The Plant Kingdom
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
Green algae are thought to have given rise to the
“higher” plants.
They have the same pigments, storage products, and cell-wall type. Also, many of them live in fresh water…
The different plants selected for adaptations that allowed them to exploit more of the terrestrial regions…
What adaptations would you need for transition of life on to land?
The Plant Kingdom
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 secondary thickening, 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 organisms for both fertilization and dispersal… more later…
Although liverworts, mosses, and particularly ferns have many adaptations for life on land, gymnosperms and angiosperms are the only plants that are most adapted for life on land… hence their success!!!
The Plant Kingdom
The Plant Kingdom – structure of a leaf
What is the function of the leaf?
What structural form will best suit this function?
What are the problems associated 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 tissues found 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 way to 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 – Reproduction
Alternation of Generations
Mosses:
The Plant Kingdom – Reproduction
Ferns:
The Plant Kingdom – Reproduction
Gymnosperms:
The Plant Kingdom – 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
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 a vascular 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, so liquid water is not needed for the transfer of male gametes.
Gymnosperms have a life cycle in which naked seeds are produced on the scales of cones
Angiosperms are distinguished by the production of flowers and fruits.
