Transport in the Flowering Plant Chapter 18 Transport in the Flowering Plant

Plants are Autotrophic, they make their own food during Photosynthesis in the leaves.

Why do plants need a transport system? To provide the materials needed for various plant metabolic processes including Photosynthesis, Respiration , Growth and Reproduction

What materials are transported in plants Water Carbon dioxide Minerals Carbohydrates produced in photosynthesis Plant growth regulators

Water uptake Root epidermal cells absorb water by osmosis. Adaptations for absorption: Root hairs give a large surface area Have thin walls Don’t have a waxy cuticle The cell sap has a lower water concentration than soil water

Water uptake Root Hair Ground tissue Xylem Xylem form continuous hollow pipes from roots to leaf Water

Water movement through the root Water moves from the epidermal cells across the ground tissue of the cortex and into the xylem vessels.

Giant Redwoods The largest and oldest trees in the world A single mature giant redwood can draw 650,000 litres of water up through it in one season! How is this possible?

Upward movement of water Two mechanisms combine to cause upward movement of water through the stem in the xylem. They form a continuous hollow pipeline from the roots to the leaves.

Root pressure – When water is drawn into roots by osmosis the extra volume causes pressure to build up. This pressure pushes water up through the xylem Root Pressure

Transpiration - the loss of water vapour from the plant Transpiration - the loss of water vapour from the plant. As water evaporates from the leaf, more water is pulled upwards through the xylem into the leaf. Transpiration Transpiration.swf

Role of Transpiration Water evaporates from the leaf cells during transpiration – 99%. The cells become less turgid. The evaporation of water from the leaf cells causes more water to be pulled upwards as a contionus column to replace it through the xylem vessels. Animation of Transpiration stream

Water_movement

Learning check 1 Define Autotroph. Why do plants need a transport system? What materials are transported in plants? How are root hairs are adapted to the process of absorbing water? Outline the pathway taken by water into the plant. Name the two mechanisms combined to cause the upward movement of water through the stem in the xylem

The control of Transpiration Leaves need to replace the water they lose in transpiration or they may wilt and die. To prevent wilting plants need to control how much water they lose in transpiration.

Plasmolysis of plant cell

Presence or absence of a cuticle Leaves have a waxy cuticle through which water cannot pass – this is mainly on the upper side of a leaf as this side is more exposed and more water can evaporate here. Plant cuticles are a protective waxy covering produced only by the epidermal cells [1] of leaves, young shoots and all other aerial plant organs without periderm. The cuticle tends to be thicker on the top of the leaf, but is not always thicker in xerophytic plants living in dry climates than in mesophytic plants from wetter climates, despite a persistent myth to that effect. The cuticle is composed of an insoluble cuticular membrane impregnated by and covered with soluble waxes.

2. Opening and closing of the stomata Openings on the lower epidermis of leaves for gas exchange. Guard cells control the opening - increases water loss and the closing - reduces water loss of the Stomata.

Structure and working of Stomata

Summary of Transpiration

Adaptation How it works Example thick cuticle stops uncontrolled evaporation through leaf cells most dicots small leaf surface area less area for evaporation conifer needles, cactus spines low stomata density fewer gaps in leaves   stomata on lower surface of leaf only more humid air on lower surface, so less evaporation shedding leaves in dry/cold season reduce water loss at certain times of year deciduous plants

sunken stomata maintains humid air around stomata marram grass, pine stomatal hairs marram grass, couch grass folded leaves marram grass, succulent leaves and stem stores water cacti extensive roots maximise water uptake

When are stomata open and closed? Stomata open during the day when photosynthesis is taking place to allow water vapour out and CO2 in. Stomata close at night reducing water loss and CO2 intake as photosynthesis is not occurring. Animations showing movement of water during transpiration

Conditions when stomata close at day Two reasons stomata may close during the day: If the plant has lost too much water If temperatures are too high By closing stomata the plant reduces water loss. In dry conditions stomata remain closed for long periods, photosynthesis cannot occur and food crops are reduced.

Learning Check 2 What is Transpiration? Explain the role of Transpiration in water transport. What controls Transpiration? What controls the loss of water from leaf? 3 Methods of controlling transpiration are? When are stomata open and closed? Explain the role of Root pressure in water transport.

Cohesion-Tension Model of Xylem Transport

Need to Know How plants move water up to great heights against the force of gravity Know the contribution of Irish scientists Dixon and Joly to plant biology Understand the terms transpiration, cohesion, adhesion, tension, osmosis and use them to explain water movement up through xylem

Cohesion-Tension Model of Xylem Transport: explains how water is transported in plants to extreme heights against the force of gravity. Cohesion-Tension Model of Xylem Transport

Theory proposed by two Irish scientists Henry Dixon John Joly Working in Trinity College 1894

The cohesion-tension model of water transport in xylem Two Irish Scientists working in Trinity College Henry Dixon and John Joly put forward this model in 1894 Cohesion – the sticking of similar molecules to each other, water molecules stick to each other Adhesion – when different molecules stick together, water adheres to the walls of xylem but this force is not as great as the cohesive forces of water

Attraction between molecules Cohesion Similar molecules sticking together e.g. water sticking to water H O H O H O H O Attraction between molecules

Cohesion Animation showing Cohesion by hydrogen bonding in water

Adhesion Different molecules sticking together e.g. water sticking to xylem walls H O Attraction

The Cohesion – Tension model 1. Cohesion between water molecules in the narrow xylem tubes causes the water to form into a continuous column or stream in the xylem H2O H2O H2O H2O H2O

2. Water molecules evaporate due to transpiration at the leaf. Cohesion between the water molecules replaces the water by pulling the next water molecule up the xylem. As the column of water is hard to break this pull is felt down the entire column of water to the root. H2O

As each water molecule is “pulled” from the xylem another water molecule is “pulled” up from the root. This pulling force is passed from water molecule to water molecule all the way down the plant. This is how water is pulled up through the plant by transpiration. Animations of Cohesion-tension

3. Transpiration from the leaf Puts the column of water under tension Tension can pull a column of water to great heights in plants Tension causes the column of water to be stretched But the cohesive forces between the water molecules are strong enough to prevent the column breaking The strong lignin prevents xylem vessels collapsing inward

View An Animation of sugar and water moving through xylem and phloem

Outline of cohesion tension model

Summary points Water evaporates from the leaf, as each water molecule evaporates another is pulled up through the thin xylem column This pulling of water molecules puts all the water in the xylem vessels under tension This tension is great enough to pull water to a height of 150m

Summary points Stomata open in daylight and transpiration occurs causing xylem vessels to become narrow, stems therefore are narrower at day The strong lignin prevents xylem vessels collapsing inward When transpiration stops (at night) the tension is released and xylem vessels return to their normal width

Learning Check 3 Explain the terms Cohesion, Adhesion, Transpiration, Tension, Osmosis Name the Irish scientists who proposed the tension cohesion model of water movement. Explain how plants move water to great heights against the force of gravity.

Mineral uptake and transport Examples Calcium …… Helps make cell walls Magnesium ….. Part of chlorophyll Are absorbed by active transport which requires energy Potassium Nitrates Are transported from the roots in the xylem, dissolved in water Phosphates

Uptake & transport of Carbon dioxide Most of the Carbon dioxide comes in through the stomata from the atmosphere It diffuses into the air spaces and then into the photosynthesising cells in the ground tissue

Carbon Dioxide Sources Produced in the leaf during respiration Diffuses from the air in though the stomata CO2

Photosynthesis Products Glucose Glucose is converted to starch Starch and glucose are transported in the Phloem Oxygen Some diffuses into air spaces in the leaf and out through stomata into the atmosphere some of the oxygen produced is needed for respiration

Glucose is the carbohydrate made in photosynthesis This may be used immediately for energy for the plant in respiration or it may be stored as starch Some of this starch is stored in the spongy mesophyll cells in leaves Starch stored in leaves is important in the diet of leaf eating animals such as horses and cattle

Trans-section of a leaf

Glucose converted to sucrose When glucose get converted to sucrose it enters phloem sieve tubes and is transported through the plant This sugary water is called phloem sap An insect extracting sugary phloem sap from a plant

Food transport Phloem carries food to all parts of the plant, some food is sent to growth areas such as buds, flowers and roots. Food is used to form new plant structures, for respiration or it is stored as starch.

Learning Check 4 Name 4 Minerals taken up by the plant. How are they transported? Describe the uptake and transport of Carbon dioxide. List the Products of Photosynthesis & state their use What is the function of the phloem?

Food storage organs in plants Some parts of plants may become swollen and fleshy with stored food This food will be used by the plant to produce flowers, seeds and fruits

Modified Root E.g. Tap roots of Carrots, turnips, sugar beet

Modified stem Potato plants develop an underground stem system The tips become swollen with stored starch These swollen tips are called stem tubers In nature a potato tuber would remain dormant in the soil over winter and in spring the buds on the tuber (better known to us as the “eye”) would grow into new plants

Modified Leaves E.g. onion bulbs , daffodils bulbs and tulips bulbs

A bulb contains a tiny underground stem which have swollen fleshy leaves attached This stem has an apical bud and lateral buds can be seen where the leaves meet the reduced stem The entire bulb is protected by dry scaly leaves Some bulbs are edible (onion, garlic) while others are poisonous (daffodil, tulip) this prevents organisms in the soil from eating them!

Modified Petioles Celery and Rhubarb are modified petioles

Learning Check 5 Name 4 food storage organs in plants. What is the function of the stored food? What are Potato plants? Describe the structure of a bulb.

Websites on storage organs in plants & Transpiration http://theseedsite.co.uk/bulbs.html http://www.cactus-art.biz/note- book/Dictionary/Dictionary_S/dictionary_storage_organ.htm http://youtu.be/fNtFwQ4NpDg Told in storybook fashion, this short film narrates the struggle of one water droplet, Vladimir, who faces the bourgeoisie-promoted process of transpiration.