GRE Subject Test: Biology : Understanding Plant Macrostructures

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

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Example Questions

Example Question #3 : Cellular Structures

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

Possible Answers:

Cuticle

Xylem

Pericycle

Parenchyma

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 : Understanding Plant Macrostructures

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

Possible Answers:

Xylem

Chlorophyll

Apical bud

Plastid

Stoma

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 #2 : Understanding Plant Macrostructures

Which of the following is false?

Possible Answers:

Phloem is dead at maturity, while xylem is living

Phloem can transport material bidirectionally, while xylem can only transport material unidirectionally

Phloem consists of sieve tubes and companion cells, while xylem consists of tracheids and vessel elements

All of these statements are true

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

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.

Example Question #3 : Understanding Plant Macrostructures

Of the following answer choices, which most accurately describes the mechanism that the stems of plants use to grow toward light?

Possible Answers:

The growth of the stem is determined by metabolic processes, which are stimulated by light striking the stems

Cells on the darker side of the stem elongate more than cells on the lighter side

Photosynthetic processes dictate the growth

Contractile cells on the light side of the stems dictate the growth toward light

The plant will grow away from other plants so as to minimize competition

Correct answer:

Cells on the darker side of the stem elongate more than cells on the lighter side

Explanation:

Plants grow so as to maximize the elongation of their stems as much as possible. Cells on the lighter side of the stem are already being provided with photosynthetic energy, while cells on the darker side are receiving less of this energy input. This causes the cells on the darker side to elongate toward the energy source. When one side of the stem is longer than the other, it causes a curve in the growth, resulting in a directionality of the growth of the stem.

Example Question #2 : Understanding Other Plant Macrostructures

Plant root systems can be generally categorized as either taproot systems or fibrous root systems. Which of the following is a characteristic of a fibrous root system?

Possible Answers:

Fibrous root systems are well adapted to soil where ground water is not close to the surface

Fibrous root systems usually penetrate deeply into the soil

Fibrous root systems consist of a series of roots that spread out from a major single root

Fibrous root systems do not penetrate deeply into the soil

Correct answer:

Fibrous root systems do not penetrate deeply into the soil

Explanation:

Fibrous root systems are common in seedless vascular plants and in most monocots, such as grasses. Many small roots grow from the stem of the plant and are considered adventitious (a term describing a plant organ that grows in an unusual location). 

Fibrous roots have no main root and do not penetrate deeply into the soil, usually penetrating only a few centimeters. As such, fibrous root systems are best adapted to shallow soil. This also helps prevent erosion, as the shallow, highly-branched roots hold the topsoil in place. 

Example Question #4 : Understanding Plant Macrostructures

Which of the following is a type of stem?

Possible Answers:

Rhizomes

Lateral roots

Pith

Stele

Correct answer:

Rhizomes

Explanation:

Stems are one of the three basic plant organs, and consist of an alternating system of nodes (where leaves attach) and internodes (regions of the stem that span between nodes).

Some plants have evolved to have stems with additional functions, such as the ability to store food or to participate in asexual reproduction. These modified stems include rhizomes, bulbs, tubers and stolons.  

A rhizome is a horizontal shoot of the plant that grows just below the surface. Vertical shoots (and resulting leaves) grow from axillary buds on the rhizome. Examples of plants with rhizomes include irises, hops, and asparagus. 

Example Question #1 : Understanding Water And Nutrient Transport

Which plant tissue system is similar to the human circulatory system?

Possible Answers:

Vascular tissue

Sclerenchyma

Dermal tissue

Ground tissue

Vascular cambium

Correct answer:

Vascular tissue

Explanation:

A plant's vascular tissues transport nutrients throughout the plant, just as the circulatory system transports nutrients throughout human bodies. While blood is the primary solvent for nutrients in humans, water is the primary solvent for nutrients in plants. Animals, however, use blood pressure to propel nutrients throughout the body while plants use gravity and the cohesive properties of water to transport nutrients.

The two primary types of plant vascular tissue are xylem, which transports water, and phloem, which transports organic molecules like glucose.

Example Question #5 : Understanding Plant Macrostructures

What is the function of lateral meristems?

Possible Answers:

Provide secondary growth in woody plants

Maintain water homeostasis

Provide nutrients to apical meristems

Stimulate root hair growth

Correct answer:

Provide secondary growth in woody plants

Explanation:

In addition to growing in height, woody plants also grow in thickness. This is the function of lateral meristems. Lateral meristems are comprised of the vascular cambrium, and by cork cambrium that form vascular cylinders. The vascular cambrium adds layers of secondary xylem and phloem (wood), whereas the cork cambrium replaces the outer epidermis with a thicker and tougher layer called periderm.

Example Question #6 : Understanding Plant Macrostructures

What is the tissue found in many vascular plants which forms as part of the periderm and generates secondary growth in roots and stems?

Possible Answers:

Cork cambium

Vascular cambium

Cortex

Phloem

Phelloderm

Correct answer:

Cork cambium

Explanation:

The periderm forms a protective layer around the outside of many stems and roots and consists of cork cambium, cork, and phelloderm. Cork cambium is the site of active secondary growth within the periderm of vascular plants. Phloem is a type of vascular tissue that directs the flow of nutrients and metabolic products from the leaves down to the roots.

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