AP Biology : Understanding Leaves

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understanding Leaves

What structure in plants allows for CO2 and O2 exchange and transpiration?

Possible Answers:

Xylem

Plastid

Stoma

Apical bud

Chlorophyll

Correct answer:

Stoma

Explanation:

The stoma allows for gas exchange and transpiration. The stoma usually opens following stimulation by sunlight and closes in low water environments. Other answers are parts of a typical plant, however do not play a role in gas exchange or transpiration.

Example Question #2 : Understanding Leaves

In plants, leaves contain specialized pores used for gas exchange. Each pore is formed by a pair of cells that control its closing and opening. What are these cells called?

Possible Answers:

Epidermal cells

Stoma cells

Cuticle cells

Guard cells

Correct answer:

Guard cells

Explanation:

For proper functioning, plants must take in carbon dioxide, expel oxygen, and limit the loss of water vapor. This gas exchange takes place via pores called stomata. These pores are formed by a pair of adjacent cells that can open and close in response to a number of factors. These cells are called guard cells.

The cuticle and epidermis are layers of leaf structure, and do not correspond to specific cell types. The stoma is the name of a single pore itself, not its surrounding cells.

Example Question #1 : Macrostructures

Which of the following are true of parenchyma cells?

Possible Answers:

Their main function is transport

They are strengthened with lignen

They carry out many metabolic functions such as photosynthesis

They contain sieve-tube members

They are the primary support cells of a plant

Correct answer:

They carry out many metabolic functions such as photosynthesis

Explanation:

Parenchyma cells are the main photosynthetic cells of a plant, but also function in storage of water and nutrients. Parenchyma cells are usually soft cells that are located in leaves and fruit. Phloem cells contain sieve-tube members, and function in transport of water and nutrients throughout the plant. Schlerenchyma cells are strengthened with lignen, and are support cells.

Example Question #2 : Understanding Leaves

The layer of cells that separates the a leaf from the environment (the outermost layer of leaf tissue) is called the __________.

Possible Answers:

bundle sheath

epidermis

stomata

spongy mesophyll

xylem

Correct answer:

epidermis

Explanation:

The outer layer of cells on a leaf is called the epidermis. It is composed of the upper epidermis and the lower epidermis and the two have somewhat different structures and function, but both serve to protect the leaf from the outside environment. Spongy mesophyll and bundle sheath cells are both structures on the interior of the leaf, which house chloroplasts. Stomata are found on the outside layer of a leaf, but they are pores that allow gas exchange. Xylem is a transport structure that is used to conduct water and nutrients through a plant.

Example Question #3 : Understanding Leaves

In which of the following leaf tissues does the most photosynthesis take place?

Possible Answers:

Epidermis

Guard cells

Cuticle

Stoma

Mesophyll

Correct answer:

Mesophyll

Explanation:

The mesophyll of a leaf contains palisade parenchyma cells (along with other cell types) which contain a high concentration of chloroplasts and are located near the edge of the leaf. These parenchyma cells in the mesophyll perform the bulk of the photosynthesis in a plant, though any part of a plant that contains chlorophyll can photosynthesize, including the spongy mesophyll.

Example Question #4 : Macrostructures

What is the name of the structure of the leaf that attaches the leaf to the stem?

Possible Answers:

Phloem

Filament

Mesophyll

Petiole

Xylem

Correct answer:

Petiole

Explanation:

The petiole attaches the leaf to the stem. Xylem is a tissue that transports water and minerals from the roots to other areas of a plant. Phloem is a tissue that transport water and nutrients from the leaves down to other areas of the plant. A filament is a part of a flower, not a leaf. Mesophyll is the tissue that makes up much of the body of the leaf and is where most photosynthesis takes place, but does not attach the leaf to the stem.

Example Question #13 : Plant Structures

Which of the following can be defined as the tissue in the interior of the leaf?

Possible Answers:

Mesophyll

Chlorophyll

Grana

Stomata

Correct answer:

Mesophyll

Explanation:

The mesophyll is the interior of the leaf. Chloroplasts are mainly found within the mesophyll and leaves are the major sites of photosynthesis in plants.

Example Question #6 : Macrostructures

Which of the following terms is best defined as the microscopic pores on the leaf?

Possible Answers:

Thylakoids

Stomata

Chlorophyll

Stroma

Correct answer:

Stomata

Explanation:

Stomata are the pores on the leaves that allow for carbon dioxide to enter and oxygen to leave the leaf. Stroma, thylakoids, and chlorophyll are all components of the chloroplasts.

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