Tiêu đề Biology_IX_4_Review Questions.pdf ✅

ClassNotes UNDERSTANDING THE CONCEPTS Q#1 Explain the functions of cell membrane? Ans: Function of Cell Membrane: All prokaryotic and eukaryotic cells have a thin and elastic cell membrane, covering the cytoplasm. The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of chemicals inside the cell. In this way the membrane maintains the internal composition of the cell to a constant or nearly constant level. In addition to this vital role, cell membrane can also sense chemical messages and can identify materials and other cells. Q#2 Describe the structure of cell wall? Ans: Cell wall: The cell wail is a non-living and strong component of the cell, located outside the plasma membrane. It provides shape, strength, protection and support to the inner living matter (protoplasm) of the cell. Structure of Cell wall: Plant cells have a variety of chemicals in their cell walls. The outer layer of the plant cell wall is known as primary wall and cellulose is the most common chemical in it. Some plant cells, for example xylem cells, also have secondary walls on the inner side of the primary wall. It is much thicker and lignin and other chemicals are embedded in it in the walls of neighboring cells there are cytoplasmic connections called Plasmodesmata. Through these connections, cells transfer chemicals among each other. Presence of Chitin in the Cell wall of fungi: www.classnotes.xyz Biology ClassNotes, Inc. © 2020 1
ClassNotes Fungi and many protists have cell walls although they do not contain cellulose. Their cell walls are made of a variety of chemicals. For example, chitin is present in the cell wall of fungi. Prokaryotes have a cell wall composed of peptidoglycan that is a single large polymer of amino acids and sugar. Q#3 Discuss nucleus structure and function? Ans: Nucleus: A prominent nucleus occurs in eukaryotic cells. In animal cells it is present in the center while in mature plant cells, due to the formation of large central vacuole, it is pushed to side. Structure of Nucleus: The nucleus is bounded by a double membrane known as nuclear envelope. Nuclear Envelope: The nuclear envelope contains many small pores that enable it to act as a differentially-permeable membrane. Nucleoplasm: Inside the nuclear envelope a granular matrix, the nucleoplasm, is present. The nucleoplasm contains one or two nucleoli (singular, nucleolus) and chromosomes. www.classnotes.xyz Biology ClassNotes, Inc. © 2020 2
ClassNotes Visibility of Nucleolus: The nucleolus is usually visible as a dark spot and it is the site where ribosomal RNA is formed and assembled as ribosomes. Chromosomes: One of the rod shaped bodies found in the nucleus of cells that contain genetic information (DNA) Chromosomes are visible only during cell division while during interphase (non-dividing phase) of the cell they are in the form of fine thread-like structures known as chromatin Structure of DNA: Chromosomes are composed of Deoxyribonucleic acid (DNA) and histone proteins Histone proteins provide structural support to DNA for making the structure of chromosome. messenger Ribonucleic Acid (mRNA): DNA contains the message for the synthesis of specific proteins. According to this message, a molecule of messenger Ribonucleic Acid (mRNA) is synthesized. In this way, message is handed over to mRNA, which carries it to ribosomes. Ribosomes manufacture specific protein according to the message present on mRNA. Function of DNA: In this way DNA controls all the activities of the cell and is also responsible for the transmission of characteristics to the next generation. That is why it is honored as the hereditary material. Main Function of Nucleus: Nucleus is called brain of the cell. Nucleus controls all the activities of cell. Note: The prokaryotic cells do not contain prominent nucleus rather their chromosome is made of DNA only and is submerged in the cytoplasm. www.classnotes.xyz Biology ClassNotes, Inc. © 2020 3