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Algae - 3 General characters.

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Presentation on theme: "Algae - 3 General characters."— Presentation transcript:

1 Algae - 3 General characters

PHYCOLOGY=STUDY OF ALGAE Phycology is the science (gr. logos) of algae (gr. phycos). This discipline deals with the morphology, taxonomy, phylogeny, biology, and ecology of algae in all ecosystems

3.5 billion yrs ago Cyanobacteria—first algae Prokaryotes—lack membrane bound organelles Later eukaryotes evolved—mitochondria, chloroplasts, and chromosomes containing DNA.

4 Where do algae abound? Kelp  forest up to 50 m height are the marine equivalent to terrestrial forest; mainly built by brown algae. Some algae encrust  with carbonate, building reef-like structures; Cyanobacteria can from rock-like structures in warm tidal areas: stromatolites.

5 Where do algae abound? Algae grow or are attached to animals and serve  as camouflage for the animal Algae live as symbionts  in animals such as Hydra, corals, or the protozoan ciliate Paramecium; in corals they are referred to as zooxanthellae

6 Where do algae abound? Small algae live on top of larger algae: epiphyton Algae in free water: phytoplankton Terrestrial algae Algae have adapted to life on land and occur as cryptobiotic  crusts in desert and grassland soils or endocryptolithis algae in rocks 

7 Where do algae abound? Algae live on the snow cover of glaciers and in the brine  channels of sea ice. A symbiosis  of algae and fungi produced the lichens, which are pioneer plants, help convert rock into soil by excreting acids, stabilize desert soil, are sensitive to air pollution

8 Where do algae abound? Algae can cover trees or buildings green or live in the hollow  hairs of ice bears

9 Algal Blooms Algae can be so dominant that they discolor the water
Higher amounts of nutrients are usually the cause Algal blooms can have harmful effects on life and ecosystem: Reduced water clarity causes benthic communities to die off Fish kills are common effects 50% of algal blooms produce toxins harmful to other organisms, including humans Algal blooms produce a shift  in food web structure and species composition Algal blooms can mostly be linked to sewage input or agricultural activities, leading to nutrient pollution: Eutrophication

10 Similarities Presence of cell wall—mostly cellulosic.
Autotrophs/Primary producers—carry out photosynthesis Presence of chlorophyll a

11 Differences Algae lack the roots, stems, leaves, and other structures typical of true plants. Algae do not have vascular tissues—non vascular plants Algae do not form embryos within protective coverings—all cells are fertile. Variations in pigments. Variations in cell structure—unicellular, colonial and multicellular forms.

Prokaryote algal cell Prokaryotes ---No nuclear region and complex organelles—chloroplasts, mitochondria, golgi bodies, and endoplasmic reticula. -- Cyanobacteria. Chlorophylls are on internal membranes of flattened vesicles called thylakoids-contain photosynthetic pigments. Phycobiliproteins occur in granular structures called phycobilisomes. Source:

13 Prokaryotic and Eukaryotic Algae
Eukaryotes ---Distinct chlorplast, nuclear region and complex organelles. --- Thylakoids are grouped into grana pyrenoids are centers of carbon dioxide fixation within the chloroplasts of algae and hornworts. Pyrenoids are not membrane-bound organelles, but specialized areas of the plastid that contain high levels of ribulose-1,5-bisphosphate carboxylase/oxygenase granum with a Stack of thylakoids pyrenoid

14 Forms of Algae Forms of algae Multicellular Unicellular Colonies
2. Aggregations Palmelloid (Tetraspora) Dendroid (Dinobryon) Amoeboid (Chlororachnion) 3.Filaments 4. Coenocytic / Vaucheria 5.Parenkematus/ Ulva 6. Psedoparenkematus / Batrachospermum 7. Erect thallus / Chara Non motile(Chlorella) Motile (Euglena)

----MICROSCOPIC Unicellular, Colonial and Filamentous forms. Source:

16 Forms of Algae MACROALGAE

17 Forms of Algae MICRO ALGAE

18 Forms of Algae Unicells: single cells, motile with flagellate (like Chlamydomonas and Euglena) or nonmotile (like Diatoms)

19 2. Multicellular form: the vegetation forms are in six forms:
Colonies: Assemblage of individual cells with variable or constant number of cells that remain constant throughout the colony life in mucilaginous matrix (containing an extracellular matrix made of a gelatinous glycoprotein), these colonies may be motile (like Volvox and Pandorina) or nonmotile (like Scendesmus and Pediastrum).

20 Coenobium: Colony with constant number of cells, which cannot survive alone; specific „tasks“ among groups of cells is common (is a colony containing a fixed number of cells, with little or no specialization)

21 b. Aggregations: is aggregation of cells that have ability to simple division (so, its colony but unconstant in form and size), the aggregations are in several types: Palmelloid form: non-motile cells embedded in mucilage (like Tetraspora).

22 Dendroid form: resembling a tree in form or in pattern of growth (Dinobryon).

23 Amoeboid or Rhizopodial form such as Chlorarachnion.

24 c. Filaments: daughter cells remain attached after cell division and form a cell chain; adjacent cells share cell wall (distinguish them from linear colonies!); maybe unbranched (uniseriate such as Zygnema and Ulthrix) or branched (regular mutiseriate such as Cladophora or unreguler mutiseriate such as Pithophora). Cladophora Pithophora

25 d. Coenocytic or siphonaceaous forms: one large, multinucleate cell without cross walls such as Vaucheria

26 e. Parenchymatous (such as Ulva ) and algae: mostly macro-scopic algae with tissue of undifferentiated cells and growth originating from a meristem with cell division in three dimensions

27 ; pseudoparenchymatous (such as Batrachospermum) pseudoparenchymatous superficially resemble parenchyma but are composed of apprised filaments

28 f. Erect thallus forms: Thallus, from Latinized Greek (thallos), meaning a green shoot or twig, is an undifferentiated vegetative tissue (leaves, roots, and stems) of some non-mobile organisms such as Chara and Nitella. Chara

Flagella=organs of locomotion. Chloroplast=site of photosynthesis. Thylakoids are present in the chloroplast. The pigments are present in the thylakoids. Pyrenoid-structure associated with chloroplast. Contains ribulose-1,5-bisphosphate Carboxylase, proteins and carbohydrates. Eye-spot=part of chloroplast. Directs the cell towards light. Source: A Biology of the Algae By Philip Sze, third edition, WCB MCGraw-Hill

30 Variations in the pigment constitution
Chlorophylls (green) Carotenoids (brown, yellow or red) Phycobilins (red pigment-phycoerythrin blue pigment –phycocyanin)

31 Growth in algae Diffuse or generalized growth: (Ulva).
Localized growth: Apical growth: (Chara, Cladophora). Basal growth: (Bulbochaete). Intercalary growth: (Laminaria, Oedogonium). Trichothallic growth: (Ectocarpus)

32 Apical and intercalary
Growth in algae Apical and intercalary Tricothallic

33 Reproduction in algae The reproduction of algae can be discussed under two types, namely, asexual reproduction and sexual reproduction. The former type refers to reproduction in which a new organism is generated from a single parent. In case of sexual type, two haploid sex cells are fused to form a diploid zygote that develops into an organism. Let's discuss in brief about the asexual and sexual reproduction in algae along with examples.

34 First: Asexual Reproduction includes: 1. Vegetation reproduction:
In unicellular algae: simple cell division some time called binary fission (such as Gleocapsa). In multicellular (colonies, filamentous, thallus, etc) by: Fragmentation such as Microsystis. Hormogonia: A small, motile filament, formed by some Cyanobacteria, that detaches and grows by cell division into a new filament such as Oscillatoria. Propagules: a structure capable of producing a new individual such as Sphacelaria.

35 Vegetative reproduction
Cell Division A cell could not keep growing bigger forever. Food molecules could not reach the inside of a large cell fast enough to keep it alive. So when a cell reached a certain size it had to divide into two smaller cells called daughters. The daughters grew and, when they reached that certain size, they too divided, this processes called binary fission. But this caused a problem, Why?.

36 Vegetative reproduction
Hormogonia in Oscillatoria

37 Vegetative reproduction

38 2. Another method of asexual reproduction in algae is by formation of spores; the algal species Ulothrix, Chlamydomonas and Chlorella reproduce by this method. Depending upon the algal species, the spores can be produced in normal vegetative cells or specialized cells called sporangia. They are either motile called zoo spores or non motile called akinete spores.

39 Ulotrix

40 There are a lot of types of akinete spores such as:
Autospores: immobile spores that cannot develop flagella such as Chlorella. Aplanospores: immobile spores that may nevertheless potentially grow flagella. Hypnospores: A thick-walled resting cyst. Tetraspores: spores produced by a tetrasporophyte, characteristic of red algae. Statospores: spores that are not actively discharged from the algal fruiting body Auxospores: A spore in diatom algae that leads to reformation of an enlarged vegetative cell.

41 Second: Sexual Reproduction:
As already mentioned, sexual reproduction takes place by the union of male and female gametes. The gametes may be identical in shape and size called isogamy or different called heterogamy. Some of the simplest forms of algae like Spirogyra reproduce by the conjugation method of sexual reproduction. In the process of conjugation, two filamentous strands (or two organisms) of the same algae species exchange genetic material through the conjugation tube. Among two strands, one acts as a donor and another serves as a receiver. After exchanging the genetic material, two strands separate from each other. The receiver then give rise to a diploid organism.

42 Second: Sexual Reproduction:
Isogamy: is the form of sexual reproduction in which the gametes produced are identical in shape, size and motility. There is no structural distinction between "male" and "female" gametes. Pairs of isogametes align themselves with their flagellar poles touching and after several seconds, the motile gametes fuse to form a single, non-motile, diploid zygote.

43 Second: Sexual Reproduction:
Isogametes, less commonly, may be non-motile structures. A specific example exhibiting non-motile isogametes is the reproductive process known as conjugation, in Figure below, the conjugating Spirogyra identify the four stages of the process as outlined. Isogamy in Spirogyra sp.

44 A. Resting filaments of alga cells.
B. Formation of conjugation tubes between two adjacent filaments. C. Cytoplasmic contents of each cell form a compact mass, representing an isogamete. The isogametes from one filament migrate through the conjugation tubes into the adjacent filament. The two isogametes unite to form a zygote. Each zygote eventually undergoes meiosis to form four haploid cells. One haploid cell will form a new filament by mitosis, the other three degenerate.

45 Heterogamy In heterogamy, two different types of gametes are produced. The male gamete, the sperm cell, is typically very small, highly motile and is produced in very large numbers. The female gamete, the egg cell, is much larger and non-motile, called Oogamy. Fewer female gametes are produced but each is usually afforded some protection. Heterogametes are also produced by higher plants and animals. Oedogonium sp. is a green alga that produces heterogametes. The figure bellow illustrates the life cycle of this alga. You can locate a mature egg cell and the small male filaments, which are the site of sperm production, the egg cells and male filaments are usually adjacent to one another on the same algal strand.

46 Heterogamy in Oedogonium sp.

47 SEXUAL REPRODUCTION ISOGAMY-Both gametes have flagella and similar in size and morphology. ANISOGAMY-Gametes have flagella but are dissimilar in shape and size. One gamete is distinctly smaller than the other one. OOGAMY-gamete with flagella (sperm) fuses with a larger, non flagellated gamete (egg).

48 REPRODUCTION Sexual-Gametes Vegetative Cell divisions/Fragmentation
=part of the filament breaks off from the rest and forms a new one. Asexual Reproduction Zoospores after losing their flagella, form new filaments. No sexual fusion.

49 a, b, and c are zoospores d, e, and f are aplanospores g, and h are hypnospores K is autospores. L is Isogamous, m is Anisogamous, and n is Oogamous

50 Gametes look like vegetative cells or very different
Isogamy: both gametes look identical Anisogamy: male and female gametes differ morphologically Oogamy: One gamete is motile (male), one is nonmotile (female) Monecious: both gametes produced by the same individual Diecious: male and female gametes are produced by different individuals Homothallic: gametes from one individual can fuse (self-fertile) Heterothallic gametes from one individual cannot fuse (self-sterile)

51 The life cycles in algae
Three different types of life cycle, depending on when miosis occurs, the type of cells produced, and if there is more than one free-living stage present in the life-cycle.

52 The life cycles in algae
Life-cycle I (haploid life cycle): major part of life-cycle (vegetative phase) in haploid state, with meiosis upon germination of the zygote (zygotic meiosis) also referred to as haplontic life cycle, a single, predominant haploid phase

53 The life cycles in algae
Life-cycle II (Diploid life cycle): vegetative phase is diploid, with meiosis upon formation of gametes (gametic meiosis) also referred to as diplontic life cycle, a single, predominant diploid phase

54 The life cycles in algae
Life-cycle III (Diplobiontic life cycle): three multicellular phases, the gametophyte and one or more sporophyte(s) Gametophyte: typically haploid, produces gametes by mitosis Sporophyte: typically diploid, produces spores by meiosis Isomorphic: sporophyte and gametophyte look alike Heteromorphic: sporo- and gametophyte look different

55 Basis of algal Classification
the different groups of algae can be classified on the basis of a number of characteristics. 1. Color has been an important means of classifying algae, and gives many groups their names. However, other characteristics, such as type of photosynthetic food reserve, flagella type, cell wall structure and composition, and life history, have been important in further distinguishing the algal divisions.

56 Flagella Locomotion in algae is largely based on the action of flagella. The figure below illustrates the wide variety of flagella present in the algae. The primary distinctions used for classification are the number of flagella, their location on the cell, and their morphology. Two major types of flagella are recognized: the smooth, or acronematic, and the hairy, or pleuronematic, types. The smooth flagella generally moves by whiplash motion and the hairy flagella moves by a pulling motion.



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