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Distributing Materials. Chapter 6. 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:
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Distributing Materials Chapter 6
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
Transport in larger organisms • 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
What needs to be transported? • Nutrients • Respiratory 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 systems • The 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 activity • reproductive 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 fluid Intracellular 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 spacesbetween cells in tissues. Exchange of substances between blood and body tissues occurs between plasma and interstitial fluid. Composition of fluid in an average human (Total ~ 40 L)
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 systems • Usually 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.
Heart chambers • 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
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.
Internal structure of the heart • Septum • Internal wall of tissue • Divides right and left sides of the heart • Chambers • 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 • aortic (ay-OR-tik) • tricuspid (tri-CUSS-pid) • pulmonary • mitral (MI-trul)
Mammalian Heart in Action The animation shows how the heart pumps blood. http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html
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.
Blood pressure: Giraffe facts! • 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!
Heartbeat • "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.
Blood vessels • Main blood vessels: • Arteries • Veins • Capillaries
‘Blue’ babies: hole in the heart • In human embryos, blood bypasses the lungs • by two means: • by flowing through the foramen ovalebetween the right and left atria • through the ductusarteriosusbetween 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: • vascular and non-vascular plants • phloem and xylem • transpiration and translocation Use labelled and annotated diagrams to support your ideas. Now use your text to check your ideas.
Transport systems in plants • Plants 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) • Dawsoniasuperba: • largest non-vascular plant • grows in moist mountain ash forests • reaches 30 - 40 cm in height. Selection of bryophytes: moss, liverworts, hornworts. Dawsonia superba (largest moss)
Vascular plants • Have 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 systems • Xylem: 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: • parallel veins in grasses • branching veins in many other leaves • 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 bundles • The 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.
Xylem • In 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.
Xylem elements • Vessels: • found in flowering plants • joined end-to-end • form a long channel • Tracheids: • present in all vascular plants • exist singly
Tracheids • 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 bordered pits (pine)
Tracheids • Single large, tapering water-filled cells • Many pitsin 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
Phloem • Mature 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 • 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 Phloem: sieve tube cells and companion cells.
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 continues • when cut flowers and leafy shoots are put in a vase of water. • if the stem is killed with poison or heat.
