BIOL 171: Exam 1 Homeworks

Which of the following structures allows a plant cell to be larger than an animal cell?

A large vacuole, which reduces the volume of cytoplasm.

Which of the following domains contain prokaryotes? 1. Archaea 2. Bacteria 3. Eukarya

Archaea and Bacteria

The major role of the cell wall in bacteria is protecting the cell against changes in osmotic pressure, pressure caused by different solute concentrations in the environment. Bacterial cells swell, but do not burst, in low solute concentrations. What happens to bacterial cells if a compound that interferes with the synthesis of the cell wall is added to an environment with low solute concentrations?

Bacterial cells may burst due to the influx of water

Discuss how buffers help prevent drastic swings in pH.

Buffers absorb excess hydrogen and hydroxide ions to prevent increases or decrease in pH. An example is the bicarbonate system in the human body.

Which of the following statements is false? a) Molecules with the formulas CH3CH2COOH and C3H6O2 could be structural isomers. b) Molecules must have a double bond to be cis-trans isomers. c) To be enantiomers, a molecule must have at least three different atoms or groups connected to a central carbon. d) To be enantiomers, a molecule must have at least four different atoms or groups connected to a central carbon.

C

What property of carbon makes it essential for organic life?

Carbon can form up to four covalent bonds, allowing it to form long chains.

How many neutrons do carbon-12 and carbon-13 have, respectively?

Carbon-12 contains 6 neutrons while Carbon-13 contains 7 neutrons.

What property of carboxyl containing molecules hydrophilic? Which macromolecules contain carboxyl?

Carboxyl groups release H+, making its parent molecule hydrophilic. It is found in amino acids and fatty acids.

What are the similarities and differences between the structure of centrioles and flagella?

Centrioles and flagella are made of microtubules but show different arrangements

What type of compound functions in hormone production, contributes to membrane flexibility, and is the starting molecule for bile salts?

Cholesterol, which is a lipid and also a steroid, functions here.

A change in DNA on a chromosome affects all proteins made that gene for the life of the cell. A change in the RNA involved in proteins production is short lived. What is the difference between the effects of the changes in the two types of nucleic acids?

DNA is the genetic material that is passed from parent cells to daughter cells and to future generations.

What makes ionic bonds different from covalent bonds?

Ionic bond involves the transfer of electrons whereas covalent bond involves the sharing of electrons.

What characteristic would you expect to find in an organism that appeared early in the history of Earth?

It can grow under extremely harsh conditions.

How do phospholipids contribute to cell membrane structure?

Phospholipids orient their heads towards the polar molecules and tails in the interior of the membrane, thus forming a bilayer.

What are two similarities and two differences between plant and animal cells that can be seen under a microscope?

Plant cells have cell walls which provide structure to the plant and also chloroplasts which allow for photosynthesis. Animal cells do not have either of these structures. Both cells have nuclei, the command center of the cell, and cytoplasm, the gel-like solution that fills the cell.

Which of these is a possible explanation for the presence of a rigid cell wall in plants?

Plants are subjected to osmotic pressure and a cell wall helps them against bursting and shrinking.

What categories of amino acids would you expect to find on the surface of a soluble protein and which would you expect to find in the interior? Which of these are some examples for each part of the answer?

Polar and charged amino acids will be found on the surface whereas non-polar in the interior.

Why can water be a good insulator within the body of endothermic (warm-blooded) animals?

Specific Heat Capacity

Dehydration is a word usually used to mean the removal of water. How does this apply to macromolecules?

The hydroxyl groups of two monomers are used to form a bond by removing a hydrogen from one monomer and a hydroxyl group from the second forming a molecule of water.

What causes the changes in protein structure through the three or four levels of structure?

The primary structure attains a curved shape and covalent bonds, which further acquire hydrogen bonds at specific pH.

List the mass number and atomic number of carbon-12 and carbon-13, respectively.

carbon-13 mass number: 13 atomic number: 6 carbon-12 mass number: 12 atomic number: 6

With which cellular structure does the extracellular matrix interact?

cytoskeleton

Which organelles would be present in high numbers in the leg muscles of a marathon runner?

mitochondria

Which of these describe some of the similarities and differences between glycogen and starch?

Starch is less branched than glycogen and is found in plants.

How do the nucleus and the endomembrane system work together for protein synthesis?

The endomembrane system processes and ships proteins specified by the nucleus. In the nucleus, DNA is used to make RNA which exits the nucleus and enters the cytoplasm of the cell. The ribosomes on the rough ER use the RNA to create the different types of protein needed by the body.

How does the extracellular matrix function?

The extracellular matrix helps in the attachment of the cell to other cells and to various substrata.

Is the nuclear membrane part of the endomembrane system? Why or why not?

The nuclear membrane is part of the endomembrane system as it is continuous with the rough ER.

Describe the pH scale and how it relates to living systems. Give an example of how drastic pH changes are prevented in living organisms.

The pH scale ranges from 0 to 14, where anything below 7 is acidic and above 7 is alkaline. The bicarbonate system in the human body buffers the blood.

How do phospholipids contribute flexibility to cell membrane structure?

The phospholipids containing unsaturated fatty acids cannot be tightly packed which provides membrane flexibility.

Vesicles pinch off the rough ER. Where do they go from there?

Golgi Apparatus

What role do electrons play in dehydration synthesis and hydrolysis?

H+ and OH- ions share electrons with the respective monomers in hydrolysis.

Which molecule carries information in a form that is inherited from one generation to another?

Hereditary information is stored in DNA.

Why are hydrogen bonds and van der Waals interactions necessary for cells?

Hydrogen bonds and van der Waals interactions form weak associations between molecules, providing the necessary shape and structure of DNA and proteins to function in the body.

K-41 is one of the naturally occurring isotopes of potassium. Use the periodic table to explain how the structure of K-41 differs from the normal K atom.

K-41 has a total of 22 neutrons and normal K atom has 20 neurons

What are three functions that lipids serve in plants and/or animals?

Lipids serve in the storage of energy, as a structural component of hormones, and also as signaling molecules.

Macrophages ingest and digest many pathogens. Which organelle plays a major role in the activity of macrophages?

Lysosome

Mitochondria are observed in plant cells that contain chloroplasts. Why do you find mitochondria in photosynthetic tissue?

Mitochondria are required to break down sugars and other material for energy.

You are making a poster of a generic bacterium for your class. Which of the following structures will you leave out of your poster?

Nucleolus

carboxyl group

O=C-OH

carbonyl group

O=C-R'

Water takes up 333 million cubic miles on Earth, yet access to drinking water is a critical issue for many communities around the world. Explain why this is so.

Only 4 percent of the total water on Earth is freshwater, out of which 68 percent is found in glaciers.

The word hydrolysis is defined as the lysis of water. How does this apply to polymers?

Polymers break by separating water into hydrogen and hydroxyl groups that are added to the monomers.

Why is the process of protein synthesis critical to life?

Protein is required for tissue formation and constitutes hormones and enzymes.

Compare and contrast saturated and unsaturated triglycerides.

Saturated triglycerides contain single bonds and are solids at room temperature, while unsaturated triglycerides contain double bonds and are liquids at room temperature.

On average, prokaryotic cells are smaller than eukaryotic cells. What are some advantages to small cell size? What are some advantages to large cell size?

Small, prokaryotic cells do not expend energy in intracellular transport of substances. Larger eukaryotic cells have organelles, which enable them to produce complex substances.

The unique properties of water are important in biological processes. For the following three properties of water, define the property and give one example of how the property affects living organisms: 1. Cohesion 2. Adhesion 3. High heat of evaporation

Cohesion is the attraction between the water molecules, which helps create surface tension. Insects can walk on water because of cohesion. Adhesion is the attraction between water molecules and other molecules. Water moving up from the roots of plants to the leaves as a result of capillary action is because of adhesion. Heat of vaporization is the amount of energy required to convert liquid into gas. This property helps humans maintain homeostasis of body temperature by evaporation.

How does the structure of a plasmodesma differ from that of a gap junction?

Gap junctions are essential for transportation in animal cells and plasmodesmata are essential for the movement of substances in plant cells.

Inhibitors of microtubule assembly, vinblastine for example, are used for cancer chemotherapy. How does an inhibitor of microtubule assembly affect cancerous cells?

The inhibitors restrict the separation of chromosomes, thereby stopping cell division.

The shape of hair proteins is maintained by a combination of hydrogen bonds and covalent, disulfide bonds. Heat is sufficient to break the hydrogen bonds, but harsh chemicals are required to break the disulfide bonds. Why is it harder to break the disulfide bonds than the hydrogen bonds?

Covalent bonds are stronger than hydrogen bonds.

What are some reasons that DNA is double stranded and RNA is single stranded in plants and animals?

DNA encodes multiple genes and is stable. RNA codes for particular genes, is always functional, and can exit the nucleus.

How do the differences in amino acid sequence lead to different protein functions?

Different amino acids provide different geometric configurations and thus varied functions.

What are three examples of how the characteristics of water are important in maintaining life?

First, the lower density of water as a solid versus a liquid allows ice to float, forming an insulating surface later for aquatic life. Second, the high specific heat capacity of water insulates aquatic life or bodily fluids from temperature changes. Third, the high heat of vaporization of water allows animals to cool themselves by sweating.

What would happen if even one amino acid is substituted for another in a polypeptide? What would be an example?

The amino acid may not show any significant effect the protein structure and function or it may have a significant effect, as in the case of hemoglobin in individuals with sickle cell trait.

The fatty acids of triglycerides are classified as saturated, unsaturated, or trans fats. What is it about the structure of these compounds that gives them their physical characteristics?

Unsaturated fats and trans fats have some double bonded carbon atoms, while saturated fats do not.