Basic characteristic of the algae

2. Basic characteristic of the algae

3. Structure of the algal cell There are two basic types of cells in the algae, prokaryotic and eukaryotic. Prokaryotic cells lack membrane-bounded organelles (plastids, mitochondria, nuclei, Golgi bodies, and flagella) and occur in the cyanobacteria (Fig.1). • Fig.1.:Drawing of the fine-structural features of a cyanobacterialcell. (C) Cyanophycin body (structured granule); (Car) carboxysome (polyhedral body); (D) DNA fibrils; (G) gas vesicles; (P) plasmalemma; (PB) polyphosphate body; (PG) polyglucan granules; (Py) phycobilisomes; (R)ribosomes; (S) sheath; (W) wall.

4. The remainder of the algae are eukaryotic and have organelles. A eukaryotic cell (Fig. 1.2) is often surrounded by a cell wall composed of polysaccharides that are partially produced and secreted by the Golgi body. The plasma membrane (plasmalemma) surrounds the remaining part of the cell; this membrane is a living structure responsible for controlling the influx and outflow of substances in the protoplasm. Locomotory organs, the flagella, propel the cell through the medium by their beating. The flagella are enclosed in the plasma membrane and have a specific number of microtubules. The nucleus, which contains the genetic material of the cell, is surrounded by a double membrane with pores in it. The contents of the nucleus are a nucleolus, chromosomes, and the background material . The chloroplasts have membrane sacs called thylakoids that carry out the light reactions of photosynthesis.

5. The thylakoids are embedded in the stroma where the dark reactions of carbon fixation take place. The stroma has small 70S ribosomes, DNA, and in some cases the storage product. Chloroplasts are surrounded by the two membranes of the chloroplast envelope. the pyrenoid , which is associated with storage-product formation. • Double-membrane-bounded mitochondria have 70S ribosomes and DNA, and contain the respiratory apparatus. The Golgi body consists of a number of membrane sacs, called cisternae, stacked on top of one another. The Golgi body functions in the production and secretion of polysaccharides. The cytoplasm also contains large ribosomes and lipid bodies.

6. Fig. 1.2: Drawing of a cell of the green alga Chlamydomonasshowing the organelles present in a eukaryotic algal cell. (C) Chloroplast; (CV) contractile vacuole; (E.R.) endoplasmic reticulum; (F) flagella; (G) Golgi body; (M) mitochondrion; (N) nucleus; (P) pyrenoid; (S) starch; (V) vacuole; (W) wall.

7. Flagella • They are thin organelles present on the surfaces of cells. • Each has the same basic structure. • they both serve for locomotion, either pulling or pushing the cell . • they have a 9 + 2 microtubule arrangement, consisting of 9 pairs of microtubules around 2 single ones at the center; other proteins link the microtubules together. • Energy ATP is used to move flagella, connects dynein arms with the inner and outer microtubules, and causes the outer microtubules to bend. • The basal body is the organizing center of a cilium or flagellum, and is found at the junction of the organelle with the cell membrane, it has a 9 + 0 arrangement.fig.1-3

8. Fig 1-3

9. The flagella membrane may have no hairs (mastigonemes) on its surface (whiplash or acronematicflagellum) or it may have hairs on its surface (tinsel or hairy or pantonematic). There are two types of flagellar hair (Fig. 1.4): 1 Non-tubular flagellar hairs made up of solid fibrils 5–10 nm that are composed of glycoproteins. These hairs are flexible and wrap around the flagellum increasing the surface area and efficiency of propulsion. 2 Tubular flagella hairs about 2 mm long composed of three regions: (1) a tapering basal region 200 nm long attached to the flagellar membrane. (2) a micotubular shaft 1 mm long. (3) a few 0.52 mm-long terminal filaments .

10. Fig. 4 Drawings of the types of hairs on algal flagella. (a) Tripartite hairs (example Ascophyllumsperm). Each hair is composed of a basal region attached to the flagellar membrane, the microtubularshaft, and a terminal hair. (b) Non-tubular hairs (example Chlamydomonasgamete).

11. Algal cells can have different arrangements of flagella (Fig. 1.5). If the flagella are of equal length, they are called isokontflagella; if they are of unequal length, they are called anisokont flagella; and if they form a ring at one end of the cell, they are called stephanokontflagella. Heterokontrefers to an organism with a hairy and a smooth flagellum . Fig. 1.5 The shape of eukaryotic motile algal cells and their flagella. The drawings represent the common arrangement of flagella in the groups. There are a number of modifications in structure that are not included here. (a) Cryptophyta; (b) most of the Heterokontophyta; (c) Bacillariophyceae of the Heterokontophyta; (d) Prymnesiophyta; (e) Chlorophyta; (f) Dinophyta; (g) Euglenophyta; (h) Eustigmatophyceae of the Heterokontophyta; (i, j) Chlorophyta.

12. Cell walls and mucilages In general, algal cell walls are made up of two components: (1) the fibrillar component, which forms the skeleton of the wall, and (2) the amorphous component, which forms a matrix within which the fibrillar component is embedded. The most common type of fibrillarimponent is cellulose, .Cellulose is replaced by a mannan, in some siphonaceous greens, and in Porphyra and Bangia in the Rhodophyta. In some siphonaceous green algae and some Rhodophyta (Porphyra, Rhodochorton, Laurencia, and Rhodymenia), fibrillarxylans of different polymers occur. The amorphous mucilaginous components occur in the greatest amounts in the Phaeophyceae and Rhodophyta, the polysaccharides of which are commercially exploited. Alginicacid is present in the intercellular spaces and cell walls of the Phaeophyceae. Fucoidin also occurs in the Phaeophyceae . In the Rhodophyta the amorphous component of the wall is composed of galactans or polymers of galactose. These galactans include agar (made up of agaropectin and agarose and carrageenan

13. Plastids • The basic type of plastid in the algae is a chloroplast, a plastid capable of photosynthesis. • Chromoplastthat has a color other than green is often called a chromoplast. • A proplastidis a reduced plastid with few if any thylakoids. • A proplastidwill usually develop into a chloroplast although in some hetero trophic algae it remains a pro plastid. • A leucoplast or amyloplastis a colorless plastid that has become adapted for the accumulation of storage product. • In the Rhodophyta and Chlorophyta, the chloroplasts are bounded by the double membrane of the chloroplast envelope .In the other eukaryotic algae, the chloroplast envelope is surrounded by one of two membranes of chloroplast endoplasmic reticulum (chloroplast E.R.), which has ribosomes attached to the outer face of the membrane adjacent to the cytoplasm. fig 1-6(a , e)

14. In the Euglenophyta and Dinophyta, there is one membrane of chloroplast E.R. fig 1-6 (c) .In the Cryptophyta, Prymnesiophyta, and Heterokontophyta, there are two membranes of chloroplast E.R., with the outer membrane of chloroplast E.R. usually continuous with the outer membrane of the nuclear envelope, especially if the chloroplast number is low .fig 1-6 (b , d)

15. Fig. 1-6:Types of chloroplast structure in eukaryotic algae. (a) One thylakoid per band , no chloroplast endoplasmic reticulum (Rhodophyta). (b) Two thylakoids per band, two membranes of chloroplast E.R. (Cryptophyta). (c) Three thylakoids per band, one membrane of chloroplast E.R. (Dinophyta, Euglenophyta). (d) Three thylakoids per band, two membranes of chloroplast E.R. (Prymnesiophytaand Heterokontophyta). (e) Two to six thylakoids per band, no chloroplast E.R. (Chlorophyta).

16. Many motile algae have groups of tightly packed carotenoid lipid-globules that constitute an orange-red eyespot or stigma that is involved in response to light. Motile algae exhibit three types of responses to light : phototaxis, photophobia, and gliding(Fig. 1-7). Fig. 1-7: Three types of flagellar orientation in Chlamydomonas. In phototaxis, the cells swim forward and rotate. Phototaxis requires that cells swim forward in a spiral path that causes rotation of the symmetrically placed eyespot. In photoshock, the cell has a transient avoidance response that causes the cell to swim backwards. In gliding, the leading flagellum and passive flagellum are 180° apart.

17. Phototaxis. In phototaxis, the orientation of cell movement is effected by the direction and intensity of light. The cells move toward them light in positive phototaxisand away from the light in negative phototaxis 2) Photophobia (photoshock). Photophobia is a change in direction of movement of the cell caused by a rapid change in light intensity, irrespective of the direction of the light. 3) Gliding .In gliding, the flagella stop beating and adhere to a surface or anair/water interface .The cells can glide over the surface with one flagellum actively leading and the other passively trailing

18. The photosynthetic algae have chlorophyll in their chloroplasts. Chlorophyll is composed of a porphyrin-ring system that is very similar to that of hemogloblin but has a magnesium atom instead of an iron atom Chlorophyll structure

19. The algae have four types of chlorophyll, a, b, c (c1 and c2), and d. • Chlorophyll ais the primary photosynthetic pigment in all photosynthetic algae and ranges from 0.3% to 3.0% of the dry weight. • Chlorophyll a is insoluble in water and petroleum ether but soluble in alcohol, diethyl ether, benzene, and acetone. The pigment has two main absorption bands in vitro, one band in the red light region at 663 nm and the other at 430 nm .Whereas chlorophyll a is found in all photo - synthetic algae, the other algal chlorophylls have a more limited distribution and function as accessory photosynthetic pigments • Chlorophyll bis found in the Euglenophyta and Chlorophyta. Chlorophyll b functions photosynthetically as a light-harvesting pigment transferring absorbed light energy to chlorophyll a. The ratio • of chlorophyll a to chlorophyll b varies from 2:1 to 3:1. The solubility characteristics of chlorophyll a are similar to chlorophyll b, and in vitro chlorophyll b has two main absorption maxima in acetone or methanol, one at 645 nm and the other at 435 nm (Fig 1-8)

20. Fig. 1-8: The absorption spectra of chlorophylls a, b, c , and d.

21. Chlorophyll cis found in the Dinophyta, Cryptophyta, and most of the Heterokontophyta. Chlorophyll c has two spectrally different components: chlorophyll c1 and c2. Chlorophyll c2 is always present, but chlorophyll c1 is absent in the Dinophyta and Cryptophyta. The ratio of chlorophyll a to chlorophyll c ranges from 1.2:2 to 5.5:1. Chlorophyll c probably functions as an accessory pigment to photo system II. The pigment is soluble in ether, acetone, methanol, and ethyl acetate, but is insoluble in water and petroleum ether. Extracted chlorophyll c1 has main absorption maxima at 634, 583, and 440 nm in methanol, whereas chlorophyll c2 has maxima at 635, 586, and 452 nm. Chlorophyll d:occurs in some cyanobacteria It has three main absorption bands at 696, 456, and 400 nm.

22. Carotenoids are yellow, orange, or red pigments that usually occur inside the plastid. In general, naturally occurring carotenoids can be divided into two classes: oxygen-free hydrocarbons, the carotenes their oxygenated derivatives, the xanthophylls. The most widespread carotene in the algae is -carotene .There are a large number of different xanthophylls , with the Chlorophyta having xanthophylls that most closely resemble those in higher plants. Fucoxanthin is the principal xanthophyll in the golden-brown algae (Chrysophyceae, Bacillariophyceae, Prymnesiophyceae, and Phaeophyceae), giving these algae their characteristic color. Like the chlorophylls, the carotenoids are soluble in alcohols, benzene, and acetone but insoluble in water.

23. in cyanobactria ,The photosynthetic pigments are located in thylakoids , which lie free in the cytoplasm . Each outer facing into the cytosol of each thylakoid is studded with particles called phycobilisomes, which consist of Chlorophyll a and accessory pigments, called phycobiliproteins , such as phycoerythrin (red) , phycocyaninand allophycocyanin fig.1-9. The accessory pigments protect the chlorophyll from damaging UV light and also trap photons and funnel them to the chlorophyll, acting as antennae Fig.1-9

24. Nutrition Algae can be either autotrophic or heterotrophic (organotrophic) (Table 1.1). If they are autotrophic, they use inorganic compounds as a source of carbon. Autotrophs can be photoautotrophic ,using light as a source of energy, or chemoautotrophic ,oxidizing inorganic compounds for energy. If they are heterotrophic, the algae use organic compounds for growth. Heterotrophs can be photoheterotrophs, using light as a source of energy, or chemoheterotrophs ,oxidizing organic compounds for energy

25. Heterotrophic algae may be phagocytotic(holozoic), absorbing food particles whole into food vesicles for digestion, or they may be osmotrophic, absorbing nutrients in a soluble form through the plasma membrane. If the algae live heterotrophically on dead material, they are saprophytic; if they live off a live host, they are parasitic. Some algae, particularly the flagellates, are auxotrophic, requiring a small amount of an organic compound, but not as an energy source. These algae usually require a vitamin. Some photosynthetic algae are mixotrophic, capable of also using organic compounds supplied in the medium.

26. Table 1.1 Types of nutrition found in the algae

27. Classification There are four distinct groups within the algae. these four groups. 1 Prokaryotes. The cyanobacteria are the only prokaryotic algae. 2 Eukaryotic algae with chloroplasts surrounded by the two membranes of the chloroplast envelope. 3 Eukaryotic algae with the chloroplast surrounded by one membrane of chloroplast endoplasmic reticulum. 4 Eukaryotic algae with the chloroplast surrounded by two membranes of chloroplast endoplasmic reticulum

28. The standard botanical classification system is used in the systematics of the algae: Phylum – phyta/ Class – phyceae/ Order – ales/ Family – aceae Genus/ Species Group 1 Prokaryotic algae Cyanophyta(cyanobacteria) :chlorophyll a ; phycobiliproteins. Group 2 Eukaryotic algae with chloroplasts surrounded only by the two membranes of them chloroplast envelope. Glaucophyta:algae that represent an intermediate position in the evolution of chloroplasts; photosynthesis is carried out by modified endosymbiosis cyanobacteria. Rhodophyta(red algae) ; chlorophyll a ; phycobiliproteins ; no flagellated cells; storage product is floridean starch. Chlorophyta(green algae) : chlorophylls a and b; storage product, starch, is found inside the chloroplast.

29. Group 3 Eukaryotic algae with chloroplasts surrounded by one membrane of chloroplast endoplasmic reticulum. Euglenophyta(euglenoids) : chlorophylls a and b; one flagellum with a spiraled row of fibrillar hairs; proteinaceouspellicle in strips under the plasma membrane; storage product is paramylon ; characteristic type of cell division. Dinophyta(dinoflagellates) : mesokaryoticnucleus; chlorophylls a and c1; cell commonly divided into an epiconeand a hypoconeby a girdle; helical trans verse flagellum; thecal plates in vesicles under the plasma membrane. Apicompexa : heterotrophic flagellates with colorless plastids.

30. Group 4 Eukaryotic algae with chloroplasts surrounded by two membranes of chloroplast endoplasmic reticulum. Cryptophyta(cryptophytes): nucleomorph present between inner and outer membrane of chloroplast endoplasmic reticulum; starch formed as grains between inner membrane of chloroplast endoplasmic reticulum and chloroplast envelope; chlorophyll a and c; phycobiliproteins ; periplast inside plasma membrane. Heterokontophyta(heterokonts) : anterior tinsel and posterior whiplash flagellum; chlorophyll a and c; fucoxanthin; storage product usually chrysolaminarin occurring in vesicles.

31. Chrysophyceae(golden-brown algae) • Synurophyceae • Eustigmatophyceae • Pinguiophyceae • Dictyochophyceae(silicoflagellates) • Pelagophyceae • Bolidophyceae • Bacillariophyceae(diatoms) • Raphidophyceae(chloromonads) • Xanthophyceae(yellow-green algae) • Phaeothamniophyceae • Phaeophyceae(brown algae) • Prymnesiophyta(haptophytes) :two whiplash flagella; haptonema present; chlorophyll a and c; fucoxanthin ; scales common outside cell; storage product chrysolaminarin occurring in vesicles.