PLANTS

Chapters 23-26

Evolution of PlantsAll Plants…• multicellular, eukaryotic, autotrophic

Angiosperms

Monocots vs. Dicots• named for the numberof cotyledons present on the embryo of the plant

+ monocots- orchids, corn, lilies, grasses

+ dicots- roses, beans, sunflowers, oaks

Alternation of GenerationsSporophyte (diploid)• produces haploid spores via meiosis

Gametophyte (haploid)• produce haploidgametes via mitosis

Fertilization• joins two gametes toform a zygote

Plant MorphologyMorphology (body form)

- shoot system + stems, leaves, flowers- root system + taproot, lateral roots

• vascular tissues + transport materials between roots and shoots

- xylem/phloem

Plant Anatomy Anatomy (internal structure)• division of labor + cells differ in structure and function

- parenchyma, collenchyma, sclerenchyma (below)

ParenchymaSt: “typical” plant cellsFu: perform most metabolic functions

CollenchymaSt: thick wallsFu: provide support but allow growthin young parts of plants

SclerenchymaSt: hardened secondary walls (LIGNIN)Fu: specialized for support; dead

Plant cell types• Xylem • Phloem

WATER-CONDUCTING CELLS OF THE XYLEM

Vessel Tracheids

Tracheids and vessels

Vesselelement

Tracheids

SUGAR-CONDUCTING CELLS OF THE PHLOEM

Companion cell

Sieve-tubemember

Sieve-tube members:longitudinal view

Sieveplate

Nucleus

CytoplasmCompanioncell

Water- and Food-conducting CellsXylem (water)

• dead at functional maturityPhloem (food)• alive at functional maturity• sieve-tube cells- arranged end to end with sieve plates &Companion cells

Plant TissuesThree Tissue Systems• dermal tissue + epidermis (skin)

- single layer of cells that covers entire body- waxy cuticle/root hairs

• vascular tissue + xylem and phloem

- transport and support• ground tissue + mostly parenchyma

- filler tissue- photosynthesis, storage, support

Plant GrowthMeristems• embryonic tissues located at regions of growth

- apical meristems (primary growth- length) + located at tips of roots and shoots- lateral meristems (secondary growth- girth)

Roots• A root

– Anchors the plant– Absorbs minerals and water– Stores organic nutrients– Taproots: vertical– Lateral roots: horizontal branches– Fibrous root system in monocots (e.g. grass)

Figure 35.3

Modified Roots• Many plants have modified roots

(a) Prop roots (b) Storage roots(c) “Strangling” aerial

roots

(d) Buttress roots (e) Pneumatophores

(a) Prop roots (b) Storage roots

Modified Stems

Rhizomes(d)

Tubers (c)Bulbs

Stolons

(a)

Storage leaves

Stem

Root Node

Rhizome

Root

Buds• An axillary bud

– Forms a lateral shoot• A terminal bud

– Causes elongation of a young shoot

Gardening tip:Removing the terminal bud stimulates growth of axillary buds (e.g. makes plants bushier)

The leafIs the main photosynthetic organ of most vascular plants

Modified Leaves

Tendrils

Spines

Storage leaves

Bracts

Reproductive leaves. The leaves of some succulents produce adventitious plantlets, which fall off the leaf and take root in the soil.

Leaf AnatomyEpidermal Tissue• upper/lower epidermis• guard cells (stomata)

Ground Tissue• mesophyll +palisade/spongy parenchyma

Vascular Tissue• veins + xylem and phloem

The Vascular Cambium and Secondary Vascular Tissue

• The vascular cambium– Is a cylinder of meristematic cells one cell thick– Develops from parenchyma cells

Secondary Growth

• As a tree or woody shrub ages– The older layers of secondary xylem, the

heartwood, no longer transport water and minerals

• The outer layers, known as sapwood– Still transport materials through the xylem

PLANT REPRODUCTION

Plant ReproductionSporophyte (diploid)• produces haploid spores via meiosis

Gametophyte (haploid)• produce haploidgametes via mitosis

Fertilization• joins two gametes toform a zygote

• Flowers

Double FertilizationDouble Fertilization• pollen grain lands on stigma + pollen tube grows toward ovule + 2 sperm discharged down the tube

- egg and one of the sperm produce zygote

- 2 polar nuclei and sperm cell produce endosperm

+ ovule becomes the seed coat + ovary becomes the fruit

Seed Structure and Development

Asexual Reproduction in Plants: Vegetative Propagation

• Budding and Grafting: smaller stems from one plant are attached to another plant• Taking cuttings: pieces

of one plant are used to grow another• Stems can be modified:• Runners: horizontal

stems aboveground• Rhizome: horizontal

stems belowground• Tuber: swollen

underground stem

Plant nutrition

Plant NutritionWhat does a plant need to survive?

Soil Bacteria and Nitrogen Availability• Nitrogen-fixing bacteria convert atmospheric N2

– plants absorb ammonium (NH4+), nitrate (NO3

-)

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)

NH4+

(ammonium)

H+

(From soil)

NO3–

(nitrate)Nitrifyingbacteria

Denitrifyingbacteria

Root

NH4+

Soil

Atmosphere

Nitrate and nitrogenous

organiccompoundsexported in

xylem toshoot system

Ammonifyingbacteria

Nutritional AdaptationsSymbiotic Relationships• Mycorrhizae + symbiotic associations of fungi and roots

- mutualistic relationship: fungus receives food from plant and plant receives increased surface area for root absorption

Unusual nutritional adaptations

Plant Transport

MineralsH2O CO2

O2

CO2 O2

H2O Sugar

Light

• A variety of physical processes– Are involved in the different types of transport

Sugars are produced byphotosynthesis in the leaves.

5

Sugars are transported viaphloem to other parts of the plant.6

Through stomata, leaves take in CO2 and expel O2.

4

Transpiration, the loss of waterfrom leaves, pulls xylem sap upward.

3

Water and minerals aretransported upward in the xylem.

2

Roots absorb waterand mineralsfrom the soil.

1 Roots exchange gases with the soil, taking in O2 and discharging CO2 in cellular respiration

7

• Water and minerals ascend from roots to shoots through the xylem

• Plants lose an enormous amount of water through transpiration, the loss of water vapor from leaves

• The transpired water must be replaced by water transported up from the roots

Control of Transpiration • Water enters guard cells and causes cells to swell, opening

stomata.• Water leaves guard cell and they shrink, closing stomata

TranslocationIs the transport of organic nutrients in the plant

Phloem sapIs an aqueous solution that is mostly sucroseTravels from a sugar source to a sugar sink

Translocation through Phloem

A sugar sourceIs a plant organ that is a net producer of sugar, such as mature leaves

A sugar sinkIs an organ that is a net consumer or storer of sugar, such as a tuber or bulb

Sugar Source & Sink

HOW DO PLANTS RESPOND TO THE ENVIRONMENT?

Write down as many ways you can think of in your lab notebook.

Tropisms

• Growth toward or away from a stimulus

• Gravitropism (Gravity)• Phototropism (Light)• Thigmotropism (Touch)

Plant hormones help coordinate growth, development, and responses to stimuli

• Hormones– Are chemical signals that coordinate the different parts of

an organism

Photoperiod, the relative lengths of night and day+ Is the environmental stimulus plants use most often to detect the time of year and when to flower