Ap Biology Study Reading Guide Chapter 6 Essay Example

there is a higher surface-to-volume ratio that allows for efficient exchange of materials with the environment. Volume increases more rapidly than surface area due to its cubic nature. Therefore, smaller objects have greater surface area to volume ratios. Microvilli are elongated projections on the cell surface that enhance surface area without significantly increasing volume. This high ratio of surface area to volume plays an important role in facilitating material exchange for cells like enteric cells.

In eukaryotic cells, genetic instructions reside within the nucleus and are executed by ribosomes. The nuclear envelope encloses the nucleus and separates its contents from the cytoplasm through a double membrane connected by the atomic lamina. The atomic lamina supports the shape of the nucleus with protein fibrils while the nuclear matrix forms protein fibers throughout the nuclear interiorThese structures, which ensure efficient functioning and formation of genetic material, include chromosomes made of chromatin located within the nucleus. The chromatin fibers condense during cell division to form distinguishable chromosomes. Nucleoli can be seen in nondividing nuclei and cells involved in protein synthesis. Within the nucleolus, proteins from the cytoplasm combine with rRNA to create ribosomal units responsible for protein synthesis. Ribosomes consist of a large subunit and a small subunit.

There are two types of ribosomes based on their location: free ribosomes suspended in the cytosol produce proteins for use within the cytosol, while bound ribosomes attached to the exterior of the nuclear envelope produce proteins for insertion into endoplasmic reticulum or membranes.

The endomembrane system plays a role in regulating protein traffic and performing metabolic processes within cells. This membrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles,

vacuoles, and plasma membrane.

The endoplasmic reticulum (ER) is an essential component of this system and consists of both smooth ER and rough ER. The ER lumen forms a continuous space within the nuclear envelope. Transport vesicles are formed from rough ER and travel to the Golgi apparatus.

Unlike smooth ER that lacks ribosomes on its outer surface, rough ER is covered in ribosomes.
Smooth ER has three main functions: lipid synthesis, drug detoxification, and calcium ion transportation in muscle cells. Alcohol abuse and barbiturate use can increase smooth ER and detoxification enzymes, speeding up the detox process and building tolerance to drugs. This requires higher doses for desired effects like sedation.

On the other hand, rough ER is involved in protein synthesis through ribosomes attached to its surface. Some proteins undergo modifications with sugar additions in the ER to form glycoproteins. These secretory proteins are different from those produced by free ribosomes in cytosol and are packaged into transport vesicles that exit the ER.

Additionally, rough ER synthesizes membrane proteins and phospholipids by incorporating them into its own membrane. The expansion of the ER membrane involves transferring portions of itself to other components within the endomembrane system using transport vesicles. These transport vesicles merge with the Golgi apparatus.

The study also helps identify various regions of the Golgi apparatus, including its cis and trans faces. When a transport vesicle and its contents reach the Golgi apparatus, certain processes take place.Please refer to page 106 of your textbook for a labeled diagram (Copyright © 2011 Pearson Education.Inc.-4-24). A lysosome is a membranous sac that contains hydrolytic enzymes used by animal cells for the digestion (hydrolysis) of molecules. Lysosomes have an acidic

pH range (25). One function of lysosomes is intracellular digestion through phagocytosis, where particles are engulfed and digested by surrounding them with a food vacuole that fuses with a lysosome (25). This process releases digestion products into the cytosol to provide nutrients for the cell. Some human cells, like macrophages, perform phagocytosis to engulf and destroy bacteria and invaders. Lysosomes also play a role in recycling cellular components through autophagy. During autophagy, damaged cell organelles or small amounts of cytosol are surrounded by a dual membrane (26). The outer membrane of the cyst combines with a lysosome, where the enclosed material is broken down by lysosomal enzymes. The resulting organic monomers are then returned to the cytosol for reuse, allowing the cell community to regenerate itself. In individuals with Tay-Sachs disease, there is a deficiency in an enzyme that breaks down lipids, causing lipid accumulation in brain cells. This occurs because the lysosomes in Tay-Sachs lack a functional hydrolytic enzyme that should be present.There are different types of vacuoles, including food vacuoles formed through phagocytosis, contractile vacuoles that remove excess water from cells, and central vacuoles found in plants that develop through the merging of smaller vacuoles. The central vacuole contains cell sap which stores inorganic ions and helps with plant cell growth by absorbing water. The endomembrane system works together to release proteins and break down cellular components. Within this system, the nuclear envelope is connected to both rough ER and smooth ER. Copyright © 2011 Pearson Education.Inc.-5- The ER synthesizes membranes and proteins which are then transported to the Golgi apparatus via vesicles. Along with other vesicles such as lysosomes, specialized vesicles, and

vacuoles, these transport vesicles are received by the Golgi apparatus. Lysosomes can fuse with other vesicles for digestion purposes. Transport vesicles carry proteins to the plasma membrane for secretion. The fusion of vesicles leads to the expansion of the plasma membrane and enables protein secretion from the cell.
In Concept 6.5, mitochondria and chloroplasts convert energy from one form to another. An endosymbiont is a cell that resides within another cell.The endosymbiont theory proposes that an early ancestor of eukaryotic cells engulfed a non-photosynthetic prokaryotic cell that used oxygen, eventually merging into a single organism - a eukaryotic cell with mitochondria.It is possible that one of these cells also took up a photosynthetic prokaryoteThis theory is supported by three lines of evidence: firstly, mitochondria and chloroplasts have two membranes surrounding them, unlike organelles in the endomembrane system. Secondly, similar to prokaryotes, they contain ribosomes and circular DNA molecules attached to their interior membranes. Thirdly, they are independent organelles capable of growing and reproducing within cells, aligning with their probable evolutionary origins as cells. Despite having enclosing membranes, mitochondria and chloroplasts are not considered part of the endomembrane system. A chondriosome (also known as a mitochondrion) can be represented by labeling its outer membrane, interior membrane, interior membrane space, cristae, matrix, and ribosomes (refer to page 110 for the labeled figure). The text discusses various organelles in a cell and highlights the functions of chloroplasts, chondriosomes (mitochondria), and peroxisomes. It emphasizes the importance of organization and layout in relation to these structures. Both chloroplasts and mitochondria have outer membranes, inner membranes, interior membrane spaces,and folded surfaces that increase surface area.Chloroplasts also have thylakoids granum,and stroma.They play a

crucial role in photosynthesis by converting solar energy into chemical energy through sunlight absorption and synthesis of organic compounds from carbon dioxide and water.Thylakoid membranes within chloroplasts are responsible for conducting light-dependent reactions, while chondriosomes serve as the site of cellular respiration and generate ATP by extracting energy from various fuel sources. The inner mitochondrial membrane, which is highly folded, increases efficiency in cellular respiration. Peroxisomes contain enzymes that remove hydrogen atoms from substrates and transfer them to oxygen, resulting in the production of hydrogen peroxide.

To better understand the functions of these organelles, it is recommended to refer to labeled figures on pages 100-101 of the textbook. These figures should include labels with brief descriptions of each organelle's function (see page 111 for an example).

The cytoskeleton, which consists of a network of fibers throughout the cell's cytoplasm, plays three main roles: maintaining cell shape, providing mechanical support for cell motion, and organizing structures through microtubules, microfilaments, and intermediate fibrils composed of tubulin protein. Microtubules have multiple functions including maintaining cell form and motility, facilitating chromosome movement during cell division, and enabling organelle motion.

Animal cells possess centrioles that act as compression-resisting girders for the cytoskeleton; however, plant cells do not have centrioles.The centriole, also known as the "microtubule-organizing centre," is positioned perpendicular to each other with nine sets of three microtubules. Cilia and flagella both contain microtubules arranged in a pattern called "9 + 2." These cellular extensions have microtubules covered by the plasma membrane but differ in their movement patterns. Flagella move in an undulating motion similar to a fish's tail, while cilia function like oars and generate force perpendicular to their axis. The bending

and movement of cilia are facilitated by dyneins, motor proteins powered by ATP. Microfilaments consist of actin chains and play various roles, such as muscle cell contraction where myosin motors cause the projections to slide past each other, shortening the muscle cell length simultaneously. Actin fibrils interacting with myosin contribute to ameboid motion where cells contract and pull their tail end forward. Plant cells exhibit cytoplasmic cyclosis, a movement driven by myosin motors attached to organelles within the fluid cytosol that interact with parallel actin fibrils forming a network around the cell. Myosin is responsible for moving along microfilaments as a motor protein.Intermediate fibrils are larger than microfilaments but smaller than microtubules. They serve as permanent structures within cells, maintaining cell shape and anchoring the nucleus and certain organelles. They also form the nuclear lamina (Concept 6.7). Extracellular components and connections between cells play a role in coordinating cellular activities.

The cell wall has three functions: protecting plant cells, maintaining their shape, and preventing excessive water intake. It consists of microfibrils composed of polysaccharide cellulose, which is synthesized by an enzyme called cellulose synthase and secreted into the extracellular space. In this space, the microfibrils become embedded in a matrix of other polysaccharides and proteins.

The primary cell wall of plant cells is less rigid and more flexible compared to other walls produced by these cells. It consists of pectins that form a sticky polysaccharide layer between the primary walls of adjacent cells. On the other hand, the secondary cell wall is made up of multiple layers with a strong matrix that provides protection and support to the cell.

In contrast, animal cells do not have a cell

wall but instead possess an extracellular matrix (ECM). The ECM is composed of various components with their functions indicated on a diagram.Unlike animal cells, plant cells have plasmodesmata, which are intercellular junctions that allow cytosol to pass through and connect neighboring cells' internal chemical environments. Another diagram can summarize and label the functions of three types of intercellular junctions found in animal cells. On page 123, there is an informative chart summarizing Concepts 6.3–6.5 in the text. Please review and answer the following questions: 1.B 2.Vitamin D 3.B 4.Vitamin E 5.A 6.Vitamin D 7.°C cytosol.Copyright © 2011 Pearson Education, Inc.–10– Copyright © 2011 Pearson Education, Inc.–11–