Biology Chapter 12 Notes:
Plant and Fungi Diversification
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Plants are organisms that are fixed in place; multicellular eukaryote that produces its own food
by photosynthesis and has an embryo that develops within the protected environment of the
female parent; varies in size
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Other photosynthetic eukaryotes include species of algae (seaweed); sharp contrast to most
plants
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A plant needs nitrogen to build proteins; phosphorus to make ATP; salts to create concentration
gradients
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Plants use roots to obtain these needed substances from the soil; plants have a shoot that
consists of a stem and leaves; the stem supports the main photosynthetic organ of a plant (its
leaves)
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Some plants have no chlorophyll; lives as parasites instead; Dodder is a parasitic plant that gets
sugar from host plants it grows on
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If the seed sprouts (germinates) shade, the young plant needs to somehow get to the nearest
sunny spot so it grows towards the direction of the sun
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Sexual reproduction can be a challenge for plants and have various tactics; resisting predators
are another challenge for plants (thorns and chemicals are used to deter predators); earliest
plants were the first multicellular organisms to live on land; were non-vascular plants (no vessels
to transport water and nutrients); evolutionary tree of plants show the stages of development
(vessels, seeds, flowers)
Non Vascular Plants
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Water algae were multicellular and obtained water and nutrients with osmosis; sea lettuce and
stone worts looked like plants; coleochaetes can withstand exposure to air, survie when water
level in lake falls and leaves them high and dry (closest relative to plants) and drying resistance
was the first evolutionary step that plants took to make its way to land

First land plants appeared about 475 million years ago; nothing on land for other land organisms
to eat; first land plants set the diversity for plant life and paved the way for the diversification of
land animals; two initial problems were they had trouble resisting from gravity and faced it by
growing close to the ground; other problem was drying out and it was solved by developing a
waxy layer called a cuticle that covers their leaves and stems

Earliest land platns were low-growing; had no structures that could transport water and
nutrients from soil upward into the plant; diffusion is a slow process and plants that rely on this
only can grow a few centimetres tall; three groups of plants (liverworts, hornworts and mosses)
still use diffusion to move substances (bryophytes) and are considered non-vascular
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Liverworts and hornworts are small, simple plants that grow into moist and shady places that
resemble flattened moss; grow in moist and shady places and resembles flattened moss
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Mosses are more familiar; over 12,000 species grow in habitats from the arctic and alpine
regions to the tropics
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Must live in environments where soil is always moist or become dormant when the soil surface
dries out; had to adapt to reproduction that protected the plant embryo from drying out and
provided it with a source of nutrients; this innovation was alternating the life cycle between
haploid and diploid generations
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Alternation of generations: radically different from the human life cycle; when the spongy mass
of moss appears, it is the part of a haploid life cycle; cells only have one set of chromosomes;
the male and female reproductive structures are located among the feathery leaves at the tips
of the stems and the sperms swim during rainfall; after fertilization, a diploid zygote is formed
and it divides to become an embryo; it is sheltered within the female reproductive structure and
both the embryo and the reproductive structure enlarges; the female structure elongates to the
point where it breaks into two forming a capsule extending over the top of the plant; the
haploid spores are formed by meiosis inside the capsule; a spore is a single cell containing DNA,
RNA and a few proteins; as hundreds of spores are released from the ruptured capsules, the
spores land in moist sheltered spots to grow into new haploids
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Peat moss (sphagnum moss) is harvested and sold as a soil enhancer; some are important for
flood control because they can absorb enormous amounts of water; barleys are used to produce
scotch; important components of biological crust that holds desert soils in place
Vascular Plants
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Vascular tissue is an infrastructure of tubes that begin in the roots and extends up the stem of a
plant and out to the farthest tips of its leaves; evolution of vascular tissue allowed early land
plants to transport water and nutrients faster and more effectively than the cell-to-cell
diffusion; roots reach deep into the soil provide support that a plant needs to grow upward
without falling over; vascular plants can grow taller than non-vascular plants
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Carboniferous ancestors grew in wet habitats where the oxygen concentration around the roots
is low (360-300m years ago); developed hollow stems to absorb oxygen in the wet environment

Having vessels was an important evolutionary step; ferns took an additional step; the leaves of
the ferns have vessels branching from the central vessel to the edges of the leaflet; placed a
channel for the movement of water and nutrients close to each cell in the leaf
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Sporangia: structures in which spores are produced; located on the underside of the leaves;
spores can be blown by the wind when they are released and settled away some distance from
the parent plant
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Prothallus: a spore that lands on moist soil grows into a tiny heart-shaped structure; produces
the haploid gametes and some of which produce eggs or sperm; sperm travels with rain water