The Cell as the Basic Unit of Life - PDF

2 The cell as the basic unit of life A Inorganic chemical constituents of organi...

2 The cell as the basic unit of life A Inorganic chemical constituents of organisms Water and inorganic ions are the two main inorganic chemical constituents of organisms. Water Water makes up about 60% of our Organisms consist mostly of water. (about 98%). body weight, and even more in organisms like jellyfish Some functions of water in organisms are shown below. As a reactant Water iS reactant" in some chemical reactions. As a medium for chemical reactions from water and dissolve many substances. e.g. In plants, food is produced Water can carbon dioxide in photosynthesis. Water in cells provides an aqueous light food medium for chemical reactions to take carbon dioxide + water oxygen chlorophyll place. As a cooling agent* As a medium of transport Water removes heat when it evaporates Many substances are transported in from the body of the organisms. organisms by water. e.g. Humans produce more sweat when e.g. In plants, inorganic ions dissolve body temperature is high. Evaporation of in water and are carried from the sweat helps cool down the body. roots to other parts. Provides support As a component of lubricant* Water gives shape and provides support Water is the major component of to organisms. many lubricating fluids in organisms. of water, e.g. When plant cells are full These fluids reduce friction during against they become turgid* and press movement. one another. This gives support to e.g. Pleural fluid around human lungs seedlings so that they can stand upright. reduces friction during breathing. pleural fluid* turgid cells press against one another seedling stands upright Fig 2.3 Functions of water in organisms pleural fluid RK reactant 52 FiT 17D turgid Al AR friction lttn lubricant 74A cooling agent 2-3  Cells and Molecules of Life Inorganic ions Inorganic ions are also called minerals* in Various inorganic ions are present in organisms. The table below shows biology. some of their functions in animals and plants. Inorganic ion Function in animals Function in plants Nitrate* A source of nitrogen* for the synthesis of proteins Cross-link Magnesium* Activates some A component of The role of enzymes in chemical reactions will be enzymes*, which regulate chlorophyll* discussed in Ch 4. chemical reactions in the Activates some body enzymes Iron* A component of Activates some haemoglobin*, an enzymes oxygen-carrying molecule in red blood cells Activates some enzymes Calcium* A component of bones Helps strengthen cell and teeth walls* Needed for processes like blood clotting, muscle contraction and sending messages in the nervous system* Cross-link Phosphate* A component of bones A component of Phospholipids and nucleic and teeth phospholipids and acids will be introduced in A component of nucleic acids Part B of this section. phospholipids* (which make up cell membranes*) and nucleic acids* (e.g. DNA*) Visit the following website and learn more about the importance of water for life. Discuss with your classmates whether life can exist without water. https://science.howstuffworks.com/environmental/earth/geophysics/water-vital-to- life.htm calcium 915 cell membrane AT REL AL chlorophyll *** DNA (deoxyribonucleic acid) BAL $T1 NE H& E 2-4 enzyme Ef haemoglobin mkITE iron ft magnesium * mineral MthH nitrogen A nucleic acid 3h phospholipid tit Al  of life 2 The cell as the basic unit B Organic chemical constituents of organisms Carbohydrates, lipids, proteins and nucleic acids are the major are often called Organic substances refer organic chemical constituents of organisms. Thus they complex molecules biomolecules*. They all contain the element carbon. containing the element carbon. Carbohydrates Carbohydrates contain the elements carbon, hydrogen and oxygen. Glucose', starch"', glycogen" and cellulose" are four common carbohydrates found in organisms. Glucose is the main energy source for cells. It is directly broken cells for chemical reactions in down in respiration to release energy and various activities of organisms. an Starch acts as an energy reserve" in plants and glycogen acts as energy reserve in animals (Fig 2.4 and 2.5). They are broken down to glucose to provide energy when needed. Cellulose is a major component of plant cell walls. starch grain glycogen granule photomicrograph of potato cells (x180) electron micrograph of a liver cell (x10 000) Fig 2.4 Starch stored as starch grains in potatoes Fig 2.5 Glycogen stored as glycogen granules in (starch grains are stained so that they the human liver appear orange) Lipids Lipids also contain the elements carbon, hydrogen and oxygen, but with a higher hydrogen-to-oxygen ratio. Triglycerides* and phospholipids are two common lipids found in organisms. Triglycerides (fats and oil) act as an energy reserve in organisms. They also have the following functions in animals: a Fats stored in adipose tissues* under the skin act as an insulator to reduce heat loss from the body. Fats stored in adipose tissues around the internal organs act as a shock absorber, which protects the internal organs. Phospholipids are a major component of cell membranes. biomolecule E179f cellulose #W # energy reserve AL a glycogen HE 5 dipose tissue AHA5 AEAE triglyceride tEEM 2-5  Cells and Molecules of Life Proteins and nitrogen. Cross-link Proteins contain the elements carbon, hydrogen, oxygenin some functions of proteins organisms are 0 The structures and functions of carbohydrates, lipids and Some also contain sulphur. proteins will be discussed in shown below. detail in Ch 5. muscles and skin tissues. Hair, are Some proteins make up body mainly made up of proteins (Fig 2.6). hair skin muscle Fig 2.6 Hair, muscles and skin are mainly made up of proteins Some proteins act as enzymes. They regulate chemical reactions in organisms. For example, enzymes are involved in regulating certain reactions in respiration. Some proteins act as hormones* They help regulate body processes in growth. organisms. For example, growth hormone* regulates Pathogens are viruses* Some proteins act as antibodies* or organisms that cause They help protect the body diseases. against pathogens*. Some proteins are involved in the transport of substances, e-g. haemoglobin is an oxygen-carrying protein in red blood cells. Nucleic acids Cross-link D Nucleic acids The structures and functions contain the elements carbon, hydrogen, oxygen, nitrogen and phosphorus. There are two of nucleic acids will be types of nucleic acid (DNA) and ribonucleic acia* acids, deoxyribonucleic discussed in detail in Bk 4, (RNA). Ch 25 and Ch 26. DNA is the genetic material* in organisms. It carries genetic information* which controls activities of cells and determines the features of organisms. RNA is involved in the synthesis of proteins. antibody Inie genetic information 1 14 a E. genetic material E1417 growth hormone ERBE 2-6 ribonucleic acid 1ZME1Z hormone #k33 Based on the above findings and the work of other scientists, Schwann proposed the Cell Theory* in 1839. This theory became one of the foundations of biology. The Cell Theory (with subsequent modifications by other scientists) states that: all organisms are made up of one or more cells. the cell is the basic unit of life; it is the smallest unit that shows all the characteristics of life. all cells come from pre-existing cells.  Cells and Molecules of Life Microscopes: tools for 2.3 studying cells A Types of microscopes available for are of microscopes Nowadays, many different types andelectron microscopes are observing cells. Light microscopes tablebelow shows their microscopes. The two types of commonly used differences. Electron microscopes Scanning electron Light microscopes electron Transmission e microscopes* (SEM) microscopes* (TEM) Working Light passes Electron beams scan over principle through a Electron beams* pass specimen or a thin slide of of a the surface of a specimen through a very thin slide it to form an image. to form specimen to form an image. an image. Maximum 1600 times magnification 1 500 000 times 200 000 times Appearance Coloured image of the image Black and white Black and white produced two-dimensional image three-dimensionalimage showing the internal showing the external structures of the specimen Most electron structures of the specimen micrographs in guard cell this book are in colour because 'false colour' added to them using computer software.