Plant Growth and Structure

Chapters 24 and 27

I. Growth and Development of EmbryosA. embryo develops from the zygote

1. fertilization diploid zygote mitotic divisions embryo2. embryos contained and develop within protective seeds

B. structure of embryos1. one or two cotyledons (“seed leaves”)

a. main part of embryob. first to begin photosynthesis

2. epicotyl• develops into shoot system (stem)

3. hypocotyl• radicle portion develops into root system

4. suspensor• connects embryo to endosperm

Fig. 27.7 Development of a eudicot embryo

II. Growth and Development of SeedsA. after fertilization, each ovule develops into a seedB. seeds consist of 3 basic parts

1. developing plant embryo (with all its parts)2. endosperm3. outer seed coat

• develops from the ovule integumentsC. viability and dormancy of seeds

Fig. 27.8 Monocot vs. eudicot seeds

III. Growth and Development of FruitsA. after fertilization, the ovary develops into a fruitB. fleshy vs. dry fruitsC. simple vs. aggregate vs. multiple fruitsD. function of all fruits is seed dispersal

Fig. 27.9 Different types of fruits and fruit anatomy

IV. Seed GerminationA. requires proper conditionsB. process

1. radicle thrusts through seed coat and into soil2. formation of primary root development of root system

• mycorrhizal associations (mycorrhizae)3. epicotyl breaks through seed coat and into air4. formation of shoot system5. beginnings of photosynthesis

Fig. 27.11 Bean (eudicot) vs. corn (monocot) germination

V. Primary GrowthA. apical meristems

1. found at tips of roots and shoots 2. increases in length, both up and down 3. occurs in both herbaceous and woody plants4. after division, the cells become primary meristems

a. protoderm• becomes plant's protective tissues

o epidermisb. procambium

• becomes plant's vascular tissueso primary xylem and primary phloemo some cells become the vascular cambium

c. ground meristemi. becomes plant's support/structure tissues

• cortex, pith, and other tissueso cells are parenchyma, collenchyma, or sclerenchymao parenchyma also perform metabolic functions

ii. some cells of the cortex become the cork cambium5. primary tissues

• xylem, phloem, pith, cortex, epidermis

Fig. 24.5 Cells of the ground meristem

Fig. 24.13Shoot tip and primary meristems

B. primary growth of roots1. radicle portion of hypocotyl2. root apical meristems

• protected by a root cap3. several zones of growth:

a. zone of cell division• apical and primary meristems active mitosis

b. zone of elongation and differentiation• cells growing and developing into their appropriate tissue

c. zone of maturationi. cells fully grown and functioning as their tissueii. contains root hairs

• increase absorptive surface area4. roots contain two unique tissues:

a. endodermis• regulates amount of water entering vascular tissues of root

b. pericycle• divides to form lateral roots

Fig. 24.8Eudicot root tip

5. functions of rootsa. anchor the plant

i. how to improve anchoringii. development of a root systemiii. tap vs. fibrous root systemiv. adventitious roots

• develop from stem tissues• accompany others

b. absorbing water and nutrients i. root hairs increase surface area for

absorptionii. root hairs lateral roots main rootsiii. vascular tissues in central portion

c. storing sugars (and other carbs.) as starch• plants rely on stored food during winter

Fig. 24.11 Types of root systems

C. primary growth of stems1. epicotyl portion of embryo2. shoot apical meristems

• no “shoot caps” (why?)3. same zones of growth as roots4. nodes

a. specialized regions where leaves formb. leaves begin as leaf primordiac. internodes

• regions where no leaves grow5. axillary (lateral) buds

• special regions that become new stems or flowers

6. functions of stemsa. produce/support leaves, flowers, fruitsb. transport of water and minerals

i. occurs in vascular bundlesii. lateral transport of materials

• xylem and phloem raysc. minor photosynthesisd. storing sugars (and other carbs.) as starch

Fig. 24.1 Organization of a plant body

D. leaves1. blade and petiole2. classified as simple or compound

• leaflets

Fig. 24.21 Classification of leaves

3. leaf structure and anatomya. cuticle

• waxy layer protection and water retentionb. epidermis (upper and lower)

i. protection and gas exchangeii. contains numerous small pores called stomata

• gas exchange CO2 in; H2O vapor and O2 out• guard cells open and close the stomata

c. mesophylli. photosynthetic tissue of plants (chloroplasts)ii. palisade layer

• pillar-shaped cells found in eudicots onlyiii. spongy mesophyll

• contains numerous air spacesd. vascular bundles

i. xylem and phloem that form “leaf veins” (leaf venation)• net vs. parallel venation

ii. support and structure4. leaf functions

• photosyn., gas exch., cons. of H2O, structural support

Fig. 24.20 Leaf structure

Fig. 25.13 Opening and closing of stomata

VI. Secondary Growth A. lateral meristems (cambia)

1. only found in woody plants• primarily in stems, but also in roots

2. occur in rings3. increases in width4. secondary tissues

a. secondary xylem and phloem, cork• sec. xylem forms annual growth rings and becomes wood

b. bark vs. peridermB. two types of lateral meristems

1. vascular cambiuma. near center of stem

• derived from the procambiumb. forms new secondary xylem and secondary phloem

2. cork cambiuma. near outside of stem

• derived from cortex that develops from ground meristemb. forms new cork and cortex cells

Fig. 24.16Secondary growth of stems

Fig. 24.17 Three-year-old woody twig

Apical meristem of stem

Protoderm

Procambium

Ground meristem

Epidermis

Primary phloem

Primary xylem

Pith and Cortex

Vascular cambium

Cork cambium

Secondary phloem

Secondary xylem

Cork

Primary Meristems Primary Tissues Lateral Meristems Secondary Tissues

A summary of primary and secondary growth in woody stems