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Transport in Plants

 

 

SPECIFIC OBJECTIVES

By the end of these lessons, you should be able to

:

Explain the importance of transport in animals

Distinguish between open and closed circulatory systems

Relate the structure of the heart and the blood vessels to their functions

Trace the path taken by blood  from the heart to all parts of the body and back to the heart

Name the common diseases of the circulatory system in humans and suggest methods off control/prevention

Relate the structure of the components of blood to their functions

Explain how oxygen and carbon (iv) oxide are transported in blood

Describe the mechanism of blood clotting and its importance

Describe the human blood groups and their importance in blood transfusion

Explain immunity and describe immune responses.

Welcome to these Form Two Biology lessons

You will learn the following:

Transport in Plants and Animals

Gaseous exchange

Respiration

Excretion and homeostasis

TRANSPORT IN PLANTS

In this topic you will learn how plants transport materials from one part to another, transport structures involved, factors affecting transport and adaptations of plants to their various habitats. In this topic you will learn how plants transport materials from one part to another, transport structures involved, factors affecting transport and adaptations of plants to various habitats.

Objectives

By the end of this lesson you should be able to:

  1. Relate the structure of roots, root hair, xylem and phloem to their functions.
  2. Relate the internal structure of the leaf to transpiration.
  3. Explain the possible forces involved in the movement of water and mineral salts through the plant.
  4. Explain the significance of and factors affecting transpiration.
  5. Demonstrate simple experiments on transpiration.

Background

In form one we learnt that plants take in raw materials for photosynthesis and also give out waste products from various metabolic activities. These raw materials and the products need to be moved from one place to another within the plant. Unicellular organisms such as amoeba have a large surface area to volume ratio, hence transport is by simple diffusion unlike multicellular organisms such as plants and animals where the surface area to volume ratio is small and materials have to move over long distances within the organism. These organisms need an elaborate transport system. Transport is the movement of substances such as water, nutrients, respiratory gases and waste products of metabolism from one part of an organism to another.

BACKGROUND

Transport is the movement of substances such as water, nutrients, respiratory gases and waste products of metabolism from one part of an organism to another, or out of the body. Animals take in food materials necessary for their metabolic processes.These food materials need to be moved to the cells where they are required. The animals give out waste products from the various metabolic activities. These need to be moved to organs of excretion for elimination from the body.

Small organisms such as amoeba have a large surface area to volume ratio, hence transport is by simple diffusion. On the other hand many multicellular organisms such as man have a small surface area to volume ratio hence materials have to move over long distances to cells located deep within the organism. Such organisms need an elaborate transport system.
 

 

 

Introduction

In the last lesson, we learnt the importance of transport in plants. Roots play an important role in transport. Different plants have different types of roots.

A fibrous root system

 

    Buttress root

    Prop roots

    Mangroves: Have breathing roots that sprout above the water in which they grow. See photo on next plate

    Breathing roots of mangroves

    The diagram shows cassava roots. These store food.

Roots
In addition to transport, roots also have the following functions:

Anchorage, that is, they hold the plant firmly in the soil.

Storage, for example in root tubers such as carrot and arrow root. Others store water for the plant.

 

Gaseous exchange

Absorption of water and mineral salts.

 

The graphic on next plate shows a generalised longitudinal section through a root tip of a dicot. Apical meristem cells are located behind the root cap and actively divide to give rise to new cells that are responsible for the elongation of the root. The root cap consists of simple parenchyma cells that protect the delicate apical meristem cells from mechanical damage.

You might have observed the following differences:

The monocot root has a pith at center.Phloem and xylem alternate around the pith.

The dicot root lacks a pith. Xylem forms a star shape and phloem occur between extentions of xylem.

The root cap consists of simple parenchyma cells that protect the delicate apical meristem cells from mechanical damage. Behind the root cap is the apical meristem cells which actively divide to give rise to new cells that are responsible for growth and elongation of the root.

Internal Structure of Roots

 

This illustration shows a longitudinal section through a carrot root tip.

This illustration shows a transverse section through a dichotyledonous root. Details of the cells in each tissue are shown.

In a dicotyledonous root the vascular tissue has the xylem at the centre with phloem occurring between the extensions of the xylem.

In a dicotyledonous root the vascular tissue has the xylem at the centre with phloem occurring between the extensions of the xylem. Notice the following parts:

Piliferous layer: Cells of this layer are thin walled for efficient passage of water and mineral salts. On maturity it is replaced by a less permeable epidermis.

Cortex: is made of loosely parked thin walled parenchyma cells. Acts as a storage tissue. Water molecules pass through it to the xylem.

Endodermis: Is made of a single layer of cells surrounding the vascular bundle that is made of xylem and phloem. The endodermis controls the amount of water entering the xylem.

Pericycle: Is made of a single layer of cells giving rise to lateral roots.

Vascular bundles: Occupy the central position. Each bundle consists of xylem and phloem.

Root hairs: microscopic outgrowths on the piliferous layer. These are thin walled. They are numerous in number, hence provide a large surface area for absorption of water and mineral salts.

Note that the monocotyledonous root has pith at the centre and that the phloem and xylem alternate around the pith.

The piliferous layer cells are thin walled for efficient passage of water and mineral salts. On maturity the piliferous layer is replaced by a less permeable epidermis.

Endodermis: This is a single layer of cells surrounding the vascular bundles. It controls the amount of water entering the xylem.

Pericycle: This is a single layer of cells giving rise to lateral roots.Vascular bundles: These occupy the central position.Each bundle consists of xylem and phloem tissues.

Root hairs

These are microscopic outgrowths on the piliferous layer.

They are thin walled and numerous, hence provide a large surface area for absorption of water and mineral salts.

The illustration shows the structure of a root hair cell.

 

 

 

 

 

 

The Stem

Sugar cane

 

 

Cactus

A woody stem
 

 

 

In this lesson, you will learn about the structure and role of the stem. The illustrations below show transverse sections through dicot and monocot stems. Compare the monocot and dicot stems shown.

You might have noticed that in dicots a pith and cambium are present. Vascular bundles arranged in a circle.In monocot stems vascular bundles are scattered and pith and cambium are absent.

Functions of stems

Functions of stems are:

  • Support and expose the leaves and flowers to the environment.
  • Conduct water and mineral salts from the roots to the rest of the plant.
  • Conduct manufactured food from leaves to the other plant cells.
  • Certain other plant stems have following functions.
  • Storage of water and food.
  • Allow gaseous exchange especially through lenticels.
  • Act as vegetative structures giving rise to new plants.

 

 

Transverse sections through young stems

The epidermis is covered with cuticle. It protects the inner tissues from mechanical damage, infections and drying up. It contains lenticels for gaseous exchange.

The cortex is made of the following tissues:

  • Collenchyma: It is made of elongated cells for strengthening and support.
  • Parenchyma: Irregular in shape, thin walled and loosely packed, for storage of food and water.
  • Sclerenchyma: Found in association with the vascular bundles. Walls of cells are thickened by deposition of lignin. It is a strengthening tissue.

Pith:Found at the centre of the stem.It is made of parenchyma tissue for storage of water and food substances. It may be hollow in some stems.

Vascular bundles. These are made of highly specialized tissues xylem and phloem.

  • Xylem: Transports water and mineral salts from roots to other parts of the plant.
  • Phloem: Transports products of photosynthesis from leaves to rest of the plant.

 

Stem Tissues

Epidermis: The epidermis is covered with cuticle. It protects the inner tissues from mechanical damage, infections and drying up. It contains lenticels for gaseous exchange.

Cortex: The cortex is made of the following tissues: Collenchyma: It is made of elongated cells, for strengthening and support.Parenchyma: The cells are irregular in shape, thin walled and loosely packed. They are for storage of food and water.Sclerenchyma: Found in association with the vascular bundles. Walls of cells are thickened by deposition of lignin. It is a strengthening tissue.

Pith: This is found at the centre of the stem.It is made of parenchyma tissue for storage of water and food substances. The pith may be hollow in some stems.

Vascular bundles are made of highly specialized tissues called xylem and phloem.

Xylem: Transports water and mineral salts from roots to other parts of the plant.

Phloem: Transports products of photosynthesis from leaves to rest of the plant.This illustration represents a cross section through a young dicot stem. Pass your cursor over each labeled part to access a summary of the features and functions of each.

Structure and Functions of Xylem Vessels

Xylem tissue is made of vessels and tracheids.

Xylem vessels

Xylem vessels are a characteristic of flowering plants. These are tubular and non living tissues. Cross walls of the cells have disintegrate during growth resulting into long hollow tubes that are continuous from theroots, through the stem tem to the leaves. Deposition of lignin material strengthens the vessel walls, this happens in different ways as illustrated in the diagrams. Bordered pits allow for movement of water from the xylem vessels into the surrounding cells.

Tracheids

Tracheids are non living and have lignified pitted walls.They have tapering or chisel shaped ends with perforated cross walls. Pits on sidewalls allow water to cells surrounding the xylem, which lowers their efficiency as conducting vessels.

Formation of Xylem vessels

A xylem vessel is formed from a chain of cylindrical cells placed end to end. The horizontal end walls break down completely or partially leaving hollow tubes. The cellulose side walls become impregnated with lignin rendering them impermeable to water and solutes. The hollow tubes are formed after the protoplasmic contents of the cells die as a result of lacking nutrients due to their curtailed permeability. Where the lignin fails to impregnate the walls bordered pits are formed. As the cells develop, lignified ribs of various kinds are laid down on the immediate inside of the walls. These give the vessels added strength and prevent its wall from caving in.Tracheids are formed similarly but they have six or five sided cross section and their ands are tapering with perforated pits.

The functions of the stem are:-
Support and expose the leaves and flowers to the environment.

Conduct water and mineral salts from the roots to the rest of the plant.

Conduct manufactured food from leaves to the other plant cells.

Certain other plant stems have following functions:

Storage of water and food.

Allow gaseous exchange especially through lenticels.

Act as vegetative structures giving rise to new plants.

Absorption of Water

Water is absorbed into the root hair cells by osmosis. The concentration of the cell sap is greater than that of the surrounding solution in the soil. Therefore water molecules are drawn from the soil into the root hair.

Water drawn into the root hair cells dilutes the cell sap making it less concentrated than that in the adjacent cortical cells of the root. Water then moves by osmosis to the adjacent cortical cell.

By a similar flow water passes through successive cortical cells until it reaches the xylem vessels at the centre of the root.

This animation shows the process of absorption of water.

Uptake of Mineral Salts

Uptake of mineral salts into the root hairs is by active transport. This is because the concentration of the cell sap in the root hair is higher than in the solution in the soil that surrounds the root hair. For mineral ions to move against a concentration gradient substances called carriers are believed to combine with mineral ions and then carry them across the plasma membrane of the cell. Energy is required for the process of active transport to occur.

After absorption mineral salts move through the root cells into the xylem vessels at the centre of the root and then they move up the stem and into the leaves.

Transpiration

Transpiration is the process by which plants lose water if form of water vapour into the atmosphere. It occurs by evaporation of water from a plant through the stomata, cuticle and lenticels.Stomatal transpiration accounts for 80-90% of total transpiration in plants. It is the evaporation of water through the stomata. Cuticular transpiration accounts for up to 20% of the total transpiration in plants. It is the evaporation of water through the cuticle. Lenticular transpiration accounts for very little of transpiration taking place in a plant. It is the evaporation of water through the lenticels.

 

 

Angiosperm

 

 

 

 

 

 

 

During transpiration water moves from the stem into the leaf xylem then to spongy palisade cells and to the epidermis. A few water molecules diffuse through epidermis where there is no cuticle and others from epidermis to atmosphere through cuticle. Water evaporates from the epidermis, spongy mesophyll and palisade into the sub-stomatal air spaces and diffuses out of the leaf through the stomata. Vaporization of water from the spongy mesophyll cells next to the sub-stomatal air spaces causes them to be concentrated than the adjacent cells. This increases the osmotic pressure of the spongy mesophyll cells next to the sub-stomatal air space, causing water to move by osmosis from adjacent cells. The process goes on until cells surrounding the xylem vessels in the leaf draw the water from the vessels.

Structure of a leaf.

This illustration shows the root taken by water from the soil to the stomata. It makes up the transpiration stream.

Forces involved in the transportation of Water and Mineral Salts

The continuous flow of water and mineral salts from the roots to the leaves is known as the transpiration stream. The flow is made possible by the following forces:

  • Transpiration pull
  • Cohesion and adhesion forces
  • Capillarity
  • Root pressure

These processes are illustrated.

This video demonstrates the forces of capillarity in tubes of different bore szes.

Transpiration pull

Evaporation of water from the spongy mesophyll cells into the sub-stomatal air spaces causes their cell sap to become more concentrated than the adjacent cells raising their osmotic pressure causing water to move into them by osmosis from the adjacent cells. The adjacent cells then increase in osmotic pressure and in turn pull a stream of water from the xylem vessels in the leaf. This in turn creates a flow or stream of water in the stem and roots to replace the water evaporating from the spongy mesophyl cells into the sub-stomatal air space and eventually through the stomata into the atmosphere.

Cohesion and adhesion forces

The force that keeps water molecules together is called cohesion. The water molecules are attracted to the walls of the xylem vessels by a force called adhesive force.The xylem vessels are very thin hence the cohesive and adhesive forces can maintain very high and unbroken thin columns of water in the xylem vessels up the trees.

Capillarity

This the tendency of water to rise up in narrow tubes. The narrower the tube, the higher column of water will rise.

The attractive forces between the water molecules and the walls of xylem are very high because the xylem vessels are very narrow, hence water columns in them ascend to great heights in the stem of tall tree.

Root Pressure

Active pumping of water across the endodermis to the xylem vessels creates root pressure that pushes water up the stem. The process requires energy, hence any process that interferes with respiration affects this proces.

Significance Of Transpiration

Transpiration has the following beneficial effects to the plant:

  • Replacing water lost through the leaves
  • Transport of mineral salts and water in the plant
  • Cooling the plant in a hot environment
  • Removal of excess water especially in aquatic plants
  • Maintaining of turgor pressure in plants

Factors afffecting the Rate of Transpiration

The factors are grouped into two categories

  • Structural factors
  • Environmental factors

 

Structural factors

Leaf size and shape

Larger leaves have larger surface area over which transpiration can take place as compared to smaller leaves; hence rate of transpiration is higher in plants with broad leaves.

 

 

 

 

 

 

 

 

Cuticle

The cuticle is made of a waxy water proof material that reduces the rate of transpiration, hence the thicker the cuticle the lower the rate of transpiration from a plant. Cactus, sisal and Aloe are some of the plants that grow in semi arid or arid areas and have a thick waxy cuticles that reduces the transpiration rate. Plants growing in wet habitats have a thin layer of cuticle that allows a high rate of transpiration to get rid of excess water.

 

 

 

 

 

 

A sisal plant. The cuticle on their leaves is thick to reduce transpiration.

 

 

 

 

 

 

 

 

 

 

 

 

 

Stomata

The higher the number of stomata the higher the transpiration rate. When there are more stomata on the upper surface than on the lower surface, there is a higher rate of transpiration due to exposure to more direct sunlight. Reduced number of stomata reduces rate of transpiration. Sunken stomata leads to saturation of satmosphere surrounding the stomata hence reduces rate of ranspiration

 

 

 

 

 

 

 

Environmental Factors

The environmental factors that affect the rate of transpiration include wind, temperature, humidity, light, atmospheric pressure, and availability of water.

Wind

On a windy day more water is blown away increasing the rate of transpiration. This video shows trees swaying in strong wind.

This illustration shows the movement of an air bubble in a potometer on a windy day. How would this movement change on a still day?

Temperature

The higher the temperature, the faster the rate of transpiration, because high temperatures increase the heat of vaporization.

Humidity

High humidity lowers the rate of transpiration since air in the atmosphere is saturated with water, lowering the diffusion of water vapour into the atmosphere.

Light

Increase of light intensity increases the opening of the stomata causing water vapour from the sub-stomatal air space to diffuse out at a higher rate increasing the transpiration rate.

Atmospheric pressure

Atmospheric pressure decreases with altitude. The higher the atmospheric pressure (at low altitutdes) the lower the rate of transpiration because the pressure acts on the water molecules preventing them from evaporating.

Water availability

Inadequate supply of water leads to reduced rate of transpiration in plants. When more water is available from the soil mesophyll cells in the leaf will be moist and hence give more water to the intercellular spaces. This increases the diffusion gradient with the outside hence higher rate of transpiration. In addition when more water is available guard cells remain turgid and stomata open, hence higher rate of transpiration.

Translocation of Organic Compounds

Translocation is the movement of soluble organic products of photosynthesis. The process occurs in the phloem tissue which is made of living cells.

Structure and Function of Phloem

The flow of synthesized food from the leaf to other parts of the plant is known as translocation and it occurs in special tissues called phloem.
The phloem is made of sieve tubes and companion cells.

The sieve tubes have perforated cross walls between adjacent sieve tubes forming a sieve plate that allows continuous flow of substances. The companion cells have a dense cytoplasm with many cell organelles. Their numerous mitochondria generate energy needed for translocation.

There are cytoplasmic filaments that are made of protein and are believed to be useful in movement of material upwards or downwards.

Diagram of a phloem element.

This animation shows translocation of synthesized food substances through phloem tissue.

 

The materials that are translocated include amino acids, ions, some hormones and sugars.

 

 

 

 

 

 

 

 

Blood transfusion
Blood transfusion is the transfer of donated blood from a donor to a recipients blood stream. For a successful blood transfusion the following factors are considered: The blood is screened for pathogens of diseases such as Hepatitis and HIV. The blood group of the recipient must be compatible with that of the donor.

 

 

 

Blood Compatibility

The recipient can only receive blood from the donor if the recipient does not have or can not produce antibodies correspondng to the donor's antigens. Otherwise agglutination of the recipient's red blood cells would occur, blocking blood vessels and causing death. The chart shows blood compatibility in the ABO blood system. The ticks indicate no agglutination, therefore transfusion is possible. The crosses indicate agglutination, therefore transfusion would be dangerous.

Blood Compatibility chart

Normally, it does not matter if the donor's antibodies correspond to the recipient's antigens, because the recipient receives a relatively small amount of blood from the donor. This contains a few antibodies compared to the volume of the recipient's blood. The dilution effect minimises agglutination. Furthermore there is no permanent supply of cells that produce antibodies in the transfused blood.

Rhesus Factor

Another blood grouping is the Rhesus system. A majority of the human population, that is about 85 per cent, have a protein factor called Rhesus on their red blood cells. The remaining 15 percent do not have the factor.Individuals with the Rhesus factor are described as rhesus positive (RH +ve). Those without are Rhesus negative (Rh -ve).

Unlike in the ABO system, Rhesus negative blood does not automatically contain Rhesus antibody, but has the potential to develop them on exposure to the Rhesus factor. This means that if Rhesus positive blood is transfused into a Rhesus negative recipient, the recipient responds by producing Rhesus antibodies. The antibody production is slow, so no immediate reaction is observed.

However, should there be subsequent similar transfusions, the antibodies will cause agglutination of the donors red blood cells. This would block blood vessels of the recipient and hence causes death.

Immune responses
Immunity is the ability of the body to fight infections. It can either be acquired or innate (inborn). Innate immune responses refers to a natural body defense like the skin, sebum and mucus and sickle cell anaemia. Acquired immunity can either be natural or artificial.

Natural Acquired Immunity

This occurs when the body naturally fights and overcomes infection.
Natural acquired immunity can be achieved in two ways
Natural active immunity
Natural passive immunity
 

Natural active immunity

This occurs when the body is infected by pathogens and naturally responds by forming antibodies, which overcome the infection. An example is when a patient recovers from chicken pox, measles he develops immunity against these diseases. The patient cannot suffer from a re-infection .

 

 

Natural passive immunity

This occurs when the antibodies naturally cross the placenta from mother's blood circulation. It also occurs when antibodies in the mother's milk enters the babys body through breastfeeding.

The video shows a mother breastfeeding a baby.

 

 

 

 

 

 

 

Artificial acquired immunity

This is the immunity acquired when antibodies are artificially introduced into the body or weakened pathogens are introduced in the body. Artificial immunity is therefore of two types. Artificial active immunity. Artificial passive immunity

Artificial active immunity

Artificial active immunity is the type of immunity acquired after vaccination. This is an activity whereby weakened, dead or antigen toxins called vaccines are artificially introduced into the body to enable antibodies to be formed to overcome the pathogens when an infection occurs. Examples of vaccines are: TB vaccines Polio vaccines, -Whooping cough vaccine. Note that vaccines are not administered during infection.

 

Artificial passive immunity

Artificial passive immunity is the type of immunity acquired when pre-formed antibodies are artificially introduced into the body of a patient. These antibodies are called antisera.

Examples include anti tetanus, antirabies and antivenom antisera.

Importance of Vaccination Against Diseases

  • Vaccines prepare the body for defense against infection by pathogens .
  • Vaccination controls the spread of disease
  • It reduces the severity of a disease when infection occurs.

Allergic Reactions

An allergic reaction is an overreaction of the immune system to harmless antigens. This leads to production of histamine by the person's immune system, which cause inflammation on the part of the body affected. Examples of allergic reactions are sneezing, running nose and itchy eyes. Anything that causes such a response is called an allergen. Examples of allergens are pollen grains, dust, insect stings, animal hair and certain foods. Allergy can be controlled by taking anti-histamine drugs.

Diseases and Defects of the Circulatory System

These include thrombosis, vericose veins, arteriosclerosis and high blood pressure.

 

Thrombosis

Clotting may also occur inside blood vessels without exposure to the air. This is called thrombosis. This may lead to stroke if it happens in the brain or to cardiac arrest or heart attack if it occurs in coronary vessels. When clotting occurs in the coronary vessels it is called coronary thrombosis. Such blockage prevents food nutrients and oxygen from getting to the tissues served by the vessels and may cause death of these tissues or the whole organism.

 

Causes of thrombosis

Thrombosis may be caused by the following:

Accumulation of fatty material on the walls of arteries, hence high amount of cholesterol in blood.

Heavy intake of alcoholic drinks

Smoking

Overweight

Psychological and emotional stress.

Effects

  • Narrowing of coronary artery results in less blood flowing to the heart.
  • Insufficient oxygen reaches the heavy oxygen dependent heart muscles.

Prevention And Control
Practicing healthy life styles such as

  • Smoking less/avoid smoking
  • Fewer intake of alcoholic drinks.,
  • Take foods low in fat content.
  • Avoid psychological stress.

Vericose Veins

  • This is a condition characterized by flabby swellings of superficial veins especially at the back of the legs as a result of valves in the veins failing to function properly.

It is common when the veins swell and become permanently dilated, raising them above the level of the skin.

  • It results in retention of tissue fluid.

Prevention And Control of vericose veins
Regular physical exercise.

Arteriosclerosis
This refers to the hardening of the arteries due to deposition of cholesterol and calcium. The arteries thus thicken and lose their elasticity. This leads to an increased risk of blood clots forming and being trapped within the arteries hence a higher risk of coronary thrombosis.

Causes of arteriosclerosis
Arteriosclerosis is caused by the following:

  • Eating large quantities of fatty foods.
  • Lack of exercise.
  • Smoking.
  • Excessive intake of alcohol.
  • Psychological stress

Prevention of arteriosclerosis
To prevent arteriosclerosis you need to lead a healthy lifestyle i.e.

  • Avoid smoking
  • Avoid excessive intake of alcohol
  • Exercise regularly
  • Eat a balanced diet

Control
If one already has arteriosclerosis it can be controlled by:

  • Taking drugs that reduce fatty deposits in blood.
  • Taking drugs that reduce the risk of blood clots in blood as prescribed by a doctor.
  • Regular exercise to break down excess fat into energy.

Hypertension (High Blood Pressure).

Normal blood pressure in human beings vary between 90/60 and 140/90 mm of mercury. The numerator refers to systolic pressure during contractions. The denominator refers to diastolic pressure during relaxation. High blood pressure is a condition that occurs when the systolic pressure is above 140mmHg and the diastolic pressure is above 90mm Hg.

 

 

 

Causes of high blood pressure

High blood pressure is caused by:

  • Heavy intake of alcoholic drinks
  • Smoking
  • Taking large quantities of salt in food.
  • General body stress
  • Arteriosclerosis.

Effects

Sustained high blood pressure may lead to:

  • Overworking of the heart leading to heart failure. Heart failure is the gradual inability of the heart to pump blood.
  • Bursting of arteries and capillaries.
  • If blood vessels in the brain burst, stroke results and the brain cells in affected area die.
  • Paralysis of some parts of the body especially accompanying the stroke.
  • N.B: Hypertension is more common in humans aged above 40 years.

 

Control

If one has High blood pressure it can be can be controlled by:

  • Regular exercise.
  • Taking low quantities of salt in food.
  • Avoid excessive intake of alcoholic beverages
  • Avoid smoking cigarettes and other related drugs.

Circulatory Systems

Transport systems are also known as circulatory systems. Circulatory systems in animals consist of tubes, a transporting fluid and a means of pumping the fluids within the tubes. These systems transport various substances dissolved in the transport fluid to all parts of the animal. Tissues and cells obtain useful substances from the medium and release the metabolic wastes to the medium through simple diffusion, osmosis and active transport.

There are two types of circulatory systems namely open circulatory system and closed circulatory system.

Open circulatory system

The open circulatory system is found in arthropods. In this system the transporting fluid called haemolymph flows through open body cavities called haemocoel. This fluid is usually in direct contact with the tissues. As it flows through the body cavity, it provides nutrients to the cells and removes waste products from them. This exchange of materials is aided by difference in concentration between the composition of the haemocoel and the composition of the cells.

Closed circulatory system

In the closed circulatory system the transporting fluid is called blood and flows in closed channels called blood vessels.

Blood Vessels

The transport fluid known as blood is pumped by a muscular heart through blood vessels. There are three types of blood vessels namely arteries, veins and capillaries. Arteries carry blood away from the heart while veins carry blood to the heart. Capillaries link arteries to veins and provide site for exchange of materials.

Arteries

Arteries Carry blood away from the heart to other tissues. They carry oxygenated blood except pulmonary artery which carries deoxygenated blood to the lungs. The blood in arteries is rich in nutrients and has less metabolic waste. It flows fast and at high pressure. Blood flows in pulse.

This illustration shows the basic structure of an artery.

Veins

Veins carry blood from body tissues to the heart. The blood in all veins, except pulmonary vein, is deoxygenated. It has less nutrients but is rich in metabolic wastes. The blood flow is slow and at low pressure. It flows smoothly.


 

Capillaries

Capillaries connect arteries and veins. The exchange of oxygen and carbon dioxide takes place here.
Nutrients are released into tissues at the arteries. Wastes from tissues into the blood stream are collected across the capillaries. Blood pressure in capillaries is higher than in veins and less than in arteries. Blood flows less smoothly in capillaries than in veins but more smoothly than in arteries
.

The Heart

External structure of the heart

The heart is a muscular organ located in the chest cavity. The main function is to pump blood to all parts of the body. It is enclosed in a translucent membrane called the pericardium.

Functions of the pericardial membrane.

  • It secretes a fluid that acts as a lubricant to protect the heart from friction during its contractions.
  • Keeps the heart in position
  • Prevents overdilation of the heart

The outer part of the heart is covered by a fatty tissue that acts as a shock absorber.The heart is made up of specialised muscles known as cardiac muscles which are myogenic, that is, they initiate and sustain the heartbeat.

Note the vessels spreading over the heart tissue. These are known as coronary vessels. They supply blood rich in nutrients and oxygen to the heart muscles through the coronary artery and take away blood rich in waste products and carbon (IV) oxide through the coronary vein.

The mammalian heart consists of four chambers; two auricles forming the upper chambers and two ventricles forming the lower chambers.

Auricles are also known as atria ( singular: atrium) They are thin-walled and have a smaller volume as compared to the ventricles. The right auricle receives oxygenated blood from the tissues through the venecava while the left auricle receives oxygenated blood from the lungs through the pulmonary vein.

The left ventricle has thicker muscles than the left ventricle and is therefore able to pump blood to all parts of the body.

The interventricular septum is a thick muscular wall that separates the right and left chambers of the heart preventing the mixing of the oxygenated and deoxygenated blood.

Atrio-ventricular valves are found between the auricles and the ventricles. They prevent the backflow of blood to the auricles when the ventricles contract.The right atrio-ventricular valve is known as the tricuspid valve while the left atrio-ventricular valve is known as the bicuspid valve. These valves are attached to the walls of the ventricles on each side.

Tendons prevent the valves from turning inside out during the contraction ofthe ventricles.

Semi-lunar valves are found at the base of the pulmonary artery and aorta. They open when the ventricles contract forcing the blood out of the heart. These valves prevent the backflow of blood into the ventricles.

Composition of Blood

Blood is a specialized connective tissue composed of blood plasma and blood cells namely red blood cells, white blood cells, and platelets. Platelets are cell fragments. Plasma is the fluid medium within which these cells are suspended. We shall discuss each of these components.

Blood Tissue

Blood Clotting

When a blood vessel is cut or damaged the exposed platelets release thrombokinase enzyme. The enzyme neutralizes the anti-clotting factor called heparin. It also activates the conversion of a protein in blood called prothrombin to thrombin in the presence of calcium ions and Vitamin K. Thrombin activates the conversion of a soluble protein fibrinogen to insoluble and fibrous protein called fibrin. Fibrin forms a network of fibers which traps the blood cells forming a clot.
 

This graphic shows the process of blood clotting


 

Clotting may also occur inside blood vessels without exposure to the air. This may lead to stroke if it happens in the brain or to cardiac arrest or heart attack if it occurs in coronary vessels. Such blockage prevents food nutrients and oxygen from getting to the tissues served by the vessels and may be fatal.

 

Importance of Blood Clotting

Blood clotting prevents entry of pathogens into the body through the wound. It also prevents excessive loss of blood following injuries to the skin.

Blood Groups

There are four types of blood groups among the human population. These are blood group A, B, AB and O. The blood groups are derived on the basis of the type of antigen on the surface of the red blood cells.

In the blood plasma there are two types of antibodies that can be found. These are antibody a and antibody b. People of blood group A have antibody b in their plasma. Those of blood group B have antibody a in plasma. Blood group AB people have none of antibodies a and b. People of blood group O do not have any of the antibodies a or b originally but develop them when exposed to the corresponding antigen. Thus they produce antibody a if exposed to blood group A and produce antibody b if exposed to blood group B.

The blood groups are summarized in the table.


Open Circulation in a Cockroach

A cockroach is a typical insect.It has an open circulatory system composed of a tubular heart above the alimentary canal. The heart has thirteen chambers three of which are in the thoracic region and the remaining in the abdominal region. The anterior opening of the tubular heart is the aorta. The aorta empties the haemolymph into the haemocoel. The haemolymph bathes the body tissues. The tissues absorb useful substances from it and release waste products into it by diffusion.

Structure and function of blood vessels

Arteries

Arteries Carry blood away from the heart to other tissues. They carry oxygenated blood except pulmonary artery which carries blood to the lungs. The blood in arteries is rich in nutrients and has less metabolic waste. It flows fast and at high pressure.
Blood flows in pulse


Illustration of an artery

Veins

Veins carry blood from body tissues to the heart. The blood in all veins. Except pulmonary vein is deoxygenated. It has less nutrients but is rich in metabolic wastes. The blood flow is slow and at low pressure. It flows smoothly. The illustration shows how the valves in veins work to prevent backflow of bloob.


 

Capillaries

Capillaries connect arteries and veins. The exchange of oxygen and carbon dioxide takes place here. Nutrients are released into tissues at the arteries. Wastes from tissues into the blood stream are collected across the capillaries. Blood pressure in capillaries is higher than in veins and less than in arteries. Blood flows less smoothly than in veins but more smoothly than in arteries

Illustration of the capillary structure. In 3 dimensions.

Structure and Function of the Mammalian Heart

The mammalian heart consists of four chambers; two auricles forming the upper chambers and two ventricles forming the lower chambers.

Auricles are also known as atria ( singular: atrium). They are thin-walled and have a smaller volume as compared to the ventricles. The right auricle receives oxygenated blood from the tissues through the vene cava while the left auricle receives oxygenated blood from the lungs through the pulmonary vein.

The left ventricle has thicker muscles than the left ventricle and is therefore able to pump blood to all parts of the body.

The interventricular septum is a thick muscular wall that separates the right and left chambers of the heart preventing the mixing of the oxygenated and deoxygenated blood.

Atrio-ventricular valves are found between the auricles and the ventricles. They prevent the backflow of blood to the auricles when the ventricles contract.

The right atrio-ventricular valve is known as the tricuspid valve while the left atrio-ventricular valve is known as the bicuspid valve. These valves are attached to the walls of the ventricles on each side.

Tendons prevent the valves from turning inside out during the contraction of the ventricles.

Semi-lunar valves are found at the base of the pulmonary artery and aorta. They open when the ventricles contract forcing the blood out of the heart. These valves prevent the backflow of blood into the ventricles.

Plasma

This is a pale yellow fluid consisting of 90% water. It has proteins like fibrinogen, wastes like urea and carbon dioxide food nutrients like glucose and variety of other dissolved substunces such as mineral salts. Plasma provides a medium through which continuous exchange of materials take place. Blood plasma from which fibrinogen and blood cells have been removed is called serum.

Functions of blood plasma

It forms a medium in which the following are transported:

  • Red blood cells from lungs to the rest of the body.
  • Metabolic waste eg carbon dioxide and and urea from sites of formation to excretory organs
  • Food nutrients e.g glucose from the alimentary canal to liver and other parts of the body
  • Hormones from glands to the target organs.
  • White blood cells to sites of infection and injury

Plasma also regulates body temperature by distributing heat mainly from the liver to other body parts. It regulates the pH of body fluids and is a medium of exchange of materials such as glucose between blood and other body tissues.

TRANSPORT IN ANIMALS

In this topic you will learn about the structures and tissues concerned with transport in insects and other animals including humans, transport systems and materials transported. You will also learn about the heart, blood vessels as well as diseases related to them.

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