Question

Scientists are testing substance L to determine how it enters mammalian cells in a culture. The cells maintain a 120 millimolar (mM) intracellular concentration of substance L. The scientists determined the rate of entry of substance L into the cells at various external concentrations of substance L (10 to 100 mM) in culture medium (Table 1). Table 1. Rate of entry of substance L into mammalian cells in culture
External concentration of substance L (mM) Rate of entry of substance L into cell as a percent of maximum
10 5%
20 25%
30 45%
40 65%
50 80%
60 90%
70 95%
80 100%
90 100%
100 100%
The cells maintain substance L at an internal concentration of 120 mM.
(a) Identify the most likely mode of transport across the membrane for substance L. Explain how information provided helps determine the most likely mode of transport.

Answer 1

Substance L moves through active transport.

Active transport will be described because of the movement of drugs from a region of lower concentration to a region of upper concentration against the concentration gradient.

Further Explanation

Active transport is the movement or transfer that uses energy to secrete and enter ions and molecules through permeable cell membranes to maintain the balance of small molecules in the cell. Active transport is influenced by electrical charges inside and outside the cell, where the electric charge is determined by sodium ions (Na +), potassium ions (K +), and chloride ions (Cl -). The entry of Na + and K + ions is regulated by a sodium-potassium pump. Active transport can stop if the cell is cooled, poisoned, or run out of energy. Active transport requires a carrier molecule in the form of an integral protein in the membrane, wherein this molecule there is a binding site. The active transport process begins with the uptake of three Na + ions from the cell and occupies a binding site on an integral protein. Energy is needed to change the shape of integral proteins on the membrane that previously opened towards the inside of the cell to open to the outside of the cell. Furthermore, Na + ions are released from the binding site and exit the integral protein to the outside of the cell. Then from outside the cell, two K + ions occupy the binding site in an integral protein. The shape of the integral protein changes, from previously opening outwards to the opening towards the inside of the cell and potassium ions released into the cell.

The cell membrane is a universal feature shared by all types of cells in the form of an interface layer called the plasma membrane, which separates cells from the environment outside the cell, especially to protect the cell nucleus and the survival system that works inside the cytoplasm.

Membrane transport system

1. Passive transport

Passive transport is a movement of molecules down their concentration gradients. This passive transport is spontaneous. Diffusion, osmosis, and facilitated diffusion are examples of passive transport. Diffusion occurs due to thermal motion which increases entropy or irregularity, causing a more random mixture. Diffusion will continue as long as cellular respiration consuming O2 enters.

2. Active transport

The definition of active transport, first coined by Rosenberg as a process that causes the transfer of a substance from an area that has a lower electrochemical potential to a place with a higher potential. The process is said to require energy intake and a coupling mechanism so that energy intake can be used to carry out the process of transferring the substance.

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Grade: Middle School

Subject: Biology

keywords: Active transport

Answer 2

Answer:

The substance L moves inside the cell through active transport.

Explanation:

Active transport can be described as the movement of substances from an area of lower concentration to an area of higher concentration against the concentration gradient.

In the above question, The substance L enters the membrane despite the cell having a higher concentration of substance L. Hence, the mode of transportation is active transport as the substance L is moving from an area of lower concentration to higher concentration. This process usually consumes energy rather than releasing energy.