Plant Kingdom

Introduction

Remember Photosynthesis!

• Sun + 6CO2 + 6H2O � C6H12O6 + 6O2

Remember Respiration!

• C6H12O6 + 6O2 � 6CO2 + 6H2O + ATP +

heat

Plant Kingdom

• All Plants:

– Eukaryotic

– Multi-cellular

– Most contain chlorophyll in chloroplasts

– Use mitochondria

– Live on land and water

– Do not move from place to place

Plant Kingdom

Origin and Evolution

• For most of the history of the Earth life

existed in the ocean.

• Plants moved to land first

• Evolved from algae

Early Plants

• Oldest plant: Rhynia major, Silurian ~420

mya

• Simple, no seeds, no leaves

• Rely on water for reproduction

• Similar plants live today

Rhynia major

Plant Evolution

Conditions compared

Conditions compared

• In water:

– Lots of water (duh)

– Support

– Light limited

– Limited CO2 and O2 levels

Conditions compared

• On Land

– No support

– Water limited

– Lots of light

– Lots of CO2 and O2

Adaptations to land

• Problem: Support. In water density

supports plant

• Land Solution: Cell walls made of

cellulose, trees also have lignin for extra

support

Adaptations to land

• Problem: Protection from drying out

• Land Solution: Cell walls and waxy cuticle

that covers leaves and stems. Roots and

special cells to carry water in Vascular

plants

Classification: Seedless Plants

• Seedless Nonvascular: No vascular

tissues, reproduce with spores. Need

water for reproduction. Eg. mosses,

liverworts.

• Seedless Vascular: Vascular tissues,

reproduce with spores. Need water for

reproduction. Eg.: ferns, horsetails,

lycophyta.

Classification: Plants with Seeds

• Gymnosperms: Vascular. Reproduce

with seeds, no flowers. Eg.: pine trees,

gingko, firs, junipers.

• Angiosperms: Vascular. Reproduce with

seeds, have flowers. Eg.: grass, rose,

corn, daisy.

Evolution of Plants

Classification

Typical Land Plant

Vascular Flowering Plant

Vascular tissue

• Plants need to move materials through

their bodies

• This is done in the vascular tissues

• Vascular tissues are tube-shaped cells

• 2 kinds of vascular tissue:

– Xylem

– Phloem

Xylem

• Dead cells

• Transport water and minerals from roots

up to the shoot

Xylem Cells

Phloem

• Living cells

• Transport sugars down from leaves to the

roots and across to other parts of the plant

• “sap”

Adaptations: Roots

• Plants use their roots to absorb water and

anchor the plant

• Roots have small fungi called mycorrhizae

that live next to them (myco = fungus,

rhizae = root)

• Mycorrhizae are symbiotic fungi that help

the plant absorb minerals and water

Mycorrhizae

Adaptations: Leaves

• Most photosynthesis takes place in the leaves, but sometimes the stem is important too

• Gas exchange happens through pores in the leaf called the stomata

• Stomata are surrounded by two cells called the guard cells

• When there is enough water in the plant the guard cells open up and let CO2 in and O2 out

• A waxy layer (not cells) called the cuticle helps keep water in the plant. It coats the leaves and stems

Leaf Diagram

Leaf structure

• Most light falls on the upper side of the

leaf

• Most chloroplasts are located in the

palisade layer in the upper part of the leaf

• Most gas exchange happens in the

spongy layer on the lower side of the leaf

• Most stomata are located on the underside

of the leaf

Cuticle sem photos

• http://www.biologie.uni-hamburg.de/b-

online/e05/r03.htm

Leaf cross-section

Stomata

Leaf cross section

Water Loss: Transpiration

• Water moves out of cells by osmosis

• Water lost through stomata by osmosis is

transpiration

• Plants minimize transpiration by closing

the stomata

• Transpiration helps “pull” water through

plant to the leaves where it is used in

photosynthesis (remember water is polar!)

Trees and water

Support

• In water the density of the water supports the algae

• On land, plants had to adapt a support system

• Support is provided by the cell walls (cellulose)

• Plants also have a chemical called lignin that hardens the cell walls

• Lignin provides tremendous support

Lignin Support!