[BIO] Chapter 6 - Transport in Flowering Plants

© Hee Xin Wei (Copyrighted) Topic 6: Transport in Plants

Chapter Analysis FOCUS EXAM WEIGHTAGE •straightforward chapter •incorporate knowledge from previous chapter •Constitute to around 5% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions

Xylem Phloem Translocation Key Concept

V ascular Bundle Xylem Structure Function Adaptation -Xylem cells are dead at maturity -Xylem vessels are long and hollow tubes that are made of xylem cells Transport water and mineral salts from the roots to the leaves Absence of protoplasm and cross-walls which could impede water flow through the lumen -Inner walls of vessels are deposited with lignin in different shapes Mechanical support for the plant Deposition of lignin on the cell walls which strengthens vessel walls, providing support

V ascular Bundle Phloem Structure Adaptation •Sieve tube elements have degenerate protoplasm, they have no organelles such as the nucleus or vacuole •There are porous walls between sieve tube elements called sieve plates Pores in sieve plates allow uninterrupted flow of food substances through the sieve tubes •one companion cell is closely associated with each sieve tube element, which contains organelles and support the the metabolic functions of the sieve tube elements. •Companion cells have many mitochondria Companion cells contain mitochondria that can carry out respiration and release energy for active transport of manufactured food substances from photosynthesis Function: Transport sugars and amino acids from the leaves to other parts of the plant. A phloem is made up sieve tube elements and companion cells

Position of vascular bundle Epidermis Cortex Phloem Cambium Xylem Vascular bundle in dicotyledonous rootsVascular bundle in dicotyledonous stems

Translocation •Translocation is the transport of sugars from the leaves to other parts of the plant via the phloem tissues. •The source of sugars is the leaves, which is the site of photosynthesis, while other parts of the plant which require sugar are known as the sink. •Energy is required for this process as the mode of uptake of sugars into sieve tube elements in the leaves is active transport. •At the end of the sieve tube where sugars are being unloaded for use, sugars are also removed from the sieve tube by active transport. 1.In the ringing experiment, a ring of bark that contains the phloem is removed, exposing the xylem. When sugar is transported from the leaves to the roots, it cannot move beyond the cut, leading to a bulge to form on top of the cut. The bulge is due to accumulation of sugar and retention of water 2.Aphids can be used to collect sap. When an aphid is introduced to a plant, it knows where to insert its proboscis into the phloem sieve tubes to feed on the sucrose.

Root Hair Transpiration Key Concept

Root Hair Function: Water and ion uptake by root hair Structure and adaptations •Root hairs are long and narrow, thus increasing surface area to volume ratio for rapid absorption of water and minerals. •The cell sap contains sugars, amino acids and mineral salts which makes the water potential of cell sap lower than that of soil solution Water uptake 1.Soil particles are usually coated with water and dissolved mineral salts. 2.The cell sap in the root hair cells contains sugars and ions thus it has a lower water potential than soil solution 3.Water enter root hair cells from the soil by osmosis. 4.The cell sap of the root hair cell now has a higher water potential than the cell sap in the adjacent cells, thus water moves across to the adjacent cell by osmosis 5.This process continues until the water enters the xylem vessels and moves up the plant. Ions and mineral salts uptake •When the concentration of ions and mineral salts in the soil solution is lower than that in the root hair cell sap, they are absorbed by active transport •when the concentration of certain ions in the soil solution is higher than that in the root hair cell, they move into the root hair cells by diffusion

Root Pressure Water travels from the roots to the leaves against gravity through 3 primary mechanisms: 1.Root pressure •Root hair cells pump mineral salts into the xylem vessels using active transport. This lowers the water potential of the xylem vessels, thus water moves from the surrounding cells into the xylem vessels by osmosis, creating a pressure that forces water to move upwards •Not the main mechanism for movement of water in most plants as it can only force water to travel a short distance.