Critical Thinking Questions

What materials can easily diffuse through the lipid bilayer, and why?

Only materials that are relatively small and nonpolar can easily diffuse through the lipid bilayer. Large particles cannot fit in between the individual phospholipids that are packed together, and polar molecules are repelled by the hydrophobic/nonpolar lipids that line the inside of the bilayer.This includes gases like oxygen and carbon dioxide, as well as small nonpolar molecules.

Why is receptor-mediated endocytosis said to be more selective than phagocytosis or pinocytosis?

Receptor-mediated endocytosis is more selective because the substances that are brought into the cell are the specific ligands that could bind to the receptors being endocytosed. Phagocytosis or pinocytosis, on the other hand, have no such receptor-ligand specificity, and bring in whatever materials happen to be close to the membrane when it is enveloped.

What do osmosis, diffusion, filtration, and the movement of ions away from like charge all have in common? In what way do they differ?

are similar in the sense that they describe the movement of substances down a particular type of gradient. Osmosis and diffusion involve the movement of water and other substances down their concentration gradients, respectively. Filtration describes the movement of particles down a pressure gradient, and ion movement can be both passive or active, depending on the energy requirement and is down their electrical gradient.

Explain why the structure of the ER, mitochondria, and Golgi apparatus assist their respective functions.

A mitochondrion is a membranous, been-shaped organelle it generates ATP in the cell. The inner membrane is buried in the matrix which increases the surface area for increased gaseous exchange is known as cristae. Enzymes and other molecules are associated with inner membrane which helps in cellular respiration. Cellular respiration results in production of ATP from nutrient molecules like glucose.

The Golgi apparatus is a cell organelle responsible for processing or modification of proteins, sorting out protein and translocation to different locations in the cell. The proteins after processing in the endoplasmic reticulum are transported to Golgi bodies for further modification.

Golgi apparatus and ER work together to synthesise proteins and lipids. Mitochondria are called the power house of the cell. Respiration takes place inside mitochondria which produces ATP.

Compare and contrast lysosomes with peroxisomes: name at least two similarities and one difference.

Peroxisomes and lysosomes are both cellular organelles bound by lipid bilayer membranes, and both contain many enzymes. However, peroxisomes contain enzyme that detoxify substances by transferring hydrogen atoms and producing H2O2, whereas the enzymes in lysosomes function to break down and digest various unwanted materials.

Explain in your own words why DNA replication is said to be “semiconservative”?

DNA replication is termed "semiconservative" because each new double helix contains one original strand and one newly synthesized strand. This method ensures that each daughter DNA molecule preserves half of the parental DNA, thus conserving genetic information.

Why is it important that DNA replication take place before cell division? What would happen if cell division of a body cell took place without DNA replication, or when DNA replication was incomplete?

It is crucial for DNA replication to occur before cell division to ensure that each daughter cell receives an identical set of genetic material. If cell division occurs without complete DNA replication, it could result in cells with incomplete or damaged DNA, leading to genetic abnormalities and dysfunctional cell function.

Briefly explain the similarities between transcription and DNA replication.

Both transcription and DNA replication involve the synthesis of nucleic acid from a DNA template. They share similar processes in unwinding the DNA helix and using complementary base pairing, but while replication synthesizes DNA, transcription produces RNA.

Contrast transcription and translation. Name at least three differences between the two processes.

Transcription is really a "copy" process and translation is an "interpretation" process, because transcription involves copying the DNA message into a very similar RNA message whereas translation involves converting RNA message into the very different amino acid message. Transcription is the process of synthesizing RNA from a DNA template, while translation involves converting RNA sequences into amino acids to form proteins. Key differences include: 1) Transcription occurs in the nucleus while translation takes place in the cytoplasm. 2) Transcription produces RNA, whereas translation produces proteins. 3) Transcription uses RNA polymerase, whereas translation relies on ribosomes.

What would happen if anaphase proceeded even though the sister chromatids were not properly attached to their respective microtubules and lined up at the metaphase plate?

It could result in an unequal distribution of chromosomes to the daughter cells. This would lead to aneuploidy, where one cell may end up with an extra chromosome while the other may lack one, potentially causing severe developmental issues or diseases.

What are cyclins and cyclin-dependent kinases, and how do they interact?

A cyclin is one of the primary classes of cell cycle control molecules, while a cyclin-dependent kinase is one of a group of molecules that work together with cyclins to determine past cell checkpoints. By interacting with many additional molecules, these triggers push the cell cycle forward unless prevented from doing so by "stop" signals, if for some reason the cell isn't ready.

Cyclins are regulatory proteins that control the progression of the cell cycle by activating cyclin-dependent kinases (CDKs). CDKs are enzymes that, when bound to cyclins, phosphorylate target proteins to advance the cell through various checkpoints in the cell cycle.

Explain how a transcription factor ultimately determines whether or not a protein will be present in a given cell?

Transcription factors bind to DNA and either promote or inhibit the transcription of a gene. If they promote the transcription of a particular gene, then that gene will be transcribed and the mRNA subsequently translated into protein. If gene transcription is inhibited, then there will be no way of synthesizing the gene's corresponding protein.

Discuss two reasons why the therapeutic use of embryonic stem cells can present a problem.

One reason is the ethical concerns surrounding the destruction of embryos during the harvesting process. Additionally, there is a risk of immune rejection when the stem cells are transplanted into patients, as they may be perceived as foreign by the patient's immune system.

Identify the four types of tissue in the body, and describe the major functions of each tissue.

The four types of tissue in the body are epithelial, connective, muscle, and nervous. Epithelial tissue is made of layers of cells that cover the surfaces of the body that come into contact with the exterior world, line internal cavities, and form glands. Connective tissue binds the cells and organs of the body together and performs many functions, especially in the protection, support, and integration of the body. Muscle tissue, which responds to stimulation and contracts to provide movement, is divided into three major types: skeletal (voluntary) muscles, smooth muscles, and the cardiac muscle in the heart. Nervous tissue allows the body to receive signals and transmit information as electric impulses from one region of the body to another.

The zygote is described as totipotent because it ultimately gives rise to all the cells in your body including the highly specialized cells of your nervous system. Describe this transition, discussing the steps and processes that lead to these specialized cells.

The zygote divides into many cells. As these cells become specialized, they lose their ability to differentiate into all tissues. At first they form the three primary germ layers. Following the cells of the ectodermal germ layer, they too become more restricted in what they can form. Ultimately, some of these ectodermal cells become further restricted and differentiate in to nerve cells.

What is the function of synovial membranes?

Synovial membranes are a type of connective tissue membrane that supports mobility in joints. The membrane lines the joint cavity and contains fibroblasts that produce hyaluronan, which leads to the production of synovial fluid, a natural lubricant that enables the bones of a joint to move freely against one another.

The structure of a tissue usually is optimized for its function. Describe how the structure of individual cells and tissue arrangement of the intestine lining matches its main function, to absorb nutrients.

Columnar epithelia, which form the lining of the digestive tract, can be either simple or stratified. The cells are long and narrow. The nucleus is elongated and located on the basal side of the cell. Ciliated columnar epithelium is composed of simple columnar epithelial cells that display cilia on their apical surfaces.

One of the main functions of connective tissue is to integrate organs and organ systems in the body. Discuss how blood fulfills this role.

Blood is a fluid connective tissue, a variety of specialized cells that circulate in a watery fluid containing salts, nutrients, and dissolved proteins in a liquid extracellular matrix. Blood contains formed elements derived from bone marrow. Erythrocytes, or red blood cells, transport the gases oxygen and carbon dioxide. Leukocytes, or white blood cells, are responsible for the defense of the organism against potentially harmful microorganisms or molecules. Platelets are cell fragments involved in blood clotting. Some cells have the ability to cross the endothelial layer that lines vessels and enter adjacent tissues. Nutrients, salts, and waste are dissolved in the liquid matrix and transported through the body.

Why does an injury to cartilage, especially hyaline cartilage, heal much more slowly than a bone fracture?

A layer of dense irregular connective tissue covers cartilage. No blood vessels supply cartilage tissue. Injuries to cartilage heal very slowly because cells and nutrients needed for repair diffuse slowly to the injury site.

You are watching cells in a dish spontaneously contract. They are all contracting at different rates; some fast, some slow. After a while, several cells link up and they begin contracting in synchrony. Discuss what is going on and what type of cells you are looking at.

The cells in the dish are cardiomyocytes, cardiac muscle cells. They have an intrinsic ability to contract. When they link up, they form intercalating discs that allow the cells to communicate with each other and begin contracting in synchrony.

Why does skeletal muscle look striated?

Under the light microscope, cells appear striated due to the arrangement of the contractile proteins actin and myosin.

Which morphological adaptations of neurons make them suitable for the transmission of nerve impulse?

Neurons are well suited for the transmission of nerve impulses because short extensions, dendrites, receive impulses from other neurons, while a long tail extension, an axon, carries electrical impulses away from the cell to other neurons.

What are the functions of astrocytes?

Astrocytes regulate ions and uptake and/or breakdown of some neurotransmitters and contribute to the formation of the blood-brain-barrier.

Why is it important to watch for increased redness, swelling and pain after a cut or abrasion has been cleaned and bandaged?

These symptoms would indicate that infection is present.

Aspirin is a non-steroidal anti-inflammatory drug (NSAID) that inhibits the formation of blood clots and is taken regularly by individuals with a heart condition. Steroids such as cortisol are used to control some autoimmune diseases and severe arthritis by down-regulating the inflammatory response. After reading the role of inflammation in the body's response to infection, can you predict an undesirable consequence of taking anti-inflammatory drugs on a regular basis?

Since NSAIDs or other anti-inflammatory drugs inhibit the formation of blood clots, regular and prolonged use of these drugs may promote internal bleeding, such as bleeding in the stomach. Excessive levels of cortisol would suppress inflammation, which could slow the wound healing process.

As an individual ages, a constellation of symptoms begins the decline to the point where an individual's functioning is compromised. Identify and discuss two factors that have a role in factors leading to the compromised situation.

The genetic makeup and the lifestyle of each individual are factors which determine the degree of decline in cells, tissues, and organs as an individual ages.

Discuss changes that occur in cells as a person ages.

All cells experience changes with aging. They become larger, and many cannot divide and regenerate. Because of alterations in cell membranes, transport of oxygen and nutrients into the cell and removal of carbon dioxide and waste products are not as efficient in the elderly. Cells lose their ability to function, or they begin to function abnormally, leading to disease and cancer.