Biology Past Paper PDF

TOPIC: THE CELL AND THE MODERN CELL THEORY 1. The Discovery of Cell and the Development of the Modern Cell Theory - Robert Hooke (1665): He was the first to discover cells when observing thin slices of cork through a microscope. He described the small, box-like structures as "cells," which were act...

TOPIC: THE CELL AND THE MODERN CELL THEORY 1. The Discovery of Cell and the Development of the Modern Cell Theory - Robert Hooke (1665): He was the first to discover cells when observing thin slices of cork through a microscope. He described the small, box-like structures as "cells," which were actually the walls of dead plant cells. - Concept: Discovery of cell walls in dead plant material, marking the beginning of cell biology. - Antoni van Leeuwenhoek (1674): Improved the microscope and became the first to observe living cells, which he called "animalcules," such as bacteria and protozoa. - Concept: First to observe living cells, expanding knowledge beyond dead structures. - Robert Brown (1831): He identified the nucleus as an important structure within cells, showing its presence in both plant and animal cells. - Concept: Discovery of the nucleus, a critical component of cells. - Matthias Schleiden (1838): Proposed that all plants are made of cells, which was crucial in understanding the role of cells in plants. - Concept: Plants are composed of cells, making cells the building blocks of plant life. - Theodore Schwann (1839): Extended Schleiden’s findings to animals, showing that all animals are also made up of cells. - Concept: Cells as the basic unit of both plants and animals. - Rudolf Virchow (1858): Proposed that all cells arise from pre-existing cells, solidifying the concept that cells reproduce to form new cells. - Concept: Cells originate from other cells, a fundamental principle in biology. 2. The Modern Cell Theory States - (a): All living organisms are composed of one or more cells. This highlights the universality of cells as the structural and functional units of life. - Concept: Cells are the basic unit of all life forms. - (b): The smallest living organisms are single cells, and these cells perform all necessary functions of life, including growth and reproduction. - Concept: Single-celled organisms carry out all life functions independently. - (c): New cells are produced by the division of pre-existing cells, which is essential for growth, repair, and reproduction. - Concept: Cells replicate through division, forming new cells. 3. Cells are Fundamental to Life All living organisms, from simple bacteria to complex plants and animals, share a common ancestry. This is why, despite the diversity of life, cells have similar features such as a membrane, DNA, and ribosomes. Over time, cells have adapted to different environments, but their core structures remain largely unchanged. - Concept: Cells share a common origin and basic features, with modifications over evolutionary time. Bacteria Cell Parts - Cell Wall: Provides structure and protection to the bacterial cell. It helps maintain the shape of the cell and prevents it from bursting in a hypotonic environment. - Concept: The protective outer layer that provides rigidity. - Plasma Membrane: A selectively permeable barrier that controls what enters and exits the cell. - Concept: Regulates exchange between the cell and its environment. - Cytoplasm: The jelly-like substance inside the cell where the cell’s metabolic reactions occur. - Concept: The medium for chemical reactions inside the cell. - Nucleoid: An irregularly shaped region within the cell where the bacterial chromosome (DNA) is located. - Concept: Contains the genetic material of bacteria, essential for reproduction. - Ribosomes: The site of protein synthesis in the cell, where genetic information is translated to build proteins. - Concept: Machinery for making proteins, crucial for cell function. - Flagella: Long, whip-like structures used for movement. - Concept: Enables bacteria to move toward or away from stimuli. Plant Cell Parts - Cell Wall: A rigid outer layer made of cellulose that provides structural support and protection. - Concept: Structural support for plant cells, helping maintain their shape. - Chloroplast: Organelles that perform photosynthesis, converting sunlight into energy. - Concept: The site where light energy is converted into chemical energy (sugars). - Vacuole: A large, fluid-filled sac that stores water, nutrients, and waste products, helping maintain pressure within the cell. - Concept: Storage compartment for water and other substances, providing internal support. - Nucleus: Contains the cell’s genetic material and regulates the activities of the cell. - Concept: Control center of the cell, managing DNA and cellular functions. Animal Cell Parts - Plasma Membrane: Like bacteria, it is a selectively permeable barrier that controls the exchange of substances between the cell and its environment. - Concept: Maintains homeostasis by controlling entry and exit of substances. - Lysosome: Contains digestive enzymes to break down waste material and cellular debris. - Concept: Waste disposal system, breaking down harmful substances. - Mitochondria: Known as the powerhouse of the cell, they produce energy through cellular respiration. - Concept: Energy production center, converting food into usable energy (ATP). - Nucleus: Like plant cells, it stores genetic information and regulates cell functions. - Concept: Oversees cellular activities through genetic regulation. TOPIC: CELL MODIFICATIONS 1. Apical Modification - Pseudopods: Extensions of the cell membrane that help in movement and capturing food in some cells, like amoebas. - Concept: Temporary protrusions aiding in cell movement and food intake. - Cilia/Flagella: Hair-like or whip-like structures that help in locomotion or moving substances along the surface of the cell. - Concept: Motility structures for movement or moving external substances. - Villi/Microvilli: Finger-like projections that increase surface area for absorption, especially in the intestines. - Concept: Enhanced surface area to improve absorption of nutrients. - Extracellular Matrix (ECM): A network of proteins and carbohydrates outside cells that provides structural support and helps in cell signaling. - Concept: Supportive structure outside cells, also involved in communication between cells. 2. Lateral Modification - Gap Junction: Channels that allow the passage of ions and small molecules between adjacent cells for communication. - Concept: Communication channels between neighboring cells. - Tight Junction: Seals between cells that prevent the passage of substances between them, maintaining distinct environments on either side of the cell layer. - Concept: Barriers between cells to prevent leakage. - Adhering Junction: Specialized regions that hold cells together, providing mechanical stability. - Concept: Cell-cell adhesion for stability and structure. 3. Basal Modification - Desmosomes/Hemidesmosomes: Structures that anchor cells to each other or to the extracellular matrix, providing strength and preventing cells from being pulled apart. - Concept: Anchoring points that keep cells attached to each other or the surrounding structures. --- Specialized Cells - Specialized Animal Cells: Nerve cells transmit electrical signals, muscle cells contract for movement, and blood cells transport oxygen. - Concept: Cells adapted for specific functions like signaling, movement, or transport. - Specialized Plant Cells: Guard cells regulate gas exchange in plants, xylem cells transport water, and phloem cells transport nutrients. - Concept: Cells adapted for functions like water transport, nutrient distribution, and gas exchange.