apoplastic route due to the Casparian Strip. This helps to regulate ion concentration

– H+ ion is actively pumped out of the cell. This disrupts the cations within the soil and they inturn will diffuse into the cells taking with them negative anions. Active transport is sometimes also used to bring in specific ions such as potassium

– Root pressure is generated by water moving into the roots - pushes xylem sap

9.7 Uptake and Transport of Nutrients

• Cohesion-Tension Model of Xylem Transport– Relies on the properties of water– Transpiration-evaporation from the leaves creates a

“sucking” force that pulls water upward through the xylem– Adhesion-water molecules interact with the walls of the

xylem vessels to reinforce strength of column– Cohesion-water molecules are attracted to each other and

form a continuous column within xylem from leaves to roots

– Tension-created by transpiration; reaches from the leaves to the roots as long as column is continuous

Cohesion Tension Theory• 1. Light absorbed by leaf increases the temperature

within• 2. Water in the spongy mesophyll enters vapour phase• 3. Water vapours evaporates through the stomata

(plural of stomate) to a lower water concentration• 4. Loss of water due to evaporation creates a tension

within the xylem so water is replaced due to adhesion and cohesion

• 5. Water enters the xylem cells from the root – there is transpirational pull as well as root pressure of water

• 6. Due to the transpirational pull- water is pulled into the roots from soil. Of course osmosis assists as well

Cohesion-Tension Model of Xylem Transport

Conducting Cells of Xylem

9.7 Uptake and Transport of Nutrients

• Opening and Closing of Stomata– Each stoma in leaf epidermis is bordered by guard

cells

– Increased turgor pressure in guard cells opens stoma

– Caused by active transport of K+ into guard cells

Opening and Closing of Stomata

9.7 Uptake and Transport of Nutrients

• Mineral Uptake and Transport– Epiphytes- “air plants” that grow on larger plants;

absorb moisture from the air– Parasitic plants have haustoria that tap into the xylem

and phloem of hosts– Carnivorous plants have various adaptations for

catching insects– Root nodules- in leguminous plants, house nitrogen-

fixing bacteria– Mycorrhizae - symbiotic relationship between roots and

fungi that increases surface area for absorption and the fungi break down organic matter for the plant to absorb

Root Nodules

Mycorrhizae

9.7 Uptake and Transport of Nutrients

• Organic Nutrient Transport– Role of Phloem

• Transports products of photosynthesis from the leaves to the site of storage

– Pressure-flow Model of Phloem Transport• Sugars produced in the leaves are actively transported into

sieve tubes; water follows by osmosis• The buildup of water in the sieve tubes creates pressure that

starts the phloem sap flowing• Other plant organs serve as the “sink”- sugars are actively

transported out for use or storage and water follows by osmosis

• Phloem sap always flows from source to sink

Pressure-flow Model of Phloem Transport