Leaves Tissues of leaves and their function

Palisade mesophyll – consists of densely packed cylindrical cells with many chloroplast. This is the main photosynthetic tissue and is positioned near the upper surface where the light intensity is highest

Upper epidermis – a continuous layer of cells covered by a thick waxy cuticle. Prevents water loss from the upper surface even when heated by sunlight. Lower epidermis is in a cooler position and has a less thick waxy covering

Note stomata on epidermis Note stomata on epidermis. The stomata is a pore that allow carbon dioxide for photosynthesis to diffuse in and oxygen out

Xylem – brings water to replace losses due to transpiration

Phloem – transports products of photosynthesis out of leaf. Both xylem and phloem are called the vascular system of plants. The vein is centrally located to be close to all cells.

phloem

Transport in phloem Phloem is located inside leaves. Used to transport sugars, amino acids, and other organic compounds from photosynthesis. Structures called sieve tubes do the transporting. This is an active process requiring ATP High concentration in sieve tubes of solute cause water to move in by osmosis

This creates a high enough pressure for movement where ever the plant needs these products. The transport of any biochemical (includes sprayed on chemicals) in phloem is called translocation. Sugar Transport in Plants

Transpiration Flow of water from the roots, through the stems to the leaves of plants (transpiration) Starts with evaporation of water from the cell walls of spongy mesophyll. Water is replaced with water from the xylem

Xylem and transport of water Google Image Result for http://www.phschool.com/science/biology_place/labbench/lab9/images/xylem.gif

Structure of xylem

Factors which affect transpiration Light – closed guard cells in stomata in darkness Temperature high temp increase rate of diffusion through air spaces in spongy mesophyll Humidity – movement by osmosis requires water potential gradient. Low humidity increases transpiration Wind blows saturated air away from leaf thus increasing transpiration

Food storage in plants The excess products of photosynthesis may be stored in storage area called tubers.

Roots

Roots absorb mineral ions and water from the soil Anchor the plant and are sometimes used for food storage Plants: Transport and Nutrition - Water Movement

Mineral uptake by roots Plants absorb potassium, nitrate and other mineral ions Concentration is lower than inside roots = active transport Root hairs provide surface area for ion uptake