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Free AIOU Solved Assignment Code 6452 Spring 2023
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Course: Biology–II (6452)
Semester: Spring, 2023
ASSIGNMENT No. 1
Q.1 Write in detail diagnostic characteristics, economic importance and distribution pattern of family Ranuculaceae.
Characters of Ranunculaceae:
- Diagonostic Characters:
Herbs, leaves exstipulate, incised blades, sheathing bases, flowers hypogynous, spiral or spirocyclic; sepals often decidous, usually petaloid; calyx and corolla free; stamens indefinite, free; carpels polycarpellary, apocarpous; fruit aggregate.
- Vegetative Characters:
The plants are annual or perennial herbs or a climbing shrubs (Clematis, Naravelia), rarely trees. They perennate by means of tuberous roots (Aconitum) or rhizomes.
Tap root, adventitious or tuberous (Ranunculus spp. and Aconitum). The tap root system is in the initial stage but sooner or later replaced by the adventitious roots.
Herbaceous, in some climbing (Clematis) or underground rhizome or erect, branched.
Generally simple, alternate, or opposite (Clematis) exstipulate rarely stipulate (Thalictrum), sheathing leaf base, petiolate rarely sessile (Delphinium). In some aquatic species leaves may show dimorphy (Ranunculus aquatilis); unicostate or multicostate reticulate venation.
- Floral Characters:
Solitary terminal (Anemone), axillary (Clematis), raceme (Aconitum, Delphinium) and cymose (Ranunculus spp.).
Pedicellate, ebracteate rarely bracteate, hermaphrodite, (unisexual in Thalictrum). Mostly actinomorphic (Ranunculus) rarely zygomorphic (Delphinium and Aconitum) hypogynous, complete, pentamerous.
There is no distinction of calyx and corolla in most of the flowers. Sepals 5, caducous, polysepalous, petaloid, imbricate or valvate aestivation.
Petals 5, polypetalous, variously coloured, caducous or wanting; nectaries present at the base of petals. Petals are united to form spur (Delphinium).
Stamens indefinite, polyandrous, spirally arranged on the thalamus, inferior; anthers dithecous, extrorse and adnate.
Polycarpellary (one carpel in Delphinium and 3 to 5 in Aconitum), apocarpous rarely syncarpous (Nigella), ovary superior, marginal placentation (axile in Nigella).
Aggregate, etario of achenes (Ranunculus), etario of follicle (Aconitum), follicle (Delphinium), septicidal capsule (Nigella) or berry (Actaea), etario of drupes (Adonis), etario of berries (Hydrastis) and simple pod (Xanthorhiza).
Small, oily and endospermic.
Generally entomophilous (Delphinium, Aconitum, Aquilegia) and anemophilous in Thalictrum.
Range of floral structure:
Three sub-families have been recognised on the basis of floral structure viz.:
(b) Anemoneae, and
Rendle is inclined to believe that the Anemoneae is more primitive than the Helleboreae.
In the Anemoneae the flowers are actinomorphic. In Anemone, for instance, flowers are solitary with five or six or more perianth leaves which are petaloid. True petals are altogether absent and as many as 13 rows of stamens along with numerous free carpels are found.
In Thalictrum, the inflorescence is a corymb or panicle; the perianth consists of 4-5 sepaloid structures. Stamens are numerous but carpels may be few. In Clematis there are 4 or more petaloid sepals with several stamens and carpels. In all the above three genera there is a pendulous ovule while in Ranunculus the ovule is erect.
In this genus there are 5 sepals followed by 5 petals. The stamens and carpels are numerous and free. The arrangement of stamens and carpels is typically spiral. In Myosurus all the five sepals have a basal spur; the stamens are few but carpels are many. In Adonis five sepals are followed by 8-16 coloured petals. As many as 23 rows of stamens may be counted; carpels also numerous.
In the Helleboreae the perianth is spirally arranged in the primitive genera but in the advanced forms it is arranged in a cyclic manner.
Two distinct tendencies are noticeable in this subfamily viz.:
(i) With actinomorphic flowers-considered more primitive.
(ii) With zygomorphic flowers – considered more advanced.
In Helleborus the perianth has five members followed by a number of honey leaves. These are nothing else but modified stamens belonging to the outermost row. The number of stamens may be 100 arranged in 13 rows.
In Isopyrum and Coptis also there are 13-rows of stamens but their total number is decreased. In Aquilegia the number of stamens may be only 15 or sometimes 20-25; there are only five carpels. Xanthorhiza also has a typical pentamerous condition with 5-10 stamens and 5 carpels. In Cimicifuga the number of carpels has been reduced. In Actaea the reduction in carpel has gone further so that only one carpel is found.
Zygomorphic tendencies are found in Trollius, Nigella, Delphinium, Aconitum etc. In Trollius there are 5-15 perianth leaves, 23 rows of stamen and 5-10 carpels. In Nigella we come across 5-perianth leaves, 8 honey-leaves, 8 rows of stamens and 5-12 syncarpous carpels.
In Delphinium and Aconitum zygomorphy arises due to spur on the posterior side. Normally there are only three carpels but in D. ajacis only one carpel is found.
In the sub-family Paeonieae the flowers have become hemicyclic or acylic. In Paeonia the flower is pentamerous with 5 sepals and petals each, indefinite stamens but only two to three carpels. Definite nectariferous structures cannot be found but a disc or ring like swelling around the carpels may develop.
Distribution of Ranunculaceae:
It is commonly known as buttercup family. It includes 35 genera and 1500 species out of which 163 species are confined to India. They are chiefly found in temperate and arctic regions.
Economic Importance of Ranunculaceae:
The seeds of Nigella sativa (H. Kalongi) are used as spice in pickles.
Aconitum hererophyllum and A. napellus yield a number of alkaloids specially aconitin. This is used in acute and inflammatory diseases. The roots of Thalictrum yields “mamira”, which is used in opthalamia. Anemone pulsatilla is mostly used in feminine diseases and in gastric derangements. Pulsatilla obtained from Anemone pulsatilla is a good medicine for menstrual disorder.
Cimicifuga racemosa gives the black Snake root containing resins. This has been recommended for treatment of cholera and nervous pain. Helleborus niger and H. foetida produce glycosides useful as purgatives in veterinary practices. Delphinium staphisagria is used as antiparasitic ointment.
Some of the plants are cultivated in gardens for their beautiful flowers viz., Ranunculus, Delphinium, Naravelia, Clematis, Nigella and Caltha.
Affinities of Ranunculaceae:
The family Ranunculaceae is one of the most primitive of the dicotyledons. Hutchinson, Bentham and Hooker have placed the family in the class of very early dicotyledons. Engler, Rendle and others put the family under the archichlamydeae.
The family is in its close relationship with the monocotyledons due to the a following facts:
(i) Tubular cotylar sheath formation and union of two cotyledons in Ranunulus ficaria, the sheath during germination is pierced by epicotyl.
(ii) Leaf bases are broadened into sheath and rhizome formation.
(iii) The course of vascular bundles and scattered arrangement in the stem of certain genera, e.g., Cimicifuga.
(iv) The endospermous seed with apical small embryo and copious endosperm.
(v) Lastly the free carpels, the resemblance of flowers with Alismaceae.
The family can be linked with Rosaceae on account of free and numerous stamens and carpels. The dimorphic leaves and hypogynous followers of Ranunculaceae trace the relationship with the family Nymphaeaceae.
- Perennial habit (Aconitum, Clematis).
- Presence of tree or shrub (Paeonia).
- Presence of stipules (Thalictrum).
- Leaves with reticulate venation.
- Flowers hermaphrodite.
- Actinomorphic symmetry.
- Large number of petals.
- Calyx and corolla free.
- Gynoecium polycarpellary and apocarpous.
- Ovule anatropous.
- Plants are generally herbs.
- Leaves compound (Clematis).
- Stipules are absent except in Thalictrum.
- Zygomorphic symmetry (Delphinium).
- Unisexual flowers (Thalictrum).
- Petals fused and forming spur (Delphinium).
- Gynoecium syncarpous (Nigella).
Common plants of the family:
Herb with medicinal properties due to the presence of several alkaloids.
Ornamentanal, cultivated in gardens.
Annual or perennial herb.
The seeds of Nigella sativa are used as a condiment.
Perennial herb with medicinal properties.
Division of the family and chief genera:
Engler and Prantl have divided the family into three tribes viz., Helleboreae, Anemoneae and Paeoniaeae. According to Hutchinson (1924) the family Ranunculaceae is divided into two sub-families.
Carpels with more than one ovule; fruit follicle or berry.
Tribe (i) Helleboreae – Flowers actinomorphic.
Nigella, Helleborus, Aquilegia.
Tribe (ii) Delphinieae – Flowers zygomorphic.
Carpels with one ovule; fruit a bunch of dry achenes very rarely berry.
Tribe (iii) Ranunculeae – Leaves alternate, sepal imbricate, flowers are not subtended by involucral leaves, sepal mostly caducous.
Tribe (iv) Anemoneae – Leaves alternate, sepals mostly coloured and persistent, flowers subtended by an involucral leaves.
Tribe (v) Clematideae – Leaves opposite, sepals valvate or imbricate; corolla absent or represented by staminodes.
Clematis, Clematopsis, Naravelia.
Important Types of Ranunculaceae:
- Ranunculus scleratus, Linn. (Fig. 24.5):
An erect, annual herb.
Tap root, replaced by adventitious branched roots.
Erect, herbaceous, green, glabrous, solid or fistular, branched with distinct nodes and internodes.
Simple, trilobed, or tripartite, each lobe is further divided with ovate cuneate segments. Alternate, petiolate, sheathing leaf-base, exstipulate, venation is reticulate multicostate.
Pedicellate, bracteate, hermaphrodite, actinomorphic, complete, hypogynous, yellow.
Sepals 5, polysepalous, petaloid, aestivation quincuncial.
Petals 5, Polypetalous, obovate with pocket-shaped nectary on the inner side at the base of each petal, yellow, aestivation imbricate.
Stamens indefinite, polyandrous, spirally arranged, anthers elongated, filament long, basifixed, extrorse.
Polycarpellary, apocarpous, ovary superior, unilocular, with basal placentation.
- Delphinium ajacis, Linn. (Fig. 24.6):
Tap root, branched, fibrous and annual.
Erect, branched, herbaceous, green, glabrous, solid and cylindrical.
Cauline, simple, much dissected palmately lobed, alternate, exstipulate, sessile, venation reticulate multicostate.
Pedicellate, bracteate, bracteolate (two violet coloured) complete, hermaphrodite, hypogynous and zygomorphic.
Sepals 5, petaloid, polysepalous, posterior sepal produced into a long spur, aestivation quincuncial.
Petals 4, gamopetalous, the posterior two petals are fused to form spur and projected into the spur of posterior sepal, violet, imbricate aestivation.
Stamens indefinite, polyandrous, arranged spirally in 3 whorls of 5 stamens each alternating with the petals. Filaments are flattened, anthers basifixed.
Monocarpellary, unilocular, ovary superior, marginal placentation, pubescent, stigma simple.
AIOU Solved Assignment Code 6452 Spring 2023
Q No.2 Write distinguishing features of family Liliaceae and family Poaceae.
According to the plant taxonomists, it has been estimated that a total of 2 to 3 million plant species exists on our planet. Among them, around two lakh species are angiosperms (flowering plants), while others include gymnosperms, bryophytes, hydrophytes and other vascular and non-vascular plants. These plants are grouped into different families depending upon their characteristics.
Poaceae family is also known as the potato family. Around 2000 species of dicotyledonous plants belong to this family. Its important characteristics are mentioned below.
Characteristics of Poaceae Family
Following are the characteristic features of the Poaceae family:
- Root System: Taproot system.
- Stem: Erect or climber; Poaceae includes herbs, shrubs, small trees, and climbers.
- Leaves: Alternate, simple or pinnately compound (rarely); exstipulate; reticulate venation.
- Inflorescence: Racemose- terminal or axillary raceme; Cymose- solitary in Solanum.
- Flower: Complete, bisexual, actinomorphic, hypogynous.
- Calyx: Five sepals, gamosepalous; valvate aestivation.
- Corolla: Five petals, gamopetalous, valvate aestivation.
- Androecium: Five stamens, epipetalous; anthers basifixed.
- Gynoecium: Syncarpous, bicarpellary, bilocular, superior ovary, axile placentation.
- Fruit: Berry/ capsule.
- Seed: Numerous, endospermous
The economic importance of some plants belonging to the Poaceae family are as follows:
- These are an important source of food. E.g. tomato, brinjal and potato
- These are important sources of spices. E.g. chilly
- The leaves of Nicotiana tabacum are a major source of tobacco.
- These are also used as ornamental plants. E.g. petunia
- Plants such as belladonna and ashwagandha are also used as medicinal plants.
The Fabaceae family is a large family of the plant kingdom, including several economically important plants. The family Fabaceae is also known as Leguminosae or Papilionaceae since it belongs to the pea or legume family. There are around 20,000 species of dicotyledonous Fabaceae plants widely distributed all over the world.
Characteristics of Fabaceae Family
Listed below are the morphological and floral characteristics of the Fabaceae family.
- Root: Dicotyledons, taproot with root nodules.
- Stem: Erect or climber; Fabaceae includes shrubs, herbs, trees and majorly climbers.
- Leaves: Petiolate, pinnately compound or simple; pulvinus leaf base, stipulate; reticulate venation.
- Inflorescence: Racemose.
- Flower: Complete, bisexual, zygomorphic, hypogynous, bracteate/ ebracteate.
- Calyx: Five sepals, gamosepalous; valvate or imbricate aestivation.
- Corolla: Five petals, polypetalous, papilionaceous, vexillary aestivation.
- Androecium: Ten stamens (9+1), diadelphous, anther dithecous.
- Gynoecium: Superior ovary, monocarpellary, unilocular, single, short -style and flat, hairy-stigma.
- Fruit: Legume.
- Seed: One or more, non-endospermic.
Many plants belonging to this family are economically useful. Few of them are listed below:
- The plants of this family are unique and have root nodules which contain nitrogen-fixing symbiotic bacteria, capable of transforming atmospheric nitrogen into fixed nitrogen or ammonia.
- Pulses like gram, moong, soya bean are the main source of food.
- Mulethi plant is known for its medicinal value.
- Soya bean and groundnuts are used to extract oil that is used for cooking.
- Sunn hemp is the source of timber and fibre.
- Indigofera is used to make dye.
- Sesbania and Trifolium are the sources of fodder or livestock feed.
- Lupin and sweet pea are known as ornamental plants.
Liliaceae is the family of around 2500 species of perennial, herbaceous monocots. It is also known as the ‘lily family’. Its characteristics are discussed below.
Characteristics of Liliaceae Family
Following are the important characteristics of the Liliaceae family.
- Root: Fibrous root system.
- Stem: Erect; Liliaceae includes perennial herbs which propagate through bulbs or rhizomes.
- Leaves: Alternate, simple; exstipulate; parallel venation.
- Inflorescence: Cymose- solitary; umbellate clusters.
- Flower: Complete, bisexual, actinomorphic; hypogynous, perianth present.
- Perianth: Indistinctive sepal and petal; six tepals (3+3), often united tepals; valvate aestivation.
- Androecium: Six stamens in two whorls (3+3).
- Gynoecium: Syncarpous, tricarpellary, trilocular, superior ovary with axile placentation.
- Fruit: Mostly Capsule and sometimes berry.
- Seed: Endospermic seeds.
The economic importance of the plants belonging to the Liliaceae family are:
- Source of Medicine -Aloe vera, Smilax and Colchicine.
- Ornamental Plants -Lilium, tulips, Gloriosa and Ruscus.
- Source of food (or) Vegetables-Asparagus.
- Bulbs of Allium cepa and the roots of various species of Smilax are used as flavouring agents.
AIOU Solved Assignment 1 Code 6452 Spring 2023
Q.3 Define Embryology. Give brief information about early growth of plant body.
Embryology, the study of the formation and development of an embryo and fetus. Before widespread use of the microscope and the advent of cellular biology in the 19th century, embryology was based on descriptive and comparative studies. From the time of the Greek philosopher Aristotle it was debated whether the embryo was a preformed, miniature individual (a homunculus) or an undifferentiated form that gradually became specialized. Supporters of the latter theory included Aristotle; the English physician William Harvey, who labeled the theory epigenesis; the German physician Caspar Friedrick Wolff; and the Prussian-Estonian scientist Karl Ernst, Ritter von Baer, who proved epigenesis with his discovery of the mammalian ovum (egg) in 1827. Other pioneers were the French scientists Pierre Belon and Marie-François-Xavier Bichat.
Baer, who helped popularize Christian Heinrich Pander’s 1817 discovery of primary germ layers, laid the foundations of modern comparative embryology in his landmark two-volume work Über Entwickelungsgeschichte der Thiere (1828–37; “On the Development of Animals”). Another formative publication was A Treatise on Comparative Embryology (1880–91) by the British zoologist Frances Maitland Balfour. Further research on embryonic development was conducted by the German anatomists Martin H. Rathke and Wilhelm Roux and also by the American scientist Thomas Hunt Morgan. Roux, noted for his pioneering studies on frog eggs (beginning in 1885), became the founder of experimental embryology. The principle of embryonic induction was studied by the German embryologists Hans Adolf Eduard Driesch, who furthered Roux’s research on frog eggs in the 1890s, and Hans Spemann, who was awarded a Nobel Prize in 1935. Ross G. Harrison was an American biologist noted for his work on tissue culture. Systems biology, the study of the interactions and behaviour of the components of biological entities, including molecules, cells, organs, and organisms.
The organization and integration of biological systems has long been of interest to scientists. Systems biology as a formal, organized field of study, however, emerged from the genomics revolution, which was catalyzed by the Human Genome Project (HGP; 1990–2003) and the availability to biologists of the DNA sequences of the genomes of humans and many other organisms. The establishment of the field was also influenced heavily by the general recognition that organisms, cells, and other biological entities have an inherently high degree of complexity. Two dominant themes of modern biology are rooted in that new outlook: first, the view that biology is fundamentally an informational science—biological systems, cells, and organisms store and transfer information as their most-fundamental processes—and second, the emergence of new technologies and approaches for studying biological complexity.
Biological organisms are very complex, and their many parts interact in numerous ways. Thus, they can be considered generally as integrated systems. However, whereas an integrated complex system such as that of a modern airliner can be understood from its engineering design and detailed plans, attempting to understand the integrated system that is a biological organism is far more difficult, primarily because the number and strengths of interactions in the system are great and they must all be inferred after the fact from the system’s behaviour. In the same manner, the blueprint for its design must be inferred from its genetic material. That “integrated systems” point of view and all the associated approaches for the investigation of biological cells and organisms are collectively called systems biology.
Many of the most-critical aspects of how a cell works result from the collective behaviour of many molecular parts, all acting together. Those collective properties—often called “emergent properties”—are critical attributes of biological systems, as understanding the individual parts alone is insufficient to understand or predict system behaviour. Thus, emergent properties necessarily come from the interactions of the parts of the larger system. As an example, a memory that is stored in the human brain is an emergent property because it cannot be understood as a property of a single neuron or even many neurons considered one at a time. Rather, it is a collective property of a large number of neurons acting together.
One of the most-important aspects of the individual molecular parts and the complex things they constitute is the information that the parts contain and transmit. In biology information in molecular structures—the chemical properties of molecules that enable them to recognize and bind to one another—is central to the function of all processes. Such information provides a framework for understanding biological systems, the significance of which was captured insightfully by American theoretical physical chemist Linus Pauling and French biologist Emil Zuckerkandl, who stated in a joint paper, “Life is a relationship among molecules and not a property of any one molecule.” In other words, life is defined in terms of interactions, relationships, and collective properties of many molecular systems and their parts.
AIOU Solved Assignment 2 Code 6452 Spring 2023
Q.4 Describe characteristics of wood with respect to diffuse porous and ring porous, sapwood and hard wood, soft and hard wood and annual rings
Wood is a I–41 fibrous tissue found in many plants. It has been used for centuries ice noth fuel and as a construction material. It is composed of 2 natural composite of cellulose fibers (which are strong in tensio .) embedded in a matrix of lignin. Lignin resists compression. W md is produced as secondary xylem in the stems of trees. In a living tree it transfers water and nutrients to the leaves and other growing tissues. It has a support function, enabling woody plants to reach large sizes or to stand up for themselves.
Wood is yielded by trees. A tree increases in diameter by the formation of new woody layers between the existing wood and the inner bark. It envelops the entire stem, living branches, and roots. Technically this is known as secondary growth. Secondary growth takes place by the cell division in the vascular cambium, a lateral meristem, and subsequent expansion of the new cells.
- Growth rings
In some areas like Pakistan, there are clear seasons. Here growth can occur in a discrete annual or seasonal pattern, leading to growth rings. These rings can be clearly seen on the end of a log. These are also visible on the other surfaces. If these seasons are annual these growth rings are called as annual rings. Where there is no seasonal difference growth rings may be indistinct or absent. In some cases, there are differences within a growth ring. Wood is divided into two types on the basis of type of growth rings:
- a) Early wood or springwood: The part of a growth ring nearest
the center of the tree arc formed early in the growing season. Growth is rapid during these seasons. They are composed of wider elements. It is lighter in color than that near the outer portion of the ring. It is known 3S early wood or springwood.
- h) Late wood or summer wood; The outer portion formed later in the season is then known as fir: latewood or suminerwood.
A knot is a particular type of imperfection in a piece of wood. It will affect the technical properties of the wood. It makes the wood imperfect. But knots may be exploited for artistic effect. In a longitudinally sawn plank, a knot will appear as a roughly circular solid piece of wood. The grains of the rest of the wood flow around this piece of wood. Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the re ular wood.
Heartwood and sapwood
- a) Heart wood: Heartwood (or “xylem”) is wood that as a result of tylosis become more resistant to decay. Tylosis is the deposition of chemical substances (a genetically programmed process). Once heartwood formation is complete, the heartwood is dead. Some uncertainty still exists as to whether heartwood is truly dead, as it can still chemically react to decay organisms. Usually heartwood looks different; in that case it can be seen on a cross-section. Heartwood may (or may not) be much darker than living wood. It may (or may not) be sharply distinct from the sapwood. However, other processes, such as decay, can discolor wood, even in woody plants. The term heartwood derives from its position and not from any vital importance to the tree. A tree can thrive with its heart completely decayed.
- b) Sapwood: Sapwood is the younger, outermost wood. In the growing tree it is living wood. Its principal functions are to conduct water from the roots to the leaves. It also store up and give back aecording to the season the reserves prepared in the leaves. All xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead in sapwood. All wood in a tree is first formed as The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees grown in the open may become of considerable size, 30 cm or more in diameter, before the formation of heartwood. Some species begin to form heartwood very early in life. Therefore, they have only a thin layer of live sapwood. But in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras. But it is thick in maple, ash, hickory, hackberry, beech, and pine. Some others never form heartwood.
Hard and soft woods
There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it. For every tree species there is a range of density for the wood it yields. There is a rough correlation between density of a wood and its strength (mechanical properties). For example, mahogany is a medium-dense hardwood. It is excellent for fine furniture crafting, making it useful for model building. The densest wood may be black ironwood.
It is common to classify wood as either softwood or hardwood.
- a) The wood from conifers (e.g. pine) is called
- b) The wood from dicotyledons (usually broad-leaved trees, e.g. oak) is called
These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwood (e.g. yew) are harder than many hardwoods.
Some species show a distinct difference between heartwood and sapwood. In these species, natural color of heartwood is darker than that of the sapwood. Very frequently the contrast is conspicuous. This is produced by deposition of chemical substances in the heartwood. A dramatic color difference does not mean a dramatic difference in the mechanical properties of heartwood and sapwood. Some experiments on very resin( us Longleaf Pine specimens indicate an increase in strength, due to the resin. It increases the strength when wood is dry. Such resin-sat irated heartwood is called fat lighter. Structures built of fat lighter are r Dt attacked by termites. But they are very flammable. Stumps of old ilngleaf pines are often dug and split into small pieces. These are sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks.
Wood is a heterogeneous, hygroscopic, cellular and anisotropic material. It is composed of cells. Theircell walls are composed of micro-fibrils of cellulose (40% — 50%) and hemicelluloses (15% — 25%) impregnated with lignin (15% — 30%). The cells are mostly of one kind, tracheids. They are much more uniform in structure than that of most hardwoods. There are no vessels (“pores”) in coniferous wood such as one sees so prominently in oak and ash. The structure of hardwoods is more complex. The water conducting capability is depends on vessels. In some cases (oak, chestnut, ash) vessels are quite large and distinct. But in others (buckeye, poplar, willow) it is too small to be seen without a hand lens. Such woods are divided into two large classes, ring-porous and diffuse-porous.
- a) Ring porous species:. In ring-porous species, the larger vessels
or pores are localized in the part of the growth ring formed in spring. Thus they form a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels. It is composed of much greater proportion of wood fibers. These fiber are the elements which give strength and toughness to wood. But the vessels are a source of weakness. Such wood is present in ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak,
- b) Diffused porous woods: In this case, the pores are evenly sized. Therefore, water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are basswood, birch, buckeye, maple, poplar, and willow. Intermediate groups: Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group.
- Early wood and latewood in softwood
In temperate softwoods there often is a marked difference between latewood and early wood. The latewood will be denser than that .formed early in the season. When examined under a microscope the cells of dense latewood are very thick-walled. They have very small cell cavities. But those formed first in the season have thin walls and large cell cavities. The strength is in the walls, not the cavities. Thus there is greater the proportion of latewood the greater the density and strength. In choosing a piece of pine the principal thing to observe is the comparative amounts of early wood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring.
- a) Early v ad and latewood in ring-porous woods: In the case of
the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties. Generally, if there is more rapid growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.
- b) Earlywood_and latewood in diffuse-porous woods: In the
diffuse-porous woods, the demarcation between rings is not always so clear. In some cases, it is almost (if not entirely) invisible to the unaided eye. Conversely, when there is a clear demarcation there may not be a noticeable difference in structure within the growth ring. In diffuse-porous woods, the vessels or pores are even-sized, so that the water conducting capability is scattered throughout the ring instead of collected in the early wood. The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers.
- Monocot wood
Some structural material roughly resembles ordinary, dicot or conifer wood. These are produced by a number of monocot plants. These also are called wood. Its example is bamboo. It is a member of the grass family. It has considerable economic importance. Large culms are widely used as a building and construction material. Another major plant group is called wood are the palms. Of much less importance are plants such as Pandanus, Dracaena and Cordyline. With all this material, the structure and composition of the structural material is quite different from ordinary wood.
- Water content
Water occurs in living wood in three conditions, namely: I. In the cell walls
- In the protoplasmic contents of the cells.
- As free water in the cell cavities and spaces.
In heartwood it occurs only in the First and last forms. Wood that is thoroughly air-dried retains from 8-16% of water in the cell walls. The oven-dried wood also retains a small percentage of moisture. The water contents make the wood softer and more pliable. A similar effect is in the softening action of water on paper or cloth. Within certain limits, the greater the water content, the greater its softening effect.
- Uses of wood
- Fuel: Wood has a long history of being used as fuel. It is stills used as fuel in rural areas of the world. Hardwood is preferred er softwood because it creates less smoke and burns longer.
- Construction: Many buildings are made and decorated with wood. Wood is an important construction material. Wood remains in common use today in boat construction. Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber is called as felled trees. New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials. In buildings made of other materials, wood will still be found as a supporting material. It is especially used in roof construction, in interior doors and their frames, and as exterior cladding. Wood is also commonly used as shuttering material.
- Engineered wood: Wood used in construction includes products such as glued laminated timber (glulam), laminated veneer lumber (LVL), parallam and I-joists. These products allow the use of smaller pieces. They may also be selected for specific projects such as public swimming pools or ice rinks Wood will not deteriorate in the presence of certain chemicals. These engineered wood products are more environmentally friendly. They are sometimes cheaper, than building materials such as steel or concrete.- Wood unsuitable for construction is broken down mechanically (into fibers or chips) or chemically (into cellulose). It is used as a raw material for other building materials such as chipboard, engineered wood, hardboard, medium-density fiberboard (MDF), oriented strand board (OSB). Such wood derivatives are widely used. Wood fibers are an important component of most paper. Cellulose is used as a component of some synthetic materials. Wood derivatives can also be used for kinds of flooring, for example laminate flooring.
- Next generation wood products: Further developments include new lignin glue applications, recyclable food packaging, rubber tire replacement applications, anti-bacterial medical agents, and high strength fabrics or composites. As scientists and engineers further learn and develop new techniques to extract various components from wood.
- Furniture and utensils: Wood has always been used extensively for furniture, including chairs and beds. Also for tool handles and cutlery, such as chopsticks, toothpicks, and other utensils, like the wooden spoon.
- In the arts: Wood has long been used as an artistic medium. It has been used to make sculptures and carvings for millennia. Examples include the totem poles carved by North American indigenous people from conifer trunks. Certain types of musical instruments, such as those of the violin family, the guitar, the clarinet and recorder, the xylophone, and the marimba, are made mostly or entirely of wood.
- Sports and recreational equipment: Many types of sports equipment are made of wood, or were constructed of wood in the past. For example, cricket bats are typically made of white willow. The baseball bats are legal for use in Major League Baseball. These are frequently made of ash wood or hickory
- Medicine: In January 2010 Italian scientists announced that wood could be used to become a bone substitute. It is likely to take at least five years.
AIOU Solved Assignment Code 6452 Autumn 2023
Q.5 Write a detailed note on structure of lipids, structure of fatty acids, fats and oils and Phospholipids.
“Lipids are organic compounds that contain hydrogen, carbon, and oxygen atoms, which forms the framework for the structure and function of living cells.”
These organic compounds are nonpolar molecules, which are soluble only in nonpolar solvents and insoluble in water because water is a polar molecule. In the human body, these molecules can be synthesized in the liver and are found in oil, butter, whole milk, cheese, fried foods and also in some red meats.
Let us have a detailed look at the lipid structure, properties, types and classification of lipids.
Properties of Lipids
Lipids are a family of organic compounds, composed of fats and oils. These molecules yield high energy and are responsible for different functions within the human body. Listed below are some important characteristics of Lipids.
- Lipids are oily or greasy nonpolar molecules, stored in the adipose tissue of the body.
- Lipids are a heterogeneous group of compounds, mainly composed of hydrocarbon chains.
- Lipids are energy-rich organic molecules, which provide energy for different life processes.
- Lipids are a class of compounds characterised by their solubility in nonpolar solvents and insolubility in water.
- Lipids are significant in biological systems as they form a mechanical barrier dividing a cell from the external environment known as the cell membrane.
Lipids are the polymers of fatty acids that contain a long, non-polar hydrocarbon chain with a small polar region containing oxygen. The lipid structure is explained in the diagram below:
Lipid Structure – Saturated and Unsaturated Fatty Acids
Classification of Lipids
Lipids can be classified into two main classes:
- Nonsaponifiable lipids
- Saponifiable lipids
A nonsaponifiable lipid cannot be disintegrated into smaller molecules through hydrolysis. Nonsaponifiable lipids include cholesterol, prostaglandins, etc
A saponifiable lipid comprises one or more ester groups, enabling it to undergo hydrolysis in the presence of a base, acid, or enzymes, including waxes, triglycerides, sphingolipids and phospholipids.
Further, these categories can be divided into non-polar and polar lipids.
Nonpolar lipids, namely triglycerides, are utilized as fuel and to store energy.
Polar lipids, that could form a barrier with an external water environment, are utilized in membranes. Polar lipids comprise sphingolipids and glycerophospholipids.
Fatty acids are pivotal components of all these lipids.
Types of Lipids
Within these two major classes of lipids, there are numerous specific types of lipids important to live, including fatty acids, triglycerides, glycerophospholipids, sphingolipids and steroids. These are broadly classified as simple lipids and complex lipids.
Esters of fatty acids with various alcohols.
- Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state
- Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols
Esters of fatty acids containing groups in addition to alcohol and a fatty acid.
- Phospholipids: These are lipids containing, in addition to fatty acids and alcohol, a phosphoric acid residue. They frequently have nitrogen-containing bases and other substituents, eg, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is sphingosine.
- Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine and carbohydrate.
- Other complex lipids: Lipids such as sulfolipids and amino lipids. Lipoproteins may also be placed in this category.
Precursor and Derived Lipids
These include fatty acids, glycerol, steroids, other alcohols, fatty aldehydes, and ketone bodies, hydrocarbons, lipid-soluble vitamins, and hormones. Because they are uncharged, acylglycerols (glycerides), cholesterol, and cholesteryl esters are termed neutral lipids. These compounds are produced by the hydrolysis of simple and complex lipids.
Some of the different types of lipids are described below in detail.
Fatty acids are carboxylic acids (or organic acid), usually with long aliphatic tails (long chains), either unsaturated or saturated.
- Saturated fatty acids
Lack of carbon-carbon double bonds indicate that the fatty acid is saturated. The saturated fatty acids have higher melting points compared to unsaturated acids of the corresponding size due to their ability to pack their molecules together thus leading to a straight rod-like shape.
- Unsaturated fatty acids
Unsaturated fatty acid is indicated when a fatty acid has more than one double bond.
“Often, naturally occurring fatty acids possesses an even number of carbon atoms and are unbranched.”
On the other hand, unsaturated fatty acids contain a cis-double bond(s) which create a structural kink that disables them to group their molecules in straight rod-like shape.
Role of Fats
Fats play several major roles in our body. Some of the important roles of fats are mentioned below:
- Fats in the correct amounts are necessary for the proper functioning of our body.
- Many fat-soluble vitamins need to be associated with fats in order to be effectively absorbed by the body.
- They also provide insulation to the body.
- They are an efficient way to store energy for longer periods.
Waxes are “esters” (an organic compound made by replacing the hydrogen with acid by an alkyl or another organic group) formed from long-alcohols and long-chain carboxylic acids.
Waxes are found almost everywhere. Fruits and leaves of many plants possess waxy coatings, that can safeguard them from small predators and dehydration.
Fur of a few animals and the feathers of birds possess same coatings serving as water repellants.
Carnauba wax is known for its water resistance and toughness (significant for car wax).
Membranes are primarily composed of phospholipids that are Phosphoacylglycerols.
Triacylglycerols and phosphoacylglycerols are the same, but, the terminal OH group of the phosphoacylglycerol is esterified with phosphoric acid in place of fatty acid which results in the formation of phosphatidic acid.
The name phospholipid is derived from the fact that phosphoacylglycerols are lipids containing a phosphate group.
Our bodies possess chemical messengers known as hormones, that are basically organic compounds synthesized in glands and transported by the bloodstream to various tissues in order to trigger or hinder the desired process.
Steroids are a kind of hormone that is typically recognized by their tetracyclic skeleton, composed of three fused six-membered and one five-membered ring, as seen above. The four rings are assigned as A, B, C & D as observed in the shade blue, while the numbers in red indicate the carbons.
- Cholesterol is a wax-like substance, found only in animal source foods. Triglycerides, LDL, HDL, VLDL are different types of cholesterol found in the blood cells.
- Cholesterol is an important lipid found in the cell membrane. It is a sterol, which means that cholesterol is a combination of steroid and alcohol. In the human body, cholesterol is synthesized in the liver.
- These compounds are biosynthesized by all living cells and are essential for the structural component of the cell membrane.
- In the cell membrane, the steroid ring structure of cholesterol provides a rigid hydrophobic structure that helps boost the rigidity of the cell membrane. Without cholesterol, the cell membrane would be too fluid.
- It is an important component of cell membranes and is also the basis for the synthesis of other steroids, including the sex hormones estradiol and testosterone, as well as other steroids such as cortisone and vitamin D.
Examples of Lipids
There are different types of lipids. Some examples of lipids include butter, ghee, vegetable oil, cheese, cholesterol and other steroids, waxes, phospholipids, and fat-soluble vitamins. All these compounds have similar features, i.e. insoluble in water and soluble in organic solvents, etc.