Plant Kingdom Introduction

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/bonline/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!