Splash Contents Chapter Introduction Transport Systems in Plants 7.1Adaptations for Life on Land...

Chapter Introduction

Transport Systems in Plants

7.1 Adaptations for Life on Land

7.2 Water Transport

7.3 Nutrient Transport

Transport Systems in Animals

7.4 Circulatory Systems

7.5 Circulation in Vertebrates

7.6 The Human Heart

7.7 Molecular Basis of Muscle Contraction

Regulation and Transport

7.8 Blood Pressure

7.9 Composition of Blood

7.10 The Circulatory System and Homeostasis

Chapter Highlights

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A Summarize the adaptations made by plants to life on land.

Learning Outcomes

By the end of this chapter you will be able to:

B Compare the structure and function of xylem and phloem tissues.

C Describe the advantages offered by a closed circulatory system.

D Explain what blood pressure is and describe factors that affect it.

E Name the constituents of blood and describe the function of each.

F Explain how the circulatory system functions in homeostasis.


How do transport systems contribute to the survival of multicellular organisms?

Transport Systems What system is responsible

for the movement of blood throughout the body in humans?

An arteriogram of a human hand showing the arterial structure (enhanced).


Transport Systems• Complex multicellular organisms, such as most land

plants and animals, cannot eliminate wastes by diffusion and active transport through their surfaces.

• Transport systems play a key role in maintaining the internal balance necessary for life.

An arteriogram of a human hand showing the arterial structure (enhanced).


• The first land plants probably evolved from green algae about 430 million years ago.


7.1 Adaptations for Life on Land

• Challenges posed by life out of water include:

– loss of moisture to the air

– soil contains water and minerals, but the light and carbon dioxide needed for photosynthesis must be obtained above ground


• Two groups of plants emerged during this period:

• Vascular land plants differentiated into an underground root system that absorbs water and minerals and an aerial system of stems and leaves that makes food.

– Vascular plants with specialized tissue, called vascular tissue, that consists of cells joined into tubes that transport water and nutrients throughout the body of the plant


7.1 Adaptations for Life on Land (cont.)

– Nonvascular plants in which complex transport tissues did not evolve


Different parts of a plant have different activities, all of which require materials that must be transported where needed. Water is the material needed in greatest amounts. It also serves as the transport fluid, carrying minerals through one type of transport tissue and the products of photosynthesis through another.


• Specialization in vascular plants required additional adaptations:

– Hollow tube-shaped cells called xylem carry water and minerals up from the roots.

– The sections of roots that absorb water generally lack a cuticle and have increased surface area.

– Lignin, a hard material embedded in the cellulose matrix of the cell walls, supports trees and other large vascular plants.


7.1 Adaptations for Life on Land (cont.)

– The phloem, which distributes organic nutrients throughout the plant, consists of elongated cells arranged into tubes filled with streaming cytoplasm.


The arrows identify the path of water through this tree. Trace the path of the water from the root hairs through the xylem tissues to the leaves.


• The xylem of flowering plants consists of two types of water-conducting cells, tracheids and vessel elements, plus strong weight-bearing fibers.

7.2 Water Transport

• Columns of vessel elements form the xylem vessels through which water moves throughout the plant.



• Scientists have developed the cohesion-tension hypothesis—based on the molecular properties of water and transpiration—as the likely mechanism for water transport through the xylem.

7.2 Water Transport (cont.)

• The root system also exerts pressure that causes water and other materials to ooze out of a cut plant stem.



• Hydrogen bonds form between water molecules causing cohesion—the tendency of water to stick together.


• The positive and negative charges of water molecules form weak bonds to other charged molecules—the property called adhesion.


• Capillary action causes water to rise inside a tube because the water molecules develop adhesion to charged groups on the walls, pulling them upward; additional water molecules are then drawn up by cohesion.


• Due to cohesion, each water molecule that leaves the plant during transpiration tugs on the one behind it.


• The result is that a long chain of water molecules is continually pulled through the xylem from root to leaf.



• In vascular plants, nutrients travel through living phloem cells joined end to end.

7.3 Nutrient Transport

• Tiny pores in the walls at the ends of the phloem cells allow the contents of the cells to mix.

• Phloem channels are often called sieve tubes.



• Sugars and amino acids move through the phloem cells from the leaves to other parts of the plant.

7.3 Nutrient Transport (cont.)

• The pressure-flow hypothesis is the best explanation for the movement of sugars through the phloem.

• According to this hypothesis, water and dissolved sugars move through the phloem from sources (areas of higher pressure) to sinks (areas of lower pressure).



Sources and sinks in phloem transport

Click the image to view an animated version.


• In unicellular and other simple organisms, substances pass across the plasma membrane between each cell and a watery environment.


7.4 Circulatory Systems

Numbers indicate the pathway from endocytosis of food to exocytosis of indigestible wastes.



7.4 Circulatory Systems (cont.)

• Most larger animals have digestive and excretory organs and typically carry out transport with a pump (heart) and other organs and tissues, such as blood vessels and blood.

• Both the size of an organism and its level of activity play a role in how complex and efficient this system has to be.


• Insects, crabs, and other arthropods have an open circulatory system, in which there is no separation between blood and other intercellular fluid.




• An earthworm has a closed circulatory system, which means that the blood is confined to vessels.



• Blood travels through a closed circulatory system more rapidly than it flows through an open system.


• Humans and other vertebrates have a closed circulatory system, also called the cardiovascular system.

7.5 Circulation in Vertebrates


Blood with a high concentration of oxygen is shown in red. Blood with a low concentration of oxygen is shown in blue.

• The components of the cardiovascular system are the heart, blood vessels, and blood.


• The vertebrate heart consists of one or more atria, chambers that receive blood returning to the heart, and one or more ventricles, chambers that pump blood out of the heart.

7.5 Circulation in Vertebrates (cont.)



– Arteries carry blood away from the heart to organs throughout the body.



• There are three types of blood vessels:

– Capillaries are the network of microscopic vessels that infiltrate every tissue.

– Veins return blood to the heart.


This scanning electron micrograph, x100, of human capillaries lines the wall of the gall bladder.

Arteries and veins connect with capillaries by way of smaller vessels or connecting channels. Blood can pass from arteries to connecting channels to capillaries or directly through the connecting channels to veins.


• Fish have a two-chambered heart with one atrium and one ventricle.




• Amphibians and most reptiles have a three-chambered heart with two atria and one ventricle.



• Oxygenated and deoxygenated blood continually mix in the single ventricle, lowering the level of oxygen reaching the organs of the body.


• The four-chambered heart found in mammals, birds, and crocodilians has two atria and two completely divided ventricles.



• This double circulation system keeps oxygenated blood completely separate from deoxygenated blood which delivers high levels of oxygen.


• Each heartbeat is a sequence of muscle contraction and relaxation called the cardiac cycle.

7.6 The Human Heart

• In each cycle, the four chambers of the human heart go through phases of contraction, or systole, and relaxation, or diastole.



7.6 The Human Heart (cont.)


Blood enters the atria, which contract, forcing blood into the ventricles.

The atria relax and fill.

The ventricles contract, forcing blood into the pulmonary artery and the aorta. Then, the ventricles relax and the atria contract, repeating the cycle.


Blood flow through the human heart



• Muscle contractions are produced by a molecular motor largely composed of two proteins called actin and myosin.

7.7 Molecular Basis of Muscle Contraction

• Actin filaments are anchored to a structure called a Z-line at each end of the unit.


• Myosin filaments contact the actin with rows of globular crossbridges, which bind to the actin.


• During contraction, these crossbridges “ratchet” along the actin filaments toward the Z-lines by continually releasing their attachment at one point, changing position, and reattaching at a point farther along.

7.7 Molecular Basis of Muscle Contraction (cont.)


An enzyme uses the energy of ATP to form cross bridges between myosin and actin filaments, causing the muscle to contract.


• Blood vessels differ in the amounts of muscle and elastic tissue in their walls:

7.8 Blood Pressure

– The largest arteries, which are under high pressure, have walls made up largely of muscle and other elastic tissue.

– The walls of smaller arteries are made of muscle and elastic tissue that contract and expand to regulate blood pressure and the flow of blood into different parts of the body.

– Veins, which are under lower pressure, have thinner walls with less muscle and elastic tissues than arteries.



The structure of blood vessels



• Valves in the veins prevent blood under lower pressure from flowing backward.

7.8 Blood Pressure (cont.)


The valves regulate the flow of blood toward the heart. Note that back pressure on the valve tends to keep it closed until the pressure of blood on the other side opens it.


• Contraction of the skeletal muscles around the veins and gravity help to push the blood along.



Movement of blood in veins is brought about by pressure from adjacent muscles. Compression forces blood in both directions, but valves prevent blood from flowing backward and away from the heart.


• A healthy blood pressure is maintained through complex interactions involving hormones and the nervous, excretory, and circulatory systems.

• Various organs and tissues of the body respond differently to circulatory signals.



Note the change in the distribution of blood supply during rest and exercise.


• About 20% of the adult population in the United States has blood pressure constantly higher than the normal range. This is a condition called hypertension.

• Hypertension can be controlled by medication prescribed by a physician, regular physical examinations, proper diet, and exercise.




• Vertebrate blood contains several types of cells suspended in a fluid.

7.9 Composition of Blood

• Specialized cells called red blood cells, or erythrocytes, transport oxygen.


• Erythrocytes contain an oxygen-carrying red protein called hemoglobin.

• Hemoglobin consists of four subunits, each of which carries an iron atom suspended in an organic molecule called a heme group.


(a) Erythrocytes moving single file through a human capillary, x2000.

(d) Each subunit includes an iron-containing heme molecule.

(b) Each red erythrocyte contains many molecules of hemoglobin, x6000.

(c) Hemoglobin is a large molecule composed of four protein subunits.


• The iron of heme forms a temporary chemical bond with oxygen, which the erythrocyte transports to body cells.

• Human erythrocytes live only about 120 days. Replacement cells are manufactured in the marrow, the soft tissue in the long center of the bones of the body.

7.9 Composition of Blood (cont.)



• Specialized white blood cells, or leukocytes, circulate in the blood and form a line of defense against invading organisms such as bacteria and viruses.


• Some types of leukocytes, called macrophages, surround bacteria and absorb them.


Cells visible here include erythrocytes, x400, three types of leukocytes (left, center, and right), and platelets (the small particle, upper left).


• The fluid portion of the blood, called plasma, consists of water, proteins, dissolved ions, amino acids, sugars, and other substances.

– most of the carbon dioxide generated as a waste product during cell respiration.

– digested food from the intestine.

– hormones that are secreted by glands.

• Plasma transports:




• Dissolved ions in the plasma help maintain the osmotic balance between the blood and the intercellular fluid. They also help maintain the normal pH of the blood.

• The kidneys maintain these plasma ions (also called electrolytes) at precise concentrations.




• Some intercellular fluid is recycled into the circulatory system indirectly by the lymphatic system.

• The fluid in the lymphatic system, which contains certain specialized cells, water, large protein molecules, salts, and other substances, is called lymph.




• A vital characteristic of blood is its ability to clot, or coagulate.

• Coagulation begins when small cell fragments in the blood, called platelets, interact with a protein found in connective tissue that has been exposed at a wound site.






• The platelets form a plug and release enzymes that interact with plasma proteins known as clotting factors, beginning a chain of reactions.

• The end result of the cascade of enzymatic reactions is creation of fibrin.




Human blood clot, x2,200

• Fibrin forms a network of threads that trap additional platelets, erythrocytes, and other materials that form the clot.


• Thrombin clips two peptides from fibrinogen, reducing the solubility of the fibrin molecule and exposing sites that can bind to other fibrin molecules.

• This causes them to link up and form the long strands found in the clot.




• Clotting is vital when wounds occur, and disorders related to clotting can be very dangerous.

– If a clot blocks one of the arteries supplying blood to the heart, a heart attack occurs.

– A clot that blocks an artery in the brain causes one type of stroke.

– Problems with inadequate coagulation may be caused by hemophilia A, a serious genetic disorder.




• An organism’s ability to maintain homeostasis depends on the smooth interactions of its organ systems linked by the fluids of the transport system.

• The transport system is the essential link in maintaining homeostasis because it carries hormonal signals and needed materials to all parts of the body.

7.10 The Circulatory System and Homeostasis



• There are many control mechanisms that detect subtle changes in an organism’s external environment and that make necessary adjustments to keep the internal environment constant.

• The gas-exchange system plays an important role in maintaining homeostasis.

7.10 The Circulatory System and Homeostasis (cont.)



Summary

• Special structures have evolved in plants that transport raw materials to all the cells of the plant.

• In animals, circulatory transport food and oxygen to cells and remove waste products of cellular respiration.

• Arteries have muscular, flexible walls that withstand high blood pressure near the heart.

• Veins are less muscular and more flexible than arteries, and they are subjected to lower pressure.

• Exchanges of gases, wastes, and nutrients occur between the blood and the cells through capillaries.

• In single-celled and simple multicellular aquatic organisms, diffusion provides a sufficient supply of materials necessary for life processes.


Summary (cont.)

• Blood consists of specialized cells, proteins, and plasma.

• Vertebrate erythrocytes contain the oxygen-carrying protein hemoglobin.

• Leukocytes provide the second line of defense against invading organisms.

• Some proteins function with platelets to form clots, which repair injuries and stop blood loss.

• Some plasma and other tissue fluids are picked up and returned to the circulatory system by the lymphatic system.

• The circulatory system functions along with the nervous, excretory, gas-exchange, and endocrine systems in maintaining homeostasis.

• A four-chambered heart separates the systems for gas exchange and for circulation.


Reviewing Key TermsMatch the term on the left with the correct description.

___ xylem

___ actin

___ erythrocytes

___ platelets

___ leukocyte

___ phloem

a. small cell fragments that facilitate clotting

b. nonliving tissue that carries water and dissolved minerals from the roots to the rest of a plant

c. living cells that transport nutrients throughout a plant

d. a red blood cell

e. a protein in muscle fiber

f. a white blood cell

b

e

d

a

f

c


Reviewing Ideas1. Describe the primary difference in structure between

the circulatory system in a fish with that of a human.

Fish have a two-chambered heart and a single system for blood flow. Humans have four-chambered hearts and double circulation in which oxygenated blood is completely separated from deoxygenated blood.


Reviewing Ideas2. What is capillary action and why does it occur?

Capillary action is the phenomenon by which water will rise up inside a tube. It occurs because water molecules develop adhesion to charged groups on the walls of the tube, pulling them upward; additional water molecules are then drawn up by cohesion.


Using Concepts3. How are the circulatory system and the

lymphatic system codependent?

The lymphatic system recycles some of the intercellular fluid back into the circulatory system.


Using Concepts4. How are insects able to have an open

circulatory system and still move quickly?

Open systems work well in small animals, such as insects, that so not transport oxygen long distances in blood. Insects distribute oxygen through microscopic air ducts with branches that reach every part of the body.


Synthesize5. Leukemia is a cancer of the bone marrow. How

would leukemia affect the body’s homeostasis?

By destroying the bone marrow, leukemia reduces a body’s ability to replenish its supply of erythrocytes. This leads to a decreased oxygen carrying capacity.


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Sources and sinks in phloem transport

Blood flow through the human heart

The structure of blood vessels

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