BOT1501 Assignment 2 2021.

BOT1501 Assignment 2 2021. Plant Structure: Cytology, Morphology And Anatomy. Growth is a process that occurs in plants where the size and amount of cells increase. There are two types of growth found in plants: primary and secondary growth. Primary growth allows cell division to occur at the tips of roots and stems. It results in the formation of primary tissues which are known as apical meristems and are responsible for the increase in height/length of a plant. Secondary growth is the cell division that occurs in the cambia which causes stems and roots to thicken, increasing their girth. It is caused by cell division in the lateral meristem. Secondary growth only occurs in dicotyledonous plants, whereas primary growth occurs in both monocotyledons and dicotyledons. 1.2) A taproot root system consists of a single, main root from which many other branches may arise. This type of root system occurs in eudicot angiosperms and in gymnosperms such as conifers where the primary root generates a taproot system. A fibrous root system consists of highly branched roots. It occurs when roots originate from the stem tissue (in monocotyledons). Many adventitious roots (roots that develop from the stem or sometimes from leaves) may contribute to the formation of a fibrous root system in monocotyledons which results in no single root being the most prominent. A fibrous root system is usually found in shallower soil than a taproot system. 1.3) Sapwood is the outermost region of a woody stem/branch. It is living and is nearly always light coloured. Sapwood results from new wood formation and it is formed by the cambium (a thin layer of living cells). It contains a variety of cell types, many of which are physiologically active as well as living. Sapwood is the location in which water and dissolved minerals are transported between the roots and the rest of the plant. It also has a function of less importance of storing energy reserves. All of the wood found in young trees and the young parts of older trees is sapwood. Since sapwood contains the sap conducting cells of a tree, it generally tends to have a relatively high moisture content. Heartwood is the dead inner wood, which often makes up the majority of a stem’s crosssection. The main function of heartwood is to support the tree. It is generally darker in This study source was downloaded by from CourseH on :43:59 GMT -05:00 This study resource was shared via CourseH colour than sapwood and it contains compounds that make it more resistant to attack by decay organisms and insects. As a tree gets older and its trunk thickens, the nearest cells of the center of the trunk die but mostly remain intact. As these older sapwood cells age and die, they form heartwood. These cells no longer transport water or store energy reserves. Heartwood results from the natural ageing process of a tree. There is typically more heartwood present in a stem than sapwood. 1.4) Simple fruits result from flowers that have only one pistil. They develop from a single, matured ovary in a single flower. Most fruits and all legumes are simple fruits. They have only one flower and one ovary. They are typically fleshy fruits. Examples of simple fruits are tomatoes and avocadoes. Multiple fruits are formed when several blossoms are grouped together so that their maturing pistils grow together to form one fruit. They consist of matured ovaries of several to many flowers more or less joined into a mass. They are invariably accessory fruits. Some examples are pineapples and mulberries. 1.5) Endodermis occurs in roots and stems and is the layer surrounding the stele. Endodermal cells are very tightly packed and contain no intercellular air spaces. The transverse and radial cell walls of the endodermal cells are saturated with suberin and lignin which form the Casparian strip. This strip prevents water from moving into the stele through the cell walls of the endodermal cells. Water and dissolved nutrients thus move through the cytoplasm of the endodermal cells which can therefore regulate the amount of water that enters the vascular tissues of the central stele. Therefore the endodermis plays a very important role in the uptake of water by the roots. Pericycle is a cylinder of parenchyma or sclerenchyma cells found in roots that forms the layer of cells situated between the endodermis and phloem. These cells are important as they are meristematic. These cells divide and give rise to the vascular cambium which forms new cells during secondary thickening. In dicotyledons, the pericycle contributes to the vascular cambium often creating cork cambium. 1.6) Population bottlenecks occur when a population’s size is sharply reduced for at least one generation. This is due to environmental events (such as earthquakes, floods, disease or drought) or human activities (such as genocide). Because genetic drift acts quicker to reduce genetic variation in small populations, by undergoing the bottleneck effect, it can reduce a population’s genetic variation greatly (even if it does not last for very many generations). The genetic effect is the loss of genetic variation that occurs when a new population is established by a very small number of members from the original large population. This small population size results in the colony potentially having: reduced genetic variation from the original population, as well as a non-random sample of genes in the original population. This study source was downloaded by from CourseH on :43:59 GMT -05:00 This study resource was shared via CourseH Question 2: 2.1) Symbiosis occurs when organisms live in intimate ecological associations. There are three different types of symbioses: 1) Mutualism: It is often referred to as a beneficial symbiosis as it is a relationship between two or more organisms where all partners benefit. An example is the relationship between photosynthetic algae and/or bacteria with a fungus to form lichens. In this example, the photosynthetic algae provides the sugar and oxygen needed by the fungus and in return, the fungus provides the algae and/or bacteria with water, carbon dioxide, minerals, as well as protection from excess light. 2) Commensalism: occurs when one partner of the relationship benefits and the other neither benefits nor is harmed in the process. An example of commensalism is the relationship between orchids which grow as epiphytes (plants that grow upon other plants) in tropical rain forests on the upper branches of trees. The orchids obtain access to light and rain in the forest canopy and do not harm the trees that they grow upon in the process. 3) Parasitism: is a symbiosis in which an organism (the parasite) lives on or in another organism (the host) and feeds on it without killing it. In this relationship one partner (the host) is harmed and does not benefit. An example of this relationship is between mistletoes and trees. In this example, the mistletoe grows as an epiphytic parasite on the branches of the tree. Their roots penetrate their host’s vascular tissue, from which they then obtain water and minerals and use these substances for their own nutrition. 2.2a) Haustoria: Haustoria are known as roots. They are peg-like projections found on the roots of parasitic plants and are therefore also known as parasitic roots. Parasitic plants such as dodders and broomrapes do not have chlorophyll and have become dependent on chlorophyllbearing plants for their nutrition. They use haustoria which penetrate the host’s tissue and draw out water, minerals and organic food from it. 2.2b) Rhizome: A rhizome is a type of horizontal stem which typically grows underground, often close to the surface. Its function is to form new roots and shoots, so if a portion is cut from the parent plant, the rhizome will form a new plant, unlike many other roots which would have died in that situation. They are also used to store starches and proteins as well as allow a plant to perennate (survive annual unfavourable seasons) underground. 2.2c) Stipule spine: A stipule spine is a leaf-like structure. They occur in the form of thorns, spines, and prickles that are hard, rigid extensions of leaves with sharp, stiff ends and serve the purpose of protecting the plant. They deter herbivory by functioning as physical/mechanical This study source was downloaded by from CourseH on :43:59 GMT -05:00 This study resource was shared via CourseH defenses. In some cases, the stipule spines have also been used to protect the plant from extreme temperatures by shading or insulating the plants that grow them. 2.3) MITOSIS MEIOSIS I M.