6 th Year Biology Higher Level Wesley Hammond Structure and Transport of a Flowering Plant No part of this publication may be copied, reproduced or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from The Dublin School of Grinds. Ref: 6/bio/h/wh/ StructureandTransportFloweringPlants
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Contents Structure of a Flowering Plant: Structure of a Flowering Plant. 3 Leaf Venation..4 Structure of a Stem..5 Structure of a Root...6 Zones of a Root...7 Xylem...8 Phloem. 9 Location of Plant Tissue in Roots.10 Location of Plant Tissue in Stems 11 To prepare and examine a transverse section (TS) of a dicot stem.12 Exam Questions...14 Structure of a Flowering Plant: 2004, 2006, 2007, 2008, 2009, 2012, 2014. Transport in a plant: 2004, 2005, 2006, 2008, 2011, 2014. (C) The Dublin School of Grinds Page 2 Wesley Hammond
Structure of a flowering plant: Leaves: Leaves are attached to the stem at the node. Stalk of leaf is called the petiole. Flat part of leaf is known as the blade or lamina. (C) The Dublin School of Grinds Page 3 Wesley Hammond
Leaf Venation: 1) Parallel venation: Veins run alongside each other. Found in monocot plants (grasses, daffodils) 2) Net or reticulate venation: Veins have branching pattern. Found in dicots (horse chesnut, rose and buttercup) Function of the leaves: They can make food (photosynthesis). They exchange gases with the atmosphere (carbon dioxide and oxygen) Leaves store food (Lettuce) Leaves lose water to allow for transpiration. Stem: Herbaceous plants do not contain wood (no lignin) Woody plants contain wood(have lignin) The part of the stem between two nodes is called an internode. The tip of the stem has an apical bud (terminal bud) The apical bud has a meristem which allows the stem to grow upwards. The auxillary (lateral bud) produces new growth such as branches or flowers. (C) The Dublin School of Grinds Page 4 Wesley Hammond
Structure of a stem: NOTE: Lenticel is an opening for gas exchange found in stems of plants. Functions of a stem: 1) Support the aerial parts of the plant. 2) Transport water and minerals from the roots to the leaves. 3) Transport food from the leaves to the roots 4) Carry out photosynthesis (if it is green) 5) May store food (C) The Dublin School of Grinds Page 5 Wesley Hammond
A closer look at the structure of a stem: A = apical bud B = Leaf scar C = Scale scar D = Lateral bud NOTE: A scale scar shows the location of the previous apical bud (distance between the scale scars indicates the amount of growth that year). How old is the stem above? 4 years Types of roots: 1) Tap roots 2) Fibrous roots Roots Tap Roots: Tap roots consist of a main root called the primary root or tap root. Secondary roots appear from the tap root. Found in dicots (dandelions ash trees) Fibrous roots: Consist of lots of equally sized roots. Found in monocots (grasses and daffodils) (C) The Dublin School of Grinds Page 6 Wesley Hammond
Functions of roots: 1) Anchors the plant in the soil 2) Absorbs water and minerals from the soil through its root hairs. 3) Store food in some plants (carrots and turnips) What are the zones in a root? 1) Zone of protection 2) Meristematic zone (cell production) 3) Zone of elongation 4) Zone of diiferentiation Zone of protection: Root caps protect the root cells as they grow in the soil. Meristematic zone (Cell production): This zone allows the roots to grow by producing new cells. A meristem tissue is capable of mitosis. Meristems are found in the shoot tip and root tip. Zone of elongation: The cells in this zone grow longer by using plant growth regulators (auxins). Zone of differentiation: Consist of three different types of tissue: 1) Dermal tissue: protects the plant. (C) The Dublin School of Grinds Page 7 Wesley Hammond
2) Ground tissue: support and photosynthesis (Found between the dermal tissue and vascular tissue). 3) Vascular tissue: has xylem and phloem which transports materials. Xylem transports water and minerals. Note: Xylem is narrow to help the transport water. Phloem transports food. A detailed look at the structure of xylem tissue: Xylem tracheids: Long Tapering Hollow Have pits The pits allow water and minerals to move from cell to cell. NOTE: Found in coniferous trees. Xylem vessels: Tubular They have a continuous tube Have pits (C) The Dublin School of Grinds Page 8 Wesley Hammond
Features of Xylem: Have lignin (gives strength) NOTE: Lignin forms wood in trees. Function: transport water and minerals. Location: found in stems, leaves, roots and flowers. A detailed structure of phloem tissue: Consists of sieve tubes and companion cells. Sieve tubes: Long, tubular, with no nucleus Companion cells: Have a nucleus which controls the activities of a sieve tube and the companion cell. Note: Xylem and phloem are found in vascular bundles in the leaf and stem. Differences between xylem and phloem (C) The Dublin School of Grinds Page 9 Wesley Hammond
Location of plant tissues in roots: The phloem and xylem are located at the centre of root. Dermal tissue is found on the outside epidermis layer on the root and root hairs. What is an easy way to distinguish the TS of a root compared to TS of a stem? The root has root hairs. LS of a stem: Location of plant tissue in stems: TS of dicot stem (C) The Dublin School of Grinds Page 10 Wesley Hammond
Vascular bundles in stem (xylem and phloem): What is a cotyledon? Monocotyledons and Dicotyledons A cotyledon is a seed leaf which stores food for the seed. Monocots : daffodils, tulips, grasses and cereals Dicots : beans, peas, peanuts, sunflowers, roses, oak tree and ash tree. Differences between monocots and dicots (C) The Dublin School of Grinds Page 11 Wesley Hammond
To prepare and examine a transverse section (TS) of a dicot stem 1) Pick a non woody herbaceous plant which has a soft stem (e.g. sunflower, begonia) It is easier to cut. 2) Cut a short section of stem between two nodes using a scalpel. 3) Wet blade (reduces friction) and cut thin sections of the stem (cut away from finger to prevent injury) 4) Cut sections at right angles to the stem. Note: use a silt in some elder or carrot in case stem needs to be held into place. 5) Store sections in a clock glass with water (prevents stem from dehydrating). 6) Place a thin section of stem onto a microscope slide using a forceps or paint brush (allows light to pass through it easier). 7) Add a cover slip to slide at angle (eliminates bubbles). (C) The Dublin School of Grinds Page 12 Wesley Hammond
8) Observe the slide under low power (x 100) and then under higher power (x 400). NOTE: you could use a stain (iodine) to make them more visible. Results: (C) The Dublin School of Grinds Page 13 Wesley Hammond
Exam Questions: Exam paper 2004, Question 8: (C) The Dublin School of Grinds Page 14 Wesley Hammond
Solutions 2004, Question 8: Exam Paper 2006, Question 14c: (C) The Dublin School of Grinds Page 15 Wesley Hammond
Solutions 2006, Question 14c: Exam Paper 2007, Question 6: (C) The Dublin School of Grinds Page 16 Wesley Hammond
Solutions 2007, Question 6: Exam paper 2008, Question 14c: Solutions 2008, Question 14c: Exam Paper 2009, Question 7: (C) The Dublin School of Grinds Page 17 Wesley Hammond
Solutions 2009, Question 7: (C) The Dublin School of Grinds Page 18 Wesley Hammond
Exam Paper 2012, Question 5: Solutions 2012, Question 5: (C) The Dublin School of Grinds Page 19 Wesley Hammond
Exam Paper 2014, Question 12: Solutions 2014, Question 12: Exam Paper 2014, Question 14b: (C) The Dublin School of Grinds Page 20 Wesley Hammond
Solutions 2014, Question 14b: (C) The Dublin School of Grinds Page 21 Wesley Hammond
Transport in a Flowering Plants (C) The Dublin School of Grinds Page 22 Wesley Hammond
Why plants need transport? Plants need to be able to transport water, carbon dioxide, oxygen and minerals. How do roots of plants take in water from the soil? Root hairs absorb water by osmosis. NOTE: Osmosis is the movement of water across a semi permeable membrane from a region of high water concentration (in the soil) to a low water concentration (in the root). How are root hairs adapted for water absorption? Root hairs have thin walls (helps them to absorb water). Root hairs occur in large numbers (large surface area). (C) The Dublin School of Grinds Page 23 Wesley Hammond
Movement of water into xylem: Water diffuses from the root hair into the ground tissue. It then diffuses from ground tissue into the xylem in centre of root. How do the roots of plants absorb minerals? Plants require minerals to function (calcium, magnesium) Minerals are absorbed from the soil by root hairs in a process called active transport (requires energy) Root hairs have lots of mitochondria to supply energy. How does water move up through a plant in the xylem? Water moves up through a plant in two different ways: 1) Root pressure 2) Transpiration Root pressure Water taken in by the roots by osmosis causes a build up of water pressure. This root pressure pushes water up through the xylem Note: Does not fully explain how water travels up large trees (C) The Dublin School of Grinds Page 24 Wesley Hammond
Transpiration: Transpiration is the loss of water vapour from the leaves of the plant. Transpiration occurs through the stomata of a leaf (openings on the under side of a leaf). How the Cohesion Tension model helps explain transpiration and the upward movement of water: Cohesion Tension model Allows large amounts of water to move quickly from roots to leaves in warm conditions. Can move 220 litres in one hour up through a plant. This model was put forward by Henry Dixon and John Joly (Irish Scientist in Trinity College). Cohesion: the sticking of water molecules to each other. Adhesion: when different molecules stick together (water sticks to the wall of the xylem) Steps involved in the Cohesion Tension model: 1) Water evaporates from the xylem out through the stomata into the air (transpiration). 2) During transpiration each water molecule is pulled through the xylem. 3) Due to cohesion the next water molecule is pulled along by the one in front of it. 4) Xylem are adapted for movement of water because they are narrow. (C) The Dublin School of Grinds Page 25 Wesley Hammond
5) When the water column in the xylem is stretched it is said to be under tension. How is xylem adapted for transporting water? It is narrow. It has lignin. Has pits. Control of transpiration in leaves 1) Leaves have cuticle which does not allow water to pass through (cuticle thicker on upper surface as this side is exposed to the sun) 2) Stomata are located on lower surface of leaf to reduce water loss (more evaporation would occur on upper surface). (C) The Dublin School of Grinds Page 26 Wesley Hammond
3) Each stomata is surrounded by two guard cells. The stomata can open or close by the guard cells changing shape. NOTE: Stomata are normally open during the day to allow gas exchange for photosynthesis. They close at night to reduce water loss. The following environmental factors affect stomata opening or closing: 1) Plants lose too much water 2) High temperatures 3) High wind 4) Carbon dioxide concentration NOTE: Plants do not grow well in dry conditions because the stomata will remain closed for long periods. How does CO2 concentration control stomata opening or closing? High concentration of CO2: High levels of CO2 cause stomata to close. Photosynthesis rate decreases in the evening causing the build-up of CO2. Low concentration of CO2: Low levels of CO2 cause the stomata to open. When photosynthesis begins in the morning CO2 is absorbed by the mesophyll cells (ground tissue). (C) The Dublin School of Grinds Page 27 Wesley Hammond
SUMMARY: High concentration of CO2 Low concentration of CO2 Stomata close Stomata open How do stomata open or close? Guard cells open and close the stoma by changing shape. When water enters the guard cell by osmosis, they swell and become turgid. This causes the guard cells to buckle outwards creating a gap between the guard cells. When the guard cells lose water they shrink, which causes the stoma to close. Carbon dioxide: Gas exchange in a leaf: Stomata helps with gas exchange. Large number of stomata increases the amount of gas exchange. Carbon dioxide diffuses into the mesophyll of the leaf (ground tissue where photosynthesis takes place) Oxygen: Oxygen diffuses from the mesophyll of leaf into the air spaces and out of the stomata. Water vapour: Water vapour also diffuses out of the leaf through the stomata (transpiration) (C) The Dublin School of Grinds Page 28 Wesley Hammond
Gas exchange in stems: Lenticels are opening in the stem that allow gas exchange. Normally oxygen diffuses inwards through a lenticels (needed for respiration) and carbon dioxide diffuses outwards. Food storage organs in plants: Modified roots: Dicot plants can have large tap roots to store food (starch). This food is used to produce flowers, seeds and fruits. Example: Carrots, Turnips Modified stem: Potato plants produce an underground stem to store food (starch). These swollen stems are called tubers. Modified leaves: Onions, daffodils and tulips all produce a bulb. What is a bulb? A bulb is an underground stem that has swollen fleshy leaves to store food. The bulb is protected by a dry scaly leaf on the outside. (C) The Dublin School of Grinds Page 29 Wesley Hammond
Exam Paper 2004, Question 4: (C) The Dublin School of Grinds Page 30 Wesley Hammond
Solutions 2004, Question 4: Exam Paper 2005, Question 14a: (C) The Dublin School of Grinds Page 31 Wesley Hammond
Solutions 2005, Question 14a: Exam Paper 2006, Question 11c: Solutions 2006, Question 11c: (C) The Dublin School of Grinds Page 32 Wesley Hammond
Exam Paper 2008, Question 14a: Exam paper 2008, Question 14a: Exam Paper 2011, Question 15b: (C) The Dublin School of Grinds Page 33 Wesley Hammond
Solutions 2011, Question 15b: Exam Paper 2014, Question 12: (C) The Dublin School of Grinds Page 34 Wesley Hammond
Solutions 2014, Question 12: Exam Paper 2014, Question 14c: (C) The Dublin School of Grinds Page 35 Wesley Hammond
Solutions 2014, Question 14: (C) The Dublin School of Grinds Page 36 Wesley Hammond