Chapter 6Distributing

Materials

Internal transport systems: Why have one?In single-celled and very thin multicellular organisms, direct exchange with the environment may be sufficient to meet the requirements of all cells, provided that:

the surface area to volume ratio of the organism is high

the distances to be covered are short – no cell is very far from the external environment.

there are low requirements for oxygen

Liverworts Flatworms Algae

Diffusion is inadequate or too slow to meet cellular needs.

To meet these needs:•most animal species have specialised circulatory systems•most land plants also have specialised transport systems

Transport occurs across specialised exchange organs:•leaves and roots in plants•gills, lungs, digestive systems in animals

Transport in larger organisms

What needs to be transported?

NutrientsRespiratory gases Wastes Hormones (for

coordination)Heat

How are they transported?In mammals and birds, heat is transported by:

the blood throughout the body between the external surface and interior of the

body in order to maintain a reasonably uniform body

temperature.

Blood cells are involved in: gas transport defence immunity blood clotting

Circulated fluids carry materials between exchange surfaces and sites of production, use and storage.

Influences on transport systemsThe demands placed on a transport system are

due to factors such:as body size energy and nutrient requirements source of oxygen (air or water) climate level of activityreproductive condition

Transport is normally regulated to conserve energy.

Organisms with high energy and nutrient requirements, such as mammals and birds, have high demands and must have very effective transport systems.

Features of effective transport systems

Large surface areas available for exchange both with the environment and internally.

Reliable and responsive means of moving fluid around the body.

Fluid that maximises the amount of material that can be transported (good carrying capacity)

Control mechanisms that regulate the transport according to need.

Types of fluidIntracellular fluid: the cytosol – fluid inside cells.Extracellular fluid: all other fluid in the body.Blood: contains both intracellular fluid (in blood cells) and extracellular fluid (plasma). Interstitial fluid: portion of extracellular fluid located in the spaces between cells in tissues.

Composition of fluid in an average human (Total ~ 40 L)

Exchange of substances between blood and body tissues occurs between plasma and interstitial fluid.

Types of transport systems in animals

Open circulatory systems: common to molluscs and arthropods (eg insects).

Closed circulatory systems: evolved in echinoderms and vertebrates. common in active animals (vertebrates, squid)

Open circulatory systemsUsually have:•very low pressures •long circuit times (time taken for fluid to pass from the heart, out to the tissues and back to the heart)•weak pumps•fluid that does not return directly to the heart

mollusc

earthworm

Closed circulatory systems• Blood is enclosed within vessels of

different size and wall thickness.

• Blood is pumped by a muscular heart through vessels (arteries, veins, capillaries).

• Blood can be returned to the heart very rapidly.

• Higher blood pressures are possible - providing a reliable blood supply that can used in different ways for many functions at the same time.

• Blood is separated from the interstitial fluid by vessel walls - allowing blood to have different, highly specialised properties for transport and defence.

• Carrying capacity for oxygen is greatly increased by haemoglobin molecules.

Mammalian transport systems

• Mammals have two transport systems - a closed blood circulatory system and an open lymphatic drainage system.

• Components of the mammalian circulatory system are a muscular heart, pulmonary and systemic veins and arteries, thin walled capillaries and highly specialised blood.

• The four chambers of the mammalian heart contract in coordinated way to propel blood into the pulmonary and systemic arteries.

• Blood pressure is caused by the contraction of the ventricles.

• Exchange occurs across capillary walls and blood returns to the heart in veins.

Human heart: anatomy• Located under the ribcage in the centre of

the chest between the right and left lung.

• Shaped like an upside-down pear.

• Muscular walls beat, or contract, pumping blood continuously to all parts of the body.

• The size of the heart varies depending on age, size, or the condition of the heart.

• A normal, healthy, adult heart is the size of an average clenched adult fist.

• Some diseases of the heart can cause it to become larger.

4 chambers:•right and left atria (AY-tree-uh) •right and left ventricles (VEN-trih-kuls) Right ventricle: •pumps blood from the heart to the lungs•oxygen added to the blood •carbon dioxide is passed from blood, to blood vessels to lungs and is removed from the body when you breathe out.Left atrium:•receives oxygen-rich blood from the lungs•pumping action of the left ventricle sends oxygen-rich blood through the aorta (a main artery) to the rest of the body

Heart chambers

Right side of the heart

The left side of the heart

Human heart: exterior

Front surface of the heart, including the coronary arteries and major blood vessels.

Human heart: interior

Cross-section of a healthy heart and its inside structures.

Septum•Internal wall of tissue•Divides right and left sides of the heartChambers•Four chambers. •Two upper chambers are the atria - receive and collect blood. •Two lower chambers are the ventricles - pump blood out of the heart into the circulatory system to other parts of the body.Valves•Control flow of blood.•Open and close in coordination with the pumping action of the atria and ventricles. •Each valve has a set of flaps (cusps) which seal or open the valves.•One way - allow pumped blood to pass through the chambers and into arteries without backing up or flowing backward•Four types

o aortic (ay-OR-tik) o tricuspid (tri-CUSS-pid) o pulmonary o mitral (MI-trul)

Internal structure of the heart

Mammalian Heart in Action

http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html

The animation shows how the heart pumps blood.

Blood pressure

Systolic and diastolic pressure fluctuate in arteries and arterioles; almost zero through the capillaries.Blood pressure is lower in pulmonary arteries than in systemic arteries. The right ventricle has a thinner muscle wall and lower pumping pressure than the left ventricle.

• In a fully grown 5 m tall giraffe, the head is about 1.5 m above the heart.

• The heart must develop a high pressure to push a column of blood against gravity up the arteries to the brain.

• The mean blood pressure in the giraffe’s aorta is about 200 mmHg - about twice that of many mammals, including humans.

• To produce such a pressure, the walls of the giraffe’s left ventricle are extremely thick!

Blood pressure: Giraffe facts!

• "lub-DUB" sound. • Between the "lub" and "DUB," blood is pumped through the heart

and circulatory system.• Complicated series of very precise and coordinated events.• Each side of the heart uses an inlet valve to help move blood

between the atrium and ventricle:• tricuspid valve between the right atrium and ventricle. • mitral valve between the left atrium and ventricle.

• The "lub" is the sound of the mitral and tricuspid valves closing.• Each of the heart’s ventricles has an outlet valve:

• right ventricle uses the pulmonary valve to move blood into the pulmonary arteries.

• left ventricle uses the aortic valve to move blood into the aorta. • The "DUB" is the sound of the aortic and pulmonary valves closing.• Each heartbeat has two basic parts:

• diastole (relaxation)• systole (contraction) - atrial and ventricular

• During diastole, the atria and ventricles of the heart relax and begin to fill with blood.

• At the end of diastole, the heart's atria contract (atrial systole) and pump blood into the ventricles.

• The atria then begin to relax. • Next the heart's ventricles contract (ventricular systole) and pump

blood out of the heart.

Heartbeat

Blood components

Main blood vessels: •Arteries•Veins•Capillaries

Blood vessels

Name that part!

Check your knowledge!

‘Blue’ babies: hole in the heart

In human embryos, blood bypasses the lungsby two means:

by flowing through the foramen ovale between the right and left atria

through the ductus arteriosus between the pulmonary artery and aorta (remnant of the original sixth aortic arch.

•Sometimes one or both connections do not close over completely. •Both can be surgically repaired, leaving a perfectly healthy heart.•Blood is not completely oxygenated - continues to bypass the lungs. •Deoxygenated haemoglobin is a darker bluish-red•and gives the skin (particularly the lips) a bluish tinge.

Lymphatic system• Extensive network of vessels• Open system• Drains fluid from body; returns it to the

blood circulation• Fine, blind-ending lymphatic capillaries in

tissues join to form increasingly larger vessels that eventually empty into the large veins near the heart.

• Returning interstitial fluid is called lymph.• Contains proteins that leak out of the

capillaries• Larger lymph vessels contract• Most lymph flow results from external

compression of lymph vessels by muscular activity (eg during movement and breathing).

• Lymph fluid is forced in one direction because of numerous one-way valves, like those in veins, located along the vessels.

• Build up of lymph causes swelling (oedema).

What do you know? - Plant transport systems

Without referring to your text, explain the difference between:

1.vascular and non-vascular plants2.phloem and xylem3.transpiration and translocation

Use labelled and annotated diagrams to support your ideas.

Now use your text to check your ideas.

Transport systems in plantsPlants need water, carbon dioxide and light for photosynthesis.

Vascular land plants:

•ferns, cycads, conifers and flowering plants

•absorb water through roots and carbon dioxide through leaves

Non-vascular land plants (bryophytes):

•liverworts, mosses and hornworts

•absorb water directly from the environment into their body tissue

•water is moved throughout these plants by the slow processes of diffusion, capillary action and cytoplasmic streaming

•lack the vascular tissue that provides support in larger plants - usually sprawl horizontally (most only 1-2 cm)

•Dawsonia superba:

• largest non-vascular plant

• grows in moist mountain ash forests

• reaches 30 - 40 cm in height.

Dawsonia superba (largest moss)

Selection of bryophytes: moss, liverworts, hornworts.

Vascular plantsHave a transport system that:•is continuous through roots, stems and leaves.•carries water and inorganic nutrients obtained from the soil by the roots throughout the plant. •transports the sugars made in leaves to other parts of the plant.•vascular tissues - xylem and phloem - tubular pathways through which fluids flow.

Plant transport systemsXylem: transport water and inorganic nutrients up the plant from the soil.Phloem: transport sugars (in solution) produced by photosynthesis throughout the plant.

Vascular tissue:•composed of phloem and xylem•tubular pathways through which fluids flow•continuous through roots, stems and leaves•found in ferns, cycads, conifers and flowering plants•easily visible in leaves as:

o parallel veins in grasses o branching veins in many other leaves o stringy parts of celery and silver beet leaf stalks

•extend from roots to the very ends of leaves, into developing buds and fruit •few cells in plants are far from vascular tissue

Vascular bundlesThe arrangement of xylem and phloem tissues in

roots and stems is distinctive. In roots, xylem and phloem tissues are located

alternately around a central core of xylem.In stems, xylem and phloem tissue form

‘vascular bundles’ in which the phloem lies outside the xylem on the same radius.

Extend into the leaves.

XylemIn flowering plants, the xylem includes: •tracheids •vessel elements•parenchyma - only living cells in mature, functioning xylem•sclerenchyma cells (supporting fibres).

Mature xylem vessel: •long, water-filled tube •cylindrical skeletons of dead cells joined end to end•as they mature, the primary cell wall of cellulose is strengthened with lignin•becomes a stronger and more rigid secondary cell wall •cytoplasm and nucleus disintegrate•at each end the cell walls are perforated or completely open•fluid can flow directly through them (like a pipe) •pits (unthickened areas) and perforations in the sidewalls of the xylem vessels allow sideways movement of substances between neighbouring vessels.

Vessels:•found in flowering plants•joined end-to-end•form a long channel

Xylem elements

Tracheids:•present in all vascular plants•exist singly

Tracheids

bordered pits (pine)

Tracheids of the primary xylem:•mature first •stretched during development•walls are rings or spirals

Tracheids of secondary xylem: •walls develop after all length-wise growth has ceased •not stretched during development•more continuous•connected to one another by numerous pits•pits may occur anywhere on the cell wall •particularly numerous on the tapered end of the cell where it abuts with the adjacent cell. •water and dissolved substances move upwards from the tracheid through the pits

Tracheids

• Single large, tapering water-filled cells • Many pits in their lignified cell walls• Mature tracheids are dead • no nucleus or cytoplasm• not connected end to end

• Water transfers from tracheid to tracheid through the pits.

• In conifers (eg pines), xylem contains:• tracheids • no xylem vessels• wood is softer (referred to as softwoods)

Xylem parenchyma cells

• living cells • store starch manufactured in one growing season for

use at the beginning of the next• scattered as packing tissue between the xylem

vessels• pith (innermost region of a stem) - involved in starch

storage in plants (eg sago and sugar cane)• lateral (sideways) movement of water and nutrients

through woody stems occurs along horizontally arranged rays - specialised xylem parenchyma cells orientated radially

• structural pattern of xylem vessels, fibres and rays is characteristic for different species of trees

• xylem forms the inner woody parts of stems and trunks

• central heartwood has no living cells

PhloemMature sieve tubes:• living cells• no nucleus• non-lignified cell walls • linear rows of elongated cells• cell walls at each end perforated by a number of holes

(like a sieve)• strands of cytoplasm pass through the perforations,

connecting cells together• usually associated with one or more companion cells• connected to the companion cells by very thin

cytoplasmic strands (plasmodesmata)

Companion cells:• keep their nucleus• active in moving sugars into and out of sieve tubes• like sieve tube cells, have thin cell walls

Supportive fibres: • similar to those of xylem tissue

Phloem

Phloem: sieve tube cells and companion cells.

• involved in the transport of sugars

• composed of:• sieve tubes• parenchyma

cells • companion cells

• supportive fibres

• in woody stems, located outside xylem and forms the inner part of bark.

• ring barking severs phloem tissue causing the tree’s death

Transport of sucrose

Sucrose is moved into the sieve cells against a concentration gradient.

This causes water to move from the xylem by osmosis into the sieve cells.

Transpiration

Loss of water vapour from leaves. Involves the xylem.Driven by radiant energy of the sun As water evaporates from the cell walls, the leaf draws

water from nearby xylem vessels to replace the lost water.

Thousands of leaf cells, each drawing water from xylem, create a suction that pulls water up xylem vessels from roots.

Movement of xylem sap from roots to leaves is driven by transpiration and, to some extent, by root pressure.

Transpiration

Root pressure

Under some circumstances, internal fluid pressure (root pressure) in the roots of some plants causes fluid to rise up through xylem vessels.

The movement of fluid through xylem vessels is caused largely by transpiration.

Guttation

• Loss of liquid water from leaves - visible consequence of root pressure.

• In relatively small plants, root pressure forces droplets of water from specialised pores at the tips of principal leaf veins.

• Occurs • at night, when air is moist• when the soil is very wet (eg over-watered pot

plant) • Assists the survival of plants - ensures continual

upward movement of sap, transporting essential nutrients from the soil to the leaves - in tropical conditions, where humidity in the surrounding air is so high that little transpiration occurs,

Transpiration Facts

The pull of transpiration, plus the cohesion of water, can be strong enough to draw water 100 m up a tree trunk.

Transpiration does not require an intact root system. It continueswhen cut flowers and leafy shoots are put in

a vase of water. if the stem is killed with poison or heat.

Factors affecting transpirationDependent on factors that affect the rate of evaporation:

temperature, wind, available surface area and humidity.Water vapour is largely lost from leaves through open

stomata.Transpiration rate is low at night because conditions are

cooler, more humid and stomata are usually closed.Evaporation is reduced when there is a high level of

water vapour in the air (decreases the water concentration gradient between leaf spaces and air).

Air currents increase the rate of transpiration because they reduce the humidity in the vicinity of the leaf surface by moving water vapour away from the leaf.

Hairs create a layer of relatively undisturbed air over the leaf surface, reducing the rate of evaporation of water.

Translocation

• Movement of fluid through phloem

• Result of active pumping of sugars, with water following along an osmotic gradient.

• Sugars and water enter phloem sieve tubes in leaves and are translocated throughout the plant.

• Sugars are actively unloaded from sieve tubes at sites where they are required.

TranslocationTransport of organic materials through phloem.Occurs through the sieve tubes. Involves both active transport and passive movement of fluid.Two principal types of organic molecules are transported:

soluble carbohydrates (sucrose) nitrogenous compounds (eg amino acids)

Photosynthetic cells in leaves are the ‘source’ of carbohydrates for the entire plant.

Once carbohydrates have been made:converted to sucrosetransported to ‘sinks’ used or converted to complex carbohydrates (starch) and stored

for future use. Storage organs are:

sinks when carbohydrates are being storedsources when carbohydrates are released again as sucrose for

growing tissues

Translocation: DirectionTranslocation is often in a downward direction:

leaves are the major site of production of sugarsroots are a major site of consumption

Can take place upwards - sucrose is translocated to growing shoots and to developing fruits for storage

Roots take up inorganic nitrogenous ions (nitrates and ammonium) from soil and transport them through xylem to leaves.

The cells in leaves contain enzymes that catalyse the formation of amino acids from these inorganic nitrogenous substances.

Amino acids are then transported throughout the plant through the phloem.

Amino acids are the basic building blocks for proteins and are required for the synthesis of enzymes, ATP and nucleic acids.

Ring barking

After being ring barked:•Trees still take up plenty of water from the soil (in xylem).•New shoots may form above the damaged bark (short while only). •Sugars made in the leaves (photosynthesis) can not get down to the roots. •Root cells eventually die - lack food to provide energy for maintenance. •As roots die, nutrient and water uptake from the soil gradually stops; plant dies.

• Removal of a complete ring of bark.

• Disrupts a plant’s transport systems.

• Phloem is cut.• Simple way of killing trees.