AP Biology : Plant Structures

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #3 : Understanding Xylem And Phloem

Which of the following best describes the primary role of xylem in plants?

Possible Answers:

Structural support of plants

Transport of nutrients

Photosynthesis

Transport of water

Correct answer:

Transport of water

Explanation:

Xylem is a type of tissue present in vascular plants that is responsible for water transport within the organism. Types of cells contained within xylem include tracheids, vessel elements, parenchyma cells, and fibers.

Example Question #1 : Understanding Xylem And Phloem

Xylem is responsible for water transport within plants. Which of the following forces makes the upward movement of water through the xylem possible?

Possible Answers:

Transpirational pull

All of these

None of these

Root pressure

Correct answer:

All of these

Explanation:

The transport of water through xylem in plants includes the upward movement of water. The forces of transpirational pull and root pressure are responsible for counteracting gravity and producing water’s upward movement. Transpirational pull is defined as the surface tension caused by water evaporation that pulls water upward through xylem. Root pressure is characterized by the difference in water potential between the soil and plant, causing water to travel into plant roots.

Example Question #1 : Understanding Xylem And Phloem

Which of the following is not true regarding tracheids?

Possible Answers:

They are a type of cell in xylem tissue

They hold water against gravitational force

They have thick cell walls

They are square-shaped

Correct answer:

They are square-shaped

Explanation:

Tracheids are elongated cells that are contained within xylem tissue. Tracheids are responsible for water and mineral transport. The thick cell walls of tracheids allow them to hold water against gravitational pull due to the adhesion property of water.

Example Question #1 : Understanding Xylem And Phloem

Which of the following is true regarding vessel elements in plants?

Possible Answers:

They have thick cell walls

They are not found in gymnosperms

They form tubular vessels

All of these

Correct answer:

All of these

Explanation:

Vessel elements are a cell type contained within xylem tissue of angiosperms. Vessel elements aid in the transport of water and minerals. Morphologically, vessel elements are described as hollow tubular cells that have thick cell walls and are open at both ends.

Example Question #1 : Understanding Xylem And Phloem

What is the primary function of phloem in plants?

Possible Answers:

Wound repair

Transport of organic nutrients

Secretion of hormones

Photosynthesis

Correct answer:

Transport of organic nutrients

Explanation:

Phloem is a type of tissue in vascular plants that transports organic nutrients. Among other components, phloem contains sieve elements, parenchyma cells, and supportive cells.

Example Question #1 : Understanding Xylem And Phloem

Which of the following is an accurate comparison between sieve tube elements and vessel elements?

Possible Answers:

Vessel elements are living cells and sieve tube elements are technically dead

Sieve tube elements are living cells while vessel elements are technically dead

Vessel elements transport nutrients while sieve tube elements transports mostly water

Sieve tube elements are in xylem tissue and vessel elements are in phloem tissue

Correct answer:

Sieve tube elements are living cells while vessel elements are technically dead

Explanation:

Vessel elements are cells in phloem tissue that are technically dead. Upon maturation, the living material in the cells disappears while the cell wall remains; the cells are dead; however, sieve tube elements contain living tissue.

Example Question #1 : Understanding Xylem And Phloem

Which of the following are characteristics of companion cells in vascular plants?

Possible Answers:

They have a large number of ribosomes and mitochondria

They have a large number of ribosomes and mitochondria and are a specialized type of parenchyma cells

They do not contain a nucleus

They do not contain a nucleus and are a specialized type of parenchyma cells

Correct answer:

They have a large number of ribosomes and mitochondria and are a specialized type of parenchyma cells

Explanation:

Companion cells are a type of specialized parenchyma cells in vascular plants. They contain a large number of ribosomes and mitochondria and perform cellular functions for sieve-tube elements, which they are connected to by plasmodesmata.

Example Question #51 : Plant Biology

Which of the following is true?

Possible Answers:

Xylem transports water and nutrients, and does not have nuclei, ribosomes, and vacuoles at maturity

Phloem transports sugars, and dies at maturity

Xylem transports water and nutrients, and dies at maturity

Phloem transports water and nutrients, and does not have nuclei, ribosomes, and vacuoles at maturity

Xylem transports sugars, and dies at maturity

Correct answer:

Xylem transports water and nutrients, and dies at maturity

Explanation:

Xylem are water-conducting cells that transport water and nutrients. They die at maturity and leave behind secondary walls. Phloem transports sugars through sieve-tube elements, but do not have nuclei, ribosomes, and vacuoles. However, phloem remains alive at maturity. 

Example Question #11 : Plant Biology

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

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

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

Photosynthetic processes dictate the growth

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

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

Fibrous root systems do not penetrate deeply into the soil

Fibrous root systems usually 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. 

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