AP Biology › Understanding Xylem and Phloem
Which of the following is true?
Xylem transports water and nutrients, and dies at maturity
Xylem transports sugars, and dies at maturity
Phloem 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 does not have nuclei, ribosomes, and vacuoles at maturity
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.
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.
II and III
I and III
I and II
I only
II only
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.
Which of the following best describes the primary role of xylem in plants?
Transport of water
Transport of nutrients
Structural support of plants
Photosynthesis
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.
Xylem is responsible for water transport within plants. Which of the following forces makes the upward movement of water through the xylem possible?
All of these
Transpirational pull
None of these
Root pressure
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.
Which of the following is not true regarding tracheids?
They are square-shaped
They are a type of cell in xylem tissue
They have thick cell walls
They hold water against gravitational force
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.
Which of the following is true regarding vessel elements in plants?
All of these
They are not found in gymnosperms
They have thick cell walls
They form tubular vessels
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.
What is the primary function of phloem in plants?
Transport of organic nutrients
Secretion of hormones
Wound repair
Photosynthesis
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.
Which of the following are characteristics of companion cells in vascular plants?
They have a large number of ribosomes and mitochondria and are a specialized type of parenchyma cells
They do not contain a nucleus and are a specialized type of parenchyma cells
They have a large number of ribosomes and mitochondria
They do not contain a nucleus
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.
Which of the following is an accurate comparison between sieve tube elements and vessel elements?
Sieve tube elements are living cells while vessel elements are technically dead
Vessel elements transport nutrients while sieve tube elements transports mostly water
Vessel elements are living cells and sieve tube elements are technically dead
Sieve tube elements are in xylem tissue and vessel elements are in phloem tissue
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.
Which of the following is false?
Phloem is dead at maturity, while xylem is living
Phloem is responsible for food transfer, while xylem is responsible for water transfer
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
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.