Chapter 36

Plant Form

Parts of Vascular Plants (fig.36.1)• Consists of root and shoot systems• Both grow at their tips – shoot and root apices• Root system anchors and provides nutrition to the

soil by penetrating into the soil to absorb water and ions

• Shoot system consists of stems and their leaves• Leaves, flowers, fruits and seeds are formed on the

shoot• Stems serve as scaffold for positioning leaves

(arrangement, size and other features of leaves) decides a plant’s production of food

Parts of vegetative shoot• Consists of internode, node, leaf and axillary buds.• Nodes are regions where leaves are attached to

stems (figure – 36.22)• Region between two nodes - internodes• An axillary bud is a lateral shoot apex that allows the

plant to branch or replace the main shoot. Develop in axils (region between stem and leaf).

• Reproductive phase produces flowers or floral shoots• A vegetative axillary bud has capacity to reiterate the

development of primary shoot

What are the three tissues present in roots, shoots and leaves?

• Dermal, ground and vascular tissues systems• Dermal tissue – epidermis is the outer protective

covering. Coated with layer of wax (desert succulents)

• Ground tissue – function in storage, photosynthesis and secretion (support and protection of the plant)

• Vascular tissue- conducts fluids and dissolved substances throughout plant body. Xylem – conducts water and dissolved minerals and phloem – conducts a solution containing nutrients like sucrose

Apical and lateral meristems fig.-36.5• Apical meristems- elongation of shoot and root apices

(primary stem and root) because of repeated cell divisions

• Apical meristem – three primary meristems – protoderm forms epidermis, procambium produces primary xylem and phloem, and ground meristem forms ground tissue

• Lateral meristems- produce an increase in root and shoot diameter (girth)

• Two lateral meristems are Cork cambium-produces outer bark of tree and vascular cambium-produces secondary vascular tissues

• Older roots and shoots – secondary tissues – secondary plant body

Dermal tissue• Epidermis is covered

with fatty cutin (cuticle)• Specialized cells

occurring in epidermis – stomata guarded by guard cells, trichomes and root hairs

• Guard cells flanking stomata regulate in passage of water and gases

stomata

Guard cells

Trichomes and Root hairs

• Trichomes are cellular or multicellular hairlike growth of epidermis. It keeps leaves cool and reduces evaporation.

• Some trichomes are glandular secreting substances that deter herbivores (figure 36.8)

• Root hairs are extensions of root epidermis that help roots in absorption of water and minerals (figure 36.10).

Ground tissue• Thin walled, spherical

parenchyma cells (apple)

• Function in storage, photosynthesis and secretion

• Parenchymal cells containing chloroplasts are called Chlorenchyma

Collenchyma

• Collenchymal cells – support and protection

• Present in celery- allow plant organs to bend without breaking them

Sclerenchyma

• Sclerenchyma have thick cell walls-provide support and protection

• Secondary cell walls have lignin

• Fibers are long, slender cells and grouped together

• Sclereids (single or in groups) – gritty nature of pears

What are the four zones in roots? (fig. 36.14)• Developing roots are divided into four zones• Root cap is composed of inner columella cells and

outer lateral root cap cells. Protects the roots during their extension across abrasive soil particles

• Zone of cell division• Zone of elongation – roots lengthen due to activity

of primary meristem (longer and wider)• Zone of maturation- Cells differentiate.• Cortex differentiates to form endodermis, casparian

strips has suberin produced in bands, all tissues internal to endodermis form stele (ground meristem)

Stems: support for above-ground organs• Stems support plants against gravity

• The apical shoot meristem produces stem tissues, leaf primordia and bud primordia that develops into shoots, leaves, and flowers

• Arrangement of leaves – phyllotaxy –exposure of leaves to sun

• Regions where stipules fall off – leaf scars with tiny bundle scars where vascular connections were present (deciduous trees)

Vascular tissue arrangement in stems• Vascular bundles in monocots stems are

scattered throughout ground tissue and in dicots stems the bundles are arranged in a ring (figure 32.23)

• Parenchymal cells located in centre of stem – Pith

• Modified stems and roots serve different specialized functions of storage and reproduction

What are lenticels?

• In woody trees, cork cambium produces suberin impregnated cork cells (outside) and phelloderm (inside).

• Cork cambium+cork+phelloderm = periderm

• Lenticels are unsuberized cells of cork cambium – gaseous exchange

Lenticels

Leaves are main photosynthetic organs• Two basic types of leaves – microphylls and

megaphylls• Microphyll is a leaf with one vein branching and

megaphyll has several veins• Vein consists of xylem and phloem (vascular

bundles) and are distributed throughout the leaf blade• Simple leaves have undivided blades• Compound leaves – blades are divided into leaflets

(Pinnately and palmately arranged leaves – figure 36.31)

• Dicots have reticulate or netted veins whereas monocots have parallel veins (figure 36.30)

Structure of leaf• Leaves have upper and lower epidermis with

numerous stomata flanked by guard cells.

• Palisade mesophyll - parenchyma is present below upper epidermis – barrel shaped to cylindrical chlorenchyma cells

• Spongy mesophyll present between palisade mesophyll and lower epidermis – many interconnected air spaces with stomata – help in gas exchange and passage of water from leaves

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