BIOL 371 theme 3

Cellulose

• most abundant organic polymer (umbranched)

Hemicellulose

Branched

Things in primary plant cell wall

Cellulose, structural proteins, hemicellulose, protein

Secondary cell wall

• xylem and sclerenchyma

• Cellulose anchored with lignin

• Waterproof

• Stronger and more rigid

• Is laid down second

• Contains lignin

Why alternation of generations?

Amplifies reproductive success

Xylem

Water conducting cells

Rigid and dead at maturity

Stronger bc of lignin

Xylem and sclenernchyma sandwich and protect phloem

Phloem cells

Transport sugars and solutes

Live cells

Softer

Parenchyma

Unspecialized tissue

Challenges on land

• desiccation

• Respiration

• Reproduction

• Locomotion

• Senses

Major plant adaptations to land

• waxy cuticle

• Stomata

• Vascular tissue

• Root system

Waxy cuticle

Waxy layer that prevents water loss and protects from pathogens

Stomata

• pores for gas exchange

• Controlled by guard cells

• Transpiration

• Flaccid, come together

Tracheids (ferns and conjfers)

Closely packed

Thickened secondary cell walls

Vessels

Angiosperms

Shorter and wider

More efficient transfer

Root system

Underground lignified vascular tissue

Rhizoids in non vascular plants

First animals on land

Trilobites and Chilisorates

Which phyla had multiple transitions to land

• Molluscs

• Insects

• Arachnids

• Myriapods

• Some vertebrates

Living in water

• stable temp

• Removed waste

• Sound

• Support

• Wet gametes

• Modified locomotion and lower visual range

• Limited metabolic rate

Land challenges

• desiccation

• Concrete waste, reduce water loss

• Gas exchange mechanism

• Weight supporting strategy

• Protective coating or internal structure for gametes