GRE Subject Test: Biology : GRE Subject Test: Biology

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Organogenesis

Which germ layer gives rise to the digestive tract?

Possible Answers:

Epiderm

Mesoderm

Ectoderm

Endoderm

Correct answer:

Endoderm

Explanation:

The three primary germ layers are the ectoderm, mesoderm, and endoderm. There are some general structures that can be attributed to the germ layers during development. The ectoderm gives rise to the outer coverings of the body, such as the skin, and to the central nervous system. The ectoderm produces the notochord and primitive neural structures very early in development. The mesoderm gives rise to the muscles and bones. Finally, the endoderm gives rise to the digestive tract and the liver.

Example Question #2 : Animal Development

Formation of the primitive streak occurs during what stage of embryogenesis?

Possible Answers:

Neurula

Blastula

Gastrula

Morula

Correct answer:

Blastula

Explanation:

The primitive streak forms in the blastula stage and establishes symmetry (left-right and cranial-caudal body axes). This spatial differentiation determines the site of gastrulation and initiates formation of the three germ layers. The epiblast (precursor to the ectoderm) invaginates to form the primitive streak. Cells from the primitive streak give rise to the mesoderm and the endoderm. Formation of the primitive streak marks the beginning of gastrulation.

Example Question #3 : Animal Development

The inner cell mass (or embryoblast) of the blastocyst gives rise to all of the following layers except __________.

Possible Answers:

the primitive endoderm

the trophoblast

the mesoderm

the epiblast

Correct answer:

the trophoblast

Explanation:

The blastula, or blastocyst, is made up of blastomere cells and a fluid-filled cavity called the blastocoel. 

There are two regions of the blastocyst: the inner cell mass and the trophoblast. The inner cell mass gives rise to the primitive endoderm and the epiblast, which later gives rise to the three germ layers during gastrulation. The trophoblast is the layer of cells forming the outer ring of the blastocyst. It secretes factors to make the blastocoel and is kept separate from the inner cell mass. All fetal structures eventually develop from the inner cell mass, while the trophoblast helps maintain the fetal environment and placenta.

Example Question #1 : Understanding Determination And Differentiation

During embryogenesis, the process in which a committed cell develops distinctive functions and characteristics is known as __________.

Possible Answers:

determination

induction

specification

differentiation

Correct answer:

differentiation

Explanation:

Once a committed cell begins to develop specialized functions, it is known as differentiation. Before a cell differentiates, it makes a commitment to a certain cell type, first by specification, which is reversible, and then by determination, which is irreversible. Once a cell is committed to a cell type, it undergoes differentiation to develop specific cell characteristics.

Induction is a process in which cells induce adjacent cells to commit to a certain cell type. 

Example Question #4 : Animal Development

What gene expression regulatory proteins control cell type specific genes and define cell identities that are indispensible in differentiation and development?

Possible Answers:

Mediator

All of these answers

Master transcription factors

Pioneering transcription factors 

Chromatin remodelers

Correct answer:

Master transcription factors

Explanation:

The correct answer is master transcription factors. The type of master transcription factor expressed in a cell depends on the ultimate cell type it will become. Master transcription factors have higher affinity for cell identity genes. Each cell type has a different profile of master transcription factors that are reliably expressed. Mediator facilitates binding and recuitment of many transcription factors. Chromatin remodelers change the epigenetic state in a cell, and pioneering transcription factors are the first factors to bind DNA, even in heterochromatin regions. 

Example Question #1 : Plant Functions

How do plants transport water against gravity?

Possible Answers:

Active transport

Capillary action

Aquaporins

Passive diffusion

Water pumps

Correct answer:

Capillary action

Explanation:

Plants do not have the ability to actively transport water to their respective cells. Instead, water undergoes capillary action, which allows it to flow upward against gravity. When the water is located in a very narrow chamber, such as the xylem of a plant, it creates intermolecular interactions with the walls of the chamber. These interactions allow small amounts of the water to "climb" the chamber walls. Due to the cohesion of water, whereby it is attracted to itself, more water molecules follow the "climbing" adhesion molecules. This subsequently allows the adhering molecules to climb higher, and the joint interaction of the adhesion and cohesion eventually allow the water to reach the topmost region of the plant (the leaves). Water is then released from the stomata, furthering the pull of water to the region of low pressure.

Example Question #71 : Plant Biology

Which of the following best describes how water is transported from the roots of a tree to the tallest branches?

Possible Answers:

Transpiration from the tree's leaves causes tension (negative pressure) to increase in the tree's xylem. As water exits the leaves, the cohesion of water molecules pulls more molecules into the roots and upward.

Transpiration from the tree's leaves causes tension (negative pressure) to increase in the tree's xylem. As water exits the leaves, the adhesion of water molecules pulls more molecules into the roots and upward.

Transpiration from the tree's leaves causes tension (negative pressure) to increase in the tree's phloem. As water exits the leaves, the adhesion of water molecules pulls more molecules into the roots and upward.

Transpiration from the tree's leaves causes tension (negative pressure) to increase in the tree's phloem. As water exits the leaves, the cohesion of water molecules pulls more molecules into the roots and upward.

Correct answer:

Transpiration from the tree's leaves causes tension (negative pressure) to increase in the tree's xylem. As water exits the leaves, the cohesion of water molecules pulls more molecules into the roots and upward.

Explanation:

One of water's most distinctive properties is cohesion—that is, the tendency of water molecules to "stick" to one another. In plants, this cohesion results in columns of water that stretch through the plant's xylem (the vascular tissue responsible for transport of water), from the roots all the way to the leaves. During transpiration, water evaporates from plants' leaves. Because of the cohesion of water, whenever water evaporates, more molecules are "pulled" into the roots to maintain the column of water. This is the transpirational pull-cohesion tension theory.

In contrast, adhesion is the tendency of water molecules to "stick" to other substances, such as the walls of a glass. Adhesion is responsible for the curved meniscus of water in a graduated cylinder. Phloem is responsible for sugar and carbohydrate transport in plants, while xylem transports water.

Example Question #1 : Plant Biology

The Calvin cycle takes place in the __________ and occurs __________.

Possible Answers:

stroma . . . only during the absence of light

cytoplasm . . . only during the absence of light

stroma . . . whenever the appropriate nutrients are present

cytoplasm . . . whenever the appropriate nutrients are present

Correct answer:

stroma . . . whenever the appropriate nutrients are present

Explanation:

The Calvin cycle takes place in the stroma of the chloroplast, which is the region in the chloroplast lumen outside of the thylakoids. It does not actually matter whether or not light is present for the reactions of the Calvin cycle to take place. They are light independent, but light will not prevent the reactions from occurring, similar to how glycolysis is independent of oxygen. As long as the appropriate nutrients and reactants are present, including ATP and NADPH generated from the light reactions, the Calvin cycle will occur. 

Example Question #1 : Plant Biology

What is the purpose of photosystem II in photosynthesis? 

Possible Answers:

Split water to create a high concentration of hydrogen ions

Donate electrons to NADP+ reductase

Sequester carbon dioxide and facilitate its binding to rubisco

None of the other answers

Donate electrons to ATP synthase 

Correct answer:

Split water to create a high concentration of hydrogen ions

Explanation:

Photosystem II splits water into hydrogen and oxygen. Hydrogen ions accumulate in the thylakoid space, creating an electrochemical concentration gradient. Due to this gradient, hydrogen ions pass through ATP sythase, powering the synthesis of ATP from ADP + Pi

Example Question #1 : Cellular Structures

Which of the following structures is unique to plant cells?

Possible Answers:

Lysosomes

Mitchondria

Vacuoles

Endoplasmic reticulum

Chloroplasts

Correct answer:

Chloroplasts

Explanation:

Chloroplasts are organelles in plant cells that conduct photosynthesis; therefore they are unique to plant cells. All the other mentioned organelles can be found in both animal and plant cells.

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