Q21.Large trees hold up branches and leaves adding up to many tons sinceplant cells comprise semi-rigid or rigid walls (Cohen, 2009). Thewalls provide support and strength for plants. In addition, theysafeguard the weak cell contents. Millions of the cells work astissue making their combined strength massive. The main structuralconstituent of cell walls is cellulose, which is plentiful (Cohen,2009). Cellulose polymers comprise hundreds to thousands of glucosemonomers linked on ends to lengthy chains. Different cell wallconstituents involve the polysaccharide pectin. It is the compoundorganic substance, which provides firmness to fruit jellies. Adifferent polysaccharide is hemicellulose. It is glue-like, bindingfibrils. Last are glycoproteins. They have sugars linked to theirmolecules. The lengthy cellulose molecules are merged in groupscalled microfibrils, which are supported by pectin and associatedsubstances making up the cell wall bulk (Cohen, 2009).
Q22.Eukaryotic cells have an actual nucleus joined by a double membranewhile prokaryotic lack a nucleus. The nucleus seizes DNA-linked rolesof the large eukaryotic cell to a lesser chamber, for enhancedeffectiveness. The role is not important in the prokaryotic cell,since it is small (Cohen, 2009). In the eukaryotic cell DNA is linearwhile round in the prokaryotic. Eukaryotic DNA comprises proteinsreferred to histones and is arranged to chromosomes. Prokaryotic DNAis bare, implying it lacks histones and does not organize tochromosomes. The cell types comprise ribosomes. However, ineukaryotic cells they are bigger and multifaceted, while prokaryoticcells comprise a special group of RNA molecules (Cohen, 2009).
Plantcells are bigger compared to animal cells. Mitochondria in animalcells make up most of the cells energy from food. Plant cells employsunlight as energy. Sunlight is transformed to energy within the cellin a procedure referred to photosynthesis. The procedure is carriedout by chloroplasts than contain chlorophyll to take up sunlight.Plant cells have a firm cell wall, which surrounds the cell membrane,lacking in animal cells. Animal cells have more than one vacuole,which stores waste, water and ions. Plant cells have a single hugevacuole for water storage and ensuring cell turgidity (Cohen, 2009).
Q23.Cell theory is the notion that cells are the fundamental unit ofstructure in each living thing. Developments in microscopy during themid 17th century facilitated advancement of the theory. It is one ofthe bases of biology stating that new cells arise from otheravailable cells. The theory also argues that the cell is a basic unitof organization, structure and function in all living creatures(Cohen, 2009). By 1809, Lamarck had observed many cells and tissuesresulting in his conclusion that a body cannot have life if itscomponents are not cellular, or not made by cellular tissue. Virchowsuggested that all cells arise from the separation of past existingcells, and this notion became a central piece of current cell theory.He also came up with the discipline of cellular pathology founded onthe notion that illnesses do not affect a whole organism rather,concentrate on specific cell group. This made it simpler to detectand treat illnesses (Cohen, 2009).
Q24.The phases of the cell cycle are interphase and mitosis. Mitosis issubdivided to four phases (Cohen, 2009). During interphase, the G1period starts soon after division of a nucleus. The cell sizeincreases and RNA, ribosomes and substances, which slow or rouse theS period, are produced. DNA replication occurs during the S period.Division of mitochondria and different organelles engaged in mitosisare produced in the G2, which follows S period. Mitosis is aprocedure commenced by the presence of ringlike preprophasemicrotubule bands below the plasma membrane. The procedure is dividedto four arbitrary phases. Prophase is the initial stage of mitosis.During the phase, the chromatin compresses and the membrane aroundthe nucleus fades away. In metaphase, chromosomes organize themselvesat the center of the cell. The breaking of centro meres signifiesanaphase as the chromatid begins to move to either cell side. Duringtelophase, the cell membrane begins squishing together withprobability of cell division. Last is cytokenesis, during which celldivision has occurred and membranes structure around the nucleus.Chromosomes compress back to chromatid (Cohen, 2009).
Q25.In parenchyma tissue, cell walls are somewhat thin. The cells areslackly packed, while the cell wall comprises cellulose. Incollenchymas, the cell wall has sporadic thick corners. There islittle space amid the cells, while the cell wall comprises pectin andhemicelluloses. The cells are noticeable when observed with amicroscope because of the greater refractive indicator of their thickcell wall. Sclerenchyma tissues comprise uniform and thick cell wallswithout intercellular spaces. The cell wall has an extra layercontaining majorly of lignin (Cohen, 2009).
Q26.In dicots, apical meristems are located in the root and shoot tips.In monocots, they are in the root tips. Apical meristems result inprimary growth extending the plant length above and belowground.Vascular cambium produces xylem and phloem situated amid vasculartissues in the root and stem. They add to the plant thickness. It isjust a cell thick creating a ring around the plant stem. The corkcambium refers to tissue located in numerous vascular plants assection of the periderm. It causes cells to develop outwardsproducing cork, which is a protective substance. Intercalarymeristems are only located in monocots and is the area of fast celldivision at the bottom of nodes. The meristems are significant tomonocots since they permit stems to elongate fast, as well asensuring rapid re-growth of leaves following damage (Cohen, 2009).
Cohen,M. (2009). Cells.Canada: Crabtree Publishing Company.