High School Biology : Transport and Signaling

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Transport And Signaling

What type of transport involves the cell engulfing matter from the outside environment?

Possible Answers:

Exocytosis

Pinocytosis

Phagocytosis

Diffusion

Correct answer:

Phagocytosis

Explanation:

Phagocytosis is the event of a cell engulfing particular matter from outside the cell and bringing it into the cell. Macrophages are the most prominent phagocytic cells, and help to eliminate pathogens and bacteria through phagocytosis.

Pinocytosis allows extracellular fluid to enter the cell, using invaginations on the cell membrane to create vesicles. Exocytosis involves vesicles leaving the cell, not entering. Diffusion is the passive transport of substances across the membrane and does not involve vesicles.

Example Question #1 : Understanding Endocytosis And Exocytosis

Which of the following normally gets exocytosed from a cell?

Possible Answers:

RNA

Hormones

Cytoplasmic constituents

DNA

Integral membrane proteins

Correct answer:

Hormones

Explanation:

Exocytosis is a process by which the cell packages content and secretes it from the cell in a vesicle. Hormones, which act on cells far away from where they are produced, will travel out of the cell to reach their target tissues and organs. Vesicles of hormones will fuse with the membrane of the cell and release the hormone into the blood for transport.

DNA, RNA, and cytoplasmic constituents do not leave the cell and would not be exocytosed. Integral membrane proteins are placed in the membrane via vesicle fusion, but are not exocytosed in the process.

Example Question #1 : Understanding Endocytosis And Exocytosis

Particle A is observed to be brought into the cell through endocytosis. This means that the destination of particle A is most likely ___________.

Possible Answers:

the cytosol because vesicles aren’t involved

the cytosol because it is being transported via a vesicle

one of the membrane-bound organelles because it is being transported via a vesicle

one of the membrane-bound organelles because vesicles aren’t involved

Correct answer:

one of the membrane-bound organelles because it is being transported via a vesicle

Explanation:

There are two topologically different structures inside the cell: the lumen and the cytosol. Lumen consists of the inside of the organelles and the inside of vesicles. Cytosol consists of the fluid that surrounds the organelles.

The questions states that particle A undergoes endocytosis. In endocytosis particles from outside of the cell are brought to the inside of the cell by vesicles that bud off from the cell membrane. These vesicles deliver the particles to the target organelle. The vesicles fuse with the organelle’s membrane and the particles are released into the lumen of the organelle. These particles never make contact with the cytosol side of the cell; therefore, the best answer is that particle A is destined for one of the membrane-bound organelles because it is being transported via a vesicle. This mechanism is also relevant for exocytosis. Secretory vesicles carry contents from inside the cell to the outside, without letting the contents touch the cytosol.

Example Question #1 : Transport And Signaling

Given below are four events that occur during the synthesis and transport of proteins. 

1. Protein is transported to Golgi apparatus for packaging

2. Translation of mRNA occurs in the cytosol

3. Protein is transported to the cell membrane

4. Protein is transported to rough endoplasmic reticulum for processing

Which of the following is the correct order of these events?

Possible Answers:

1, 3, 2, 4

2, 4, 1, 3

3, 2, 1, 4

2, 1, 4, 3

Correct answer:

2, 4, 1, 3

Explanation:

To answer this question you need to know the sequence of events that a protein goes through during and after synthesis.

The first step is the synthesis of protein. This occurs when mRNA is translated to protein by ribosomes. The first event is statement 2.

After its synthesis, the protein is transported to the rough endoplasmic reticulum where it is processed. This processing involves removal of unwanted amino acid sequences, such as signal sequences. The second event is statement 4.

From the rough endoplasmic reticulum the protein is transported to Golgi apparatus where it is further processed and packaged. This next event is statement 1.

The last step is the delivery of protein to the cell membrane (statement 3). Once the protein reaches the cell membrane it can either be exported to the outside (exocytosis) or become part of the membrane (integral and peripheral membrane proteins). Remember that the protein is transported by vesicles and that it never makes contact with the cytosol.

Example Question #1 : Understanding Endocytosis And Exocytosis

Which of the following is an example of endocytosis?

Possible Answers:

A vesicle transporting materials out of a cell

Light and carbon dioxide being converted into carbohydrate and oxygen

A plasma membrane engulfing large materials so that they can enter the cell

A vesicle transporting materials in to a cell

Correct answer:

A vesicle transporting materials in to a cell

Explanation:

Endocytosis is the process of a cell receiving the contents of a vesicle. The vesicle will fuse with the cell membrane and release its contents into the cytoplasm for cellular use.

In contrast, exocytosis is the release of compounds from a cell via vesicle transport. Vesicles are formed at the Golgi apparatus and transported through the cytoplasm to fuse with the cell membrane, where the contents are released into the extracellular space. Transport vesicles can also be formed to contain and carry molecules away from the cell.

The plasma membrane engulfing particles to enter the cell would be an example of pinocytosis, and the conversion of light and carbon dioxide to carbohydrate and oxygen is the process of photosynthesis.

Example Question #1 : Understanding Endocytosis And Exocytosis

Which process best decribes how a macrophage (immune cell) engulfs a bacterial pathogen? 

Possible Answers:

Phagocytosis

Endocytosis

Pinocytosis

Active transport

Diffusion

Correct answer:

Phagocytosis

Explanation:

The correct answer is phagocytosis. Phagocytosis involves the engulfing of an external particle to form a phagosome (a vesicle inside the cell). This process differs from pinocytosis in that pinocyotsis refers to the engulfing of liquids from the environment. Phagocytosis is a specific form of endocytosis; thus, phagocytosis is the better answer as endocyotsis can also describe processes such as pinocytosis. Diffusion and Active Transport both do not relate to the phenomenon as no concentration gradient is in place. 

Example Question #1 : Understanding Receptors And Ligands

Which of the following cannot act as a ligand?

Possible Answers:

Steroids

Integral membrane proteins

Inhibitors

Calcium ions

Neurotransmitters

Correct answer:

Integral membrane proteins

Explanation:

Ligands bind to receptors, which cause conformational changes and various effects on the cell. Integral membrane proteins span the lipid bilayer. These proteins commonly act as receptors and bind to ligands to produce conformation changes. They cannot leave the lipid bilayer, and thus are never ligands that can bind to other receptors.

Ligands are generally small ions or molecules, such as glucose or triglycerides. Calcium ions act as second messenger ligands in signal transduction. Steroid hormones, like testosterone, bind to proteins in the nucleus to alter transcription patterns. Neurotransmitters bind to receptors on dendrites to cause action potential propagation. Inhibitors can bind to receptors to block other ligands from interacting.

Example Question #1 : Understanding Receptors And Ligands

Which of the following is NOT true regarding receptors and ligands?

Possible Answers:

Ligands usually make covalent bonds with their receptors.

It is possible for a receptor to bind more than one ligand.

Ligands are usually proteins.

The receptor for a ligand may either be on the cell's surface or inside the cytoplasm.

Binding of a ligand always turns on the protein to which it is bound.

Correct answer:

Ligands usually make covalent bonds with their receptors.

Explanation:

Ligands and receptors are both usually proteins. Since proteins can fold into a wide variety of shapes, the receptor-ligand interaction is very specific. In some cases, certain receptors will bind two ligands that are similar in structure. For example, hemoglobin binds to both  and , but binds  with much higher affinity. Ligands bind receptors using only weak bonds (hydrogen bonds and Van der Waals forces). Depending on the nature of the ligand (whether it can cross the lipid bilayer or not), its receptor may be either on the cell's surface, floating in the cytoplasm, or on the nuclear membrane.

Example Question #1 : Understanding Receptors And Ligands

Which of the following includes the four most common groups of ligands in biology?

Possible Answers:

Substrates, activators, neurotransmitters, and tracers

Substrates, inhibitors, activators, and neurotransmitters

Inhibitors, activators, neurotransmitters, and tracers

Substrates, inhibitors, activators, and tracers

Substrates, inhibitors, neurotransmitters, and tracers

Correct answer:

Substrates, inhibitors, activators, and neurotransmitters

Explanation:

In biochemistry, ligands are any substance that forms a complex with a biomolecule to serve a biological purpose. The four primary types of ligands have their functional state determined by their three-dimensional chemical conformation. Tracers in the body often take the form of radioligands, but are not ligands themselves.

Example Question #1 : Transport And Signaling

Chemotaxis refers to movement of an organism in response to which of the following stimuli?

Possible Answers:

Vibrations

Chemicals

Sound

Gravity

Light

Correct answer:

Chemicals

Explanation:

Chemotaxis refers to the movement of an organism in response to a chemical stimulus. Single or multicellular organisms may direct their movements according to certain chemicals in their environment. This is important because these organisms need to find food, flee from harmful substances, and chemotaxis also aids in development. Positive chemotaxis is movement towards a higher concentration of the chemical, whereas negative chemotaxis is movement away from the chemical.  

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