GRE Subject Test: Biology : Plant Biology

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

varsity tutors app store varsity tutors android store

Example Questions

← Previous 1 3

Example Question #1 : Plant Biology

How do plants transport water against gravity?

Possible Answers:

Aquaporins

Water pumps

Passive diffusion

Capillary action

Active transport

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 #1 : 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 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 adhesion 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 #3 : Plant Biology

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

Possible Answers:

stroma . . . whenever the appropriate nutrients are present

cytoplasm . . . only during the absence of light

cytoplasm . . . whenever the appropriate nutrients are present

stroma . . . only during the absence of light

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 #4 : Plant Biology

What is the purpose of photosystem II in photosynthesis? 

Possible Answers:

Donate electrons to ATP synthase 

None of the other answers

Donate electrons to NADP+ reductase

Sequester carbon dioxide and facilitate its binding to rubisco

Split water to create a high concentration of hydrogen ions

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 #5 : Plant Biology

Which of the following structures is unique to plant cells?

Possible Answers:

Vacuoles

Mitchondria

Lysosomes

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.

Example Question #6 : Plant Biology

Which of the following can be found in plant cells, but not animal cells?

Possible Answers:

Chloroplasts

Mitochondria

Ribosomes

Cell membrane

Correct answer:

Chloroplasts

Explanation:

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 #1 : Plant Structures

Where in the chloroplasts does the Calvin Cycle of photosynthesis take place?

Possible Answers:

Intermembrane space

Grana

Thylakoid membrane

Thylakoid lumen

Stroma

Correct answer:

Stroma

Explanation:

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 #8 : Plant Biology

Which of the following is a key component of a plant's vascular system?

Possible Answers:

Parenchyma

Cuticle

Xylem

Pericycle

Correct answer:

Xylem

Explanation:

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 #1 : Plant Biology

What structure in plants allows for CO2 and O2 exchange and transpiration?

Possible Answers:

Chlorophyll

Xylem

Plastid

Stoma

Apical bud

Correct answer:

Stoma

Explanation:

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?

Possible Answers:

All of these statements are true

Phloem is dead at maturity, while xylem is living

Phloem is responsible for food transfer, while xylem is responsible for water transfer

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

Correct answer:

Phloem is dead at maturity, while xylem is living

Explanation:

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.

← Previous 1 3
Learning Tools by Varsity Tutors