Characteristics of living things
Why does maintaining homeostasis require feedback mechanisms?
Feedback mechanisms detect unusual stimulations from the environment and send signals to the body to trigger responses.
Explain why polysaccharides like glycogen and cellulose have such different functions despite both being made of glucose.
The glucose molecules have different glycosidic bonds, meaning that they are bonded to each other in different ways in the two molecules.
(glycogen has α-1,4 and α-1,6 linkages allowing branching for storage, while cellulose has β-1,4 linkages forming strong hydrogen-bonded fibers for structure.)
Why do enzymes only catalyze specific reactions, even though many substrates exist in a cell?
Enzymes are highly specific proteins, as their active sites only bind to a specific type of substrate.
(lock and key/induced fit model)
Why was the invention of the microscope crucial for the development of cell theory?
the microscope allowed scientists to see microscopic organisms, which provided evidence for this theory as cells are to small to observe with naked eye.
Why do lysosomes need to maintain an acidic pH to function?
Their hydrolytic enzymes work optimally in acidic conditions; this also prevents damage if enzymes leak into the cytoplasm (neutral pH inactivates them).
How does the distinction between growth and development explain why some organisms reach the same size but have different levels of complexity?
Growth means the increase in size, while development means a change in complexity of the organisms. Two organisms may easily reach the same size, but it is impossible for them to experience the same level of development, leading to their different levels of complexity.
Why can’t humans digest cellulose but can digest starch?
Humans lack enzymes that breaks down cellulose but they do have enzymes such as amylase that breaks down starch.
(Humans lack cellulase to break β-1,4 bonds, but have amylase to hydrolyze α-1,4 bonds in starch.)
Explain why enzymes in thermophilic bacteria can function at 80°C while human enzymes denature at 45°C.
Different enzymes have different optimal temperatures, which corresponds to the organisms environment. Human enzymes are made to function inside the human body (37 degrees celsius) while thermophilic bacteria enzymes are a different type of protein.
(Thermophilic enzymes have stronger intramolecular forces (extra ionic bonds, disulfide bridges) that stabilize structure at high temperatures.)
What structural limitation prevents light microscopes from achieving the resolution of electron microscopes?
Resolution of light microscopes is limited by the wavelength of visible light, while electron beams have a much shorter wavelength.
Why do muscle cells contain more mitochondria than skin cells?
Muscle cells require more energy and ATP to function, so they have more mitochondria to support their demand.
Compare the evolutionary advantages of asexual and sexual reproduction in the same environments.
Organisms that undergo asexual reproduction are less genetically variant because the offsprings usually share the same genetic code as the parent. For sexual reproduction, because crossing over of genes occur, offsprings are more genetically diverse. Therefore, it is easier for them to adapt to changing environments. However, under stable conditions, because asexual reproduction consumes less energy, it is able to produce more offsprings and will less likely go extinct.
If a mutation alters the R-group of an amino acid in hemoglobin, why might this cause sickle cell disease?
The change in this variant group changes hemoglobin's shape, which impacts oxygen transportation.
Why does the rate of an enzyme-catalyzed reaction plateau at high substrate concentrations?
All enzyme active sites become saturated, so the maximum reaction rate (Vmax) is reached; further increases in substrate concentration have no effect.
What is the endosymbiotic theory?
Eukaryotic cells came from originally existing prokaryotic cells.
Why do plant cells need both mitochondria and chloroplasts?
Rough ER ribosomes are bound to the ER membrane, directing proteins into the endomembrane system for packaging and export, while free ribosomes stay in the cytosol for local use.
Why is metabolism considered a unifying theme of life?
Metabolism is a process that all living organisms go through, meaning that it unifies all living organisms under the same chemical principles.
Compare the structural consequences of saturated vs. unsaturated fats on biological membranes.
Saturated fats are packed more closely together, which form cell membranes that are more rigid. Unsaturated fats have double bonds that are higher in fluidity and makes cell walls more loosely packed with each other.
Compare how competitive inhibitors and poisons affect enzyme activity differently in terms of reversibility.
Competitive inhibitors bind reversibly to the active site, while poisons often bind irreversibly (covalent modification), permanently disabling the enzyme.
Why is magnification not enough to describe microscope quality without also considering resolution?
Magnification enlarges images, but resolution determines clarity and the ability to distinguish close objects. High magnification with poor resolution gives a blurry image.
Explain the endosymbiotic theory and provide one piece of evidence supporting it.
The endosymbiotic theory proposes that mitochondria and chloroplasts originated from prokaryotes that were engulfed by ancestral eukaryotic cells. Evidence: both have their own DNA and double membranes.
Design an experiment to test whether a newly discovered microscopic entity is living or nonliving. What criteria from the characteristics of life would you measure?
(answers may vary)
test for the presence of metabolism, growth/development, asexual reproduction (if unicellular), and its use of energy (both in response to sunlight and consumption of food)
Why is DNA more chemically stable than RNA, and how does this relate to their biological roles?
DNA has thymine instead of uracil, which reduces spontaneous hydrolysis and reactivity. DNA's unreactiveness makes it more suitable for storing genetic information on a long termed basis, while RNA is more suitable for transporting temporary role of transporting codons and messages.
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If you were given an unknown micrograph, what features would help you distinguish between prokaryotic and eukaryotic cells?
(answers may vary)
the presence of a nucleus and membrane bound nuclei.
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