La botánica (del griego βοτάνη, 'hierba') o fitología (del griego φυτόν, 'planta' y λόγος, 'tratado') es la rama de la biología que estudia las plantas bajo todos sus aspectos, incluyendo la descripción, clasificación, distribución, identificación, estudio de la reproducción, fisiología, morfología, relaciones recíprocas, relaciones con los otros seres vivos y efectos provocados sobre el medio en el que se encuentran.

1. CÓDIGO DE HONOR
Escriba el compromiso y firme su nombre.
“Acepto la responsabilidad de mi función de garantizar
la integridad y honestidad del trabajo presentado por el
grupo en el que participé”.
Firma ________________________
Firma ________________________

2. Lab Exercise 1
Cyanobacteria, Euglenoids, Dinoflagellates
Lab Objectives:
• To recognize the characteristic morphological features of major groups of algae
• To relate structure to function in algal groups
Introduction
Most of us think of algae as photosynthetic aquatic organisms, essentially unicellular plants.
However, this definition is oversimplified and omits many groups of algae. It is very difficult to
generalize about this very diverse group of organisms and to arrive at a simple definition.
Graham and Wilcox (2000) define algae as: (generally) aquatic organisms that (with frequent
exceptions) are photosynthetic, oxygenic autotrophs that are (except for the kelps) typically
smaller and less structurally complex than land plants. The term “algae” includes prokaryotes
(the Cyanobacteria), and several diverse groups of remotely related protists, hypothesized to
have acquired plastids and other organelles via endosymbiosis.
Algae are found in aquatic (marine and freshwater) environments, and a diversity of terrestrial
habitats. They exhibit a range of adaptations to these environments as free-living forms and in
close association with other organisms (e.g. as mutualists, parasites). With nearly 70% of the
earth’s surface covered with water, the importance of algae to the overall oxygen and carbon
budgets cannot be overstated. They are key consumers of CO2 and it is estimated that they
produce 50-70% of the world’s oxygen.
Algae are also very diverse morphologically and can occur as single cells, colonies, filaments or
multicellular forms and range in size from <1 µm (unicells) to >60m in length (filaments). As
discussed in class, they exhibit a range of asexual and sexual reproductive strategies.
Traditionally, algal classification has been based on whether they are prokaryotic or eukaryotic,
their major cell wall components, the number and type of flagella and, most importantly, by the
composition of their accessory pigments. However, these phylogenetic relationships are under
continuous revision and often much debated, due to the ultrastructural, biochemical and genetic
evidence more recently collected. Hence there is often a rather confusing variation in algal
systematics among different texts, as different authors adopt different nomenclature. As noted in
class, we are following the classification of Raven et al., (2004).
Cyanobacteria
These prokaryotes are often called blue-green algae, because of one of their major accessory
pigments, phycocyanin, although these organisms actually show a range of colours (e.g. red,
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3. green or black). Cyanobacteria were the dominant life-forms on earth for more than 1.5 billion
years, and were the most ancient O2-producing photosynthesizers (Graham and Wilcox, 2000).
The chloroplasts of eukaryotic algae and land plants descended from cyanobacterial
endosymbionts. Cyanobacteria occur in soil, in all aquatic environments including hot springs
and form symbiotic associations with certain fungi (forming lichens) as well as certain plants.
They reproduce asexually through binary fission and fragmentation. Cyanobacteria range in size
and morphology from minute unicellular forms, to filamentous or large colonial species visible
to the naked eye. Some of these produce noxious blooms under eutrophic conditions, which can
severely degrade water quality. A number of species produce cyanotoxins (neurotoxins and
hepatotoxins, cytotoxins) that can be toxic to herbivores, fish and large vertebrates.
Cyanobacteria exhibit similar cell structure and physiology to other prokaryotes:
• no membrane-bound organelles and prokaryotic flagella (no 9+2 microtubule structure);
• cell walls composed of peptidoglycan with a lipopolysaccharide layer;
• mucilaginous sheaths;
• DNA is concentrated in the central part of the cytoplasm (the nucleoplasm);
• cell division via binary fission
In addition, Cyanobacteria have
• Chlorophyll a, β-carotene and xanthophylls, located in thylakoids; unstacked thylakoids that
lie free in the cytoplasm;
• phycobiliproteins (phycobilin pigments bound to proteins): phycocyanin
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, allophycocyanin
and phycoerythrin. These pigments absorb light in the spectrum not captured by chlorophyll
a and carotenes, allowing these organisms a wide distribution over different light regimes.
Phycobiliproteins occur as disk-shaped phycobilisomes on the thylakoid surface.
Cyanobacteria and other algae adapt to different light regimes by modifying their pigment
content (chromatic adaption).
• carbohydrate reserve as cyanophycean starch (glycogen; an α-1,4-linked polyglucan) in
small granules between the thylakoids;
• gas vesicles (in many species).
• one group (the Nostocales) produce specialised cells (heterocysts) that fix atmospheric
nitrogen into a usable form, ammonium. This process requires localised anaerobic conditions.
• Large, thickened resting cells (akinetes) that tolerate extreme conditions (e.g. desiccation);
similar to endospores produced by non-photosynthetic bacteria.

4. Gloeocapsa is common in freshwater and intertidal zones, moist or arid soil and other terrestrial
habitats. This species is one of the Cyanobacteria that are found closely associated with fungae in
lichens. Gloeocapsa occurs typically as colonies of 2-4 cells, each surrounded by a tough layered
mucilaginous sheath.
1. Place a small drop of Gloeocapsa culture on a microscope slide in a small drop of India ink.
The ink will help you see the mucilaginous sheath surrounding the cells. Draw a diagram of one
colony, noting the vegetative cells and the sheath. As well as holding the cells together, what
adaptive advantage is provided by the thick sheath?
Microcystis consists of colonies of small cells, randomly distributed in a gelatinous matrix, and
can sometimes grow to very large colonies, visible to the unaided eye. A sometimes toxic and
odorous component of freshwater plankton communities, it also occurs in masses on lake
bottoms.
2. Place a drop of Microcystis culture on a microscope slide in a small drop of India ink. Draw a
colony. Can you see the gas vesicles? What is their function?
3. Microcystis lacks heterocysts, but can fix N2 at a slow rate in the dark. How might this be
possible?
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5. Oscillatoria is a filamentous cyanobacterium that reproduces by fragmenting at separation disks,
which are dead cells located along the filament between groups of living cells or hormogonia.
4. Some members of this genus cause thick, toxic blooms in eutrophic waters under ice, as well
as during the summer. What characteristics might facilitate these blooms?
5. Observe the living and prepared slides of Oscillatoria and diagram one filament. Label the
separation disks and hormogonium. Can you see the oscillations (waving) of the Oscillatoria
filaments? What is the adaptive advantage to this movement?
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6. Anabaena is another filamentous cyanobacterium that is chiefly planktonic. It is mostly found in
freshwater. Anabaena reproduces through fragmentation similar to Oscillatoria, but does not
produce separation disks. Anabaena produces akinetes. In some cases, the vegetative cells of the
entire filament are converted into akinetes in periods of environmental stress. Under low nitrogen
(NH4, NO3) levels Anabaena also produces heterocysts, while some species form large
secondary colonies of interwoven filaments.
6. Using the live culture of Anabaena and prepared slides, sketch and label a filament, showing
heterocysts and akinetes. How do these two cell types differ in appearance to vegetative
cells? Did you observe any akinetes in the live culture? If not, why do you think they are
not present?
Nostoc has a filamentous cell arrangement similar to that of Anabaena, but these are usually
coiled into large balls held together in a tough gelatinous matrix, common in soil, and in the
benthos of many shallow ponds.
7. Prepare a wet mount of Nostoc. Make sure to spread out the sample. Are heterocytes
present? Can you see any akinetes?
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