The Plant Kingdom

The oldest and most simple photosynthetic organisms on earth are algae.

The multicellular algae are separated into divisions based on their photosynthetic pigments, food storage products, and cell-wall components. The three major groups include:

Brown algae Red algae Green algae

The Plant Kingdom

                                         

                

Green algae are thoughtto have given rise to the “higher” plants.

The different plants selectedfor adaptations that allowedthem to exploit more of theterrestrial regions…

What adaptations would youneed for transition of life on to land?

They have the same pigments,storage products, and cell-wall type. Also, many of them livein fresh water…

The Plant Kingdom

What are the problems of the transition from water to land?

Problem 1: Desiccation

Solution: waxy cuticle covers surfaces of leaves.

Problem 2: Waxy cuticle also impermeable to gases… how does gas exchange occur?

Solution: stomata – small pores typically found on the underside of leaves.The opening and closing of the pores can be controlled as needed.

Problem 3: Structural support… there is no water to hold the plants up

Solution: lignin – an organic polymer that when deposited during secondarythickening, makes the plant woody and therefore rigid.

Problem 4: Source of water and nutrients?

Solution: Water and nutrients are taken up by the root and vascular systems.

Problem 5: Reproduction – fertilization and dispersal without a liquid medium

Solution: Use complex systems to employ wind, water, and different organismsfor both fertilization and dispersal… more later…

The Plant Kingdom

Although liverworts, mosses,and particularly ferns have many adaptations for life onland, gymnosperms and angiosperms are the only plants that are most adaptedfor life on land… hence theirsuccess!!!

The Plant Kingdom – structure of a leaf

What is the function of the leaf?

What structural form willbest suit this function?

What are the problemsassociated with this structural form?

How does the plant deal with these problems?

(cuticle, stoma and guard cells, vascular bundle)

The Plant Kingdom – Vascular system

The vascular tissue system is responsible for transport of water, minerals, sugars,and plant hormones. There are primarily two types of vascular tissuesfound in plants:

1. Xylem – responsible for moving water and minerals from roots to shoots. Typically they make up of non-living tissue…

2. Phloem – carries substances synthesized by the plant, including sugars, amino acids, and hormones. Phloem cells are however all living… why?

Note that this system is continuous throughout the plant, from the roots all the wayto the smallest of the leaves…

So how do you think water and nutrients get transported using the vascular system?What are the forces acting on each tissue type?

The Plant Kingdom – ReproductionAlternation of Generations

The Plant Kingdom – Reproduction

Mosses:

The Plant Kingdom – Reproduction

Ferns:

The Plant Kingdom – Reproduction

Gymnosperms:

The Plant Kingdom – Angiosperm Reproduction

The Plant Kingdom – Angiosperm Reproduction

The Plant Kingdom – Angiosperm Reproduction

The Plant Kingdom – Angiosperm Reproduction

The Plant Kingdom – Angiosperm Reproduction

The Plant Kingdom – Angiosperm Reproduction

So why are angiosperms so successful?

The Plant Kingdom

How do plants defend themselves against herbivores?

Mechanical defenses:

Waxy cuticle – prevents bacterial and fungal growth

Hairy or sticky leaves – discourage caterpillars and other tiny herbivores

Spines, thorns, and prickles – fend off larger mammalian herbivores

Chemical defenses:

Thousands of different compounds are produced and used by plants.Some of these chemicals include some of the most powerful drugs known to humans (e.g. caffeine, nicotine, cocaine, morphine, etc.)

The Plant Kingdom

Review of some major concepts in plants:

Plants are multicellular, photosynthetic eukaryotes.

Plants evolved from a green algal ancestor

All plants alternate between sporophyte and gametophyte generations

Major trends in evolution of the plant kingdom* growing independence from liquid water* increasing size and independence of the sporophyte generation

Non-vascular plants include mosses and liverworths… they lack true leaves and roots… why?

Xylem is a vascular tissue for conducting water and minerals; phloem is avascular tissue for conducting foods.

Gymnosperms and angiosperms possess seeds; ferns do not

Non-vascular plants and ferns depend on liquid water for fertilization

The Plant Kingdom

Review of some major concepts in plants (cont.):

The pollen of seed plants has evolved mechanisms for dispersal, soliquid water is not needed for the transfer of male gametes.

Gymnosperms have a life cycle in which naked seeds are produced onthe scales of cones

Angiosperms are distinguished by the production of flowers and fruits.