Plant Biology

What happens to surface area-to-volume ratio as organisms increase in size?

It decreases, making exchange of materials more difficult.

Define gas exchange.

The process by which organisms obtain oxygen and release carbon dioxide across a surface.

What is the role of diffusion in gas exchange?

Diffusion allows gases to move from areas of high concentration to low concentration across membranes.

Why do larger organisms need specialized structures for gas exchange?

Because their surface area-to-volume ratio is smaller and diffusion alone is insufficient to meet metabolic demands.

What is the function of permeability in gas-exchange surfaces?

It allows gases to diffuse easily through membranes.

Why must gas-exchange surfaces have a thin tissue layer?

To reduce diffusion distance and increase efficiency.

Why must gas-exchange surfaces be moist?

Moisture allows gases to dissolve and diffuse across membranes more easily.

Why is a large surface area important for gas exchange?

It increases the amount of gas that can be exchanged at one time.

List structural adaptations in leaves for gas exchange.

Waxy cuticle, epidermis, air spaces, spongy mesophyll, stomatal guard cells, and veins.

In what direction do gases move during leaf gas exchange?

Carbon dioxide moves in, oxygen and water vapor move out.

What is the function of stomatal guard cells?

They control the opening and closing of stomata to regulate gas exchange and water loss.

What does a plan diagram of a leaf show?

It shows the distribution of tissues, not individual cells.

Which tissues should be labeled in a transverse section of a dicot leaf?

Upper and lower epidermis, palisade and spongy mesophyll, xylem, and phloem.

Define transpiration.

The loss of water vapor from plant leaves through stomata.

What is the relationship between water evaporation and transpiration?

Evaporation from cell surfaces drives transpiration from leaves.

How do temperature and humidity affect transpiration rate?

Higher temperature increases transpiration; higher humidity decreases it.

Why do plants open and close stomata at different times of day?

To balance gas exchange with water conservation.

How is stomatal density determined?

By counting stomata per area in leaf casts or micrographs.

How do you calculate stomatal density?

Divide the number of stomata by the area of the field of view.

What is the purpose of repeated counts in stomatal density studies?

To improve reliability and account for biological variability.

What tissue transports water from roots to leaves?

Xylem.

What role does cellulose play in water transport?

It provides microscopic capillary spaces that aid capillary action.

What causes transpiration pull?

Water loss by transpiration creates tension that draws water upward in xylem.

Why is cohesion between water molecules important?

It maintains a continuous column of water in the xylem.

Is transpiration an active or passive process?

It is a passive process.

How are xylem vessels adapted for water transport?

They have lignified walls, no cytoplasm, and open ends for unimpeded flow.

How does lignin help xylem function under low pressure?

It provides strength and prevents vessel collapse.

Which tissues should be labeled in a stem plan diagram?

Vascular bundles, xylem, phloem, cambium, cortex, pith, and epidermis.

What are the functions of xylem and phloem in a stem?

Xylem transports water and minerals; phloem transports sugars and nutrients.

How can xylem and phloem be differentiated in a stem cross-section?

Xylem is inside and has thicker walls; phloem is outside and has thinner walls.

Which tissues should be labeled in a root plan diagram?

Vascular bundles, xylem, phloem, cortex, and epidermis.

What are the functions of xylem and phloem in a root?

Xylem transports water upward; phloem transports sugars from leaves to roots.

How can xylem and phloem be differentiated in a root cross-section?

Xylem forms a central star shape; phloem is between the arms of the star.

Outline the lifecycle stages of flowering plants.

Gamete formation, pollination, fertilization, embryo formation, seed development, germination.

Where are gametes produced in flowering plants?

In ovules (female) and pollen grains (male).

What is the difference between pollination and fertilization?

Pollination is transfer of pollen to stigma; fertilization is fusion of gametes.

List structures to label in an insect-pollinated flower.

Petals, sepals, stamens, anthers, filaments, pollen, carpel, stigma, style, ovary, ovule.

What is the function of petals in insect-pollinated flowers?

They attract pollinators with color and scent.

Why are flowers homologous structures?

They have similar origins and structures despite functional differences.

Define cross-pollination.

Transfer of pollen from one plant to the stigma of another plant of the same species.

What are the benefits of cross-pollination?

It increases genetic diversity and reduces inbreeding.

List mechanisms promoting cross-pollination.

Different maturation times of pollen and stigma, separate male and female flowers, or use of animals or wind.

Why is self-pollination generally avoided?

It leads to inbreeding and reduced genetic diversity.

How do plants prevent self-pollination?

Through self-incompatibility mechanisms that prevent pollen from fertilizing the same plant.

What is the difference between seed dispersal and pollination?

Pollination transfers pollen; seed dispersal spreads seeds away from the parent plant.

What is the function of a seed?

To protect and nourish the embryo during dormancy and dispersal.

List mechanisms of seed dispersal.

Wind, water, animals, and mechanical ejection.

Define germination.

The process by which a seed develops into a new plant.

Why are water, oxygen, and warmth needed for germination?

Water activates enzymes, oxygen supports respiration, and warmth speeds metabolism.

What is the role of gibberellin during germination?

It stimulates enzyme production for mobilizing food reserves in the seed.