Plant Organs Stems: Structure & Function Transport in Plants 1 Structure, Functions & Adaptations

Stems: Types Herbaceous Woody Growth Die at the end of a growing season (annuals) Grow larger every growing season (Trees and shrubs) Colour Green Bark Example Ferns & grass Oak, Maple, & Pine

Stems: function 1. Support - for leaves and reproductive structures (more support is offered by woody stems than by herbaceous) 2. Transport - vascular system (xylem & phloem) 3

Structure of stems

Internal structures Vascular Tissue Cambium - between xylem & phloem - forms the rings in trees - divides to form secondary xylem & phloem Epidermis - outer covering - single layer in herbaceous stems - multi-layered in woody stems Pith & Cortex - made of parenchyma tissue

Do you know? Tree rings are made from the growth of secondary xylem (Cambium)!

Vascular Tissue Xylem Hollow Vessels (like straws) Joined end to end End walls are perforated Secondary xylem is thickened with LIGNIN

Vascular Tissue Phloem Hollow tubes connected end to end with perforations at the end (sieve tubes) Companion cells carry out life functions to maintain both types of cells

Transport Structures Leaf Stem Root Xylem Phloem Xylem Xylem Phloem

https://www.youtube.com/watch?v=MxwI63rQubU

Root Stem Leaves 11

Early Transport (mosses) NO VASCULAR SYSTEM PASSIVE TRANSPORT: when particles move down the concentration gradient (High - Low) DIFFUSION: movement of particles from an area of high concentration to an area of lower concentration OSMOSIS: the movement of water molecules across a membrane 12

How water gets in the Roots? - Roots have a higher concentration of nutrients than the water outside the root - Water moves into the root (down the concentration gradient)

How Water Moves UP Against Gravity 1 - Pushing water up * Root pressure 2 - Pulling water up * Transpiration, cohesion, adhesion

Pushing water UP - Root Pressure Once water moves into the root cortex pressure is exerted on the fluid in the xylem and pushes it upward Some water moves from the cortex into the xylem More water is absorbed by the root hairs 15

Root Pressure

Pulling Water UP (Cohesion-Tension Model) A. Transpiration - water evaporation from leaves ~ 100 L / day - exerts tension on the water attached in the xylem tubes C. Adhesion - water molecules stick to the xylem walls B. Cohesion - force of attraction between water molecules

A variety of physical processes are involved in the different types of transport TRANSPIRATION, the loss of water from leaves, creates a force within leaves that pulls xylem sap upward. 3 CO2 O2 Light H2O Sugar Sugars are produced by photosynthesis in the leaves. Source to Sink explains how it is carried DOWN the phloem 4 COHESION and ADHESION work to carry water molecules up from the roots to the leaves. 2 OSMOSIS - Roots absorb water and dissolved minerals from the soil. 1 O2 H2O CO2 Minerals Figure 13.22 (page 563)

Transport of Sugar through Phloem Photosynthesis in the leaves produces GLUCOSE Translocation is the process of transporting glucose to all other parts of the plant, through the phloem Source to Sink http://www.youtube.com/watch?v=- b6dvKgWBVY