More than just the scum
of the earth
 These water plants are tied closely to an
aquatic environment and we have numerous
representatives along the coast of British
Columbia
 Algae must be supported by water unlike land
plants which require stems to support them
 All algae contain
chlorophyll “a” as a
primary
photosynthetic
pigment
 They absorb carbon
dioxide, minerals, and
water by diffusion
through cell
membranes
KINGDOM PLANTAE
Phylum
Common Name
Chlorophyta
Green algae
Phaeophyta
Brown algae
Phodophyta
Red algae

Three main characteristics separate the phyla:
The photosynthetic pigments other than
chlorophyll “a”
2) Method of food storage (ex. starch)
3) The characteristics of locomotory
structures, when present
1)

We should consider algae from another point
of view. As photosynthesizers, algae
produce approximately 50-80% of the earth’s
oxygen and as phytoplankton, they form the
basis of the entire aquatic food chain
Chlorophyta
 Examples: Ulva,
Chlamydomonas,
Spirogyra, Volvox
 Green algae comprise
the largest number of
species
 Many are unicellular
chlorophytes that are
colonial, filamentous,
symbiotic
Chlorophyta
 Evidence suggests that green algae evolved into
land plants and that they shared a common
ancestor because they both have chlorophyll “a”
and “b” and they both store food in the form of
starch.
 This is one reason why algae are considered “lower
plants”, along with mosses and liverwarts.
 The green algae have complex life cycles with both
sexual and asexual reproductive stages
Rhodophyta
 Examples: Porphyra
(nori), Halosaccion,
Corallina
 Larger seaweeds that
are more abundant in
tropical waters
 Usually grow attached
to rocks
Rhodophyta
 Accessory pigments called phycobilins mask
the grass-green colour of chlorophyll “a” and
give red algae its distinctive colour
 Red algae are suited for absorption of the
green, violet, and blue light that penetrates
into deep water
 Cell walls contain calcium carbonate, thus
giving some species a stronger structure.
Rhodophyta
Phaeophyta
 Examples:
Macrocystis, Fucus,
Laminaria
 Often commonly
referred to as “kelps”
 Macrocystis and
Nereocystis may be
more than 60 m long
Phaeophyta
 Most life cycles involve alternation of
generations which means they will switch back
and forth between the production of diploid
and haploid cells
 The brown/olive colour of brown algae is due to
fucoxanthin, a carotenoid pigment
Reproduction in Algae
 The life cycles of most algae include both a
diploid and a haploid generation
 The switching back and forth between the
production of diploid and haploid cells is called
alternation of generations
 Most species of algae also shift back and forth
between sexual reproduction that involves
gametes and asexual reproduction that involves
haploid cells called zoospores
Alternation of Generations
 In this life cycle, a sporophyte (2N) which
represents the diploid generation, alternates
with the gametophyte (N), which represents the
haploid generation
 Each generation produces the other
Alternation of Generations
 The sporophyte produces spores by meiosis
 A spore is a haploid reproductive cell that
develops into a new organism without the need
to fuse with another reproductive cell
 In the plant life cycle, a spore undergoes
mitosis and becomes a gametophyte
Alternation of Generations
 The gametophyte produces gametes by
mitosis. A sperm and egg fuse to form a zygote
(2N) that grows by mitosis and becomes the
sporophyte
 Plants differ as to which generation is dominant
or conspicuous
Reproduction in Chlamydomonas
 Chlamydomonas spends most of its life in the haploid stage
 As long as environmental conditions are favorable, the
haploid cell reproduces by mitosis. This produces zoospores
which then mature and are able to reproduce asexually
 If conditions are unfavourable, Chlamydomonas will switch
to reproducing sexually
 The haploid cells will still undergo mitosis, but instead of
releasing zoospore, the cells release gametes
Reproduction in Chlamydomonas
 There are two types of gametes (+) and (-);
however, they appear identical. This is known as
isogamy
 During sexual reproduction, the gametes gather in
a large group and then (+) and (-) gametes pair up
and move away from the group
 The paired gametes join flagella and spin around in
the water
 Both members shed their cell walls and fuse,
forming a diploid zygote. This fusing is called
syngamy
Reproduction in Ulva
 The diploid plant is called the sporophyte
because it produces spores and the haploid
plant is called the gametophyte because it
produces gametes
 Ulva actually produces two different types of
gametes, one of which is larger then the other.
Two different kinds of gametes is referred to as
heterogamy
 When the two different gametes fuse, the
resulting diploid zygote does not enter a resting
stage