Leaf structure: Practice Questions

• a.Palisade mesophyll cells: located near the top of the leaf and packed with many chloroplasts.
• b.Guard cells: tightly packed to prevent any gas exchange from occurring in the spongy mesophyll.
• c.Cuticle: a thick, opaque layer that absorbs most of the light energy for the plant.
• d.Upper epidermis: contains a high density of stomata to maximize the intake of carbon dioxide.

• a.It is a waxy layer on the outer surface that reduces water loss by evaporation while remaining transparent.
• b.It is a protein-based coating that actively absorbs carbon dioxide from the surrounding air.
• c.It is a cellular layer located between the epidermis and mesophyll that stores starch grains.
• d.It is found only on the lower surface to prevent the entry of pathogens through the stomata.

• a.They allow for the efficient diffusion of gases to and from the mesophyll cells.
• b.They provide structural support to keep the leaf from wilting during the day.
• c.They act as a reservoir for liquid water to be used in the light reactions.
• d.They help the leaf float on water to reach higher light intensities.

• a.Open stomata allow carbon dioxide to enter and diffuse through the air spaces of the spongy mesophyll to reaching the photosynthesizing cells.
• b.Stomata close to force the air spaces in the spongy mesophyll to increase in pressure, speed up sugar transport.
• c.The spongy mesophyll cells expand to push the stomata open, allowing more water to be absorbed from the atmosphere.
• d.Stomata only allow the exit of water vapour, while the spongy mesophyll handles the entry of carbon dioxide via the cuticle.

• a.Xylem brings water for photosynthesis; phloem removes manufactured sucrose to other parts of the plant.
• b.Xylem transports oxygen to the roots; phloem brings mineral ions up to the palisade cells.
• c.Xylem carries glucose away from the mesophyll; phloem provides mechanical strength through lignin.
• d.Xylem and phloem both transport water upwards to maximize the turgidity of the guard cells.

Write your answer out first, then check it against the worked solution.

Write your answer out first, then check it against the worked solution.