Chapter 35

Plant Structure and Growth

I. Two Systems

A. Root System

B. Shoot System

A. Root System

• Used for absorption of minerals and water

• Root hairs are used for most of the absorption

• Adventitious roots are found above ground for support

B. Shoot System

1. Stems- nodes are where the leaves attach- internodes are segments between nodes- axilliary buds are found in an angle between leaf and stem / can produce a branch- terminal buds are where growth is occurring- modified shoots: stolons, rhizomes, tubers, bulbs

2. Leaves- blade and petiole which attaches the leaf to node

II. 3 Tissue Types

Plant organs (leaves, stems, roots) are made of:

• Dermal• Vascular• Ground

A. Dermal Tissue

• Responsible for protection

• Epidermis

• Single layer of cells that make up the skin of the plant

B. Vascular Tissue

• Responsible for Transport of Materials• Made of xylem and phloem1. Xylem – carries water and minerals up

- tracheids are pitted, tapered, elongated cells dead at maturity, with lignified cell walls- vessel elements are pitted, squatty, wide, dead, and lignified and make up long tubes, form xylem vessels

B. Vascular Tissue

2. Phloem – carries glucose and hormones down from leaves

- sieve-tube members are alive at maturity and move sugars with the help of companion cells that load the sugar, separated by sieve plates

C. Ground Tissue

• This is a filler with diverse function from photosynthesis to storage to support

• Divided into the pith which is inside the vascular tissue, and the cortex with lies outside the vascular tissue

III. 3 Cell Types

The tissues we just went over are made up of:

• Paranchyma• Collenchyma

• Sclerenchyma

A. Paranchyma Cells

• “Typical” Plant Cell• Thin, flexible primary cell wall• No secondary cell wall• Large central vacuole• Least specialized• Most metabolic functions / photosynthesis and

starch storage in plants• All cells start here / embryonic “stem” cells• Retain ability to differentiate• Alive at maturity

B. Collenchyma Cells

• Thicker primary cell wall / unevenly thick

• Grouped in cylinders to provide support to young shoots

• Lack of secondary cell wall

• Living and flexible / don’t restrict growth

C. Sclerenchyma Cells

• Thick secondary walls filled with lignin• Rigid• Can not elongate• Dead at maturity• Make up vessel elements and tracheids• Fibers are long, slender, and tapered /

hemp• Sclereids are shorter with irregular shape /

nutshells

IV. Types of Meristems (Embryonic Tissue)

A. Apical Meristems allow for growth in length and are found at the tips of roots and buds

- They allow for primary growth (length)

B. Lateral Meristems allow for growth in girth called secondary growth

V. Primary Growth

A. Roots

B. Shoots

A. Roots

1. Root Cap covers the meristem and lubricates the soil

2. Zone of Cell Division which is where you’ll find the apical meristem, quiescent center and the three primary meristem: protoderm (dermal), procambium (VT, stele, runs down center), and ground meristem (ground)

3. Zone of Elongation is where the cells lengthen and push the root tip forward

4. Zone of Maturation is where cells complete differentiation and become functionally mature

A. Roots

4. Other Terms

Stele – arises from the procambium / vascular tissue develops here

Pericycle – outermost layer of stele

Endodermis – innermost layer of endodermis

Monocot Root

Dicot Root

B. Shoots• Dome shaped apical meristem still gives rise to

primary meristems: protoderm, procambium, and ground meristem

1. Stems- VT runs through stem in strands of vascular bundles instead of down the middle- Dicots have phloem facing out and xylem facing the pith and monocots have the bundles scattered throughout

2. Leaves- Stomata are holes in epidermis flanked by guard cells- Mesophyll is an area of ground tissue mostly made of paranchyma cells with columnar palisade parenchyma cells on top and spongy parenchyma cells on the bottom

Monocot Stem

Dicot Stem

Dicot Leaf

VI. Secondary Growth

• 2 types of lateral meristems function in secondary growth:

- The vascular cambium which creates secondary xylem (wood) and the secondary phloem

- The cork cambium which makes thick coverings replacing the epidermis

A. Stems1. Vascular Cambium

- produces secondary xylem in and secondary phloem out- forms between primary xylem and phloem- as time goes on layers of secondary xylem accumulate / the spring tracheids and vessel cells are large with thin walls and later they become thinner with thick walls- form rings of trees

A. Stems

2. Cork Cambium- early in secondary growth the epidermis falls off and CC makes new tissue- produces cork to the outside for protection and cork and CC are called the periderm- Bark is the periderm plus primary and secondary phloem- old phloem and cork are sloughed off through growth- heartwood, dark with no water / sapwood, carries water and is the secondary xylem

B. Roots

• Very similar to stems but only newest roots can take in water because the periderm is waterproof

VII. Mechanisms of Plant Growth

• Asymmetrical Cell Division creates guard cells and determines the top and bottom of the plant

• Plane is determined by preprophase bands

• Gradients effect positional information

• Homeotic Genes play a role (master genes)