Volvox is a common freshwater free-floating chlorophytic green alga that belongs to Volvocaceae family under order Volvocales of division Chlorophyta. They occur in temporary and permanent freshwater tanks, ponds, pools, ditches, etc. There are some 20 freshwater species of Volvox which prefer to live in colonies with up to 60,000 cells by making a gelatinous wall. These colonies have an ovoid or spherical hollow shape which may be larger than a pinhead size. Dutch microscopist Antonie van Leeuwenhoek first reported the Volox colonies in 1700.
The mature Volvox colony contains two separate cell types namely germ cells of the smaller number and numerous flagellated somatic cells. In this case, adult somatic cells have a single layer that contains two flagella which allow the organism to swim in a coordinated fashion in water. The cells have distinct anterior and posterior poles. The anterior pole possesses photosensitive eyespots that make it possible for the colony to move towards the light. The Volvox colonies are asexual which produce daughter colonies within the parent colony. After maturing, the daughter colony comes out from the parent colony.
Each Volvox species are able to make its own food through photosynthesis due to the presence of chlorophyll in its body. During spring, the surface of the water in which Volox occurs looks green. During early summer, the Volox abruptly disappears and it remains in resting zygote condition. Volvox colony appears in the rainy season.
Volvox occurs in the colony because it is a coenobial form (hollow ball) like a structure. In the young colony, the vegetative cells are similar in size and green in color. Each motile colony (coenobium) is free-swimming and appears as small pinhead like spherical to ovoid shape with hollow mucilaginous mass which consists of numerous small pear-shaped cells arranged in a single layer joined with one another by delicate strands of cytoplasm within the periphery of the gelatinous colonial matrix. The total number of cells in the colony varies from about 500 (Volox aureus) to about 2000 or more (Volvox globate). Each colony develops the following three types of cells:
The cell of the coenobium varies based on species and is mostly ovoid-shaped. Each cell measured about 16.25 µm in length. The cell wall encloses a mass of protoplast. The cell wall is thin and firm in nature composed of cellulose. Protoplast contains a basal cup-shaped chloroplast with several pyrenoids (Volvox aureus) or plate-shaped with a single pyrenoid (Volovox globator), a central nucleus, reddish-brown eyespot surrounded by a plasma membrane. The central cytoplasm possesses mitochondria, endoplasmic reticulum, ribosome, dictyosomes, etc. At the apical portion of the cell, two equal length whiplash types of flagella arise from the two basal granules, i.e. the blepharoplast. At the base of the flagella, 2-3 contractile vacuoles are present. They act as excretory organs.
The Volvox coenobium (colony) is motile and movement is brought by the simultaneous action of the flagella of all the cells of the colony. The entire colony rolls over the surface of the water. Hence they are called ‘rolling algae’. The eyespot controls the movement of the flagella as they are photoreceptive organs.
Volvox species are either dioecious or monoecious. In this case, the male colony produces lots of sperm packets while the female colony releases oogamete or ovum. They are facultatively sexual but can reproduce both asexually and sexually. The environmental factors and sex-inducing pheromone trigger Volvox reproduction.
As the colony grows older, several cells in the posterior region lose their flagella and increase ten or more times; these enlarged cells are reproductive cells and may be asexual or sexual. The vegetative or somatic cells are unable to take part in reproduction. Sexual reproduction occurs through the formation of sperms and egg cells. The process of sperm and egg production is known as spermatogenesis and oogenesis, respectively. Asexual reproduction takes place at the beginning of the growing season whereas sexual reproduction occurs at the end of the growing season.
Asexual reproduction takes place during summer in a rapid manner under favorable conditions. In a young colony known, as coenobium, all the cells are the same but later, a few cells of the posterior half of the Volvox colony increase in size by storing up the food. These cells become enlarged in size and form asexual reproductive cells, called gonidia or parthenogonidia. The number of gonidia varies from 2-50 in each coenobium. They drop their flagella, become rounded in outline, contain dense cytoplasm and lie within the globose mucilaginous sac which projects towards the inside of the colony.
Each gonidium divides repeatedly and produces a spherical group of daughter cells. In this case, all cells are held together to form a new daughter colony. The divisions of the gonidial protoplast occurring in the formation of a daughter colony are always longitudinal and all cells of each cell generation divide at the same time. Continue longitudinal divisions of daughter cells occur simultaneously and produce several cell generations.
In the second generation, four cells are arranged quadrately while in the third cell generation, the 8 cells are crucially arranged, to form a curved plate, known as the plakea stage. Plakea takes the shape of a hollow sphere at the end of the 16-celled stage. Next, a pore called the phialopore is formed at the anterior pole of the daughter colony, when the cell division stops.
The young daughter colony turns itself out by inverting through the phialopore. After this, the cells develop flagella and the daughter colony escapes by moving through a pore-like opening at the free face of the sac. Finally, the daughter colony comes out due to the rupture or decay of the mother colony or coenobium.
Sexual reproduction of Volovx is of oogamous type. The coenobium may be homothallic or heterothallic based on species. The posterior half of the coenobium forms some specialized enlarged cells or gametangia which may be either the female sex organs (oogonia) or the male sex organ (antheridia). They are produced fewer in number.
During the development of gametangia (oogonia or antheridia), the cell becomes rounded and enlarged and cast off flagella but they remain linked with other cells through fine protoplasmic threads. In this case, the male sex organ or gametangium is called antheridium and the female sex organ or gametangium is known as oogonium.
In the monoecious species, such as Volvox globator, antheridia and oogonia are formed on the same coenobium but in the dioecious species such as in Volvox aureus, antheridia and oogonia are formed on different coenobium. In monoecious species, antheridia develop first and the fertilization occurs between the antherozoid and ovum of other plants.
Antheridium also possesses an enlarged structure similar to gonidia. The protoplast of an antheridium divides repeatedly to form 16, 32, 64, 128 or more small, spindle-shaped, yellowish, biflagellate antherozoids. Each antherozoid contains a single nucleus and a small pale green or yellow-green chloroplast.
Oogonium is a unicellular, enlarged, semi flask-shaped cell, with a gelatinous sheath-like wall. The protoplast of each oogonium forms a larger uni-nucleate spherical oosphere or egg with a beak-like protrusion towards one side. Antherozoid enters into the oogonium through this end.
The oosphere possesses a parietal chloroplast, pyrenoids, and a centrally placed large nucleus. Oogonium absorbs reserve substances from the neighboring cells through the protoplasmic strands.
During the fertilization, antherozoids after liberation from the antheridium swim about as a group and remain intact until they reach the egg. Only one antherozoid fuses with the egg resulting in the formation of a zygote or oospore. After fertilization, the zygote develops a thick wall around it.
The protoplast of the zygote becomes orange-red in color. The zygote comes out of the parent coenobium by the disintegration of the gelatinous matrix of the coenobium and sinks to the bottom of the water and undergoes a period of rest.
The zygote reserves enough food materials with other inclusions. The two outer layers of the zygote split and gelatinize. The outer layer is known as exospore which may be smooth in Volvox globator or spiny in Volvox speematospaera. The middle layer is known as mesopore while the inner layer is endospore. After releasing from the coenobium by disintegrating the gelatinous matrix, the zygote settles down at the bottom of the water body and may remain intact for several years.
Under favorable conditions, the inner wall layer extrudes out in the form of a vesicle and surrounds the protoplast of the zygote. Diploid zygote nucleus divides meiotically into four haploid nuclei; of these, 3 degenerates and the remaining one nucleus survive with cytoplasmic contents escapes from the vesicle. At this stage, it is known as a swarmer who swims freely and forms a zoospore and develops into a new coenobium (colony).
Each coenobium also contains a smaller number of cells which perform asexual reproduction for the next several generations. In the case of Volvox rouseletti and Volvox minor, the zygote`s protoplasm is changed into a single zoospore and it divides again to form a new coenobium.
There are about 20 species of Volvox worldwide. They are an important part of the aquatic ecosystem as primary producers. They can produce oxygen during photosynthesis which is needed in significant quantities by many aquatic life forms. They also act as a part of the food chain which makes them an important component of the food items of many aquatic organisms such as fish.
The liquid filled cavity between alimentary canal and body wall of multicellular triploblastic animals is known as body cavity. Generally, the body cavity that is lined by mesodermal peritoneal membrane is known as coelom. According to Hyman (1955), coelom is the hollow space between alimentary canal and body wall which is lined by mesodermal peritoneal tissues. Coelom gives the space for most of the visceral organs. Between two embryonic layers of mesoderm, coelom originates as a secondary body cavity. Haeckel first proposed the term coelom in 1972.
Coelom is also known as the perivisceral cavity that has fluid filled compartments, transversely partitioned by septa. In arthropods and mollusks, coelom is reduced or absent but it is present in the embryonic stage. Instead of coelom, they have space with blood and lymph, known as haemocoel. In these animals, the haemocoel is the primary body cavity while the coelom is the secondary body cavity.
There are the following three types of coelom, such as:
In this case, coelomic fluid-filled cavity is absent but the space between the body wall and the gut is filled by connective tissue, known as mesenchyme. The animals without a coelomic fluid-filled body cavity between the body wall and digestive tract are known as acoelomates and the group of animals is referred to as acoelomata.
In this case, coelom is not originated by the mesodermal epithelium. Embryologically, the pseudocoelom is developed from the blastocoel of the embryo. The pseudocoelom is also known as false coelom. The pseudocoelom is not bounded by the peritoneum. The fluid of pseudocoelom contains pseudocoelocytes which has no relation with the reproductive and excretory organs. Animals with a pseudocoelom are known as pseudocoelomates and the group of animals is referred to as pseudocoelomata. Pseudocoelomata are also referred to as blastocoelomata or haemocoelomata.
In this case, the body cavity between the gut and body wall is bounded by peritoneum. Peritoneum is derived from the embryonic mesoderm. This type of cavity or coelom is known as eucoelom or true coelom. The coelomic fluid of true coelom contains amoebocytes. The animals with true coelom are known as coelomates and the group of animals is referred to as coelomata.
The following table shows the differences between coelom and pseudocoelom:
Coelom is a fluid filled true body cavity, present between the body wall and the digestive tract.
Pseudocoel is a fluid-filled body cavity, present between the mesoderm and the endoderm.
Coelom is also known as eucoelom or true coelom.
Pseudocoelom is also known as false coelom.
The animals with true coelom are known as coelomates and the group of animals is referred to as coelomata.
Animals with a pseudocoel are known as pseudocoelomates and the group of animals is referred to as pseudocoelomata.
Coelom or true body cavity is lined with peritoneum.
Pseudocoelom or false body cavity is partially lined with peritoneum.
The coelom is developed by splitting of the mesoderm.
The pseudocoelom is developed from the blastocoel of the embryo.
In this case, the blood stream carries the nutrients.
In this case, the nutrient transportation occurs through osmosis and diffusion.
Pseudocoelom is present only in invertebrates.
The organs present inside the coelom are Well-organized.
The organs present inside the pseudocoelom are less-organized.
Examples: Nematoda, Entoprocta, Rotifera, Acenthocephala, and Gastrotrica, etc.
Coelom makes the partition to separate biological systems that perform various major functions. Acoelomates transport nutrients around the body through diffusion due to relatively small with less intricate body plan. In this case, diffusion is enough to perform transport function. The coelomates have complex body plan that need special transport system (circulatory system) to ship the nutrients around the body. In this case, coelom is useful to separate circulatory system from abdominal organs.
Plants can be broadly divided into two types: flowering plants and non-flowering plants. In this case, flowering plant is also known as angiosperms while non-flowering plant is known as gymnosperms. Based on the nature of the embryo in the seed, angiosperms are again divided into the following two types:
Monocotyledon is commonly known as monocot. They have seeds with one embryonic leaf or cotyledon; hence they are called monocotyledonous plants. This group contains about 60,000 species. Among them, the family Orchidaceae (orchids) contains more than 20,000 species. Besides these, the Poaceae (true grasses) is the most important family. Other prominent monocot families include Arecaceae (palms), bananas, plantains (Musaceae), Liliaceae (lilies), and Iridaceae (irises). This group includes different type of grains (rice, wheat, maize, etc.), forage grasses, sugarcane, the bamboos, etc.
The dicotyledonous plants are also known as dicots. These plants have two embryonic leaves or cotyledons. They contain about 200,000 species. Garden plants, shrubs and trees, broad-leafed flowering plants such as magnolias, daisies, roses, geraniums, cacti, peas, mint, hollyhocks and many more are dicots.
Dicotyledonous Plants are generally trees; few are herbs and shrubs.
Monocotyledonous Plants are generally herbs. Few are trees.
They are branched trees.
They are unbranched trees.
Perennial plants; very few plants possess underground stems.
Perennial plants, underground stems are present which helps in penetration in the soil.
Main roots or true roots are formed, they are generally branched.
Main root or true root does not form. In most cases, the radical degenerates and later on produces adventitious roots from the base of the stem.
The number of radial vascular bundles lies between 2-6.
The number of radial vascular bundles are more than 6.
Xylem vessels are polygonal in shape.
Xylem vessels are oval in shape.
In most cases pith is absent. If present, it occupies a smaller area in the center.
The well developed pith is present and it occupies a larger area in the center.
In this case, secondary growth occurs due to the presence of cambium.
Secondary growth does not occur due to the absence of cambium.
Stem is branched.
Stem is generally unbranched and jointed in nature.
The vascular bundles are conjoint, collateral and open. It is composed of xylem, phloem and cambium. Vascular bundles may be bi-collateral.
The vascular bundles are conjoint collateral and closed. It is composed of only xylem and phloem, cambium is absent.
The number of vascular bundles is lesser. The vascular bundles are arranged within a ring.
The number of vascular bundles is greater. The vascular bundles are scattered within the ground tissue.
The epidermis (without cuticle layer) generally possesses multicellular hairs (stem hairs).
The epiblema (without cuticle layer) is generally without hairs.
Hypodermis is collenchymatous type.
Hypodermis is parenchymatous or sclerenchymatius type with thick walled.
Each vascular bundle is generally with bundle cap (sclerenchymatous). Bundle sheath is absent.
A bundle sheath surrounds each vascular bundle. Bundle cap is absent.
Due to the presence of cambium, secondary growth occurs
Secondary growth does not take place due to the absence of cambium.
Annual rings are formed due to secondary growth.
Due to non occurance of secondary growth, annual rings are not formed.
Leaves are broad, remains parallel with the earth`s surface. The leaves are not provided with sheathing leaf bases.
Leaves are elongated, remains angular with the earth`s surface and they are provided with sheathing leaf bases.
The leaf margins are broken.
The leaf margins are entire (smooth).
In the axil of leaves, axillary bud lies.
In the axil of leaves, no formation of axillary bud.
The leaves are provided with reticulate venetion (exception: Calophyllum inophyllum).
The leaves are provided with parallel vanation (exception: Arum).
Leaves are mainly dorsiventral. The upper surface and the lower surface are not similar.
Leaves are mainly isobilateral. The upper and lower surface are similar.
The mesophyll tissue of the leaf is differentiated into upper elongated palisade parenchyma and lower more or less round spongy parenchyma.
The mesophyll tissue is composed of only one type of similar parenchyma cells like spongy parenchyma.
Stomata is mainly present on the lower epidermis.
Stomata is present on both the upper and lower epidermis.
The flowers are mainly pentamerous or tetramerous or multiples of 5.
The flowers are mainly trimerous or multiples of 3.
Inflorescence are of different types.
Inflorescence are of different types. But in case of grass like plants, spikelet inflorescence is present.
Embryo possesses two thick cotyledons.
Embryo possesses only one thin and scaly cotyledon.
Seed coat and fruit coat remains separate, not fused together.
Seed and fruit coat fused together.
The nature of the seed is generally non endospermic.
The nature of the seed is generally endospermic.
The embryo of the seed is larger in size.
The embryo of the seed is smaller in size.
The radical and plumule is not covered by means of coleorhizae and coleoptyle respectively.
The radical and plumule is covered by means of coleorhizae and coleoptyle respectively.
Germination mainly hypogeal or epigeal.
Germination is mainly hypogeal.
Radicle and plumule comes out directly without any covering (i.e., coleorhizae and coleoptyle).
During seed germination the radical and plumule comes out along with their covering coleorhizae and coleoptiles.
Radicle and plumule is not covered by means of membranes like coleorhizae and coileoptile, respectively.
Radicle and plumule is covered by means of membranes like coleorhizae and coileoptile, respectively.
In epigeal germination, the cotyledons come out above the soil surface and take green coloration.
The radical penetrates the soil and forms main roots with permanent root system.
The radical after its preliminary growth within the soil is destroyed and from the region fibrous adventitious roots are formed.
The position of embryo is terminal.
The position of embryo is lateral.
Dicotyledonous plants: Sunflower: Helianthus annuus, Mango: Mangifera indica
Monocotyledonous plants: Paddy: Oryza sativa, Banana: Musa paradisiaca, etc.
You might also read: Difference Between Angiosperms and Gymnosperms
Spirogyras are common free-floating freshwater algae that inhabit ponds, pools, tanks, lakes, ditches, etc. The word ‘Spirogyra’ is derived from the two Greek words, ‘Speria’, meaning coil, and ‘gyras’ meaning twisted. Spirogyra has many common names, including blanket weed, water silk, mermaid`s tresses, etc. It grows up to several centimeters in length and 10-100 μm in width. There are about 400 known species of Spirogyra worldwide. They are filamentous and slippery in natures due to the presence of external mucilaginous sheath; hence, they are called pond scum or pond silk. Some of the species of Spirogyra (Spirogyra adnata, S. jogensis) bear holdfast or haptera by which they remain attached to the substratum.
Species: Spirogyra maxima, S. negnecta, S. elongate, S. adnata, S. nitida, etc.
Spirogyra is un-branched green algae that belong to the class Chlorophyceae under order Zygnematales. It consists of long identical cylindrical cells situated one above the other, without any differentiation into base and apex. It bears 2-10 spiral ribbon-shaped chloroplasts with many pyrenoids, which are the distinctive characteristic features of Spirogyra.
Their margins may be smooth or serrated. Spirogyra floats freely in masses over the surface of the water and is moved in favor of water current. But Spirogyra adnata remain attached to the substratum by means of holdfast. They are autotrophic in nature because they contain photosynthetic pigments and perform photosynthesis for producing their own food.
You might also read: Volvox : Characteristics, Structure, and Reproduction
The plant body is un-branched filamentous, green-colored with cylindrical cells placed end to end. In free-floating species, there is no basal differentiation, but in some sedentary species, the basal cell is modified into a haptera or holdfast, which is the organ of attachment. The lateral cell wall is stratified and three-layered, the inner two layers are composed of cellulose, and the outermost layer is composed of pectose. The cross walls are also three-layered, the middle lamella is composed of pectose bounded on either side by layers of pectin, in some other species, there is an additional annular ingrowth of cellulose along with the cross wall, giving rise to the so-called replicate wall which again is of five types such as plane, replicate, semi-replicate, colligate (cross wall looks like a short H-like piece) and unduliseptate, respectively.
A vacuolated, granular protoplast is present in each cell in the form of a thin lining along the cell wall and is termed as the primordial utricle. The vacuole is separated from the surrounding cytoplasm by a semi-permeable membrane, the tonoplast. The eukaryotic nucleus with a distinct nucleolus remains embedded within the cytoplasm or resides at the center being supported by the cytoplasmic strands. Each cell bears a varying number of ribbon-shaped, spiral chloroplasts with either serrated or smooth edges. In the chloroplasts, dense, highly refractive, granular, protein body surrounded by starch called pyrenoids at short intervals. In some cases, pyrenoid like bodies without starch sheath is also present called protopyrenoids.
They increase in length of the filament takes place by ordinary cell divisions and by subsequent growth of individual cells, each of which may divide further. Spirogyra reproduces vegetatively and sexually. In this case, asexual reproduction is absent.
Vegetative reproduction in Spirogyra takes place by means of fragmentation. This is performed by softening of the cross wall between the two adjacent cells, as a result of which each part or piece of the broken filament grows out into a filament by repeated cell divisions, or by the accidental breaking of the filament by external mechanical injury.
Spirogyra may be monoecious or dioecious. Sexual reproduction takes place by conjugation of two morphologically identical gametes and each of which is called a gametangium. The sexual reproduction shows physiological anisogamy, as out of the two isogametes, one is motile, and the other one is non-motile. Sexual reproduction occurs at different times of the year according to species. Two types of conjugation are found in Spirogyra, which is described below:
This type of conjugation takes place in the heterothallic species. In such cases, two filaments of opposite strains, i.e., + and – approach each other and lie in close association throughout their entire length. Now, the cells of the two associated filaments send out protuberances from the walls of the cells in opposite directions. These protuberances in due course come in contact with each other. Finally, the end walls of these protuberances are dissolved, forming a continuous passage, i.e., the conjugation tube. The protoplasts of the conjugating cells begin to shrink to form gametes. The gamete of the cells of one filament shows amoeboid movement and move across the conjugation tube to the cells of the other filament. Now, the two gametes undergo fusion to form a dark-colored diploid zygospore body. The cell of the two filaments, along with the conjugation tube, gives a ladder-like appearance; hence, this type of conjugation is termed as scalariform or ladder-like conjugation.
This type of conjugation takes place between the adjacent cells of the same filament, i.e., in the homothallic species. Lateral walls of the conjugating cells of the same filament develop protuberances on either side of the cross wall. As the protuberance increases, the cross wall fails to maintain its connection with the lateral wall, whereby a passage is established between the two cells. Through this side passage, the shrunk protoplasts, i.e., the gamete (aplanogamete) of one cell, migrates into the adjacent cell and fuses with the other gamete. Fusion results in the formation of a diploid zygospore. This type of conjugation is termed as the lateral conjugation.
The zygospore surrounds itself with a three-layered thick wall and is resistant to cold and drought. The zygospore generally sinks to the bottom of the water and after remaining dormant for some time, undergoes germination. The diploid nucleus undergoes meiosis forming four haploid nuclei, three of which degenerate, and one remains functional.
The wall ruptures, and the innermost cellulose layer emerges out in the form of a cylindrical germ tube. The germ tube undergoes transverse division to form 2 celled spirogyral filaments, which by repeated division gives rise to the cylindrical multi-cellular spirogyral filament. The functional haploid nucleus constitutes the nucleus of the haploid zygospore.
Parthenogenesis may occur in Spirogyra by the development of perthenospore or azygospore. These are formed at the condition when the gametes fail to fuse. The gametes secrete a thick wall around it to become a perthenospore, which after a period of rest, germinate to form a new filament.
In the life cycle of Spirogyra, alternation of haploid (n) generation and diploid (2n) generation is noted. The haploid (n) phase is long, but the diploid (2n) phase is very short-lived. The diploid phase is restricted within the zygospore only.
The Spirogyra produces food matters by means of photosynthesis, and many aquatic animals use them as food. Spirogyra is used as fish`s food. Dried Spirogyra used in the preparation of soups. Spirogyra contains lots of vitamins A and E. It is cultured in garden tanks for ornamental purposes. Spirogyra is also used in the aquarium. Besides these, Spirogyra spoils the water of drinking tanks. If it grows in abundance, Spirogyra, create disturbances in swimming and fishing.
Algae are a diverse group of eukaryotic cellular or multi-cellular organisms. They inhabit both in aquatic and terrestrial environments. Some occur in moist stones, wood, soils, on ice, or snow. They have photosynthetic pigments that perform photosynthesis, produce oxygen, and remove at least half of the total carbon dioxide from the earth`s atmosphere.
Algae perform reproduction in various ways. It can be vegetative, asexual, or sexual. In this case, vegetative propagation occurs through fragmentation; asexual reproduction occurs by forming different spores and binary fission, while sexual reproduction occurs by fusion of two haploid gametes. Generally, many environmental factors influence the reproduction of algae.
You might also read: Structure of Algae
The following three main types of reproduction process occur in algae:
It is simple and the most common process of reproduction in algae. By this process, vegetative parts of thallus divide into small fragments, and each part, later on, gives rise to a new plant. This process is termed as fragmentation. This type of reproduction occurs in Spirogyra, Ulothrix, etc. In this process, no alternation of generations occurs, and it does not require any spore formation.
The vegetative reproduction in algae is of the following types:
In this process, unicellular algae reproduce new individuals. It is a very simple method, and often it is known as binary fusion. During reproduction by this process, mitosis occurs in the vegetative cell and produces two daughter cells and finally acts as new individuals. This type of reproduction occurs in Synechococcus, Chlamydomonas, diatoms, etc.
This process occurs in multi-cellular filamentous algae. In this process, the thallus breaks down into many fragments; among them, each fragment gives rise to a new individual. Generally, the fragmentation process occurs accidentally or by any other mechanical injury. This type of vegetative reproduction occurs in Ulothrix, Spirogyra, Zygnema, Oedogonium, Cylindospermum, etc.
This type of reproduction occurs in blue-green algae such as Oscillatoria, Nostoc, Cylindosporium, etc. In this process, trichome breaks down within the sheath into many segments, and each segment forms a new individual. In this case, each segment is known as hormogonium.
In many large thalloid algae, adventitious branches form and detach from the mother`s body to develop new individuals. In this case, internodes, stolons, etc. form adventitious branches. This type of reproductions occurs in Fucus, Dictyota, Chara, Cladophora, etc
Bulbils are the tuber-like outgrowth, which occurs due to the storage of food at the tip of the rhizoids and lower nodes of the plants. During reproduction, bulbils detach from the plant body and give rise to new individuals. This type of reproduction occurs in Charophyta, such as chara, Lamprothamnium, Nitellopsis, etc.
In Chara, amylum stars occur and detach from the plant body; they develop into new plants. The cells of the lower nodes of plants store starch and form star-shaped aggregation, which is known as amylum stars.
The bud-like outgrowth occurs in some algae, such as Protosiphon. In this process, the nucleus from the parent body divides by mitosis and produces daughter nucleus, which migrates to develop bud. The newly formed buds detach from the parent body and live independently as a new individual.
Asexual reproduction occurs by forming a specific type of spores. In this process, some cells or protoplasm of few cells of the plant divide to create a small-sized structure, the spore. Each spore is germinated and liberated from the mother cell and gives rise to a new plant. It generally takes place by the following method:
In this process, under favorable conditions, biflagellate, tetra-flagellate, multi-flagellate, naked, motile zoospores are formed and on bursting of mother cells (sporangium) come out and give rise to the new plant. The zoospores may be either haploid or diploid, which are formed within the zoosporangium. In this case, biflagellate zoospores occur in Ulothrix, Chlamydomonas, Ectocarpus, etc. while tetra-flagellate zoospores occur in Ulothrix and Oedogonium, Vaucheria, multi-flagellate zoospores occur.
In this case, protoplasm gets separated from the cell wall to form one or more thin-walled, non-nucleated aplanospores, and each aplanospore gives rise to a new plant. In this case, aplanospores are non-motile spores that occur inside sporangium under unfavorable conditions. This process of reproduction occurs in Chlorella, Ulothrix, Scenedesmus, Microspora, Pediastram, Sphaerella, etc.
In this process, under unfavorable conditions, the protoplasm of the cells separate from the cell wall and collects in the center. These are non-motile with thickened walls and abundant food reserves, known as hypnospores. They give birth to a new plant on the commencement of favorable conditions. This process occurs in Vaucheria.
In certain filamentous algae, the vegetative cells become thick and develop into spore-like structures with abundant food reserves, known as akinetes. Akinets are formed under unfavorable conditions, and on commencement of favorable conditions, each akinete develops into a new plant. This type of process occurs in Cladophora, Oedogonium, etc.
In most of the members of Myxophyceae, the development of a large number of endospores takes place inside the mother cell. Endospores germinate directly and give rise to a new plant under favorable conditions. In this case, the mother protoplasm divides and forms small spores. These spores are known as conidia or gonidia. This type of reproduction occurs in Dermocarpa.
Under dry conditions, zoospores or aplanospores don't come outside the mother cell but get encompassed by an adhesive sheath. The division proceeds with the outcome; they take the form of a colony. This is known as the pamella stage. Under suitable conditions, they turn out. Every zoospore or aplanospore offers ascend to another plant. This procedure happens in Chlamydomonas sp.
In some algae, the undeveloped spores grow into new plants within the mother cell. This type of reproduction occurs in Chlorococcus.
In some algae, under unfavorable conditions and abundant food supply, the thallus divides into multinucleate and thick-walled smaller segments, which are termed as cysts. In favorable conditions, cysts give rise to new plants. It occurs in Vaucheria sp.
All the members of the algae reproduce sexually except the representatives of the class Cyanophyceae. Sexual reproduction occurs by fusion of gametes. These gametes grow within gametangia. Sexual reproductions are of the following five types:
In some algae, the gametes and their size and external morphology are alike. In this type of reproduction, Positive (+) and negative (-) strain gametes combine together to form zygospore or zygotes. These gametes are known as isogametes, which may be motile (zoogametes) or non-motile. In this case, isogametes of Chlamydomonas and Ulothrix are motile, while isogametes (aplanogametes) in Spirogyra are non-motile type.
In some algae, the gametes and their external morphology are alike, but their behavior and size vary. In this case, the large-sized and passive gamete is known as macrogamete, while the smaller and active gamete is known as microgamete. These two gametes fuse and produce a zygote, which later on undergoes mitotic division to form new individuals. This type of reproduction occurs in Chlamydomonas.
In this type of sexual reproduction, fertilization occurs between small, biflagellate, or multi-flagellate, active male gamete with large non-flagellate, passive female gamete, and form zygote (oospore). In this case, male gametes grow within antheridium while the female gametes within the oogonium. This type of reproduction occurs in Oedogonium, Chlamydomonas, Vaucheria, Laminaria, Chara, Poly-siphonia, Sargassum, Batrachospermum, etc.
Algae act as a significant component of the food chain in the aquatic ecosystem as a primary producer. Algae have a huge source of carbohydrates, lipids, proteins, and vitamins A, B, C, and E, etc. They also contain very important minerals sources for animals such as iron, magnesium, potassium, manganese, calcium, and zinc. Some algae use as human foods such as agar is used as commercial products while Graularia, Gelidium, etc. are used to grow microbes for making ice creams and jellies. Chlorella and Spirullina contain rich proteins that are used as food supplements.To make the aquatic ecosystem friendly, we should take conservation measures for protecting the algae species.
Algae are photosynthetic microorganisms that perform photosynthesis and produce oxygen (O2) and consume carbon dioxide (CO2) from the atmosphere. During photosynthesis, algae produce at least half of the oxygen in Earth’s atmosphere. Most of the algae inhabit the aquatic environment, either freshwater or marine habitats. They can also occupy on rocks, soils, vegetation, or moist terrestrial habitats. Some marine algae use as seafood, while some algae produce toxins.
The vegetative structures (thallus) of algae vary from species to species. They may be simple unicellular to complex multi-cellular. Their size ranges from small as less than 2 micrometers (Micromonas) to large as 30-60 meters long (Macocyctis, a type of marine algae). The following are the diverse vegetative structures of algae:
Unicellular non-motile: They are single-celled round algae. They exist as solitary or in the group within mucilage covering. Examples: Chlorella, Gloeocapsa, etc.
Motile colonial: In this case, definite numbers of unicellular algae form colony and they are motile. This type of colony is known as a motile colony. Examples: Volvox.
Non-motile Colonial: In colonial forms, the number of unicellular algae is indefinite, and they are non-motile such as Scenedesmus, Hydrodictyon (water net), etc.
Palmelloid type: In this case, algae cells are surrounded by a viscous mucilaginous substance such as Teyraspora, Aphanothce, etc.
Dendroid type: In this case, cells produce a mucilaginous substance, and they are folded in such a manner that they look like branches of a plant such as Prasino cladus.
Filamentous: These types of algae are of two types: Among them, some are simple un-branched filamentous such as Ulothrix, Spirogyra, and some are simple branched filamentous such as Cladophora.
Heterotrichous: Thallus of the algae consists of the following two parts: main shoot or trichome, which runs horizontally, termed as a prostrate system and a vertical erect trichome or shoot termed as erect system. This type of body is known as a heterotrichous form.
Parenchymatous: In these algae, cell division takes place on different sides, with the result that they become parenchymatous such as Ulva.
Siphonous: These algae consist of the multinucleate tube-like cells having no septa such as Vaucheria, Polysiphoni, etc.
Nodous: In this case, algae bodies contain nodal and intermodal areas such as Chara.
Complex: In this case, algae look like multi-cellular plants — the body divisible into holdfast, stipe, and frod, such as Sargassum, Laminaria.
The algal cells consist of the following structures:
Most of the algal cells have a cell wall. Some flagellated algae are lacking a cell wall. Algae cell-wall consists of two layers: inner microfilamentous and outer gelatinous irregular layer. Chemically, the cell wall is composed of cellulose, pectin, mucilage like a carbohydrate. It also contains other substances like alginic acid, calcium carbonate, fucoidan, fucin, silica, etc. The thickness of the cell wall varies with variously oriented in a granular matrix. In some cases, cell wall bears stored protein. Unicellular diatom algae have strong, rigid, siliceous ornamental, two valves cell walls. The siliceous ornamental cell wall is called frustule. The cell wall of the members of Cyanophyceae contains mucopeptide. In certain algae such as Gymnodinium and Pyramimonas, a true cell wall is absent. In this case, the cell is bounded by a membrane, known as a pellicle.
It occurs below the cell wall. The structure of the algal plasma membrane is like other eukaryotic cells. Some filamentous algae lack cell wall having stout and strong plasma membrane. This type of plasma membrane is known as periplast.
The eukaryotic algal protoplasm consists of one or more nucleus and cytoplasm. The cytoplasm is divided into cytosol and cell organelles. The protoplasm is bounded by lipoproteinaceous cell membrane, which is fluid mosaic in nature. The membrane is elastic and very thin, with selectively permeable in nature. It performs to control the passage of materials in and out of the cells. The algae have well organized spherical or elliptical shaped nucleus, which is surrounded by a distinct and double layer nuclear membrane. In this case, the outer membrane is attached to the endoplasmic reticulum(ER), while the inner membrane contains a matrix or karyolymph with chromatin reticulum.
The numbers of nucleoli or endosomes vary in different algal cells with varying numbers of chromosomes. Porphyra linearis contains the lowest numbers of chromosomes (n=2), while the highest numbers of chromosomes are found in Netrium digitali (n=592).
Like other eukaryotic cells, eukaryotic algal cells have membrane-bound cell organelles like chloroplasts, mitochondria, Golgi apparatus, ribosomes, endoplasmic reticulum, and in some cases, eyespot or stigma. In the prokaryotic algal cell, the nucleus is not surrounded by a membrane. In this case, the protoplasm is separated by photosynthetic pigments containing outer peripheral chromoplasm and colorless inner centroplasm.
Most of the algal cells are uni-nucleated, but in some cases, they are multinucleated.
Algal cells have colorful plastids, the chloroplasts. It is the prominent feature which is bounded by double-membrane structure; their number and shape vary in different species.
The chloroplasts of algae have various forms and shapes; in algae, eight main types are recognized: discoid (Chara), cup-shaped (Volvox), parietal, spiral (Spirogyra), C-shaped or girdle shaped (Ulothrix), reticulate (Oedogonium), ribbed (Volvocales), and stellate (Zygnema).
The chloroplast contains the following three major structural regions:
Envelope: It is the two membranous enclosed spaces.
Internal lamellar membranes: It is a highly organized membrane that contains different types of pigments for capturing energy. This lamellar system forms sac-like discs or thylakoid, which are stacked together and form grana. This thylakoid provides space for the chlorophyll a and other accessory pigments.
In most cases, chloroplasts have a glycoprotein structure, known as a pyrenoid. Chloroplasts of all kinds of algae have photosynthetic chlorophyll pigments which provide the actual color of the thallus.
In algae, five types of chlorophylls are found (Chlorophyll a, b, c, d, and e). Among them, chlorophyll a is found in all groups of algae, while chlorophyll b is present only in Chlorophyceae. Chlorophyll c is located in the representatives of Bacillariophyceae Cryptophyceae, Chryso-phyceae, and Phaeophyceae, chlorophyll d is seen in some red algae, and chlorophyll e is found in certain Xanthophyceae.
Besides chlorophyll, they also show various carotenoid pigments that impart different colors to algae as blue phycocyanin, yellow-brown fucoxanthin, brown phaeophycin, red phycoerythrin, etc. In this case, carotenoids are composed of carotenes and xanthophylls. In algal cells, the following five types of carotenes are found: α-carotene, β-carotene, c-carotene, e- carotene, and flavacene.
Besides carotene, several types of xanthophylls are found, such as lutein, violaxanthin, neoxanthin, fucoxanthin, myxoxanthophyll, myxoxanthin and oscilloxan. In this case, fucoxanthin is the main xanthophyll pigment.
In algae, phycobilins are also found as accessory pigments. They act as bilioproteins and provide either blue (phycocyanin) or red (phycoerythrin) in color. These types of pigments are found only in Rhodophyceae and Cyanophyceae, which absorb and transfer the light energy to the reaction center. Chloroplasts also contain proteinaceous bodies, known as pyrenoids. They perform to synthesize and store starch.
The staple reserve food of algal cells is carbohydrate. Different algae have different types of reserve carbohydrates. Green algae (Chlorophyceae) have starch, brown algae (Phaeophycea) have laminarin, and mannitol, yellow-golden (Chlorophytes) algae have volutin, red algae (Rhodophyceae) have Floridian starch as reserve food. Besides, these algae have oil and fat, leucocin, paramylum as reserve food.
Algae are a diverse group and very familiar to most people. They play an important role in the freshwater environment and act as the base for the aquatic food chain supporting all fisheries in the inland and oceans. They also remove excess nutrients and pollutants from the water controlling eutrophication. In some cases, excessive growth of algae can cause harmful effects to aquatic environments.
Algae are the green slimy blanket which covers the rock surface or the top of the ponds or a poorly kept aquarium that have the ability to conduct photosynthesis. The algae belong to the subphylum Thallophyta of the kingdom Protista in modern classification of organisms. Latin ‘alga’ means seaweed. These are eukaryotic organisms, autotrophic in nature as have chlorophyll in their cells. During photosynthesis, they produce oxygen with help of light energy from the sun and generate carbohydrates.
More than 30000 species of algae have been identified. Most algae are aquatic but some grow in semi-aquatic and terrestrial environments. Many algae live as endophytes in plant or animal tissue and many grow on plant or animal as epiphytes. Some of them make asymbiotic relationship with fungi and exist as lichen. Green algae, brown algae, red algae, golden-yellow algae are main types of algae. The study of algae is known as Phycology.
Examplses: Chlorella, Chlamydomonas, Oedogonium, Dunaliella, Volvox, etc.
Order-1: Dunaliellales (e.g. Dunaliella)
Order-2: Chlamydomonadales (e.g. Volvox, Chlamydomonas)
Order-3: Oedogoniales (e.g. Oedogonium)
Order-7: Tetrasporales (e.g. Tetraspora)
Examples: Stonewort (Chara), filamentous (Spirogyra) and desmids.
Examples: Marine flagellate (Tetraselmis).
Examples: Micromonas, Ostreococcus, Pyramimonas, etc.
Examples: Sea lettuce (Ulva), Acetabularia, Caulerpa, Monostroma, etc.
Examples: Cyclotella, Thalassiosira , Bacillaria, Navicula, Nitzschia, etc.
Examples: Chrysamoeba, Lagynion, Chrysocapsa, Ochromonas, etc
Examples: Apedinella, Mesopedinella, Parapedinella, Actinomonas, Pteridomonas, Dictyocha, Pseudopedinella, Pedinella, etc
Examples: Eustigmatos, Botryochloropsis,Pseudocharaciopsis, Ellipsoidion , Pseudellipsoidion, Nannochloropsis,Pseudostaurastrum, etc.
Examples: Ascophyllum, Ectocarpus, Laminaria, Fucus, Nereocystis, Macrocystis, Pelagophycus, Postelsia, Pelvetia, Sargassum, etc.
Examples: Chrysochromulina, Emiliania, Phaeocystis, Prymnesium, etc.
Examples: Gonyostomum, Vacuolaria, Merotricha, Chattonella, Chlorinimonas, Haramonas, Psammamonas,Fibrocapsa, Heterosigma, and Viridilobus, etc.
Examples: Mallomonas, Synura
Examples: Botrydium, Tribonema, Bumilleriopsis, Vaucheria, etc.
Examples: Cryptomonas, Chilomonas, Falcomonas, Rhinomonas, Plagioselmis, Teleaulax, etc.
Examples: Palmaria, Polysiphonia, Bangia, Corallina, Gelidium Chondrus, Kappaphycus, Gracilaria, Porphyra, Rhodymenia, etc.
Examples: Dinophysis, Alexandrium, Gonyaulax, Ceratium, Noctiluca, Gymnodinium, Polykrikos, Peridinium, etc.
Examples: Colacium, Euglena, Eutreptiella, Phacus, etc.
Based on colors, algae are divided into the following major four groups:
They belong to the class Cyanophyceae under the phylum Cyanophyta. They inhabit in freshwater or in a wide variety of moist soils of a terrestrial environment. They also form a symbiotic relationship with plants or lichen-forming fungi. They contain pigments like chlorophyll 'a', 'b', and phycobilins and they appear in blue green color. They are also known as Cynabacteria.
They may be either unicellular or multicellular algae which belong to the class Chlorophyceae under the phylum Chlorophyta. They contain pigments like chlorophyll a, chlorophyll b, carotenoids, and xanthophylls.
Examples: Chlamydomonas, Spirogyra, and Chara
Red algae belong to the class Rhodophyceae under the phylum Rhodophyta which is one of the largest phylum of algae. This phylum contains over 7000 recognized species. Among them, 6,793 species are found in the Class Florideophyceae. Most of the algae are multicellular and marine algae (seaweeds). Red algae contain pigments like chlorophyll a, chlorophyll d, carotenoids, xanthophylls, and phycobilins. About 5% of the red algae inhabit in freshwater environments. They are used as a stabilizer in milk products.
Examples: Porphyra, Gracilaria, and Gelidium.
These types of algae belong to the class Phaeophyceae under the phylum Phaeophyta. They contain pigments like chlorophyll a, chlorophyll c, carotenoids and fucoxanthin. They form a large group of multicellular algae. Majority of them inhabit in marine environments. Over 1500 known species of brown algae are available worldwide.
Examples: Dictyota, Laminaria, Sargassum, etc.
Based on morphology, algae can be divided into several types. Some are filamentous forms having cells arranged in chains like strings of beads. Some filamentous are un-branched such as Spirogyra while others are branched and bushlike such as Stigeoclonium.
Algae are almost ever-present throughout the world. Ecologically, they can be grouped into the following types by their habitats.
Algae are living organisms which are distributed throughout the world. They have different sizes, shapes, and colors. They can inhabit in freshwater and marine environments. They also grow on the body surfaces of other organisms such as turtles and polar bears, on rocks or in the soils, or under or inside porous rocks, such as limestone and sandstone. The algae have great important because they produce much oxygen on the earth for animals and human beings. Nutritionally, they contain several healthy elements such as proteins, fats, carbohydrates, and vitamins A, B, C, and E. They also contain a number of important minerals such as iron, potassium, calcium, magnesium, zinc and manganese.
The chordates were originated from a fish-like ancestor, very similar to the larva of the Ascidia (Tunicata) and it is assumed that they became the ancestor of the chordates by retaining the larval form throughout the life. In the palaeozoic age, the chordates were originated from some sessile Echinoderms, which were bottom dwellers of the sea. The primitive chordates resemble the non-chordates in some respects and are known as protochordates or invertebrate chordates. In the evolutionary course, They acquired new novelties and became vertebrates that were radiated on all ecological niches and became strong rivals of the non-chordates in the course of time.
The phylum chordata is a very diverse phylum which contains about 43,000 living species. Among them, most organisms belong to the subphylum, Vertebrata. This phylum is considered as the third largest phylum in the animal kingdom.
At different stages in their life, chordates show the following four features. They are:
Notochord: It is an elastic, rod-like longitudinal structure that is made up of cartilage. It is situated immediately above the alimentary canal (digestive tract) and just below the dorsal tubular nerve cord. The notochord is formed of special type of vacuolated cells and remains covered by a sheath, known as notochordal sheath. In the invertebrate chordates (urochordata and cephalochordada), it is formed of endothermal cells, but in the case of the vertebrate-chordates, it persists in the adult (with some exception), but in vertebrates, notochord is either partially, or wholly replaced by vertebral column. The main function of notochord is to support nerve cord.
Dorsal tubular nerve cord: It is a single hollow nerve cord which consists of bundle of nerve fibers that exists dorsally along the antero-posterior axis of the body, just above the notochord. Embryologically, this nerve cord originates from the dorsal ectoderm. It connects the brain to the muscles and other organs.
Paired Pharyngeal gill-slits: A pair of openings which connect the mouth and the throat, known as Pharyngeal gill-slits. At some stages of the life, all chordates possess paired pharyngeal gill-slits. In the primary aquatic animals, these remain persist in the adult and functions as the passage for the respiratory water current through the mouth, without entering the digestive system. The transition from aquatic to the land life involves pulmonary respiration and consequently the gill-slits lose their function. However, the initial stage of their formation is clearly observed in the embryos of the terrestrial chordates. In the adults, however, these are totally obliterated and become transformed into other organs like endocrine system.
Post-anal tail: It is an extension of the body away from the anus. Some chordates bear the tail with skeletal muscles, which assist in locomotion.
The phylum Chordata also contains the following characteristic features:
Among the above three sub-phyla, the major subphylum is vertebrata because it contains a variety of organisms like fishes, amphibians, birds, reptiles and mammals while the first two sub-phyla, urochordata and cephalochordata are collectively known as protochoradata that have very few species in between them which are all marine animals. Besides, the phylum vertebrata bears a distinguishing backbone that is built up of bone or cartilage. They have a brain which is enclosed in a skull. They also have proper nervous system, circulatory system, and a skeletal system that provides proper shape and support.
The main characteristics of urochordata are:
Examples: Ascidia mentula , Salpa fusiformis, Doliolum nationalis.
The sub-phylum Urochordata contains the following three classes:
Example: Ascidia mentula
Example: Doliolum denticulatum
Example: Oikopleura longicaudata
Examples: Mediterranean amphioxus or European lancelet: Branchiostoma lanceolatum
The sub-phylum vertebrata incorporates the remarkable chordates which occupy high taxonomical ranks. All the vertebrates are placed under the single sub-phylum Vertebrata or craniata. The vertebrate possess a ‘back-bone’ which is the most characteristic features of the vertebrates. Thus, a vertebrate is defined as an animal having back bone consisting of a series of small bones (ring-like)or cartilage running throughout the length of the body along the mid-dorsal side, enclosing and protecting the spinal cord. On the other hand, all animals which do not possess vertebral column, are known as invertebrate. The vertebrates have acquired a number of characteristics features in addition to the basic chordates characterizes which are of high adaptive value and as much they are readily distinguished from the invertebrate-chordates.
Sub Phylum Vertebrata is further classified into the following classes. They are:
Examples: Petromyzon marinus (Lamprey) and Myxine glutinosa (Atlantic Hagfish).
All bony fishes belong to the class Osteichthyes. All the representatives of Osteichthyes are cold-blooded which bear one pair of gill openings for breathing and different types of fins for swimming. Besides these, they have bony skeleton, jaws and one pair nostrils. The class Osteichthyes is the largest group of vertebrates in the world and it contains more than 30,000 fish species which account for about 96% of all fish species. This class does not contain sharks, rays, skates, lampreys and hagfishes. They have very keen sense organs with very good eyesight. They take a wide variety food, among them, some are herbivores, some carnivores and some take any kind of food at all(omnivores).
The class Osteichthyes is divided into the following two subclasses:
Examples: Labeo rohita, Catla catla, Anabas testudineus, Lates calcarifer, Tenualosa ilisha, Ompok pabo, Heteropneustes fosilis
The term ‘amphibian’ is derived from the Greek word ‘amphíbios’ meaning both kinds of life. They are cold-blooded vertebrate tetrapods which inhabit a wide variety of habitats, including terrestrial, arboreal, fossorial, or freshwater aquatic ecosystems. There are approximately 8,100 species, of which, about 90% are frogs. Paedophryne amauensis is the world smallest amphibians, found in Papua New Guinea which grows up to 7.7 mm in length while the largest living amphibian is Andrias sligoi (South China giant salamander) which grows up to 1.8 m in length (5 ft 11 in).
You might also read: Detailed Classification of Amphibia
The word reptile comes from Latin “Reptilis’ meaning creeping. They are the creeping and burrowing vertebrates with epidermal scales. There are about 8,000 living reptiles species in the world today that inhabit all continents on Earth except Antarctica. It includes verities group ectothermic vertebrates including lizards, snakes, crocodiles, alligators, turtles, caimans and worm-lizards, etc. They can inhabit different type habitats such as forests, deserts, freshwater wetlands and the open seas.
Examples: Green sea turtle (Chelonia mydas), Aldabran giant tortoise ( Aldabrachelys gigantea ), Spectral pygmy chameleon (Rhampholeon spectrum), Oriental Garden lizard (Calotes versicolor), Saltwater crocodile (Crocodylus porosus), Naja naja (Cobra), Indian Krait ( Bangarus caeruleus),Horned viper ( Vipera ammodytes).
You might also read: Detailed Classification of Extant Reptiles
All birds belong the class Aves, they are egg-laying endothermic vertebrate animals. There are about 10,000 living species of birds in the world that inhabit in nearly all habitats on Earth. It constitutes the largest number of species among the tetrapod classes.
Examples : Corvus splendens ( house crow), Columba livia (Domestic pigeon), Indian vulture (Gyps indicus) etc.
You might also read: Classification of Aves in details
The word ‘Mammalia’ is derived from Latin word ‘mamma’ meaning "breast". The class Mammalia includes the vertebrate animals which contain mammery glands. These glands are active in female and produce milk for feeding their babies. These vertebrate animals are also characterized by the presence of fur or hair, a four-chambered heart and three middle year bones which distinguish them from birds and reptiles. There are about 5500 living mammal species under 161 families and 29 orders. The rodents, bats and shrews constitute the largest order which is followed by the Primates, Cetartiodactyla and Carnivora, respectively.
Examples: Oviparous – Platypus (Ornithorhynchus anatinus); Viviparous – Royal Bengal Tiger (Panthera tigris),Red kangaroo (Macropus rufus), flying fox (Pteropus vampyrus), Short-beaked common dolphin (Delphinus delphis) , blue whale (Balaenoptera musculus) , etc.
They are cold or worm blooded organisms.
They are cold blooded organisms.
Notochord is present at some stage or it is replaced by a ring like vertebrae at adult stage.
Notochord or backbone is absent.
They have central nervous system which is dorsal, hollow and single.
In this case, central nervous system is ventral, solid and double.
Pharynx is perforated by gill-slits.
In this case, gill-slits are absent.
They perform respiration through gills or lungs.
They perform respiration through body surface, gills,or tracheae.
The position of heart is ventral.
Usually, the heart is absent, if present the position of heart is dorsal or lateral.
A post-anal part or tail is present.
In this case, post-anal tail is absent.
They are true coelomate organisms.
They may be acoelmate, pseudocoelmate or truly coelmate organisms.
Blood vascular system is closed type.
Generally, blood vascular system is absent; if present, it may be open or closed type.
Their body is bilaterally symmetrical.
Their body is radial, bi radial, bilateral or without symmetry.
Nerve cord is single, dorsal, without ganglia.
Nerve cord is double, ventral, usually with ganglia.
The gut is situated ventral position to nerve cord.
In this case, gut is found dorsal position to nerve cord.
They mainly perform sexual reproduction.Enter your text here...
In this case, asexual reproduction is predominant.
Their regeneration power is usually poor.
Their regeneration power is usually good.
They possess both exoskeleton and endoskeleton
In this case, only exoskeleton is present.
Examples: Hemichordates, Cyclostomes, Aves, Reptiles, Amphibians, Mammals , etc.
Examples: Protozoans, Annelids, Arthropods, Echinoderms, etc
Chordates are animals which belong to the phylum Chordata. This phylum consists of three groups, namely vertebrates, tunicates, and lancelets. The members of chordates are very essential for an ecosystem because they keep up the ecosystem. Chordates consist of 43,000 living species which can consume and hunt down other types of animals and maintain the of predator and prey role. Many chordates provide food for human beings and many chordates release their excretion to the environment, provide nutrients and minerals to the ecosystem which boost up the plants growth.
You might also read: Chondrichthyes Vs Osteichthyes:General Characteristics and Differences
The representatives of the phylum Platyhelminthes are commonly known as the flatworms or tapeworms. The word ‘Platyhelminthes’ is derived from the Greek word, ‘platy’ meaning flat and ‘helminth’ meaning worm. They are simple soft-bodied, bilaterian, unsegmented invertebrate animals. The Phylum Platyhelminthes makes up the 4th largest phylum among the animal kingdom. But among the acoelomate organisms, the phylum Platyhelminthes constitutes the largest phylum with more than about 20,000 known species throughout the world. Among them, around 80% live as parasitic life on humans and other animals and few are free-living.
The parasitic forms cause some trouble to the host animals, feed on host`s tissues and make certain diseases such as Schistosomiasis, or snail fever, Taeniasis, etc. while the free-living flatworms are scavengers or predators. Generally, free-living species live in water and some in shaded, humid terrestrial ecosystems, such as leaf litter. The members of this phylum have diverse sizes which range from microscope to 3 feet long.
The Phylum Platyhelminthes is classified into the following classes:
Class Turbellaria contains about 3,000 species, of which, majority of these species live in marine environments, some are found in freshwater environments and few live in tropical terrestrial and moist temperate environments.
Examples: Pseudobiceros bedfordi, Pseudoceros dimidiatus
Class Turbellaria includes the following orders:
It is one of the largest groups of flatworms and most of the members live in the aquatic environment and they lead exclusively parasitic life (ectoparasites) of aquatic vertebrates.
Example: Diplozoon paradoxum, Gyrodactylus adspersi
Example: Gyrocotyle rugosa, Amphilina foliacea
Example: Taenia solium, Diphyllobothrium latum
The members of this class are commonly known as flukes. There are more than about 20,000 known species of class Trematoda which are all parasitic in nature.
Example: Multicotyle purvisi, Lobatostoma manteri
Example: Lecithochirium sp., Pycnoporus heteroporus
The members of the phylum Platyhelminthes are known as flatworms which can adapt to an enormous variety of habitats. Flatworms live as endoparasites in the intestines and digestive tracts of the human body. Several species such as Cestodes (tapeworms) and digeneans (flukes) can cause diseases in livestock and human beings. In many countries, serious losses of stocks in fish farms are occurred by the monogeneans. The genus Schistosoma bores skin of human and causes diseases, known as Schistosomiasis, or bilharzia or snail fever. Besides these, many species of Platyhelminthes play an important role for healthy streams, lakes, and ponds. They also offer food for animals such as dragonflies, when they are young.
You might also read: Phylum Arthropoda: General Characteristics and Its Classification
Pinus are coniferous, evergreen resinous trees which are popularly known as pine. They belong to the family Pinaceae under order Coniferales of class Coiniferosida. Different species of the genus Pinus are distributed throughout the temperate and sub-alpine regions of Northern Hemisphere where they form dense forests of evergreen trees. They can grow up to 80 (260 ft) meters in height. The tallest pine tree is ponderosa pine which can grow about 81.79 m (268.35 ft) tall. They are long lived plant and can live up to 1000 years or more under favorable conditions.
There are about 120 species of pine tree throughout the world. They are widely distributed in the hills and have economic value because many pines are used in the construction, paper-products industries as the source of timber and resin. Some pine trees are also sources of wood tars, resin, turpentine, and oils while some produce edible seeds such as pine nuts, piñons, or pinyons. Besides these, white, black, Himalayan, and stone pines are cultivated as ornamental pine trees.
Species: P. wallichiana, P. insularis, P. armandi, Pinus khasya, Pinus geradiana, Pinus roxburghii, etc.
You may also read: Gymnosperms: Salient Characteristic Features
The plant body represents the sporophyte. The sporophytes are evergreen and tall tree (10 -80 m in height). The body has three parts: root, stem and leaves. The plants bear well developed tap root system. The stem is stout, branched and pyramidal in shape with recemose branches.
Root: A strong tap root system is present in young plant which may persist or roots develop and become stronger adventitious roots with increasing age. The roots can grow on rocks or hard ground and spread over a large area. The lateral roots are well developed with insufficient root hairs. Often a branch roots are infested with mycorrhizal fungus and hence it is called the mycorrhizal root.
Stem: The stem is erect, stout, cylindrical and pyramidal shape with dimorphic branches. The branches are restricted in the apical region. The stem is covered with bark. There are two types of branches:
The long shoot of unlimited growth: The main branches or long shoots have an unlimited growth with scale leaves which are found below the dwarf shoots and the needle like foliage leaves are present exclusively at their terminal ends.
The dwarf shoot of limited growth: The dwarf shoots develop in the axils of scale leaves on the main branches, which are without apical buds. It is about 1 -2 cm long with one or two scale leaves. The dwarf shoot also contains foliage leaves. In this case, a dwarf shoot with its foliage leaves is known as spur.
Leaf: The pine tree bears two types of leaves:
The scale leaves: Both long and dwarf shoots bear scale-leaves and fall off as the branches attain maturity. These leaves are small, brownish in color and membranous with protective structures.
The foliage leaves: The dwarf shoots bear foliage leaves. The leaves are long, green, simple, needle-like with photosynthetic structures. They develop in clusters at the apex of the dwarf shoots and can form the spur. Their number varies from 1-5 in different species.
Stem: A young stem in cross section resembles a dicotyledonous stem in many respects. It is wavy in outline. The general arrangement of various tissues from the periphery to the center is as follows:
Epidermis: It is the outer surface layer of the stem. It consists of a single layer of tubular close compact parenchymatous cells with a thick cuticle.
Hypodermis: Below the epidermis, a hypodermis layer is preset. It consists of a few layers of lignified sclerenchymatous cells.
Cortex: It consists of several layers of parenchymatous cells with copious resin ducts. A single layer of resin secreting glandular epithelial cells surrounds the resin duct.
Endodermis: Outside of the pericycle, endodermis is present. It consists of a single layer of parenchymatous cells.
Pericycle: It consists of several layers of parenchymatous cells which are located outer to the ring of vascular bundles.
Vascular bundles: They are conjoint, collateral, open, arranged in ring and endarch. In this case, protoxylem is directed towards the pith. Between xylem and phloem, a narrow strip of cambium is present. The xylem is composed of tracheids with bordered pits and xylem rays, without vessels. The phloem is composed of sieve tubes and phloem parenchyma without companion cells.
Pith: It is composed of a mass of parenchymatous cells.
Pith rays: It is composed by a narrow strip of cells running from the pith outwards between the vascular bundles.
Leaf: A transverse section of foliage leaf shows the following structure under the microscope. It is semi-circular in outline (centric type of leaf).
(i) Epidermis: It consists of a single layer of thick walled cells with a heavy sheet of cuticle and sunken stomata.
(ii) Hypodermis: It consists of two or three layers of very thick walled sclerenchymatous cells with resin ducts, which are broken up by stomata. It is placed just underneath the epidermis. It strengthens the tissue of the leaf.
(iii) Mesophyll: It consists of a few layer of chloroplast containing parenchyma cells with peg-like projections. In this case, wall projecting occurs inside the cell cavity which is known as arm palisade.
(iv) Endodermis: It consists of a single layer of barrel shaped cells which is present outside of the pericycle.
(v) Vascular bundles: They are collateral, closed and two in number.
(vi) Pericycle: It consists of albuminous cells and tracheidal cells. In this case, albuminous cells lie close to the phloem while tracheidal cells lie adjacent to the xylem. Albuminous and tracheidal cells together form the transfusion tissue which helps to flow of nutrients. The xylem is surrounded by pericycle.
Root: The internal organization of tissues in the root of Pinus is almost similar to that in a dicotyledonous root. A cross section of young root shows an epiblema (piliferous layer) with root hairs, a multilayered cortex and a diarch to pentrarch vascular cylinder and Y-shaped xylem bundles. 2-3 layered pericycles surround the vascular bundles while the cortex consists of a few layers of thin walled parenchymatous cells. A single layered endodermis is present which is followed by a pericycle. The root is mycorrhizal because fungus grows on the surface of the root.
The Pinus is monoecious plant which shows the sporophytic generation. The microsporophyll (male) and megasporophyll (female) are formed on the same plant but these two types of sporophylls appear usually in separate cones or strobilli.
The male and female cones are known as staminate strobilus and carpellate strobilus, respectively. The Pinus does not show vegetative reproduction. The flowers are unisexual. They always occur on the shoots of the current and a little away from the apex.
The male cones are simple, compact, oval structures and about 2-3 cm long. They are found to occur in clusters, near the tip of the long shoots.
Each male cone bears a short and elongated central axis upon which a large number of microsporophylls or stamens are arranged spirally. The microsporophylls are scaly and their number varies from 60 to 135 in each cone.
A microsporophyll consists of a short filament or stalk and a terminal leaf-like expanded structure while the apex is slightly bent upwards. Each microsporophyll bears two pouch-like microsporangia (anthers or pollen sacs) on its ventral surface. A microsporangium is sessile and oblong which is supported with a jacket of several layers of cells.
Each microsporangium produces a several microspores (pollen grains). The wall of each microspore is covered by inner intine and an outer exine. The microspores are winged and yellow in color. In this case, wings help in the dispersal of spores by wind.
The female cones are larger and compound in nature. They are formed in clusters of 1-4 in the axils of scale leaves of long shoots. Initially, they are green but ultimately become brownish red in color. It starts to produce in winter and become ready for pollination during the spring. It is hard woody and dry structure. It bears a central axis upon which a large number of megasporophylls are arranged spirally.
Each megasporophyll has short stalk with a large ovuliferous scale on the upper surface and a small bract scale on the lower surface. Each ovuliferous scale bears two inverted megasporangia on its upper surface towards the base.
Each megasporangium consists of a massive tissue which is called the nucellus and an envelope which is known as the integument. At the basal region, the integument is fused with the nucellus and open at the top by forming micropyle.
A single megaspore mother cell is differentiated within the nuceller tissue, which divides meiotically to form four megaspores. Of these four megaspores, only the lower most one is functional while others degenerate. The only functional megaspore increases in size and takes part in the development of the female gametophyte.
Male gametophyte: The microspore is the first cell of the male gametophyte. Microspore begins to germinate within the microsporangium and produces an extremely reduced male gametophyte. The microspore first divides to form a very small first prothellial cell and a large cell. The large cell then cuts off a second prothellial cell adjacent to the first one and the remaining of the large cell forms the antheridial cell. The two prothellial cells soon degenerate. The antherdial cell again divides to form a small generative cell above and a large tube cell below. The nucleus of tube cell is known as tube nucleus which regulates the growth of the pollen tube.
The microspores are dispersed with the help of wind. Further development of microspores takes place when it reaches the ovule due to pollination. A number of microspores reach the megasporangium (ovule) where they are attached with sticky mucillagenous substance from the micropyle.
When mucillagenous substance dries up, some of the microspores are drawn inside on to the apex of the nucellus. Later on, the spore coats split between the wings. Then the tube cell protrudes and grows to form the pollen tube. Ultimately, the pollen tube penetrates the nucellus. The generative cell then divides to form a sterile stalk cell and a fertile body cell (spermatogenous cell). The body cell further divides to form two non-motile unequal male gametes (sperms).
Female gametophyte: The functional megaspore is the first cell of the female gametophyte. It germinates within the megasporangium. The functional megaspore enlarges in size, its nucleus divides repeatedly by free nuclear divisions to form about 2,500 daughter nuclei. All the nuclei lie in the cytoplasm of the megaspore.
After that, a large central vacuole is produced, whereby the cytoplasm together with the nuclei moves towards the periphery. After pollination, development of the female gametophyte takes place again.
The walls are broken down around the nuclei and ultimately, a solid mass of thin walled cells are formed. The massive tissue thus formed within the megaspore. It is known as the female gematophyte. It is often referred to as the endosperm. The endosperm tissue is haploid (n).
A few flask shaped archegonia (2-3) are formed from the superficial cells (archegonial initials) that lie towards the micropylar end of the female gematophyte.
A mature archegonium consists of a neck of eight cells, one ventral canal cell and a large egg. There is no neck canal cell.
After a year of pollination, fertilization occurs. The pollen tube moves downwardly and reaches the neck of the archegonium. It then penetrates the neck and the tip of which bursts to discharge the two male gametes. One of the male gamete unites with the egg to form a diploid zygote.
The zygote is the first cell of the sporophyte which germinates almost immediately after its formation. The zygote nucleus divides to form four free nuclei. These nuclei then moves to the bottom of the zygote where they divide again to form eight nuclei. Subsequently, walls appear between these nuclei except the upper two. Further divisions result in the formation of sixteen cells in four tiers; this sixteen celled structure is termed as the proembryo.
The upper most tiers of four open cells merges into the general mass of the cytoplasm to carry out nutritive function. The next tier of four cells is called rosette tier which is capable of forming abortive embryo; normally it supplies nutrients to the suspensor and the embryo.
The third tier of four cells constitutes the suspension tier. The lower most tier of four cells is the embryo tier. The cells of the suspension tier elongate to form four separate suspensors, each carrying an embryo cell at its tip. The cells of the embryo tier form the embryos. The elongated suspensors push down the embryos into the gametophytic tissue and thus help the later to receive their nutrients.
Each cell of the embryo tier divides to form four potential embryos and secondary suspensor. Formation of more than one embryo in each megasporangium is referred to as polyembryony. In fact, only one of these embryos attains maturity and the others undergo degeneration.
After fertilization, the integument and the megasporangium are converted into seed coat and seed respectively. The seed contains embryo, the membranous nutritive layer perisperm and kernel. The nutritive tissue lies surrounding the embryo. A mature embryo consists of a radical, a hypocotyls, several cotyledons and a plumule. The seed germinates under favorable conditions to form a new sporophyte. This type of germination is called epigeal germination.
Pine trees are widely distributed throughout the world and have lots of economic value. Pine tree wood is very strong and it is extensively used to manufacture doors, electric poles, window panes, boats, railway sleepers, musical instruments, boards, boxes, veneers and plywood, building construction, paneling, etc. due to its durability. Turpentine oil is produced from the pine tree which is used as a solvent for varnishes, paints and in perfumery industry. It is also used for producing disinfectants, synthetic pine oil, denaturants, and insecticides, etc. Pine oil from the pinewood is used in pharmaceutical industries, textile industries, leather industries, etc.
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