30.1: The Plant Body
Like animals, plants contain cells with organelles in which specific metabolic activities take place. Unlike animals, however, plants use energy from sunlight to form sugars during photosynthesis. In addition, plant cells have cell walls, plastids, and a large central vacuole: structures that are not found in animal cells. Each of these cellular structures plays a specific role in plant structure and function.
Review Questions
Plant regions of continuous growth are made up of ________.
- dermal tissue
- vascular tissue
- meristematic tissue
- permanent tissue
Which of the following is the major site of photosynthesis?
- apical meristem
- ground tissue
- xylem cells
- phloem cells
Free Response
What type of meristem is found only in monocots, such as lawn grasses? Explain how this type of meristematic tissue is beneficial in lawn grasses that are mowed each week.
- Answer
-
Lawn grasses and other monocots have an intercalary meristem, which is a region of meristematic tissue at the base of the leaf blade. This is beneficial to the plant because it can continue to grow even when the tip of the plant is removed by grazing or mowing.
Which plant part is responsible for transporting water, minerals, and sugars to different parts of the plant? Name the two types of tissue that make up this overall tissue, and explain the role of each.
- Answer
-
Vascular tissue transports water, minerals, and sugars throughout the plant. Vascular tissue is made up of xylem tissue and phloem tissue. Xylem tissue transports water and nutrients from the roots upward. Phloem tissue carries sugars from the sites of photosynthesis to the rest of the plant.
30.2: Stems
Plant stems, whether above or below ground, are characterized by the presence of nodes and internodes. Nodes are points of attachment for leaves, aerial roots, and flowers. The stem region between two nodes is called an internode. The stalk that extends from the stem to the base of the leaf is the petiole. An axillary bud is usually found in the axil—the area between the base of a leaf and the stem—where it can give rise to a branch or a flower.
Review Questions
Stem regions at which leaves are attached are called ________.
- trichomes
- lenticels
- nodes
- internodes
Which of the following cell types forms most of the inside of a plant?
- meristem cells
- collenchyma cells
- sclerenchyma cells
- parenchyma cells
Tracheids, vessel elements, sieve-tube cells, and companion cells are components of ________.
- vascular tissue
- meristematic tissue
- ground tissue
- dermal tissue
The primary growth of a plant is due to the action of the ________.
- lateral meristem
- vascular cambium
- apical meristem
- cork cambium
Which of the following is an example of secondary growth?
- increase in length
- increase in thickness or girth
- increase in root hairs
- increase in leaf number
Secondary growth in stems is usually seen in ________.
- monocots
- dicots
- both monocots and dicots
- neither monocots nor dicots
Free Response
Describe the roles played by stomata and guard cells. What would happen to a plant if these cells did not function correctly?
- Answer
-
Stomata allow gases to enter and exit the plant. Guard cells regulate the opening and closing of stomata. If these cells did not function correctly, a plant could not get the carbon dioxide needed for photosynthesis, nor could it release the oxygen produced by photosynthesis.
Compare the structure and function of xylem to that of phloem.
- Answer
-
Xylem is made up tracheids and vessel elements, which are cells that transport water and dissolved minerals and that are dead at maturity. Phloem is made up of sieve-tube cells and companion cells, which transport carbohydrates and are alive at maturity.
Explain the role of the cork cambium in woody plants.
- Answer
-
In woody plants, the cork cambium is the outermost lateral meristem; it produces new cells towards the interior, which enables the plant to increase in girth. The cork cambium also produces cork cells towards the exterior, which protect the plant from physical damage while reducing water loss.
What is the function of lenticels?
- Answer
-
In woody stems, lenticels allow internal cells to exchange gases with the outside atmosphere.
Besides the age of a tree, what additional information can annual rings reveal?
- Answer
-
Annual rings can also indicate the climate conditions that prevailed during each growing season.
Give two examples of modified stems and explain how each example benefits the plant.
- Answer
-
Answers will vary. Rhizomes, stolons, and runners can give rise to new plants. Corms, tubers, and bulbs can also produce new plants and can store food. Tendrils help a plant to climb, while thorns discourage herbivores.
30.3: Roots
The roots of seed plants have three major functions: anchoring the plant to the soil, absorbing water and minerals and transporting them upwards, and storing the products of photosynthesis. Some roots are modified to absorb moisture and exchange gases. Most roots are underground. Some plants, however, also have adventitious roots, which emerge above the ground from the shoot.
Review Questions
Roots that enable a plant to grow on another plant are called ________.
- epiphytic roots
- prop roots
- adventitious roots
- aerial roots
The ________ forces selective uptake of minerals in the root.
- pericycle
- epidermis
- endodermis
- root cap
Newly-formed root cells begin to form different cell types in the ________.
- zone of elongation
- zone of maturation
- root meristem
- zone of cell division
Free Response
Compare a tap root system with a fibrous root system. For each type, name a plant that provides a food in the human diet. Which type of root system is found in monocots? Which type of root system is found in dicots?
- Answer
-
A tap root system has a single main root that grows down. A fibrous root system forms a dense network of roots that is closer to the soil surface. An example of a tap root system is a carrot. Grasses such as wheat, rice, and corn are examples of fibrous root systems. Fibrous root systems are found in monocots; tap root systems are found in dicots.
What might happen to a root if the pericycle disappeared?
- Answer
-
The root would not be able to produce lateral roots.
30.4: Leaves
Leaves are the main sites for photosynthesis: the process by which plants synthesize food. Most leaves are usually green, due to the presence of chlorophyll in the leaf cells. However, some leaves may have different colors, caused by other plant pigments that mask the green chlorophyll. The thickness, shape, and size of leaves are adapted to the environment. Each variation helps a plant species maximize its chances of survival in a particular habitat.
Review Questions
The stalk of a leaf is known as the ________.
- petiole
- lamina
- stipule
- rachis
Leaflets are a characteristic of ________ leaves.
- alternate
- whorled
- compound
- opposite
Cells of the ________ contain chloroplasts.
- epidermis
- vascular tissue
- stomata
- mesophyll
Which of the following is most likely to be found in a desert environment?
- broad leaves to capture sunlight
- spines instead of leaves
- needle-like leaves
- wide, flat leaves that can float
Free Response
How do dicots differ from monocots in terms of leaf structure?
- Answer
-
Monocots have leaves with parallel venation, and dicots have leaves with reticulate, net-like venation.
Describe an example of a plant with leaves that are adapted to cold temperatures.
- Answer
-
Conifers such as spruce, fir, and pine have needle-shaped leaves with sunken stomata, helping to reduce water loss.
30.5: Transport of Water and Solutes in Plants
The structure of plant roots, stems, and leaves facilitates the transport of water, nutrients, and photosynthates throughout the plant. The phloem and xylem are the main tissues responsible for this movement. Water potential, evapotranspiration, and stomatal regulation influence how water and nutrients are transported in plants. To understand how these processes work, we must first understand the energetics of water potential.
Review Questions
When stomata open, what occurs?
- Water vapor is lost to the external environment, increasing the rate of transpiration.
- Water vapor is lost to the external environment, decreasing the rate of transpiration.
- Water vapor enters the spaces in the mesophyll, increasing the rate of transpiration.
- Water vapor enters the spaces in the mesophyll, increasing the rate of transpiration.
Which cells are responsible for the movement of photosynthates through a plant?
- tracheids, vessel elements
- tracheids, companion cells
- vessel elements, companion cells
- sieve-tube elements, companion cells
Free Response
The process of bulk flow transports fluids in a plant. Describe the two main bulk flow processes.
- Answer
-
The process of bulk flow moves water up the xylem and moves photosynthates (solutes) up and down the phloem.
30.6: Plant Sensory Systems and Responses
Animals can respond to environmental factors by moving to a new location. Plants, however, are rooted in place and must respond to the surrounding environmental factors. Plants have sophisticated systems to detect and respond to light, gravity, temperature, and physical touch. Receptors sense environmental factors and relay the information to effector systems—often through intermediate chemical messengers—to bring about plant responses.
Review Questions
The main photoreceptor that triggers phototropism is a ________.
- phytochrome
- cryptochrome
- phototropin
- carotenoid
- Answer
-
C
Phytochrome is a plant pigment protein that:
- mediates plant infection
- promotes plant growth
- mediates morphological changes in response to red and far-red light
- inhibits plant growth
- Answer
-
C
A mutant plant has roots that grow in all directions. Which of the following organelles would you expect to be missing in the cell?
- mitochondria
- amyloplast
- chloroplast
- nucleus
- Answer
-
B
After buying green bananas or unripe avocadoes, they can be kept in a brown bag to ripen. The hormone released by the fruit and trapped in the bag is probably:
- abscisic acid
- cytokinin
- ethylene
- gibberellic acid
- Answer
-
C
A decrease in the level of which hormone releases seeds from dormancy?
- abscisic acid
- cytokinin
- ethylene
- gibberellic acid
- Answer
-
A
A seedling germinating under a stone grows at an angle away from the stone and upward. This response to touch is called ________.
- gravitropism
- thigmonasty
- thigmotropism
- skototropism
- Answer
-
C
Free Response
Owners and managers of plant nurseries have to plan lighting schedules for a long-day plant that will flower in February. What lighting periods will be most effective? What color of light should be chosen?
- Answer
-
A long-day plant needs a higher proportion of the Pfr form to Pr form of phytochrome. The plant requires long periods of illumination with light enriched in the red range of the spectrum.
What are the major benefits of gravitropism for a germinating seedling?
- Answer
-
Gravitropism will allow roots to dig deep into the soil to find water and minerals, whereas the seedling will grow towards light to enable photosynthesis.
Fruit and vegetable storage facilities are usually refrigerated and well ventilated. Why are these conditions advantageous?
- Answer
-
Refrigeration slows chemical reactions, including fruit maturation. Ventilation removes the ethylene gas that speeds up fruit ripening.
Stomata close in response to bacterial infection. Why is this response a mechanism of defense for the plant? Which hormone is most likely to mediate this response?
- Answer
-
To prevent further entry of pathogens, stomata close, even if they restrict entry of CO2. Some pathogens secrete virulence factors that inhibit the closing of stomata. Abscisic acid is the stress hormone responsible for inducing closing of stomata.
