The Need For Transport - plants Multicellular Organisms - Section 6

Surface area:volume ratio A single celled organism has a large surface area in relation to its volume - most of it’s body tissue is close to the surface - diffusion allows materials to get throughout the cell Larger organisms have much less of their inner tissue close to the surface - a transport system is needed to move substances to and from the surface

Learning Outcomes During this section you will be able to: - explain the need for transport systems in plants - describe the structures and processes involved in water and sugar movement - explain the processes of transpiration and evaporation * requires a review of photosynthesis from S3

Plant transport systems Plants need two transport systems 1) xylem for water transport - transports water from roots to leaves 2) phloem for sugar transport - transports sugar from leaves to the roots

Water transport in a plant Water enters plants by osmosis through root hair cells - root hair presents a large surface area Water then passes from cell to cell until it reaches the xylem The xylem transports the water to the mesophyll cells - where photosynthesis occurs

Exit of water Water is lost from a plant by transpiration Most water leaves through the stomata The guard cells get swollen (turgid) when water enters them This opens the stoma Allowing water to exit the plant - occurs during daylight

Experiment You will now carry out an experiment to assess what factors affect water loss (transpiration) the most Factors that could have an affect include: - wind - humidity - temperature