Leaf StructureCambridge IGCSE Biology: Flashcards

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What are the two key physical adaptations of most leaves that make them suitable for photosynthesis?

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What are the two key physical adaptations of most leaves that make them suitable for photosynthesis?: Most leaves have a large surface area and are thin. The large surface area maximises light absorption and gas exchange, whilst being thin reduces the diffusion distance for gases and increases light penetration to photosynthetic cells.
Define the cuticle in a leaf.: The cuticle is a waxy, transparent layer on the outer surface of the upper epidermis that reduces water loss through evaporation and provides protection.
Name the two epidermal layers in a dicotyledonous leaf.: The upper epidermis and the lower epidermis. The upper epidermis is exposed to light, whilst the lower epidermis is in contact with the atmosphere beneath the leaf.
What are stomata and where are they located?: Stomata are small pores in the leaf surface that allow gaseous exchange. They are located predominantly in the lower epidermis of dicotyledonous leaves, reducing water loss whilst maintaining gas exchange.
Define guard cells and explain their function.: Guard cells are specialised cells that surround each stoma. They control the opening and closing of stomata by changing shape, regulating the entry of carbon dioxide for photosynthesis and the loss of water vapour.
Identify the two types of mesophyll tissue in a dicotyledonous leaf.: Palisade mesophyll and spongy mesophyll. Palisade mesophyll is packed tightly beneath the upper epidermis for efficient light absorption. Spongy mesophyll is loosely packed with air spaces for gas diffusion.
Describe the structure and location of palisade mesophyll.: Palisade mesophyll consists of tightly packed, cylindrical cells arranged in columns beneath the upper epidermis. These cells contain numerous chloroplasts and are adapted for maximum light absorption and photosynthesis.
Explain the importance of air spaces in spongy mesophyll.: Air spaces in spongy mesophyll allow gases (carbon dioxide and oxygen) to diffuse between the stomata and the photosynthetic cells, ensuring efficient gas exchange throughout the leaf.
What are vascular bundles and what do they contain?: Vascular bundles are transport tissues in the leaf. They contain xylem, which transports water and mineral ions, and phloem, which transports sugars produced during photosynthesis.
Define xylem in the context of leaf structure.: Xylem is vascular tissue that transports water and dissolved mineral ions from the roots to the leaves, ensuring photosynthetic cells remain turgid and have adequate water for photosynthesis.
Define phloem in the context of leaf structure.: Phloem is vascular tissue that transports sucrose and other organic compounds produced during photosynthesis from the leaves to other parts of the plant.
Where are chloroplasts found in a leaf and why?: Chloroplasts are found in the palisade mesophyll and spongy mesophyll cells, with greatest concentration in palisade mesophyll. This location maximises light absorption for photosynthesis.
Explain how the large surface area of a leaf is an adaptation for photosynthesis.: A large surface area increases the amount of light that can be absorbed and the number of chloroplasts exposed to light, maximising the rate of photosynthesis.
Explain how the thinness of a leaf is an adaptation for photosynthesis.: Being thin reduces the diffusion distance for carbon dioxide to reach photosynthetic cells and allows light to penetrate through to the lower mesophyll layers, increasing overall photosynthetic efficiency.
Explain how the location of stomata on the lower epidermis is an adaptation for photosynthesis and water conservation.: The lower epidermis receives less direct sunlight, so stomata located there reduce water loss through transpiration. They still allow sufficient carbon dioxide entry for photosynthesis whilst minimising evaporation.