Question 1

Contractile vacuoles are

Accepted Answer

Contractile vacuoles are specialized organelles in some single-celled organisms, such as protozoa and certain algae, used to expel excess water from the cell. This mechanism helps to regulate the cell's osmotic pressure, particularly in freshwater environments where the outside environment is hypotonic (lower in solute concentration) compared to the inside of the cell.

Question 2

Which of the following require the cell to use energy?

Accepted Answer

Endocytosis is a process by which a cell takes in large particles or even entire cells by forming a vesicle around them. This process requires energy in the form of ATP. Osmosis, diffusion, and facilitated diffusion are passive processes that do not require energy from the cell.

Question 3

Which of the following microorganisms would find hypotonic conditions most damaging?

Accepted Answer

Protozoa lack a rigid cell wall, making them more susceptible to bursting in hypotonic environments due to osmotic pressure.

Question 4

Facilitated diffusion is limited by

Accepted Answer

Facilitated diffusion requires carrier proteins in the membrane to transport molecules across the membrane. Therefore, the availability and number of carrier proteins can limit the rate of facilitated diffusion. The other choices, such as osmotic pressure and the size of the cell, are not directly related to facilitated diffusion.

Question 5

Diffusion of water through a semipermeable membrane is called ______.

Accepted Answer

The diffusion of water through a semipermeable membrane is specifically called osmosis. This process occurs when there is a difference in solute concentration on either side of the membrane, causing water to move from an area of lower solute concentration to an area of higher solute concentration.

Question 6

Nutrient absorption is mediated by the ______.

Accepted Answer

Nutrient absorption occurs across the cell membrane, which contains transporters and channels that allow molecules to enter the cytoplasm. The other options, such as the nuclear membrane, peptidoglycan layer, and cell wall, are not involved in nutrient absorption. Proteins in the periplasmic space may be involved in nutrient transport in some bacteria, but this is not the main mechanism of absorption.

Question 7

Saprobes do not need a carbon source for growth and metabolism.

Accepted Answer

Saprobes are organisms that obtain their nourishment from the dead and decaying matter of other organisms, which serves as their carbon source. Therefore, they do need a carbon source for growth and metabolism.

Question 8

The process by which a cell uses ATP to enclose a substance in its membrane, by forming a vacuole and engulfing it, is called ______.

Accepted Answer

Endocytosis is the process by which a cell engulfs a substance by forming a vesicle or vacuole around it. This process requires the use of ATP, and is an active transport mechanism. Facilitated diffusion, diffusion, and osmosis do not involve the engulfment of a substance by the cell membrane.

Question 9

The cell wall will help prevent the cell from bursting in ______ conditions.

Accepted Answer

In hypotonic conditions, there is a higher concentration of water outside the cell than inside it, causing water to enter the cell. If the cell lacks a cell wall, the influx of water can cause the cell to burst, a process called lysis. However, a cell wall can help maintain the shape of the cell and prevent it from bursting in hypotonic conditions. In isotonic conditions, the concentration of water inside and outside the cell is equal, so the cell is already in a balanced state and doesn't need a cell wall to prevent bursting. In hypertonic conditions, the concentration of water outside the cell is higher than inside it, causing water to leave the cell. While a cell wall can help prevent the cell from shrinking in hypertonic conditions, it doesn't help prevent bursting. Mesotonic conditions refer to a medium salt concentration that is usually physiologically irrelevant in terms of cell bursting.

Question 10

Obligate saprobes can adapt to a living host.

Accepted Answer

Obligate saprobes are organisms that rely solely on dead organic matter for their nutrition and cannot adapt to a living host. They are different from facultative saprobes, which are able to use dead organic matter as well as living hosts for their nutrition.

Question 11

You want to experiment with microbial growth in various nutrients, so you inoculate a loopful of E. coli into a tube of honey. Which statement best describes what you expect to happen and why?

Accepted Answer

Honey has a high sugar concentration, which creates a hypertonic environment that dehydrates and inhibits the growth of most bacteria, including E. coli.

Question 12

When whole cells or large molecules in solution are engulfed by a cell, this endocytosis is specifically termed ______.

Accepted Answer

Phagocytosis is the specific term used for the process of engulfing larger particles or even whole cells by the cell. Pinocytosis refers to the engulfment of smaller dissolved molecules, while facilitated diffusion and transport refer to the passive transport of molecules across membranes. Exocytosis, on the other hand, is the process of releasing molecules or particles from a cell.

Question 13

Bacteria living in a freshwater stream that are transferred to ocean water would

Accepted Answer

Bacteria in freshwater are adapted to a hypotonic environment. When transferred to ocean water, which is hypertonic, they would lose water and become dehydrated.

Question 14

Mediated transport of polar molecules and ions across the plasma membrane utilizes a(n) _____ carrier that binds to the substance and causes a conformational change to allow its movement across the membrane.

Accepted Answer

Mediated transport of polar molecules and ions across the plasma membrane utilizes a protein carrier that binds to the substance and causes a conformational change to allow its movement across the membrane. Porins are channel proteins that allow passive movement of small polar molecules. Lipids are the structural component of the membrane and do not actively participate in transport. Enzymes are involved in catalyzing reactions within the cell but not in transport across the membrane.

Question 15

The movement of substances from lower to higher concentration across a semipermeable membrane via a specific protein carrier and cell expenditure of energy is called ______.

Accepted Answer

Active transport involves movement of molecules or ions against their concentration gradient, which requires energy input from the cell. It occurs through specific protein carriers in the membrane. Osmosis is the movement of water molecules from higher to lower concentration across a semipermeable membrane, while diffusion is the movement of molecules from higher to lower concentration without the need for a protein carrier or energy expenditure. Endocytosis involves engulfment of substances by the cell membrane and facilitated diffusion involves movement of molecules across a membrane with the help of protein channels, but does not require energy.

Question 16

Which organism has a challenge to maintain cellular electrolyte and fluid balance in its environment?

Accepted Answer

All organisms have a challenge to maintain cellular electrolyte and fluid balance in their environment, as the concentration of ions and water molecules outside the cell may differ from that inside the cell, leading to osmotic stress. Therefore, all of the given options (A, B, and C) have problems in maintaining electrolyte and fluid balance within the cell.

Question 17

The movement of molecules from an area of high concentration to an area of lower concentration is called ______.

Accepted Answer

The movement of molecules from an area of high concentration to an area of lower concentration is called diffusion. Osmosis refers specifically to the diffusion of water, facilitated diffusion involves the use of protein channels to aid in diffusion, endocytosis is the movement of large molecules or particles into a cell by engulfment, and active transport involves the movement of molecules against their concentration gradient, requiring the use of energy.

Question 18

Organisms that feed on dead organisms for nutrients are called ______.

Accepted Answer

Organisms that feed on dead organisms are called saprobes. Lithoautotrophs are organisms that obtain their energy from inorganic compounds, parasites feed on living organisms, autotrophs synthesize their own food, and phototrophs obtain energy from sunlight.

Question 19

The movement of substances from higher to lower concentration across a semipermeable membrane via a specific protein carrier but without energy expenditure is called ______.

Accepted Answer

Facilitated diffusion allows substances to move across a semipermeable membrane from higher to lower concentration without the need for energy expenditure, but protein carriers are required to assist in the transport. This process is distinct from active transport, which requires energy input, diffusion, which does not require protein carriers, endocytosis, which involves the uptake of external materials by engulfing them in a membrane-bound vesicle, and osmosis, which specifically refers to the movement of water across a membrane.

Question 20

A saprobe with a cell wall will utilize extracellular digestion.

Accepted Answer

A saprobe with a cell wall will secrete enzymes outside of its cell and break down organic matter, then absorb the resulting nutrients. This process is called extracellular digestion.

Quiz 7: Microbial Nutrition, Ecology, and Growth