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Social media influencers have not only revolutionized the way in which information is disseminated but have also established themselves as contemporary icons of society at large. They have garnered immense followings through their adept use of digital platforms, accruing considerable power and influence over public opinion. Their rise can largely be attributed to the accessibility and immediacy afforded by social media, which allows virtually anyone to become a public figure capable of shaping cultural norms. These individuals have managed to create and curate content shaping consumer habits and beliefs. Their influence extends beyond mere commercialism, encompassing social and political realms, contributing to the discourse on pressing global issues through a perceived lens of authenticity and relatability. While some argue that the democratization of media offers new opportunities for diverse voices to be amplified, concerns persist over the authenticity of influencer narratives and the potential for misleading information to be propagated unchecked. As the boundaries between entertainment, advertising, and activism have blurred, questions surrounding the ethical responsibilities of influencers have intensified. The passive consumption of carefully orchestrated content continues to elicit criticism, raising concerns about the mental well-being of susceptible audiences who may compare their lives unfavorably to those portrayed online. Simultaneously, platforms have implemented policies with varying degrees of success to ensure transparency and accountability, attempting to mitigate the potential for exploitation. The phenomenon of influence poses questions about the trajectory of society in an increasingly interconnected world, where the sway of singular voices can no longer be underestimated.

Most of the functions of a eukaryotic cell are controlled by the nucleus, shown in Figure 4-12. The nucleus is filled with a jellylike liquid called the nucleoplasm, which holds the contents of the nucleus and is similar in function to a cell’s cytoplasm. The nucleus houses and protects the cell’s genetic information. The hereditary information that contains the instructions for the structure and function of the organism is coded in the organism’s DNA, which is contained in the nucleus. When a cell is not dividing, the DNA is in the form of a threadlike material called chromatin. When a cell is about to divide, the chromatin condenses to form chromosomes. Chromosomes are structures in the nucleus made of DNA and protein. The nucleus is the site where DNA is transcribed into ribonucleic acid (RNA). RNA moves through nuclear pores to the cytoplasm, where, depending on the type of RNA, it carries out its function. Nuclear Envelope The nucleus is surrounded by a double membrane called the nuclear envelope. The nuclear envelope is made up of two phos- pholipid bilayers. Covering the surface of the nuclear envelope are tiny, protein-lined holes, which are called nuclear pores. The nuclear pores provide passageways for RNA and other materials to enter and leave the nucleus. Nucleolus Most nuclei contain at least one denser area, called the nucleolus (noo-KLEE-uh-luhs). The nucleolus (plural, nucleoli) is the site where DNA is concentrated when it is in the process of making ribosomal RNA. Ribosomes (RIE-buh-SOHMZ) are organelles made of protein and RNA that direct protein synthesis in the cytoplasm. The nucleus of a cell is surrounded by a double membrane called the nuclear envelope. The nucleus stores the cell’s DNA. FIGURE 4-12 Nuclear envelope Nucleolus Nuclear pores DNA (chromatin) Copyright © by Holt, Rinehart and Winston. All rights reserved. 80 CHAPTER 4 MITOCHONDRIA Mitochondria (MIET-oh-KAHN-dree-uh) (singular, mitochondrion) are tiny organelles that transfer energy from organic molecules to adenosine triphosphate (ATP). ATP ultimately powers most of the cell’s chemical reactions. Highly active cells, such as muscle cells, can have hundreds of mitochondria. Cells that are not very active, such as fat-storage cells, have few mitochondria. Like a nucleus, a mitochondrion has an inner and an outer phos- pholipid membrane, as shown in Figure 4-13. The outer membrane separates the mitochondrion from the cytosol. The inner membrane has many folds, called cristae (KRIS-tee). Cristae contain proteins that carry out energy-harvesting chemical reactions. Mitochondrial DNA Mitochondria have their own DNA and can reproduce only by the division of preexisting mitochondria. Scientists think that mito- chondria originated from prokaryotic cells that were incorporated into ancient eukaryotic cells. This symbiotic relationship provided the prokaryotic invaders with a protected place to live and pro- vided the eukaryotic cell with an increased supply of ATP. RIBOSOMES Ribosomes are small, roughly spherical organelles that are respon- sible for building protein. Ribosomes do not have a membrane. They are made of protein and RNA molecules. Ribosome assembly begins in the nucleolus and is completed in the cytoplasm. One large and one small subunit come together to make a functioning ribosome, shown in Figure 4-14. Some ribosomes are free within the cytosol. Others are attached to the rough endoplasmic reticulum.

What is a Plant Cell? Plant cells are eukaryotic cells that vary in several fundamental factors from other eukaryotic organisms. Both plant and animal cells contain a nucleus along with similar organelles. One of the distinctive aspects of a plant cell is the presence of a cell wall outside the cell membrane. Plant Cell Structure Just like different organs within the body, plant cell structure includes various components known as cell organelles that perform different functions to sustain itself. These organelles include: Cell Wall It is a rigid layer which is composed of polysaccharides cellulose, pectin and hemicellulose. It is located outside the cell membrane. It also comprises glycoproteins and polymers such as lignin, cutin, or suberin. The primary function of the cell wall is to protect and provide structural support to the cell. The plant cell wall is also involved in protecting the cell against mechanical stress and providing form and structure to the cell. It also filters the molecules passing in and out of it. The formation of the cell wall is guided by microtubules. It consists of three layers, namely, primary, secondary and the middle lamella. The primary cell wall is formed by cellulose laid down by enzymes. Cell membrane It is the semi-permeable membrane that is present within the cell wall. It is composed of a thin layer of protein and fat. The cell membrane plays an important role in regulating the entry and exit of specific substances within the cell. For instance, cell membrane keeps toxins from entering inside, while nutrients and essential minerals are transported across. Nucleus The nucleus is a membrane-bound structure that is present only in eukaryotic cells. The vital function of a nucleus is to store DNA or hereditary information required for cell division, metabolism and growth. 1. Nucleolus: It manufactures cells’ protein-producing structures and ribosomes. 2. Nucleopore: Nuclear membrane is perforated with holes called nucleopore that allow proteins and nucleic acids to pass through. Plastids They are membrane-bound organelles that have their own DNA. They are necessary to store starch and to carry out the process of photosynthesis. It is also used in the synthesis of many molecules, which form the building blocks of the cell. Some of the vital types of plastids and their functions are stated below: Leucoplasts They are found in the non-photosynthetic tissue of plants. They are used for the storage of protein, lipid and starch. Chromoplasts They are heterogeneous, colored plastid which is responsible for pigment synthesis and for storage in photosynthetic eukaryotic organisms. Chromoplasts have red-, orange- and yellow-colored pigments which provide color to all ripe fruits and flowers. Central Vacuole It occupies around 30% of the cell’s volume in a mature plant cell. Tonoplast is a membrane that surrounds the central vacuole. The vital function of the central vacuole apart from storage is to sustain turgor pressure against the cell wall. The central vacuole consists of cell sap. It is a mixture of salts, enzymes and other substances. Golgi Apparatus They are found in all eukaryotic cells, which are involved in distributing synthesized macromolecules to various parts of the cell. Ribosomes They are the smallest membrane-bound organelles which comprise RNA and protein. They are the sites for protein synthesis, hence, also referred to as the protein factories of the cell. Mitochondria They are the double-membraned organelles found in the cytoplasm of all eukaryotic cells. They provide energy by breaking down carbohydrate and sugar molecules, hence they are also referred to as the “Powerhouse of the cell.” Lysosome Lysosomes are called suicidal bags as they hold digestive enzymes in an enclosed membrane. They perform the function of cellular waste disposal by digesting worn-out organelles, food particles and foreign bodies in the cell. In plants, the role of lysosomes is undertaken by the vacuoles. Chloroplasts It is an elongated organelle enclosed by phospholipid membrane. The chloroplast is shaped like a disc and the stroma is the fluid within the chloroplast that comprises a circular DNA. Each chloroplast contains a green colored pigment called chlorophyll required for the process of photosynthesis. The chlorophyll absorbs light energy from the sun and uses it to transform carbon dioxide and water into glucose. Structure of Chloroplast Chloroplasts are found in all higher plants. It is oval or biconvex, found within the mesophyll of the plant cell. The size of the chloroplast usually varies between 4-6 µm in diameter and 1-3 µm in thickness. They are double-membrane organelle with the presence of outer, inner and intermembrane space. There are two distinct regions present inside a chloroplast known as the grana and stroma. • Grana are made up of stacks of disc-shaped structures known as thylakoids or lamellae. The granum of the chloroplast consists of chlorophyll pigments and are the functional units of chloroplasts. • Stroma is the homogenous matrix which contains grana and is similar to the cytoplasm in cells in which all the organelles are embedded. Stroma also contains various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs or grana. The chloroplast structure consists of the following parts: Membrane Envelope It comprises inner and outer lipid bilayer membranes. The inner membrane separates the stroma from the intermembrane space. Intermembrane Space The space between inner and outer membranes. Thylakoid System (Lamellae) The system is suspended in the stroma. It is a collection of membranous sacs called thylakoids or lamellae. The green colored pigments called chlorophyll are found in the thylakoid membranes. It is the sight for the process of light-dependent reactions of the photosynthesis process. The thylakoids are arranged in stacks known as grana and each granum contains around 10-20 thylakoids. Stroma It is a colorless, alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast present surrounding the grana. Grana Stack of lamellae in plastids is known as grana. These are the sites of conversion of light energy into chemical energy. Chlorophyll It is a green photosynthetic pigment that helps in the process of photosynthesis. Functions of Chloroplast Following are the important chloroplast functions: • The most important function of the chloroplast is to synthesize food by the process of photosynthesis. • Absorbs light energy and converts it into chemical energy. • Chloroplast has a structure called chlorophyll which functions by trapping the solar energy and is used for the synthesis of food in all green plants. • Produces NADPH and molecular oxygen (O 2 ) by photolysis of water. • Produces ATP – Adenosine triphosphate by the process of photosynthesis. • The carbon dioxide (CO2) obtained from the air is used to generate carbon and sugar during the Calvin Cycle or dark reaction of photosynthesis. Mitochondria “Mitochondria are membrane-bound organelles present in the cytoplasm of all eukaryotic cells, that produce adenosine triphosphate (ATP), the main energy molecule used by the cell.” What are Mitochondria? Popularly known as the “Powerhouse of the cell,” mitochondria (singular: mitochondrion) are a double membrane-bound organelle found in most eukaryotic organisms. They are found inside the cytoplasm and essentially function as the cell’s “digestive system.” They play a major role in breaking down nutrients and generating energy-rich molecules for the cell. Many of the biochemical reactions involved in cellular respiration take place within the mitochondria. The term ‘mitochondrion’ is derived from the Greek words “mitos” and “chondrion” which means “thread” and “granules-like”, respectively. It was first described by a German pathologist named Richard Altmann in the year 1890. Structure of Mitochondria • The mitochondrion is a double-membraned, rod-shaped structure found in both plant and animal cell. • Its size ranges from 0.5 to 1.0 micrometers in diameter. • The structure comprises an outer membrane, an inner membrane, and a gel-like material called the matrix. • The outer membrane and the inner membrane are made of proteins and phospholipid layers separated by the intermembrane space. • The outer membrane covers the surface of the mitochondrion and has a large number of special proteins known as porins. Cristae The inner membrane of mitochondria is rather complex in structure. It has many folds that form a layered structure called cristae, and this helps in increasing the surface area inside the organelle. The cristae and the proteins of the inner membrane aid in the production of ATP molecules. The inner mitochondrial membrane is strictly permeable only to oxygen and ATP molecules. A number of chemical reactions take place within the inner membrane of mitochondria. Mitochondrial Matrix The mitochondrial matrix is a viscous fluid that contains a mixture of enzymes and proteins. It also comprises ribosomes, inorganic ions, mitochondrial DNA, nucleotide cofactors, and organic molecules. The enzymes present in the matrix play an important role in the synthesis of ATP molecules. Functions of Mitochondria The most important function of mitochondria is to produce energy through the process of oxidative phosphorylation. It is also involved in the following process: 1. Regulates the metabolic activity of the cell 2. Promotes the growth of new cells and cell multiplication 3. Helps in detoxifying ammonia in the liver cells 4. Plays an important role in apoptosis or programmed cell death 5. Responsible for building certain parts of the blood and various hormones like testosterone and estrogen 6. Helps in maintaining an adequate concentration of calcium ions within the compartments of the cell 7. It is also involved in various cellular activities like cellular differentiation, cell signaling, cell senescence, controlling the cell cycle and in cell growth. Disorders Associated with Mitochondria Any irregularity in the way mitochondria function can directly affect human health, but often, it is difficult to identify because symptoms differ from person to person. Disorders of the mitochondria can be quite severe; in some cases, they can even cause an organ to fail.

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