Leaf structure: แบบฝึกหัด

• 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.

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