Practice Test - Plant Nutrition and Transport

T/F: Only leaves have phloem and only roots have xylem.

• True

• False

Answer explanation

Leaves need xylem because they need water for photosynthesis. Leaves need phloem because they need to distibute the sugars they produce to the rest of the plant.

Roots need xylem to distribute the water and minerals they absorb to the rest of the plant. Roots need phloem because they need to receive the sugars produced in the leaves, which their cells use as fuel.

T/F: A waxy cuticle covers leaves but is absent from roots.

• True

• False

Answer explanation

The waxy cuticle is an adaptation of terrestrial plants to prevent water loss. Its presence in the leaves minimizes transpiration, while its absence from the roots allows water absorption which is the main function of the roots.

T/F: Because plasma membranes of the root endodermis are selectively permeable, only certain solutes reach the xylem.

• True

• False

Answer explanation

Any route the water and solutes take from the soil to the xylem requires that they pass through some of the plasma membranes of the root cells.

Because plasma membranes are selectively

permeable, only certain solutes reach the xylem. This plasma membrane selectivity provides a checkpoint that transports needed minerals from the soil and keeps many unneeded or toxic substances out.

Name one of the three tissue types found in plants.

Answer explanation

Each of these general types forms a tissue system that is continuous throughout the plant, connecting all the organs. However, specific characteristics of the tissues and the spatial relationships of tissues to one another vary in different organs.

A root hair is ___.

• an extension of the endodermis of roots

• an extension of an individual cell that absorbs water from soil

• a modified root that provides support and anchorage

• a multicellular extension of the root epidermis

Answer explanation

(A) Root hairs are not connected directly to the endodermis

(C) Root hairs increase the surface area for more efficient absorption; they are not for storage nor support

(D) Root hairs are not made of more than one cell

The plant tissue system most analogous to our circulatory system is the ___.

• dermal tissue

• vascular tissue

• ground tissue

Answer explanation

The dermal tissue system serves as the outer protective covering of the plant. Like our skin, it forms the first line of defense against physical damage and pathogens.

The chief functions of the vascular tissue system are to facilitate the transport of materials through the plant and to provide mechanical support.

Tissues that are neither dermal nor vascular are part of the ground tissue system. Ground tissue is not just filler: It includes cells specialized for functions such as storage, photosynthesis, support, and short-distance transport.

CO₂ enters the inner spaces of the leaf through the ___.

• cell wall

• cuticle

• phloem

• stoma

Answer explanation

The leaf epidermis is covered by a waxy cuticle except where it is interrupted by stomata (singular, stoma), which allow exchange of CO₂ and O₂ between the surrounding air and the photosynthetic cells inside the leaf. In addition to regulating CO₂ uptake for photosynthesis, stomata are major avenues for the evaporative loss of water. The term stoma can refer to the stomatal pore or to the entire stomatal complex consisting of a pore flanked by the two specialized epidermal cells known as guard cells, which regulate the opening and closing of the pore.

Gas exchange, which is necessary for photosynthesis, can occur most easily in which leaf tissue?

• epidermis

• palisade mesophyll

• spongy mesophyll

• vascular tissue

Answer explanation

The epidermis is a layer of tightly packed cells. As part of the dermal tissue system, it serves as the outer protective covering of the plant.

The leaf’s ground tissue, called the mesophyll (from the Greek mesos, middle, and phyll, leaf), is sandwiched between

the upper and lower epidermal layers. Mesophyll consists mainly of parenchyma cells specialized for photosynthesis.

Palisade mesophyll consists of one or more layers of elongated parenchyma cells on the upper part of the leaf. Spongy mesophyll is below the palisade mesophyll.

These parenchyma cells are more loosely arranged, with a labyrinth of air spaces through which CO₂ and O₂ circulate around the cells and up to the palisade region. The air spaces are particularly large in the vicinity of stomata, where CO₂ is taken up from the outside air and O₂ is released.

A leaf's veins brings xylem and phloem into close contact with the photosynthetic

tissue, which obtains water and minerals from the xylem and loads its sugars and other organic products into the phloem for transport to other parts of the plant. The vascular structure also functions as a framework that reinforces the shape of the leaf. Each vein is enclosed by a protective bundle sheath, a layer of cells that regulates the movement of substances between the vascular tissue and the mesophyll.

In a plant root, the one structure that water CANNOT move through via the extracellular route is the ___.

• Casparian strip

• endodermis

• root hair

• xylem

Answer explanation

The Casparian strip is a continuous waxy barrier that stops water and solutes from entering the xylem through the cell walls, instead forcing them to cross a plasma membrane into an endodermal cell.

Which is TRUE of guard cells?

• They are necessary for water absorption from the environment.

• They reduce evaporative water loss through the stomata.

• They protect the plant's roots from infection.

• They control water and solute intake by roots.

Answer explanation

(A) Guard cells control the opening of the stomata; though they are involved in controlling the evaporative loss of water, they are not involved in absorption.

(C, D) Guard cells are structures found in leaves.