Short Answers for Plant Diversity Botany Class - Assignment Example

Q1. Describe the plant cell wall, including its location, composition, origin, function and other important aspects. (http micro.magnet.fsu.edu/cells/plants/images/plantcell.jpg) Answer: Cell wall is the most important characteristic feature of the plant cell. It is important for maintaining the appropriate shape of the plant cell and hence of the plant. It is present outside the plasma membrane of the plant cell. It provides rigidity to the plant cell. It enables the plant to stand tall and also allows the leaves to get sunlight. These are the two essential features of the plant and cell wall plays the important role to carry out these functions. It prevents the plasma membrane from rupturing when the cell is placed in the hypotonic solution, as there is endosmosis of the fluid. It controls the growth of the cell and hence plays an imperative role in the cellular morphogenesis. The protein component of the cell wall is responsible to perform the function of enzymes and also to transport cellular secretions to and from the cell. Cell wall protect the cell from various pathogens as the cell wall is rigid and does not allow the pathogen to enter the cell easily thus it acts as a physical barrier and protects the cell. Cell wall also serve as a arsenal for the storage of carbohydrate molecules. These storage molecules could be used in due course of cellular metabolism. The seed coat has stored carbohydrate molecules. Oligosaccharins present in the cell wall act as hormones and play important role in cellular signalling. It induces the formation of phytoalexin and chitinase synthesis. It also enhances cytoplasmic calcium concentration. Moreover, the cell wall of roots of legumes harbour nitrogen- fixing bacteria. Cell wall is a component that is essential for producing paper, wood, fibre, shelter and roughage. It is made up of cellulose (β1, 4-glucan). Cellulose is a complex sugar molecule encompassing glucose as a monosaccharide. It also includes hemicellulose which is derived from hemicellulose. The cell wall also has pectin polysaccharides which determines the cell wall porosity. It is responsible for cellular adhesion and formation of middle lamella. It also has lognin, wax and water. Origin of the cell wall took place with the evolution of eukaryotes from the prokaryotes. The prokaryotes, bacterial cell wall got transformed into the plant cell wall. With the cell division of the plant cell the cell plate formation occurs between the daughter nuclei. The vesicles are formed by the secretory cellular organelle the Golgi apparatus, this is non-cellulosic component of the cell wall. Gradually other polysaccharides are formed by the endoplasmic reticulum and through golgi they aids in the formation of cell wall. Q2. Compare and contrast the chloroplast and the mitochondrion, including their structure, function, origin, and other important aspects. Answer: Mitochondria and Chloroplasts are the cellular organelles present in eukaryotic cell. While mitochondria is present in both the plant and the animal cell, chloroplast is confined to the plant cells. Mitochondria is called the power house of the cell. It is 1µm in length. Mitochondria helps in cellular respiration and the metabolism of the cell. It generates Adenosine Tri Phosphate (ATP) by means of Krebs Cycle. The complete oxidation of the glucose molecule takes place in mitochondria. Pyruvic acid which is generated in the cytoplasm as a result of glucose oxidation is transported to the mitochondria where the Pyruvic acid onsets the Krebs cycle for generating the energy currency, the ATP. Mitochondria is bi-layer organelle where inner membrane is folded into cristae, to enhance the surface area of the inner membrane. These cristae contains F1 particles which are responsible for oxidation. The inner membrane is permeable to oxygen, carbon-di-oxide and water. It encloses the mitochondrial matrix. In matrix all the enzymes responsible for Krebs cycle or TCA or citric acid cycle takes place.Mitochondria is the chief organelle required by all eukaryotes for the supply of energy. (http://www.ruf.rice.edu/~bioslabs/studies/mitochondria/mitotheory.html) On the other hand Chloroplasts are the photosynthetic organelles present in plants and algae. Chlorophyll is responsible for harvesting the solar energy and convert partly into the ATP molecule and rest for the formation of the carbohydrate molecules. Chloroplast like mitochondria is a double membrane structure. The inner membrane encloses the matrix called stroma. It also has disc like structures called the thylakoids. These thylakoids are stacked and arranged over one another like stacked coins, forming a structure called granum. The granum are joined together by means of lamella. (http://www.seos-project.eu/modules/agriculture/images/chloroplast_inside.jpg) The lumen of the thylakoid contains chlorophyll to carry out the photosynthesis process. It entraps the sunlight for the formation of sugar/ carbohydrate for the plant and for rest of the dependent animal world. Q3. Describe and discuss the process of primary growth in a perennial plant, including the important tissues, cell types, processes, timing, and other important aspects. Answer: Primary growth of the plant is responsible for the development of root system as well as shoot system. It is produced by apical meristems. In initial stages when the plant grows in length only the apical meristem play an imperative role and aids in the elongation of plant both the shoot as phototropic growth towards the light and roots as geotropic movement, towards the ground. The tip of the root is protected by the root cap, the root cap encloses the meristematic tissue. In the meristematic tissues the cell division occurs constantly and large no. of cells are formed. This is followed by the elongation phase where the cells elongate and thereby push the meristematic tissue further on. The zone of elongation is followed by the zone of maturation, where the cells mature. Thus in primary growth of the plant cell, three distinct phases are recognized- encompassing the zone of cell division, the zone of cell elongation, the zone of cell maturation. The tissues playing imperative role in the primary growth includes: epidermis, the ground tissue or parenchymatous tissues and the vascular tissue including the xylem and phloem. The absorption takes place through roots and hence the epidermis plays the vital role in the absorption of water and minerals. This is present a s a single layer of cells encompassing the root hair to enhance the surface area of the cell. Vascular tissue encompass radial arrangement of xylem for the transport of water. It is a continuous column and present as the spoke of wheel. The phloem is responsible for carrying the sugar molecule and is present as wedges between the radially arranged xylem tissues. The ground tissue encompass parenchyma cells, these cells are active in mineral uptake. Endodermis- a single layer demarcates the vascular tissues from the parenchyma cells. On the other hand the shoot has a terminal bud that encloses the apical meristem. In bud leaf premordia are present. Vascular tissue forms the continuous bundles. It is not arranged in the centre but are arranged in the circle so that new leaves and branches can grow form the vascular tissues. In order to provide strength to the plant the epidermis is followed by the collenchyma tissue which has thick walls and do not inter cellular space. This is essential for the strength of the plant shoot system. In certain cases sclerenchyma tissue is also present in the vascular bundles, to provide strength and support to the stem. On the other hand the vascular tissue of the leaf forms continuous vascular tissues with the stem to form the column with the stem xylem and with the stem phloem. The epidermis of the leaf is interrupted by means of opening called stomata, mediated by the guard cells. It is through these openings the leaf exchange CO2 and O2. These openings or stomata also play an imperative role in transpiration. In leaves the ground tissue is the mesophyll tissue. The parenchyma cells in a column like pattern called columnar palisade mesophyll while the lower portion has spongy mesophyll where the gaps are filled with air. The gaps are more near the stomata, the opening of the leaves. 4. Describe and discuss the process of secondary growth in a perennial plant, including the important tissues, cell types, processes, timing, and other important aspects. Answer: As the plant grows there is not only the growth in its length that occurs but for the rigidity of the plant it is imperative to have an increase in the girth of the plant. This increase in girth of the plant is called the secondary growth of the plant. It is observed that along with the primary growth, secondary growth also occurs in plants. The secondary growth takes place through the cambium tissue. Cambium forms a cylindrical ring of meristematic tissue and hence is responsible for the secondary vascular tissue. The secondary vascular tissue is responsible for the formation of secondary xylem towards the inside of the secondary vascular tissue while the secondary phloem is formed outside the secondary vascular tissue. As the plant ages and matures there is an increase in the girth of the plant. The secondary vascular cambium is formed from the parenchyma cells which have the power to divide constantly. The meristematic tissue forms a layer between the primary xylem and primary phloem of each vascular bundle. This layer forms the vascular cambium encompassing ray initials and fusiform initials. With the growth of the plant, there is an accumulation of secondary xylem. It forms a tissue called the call wood. This wood encompass tracheids, vessels and fibres. Secondary growth takes place through lateral meristems. These lateral meristems are the cylinders of separating and dividing cells throughout the length of roots and shoots. The above mentioned vascular cambium incorporates sheets of vascular tissue called secondary xylem and phloem. After their growth, the cork cambium substitute the epidermis. In temperate regions, perennial plants do not display secondary growth during the cold season i.e. winter. They also display early wood formation and late wood formation. Early wood is formed when the first tracheid and first vessels are formed. They portray larger diameter while their walls are thin as compared to the late wood that is formed in summer. Early wood enhances water supply to the emerging new leaves while the late wood has thick walls meant for stronger support and provide rigidity to the plant/ tree. It is the late wood that is responsible for the production of annual growth rings that could tell the age of the plant. As the plant ages, the old secondary xylem forms the heart wood (in the centre) and this heart wood does not transport xylem sap or water, while the outer layer the newly formed secondary xylem called the sap wood is responsible for the transport of xylem sap. With time the aging layers of the periderm fall off called the peeling bark. Bark is the tissue which is present outside of the vascular cambium encompassing secondary phloem, cork and the cork cambium. Q5. Describe and discuss how water moves in the plant body, including the important tissues, cell types, processes, mechanisms, theories, and other important aspects. Answer: Water forms the continuous column. Even in the tallest plant each and every leaf present at the top is supplied by eater. This movement of water is against the gravitational pull. It is therefore imperative to have a theory that can possibly demonstrate the movement of water along the length of the plant, as this is vital for the survival of the plant. Water transport not only transports water but also it enables various minerals required for the plant to move from the soil to the top most leaf of the plant. These minerals are the nutrients for the plant as they are rich in nitrogen, potassium and phosphorus. The theory that supports this movement of water is the Cohesion- tension theory. This theory is based on the transpiration process. Transpiration is the loss of water from the leaves. It is the process of evaporation that takes place through the stomata. It is evident that water molecules possess very high cohesion force (force between like molecules) and therefore they are bound to each other with stronger bond creating a tension of water pull. Due to evaporation there occurs a deficit of water at the surface of leaves, water molecules have the tendency to move from higher water potential to the lower water potential thus water is pulled from the stem which in turn pulls water from the roots. Besides cohesion force, water molecule also has strong H-bond, this also serves as a pulling force when the water is lost in the atmosphere due to evaporation from leaves. Xylem tissues are responsible for this uplifting of water from roots to the leaves. There is a continuous Xylem vessels throughout the plant which enables the water molecules to move from roots to leaves. This does not occur in desert plants as they do not possess proper leaves http://preuniversity.grkraj.org/html/5_TRANSLOCATION_OF_ORGANIC_SOLUTES.htm http://preuniversity.grkraj.org/html/5_TRANSLOCATION_OF_ORGANIC_SOLUTES.htm Q6. Describe and discuss how food moves in the plant body, including the important tissues, cell types, processes, mechanisms, theories, and other important aspects. Answer: Plants produce food by the process of photosynthesis. This food is transported to all the parts of the plant and excess food is stored in the form of fruits, grains, tubers, bulbs or in leaves. Each plant has its own characteristic feature that enables it to store food in different parts. Food is manufactured in the chloroplast present in the leaves. These are then converted into simple sugars for performing translocation to other parts of the plant. Thus the site of synthesis of food is different from the site of storage and need of the food. The translocation i.e. change of location of the food from the kitchen of plant i.e. leaves to the store house i.e. storage part is done by phloem tissues. The phloem sieve tubes play an important role in this translocation. Girdling experiment performed where the tissues of phloem are being removed states that the translocation could not be performed. There are various factors that govern the translocation process: 1. Temperature: Increase in temperature increases the rate of movement or the process of translocation. 2. Light: Growth of the plant, flowering, photosynthesis and also the process of germination is totally controlled by light, and also the process of translocation is controlled by light. During day translocation is slow whereas at night translocation is fast. 3. Spectrum of light: Moreover the spectrum that displays maximum translocation is red light. 4. Dividing cells: They also show maximum translocation towards them as they are in constant supply of energy and food. Translocation is an important phenomenon that is dependent on the solute concentration. It is important for the survival of the plant while the transpiration is said to be the necessary evil. Reference Tiaz, L. Plant Physiology. Sinauer Associates; 3rd edition, 2002. Read More