Basic Biology Study Material PDF

Basic Biology Study Material Cell “A cell is defined as the smallest, basic unit of life that is responsible for all of life’s processes.” Cells are the structural, functional, and biological units of all liv...

Basic Biology Study Material Cell “A cell is defined as the smallest, basic unit of life that is responsible for all of life’s processes.” Cells are the structural, functional, and biological units of all living beings. A cell can replicate itself independently. Hence, they are known as the building blocks of life. Each cell contains a fluid called the cytoplasm, which is enclosed by a membrane. Also present in the cytoplasm are several biomolecules like proteins, nucleic acids and lipids. Moreover, cellular structures called cell organelles are suspended in the cytoplasm. What is a Cell? A cell is the structural and fundamental unit of life. The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology. Robert Hooke was the first Biologist who discovered cells. All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular). Mycoplasmas are the smallest known cells. Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy. Cells are complex and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like bricks of the buildings. Our body is made up of cells of different shapes and sizes. Cells are the lowest level of organisation in every life form. From organism to organism, the count of cells may vary. Humans have more number of cells compared to that of bacteria. Cells comprise several cell organelles that perform specialised functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells. Discovery of Cells Discovery of cells is one of the remarkable advancements in the field of science. It helps us know that all the organisms are made up of cells, and these cells help in carrying out various life processes. The structure and functions of cells helped us to understand life in a better way. Who discovered cells? Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of bottle cork under a compound microscope and noticed minuscule structures that reminded him of small rooms. Consequently, he named these “rooms” as cells. However, his compound microscope had limited magnification, and hence, he could not see any details in the structure. Owing to this limitation, Hooke concluded that these were non-living entities. Later Anton Van Leeuwenhoek observed cells under another compound microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were “alive.” Eventually, after a host of other observations, these entities were named as animalcules. In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He was able to describe the nucleus present in the cells of orchids. Characteristics of Cells Following are the various essential characteristics of cells:  Cells provide structure and support to the body of an organism.  The cell interior is organised into different individual organelles surrounded by a separate membrane.  The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.  Every cell has one nucleus and membrane-bound organelles in the cytoplasm.  Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell.  Lysosomes digest unwanted materials in the cell.  Endoplasmic reticulum plays a significant role in the internal organisation of the cell by synthesising selective molecules and processing, directing and sorting them to their appropriate locations. Types of Cells Cells are similar to factories with different labourers and departments that work towards a common objective. Various types of cells perform different functions. Based on cellular structure, there are two types of cells:  Prokaryotes  Eukaryotes Prokaryotic Cells 1. Prokaryotic cells have no nucleus. Instead, some prokaryotes such as bacteria have a region within the cell where the genetic material is freely suspended. This region is called the nucleoid. 2. They all are single-celled microorganisms. Examples include archaea, bacteria, and cyanobacteria. 3. The cell size ranges from 0.1 to 0.5 µm in diameter. 4. The hereditary material can either be DNA or RNA. 5. Prokaryotes generally reproduce by binary fission, a form of asexual reproduction. They are also known to use conjugation – which is often seen as the prokaryotic equivalent to sexual reproduction (however, it is NOT sexual reproduction). Eukaryotic Cells 1. Eukaryotic cells are characterised by a true nucleus. 2. The size of the cells ranges between 10–100 µm in diameter. 3. This broad category involves plants, fungi, protozoans, and animals.  4. The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells. It is also responsible for cell to cell communication. 5. They reproduce sexually as well as asexually. 6. There are some contrasting features between plant and animal cells. For eg., the plant cell contains chloroplast, central vacuoles, and other plastids, whereas the animal cells do not. Cell Structure The cell structure comprises individual components with specific functions essential to carry out life’s processes. These components include- cell wall, cell membrane, cytoplasm, nucleus, and cell organelles. Read on to explore more insights on cell structure and function. Cell Membrane  The cell membrane supports and protects the cell. It controls the movement of substances in and out of the cells. It separates the cell from the external environment. The cell membrane is present in all the cells.  The cell membrane is the outer covering of a cell within which all other organelles, such as the cytoplasm and nucleus, are enclosed. It is also referred to as the plasma membrane.  By structure, it is a porous membrane (with pores) which permits the movement of selective substances in and out of the cell. Besides this, the cell membrane also protects the cellular component from damage and leakage.  It forms the wall-like structure between two cells as well as between the cell and its surroundings.  Plants are immobile, so their cell structures are well-adapted to protect them from external factors. The cell wall helps to reinforce this function. Cell Wall  The cell wall is the most prominent part of the plant’s cell structure. It is made up of cellulose, hemicellulose and pectin.  The cell wall is present exclusively in plant cells. It protects the plasma membrane and other cellular components. The cell wall is also the outermost layer of plant cells.  It is a rigid and stiff structure surrounding the cell membrane.  It provides shape and support to the cells and protects them from mechanical shocks and injuries. Cytoplasm  The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane.  Most of the chemical reactions within a cell take place in this cytoplasm.  The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes, are suspended in this cytoplasm. Nucleus  The nucleus contains the hereditary material of the cell, the DNA.  It sends signals to the cells to grow, mature, divide and die.   The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell.  The nucleus protects the DNA and is an integral component of a plant’s cell structure. Cell Organelles Cells are composed of various cell organelles that perform certain specific functions to carry out life’s processes. The different cell organelles, along with its principal functions, are as follows: Cell Organelles and their Functions Nucleolus The nucleolus is the site of ribosome synthesis. Also, it is involved in controlling cellular activities and cellular reproduction. Nuclear membrane The nuclear membrane protects the nucleus by forming a boundary between the nucleus and other cell organelles. Chromosomes Chromosomes play a crucial role in determining the sex of an individual. Each human cells contain 23 pairs of chromosomes. Endoplasmic reticulum The endoplasmic reticulum is involved in the transportation of substances throughout the cell. It plays a primary role in the metabolism of carbohydrates, synthesis of lipids, steroids and proteins. Golgi Bodies Golgi bodies are called the cell’s post office as it is involved in the transportation of materials within the cell. Ribosome Ribosomes are the protein synthesisers of the cell. Mitochondria The mitochondrion is called “the powerhouse of the cell.” It is called so because it produces ATP – the cell’s energy currency. Lysosomes Lysosomes protect the cell by engulfing the foreign bodies entering the cell and help in cell renewal. Therefore, they are known as the cell’s suicide bags. Chloroplast Chloroplasts are the primary organelles for photosynthesis. It contains the pigment called chlorophyll. Vacuoles Vacuoles store food, water, and other waste materials in the cell. Cell Theory Cell Theory was proposed by the German scientists, Theodor Schwann, Matthias Schleiden, and Rudolf Virchow. The cell theory states that:  All living species on Earth are composed of cells.  A cell is the basic unit of life.  All cells arise from pre-existing cells. A modern version of the cell theory was eventually formulated, and it contains the following postulates:  Energy flows within the cells.  Genetic information is passed on from one cell to the other.  The chemical composition of all the cells is the same. Functions of Cell A cell performs major functions essential for the growth and development of an organism. Important functions of cell are as follows: Provides Support and Structure All the organisms are made up of cells. They form the structural basis of all the organisms. The cell wall and the cell membrane are the main components that function to provide support and structure to the organism. For eg., the skin is made up of a large number of cells. Xylem present in the vascular plants is made of cells that provide structural support to the plants. Facilitate Growth Mitosis In the process of mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply and facilitate the growth in an organism. Allows Transport of Substances Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical processes is eliminated from the cells by active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol diffuse across the cell membrane along the concentration gradient. This is known as passive transport. The larger molecules diffuse across the cell membrane through active transport where the cells require a lot of energy to transport the substances. Energy Production Cells require energy to carry out various chemical processes. This energy is produced by the cells through a process called photosynthesis in plants and respiration in animals. Aids in Reproduction A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed as the asexual reproduction where the parent cell divides to form daughter cells. Meiosis causes the daughter cells to be genetically different from the parent cells. Thus, we can understand why cells are known as the structural and functional unit of life. This is because they are responsible for providing structure to the organisms and perform several functions necessary for carrying out life’s processes. What is Cell Cycle? The cell cycle was discovered by Prevost and Dumas (1824) while studying the cleavage of zygote of Frog. It is a series of stages a cell passes through, to divide and produce new cells. This entire process where with the help of one single parent cell a new cell population grows and develops is known as the cell cycle. Phases of Cell Cycle Cell cycle or cell division refers to the series of events that take place in a cell leading to its maturity and subsequent division. These events include duplication of its genome and synthesis of the cell organelles followed by division of the cytoplasm. Human cells exhibit typical eukaryotic cell cycle and take around 24 hours to complete one cycle of growth and division. The duration of the cycle, however, varies from organism to organism and cell to cell. A typical eukaryotic cell cycle is divided into two main phases:- Interphase Also known as the resting phase of the cell cycle; interphase is the time during which the cell prepares for division by undergoing both cell growth and DNA replication. It occupies around 95% time of the overall cycle. The interphase is divided into three phases:-  G1 phase (Gap 1) – G1 phase is the phase of the cell between mitosis and initiation of replication of the genetic material of the cell. During this phase, the cell is metabolically active and continues to grow without replicating its DNA.  S phase (Synthesis) – DNA replication takes place during this phase. If the initial quantity of DNA in the cell is denoted as 2N, then after replication it becomes 4N. However the number of chromosomes does not vary, viz., if the number of chromosomes during G1 phase was 2n, it will remain 2n at the end of S phase. The centriole also divides into two centriole pairs in the cells which contain centriole.   G2 phase (Gap 2) –During this phase, the RNA, proteins, other macromolecules required for multiplication of cell organelles, spindle formation, and cell growth are produced as the cell prepares to go into the mitotic phase. Some cells like cardiac cells in the adult animals do not exhibit division and some others only divide to replace those cells which have been either damaged or lost due to cell death. Such cells which do not divide further attain an inactive G0 phase also known as quiescent phase after they exit the G1 phase. These cells remain metabolically active but do not divide unless called upon to do so. M phase This is the mitotic phase or the phase of the equational division as the cell undergoes a complete reorganization to give birth to a progeny that has the same number of chromosomes as the parent cell. The other organelles are also divided equally by the process of cytokinesis which is preceded by mitotic nuclear division. The mitotic phase is divided into four overlapping stages:- 1. Prophase, 2. Metaphase, 3. Anaphase, and 4. Telophase Mitosis The process by which a eukaryotic cell separates the nuclear DNA and chromosomes and divides into two different but similar sets of nuclei is known as mitosis. The chromosomes are pulled apart by a mitotic spindle, which is a specialized structure consisting of microtubules. Cytokinesis In this phase, the cytoplasm of the cell divides. It begins as soon as the mitosis ends. Plant cells are much tougher than animal cells, as they have a rigid cell wall and high internal pressure. Thus, cytokinesis occurs in plant and animal cells differently. Plant physiology is a branch of study in Botany dealing with the physiological processes or functions of plants. Precisely, it is a descriptive study of variation and structure of plants at the molecular and cellular level, resulting in ecological, physiological and biochemistry related aspects of plant exploration. With terrestrial plants evolving, special techniques and procedures were needed for its survival with a distinction between water and carbon dioxide. Plant physiology deals with different plant structures and their functioning. It enables analysing processes in plants, namely – photosynthesis, mineral nutrition, respiration, transportation, and ultimately plant development and growth which are traits displayed by living entities. The description is in the context of cellular activities in molecular parameters. It also gives a brief idea of the role of physiological processes in the environment. Let us have a detailed look at the plant physiology notes for better conceptual understanding of the topic. Physiology of Plant Parts Leaves Leaves are an important organ of the plant. They can grow in a variety of shapes and sizes. They are the primary centre of photosynthesis. Stem The stem provides support and structure to the plant. They perform many important functions such as plant growth, compete and survive in different environments, etc. The structure of the stem differs in different species. Roots The roots are an underground part of the plant that absorbs water and nutrients from the soil. That is why they are an important part of the plant. Xylem and Phloem These form the vascular tissues of the plant. These are also known as sap. They transport water, sugars and other important substances between the roots, stem and leaves. Functions of Plant Transportation In Plants Plants have a distinct vascular system (xylem and phloem) which helps in transporting nutrients and water from roots to all the parts of the plant through translocation. Transport of water and nutrients in rooted plants is unidirectional or multi-directional. Modes of transportation can either be passive which occurs through diffusion, facilitated diffusion to be precise or can be through active mode carried out by specific membrane proteins which are called pumps. Water plays a pivotal role in carrying out physiological activities, hence understanding the importance of plant-water relations is essential. The concept of water potential helps in comprehending the water movement through terms such as- Solute potential and pressure potential. At the cellular level, osmosis takes place in plants which allows movement of molecules in and out of the cells. Transpiration is another aspect crucial in the life cycle of plants. Mineral Nutrition Plant nutrition is an important aspect instrumental in the growth of plants. It gives an insight into the methods used to identify essential elements for the development of plants, the role of these elements, criteria to identify their essentiality, deficiency symptoms and mechanism of absorption of these elements. It also conveys the importance of nitrogen fixation. Macro and micronutrients present in plants carry out essential processes such as cell-membrane permeability, osmotic concentration of cell sap and its maintenance, enzyme activity and so on. Inadequate supply of essential elements can lead to critical concentration in plants. Elements are absorbed through a mechanism which involves isolated cells, tissues and organs. Apart from other essential elements, nitrogen fixation also takes place in plants. Photosynthesis In Higher Plants Plants synthesize their own food through photosynthesis and hence are called autotrophs. Photosynthesis is important since it is the primary source of food for all living entities on earth and it releases oxygen in the atmosphere which we inhale to breathe. It takes place in chloroplasts through light and dark reactions using 4 pigments- Chlorophyll a, chlorophyll b, Xanthophyll, carotenoids. Extracting energy from oxidizable substances and storing in the form of bond energy is phosphorylation. In plants, cyclic and non-cyclic photo-phosphorylations take place. During photosynthesis, the Calvin cycle takes place through a set of 4 chemical reactions. Respiration In Plants Food that is required for life processes comes from photosynthesis. Cellular respiration results in the release of energy used for the synthesis of ATP which involves glycolysis. Aerobic respiration leads to complete oxidation of organic substances in the presence of oxygen, which is common in higher organisms. To release and utilize the energy stored in molecules, they undergo the following steps: electron transport system and oxidative phosphorylation. Another important aspect of respiration is the respiratory quotient. The ratio of the volume of carbon dioxide released to the volume of oxygen consumed gives the respiratory quotient. Plant Growth And Development The process of plant development starts right from germination under favourable environmental conditions. Generally, plant growth is indeterminate as they retain their capacity to grow throughout their lives because of the presence of meristems. The growth of plants is, however measurable through parameters such as – dry weight, increase in fresh weight, length, area, volume, cell number etc. The period of plant growth is categorized into three phases – meristematic, elongation and maturation. The growth rate can be determined quantitatively in 2 ways – absolute growth rate and relative growth rate. The growth of plants is controlled by plant growth regulators. Plants also produce compounds such as phytochromes that are light sensitive and stimulate the growth of the plant in response to environmental signals. Plant physiology is also an important topic related to fruits, vegetables and other edible parts of the plants. The production of food crops, including the harvest and post-harvest storage of plant products, also hinges on the plant physiology studies. Genetics: Plant genetics is the study of genes, genetic variation, and heredity specifically in plants. The breeding experiments of the monk Gregor Mendel in the mid‐1800s laid the groundwork for the science of genetics. He published only two papers in his lifetime and died unheralded in 1884. The significance of his paper published in 1866 on inheritance in peas (which he grew in the monastery garden) apparently went unnoticed for the next 34 years until three separate botanists, who also were theorizing about heredity in plants, independently cited the work in 1900. During the next 30 years, the universality of his findings was confirmed, and breeding programs for better livestock and crop plants—and the science of genetics—were well under way Inheritance can be defined as the process of how a child receives genetic information from the parent. The whole process of heredity is dependent upon inheritance and it is the reason that the offsprings are similar to the parents. This simply means that due to inheritance, the members of the same family possess similar characteristics. It was only during the mid 19th century that people started to understand inheritance in a proper way. This understanding of inheritance was made possible by a scientist named Gregor Mendel, who formulated certain laws to understand inheritance known as Mendel’s laws of inheritance. Why was Pea Plant Selected for Mendel’s Experiments? He selected a pea plant for his experiments: 1. The pea plant can be easily grown and maintained. 2. They are naturally self-pollinating but can also be cross-pollinated. 3. It is an annual plant, therefore, many generations can be studied within a short period of time. 4. It has several contrasting characters. Mendel conducted 2 main experiments to determine the laws of inheritance. These experiments were: 1. Monohybrid Cross Experiment 2. Dihybrid Cross Experiment While experimenting, Mendel found that certain factors were always being transferred down to the offspring in a stable way. Those factors are now called genes i.e. genes can be called the units of inheritance