Cell Biology Revision Questions and Answers

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Gametes are mature haploid reproductive cells that unite to form a zygote that develops into a new individual. Gametes are also called sex cells. An egg or ovum is a haploid female reproductive cell or gamete whereas a sperm is a male haploid reproductive cell. A zygote is the initial cell that is formed as a result of the union of a male and a female gamete by means of sexual reproduction. The two haploid cells merge to give rise to a diploid cell which marks the first stage of development. An allele is an alternative form of a gene and is located at a specific position in a specific chromosome. Usually, two contrasting alleles exist for each trait. A gene is a molecular unit of heredity. They reside on stretches of DNA that code for proteins of living organisms. DNA refers to Deoxyribonucleic acid. It is a nucleic acid that contains hereditary information and is necessary for the growth and development of an organism. Natural selection is a mechanism that causes evolutionary change in populations. It produces changes in the genetic composition of a population from one generation to the other. Organisms hence become better adapted to their environment. Artificial selection refers to an intentional reproduction of individuals that have desirable traits. This could be done by breeding or genetically modifying the organisms. Unicellular organisms are those organisms that are microscopic and comprise of only one cell, whereas a multicellular organism consist of many cells. Prokaryotes, protists and several fungi are unicellular. They absorb nutrients directly through their body surfaces and excrete them by use of pseudopodia. Gaseous exchange is through their body surfaces. Multicellular organisms on the other hand have their cells organized into complex tissues and organs and body processes like respiration and excretion occurs in this organs. Photosynthesis is the process in which plants use energy from the sun to break down a water molecule for use in production of simple sugars. Hydrogen obtained from water is combined with carbon from carbon dioxide to form carbohydrates. Oxygen is given off as a byproduct. Cellular respiration on the other hand refers to a set of metabolic reactions that take place in a living cell. Oxygen is required to convert energy from nutrients like sugars into Adenosine Triphosphate. Carbon dioxide is given off as a byproduct in these reactions. Plant cell’s structure consists of a cell wall which lacks in the animal cell. Plant cells have large vacuoles that are centrally placed whereas animal cells have small vacuoles in the cytoplasm. Plant cells have chloroplasts that serve in trapping of energy from the sun for photosynthesis while animal cells lack. Lipids are a group of organic compounds that are hydrophobic and include fats, oils , waxes and phospholipids. Lipids are vital in energy storage, in structure of the cell membrane and as signaling proteins. Phospholipids are a class of lipids that form a major part in cell membranes as lipid bilayers. They consist of a simple molecule, a phosphate group and glycerol. Mitosis is a process of nuclear division which involves the division of the cytoplasm in somatic cells. The process produces two identical daughter cells. The stages involved are interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Meiosis is a type of cell division that produces gametes, with half as many chromosomes as the parent cell. This division results in four daughter cells. Meiosis has 10 stages: prophase 1, metaphase 1, anaphase 1 and telophase 1, followed by prophase 2, metaphase 2, anaphase2, and telophase 2. During meiosis, crossing over occurs during prophase 1 of meiosis in a process called synapsis allowing for the exchange of genetic material. This process does not occur in mitosis. Ribose is found in RNA and is a normal sugar with an OH- group attached to the 2’...
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