Chapter 7

Transport Systems

Transport

• Small, simple organisms living in water can obtain nutrients and eliminate wastes through diffusion.

• What about larger, more complex organisms?

Plant Transport Systems• The first land plants evolved from green

algae about 430 million years ago.• Life on land presented challenges for

plants: loss of moisture to the air, ability to get nutrients from soil and air, ways to eliminate wastes.

• Plants have specialized structures to cope with the challenges.

Plant Terminology

• Vascular Plants are plants with specialized tissues for water and nutrient transport.

• Nonvascular Plants are plants without these tissues and must live in damp places.

• Lignin is a hard material embedded in the cellulose matrix of cell walls to help support large vascular plants.

Plant Terminology Continued• Xylem is hollow-tube

shaped cells that carry water and minerals up from the roots.

• Phloem are elongated cells arranged into tubes filled with streaming cytoplasm that moves organic materials throughout the plants.

Water Transport

• Xylem is made up of two types of water conducting cells.

1. Tracheids which have pitted walls through which water moves from cell to cell.

2. Vessel Elements are wide thin-walled cells that are open on the ends, so water flows freely through these.

• Water loss is especially challenging, plants lose water through their stomates, which are open to facilitate gas exchange for photosynthesis.

• A red maple growing in a humid climate loses as much as 2,000L per day (1000 2L coke bottles).

• Plants must constantly replace this lost water.

• How is the water moved from the roots to the very tip of the plant?

• The current hypothesis is the cohesion-tension hypothesis.

• Root pressure, cohesion of the water molecules, and adhesion of the water to other charged molecules (which are found in the walls of the tubular cells) and the transpiration of the water leaving the plant essentially tug the water up.

Plant Nutrient Transport

• In plants, nutrients travel through phloem cells that are joined end-to-end. Tiny pores in the walls at the ends of the phloem cells allow the contents of cells to mix.

• Tiny strainer-like cells called sieve tubes are located at the tips of the cells.

• Sugars and Amino Acids move through the phloem cells from the leaves to the other parts of the plants.

• The best explanation is that the materials move from the “source” to the “sink” or from areas of high pressure to areas of low pressure.

Transport Systems in Animals

Circulatory Systems

• Like plants, animals must also have a way to exchange materials between cells and the environment.

• Unicellular organisms living in water environments can rely on diffusion and active transport.

• Larger organisms must have specialized systems.

• The size of an organism and its activity level determine the complexity of the transport system.

• In arthropods, (insects, crabs, etc.) there is an open circulatory system. There is no separation between the blood and other fluids. These organisms may or may not have some type of heart to help pump the blood throughout their body cavity.

Open Circulatory System

• In an open system, the blood is in the body cavity or hemocoel and is pumped by the hearts.

Closed Circulatory System

• In a closed system, blood is contained in vessels.

• These vessels branch into smaller and smaller vessels.

• The heart pumps blood through the system.

Circulation in Vertebrates

• Humans and other vertebrates have closed circulatory systems also called cardiovascular systems.

• The components are:

1. The heart

2. Blood Vessels

3. Blood

Circulatory System

• This example shows some of the major vessels of the human circulatory system.

Blood Vessels

• There are 3 types of blood vessels.1. Arteries carry blood AWAY from the heart. In

all but one artery, this is oxygenated blood.2. Veins carry blood TO the heart. In all but one,

this is de-oxygenated blood.3. Capillaries are the microscopic vessels that form

a network in the tissues. These are where gas exchange occurs (remember the respiratory system)

Capillary

• Capillaries make the transition from arteries to veins.

The Heart

• Mammals have a 4-chambered heart and most amphibians and reptiles have a 3-chambered heart.

• The heart pumps to move blood throughout the body.

The Human Heart

The Cardiac Cycle

• The cardiac cycle is the series of muscle contractions and relaxations. This is the heartbeat that is heard with a stethoscope.

• Contraction is called systole and the relaxation period is called diastole.

• The chambers contract and relax together.

Blood Flow through the Heart

Heartbeat

• Each heart beat starts with the pacemaker. These are cells located in the inner wall of the right atrium.

• This pacemaker (sinoatrial node) creates electrical impulses that cause the cardiac muscle to contract.

• The impulse spreads to the atrioventricular node in the left atrium and produces a unified contraction of the atria.

• The signal is conducted through fibers in the ventricles called the bundle of HIS and the Purkinje fibers which generate a strong ventricular contraction.

Composition of Blood

• Blood contains cells, fluids, and dissolved substances.

• The main components are

1. Erythrocytes – red blood cells

2. Leukocytes – white blood cells

3. Plasma – fluid portion of blood

4. Platelets – small cell fragments

Erythrocytes

• Red blood cells contain the oxygen-transporting protein called hemoglobin.

• It gives these cells their characteristic red color.

• They live about 120 days.

Erythroctyes

• New cells are made in the marrow of the long bones.

• A hormone in the kidneys regulates the production.

• Human RBCs do not have a nucleus.

Leukocytes

• White blood cells are the body’s second line of defense after the skin and mucous membranes.

• There are 5 types of WBCs, each with its own role in defending the body.

Neutrophils

• Neutrophils ingest bacteria at a wound site.

• Most abundant white blood cell.

Eosinophils

• Eosinophils also destroy bacteria. They are cytotoxic.

Basophils

• Basophils play a role in ridding the body of foreign matter by ingesting the substances.

Monocytes

• Monocytes absorb bacteria with the body at the site of an infection.

• Mature into macrophages.

• Increase greatly in response to infection.

Lymphocytes

• Two types, called B-Cells and T-Cells.

• When stimulated, B-cells become plasma cells.

• T-cells regulate the immune response of the leukocytes – reduced by AIDS/HIV

Plasma• The fluid portion of the blood.• Contains:

1. Water,2. Proteins3. Dissolved ions4. Amino acids and sugars

• Carries CO2, wastes, digested food, hormones,

Platelets

• Platelets are irregularly-shaped, colorless bodies that form clots to stop bleeding.

• Platelets gather at the wound and attempt to block the blood flow.

Blood Pressure

• Blood vessels have different amounts of muscle and elasticity depending on the function of the vessel.

• Arteries are very muscular due to the pressure of the blood when the heart contracts. The artery is very elastic so that it can expand and contract as blood flows.

• The contraction of the artery muscles help push blood through the system.

• Veins are not as muscular or elastic because the pressure is not as great.

• Veins have valves to prevent the backflow of blood.

• Gravity and skeletal muscle contraction helps direct blood through the veins (in addition to the blood flow from “behind”).

Blood Pressure

• A healthy blood pressure is maintained by hormones, and the nervous, excretory, and circulatory systems.

• About 20% of the US adult population has high blood pressure (hypertension).

• This forces the heart work harder and can damage vessels, causes strokes and contributes to artherosclerosis.

Muscle Contraction• Heart muscle is called cardiac muscle. It is

involuntary (contacts without your control).• Muscle is made of two proteins – actin and

myosin.• Actin filaments are anchored at a z-line.

Myosin filaments contact the actin with crossbridges. During contraction the crossbridges “walk” along the actin toward the z-lines by a release-attach motion, which in turn causes contraction.

Muscle Contraction Animations

• http://bio.winona.msus.edu/berg/ANIMTNS/SlidFila.htm

• http://3dotstudio.com/zz.html

• http://www.sci.sdsu.edu/movies/actin_myosin_gif.html