Plant Organs

Roots & Stems

I. Roots

A. F(x)s

= grow underground1. Absorb water & nutrients

from soil2. Anchor plant in the soil3. Make hormones

important for growth

& development

I. Roots

B. Structure1. Root cap

F(x) = protects apical meristem

I. Roots

B. Structure2. Root hairsF(x) = increase surface area

for absorption

I. Roots

B. Structure3. Casparian

Strip

F(x) =*channel water & dissolved nutrients into vascular tissue*allow movement only into

roots

I. Roots

C. Types of Roots1. Taproots

a. Large main root that can store foodb. F(x) = absorption,

anchoringE.g.

beet carrot

C. Types of Roots

2. Fibrous rootsa. Numerous small rootsb. Grow near surfacec. F(x)= absorption,

anchoringc. E.g. grass

C. Types of Roots3. Prop or

Adventitious roots

a. Grow down to soil from stem,above ground

b. F(x)s

= support, absorption

c. E.g. corn,banyon

tree

C. Types of Roots

4. Aerial Rootsa. Grow without soil,

in airb. F(x) = absorb water

from moist airc. E.g. orchids in

tropical rainforest

II. Stems

A. F(x)s1. Hold leaves up to sunlight

2. Transport water & nutrients from roots to leaves

3. Food storage in some plants

II. Stems

B. Stem Structures1. Node

–

place where

one or more leaves areattached

Note:

At the point of attachment of each leaf, there is a lateral bud with an apical meristemcapable of developing into a new shoot

II. Stems

B. Stem Structures2. Internode

–

part of stem between nodes

II. Stems

C. Specialized stems1. Rhizome

= horizontal underground stem

2. Tuber

= Underground stem w/ buds Food storageE.g. potato, parsnip

II. Stems

C. Specialized stems3.

Bulb

= large bud w/ layersFood storageMany edibleE.g. onion, garlic

II. Stems

C. Specialized stems4. Corm

=

Upright, thickened underground stemFood storageNot usually edibleE.g. shamrock plant (Oxalis)

II. Stems

C. Specialized stems5. Some plants almost

all stem, no leavesE.g. cactus

II. Stems

D. Stem growth1. Growth in Length –

only at tips of

stems where new primary growth occurs via apical meristems

2. Growth in Circumference –width

via

lateral meristems

II. Stems

E. Primary Growth in Stems1. Vascular tissue arranged in

vascular bundles2. Dicots

–

bundles in a ring around

outside edge 3. Monocots –

bundles scattered

throughout stem

Dicot

stem CS

Vascular bundles

II. Stems

II. Stems

E. Primary Growth in Stems4. Pith

–

center of the stem

5. Cortex

–

ground tissue btwn. Vascular Bundles & epidermis

Vascular bundledicot monocot

II. Stems

F. Secondary Growth in Stems¿Which get wider year after year,

monocots or dicots?DICOTS!

**Most monocots have no secondary growth.

1. ↑stem width in dicots

due to cell ÷

in vascular cambium

II. Stems

2. Vascular Cambium arises in vascular bundle btwn. xylem & phloem

3. Cylinder formed by cambium, then secondary xylem inside,then secondary phloem on outside of cylinder

II. Stems

G. Woody Stems1. Heartwood2. Sapwood3. Bark

DRAW THIS!

II. Stems

G. Woody Stems1. Heartwood Dark colorCenter of tree trunkDead xylem , no longer transports waterF(x) =

support

II. Stems

G. Woody Stems2. SapwoodLighter in colorNearer to outside of tree trunkF(x) = transport (live xylem)

Note: In a large diameter tree, heartwood gets wider, sapwood stays relatively same width

II. Stems

G. Woody Stems3. BarkF(x) = protectionMade of cork, cork cambium & phloem

II. Stems

H. Stem F(x)s1. Phloem moves sugars

a. Translocation –

sugars moved from source (photosynthesis in leaves)to sink (where they are stored)

b.

Products of

Photosynthesis can movein ____?___ direction

ANY

II. Stems

H. Stem F(x)s1. Phloem moves sugars

c. Pressure –

Flow Hypothesisi. Sugars PUMPED into sieve tubes

@ the sourceii. Turgor

= pressure increase due to

water entering sieve tubes by osmosis

II. Stems

H. Stem F(x)s2. Xylem moves water & nutrients

a. Cohesion-Tension Theorycombination of 3 processes:i. Transpirationii. Cohesioniii. Adhesion

Transpiration

In leaves, release of excess water to atmosphereCreates negative pressure in xylemReplacement water pulled from xylemWater enters roots to replace lost water

Cohesion

Water molecules stick to each other & pull each other up narrow xylem tubesWater is a polar molecule, thereforeWater molecules attract each other!

Adhesion

Water molecules strongly attracted to xylem wall

II. Stems

b. Final words on water movement in plantsi. Varies with time of dayii. Midday –

stomata open, rapid movement

iii. Night –

stomata closed movement stops

Exception: cacti stomata open @ night¿Why?to minimize water loss