1st Quarter General Biology Handouts PDF

1st Quarter General Biology 1 Hand Outs The cell theory is a fundamental concept in biology with three main postulates: All living organisms are composed of one or more cells: This postulate states that the cell is the basic unit of life, and all forms of life, whether single-celled or multic...

1st Quarter General Biology 1 Hand Outs The cell theory is a fundamental concept in biology with three main postulates: All living organisms are composed of one or more cells: This postulate states that the cell is the basic unit of life, and all forms of life, whether single-celled or multicellular, are made up of cells. The cell is the basic unit of structure and organization in organisms: Cells are the smallest units of living matter that can carry out all necessary life processes. They form the structural and functional units of an organism. All cells arise from pre-existing cells: This postulate emphasizes that new cells are produced by the division of existing cells. This principle was crucial in understanding that cell division is a means of reproduction and growth in living organisms. Cellular organelles Ribosomes: Function: Ribosomes are the sites of protein synthesis within the cell. They translate genetic information from messenger RNA (mRNA) into proteins by linking amino acids together in the order specified by the mRNA sequence. Golgi Apparatus: Function: The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids that have been synthesized in the endoplasmic reticulum (ER). It plays a crucial role in processing and directing cellular products to their appropriate destinations, including secretion outside the cell or incorporation into the cell membrane. Mitochondria: Function: Mitochondria are known as the "powerhouses" of the cell. They generate adenosine triphosphate (ATP) through cellular respiration, which provides energy for various cellular processes. Mitochondria are also involved in other functions, such as regulating cellular metabolism and apoptosis (programmed cell death). The cell with abundant mitochondria is inferred to have higher metabolic activity and greater energy needs compared to the cell with fewer mitochondria. Lysosomes: Function: Lysosomes contain digestive enzymes that break down waste materials, cellular debris, and foreign substances within the cell. They are involved in processes such as autophagy (degradation of damaged organelles) and the breakdown of macromolecules into their constituent parts for recycling and reuse. If a mutation causes a cell to produce non-functional lysosomes, several critical processes within the cell would be affected. Lysosomes cannot effectively break down and recycle cellular waste, damaged organelles, and other debris. This leads to the accumulation of waste products within the cell. Rough Endoplasmic Reticulum (RER): Function: The RER is studded with ribosomes on its cytoplasmic surface, giving it a "rough" appearance. Its primary role is the synthesis of proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle called the lysosome. The RER is involved in the folding and modification of these proteins. Smooth Endoplasmic Reticulum (SER): Function: The SER lacks ribosomes on its surface, giving it a "smooth" appearance. It is involved in the synthesis of lipids (fats), including phospholipids and steroids. The SER also plays a role in detoxifying harmful substances and metabolizing carbohydrates. Additionally, it stores calcium ions, which are important for various cellular processes. If a cell's rough endoplasmic reticulum (RER) is damaged, the process directly affected would be protein synthesis. The RER is crucial for synthesizing proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to lysosomes. The cell walls of prokaryotic cells and eukaryotic plant cells differ in several key ways: Composition: Prokaryotic Cells: The cell walls of most prokaryotic cells (e.g., bacteria) are primarily composed of peptidoglycan, a complex polymer consisting of sugars and amino acids. In archaea, which are another group of prokaryotes, the cell wall may contain different compounds such as pseudopeptidoglycan or other unique polysaccharides. Eukaryotic Plant Cells: The cell walls of plant cells are mainly composed of cellulose, a polysaccharide made up of glucose units. The plant cell wall also contains other components like hemicelluloses, pectin, and sometimes lignin, which contribute to its strength and rigidity. 1|Page Function: Prokaryotic Cells: The cell wall in prokaryotes provides structural support and protection, helps maintain cell shape, and can also play a role in defense against environmental stresses and antibiotics. Eukaryotic Plant Cells: The cell wall in plant cells provides structural support, protection, and rigidity, allowing plants to maintain their shape and resist external pressures. It also plays a role in regulating cell growth and development and in providing a barrier to pathogen entry. Reproduction Method: Prokaryotic cells reproduce primarily through binary fission, a process where a single cell divides into two identical daughter cells. During binary fission, the cell wall plays a critical role in ensuring that the cell divides correctly by facilitating the formation of a new cell wall that separates the daughter cells. Prokaryotic DNA is located in a region called the nucleoid, which is not membrane-bound. This area is found in the cytoplasm and is where the cell's genetic material is concentrated. Eukaryotic plant cells reproduce through mitosis (for somatic cells) and meiosis (for the formation of gametes in sexual reproduction). The process involves the formation of new cell walls to separate the daughter cells after mitosis or to create new structures like pollen and ovules in sexual reproduction. In plant tissues, parenchyma, collenchyma, and sclerenchyma are types of ground tissues with distinct functions. For increasing the number of cells in plant tissue, the most relevant type of cell division would be mitosis. Parenchyma: Function: Storage: Parenchyma cells are involved in the storage of nutrients, including starch, oils, and water. They are found in various plant tissues such as roots, stems, and leaves. Photosynthesis: In leaves, parenchyma cells contain chloroplasts and are responsible for photosynthesis. Wound Healing: Parenchyma cells play a role in healing wounds and regenerating tissues due to their ability to divide and differentiate into other cell types. Collenchyma: Function: Support and Flexibility: Collenchyma cells provide structural support to growing parts of the plant, such as stems and leaves. They are found beneath the epidermis and in areas of the plant that are still elongating. Flexibility: Unlike sclerenchyma, collenchyma cells are flexible and can stretch with the growing plant. This flexibility allows them to support the plant while accommodating growth. Sclerenchyma: Function: Mechanical Support: Sclerenchyma cells provide rigid support and strength to various parts of the plant, including stems, roots, and leaves. They are important for maintaining the plant's structural integrity. Types of Cells: Fibers: Elongated cells that form bundles, providing tensile strength. Sclerids: Variable-shaped cells that can be found in seed coats, nutshells, and fruit tissues, contributing to hardness and protection. The small openings you observe on the surface of leaf cells are called stomata (singular: stoma). Stomata are small pores found mainly on the surface of plant leaves and sometimes stems. Their primary function is to regulate gas exchange between the plant and its environment. In plants, besides meristematic tissue, which is responsible for growth and cell division, there are several other types of tissue that perform specific functions: 1. Meristematic Tissue: Function: Responsible for the continuous growth of the plant. Meristematic tissue contains undifferentiated cells that can divide and differentiate into various specialized cell types. Meristematic cells are indeed involved in rapid cell division and differentiation, but they are generally characterized by their undifferentiated and relatively small, cuboidal shape rather than elongated. 2. Permanent Tissues: Function: Comprised of cells that have differentiated and are no longer actively dividing. They perform specific functions based on their type. 2|Page Types: A. Epidermal Tissue: Function: Forms the outer protective layer of the plant. It prevents water loss, protects against pathogens, and can include structures such as trichomes (hair-like projections) and guard cells (regulate gas exchange). Examples: Epidermis, periderm (in older tissues). B. Ground Tissue: Function: Provides support, storage, and is involved in photosynthesis. It includes: Parenchyma: Involved in storage, photosynthesis, and tissue repair. Collenchyma: Provides flexible support to growing parts of the plant. Sclerenchyma: Provides rigid support, often with lignified secondary walls. C. Vascular Tissue: Function: Transports water, nutrients, and food throughout the plant. It includes: Xylem: Transports water and minerals from roots to other parts of the plant. Phloem: Transports the products of photosynthesis (mainly sugars) from leaves to other parts of the plant. Some cellular structures and functions Cilia: Function: Cilia are short, hair-like projections on the surface of some cells. They are involved in movement and sensory functions. In Animal Cells: Cilia help in moving substances across the surface of the cell, such as mucus in the respiratory tract or eggs in the female reproductive tract. In Protozoa: They aid in locomotion by beating in a coordinated manner. Microvilli: Function: Microvilli are tiny, finger-like projections on the surface of some epithelial cells. They are involved in increasing the surface area for absorption. In Intestinal Cells: Microvilli are found on the surface of cells lining the intestines, where they enhance nutrient absorption by providing a larger surface area. Root Hairs: Function: Root hairs are long, thin extensions of root epidermal cells. They are found in the root zone of plants. In Plants: Root hairs increase the surface area for water and nutrient absorption from the soil. They are crucial for the uptake of essential minerals and water. Flagella: Function: Flagella are long, whip-like projections that extend from the surface of some cells. They are primarily involved in movement. In Animal Cells (e.g., sperm cells): Flagella propel the cell forward, enabling movement through fluids. In Bacteria: Flagella assist in locomotion, allowing bacteria to move towards or away from environmental stimuli. The cell cycle is the series of events that cells go through as they grow, replicate their DNA, and divide. It is essential for growth, development, tissue repair, and reproduction in organisms. The cell cycle is divided into two main phases: Interphase (the cell's preparation for division) and the Mitotic Phase (M phase), which includes both mitosis (nuclear division) and cytokinesis (cytoplasm division). Phases of the Cell Cycle: Interphase: This is the longest phase, where the cell grows and prepares for division. It is divided into three sub- phases: G1 Phase (Gap 1): The cell grows in size, produces organelles, and synthesizes proteins needed for DNA replication. This is the phase where the cell decides whether to divide or enter a resting state (G0 phase). S Phase (Synthesis): DNA replication occurs, resulting in two identical sets of chromosomes. Each chromosome now consists of two sister chromatids, which are joined at a centromere. When cells prematurely enter the S phase, it means they start replicating their DNA without ensuring that the conditions are appropriate for division, potentially leading to uncontrolled cell proliferation. This scenario is a hallmark of cancer and other proliferative disorders. G2 Phase (Gap 2): The cell continues to grow and produce proteins needed for mitosis. The cell checks for DNA replication errors and repairs them before entering the next phase. 3|Page Mitotic Phase (M Phase): The cell divides into two daughter cells, each with a complete set of chromosomes. The M phase consists of two main processes: A. Mitosis (Nuclear Division): Mitosis ensures that the two daughter cells receive identical copies of the genetic material. It is divided into five stages: Prophase: Chromosomes condense and become visible; the nuclear envelope begins to disintegrate; the mitotic spindle forms. The chromatin fibers condense into visible chromosomes. Prometaphase: The nuclear envelope breaks down completely, and spindle fibers attach to chromosomes at the centromeres. Metaphase: Chromosomes align at the cell's equatorial plane (metaphase plate). The key event that marks the transition from metaphase to anaphase in mitosis is the separation of sister chromatids. Specifically, the centromeres holding the sister chromatids together are split, allowing the spindle fibers to pull the chromatids apart toward opposite poles of the cell. So, sister chromatids are pulled apart toward opposite poles. Anaphase: Sister chromatids separate and are pulled to opposite poles of the cell. Telophase: Chromosomes de-condense, the nuclear envelope reforms around each set of chromosomes, and the spindle fibers disappear. B. Cytokinesis (Cytoplasmic Division): The cytoplasm divides, resulting in two distinct daughter cells. In animal cells, a cleavage furrow forms, pinching the cell in two. In plant cells, a cell plate forms, dividing the cell into two. Control Points (Checkpoints): The cell cycle is tightly regulated at various checkpoints to ensure the integrity of the cell’s division process: G1 Checkpoint: Determines if the cell has enough resources and undamaged DNA to proceed with division. A defect in the G1 checkpoint can have significant consequences on the mitotic process and cell division. The G1 checkpoint is crucial because it ensures that the cell is ready to enter the S phase, where DNA is replicated. Cells would enter mitosis without proper DNA replication. G2 Checkpoint: Ensures that DNA replication is complete and error-free. M Checkpoint (Spindle Assembly Checkpoint): Ensures that chromosomes are properly attached (aligned) to spindle fibers before anaphase begins. In the case where cancer cells bypass the M checkpoint and undergo abnormal mitosis, the underlying issue that should be analyzed involves the mechanisms regulating the mitotic checkpoint, specifically those that ensure proper chromosome alignment and separation. Moreover, there is a defect in spindle assembly checkpoint. The G0 phase, often referred to as the "resting phase" of the cell cycle, is a stage in which cells exit the regular cycle of division and enter a period of quiescence or dormancy. Cells in G0 are not actively preparing to divide, but they are still metabolically active and carry out their normal functions. If cells in culture remain in the G0 phase, several possible reasons could explain why they are not progressing through the cell cycle because the cells are not receiving the necessary growth signals. Mitosis/Meiosis The primary difference between metaphase in mitosis and metaphase in meiosis I lies in how the chromosomes align and how they are separated: In mitosis, during metaphase, individual sister chromatids (replicated chromosomes) line up single-file along the metaphase plate (the cell's equator). The spindle fibers attach to the centromeres of each chromatid, preparing to pull the sister chromatids apart during anaphase. In meiosis I, during metaphase I, homologous chromosomes (pairs of chromosomes, one from each parent) line up in pairs along the metaphase plate, instead of individual sister chromatids. In sexually reproducing organisms, the process that ensures offspring have a unique combination of genes is meiosis. Moreover, mitosis contributes to growth in both plant and animal tissues, while meiosis is involved only in reproduction. An error in chromosome separation during anaphase II of meiosis can have profound effects on gamete formation, leading to significant consequences for genetic inheritance. Some gametes will have an extra chromosome, while others will be missing one. As a result of this error, some gametes will end up with an extra chromosome (a condition known as trisomy), while others will be missing a chromosome (a condition known as monosomy). When these gametes participate in fertilization, they produce zygotes 4|Page with an abnormal number of chromosomes. For instance, if a gamete with an extra chromosome fuse with a normal gamete, the resulting zygote will have three copies of that chromosome, leading to disorders such as Down syndrome (trisomy 21). Conversely, if a gamete missing a chromosome fuse with a normal gamete, the resulting zygote will have only one copy of that chromosome, potentially causing conditions such as Turner syndrome (monosomy X). On the other hand, Huntington's disease is a progressive neurodegenerative disorder caused by a genetic mutation while both hemophilia and sickle cell anemia are genetic disorders with significant impacts on health. Hemophilia primarily affects blood clotting, while sickle cell anemia affects the shape and function of red blood cells. Both conditions require ongoing management and treatment to address symptoms and prevent complications. The cell membrane (also known as the plasma membrane) is a crucial structure that surrounds and protects the cell, providing a barrier between the internal contents of the cell and the external environment. Its components work together to regulate what enters and exits the cell, maintain cellular integrity, and facilitate communication with other cells. Parts of the Cell Membrane: Phospholipid Bilayer: Structure: Composed of two layers of phospholipids with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward. Function: Acts as a selective barrier, allowing only certain molecules to pass through. It provides fluidity and flexibility to the membrane. Proteins: Integral Proteins: Embedded within the phospholipid bilayer, spanning across the membrane. They function as channels, carriers, or receptors. Integral Proteins help maintain the structure of the phospholipid bilayer. Peripheral Proteins: Attached to the exterior or interior surfaces of the membrane. They are involved in signaling and maintaining the cell's shape. Function: Integral proteins facilitate transport of substances across the membrane, while peripheral proteins are involved in signaling pathways and cell recognition. Integral proteins are embedded within the lipid bilayer and typically span the membrane, while peripheral proteins are attached loosely to the membrane surfaces. Carbohydrates: Glycoproteins and Glycolipids: Carbohydrate chains attached to proteins (glycoproteins) or lipids (glycolipids) on the extracellular surface of the membrane. Function: Play a key role in cell-cell recognition, communication, and adhesion. They also contribute to the formation of the glycocalyx, a protective layer around the cell. Cholesterol: Structure: Molecules interspersed within the phospholipid bilayer. Function: Modulates the fluidity and stability of the membrane, making it less permeable to very small water-soluble molecules and maintaining membrane integrity. So, it maintains membrane fluidity by preventing the fatty acids from packing too tightly together. Functions of the Cell Membrane: Selective Permeability: Regulates the movement of substances in and out of the cell. It allows essential nutrients and ions to enter while keeping harmful substances out. Protection and Support: Provides a protective barrier against physical damage and harmful substances. It also helps maintain the cell's shape and structure. Communication: Contains receptors that bind to signaling molecules (e.g., hormones), allowing the cell to respond to changes in its environment and communicate with other cells. Transport: Facilitates the transport of materials through mechanisms such as passive transport (diffusion, osmosis) and active transport (using energy to move substances against their concentration gradient). Cell Recognition and Adhesion: 5|Page Carbohydrate molecules on glycoproteins and glycolipids help cells recognize and adhere to each other, which is important for tissue formation and immune responses. The cell membrane's structure and composition are crucial for maintaining cellular function and ensuring the proper interaction between the cell and its environment. The fluid mosaic model in understanding cell membrane structure is a widely accepted concept that explains the structure and behavior of the cell membrane. This model is significant because it describes the membrane as a dynamic and flexible structure rather than a rigid, static layer. Transport Mechanisms Facilitated diffusion and simple diffusion are both passive transport processes, meaning they do not require energy. However, they differ in how substances move across the cell membrane: In brief, simple diffusion involves direct passage through the membrane, while facilitated diffusion requires the assistance of membrane proteins to transport molecules that cannot diffuse freely. So, facilitated diffusion uses transport proteins, while simple diffusion does not. On the other hand, facilitated diffusion does not require energy, while active transport requires energy. Osmosis is the passive movement of water molecules across a selectively permeable membrane from an area of lower solute concentration (more water) to an area of higher solute concentration (less water). It involves the diffusion of water molecules specifically through a selectively permeable membrane. This process aims to equalize the solute concentrations on both sides of the membrane. In simpler terms, osmosis is how water moves to balance the concentration of substances, without requiring energy. It plays a crucial role in maintaining cell shape, hydration, and overall fluid balance in living organisms. When a cell is exposed to an environment with a high concentration of NaCl (salt), it can experience osmotic stress due to the following: Water Loss via Osmosis: The environment outside the cell becomes hypertonic (higher solute concentration compared to the inside of the cell). As a result, water will move out of the cell through osmosis to balance the solute concentrations. Cell Shrinkage. As water leaves the cell, the cell volume decreases, causing animal cells to shrink (crenate). In plant cells, the plasma membrane pulls away from the cell wall, leading to plasmolysis, which can affect cell rigidity and function. So, the cell would lose water to the surrounding environment, leading to dehydration and possible cell shrinkage. Phagocytosis and pinocytosis are both forms of endocytosis, where the cell engulfs substances from its environment. Phagocytosis: Known as "cell eating.". The cell engulfs large particles or microorganisms by extending its membrane to form vesicles. Common in immune cells like macrophages that engulf pathogens or debris. Pinocytosis: Known as "cell drinking." The cell engulfs extracellular fluid and dissolved small molecules through small vesicles. Used for nutrient absorption and sampling the extracellular environment. In brief, phagocytosis involves engulfing large particles, while pinocytosis involves engulfing fluids and small molecules. Phagocytosis involves the ingestion of solids, while pinocytosis involves the ingestion of liquids. The key functional difference between exocytosis and endocytosis in relation to cell membrane dynamics is: Exocytosis: Involves the fusion of vesicles with the cell membrane to release substances (such as proteins, hormones, or waste) from inside the cell to the extracellular space. This process adds material to the cell membrane and expands it. Endocytosis: Involves the invagination of the cell membrane to engulf substances (such as nutrients or pathogens) from the outside environment into the cell. This process reduces the surface area of the membrane by taking in vesicles. In short, exocytosis involves the cell membrane extending outward, while endocytosis involves the membrane pulling inward. To evaluate the efficiency of a cell using exocytosis versus a cell using endocytosis for nutrient uptake, the key points to consider are: Endocytosis is far more efficient for nutrient uptake because it is designed for internalizing substances, allowing the cell to selectively absorb nutrients. Exocytosis, in contrast, is unsuitable for nutrient uptake as it focuses on expelling materials rather than absorbing them. Thus, for nutrient uptake, a cell utilizing endocytosis would be far more efficient than one relying on exocytosis. 6|Page