AP Biology : Understanding Xylem and Phloem

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding Xylem And Phloem

Which of the following is false?

Possible Answers:

All of these statements are true

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

Phloem is dead at maturity, while xylem is living

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 #23 : Plant Structures

Which of the following are true regarding phloem?

I. It transports water from the roots to the leaves.

II. It transports sucrose from the leaves to the roots.

III. It is located lateral to xylem in tree stems.

Possible Answers:

II and III

I only

I and III

I and II

II only

Correct answer:

II and III

Explanation:

Phloem is located in the bark of trees and transports sugars (such as sucrose) and organic compounds to the rest of the plant from the leaves. The other plant vascular tissue is xylem. Xylem is located outer wood of trees, and transports water from the roots to the leaves of trees.

Example Question #2 : Understanding Xylem And Phloem

The primary function of xylem is __________.

Possible Answers:

To perform photosynthesis

To attract pollinators

To transport water from the roots to the leaves

To allow exchange of gasses such as carbon dioxide

To transport sugar throughout the plant

Correct answer:

To transport water from the roots to the leaves

Explanation:

Xylem transports water from the roots of a plant to the leaves. It does so through a passive process, negative water pressure created by transpiration in the leaves pulls water up from the roots through the xylem, similar to the action water moving up a paper towel when one corner of a  paper towel is placed in a pool of water. Xylem cells are dead at maturity so they cannot perform photosynthesis. Sugars are transported by phloem (from the leaves to other areas of the plant). Stomata are structures that facilitate gas exchange.

Example Question #25 : Plant Structures

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

Possible Answers:

Photosynthesis

Transport of water

Structural support of plants

Transport of nutrients

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 #26 : Plant Structures

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:

All of these

Transpirational pull

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 #27 : Plant Structures

Which of the following is not true regarding tracheids?

Possible Answers:

They are square-shaped

They are a type of cell in xylem tissue

They hold water against gravitational force

They have thick cell walls

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 are not found in gymnosperms

They form tubular vessels

All of these

They have thick cell walls

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 #22 : Macrostructures

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 #2 : Understanding Xylem And Phloem

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

Possible Answers:

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

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

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

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 #24 : Macrostructures

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

Possible Answers:

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

They do not contain a nucleus

They have a large number of ribosomes and mitochondria

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.

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