AP Biology : Plant Biology

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Plant Biology

Which is of the following is not an adaptation/modification that enabled plants to move from aquatic to terrestrial environments as they evolved?

Possible Answers:

Thylakoid membranes

Stomata

Cutin

Roots and root hairs

Correct answer:

Thylakoid membranes

Explanation:

Thylakoid membranes are found within chloroplasts, which are used for photosynthesis. Plants found in both aquatic and terrestrial environments photosynthesize, so these membranes cannot be considered adaptations uniquely benefiting terrestrial plants.

Comparatively, cutin is a waxy coating found on various parts of plants that helps prevent water loss when exposed to air. Stomata are tiny openings in the epidermis of plants that allow for the exchange of carbon dioxide and oxygen while minimizing water loss. Roots and root hairs allow plants to absorb nutrients and water from the soil. Water loss was the primary challenge plants faced when moving from aquatic to terrestrial environments; cutin, stomata, roots, and root hairs all help terrestrial plants absorb and conserve water.

Example Question #2 : Plant Biology

Which structures did not evolve after plants emerged onto land?

Possible Answers:

Waxy cuticles

Seeds

Cell walls

Vascular transport

Stomata

Correct answer:

Cell walls

Explanation:

Cell walls were present in plant cells before the transition to land. Seeds, stomata, waxy cuticles, and vascular transport all evolved to reduce water loss and circulate water to all areas of the plant. Water loss and circulation were not an issue before the transition to land; plants were forced to adapt these traits in order to survive in a terrestrial environment.

Example Question #1 : Plant Biology

As plants moved from water to land, they developed structures and lifestyles better suited to life in their new environment. Which of the following is not an example of these adaptations?

Possible Answers:

Cuticle

Increase in vertical height

Vascular tissue

Decrease in rigidity 

Roots

Correct answer:

Decrease in rigidity 

Explanation:

Plants developed more rigid structures to help maintain their growth on land as opposed to water.

Waxy cuticles developed to help reduce water loss/desiccation. Roots allowed plants greater access to water, as well as provided anchoring to the ground; this allowed plants to grow taller. Vascular tissue facilitated transport of water and nutrients to all parts of the plant. Stomata helped with gas exchange.

Example Question #2 : Plant Biology

What is a distinct feature of a C4 plant?

Possible Answers:

Bundle-sheath cells

Carbon fixation

Light independent reactions

Closed stomata during the day

Correct answer:

Bundle-sheath cells

Explanation:

Carbon fixation converts inorganic carbon dioxide into organic carbon compounds, such as glucose and cellulose. This is a characteristic function of both C3 and C4, and is a primary purpose of light independent reactions.

Closed stomata during the day is a characteristic of CAM plants, which allows for the conservation of water that is usually lost during photorespiration.

Bundle-sheath cells are a characteristic of C4 plants. The presence of bundle-sheath cells isolates rubisco, preventing rubisco from binding to oxygen during photorespiration.

Example Question #3 : Plant Biology

Which of the following refers to the principle of alternation of generations in plants?

Possible Answers:

Gamete-producing sporophytes

The differences between a tree and a seed

A life cycle which includes a unicellular haploid stage

A life cycle that includes a multicellular haploid stage

The need for external pollinators

Correct answer:

A life cycle that includes a multicellular haploid stage

Explanation:

Plants have a multicellular haploid stage called the gametophyte. Gametophytes () produce gametes () through mitosis, which combine to produce a zygote (). The zygote grows into a multicellular, diploid sporophyte (), which produces spores () through meiosis. Those spores give rise to multicellular gametophytes.

Example Question #4 : Plant Biology

How is it believed that plants first became photosynthetic?

Possible Answers:

The origin of the chloroplast is still largely unknown

An ancestor of modern plants internalized a photosynthetic prokaryote through phagocytosis

The chloroplast was a cluster of synthesized proteins, which evolved over time

A vacuole became specialized for photosynthesis

Correct answer:

An ancestor of modern plants internalized a photosynthetic prokaryote through phagocytosis

Explanation:

The chloroplast is believed to have evolved from photosynthetic bacteria that formed a mutualistic symbiotic relationship with an ancestor of plants through endosymbiosis. There is lots of evidence supporting the endosymbiotic theory, which is based on the principle of one organism phagocytosing another, resulting in mutualism.

Example Question #1 : Plant Evolution

Mutualistic relationships between angiosperms and biotic pollinators foster which of the following types of evolution?

Possible Answers:

Co-evolution

Divergent evolution

Speciation

Convergent evolution

Correct answer:

Co-evolution

Explanation:

Biotic pollinators, such as bees and hummingbirds, share a mutualistic relationship with angiosperms. This leads to co-evolution, in which the selective pressure of one species impacts the genetic composition of another. In this case, the preferences of the pollinators impact the reproductive success of specific angiosperms.

Example Question #1 : Understanding Alternation Of Generations

Fill in the blanks.

The __________ generation is dominant in the bryophyte life cycles, and the __________ generation is dominant in seedless vascular plants.

Possible Answers:

gametophyte . . . sporophyte

gametophyte . . . gametophyte

sporophyte . . . sporophyte

sporophyte . . . gametophyte

Correct answer:

gametophyte . . . sporophyte

Explanation:

Bryophytes are nonvascular plants, such as mosses. Gametophytes are species that have haploid cells during their mature lives, while sporophytes are predominantly diploid during their adult phases.

Bryophytes have the gametophyte generation as dominant, with the sporophytes relying on the parental gametophyte. Starting with the evolution of seedless vascular plants, the gametophytes become reduced and are no longer the dominant life cycle. By the formation of angiosperms (seed plants), the gametophytes have become dependent on the parental sporophyte. 

Example Question #1 : Understanding Vascular And Avascular Plants

Which of the following structures would be found in a tracheophyte, but not in a bryophyte?

Possible Answers:

Chloroplasts

Xylem

Cell walls

Plasmids

Correct answer:

Xylem

Explanation:

All plants can be classified as either bryophytes or tracheophytes. Plants that contain transport vessels (xylem and phloem) are tracheophytes, while those without transport vessels are bryophytes. All plants contain cell walls and chloroplasts, but only a tracheophyte would contain xylem. Plasmids are structures that are almost exclusively found in bacteria or protozoans.

Example Question #2 : Understanding Vascular And Avascular Plants

Which of the following is not an example of an advantage gained through the vascularization of plants?

Possible Answers:

Swimming sperm

Larger photosynthetic area

Extensive root and shoot systems

Dominant sporophyte generation

Large size

Correct answer:

Swimming sperm

Explanation:

Swimming sperm is a feature of avascular and early vascular plants, who needed to remain in moist environments in order to retain water. 

After gaining vascular systems, plants were able to circulate water and nutrients more efficiently, thus being able to grow larger, have more leaves, develop branched systems of roots and shoots to collect water and nutrients, and better dispersal of spores due to gains in size. 

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