All GRE Subject Test: Biology Resources
Example Questions
Example Question #1 : Plant Biology
How do plants transport water against gravity?
Passive diffusion
Capillary action
Water pumps
Active transport
Aquaporins
Capillary action
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 #1 : Plant Biology
Which of the following best describes how water is transported from the roots of a tree to the tallest branches?
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 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 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.
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.
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 __________.
cytoplasm . . . whenever the appropriate nutrients are present
stroma . . . only during the absence of light
cytoplasm . . . only during the absence of light
stroma . . . whenever the appropriate nutrients are present
stroma . . . whenever the appropriate nutrients are present
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 #2 : Plant Biology
What is the purpose of photosystem II in photosynthesis?
Sequester carbon dioxide and facilitate its binding to rubisco
Donate electrons to ATP synthase
None of the other answers
Split water to create a high concentration of hydrogen ions
Donate electrons to NADP+ reductase
Split water to create a high concentration of hydrogen ions
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 : Plant Biology
Which of the following structures is unique to plant cells?
Lysosomes
Mitchondria
Chloroplasts
Vacuoles
Endoplasmic reticulum
Chloroplasts
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.
Example Question #2 : Plant Biology
Which of the following can be found in plant cells, but not animal cells?
Chloroplasts
Mitochondria
Cell membrane
Ribosomes
Chloroplasts
Chloroplasts, the site of photosynthesis, are only in plant cells and are not found in animal cells. Ribosomes, a cell membrane, and a mitochondria, however, can be found in both animal and plant cells.
The other structure that may be found in plant cells, but not animal cells, is a cell wall.
Example Question #2 : Understanding Chloroplasts
Where in the chloroplasts does the Calvin Cycle of photosynthesis take place?
Thylakoid lumen
Intermembrane space
Thylakoid membrane
Grana
Stroma
Stroma
The Calvin Cycle occurs in the stroma, the aqueous fluid-filled area of the chloroplast. The stroma can be seen as analogous to the cytoplasm of a cell, in that it is the liquid in which all other substructures reside. The other processes of photosynthesis, the light-dependent reactions, take place in the thylakoid, a membrane-bound substructure within the chloroplast.
Example Question #4 : Plant Biology
Which of the following is a key component of a plant's vascular system?
Cuticle
Parenchyma
Pericycle
Xylem
Xylem
The vascular system in plants is designed to transport materials (water, nutrients, food) between the roots and shoots. There are two primary types of tissue dedicated to these processes. Xylem transports water and dissolved minerals upward from the roots; phloem transports sugars—the products of photosynthesis—from where they are synthesized to where they are needed, such as roots and new growth areas of leaves and fruits.
Both xylem and phloem are comprised of a variety of cell types that are specialized for transport and support.
Example Question #3 : Plant Biology
What structure in plants allows for CO2 and O2 exchange and transpiration?
Chlorophyll
Plastid
Xylem
Stoma
Apical bud
Stoma
The stoma allows for gas exchange and transpiration. The stoma usually opens following stimulation by sunlight and closes in low water environments. Other answers are parts of a typical plant, however do not play a role in gas exchange or transpiration.
Example Question #1 : Understanding Xylem And Phloem
Which of the following is false?
Phloem is dead at maturity, while xylem is living
All of these statements are true
Phloem consists of sieve tubes and companion cells, while xylem consists of tracheids and vessel elements
Phloem can transport material bidirectionally, while xylem can only transport material unidirectionally
Phloem is responsible for food transfer, while xylem is responsible for water transfer
Phloem is dead at maturity, while xylem is living
Xylem is dead at maturity, while phloem is living. All other answer choices are true. Xylem is also thicker and more rigid, which allows for greater pressure during water transport. It provides a strong support structure for the plant, enabling taller growth.
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