Characteristics of Algae
Algae are plantlike protists that contain photosynthetic pigments.
Algae differ from plants because they do not have roots, leaves, or other structures
typical of plants.
Many algae have chlorophyll as their main photosynthetic pigment, and also have
accessory pigments to help them absorb light at different wavelengths.
Diversity of Algae
Algae can be single or multicellular.
Some unicellular algae are called phytoplankton and form the base of many aquatic
food webs.
Algae are classified using three criteria: pigment type, method of food storage, and
cell wall composition.
Diversity of Algae
Diatoms
Diatoms are photosynthetic autotrophs that use chlorophyll and carotenoids as
pigments.
They store food as oil, making them a nutritious food source and buoyant (float) in
water.
Diatom cell walls are composed of silica.
reproduce both sexually and asexually.
Dinoflagellates
Phylum Pyrrophyta are dinoflagellates
Predominantly (mainly) unicellular, with two flagella at right angles to one another,
causing the dinoflagellate to spin as it moves.
Dinoflagellates have cell walls made of cellulose.
Some are autotrophic, some are heterotrophic
Some are bioluminescent, meaning they emit light
A particular type of dinoflagellate algal bloom is a red tide.
Red tides can be a serious threat to humans and the ecosystem because the
dinoflagellate involved produces a toxin.
The toxin is ingested by shellfish, which are then ingested by humans.
The ecosystem is affected through reduced light penetration, toxin levels, and
reduction in primary producers to the food web.
Euglenoids
Phylum Euglenophyta, euglenoids, are unicellular plantlike protists.
Contain characteristics of both plants and animals.
Most euglenoids photosynthesize, but do not have a cell wall; they can also be
heterotrophs.
Chrysophytes
Phylum Chrysophyta, chrysophytes, are yellow-green or golden-brown algae.
Have carotenoids as a photosynthetic pigment
Most chrysophytes are unicellular, but some are colonial.
A colony is a group of cells that join together and form a close association.
Brown algae
Phylum Phaeophyta contain the brown algae, some of the largest and most plantlike
multicellular algae (multicellular)
Color comes from secondary pigment called fucoxanthin.
More than 1500 species live along rocky coastlines.
Green algae
Phylum Chlorophyta, green algae, are photosynthetic r organisms that have much in
common with plants.
Can be unicellular, multicellular, or colonial
Have cell walls and store food as carbohydrates
Many scientists think there is an evolutionary link between green algae and plants.
Red algae
Phylum Rhodophyta, red algae, contains mostly multicellular organisms.
Color comes from a photosynthetic pigment called phycobilin
Phycobilin absorbs blue and violet light that penetrates deeper into the water, allowing
red algae to live in deeper water than other algae.
Uses for Algae
• Algae are a food source for animals and people worldwide
• Used as a food additive for stabilizing or improving texture without adding fat.
• Fertilizer
• Biofuel
• Bioplastic
• Pollution control
Life Cycles of Algae
Alternation of generations
• Algae can alternate between spore-producing forms and gamete-producing forms.
• Alternation of generations is a life cycle that takes two generations to complete, one
that reproduces sexually and one that reproduces asexually.
Haploid and diploid generations
• The haploid form of an organism is called
the gametophyte generation.
• Begins with spores and ends with male
and female gametes
• Gametes from two different organisms
combine to form a zygote.
• The diploid form begins with the fertilized
zygote
• Zygote develops into the sporophyte
(2n)
• Sporophyte cells divide with meiosis,
producing n spores
• Spores develop into new gametophytes
