Transpiration

Plant Structure Terms: Epidermis – Skin or layer on the outside. Vascular Tissue – components required to help transport nutrients and water through the plant. Seeds – Used for reproduction. Leaf – Contains chlorophyll used for photosynthesis. Roots – Absorbing nearby nutrients. Root Hair – Increase surface area. Rapid absorption. Root Cap – harder substance, with a low area to penetrate the soil and go deeper.

Photosynthesis Formula for photosynthesis: Carbon dioxide + Water + Sun  Glucose + Oxygen

Photosynthesis  Plants produce their very own food source from the photosynthetic process. The products of photosynthesis include: Oxygen and Glucose Oxygen might be a waste product for the plant, but helps sustain life for us! Glucose is a simple sugar – food source!

Stomata – microscopic pores found on the under side of leaves Xylem Vessel – tube like structures running from the bottom of the stem (roots) to the top of the plant. Guard cells – a mechanism which opens and closes (or controls) the rate at which vapour exits. Capillary Action in the plant roots.

Images of Stomata

Stomata Functions  Opening/Closing Stomata - allows CO2 to diffuse into the leaf - water vapor to diffuse out of the leaf. Located under the leaf. If it were on the top side the plant would lose to much water. Guard cells are partially light activated, plants under direct sunlight would constantly have their stomata open – letting out to much water which could dry the plant.

Capillary Action Xylem: Carries water and dissolved minerals up from the roots through the stem to the leaves and provides support for the softer tissues.

Comparing Xylem and Phloem

How might we measure or test for transpiration within a plant? With the person next to you or in your groups. Discuss ways in which we could test and/or measure the rate of transpiration within plants.

Measuring Transpiration

Potometer A potometer is a device that measures the rate at which a plant draws up water. Since the plant draws up water as it loses it by transpiration, you are able to measure the rate of transpiration.

Factors that affect the rate of transpiration  Light  Wind  Temperate  Humidity  Soil Water

Light Affecting Transpiration  Light Plants transpire more rapidly in the light than in the dark. This is largely because light stimulates the opening of the stomata. Light also speeds up transpiration by warming the leaf.

Wind Affecting Transpiration  Wind When there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration. When a breeze is present, the humid air is carried away and replaced by drier air.

Temperature Affecting Transpiration  Temperature Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast as it does at 20°C.

Soil Water Affecting Transpiration  Soil Water When absorption of water by the roots fails to keep up with the rate of transpiration, the stomata close. This immediately reduces the rate of transpiration. Since water is also used to maintain the structure of a plant, it can begin to wilt when water is lost rapidly.

Example of Wilting Plants

Plant Adaptations  Desert plants must reduce their loss of water by; Containing smaller stomata, but also reduce the total number of their stomata. Containing smaller stomata, but also reduce the total number of their stomata. Some species only open their stomata during night, which reduces the amount of water lost (due to colder temperatures). Some species only open their stomata during night, which reduces the amount of water lost (due to colder temperatures).

Plant Adaptations  Leaf surface area  Leaf surface area  Thickness of epidermis  Thickness of epidermis  Stomatal frequency  Stomatal frequency  Stomatal size  Stomatal size  Stomatal position