Biology SME copy 1

Key unit competence: Describe the structure of the transport tissues in plants, the mechanisms by which substances are                                                        moved within the plant and relate the structures of the circulatory and lymphatic systems to their                                                          functions in human.

Introductory activity 8

1. Have you ever seen how plants get water and minerals from roots or how does food prepared by leaves reach other parts of plants? What kind of transport system allows the passage of water and food to various parts of plants? Research using, internet and library books, about these questions and discuss your findings in the class. 

2. Have you once seen an injured person

 bleeding? Write what you think about the origin and pathway of that blood before exiting the body. 

8.1 Need for a transport system and the structure of transport tissues 

Activity 8.1

1. Discuss the needs of transport systems in plants and animals. 

2. Aim: To observe prepared slides of cross-sections showing transport structures in stem and roots and how leaves of xerophytes have adapted to reduce water loss by transpiration. 

Requirements: Electrical source, Microscope, Prepared slides of transport structures in stem, roots and leaves. You can prepare your sample to be observed using the onion or Commelina .

Procedure

1. Place the prepared slide on the stage of a microscope.

2. Adjust to observe the specimen.

3. Draw the specimen observed.

8.1.1 Need for a transport system

 Water is the most abundant constituent of all living things on this earth. Plant tissues contain more than 70 per cent water. Water content in cells affects many metabolic activities inside the plant systems. Quantity of water in plant cells is maintained because these have evolved various mechanisms to take up water from the soil through efficient conducting systems. The water content in different plant parts is variable for example the amount of water in root cells has been found to be different from that of fruits, stem and seed in sunflower plants. Different plant species also have different water content expressed as percentage of fresh weight in their plant parts. Plants suffer continuous water loss through the aerial parts by transpiration and evaporation. However, these sustain continuous water loss from aerial parts by maintaining an efficient transport system and uptake of water from the soil. It is interesting to study how plants take up water from the soil and transport it to the aerial parts.

Plants have unique mechanism for transport of water, nutrients and food. Water is taken up by the roots and transported along with minerals to other parts of the plant. Along with water, many nutrient elements that are essential for the growth of the plants are also taken up from the soil. The food manufactured in leaves is similarly translocated from the source to the other parts of the plant. The transport of food is also carried out by the conducting tissue. The unit dwells on various aspects of the transport in plants.

The transport system in animals has 3 main roles which are:

 a. Transport of respiratory gases, nutrients, hormones, metabolic wastes etc . 

b. Protection against some diseases thanks to antibodies, against permanent bleeding thanks to thrombocytes etc. 

c. Regulation (homeostasis)such as thermoregulation.

 Physical activities can make individuals including students to be stronger and healthier by: 

i. Lowering obesity rate. 

 ii. Lowering body mass indexes, benefit from developing muscles and burning calories. 

 iii. Lowering the rates of diabetes and high blood pressure.

 iv. Bettering heart and lung function. 

 v. Enabling lymph as one of the body fluids to quickly reach in different part of the organisms.

8.1.2 Structure of transport tissues in plants 

a. Structure of xylem tissue

 Xylem is involved in uptake of water and mineral elements and phloem is involved in transport of food material from source to the sink. The stem appeared coloured in the activity because the water is rising through the specialized conducting tissues called the xylem.

Xylem: forms a continuous system running from the tips of the roots to the above ground parts and also to the branches and leaves. It forms the long distance transport systems within the plants. It is a complex tissue forming a part of vascular tissue. Xylem tissue is composed of four types of cells: Tracheids, Vessels, Xylem fibres and Xylem parenchyma. 

 a. Tracheids: Tracheids are elongated cells with blunt ends, present along the long axis of the plant system. Tracheids are imperforate cells with bordered pits on their end walls. They are arranged one above the other. These have broader lumen and lignified walls that offer mechanical support to the plants. Sometimes an intermediate type of cell element is also found in vascular system known as fibre-tracheids. 

 b. Vessels: Vessels are main transporting elements in xylem. These are long cylindrical tube-like structures made up of many cells called vessel members. These vessels are joined end to end forming a continuous column. Sides of xylem vessels are lignified. These do not have protoplasm and have perforations in their end walls. 

 c. Xylem parenchyma: These are thin walled cells that act as storage cells and their walls are made up of cellulose. Radial conduction of water takes place by ray parenchyma cells in thick tall trees. 

 d. Xylem fibres: These are cells with thick obliterated walls. These have narrow lumen and their function is to attribute mechanical strength to the plants. 

 Xylem elements can be observed and studied well by using maceration technique. The slivers of stem are cut and put into maceration mixture. 

 These are separated from the mixture, washed, stained and mounted in glycerine and observed under microscope. Xylem elements in macerated plant material as seen under microscope (Figures 8.1 and 8.2).

b. Structure of phloem

An analysis of the phloem exudate obtained by making an incision into the phloem tissue provides evidence that photoassimilates are transported through phloem. 

 The phloem collects photoassimilates in green leaves, distributes them in the plant and supplies it to the other heterotrophic plant organs. Phloem is composed of various specialized cells called sieve tubes, companion cells, phloem fibres, and phloem -parenchyma.

1. Sieve tubes: Sieve tubes are series of cells joined end to end. The cross walls between successive sieve elements become perforated forming sieve plates. The cell walls are thin. Although the cell contents are living, the nucleus disintegrates and disappears. The lumen is filled with a slimy sap which is composed mainly of protein. The function of sieve tubes is transport of organic compounds. 

 2. Companion cells: These are specialized parenchyma cells which always appear with the sieve tube elements. They are also elongated, thin-walled and have distinct nucleus in the cytoplasm of the companion cell. Their function is to regulate the metabolic activities of the sieve tube elements. 

 3. Phloem fibres: These cells are elongated and tapering. They have thickened walls. Phloem fibres give mechanical strength to the plants. 

 4. Phloem parenchyma: These are living cells with thin walls. Phloem parenchyma stores compounds such as starch.

Application activity 8.1 1. 

You are provided with a list of terms; choose among them those which can complete the following statements: 

Terms list: Phloem, tracheids, vessels, parenchyma and fibres, absorb, companion cell, transport, active and passive. 

Statements: 

i. Xylem tissue is composed of four types of cells: 

 ii. ...................., ...................., .................... and .................... . 

 iii. Plants .................... water from soil and .................... it to aerial parts.

 iv. Two pathways regulating uptake of water from roots are ................. and .................. .

2. Observe the figure below and answer the following questions

8.2 Transport mechanisms of plants and the process of transpiration

Activity 8.2

I) Aim: To investigate how plants transport water and minerals. 

Requirements: A fresh green plant, a glass of water, natural food colour, a razor, slide and a microscope. 

Procedure 

i. Take a fresh green plant. 

ii. Give a cut at the basal end. 

iii. Put the cut segment in water with natural food colours. 

iv. Cut a transverse section of the stem and observe it under the microscope. 

Discussion: What do you think the stem will look like? Could you see that some part of the stem appears colored? Explain why. 

II) Aim: To demonstrate the phenomenon of transpiration by bell jar method. 

Requirement: A potted plant, glass plate, bell jar, oilcloth, grease and thread. 

Procedure 

 1. Take a watered healthy plant. Cover the soil by cloth to avoid evaporation. 

 2. Place the pot on a glass plate and cover with a bell jar. 

 3. Leave the apparatus for some time and observe. 

 4. What do you see at the inner side of the bell jar? Where do these come from? 

 5. Discuss reasons for the fact that transpiration is an inevitable consequence of gas exchange in plants.

Results: Small drops of water start appearing on the inner side of bell jar due to condensation of water vapour transpired from the plant.

III) Aim: To study the effect of different light intensities on rate of transpiration using potometer. 

Requirements: Twig of Dracaena. Potometer, Luxmeter, Table lamp. 

Procedure: Place a twig of plant in one end of the potometer and seal it airtight. Fill the entire apparatus with water so that there are no air spaces in between. The plant is exposed to different light intensities.

Do you see any changes in the level of water at the other end of the tube? Explain why. 

Results: With the increase in light intensity, the level of the water drops indicating increase in rate of transpiration. 

8.2.1 Transport of mineral sap through xylem 

a. Absorption of water through roots

 Soil is the main source of water for the plants. The principal source of soil water is the water that is stored in the spaces between the soil particles after precipitation or rainfall. From the root hair cells the water enters into the epidermis, cortex and finally endodermis

 Endodermis is impregnated with fatty substances along the wall called casparian strips. These strips form networks and these seal off the spaces between the endodermal cells. From the endodermis water enters into the vascular tissue.

The movement of water into the roots can take place by various pathways. The first pathway is referred to as apoplast. It means that water is moving along the interconnecting cell walls and spaces between the walls. Water moves through apoplast because of capillary action or free diffusion along the gradient. It is also called non-living continuum .The other pathway is the symplast, in which water moves across the root hair membrane and through the cells themselves. Plamsodesmata act as channels to transport water between the cells

In natural conditions, the apoplastic and symplastic pathway do not separate and are operating simultaneously within the system. The absorption of water through roots is affected by various abiotic and biotic factors. When the soil temperature is high, movement is fast. Low temperature reduces water uptake in plants. The branching pattern of the roots also affects the uptake of water.

Water is a polar molecule. When two water molecules approach one another, the slightly negative charged oxygen atom of one forms a hydrogen bond with a slightly positively charged hydrogen atom in the other. This attractive force, along with other intermolecular forces, is one of the principle factors responsible for the occurrence of surface tension in liquid water. It also allows plants to draw water from the root through the xylem to the leaf.

 b. Anatomy of root 

 In most of the herbaceous plants, the roots show various layers of cells through which the water travels inside the root systems. The outer layer that is protective is termed as epidermis and is followed by ground tissue consisting of multiple layers of cortex, endodermis and pericycle. Two to six exarch xylem bundles are found. Phloem tissue is alternate with the xylem tissue

c. Rise of water/ascent of sap 

Cohesive and adhesive forces are important for the transport of water from the roots to the leaves in plants. Various processes are operating inside the plant system and cells to facilitate the movement of water from soil to roots and from one cell to another. Absorption of water by root hairs from the soil and movement of water from one living cell to another within the plant is brought about by osmosis. The most important factor that affects the uptake is the mineral concentration of salts in soil. Before we discuss other things, we should understand that solutions are classified on the basis of mineral concentrations present in them. On the basis of mineral concentration in these, various types of solutions are Hypotonic solutions,

Hypertonic solutions and Isotonic solutions. You have already studied about them in Unit 2.

d. Mechanism of uptake of water and mineral salts 

 It is quite clear that various mineral elements are present in the water and these are carried along with water to the aerial parts of the plants. This is possible because water is a polar solvent and many mineral ions are highly soluble in it. Many viewpoints have been put forward to help in understanding of water and mineral ions in the plants. Different factors affect this uptake of water and mineral salts. They include the root pressure, transpiration pull, cohesion (ability of water molecules to be linked to one another ) , adhesion (ability of water molecules to be attached to a surface of an objet ) and capillarity action (the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity) .

i. Root pressure 

 As various ions from the soil are actively transported into the vascular tissues of the roots, water follows (its potential gradient) and increases the pressure inside the xylem. This positive pressure is called root pressure and can be responsible for pushing up water to small heights in the stem. How can we see that root pressure exists? Choose a small soft-stemmed plant and on a day, when there is plenty of atmospheric moisture, cut the stem horizontally near the base with a sharp blade, early in the morning. You will soon see the drops of solution ooze out of the cut stem; this comes out due to the positive root pressure. If you fix a rubber tube to the cut stem as a sleeve you can actually collect and measure the rate of exudation, and also determine the composition of the exudates. Effects of root pressure is also observable at night and early morning when evaporation is low, and excess water collects in the form of droplets around special openings of veins near the tip of grass blades, and leaves of many herbaceous parts. Such water loss in its liquid phase is known as guttation.

Root pressure can, at best, only provide a modest push in the overall process of water transport. It obviously does not play a major role in water movement up tall trees. The greatest contribution of root pressure may be to re-establish the continuous chains of water molecules in the xylem which often break under the enormous tensions created by transpiration. Root pressure does not account for 278278 the majority of water transport; most plants meet their need by transpiratory pull.

ii. Transpiration pull

Despite the absence of a heart or a circulatory system in plants, the flow of water upward through the xylem in plants can achieve fairly high rates, up to 15 metres per hour. How is this movement accomplished? A longstanding question is, whether water is ‘pushed’ or ‘pulled’ through the plant. Most researchers agree that water is mainly ‘pulled’ through the plant, and that the driving force for this process is transpiration from the leaves. This is referred to as the cohesion-tension-transpiration pull model of water transport . But, what generates this transpirational pull?

Water is transient in plants. Less than 1 per cent of the water reaching the leaves is used in photosynthesis and plant growth. Most of it is lost through the stomata in the leaves. This water loss is known as transpiration. 

 You have studied transpiration in an earlier class by enclosing a healthy plant in polythene bag and observing the droplets of water formed inside the bag. You could also study water loss from a leaf using cobalt chloride paper, which turns colour on absorbing water.

1 MPa = 10 atmospheres or 14.5 pounds/inch2 . 

The root hairs are not developed in some of conifer plants; thus, water is absorbed with the help of mycorrhizal associations. Mycorrhizal fungi also called vesicular arbuscular mycorrhizae (VAM) also play an important role in absorption of water. Mycellia absorb water and minerals and transfers to the roots. These fungal mycelia obtain their food from the roots. 

 Velamen is a specialized tissue present on the outer side of cortex found in epiphytes such as orchid that absorb water through the hanging roots.

The outer layer of the leaf is epidermis surrounded by palisade parenchyma cells. The epidermis has stomata composed of guard cells. Stomata can be present on both the leaf surfaces. In many plants, stomata are present only on the lower leaf surface. The epidermis is protective in function.

The palisade layer is made up of columnar epithelial cells joined end-to end having many chloroplasts. Below the palisade layer are round spongy parenchyma cells that have conspicuous intercellular spaces. The conducting tissue system consists of tissues present near or at the centre of midrib region. The xylem is composed of vessels and trachieds and phloem has fibres and parenchyma. Larger vascular bundles are surrounded by bundle sheaths .

 Plants do not have systems for transporting oxygen and carbon dioxide. Instead, these gases diffuse through air space within stems, roots and leaves.

e. Transpiration in plants

Transpiration is a physical process responsible for uptake of water in the form of water vapours from the plants. Most of the transpiration takes place from the leaves through stomata, cuticles and lenticels. Transpiration through stomata is called stomatal transpiration. It accounts to 90-95% of the total transpiration. Small quantity of water is also lost through cuticle. Stomatal opening and closing affects the rate of transpiration in plants. Changes in turgor pressure of the guard cells cause stomata to open or close. Both the upper and lower leaf surfaces have a flattened layer of cells called epidermis. Epidermis is covered by a waxy layer called cuticle. In many plants, the lower epidermis has a pair of bean shaped cells called guard cells which along with the subsidiary cells and other guard cells form stomatal complex. Guard cells in dicots are kidney shaped and in monocots are dumbbell shaped. Guard cells have thickenings in inner walls. The guard cells together form a stomatal pore or aperture. Of the total water taken up by the plant most of it is lost in the form of water vapour. This type is cuticular transpiration.

Stomata are also meant for gaseous exchange of oxygen and carbon-dioxide, but transpiration also occurs when they are open . 281 There is a trade off during the gas-exchange that is important for respiration and photosynthesis in the plant systems.

About less than 0.5% is lost through the lenticels, tissues on stem and fruits. This is called lenticular transpiration.

f. Factors affecting transpiration 

The absorption of water from the roots is affected by many physico-chemical properties of soil such as soil temperature, soil air, amount of water available in the soil and concentration of mineral salts in the soil . Atmospheric humidity, temperature, wind velocity, light and water availability in the soil affect the rate of transpiration in the plants. Study of various temperature treatments on plants can be studied by using simple potometers. In increased light intensity stomata open wider to allow more carbon dioxide into the leaf for photosynthesis.

With the increase in wind velocity, there is also increase in the rate of transpiration as water evaporates fast. 

Temperature affects transpiration indirectly through its effect on water vapour present in the air. An increase in temperature brings about decrease in relative humidity of the air thus increasing rate of transpiration.

g. Significance of transpiration Transpiration helps the plants in many ways. It has been considered as a necessary evil. This is because plants lose lot of water due to the process but it is vital for many other physiological processes. The reasons why this process is advantageous to plants are: 

 1. It maintains and regulates temperature by evaporative cooling.

 2. It helps in absorption and transportation of mineral ions in plants. 

 3. It provides water to keep cells turgid in order to support the plant.

 4. It makes water available to leaf cells for photosynthesis.

8.2.2 Transport of organic sap through phloem 

 Process of the movement of food synthesized during photosynthesis from the leaves to the roots and other parts of a plant through the phloem is called translocation. This is carried out by another conducting tissue phloem.

The organic sap transport requires the 3 main steps which are :

 i. Loading: movement of solutes such as carbohydrates from leaf photosynthetic cells/source to the sieve tube of the phloem . 

ii. Translocation : step in which the pressure inside the sieve tube pushes the sucrose and other substances from the source to the sink such as root or flower, stem or fruit or young leaf unable to photosynthesize. 

iii. Unloading: movement of solutes (such as sucrose)followed by water from the sieve tube to the sink cell .

 a. Movement of sugar in plants

As sugar is synthesized in the leaves by the process of photosynthesis its high concentration inside the phloem cells of the leaf creates a diffusion gradient by which more water is transported into the cells. Translocation takes place in the sieve tubes, with the help of adjacent companion cells. Food is translocated in the form of sucrose. The movement of water and dissolved minerals in xylem is always upward from soil to leaves against the gravitational pull. However, the movement of food can be upward as well as downward depending upon the needs of the plants.

b. Mechanism of uptake of food in plants 

 As explained earlier, leaves manufacture food by the process of photosynthesis and transport it to other parts of the plants. Part of plants where food is formed more than requirement is known as source. Leaves act as a source and where these are stored and sent is the sink. Roots act as sinks for food. Movement of food takes place from source to the sink. Leaves prepare food in the form of glucose that is converted into sucrose. Sucrose enters into the phloem at the expense of energy in the form of ATP.

It is noteworthy that in plants, roots, fruits and other organs also act as storage organs for food and from here the food is translocated to other parts. So, the direction of movement of the phloem can be both upwards and downwards and hence the movement is bidirectional. Sugars, hormones and amino-acids are also transported or translocated through phloem. Transport of food involves 3 steps: Phloem loading, translocation and phloem unloading. Sucrose and other carbohydrates are actively loaded into the sieve tubes at the source by a chemiosmotic mechanism. It requires ATP.

ATP supplies energy to pump protons out of the sieve tube members into the apoplast. 

Creates proton gradient. 

The gradient drives the uptake of sucrose into the symplast through channels 

by the cotransport of protons back into the sieve tube members. 

Osmotic concentration of phloem increases due to presence of sucrose. Therefore, water enters into sieve tubes by osmosis, due to which the hydrostatic pressure is created in phloem. High pressure in the phloem allows the movement of food to all parts of the plants having low pressure in their tissues. The pressure-flow hypothesis proposed by Munch is the simplest model and continues to earn widespread support among plant physiologists. The pressure-flow mechanism.

 is based on the mass transfer of solute from source to sink along a hydrostatic (turgor) pressure gradient. Translocation of solute in the phloem is closely linked to the flow of water in the transpiration stream and a continuous recirculation of water in the plant.

Theory proposes that food molecules flow under pressure through the phloem. The food is mixed with water. The pressure is created by the difference in water concentration of the solution in the phloem and the relatively pure water in the nearby xylem. Sugars manufactured in mesophyll cells are driven by energy into the companion cells and sieve tube elements of the phloem. After accumulation into the phloem, water enters in cells by osmosis. A pressure is built up in sieve tubes called turgor pressure. Due to this pressure, sugars are removed by the cortex of both stem and root and consumed or converted into storage products such as starch. Starch does not exert any osmotic effect. Hence, osmotic pressure of phloem cells decreases. Thus, the pressure gradient created between leaves and shoot and root drives the contents of the phloem up and down through the sieve tubes .

Assimilates including sucrose, amino acids and nutrients are transferred into sieve elements of fully expanded leaves against significant concentration and electrochemical gradients. This process is referred to as phloem loading. The cellular pathways of phloem loading, and hence transport mechanisms and controls, vary between plant species. Longitudinal transport of assimilates through sieve elements is achieved by mass flow and is termed phloem translocation. Mass flow is driven by a pressure gradient generated osmotically at either end of the phloem pathway, with a high concentration of solutes at the source end and a lower concentration at the sink end. At the sink, assimilates exit the sieve elements and move into recipient sink cells where they are used in growth or storage processes. Movement from sieve elements to recipient sink cells is called phloem unloading. The cellular pathway of phloem unloading, and hence transport mechanisms and controls, vary depending upon sink function.

A simple experiment, called girdling, was used to identify the tissues through which food is transported .On the trunk of a tree a ring of bark up to a depth of the phloem layer, can be carefully removed. In the absence of downstream movement of food, the portion of the bark above the ring on the stem becomes swollen after a few weeks . This simple experiment shows that phloem is the tissue responsible for translocation of food : and that transport takes place in one direction, i.e., towards the roots.

c. To Investigate Mass Flow Hypothesis In mass flow, Munch’s model demonstrates that fluid flows from the region of high hydrostatic pressure to the region of low hydrostatic pressure. 

 As fluid flows, it carries the whole mass of different substances. 

 In osmometer A, concentrated sucrose solution (leaf) has lower water potential. Water flows into it from a high water potential region (xylem vessel) to a low water potential region (leaf cells) by osmosis. 

 This create high hydrostatic pressure in A and forces sucrose solution to enter into the connecting tube (sieve tube) and pass to B (root cell). 

 As the flow of mass from osmometer A to osmometer B continues, the sucrose solution is pushed along and finally appears in B. 

 In B, contain water/dilute sugar solution, water moves out from a higher water potential region by the hydrostatic pressure gradient produced and redistributed through connecting tube (xylem vessels) between the two containers.

Mass flow continues until the concentration of sugar solution in A and B are equal (balanced). 

 In nature, equilibrium is not reached because solutes are constantly synthesized at source A and utilized at the sink B.

8.2.3 Adaptations of Xerophytes to reduce water loss by transpiration.

Many plants show various morphological features that help them survive in regions with low water availability. The morphological variations are observed in root, stem, branching pattern, types of leaves and other parameters. These variations are manifestations of changes taking place in the plants at various other levels such as anatomical and biochemical level. These variations are termed as adaptations and help plants to survive in a particular environment. Plants that grow in environments that have plenty of water have stomata on both upper and lower epidermal cells of the leaves. These have isobilateral leaves, aerenchyma in stems and undeveloped vascular bundles.

However, the plants growing in low water availability show various xeromorphic and xerophytic characters. Xerophytic plants exhibit a variety of specialized adaptations to survive in such conditions. Xerophytes may use water from their own storage, allocate water specifically to sites of new tissue growth, or lose less water to the atmosphere and so convert a greater proportion of water in the soil to growth.

Xerophytic adaptation of reducing water loss by transpiration: 

 1. Xerophytes have thick waxy cuticle which reduces evaporation as it acts as a barrier. The shiny surface also reflects heat and so lowers temperatures reducing water loss. 

2. They have rolled leaves or leaves reduced to spines to reduce water loss.

 3. Stomata are present in pits. They are sunken. They open at night to reduce the amount of water lost by transpiration. 

 4. Roots are deep and/or spreading to maximize the absorption of underground water. 

 5. They exhibit crassulacean acid metabolism, i.e., CAM Physiology. 

 6. They have fleshy stems or leaves—some cells in stems or leaves have very large vacuoles that acts as water storage areas. These stems are also called succulent stems.

Application activity 8.2

1. Choose among the following terms , those which can complete these statements.

List of terms: Root pressure,Transpiration, Potometer , potassium ion, sunken ,CAM

Statements

i. ……………….. is the loss of water from plants. 

ii. ……………….. is used to study the rate of transpiration. 

iii.Xerophytes have ……………….. stomata. 

iv. Xerophytes exhibit ……………….. metabolism.

2. Draw and describe the mass flow hypothesis in the translocation of phloem sap. 

8.3 Circulatory system in insects, annelids, fish and mammals

 Activity 8.3 

Observe the illustrations of animals below and answer the following questions

8.3. 1 Open circulatory system

The open circulatory system is common to mollusks and arthropods. Open circulatory systems evolved in crustaceans, insects, mollusks and other invertebrates. 

 In animals, circulatory system is either open or closed.

Insects and other arthropods have a heart which is an elongated tube located dorsally. The internal organs are suspended in a network of blood-filled sinuses which collectively form the haemocoel. Blood from the heart mixes with the interstitial fluid in the haemocoel to form haemolymph. The advantage of this system the direct exchange of materials between body cells and haemolymph.

8.3. 2 Closed circulatory system

The earthworm possesses a closed circulation system whereby the blood is confined to a series of blood vessels and not permitted to mix with the body tissues. Blood is pumped around the system by muscular longitudinal and ventral vessels and five pairs of lateral pseudo-hearts in segments 7 to 11. Backflow of blood is prevented by valves. The blood itself contains haemoglobin dissolved in the plasma and some phagocyte cells. It is advantageous for an organism to have closed circulatory system because:

- It helps in control of distribution of blood to different parts of the body.

- Muscular walls of vessels can constrict and dilate to vary the amount of flow through specific vessels

- Blood pressures are fairly high and the circulation can be vigorous

- It is more efficient hence the blood can reach further distances

- Allows for more control over oxygen delivery

All vertebrates including; fish, amphibians, reptiles, birds and mammals possess a prominent muscular heart which pumps blood around the body. The closed circulatory system can be single, partial and double.

Table 8.1: A comparison between open and closed circulatory systems

The closed circulatory system can be single or double.

1. Single circulation in fish

Fish have a two-chambered heart made of one atrium and one ventricle. Deoxygenated blood from the body is pumped by the heart to the gills. Here blood is oxygenated before passing around the body and ultimately returning to the heart. Blood has to pass through two capillary systems, the capillaries of the gills and then those of the body before returning to the heart. Capillaries offer considerable resistance to the flow of blood. This means that, in fish , there is a marked drop in blood pressure before the blood completes a circuit. In this type of circulation, it is an advantage that the blood circulating in the body has already been oxygenated in the gills.

2. Complete double circulation in mammals and birds

The right side of the heart delivers oxygen - poor blood to the capillary beds of the gas exchange tissue in lungs, where there is a net movement of O2 into the blood and of CO2 out of the blood. This part of the circulation is called a pulmonary circuit or pulmonary circulation .After the oxygen- enriched blood leaves the gas exchange tissues, the lungs, it enters the left side of the heart. Contraction of the left part of the heart propels this blood to the capillary beds in organs and tissues throughout of the body. Following the exchange of O2 and CO2 as well as nutrient and waste products, then the oxygen poor blood returns to the right part of the heart, completing the systemic circuit or the systemic circulation.

This circulation is called double circulation because blood must pass twice in the heart for one complete circuit. Mammals and birds have a four-chambered heart and a complete double circulation. The following are some of the advantages of double circulation:

- The heart can increase the pressure of the blood after it has passed through the lungs, so the blood flows more quickly to the body tissues.

 - The systemic circulation can carry blood at a higher pressure than the pulmonary circulation. 

- The blood pressure must not be too high in the pulmonary circulation, otherwise it may damage the delicate capillaries in the lungs.

Partial double circulation in amphibians

Frogs and other amphibians have three-chambered hearts, with two atriums and one ventricle. Blood pumped from the ventricle enters a forked artery. One fork, the pulmonary circulation, leads to the lung. The other fork, the systemic circulation, leads to the rest of the body. Blood returning from the pulmonary circulation enters the left atrium, while blood from the systemic circulation enters the right atrium. Although there is some mixing of oxygenated and deoxygenated blood in the ventricle, a ridge within the ventricle assures that most of the oxygenated blood is diverted to the systemic circulation and most of the deoxygenated blood goes to the pulmonary circulation. In reptiles, this ridge is more developed, forming a partial wall.

In crocodiles, the wall is complete, forming a four-chambered heart like that found in mammals and birds. All amphibians and most of the reptiles possess a heart with two atria and one ventricle. This circulation is called partial because the only one ventricle received oxygenated and non-oxygenated blood which can be mixed as illustrated below:

A spiral valve called conus arteriosus helps to keep deoxygenated and oxygenated blood separate to some extent. The figures below distinguish how closed circulation occurs in fishes and in amphibians.

Table 8.2: Comparison between single and double circulation

Application activity 8.3

1. Choose the statement which is incorrect about the need of transport system in animals:

a. It transports respiratory gases, nutrients, hormones, metabolic wastes etc .

b. It protects against some diseases thanks to antibodies, against permanent bleeding thanks to thrombocytes etc.

c. It contributes to regulation (homeostasis)such as thermoregulation.

d. It contains neurons that conduct the nerve impulses.

2. Show how the open and closed circulatory systems differ.

3. Draw the human double circulation

8.4 Structure of the mammalian heart

Activity 8.4

Aim: To investigate the structure of human heart

Materials: Mammalian heart, dissecting kit.

Procedure

i. Obtain an intact heart of sheep or goat from a butcher’s shop or slaughterhouse

ii. Rinse it under a tap to remove excess blood

iii. Observe the surface of the heart and identify the main visible features

iv. The blood vessels may have been cut off, but it is possible to identify where

v. These would have been attached later in the dissection

The heart is a striated muscle located between the two lungs and behind the sternum in the thorax and which contracts in order to propel blood throughout the body

The walls of the heart are composed of interconnected cardiac muscle fibers, connective tissue and tiny blood vessels. Each fiber possesses one or two nuclei and many large mitochondria. The heart is surrounded by a tough sac called pericardium. A pericardial fluid is secreted between the membranes allowing them to move easily over each other. The pericardium protects the heart from overexpansion caused by elastic recoil when it is beating very fast. The walls of the heart consist mainly of a special type of muscles called cardiac muscle.

The heart is divided into a left and a right side separated by the septum. The heart of mammals and birds is composed of 4 chambers including 2 upper thinwalled atria and 2 lower thick-walled ventricles. The right side of the heart is completely separated from the left. The right-side deals with deoxygenated blood and the left side with oxygenated blood. The muscular wall of the left ventricle is thicker than that of the right ventricle because the left ventricle has to pump blood to all round the body with much higher pressure.The left atrium is separated from the left ventricle by a bicuspid or mitral valve, whilst a tricuspid valve separates the right atrium from the right ventricle. Jointly, these two valves are known as atrioventricular valves. Atrioventricular valves are pushed open when atria contract but, when ventricles contract, they close and produce the first sound of the cardiac cycle, the second being that of the closing semi-lunar valves (aortic and pulmonary valves)

Application activity 8.4

1. Justify this statement: The right atrium is larger than the left atrium.

2. Associate the column A and B

8.5 Heartbeat and the mammalian cardiac cycle 

Activity 8.5: research activity

Use a computer simulation or a chart to observe the initiation of a heart and cardiac cycle. Then, draw the cardiac cycle that you have seen.

- Heartbeat is a rhythmic sequence of contractions of the heart. It is coordinated by two small groups of cardiac muscle cells called the sinoatrial (SA) and atrioventricular (AV) nodes. The sinoatrial node, often known 298298 as the cardiac pacemaker, is found in the upper wall of the right atrium and is responsible for the wave of electrical stimulation that starts atrial contraction by creating an action potential. The action potential causes the cardiac cells to contract. This wave of contraction spreads across the cells of the atrium, reaching the atrioventricular node (AV node) which is found in the lower right atrium.

- The atrioventricular node conducts the electrical impulses that come from the SA node through the atria to the ventricles. The impulse is delayed there before being conducted through special bundles of heart muscle cells called the bundle of His. There is a collection of heart muscle cells (fibers) specialized for electrical conduction that transmits the electrical impulses from the AV node and the Purkinje fibers, which leads to a contraction of the ventricles. This delay allows for the ventricles to fill with blood before the ventricles contract. Heartbeat is also controlled by nerve messages originating from the autonomic nervous system. 

- The bundle of His branches into Purkinje fibers. Purkinje fibers, specialized cardiac muscle cells, conduct action potentials into the ventricles and cause the cardiac muscle of the ventricles to contract in a controlled way.

The cardiac cycle is the sequence of events which take place during the completion of one heartbeat. It involves repeated contraction (systole) and relaxation (diastole) of the heart muscle.

The steps in cardiac cycle are the followings: 

1. Atrial and ventricular systoles

 - When atria diastole ends, the two atria contract simultaneously, and it results in blood being pumped into the ventricles. The ventricles contract almost immediately after the atria, about 0.1 to 0.2 seconds later. When this occurs, the pressure in the ventricles rises and closes the atrioventricular valves, preventing blood from returning to the atria. 

 - The pressure forces open the semilunar valves and blood enters aorta and pulmonary artery. Arterial blood pressure is the highest when the heart contracts during ventricular systole. The pressure at this time is called systolic pressure. The high blood pressure caused by the powerful contractions of the ventricles stretch the arteries.

2. Atrial and ventricle diastoles 

- During the time when the atria and ventricles are both relaxed, blood returns to the heart under low pressure in the veins and enters the two atria. At first the atrioventricular valves are closed but, as the atria fill with blood, pressure in them rises. Eventually it becomes greater than that in the relaxed ventricles and valves are pushed open.

- The higher pressure developed in the aorta and pulmonary artery during the ventricular systole tends to force some blood back towards the ventricles and this closes the semilunar valves. Hence backflow into the heart is prevented. The ventricular diastole ends the cardiac cycles and is followed by the atrial diastole. Hence the cycle restarts. When the heart rate is 75/min, which means 75 heartbeats per minute, the period of one cardiac cycle is 0.8 sec. During diastole, the elastic walls of the arteries snap back. As a consequence, there is a lower but still substantial blood pressure when the ventricles are relaxed (diastolic pressure).

- In healthy adults, there are two normal heart sounds often described as a lub and a dub that occur with each heart- beat (lub-dub, lub-dub). In addition to these normal sounds, a variety of other sounds may be 300300 heard including heart murmurs or clicks. A medical practitioner uses a stethoscope to listen for these sounds, which gives him or her important information about the condition of the heart.

- The closing of atrioventricular valves, mitral (bicuspid) and tricuspid, during ventricular systole produces the first heart sound, described as lub. 

- the closing of the semilunar valves during ventricular diastole causes the second heart sound described as dub.

- The electrical activity of the heart can be monitored using an Electrocardiogram (ECG). This involves attaching of sensors to the skin. Some of the electrical activity generated by the heart spreads through the tissue next to the heart and onwards to the skin. The sensors on the skin pick up the electrical excitation created by the heart and convert this into a trace. 

 - The trace of a health person has particular shape. It consists of a series of waves that are labeled P, Q, R, S and T. Wave P shows the excitation of the atria, while QRS indicates the excitation of the ventricles and T shows diastole.

1. P: P wave- indicates that the atria are electrically stimulated (depolarized) to pump blood into the ventricles: contraction of atria.

2. QRS: QRS complex- indicates that the ventricles are electrically stimulated (depolarized) to pump blood out: in pulmonary artery and in aorta.

3. ST: ST segment- indicates the amount of time from the end of the contraction of the ventricles to the beginning of the T wave.

4. T: T wave- indicates the recovery period (repolarization) of the ventricles.

5. U: U wave- rarely seen, and thought to possibly be the repolarization of the papillary muscles.

Application activity 8.5 

1. During the mass sports, the doctor made a medical check-up and found the following data from three participants A, B and C.

a. Among three participants, who has the cardiovascular problem? Why? 

b. Differentiate between systolic and diastolic pressure 

2. Observe the illustration below and answer to the following questions:

a. Interpret the shape of the electrocardiogram trace above. 

 b. Explain why the QRS complex has a larger peak than the P wave.

8.6 Control of the heart rate and the factors controlling heart rate 

Activity 8.6 

Aim: Investigate and state the effect of physical activity on the pulse rate and blood pressure. 

 Material: Watch, or stop clock.

Procedure: 

a. Place your middle finger on the artery found near the opening of the ear then determine the number of pulses during resting. Repeat this 3 time then calculate the average of heart- beat per minute.

 b. Do some warm-up exercises within 2 minutes, again place your middle finger on the artery found near the ear then determine the number of pulses during resting. Repeat this 3 time then calculate the average of heart -beat per minute. Just use the stop clock or a watch to count the number of pulse (beatings) within one minute.

 i. How does your heart rate immediately after a warm -up exercises differ from resting rate? 

ii. How would you explain the differences?

8.6. 1 Control of the heart rate

a. Nervous and hormonal control of heart rate 

Heart muscle is myogenic because it has the ability to initiate its own contractions. The initiation of an action potential to travel along the atrial walls as a wave of excitation causing the contraction is initiated by the sinoatrial node (SAN) or pacemaker. This is where one heartbeat originates, then the signal spreads through the atrioventricular node (AVN) and down the Purkinje tissue to the ventricular apex, and finally through the ventricles, causing them to contract. The signals are sent from brain to the SAN through two nerves from the autonomic nervous system specifically sympathetic nerve and vagus nerve from the brain to the heart. The cardiovascular center that sends impulses to the SAN is located in the medulla oblongata of the hindbrain. The medulla oblongata receives various signals itself, so that it can communicate with the SAN how to coordinate an appropriate response to the external changes. If the vagus nerve is stimulated, it causes a release of acetylcholine (neurotransmitter) , which slows down the rate of heartbeat but does not affect the force of ventricular contraction. Baroreceptors located in the aorta and carotid arteries detect the pressure of blood from the left ventricle. When the pressure is low, the baroreceptors stimulate the vasomotor center (VMC) of the hindbrain to send impulse via sympathetic nerve fibers. This induces vasoconstriction which causes increased resistance to blood flow and a corresponding rise in blood pressure. Conversely, when blood pressure is high, the impulses from VMC pass along parasympathetic fibers and stimulate vasodilation which causes reduction in blood pressure.

- The hormone called adrenaline (epinephrine) also affects the heart rate. In conditions of excitement, activity or stress, the adrenaline is released into the blood circulation from the adrenal glands (specifically adrenal medulla). Reaching the heart, it causes an increase in the rate and strength of the heartbeat. 

 - Epinephrine is also called adrenaline; norepinephrine is also called noradrenaline.

b. Other factors controlling heart rate 

i. Carbon dioxide

Chemically, high CO2 levels stimulate the vasomotor Centre (VMC) to vasoconstrict arterioles. The resulting high blood pressure transports CO2 more rapidly to the lungs for expulsion and exchange with O2 . Where tissues suddenly become active, they produce more CO2 . This causes vasodilation of local blood vessels, thus increasing their blood supply and allowing more oxygen and glucose to reach them for respiratory purposes.

ii. Body temperature change 

This is one of the thermoregulatory changes that occur to prevent the body’s core temperature of 370 C from increasing or decreasing. Heart rate increases when heat is gained by the body such as in hot climates and during physical exercise in order to transfer more heat away from the body. When the body loses heat such as in cold weather or a cold shower, heart rate decreases to preserve core temperature.

iii.pH and Mineral ions 

A significant heart rate increase was obtained after a decrease of potassium and calcium and an increase in pH levels and with no significant variations in indices of autonomic activity. The analysis revealed that changes in physiological range of potassium, calcium, and pH could cause large heart rate variations from 60 to 90 bpm.

c. Effect of drugs and physical activity on cardiac frequency 

 i. Physical exercise 

 The heart rate and blood pressure both rise during physical exercise. Over time, regular physical exercise can help lower the resting blood pressure and heart rate. This is because physical exercise training improves the health of the heart and blood vessels, allowing the cardiovascular system to function more efficiently. This enables increased blood flow to muscles without putting excess pressure on blood vessel walls.

While blood pressure rises during exercise, it is too much smaller degree than the increase in heart rate.

ii. Caffeine and other drugs 

Caffeine found in coffee, tea and soda is a stimulant drug that influences the nervous system to increase heart rate. It mimics the effect of adrenaline, a natural hormone in the body responsible for elevating heart rate. Other stimulants such as cocaine and ephedrine work in a similar manner.

There are specific drugs used in lowering heart rate such as beta- and calcium channel blockers. Beta-blockers work by interfering with the receptors that adrenaline binds to, subsequently decreasing hormonal influence on heart rate. Calcium channel blockers reduce the amount of calcium that enters the heart muscle. Because calcium is needed for muscle to contract, the heart beats at a slower rate when this drug is taken.

Application activity 8.6 

1. The following is a list of hormones : oestrogen, progesterone, adrenaline, cortisol. 

i. Identify the main hormone that immediately affects the heartbeat during stress. 

ii. Relate that hormone to the heartbeat rate. 

2. Some drugs like caffeine affect the heartbeat rate. Justify this statement.

8.7 Structure of blood vessels 

Activity 8.7

Aim: To observe prepared slides of blood vessels.

Materials: Microscope, prepared slides of blood vessels and electrical current.

Procedure

i. Place the prepared slides of blood vessels on the microscope slide.

ii. Adjust to observe the blood vessels

Questions

1. Draw and label the observed blood vessels.

2. Compare those blood vessels.

3. Explain the relationship between each blood vessel and its function.

Table 8.4. Comparison between arteries, capillaries and veins.

Application activity 8.7

1. Associate the following vessels with their functions

2. Link the adaptations of blood vessels to their functions.

8.8 Blood composition, its functions and cardiovascular diseases.

Activity 8.8

Aim: To examine the blood sample composition 

Materials : Blood collected from the bucher, sharp material such as blade or knife, test tube or other container, microscope, slide, coverslip, stain ( such as methylene blue) and cleaning tissue.

Procedure: 

a. Visit a bucher and collect blood of animals (such goat, cow,…)

b. Place the blood in the container.

c. Use a microscope to observe a blood smear:

i. Place 3 drops of blood on the slide.

ii. Add 2 drops of stain (such as methylene blue).

iii. Cover with a coverslip

iv. Place the prepared sample on the microscope stage.

v. Adjust for observation. 

1. Draw the structure of blood cells. 

2. Identify body fluids composition.

3. Discribe cardiovascular diseases.

4. Discuss the relationship between blood, tissue fluid and lymph.

8.8.1 Main types of body fluids and their compositions

Body fluids are liquids originating from inside the body of living humans. 

Table 8.5: Body fluids and their composition

8.8.2 Composition and functions of blood 

 The main blood components are formed elements and plasma. Formed elements are erythrocytes (red blood cells), leukocytes (white blood cells) and thrombocytes (platelets).

Table 8.6: Blood composition

Application activity 8.8

1. Choose the cells contributing to phagocytosis of pathogens :

a. Macrophage.

b. T-lymphocytes.

c. Erythrocytes

2. Relate the blood to tissue fluid.

3. Look at the figure below and answer the questions that follow.

a. Identify the blood components represented by the letters A, B, C, D, E, F, G, H, I.

b. Identify the origin of each blood component.

c. Show the functions of each of those blood components.

8.9 Transport of respiratory gases 

Activity 8.9: research

The respiratory gases are oxygen (O2 ) and carbon dioxide (CO2 ) transported by haemoglobin.

Hemoglobin is a red protein responsible for transporting oxygen in the blood of vertebrates. It is also involved in the transport of carbon dioxide.

Hemoglobin is composed of heme and globin (polypeptide chains). Heme is iron porphyrin compound. Ferrous iron occupies the center of the porphyrin ring and establishes linkages with all the four nitrogen of all the pyrrole rings. It is also linked to nitrogen of imidazole ring of histidine present in globin part.

Globin part is made of four polypeptide chains, two identical α-chains and two identical β-chains in normal adult hemoglobin. Each chain contains a “heme” in the so called ‘heme pocket’ and one hemoglobin molecule possess four heme units. Hemoglobin molecule contains hydrophobic amino acids inside and hydrophilic ones on the surface. Heme pockets of α-subunits are of just adequate size to give entry to an O2 molecule. Entry of O2 into heme pockets of β-subunits is blocked by a valine residue.

b. Transport of carbon dioxide (CO2)

 At systemic capillaries, CO2 enters red blood cells. Some CO2 combine with Hb to form HbCO2 (Carbaminohemoglobin)

 Hb + CO2 →HbCO2 (Carbaminohemoglobin). 

Most CO2 is converted to HCO3 - (bicarbonate ion), which is carried in the plasma. 

Hemoglobin is in relation with chloride shift, also known as the Hamburger shift named after Hartog Jakob Hamburger. It is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3 − ) and chloride (Cl− ) across the membrane of red blood cells (RBCs). The chloride shift occurs in this way:

HHb is reduced hemoglobin which is hemoglobin combined with hydrogen ion (H+ ).

c. Transport of oxygen 

Hemoglobin (Hb) gets oxygen in lungs from external environment to alveoli to pulmonary capillaries; Hb transports it, via the circulatory system, until it reaches the systemic capillaries from which it diffuses toward the tissue fluid and tissues cells. In tissue cells, oxygen is involved in aerobic cell respiration. The reaction between oxygen and hemoglobin is summarized as follows:

- Oxygen dissociation curve is determined by plotting the partial pressure of oxygen in blood as the abscissa and the percentage of hemoglobin combined with oxygen in the form of oxyhemoglobin as the ordinate. 

 - The s-shape of the oxygen dissociation curve can be explained by the behavior of a hemoglobin molecule as it combines with or loses oxygen molecules. When an oxygen molecule combines with one haeme group, the whole haemoglobin molecule is slightly distorted. The distortion makes it easier for a second oxygen molecule to combine with a second haeme group. This in turn makes it easier for a third oxygen molecule to combine with a third haeme group. It is then still easier for the fourth and final oxygen molecule to combine.

- Once oxygen molecule is combined with hemoglobin, it becomes successively easier for the second and third oxygen molecules to combine, so the curve rises very steeply. Over this part of the curve, a small change in the partial pressure of oxygen (2 kPa) causes a very large change in the amount of oxygen which is carried by the hemoglobin. 

 - The oxygen saturation can be calculated at this stage. It is a measurement of the percentage of oxygen binding sites. If all the oxygen binding sites contain oxygen, then the oxygen saturation is 100%. Oxygen saturation is defined as the ratio of oxyhemoglobin to the total concentration of hemoglobin present in the blood (Oxyhemoglobin + Reduced hemoglobin). Haemoglobin concentration is expressed as g/dl and the normal range for hemoglobin is 13.5 to 17.5 grams per deciliter for men, and 12.0 to 15.5 grams per deciliter for women.

Oxygen saturation 

Where: c (Hb) = concentration of deoxygenated hemoglobin, 

C (HbO2 ) = concentration of oxygenated hemoglobin. 

 - The Bohr effect is a physiological phenomenon in which a raise of carbon dioxide in the blood and a decrease in pH results in a reduction of the affinity of hemoglobin for oxygen. This causes the oxygen dissociation curve for hemoglobin to shift to the right. The Bohr Effect occurs in this way:

8.10 Blood clotting and common cardiovascular diseases 

Activity 8.10: research 

Research, using internet and library books: activity

1. The process of blood clotting.

2. The cardiovascular diseases and possible risk factors; then, present your findings to your classmates.

a. Blood clotting 

 Blood clotting also known as blood coagulation is the process by which blood becomes thick and stops flowing, forming a solid cover over any place where the skin has been cut or broken. Blood that has been converted from a liquid to a solid state is called blood clot. A blood clot called thrombus is stationary within a vessel or the heart. If a blood clot moves from that location through the bloodstream, it is referred to as an embolus.

Blood clotting is a series of different processes: 

Step1: The blood coagulation process begins when the endothelium of a vessel is damaged, exposing the connective in the vessel wall to blood. Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky. 

Step2: The thrombocytes form a plug that provides emergency protection against blood loss.

Step3: This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via a multistep process where clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma, forming an activation that converts a plasma protein called prothrombin to its active form, called thrombin. This is facilitated by calcium ions and vitamin K. Thrombin itself is an enzyme that catalyzes the final step of the clotting process. This final step is the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch. And the blood clot is formed. These threads trap red blood cells and other blood components, preventing the continuous bleeding.

b. Common cardiovascular diseases 

1. Stroke Stroke is a cardiovascular disease due to the lack of oxygen to the brain which may lead to reversible or irreversible paralysis. The damage to a group of nerve cells in the brain is often due to interrupted blood flow, caused by a blood clot or blood vessel bursting. 

2. Atherosclerosis 

Atherosclerosis is a cardiovascular disease characterized by the progressive narrowing and hardening of the arteries over time. Atherosclerosis normally begins in later childhood, and is usually found in most major arteries. It does not usually have any early symptoms. Causes of atherosclerosis include a highfat diet, high cholesterol, smoking, obesity, and diabetes.

3. Coronary heart disease

 Coronary heart disease (CHD) is a disease in which a waxy substance called plaque builds up inside the coronary arteries. 

c. Risk factors associated with cardiovascular diseases 

 1. Uncontrollable factors include the:

 i. gender (males are at greater risk),

 ii. age (old people have higher risk)/senescence 

iii. family/ genetic history in relation to heart diseases 

 iv. post-menopausal stages for females. Making some changes in lifestyle can reduce chance of having heart disease.

2. Controllable risk factors include:

i. smoking, 

ii. high blood pressure, 

iii. physical inactivity, 

iv. obesity, 

v. diabetes, 

vi. stress anger

Application activity 8.10

1. Relate smoking and much lipids consumption to the cardiovascular system diseases.

2. A woman liked to cook most food with oil. Then after 10 years most of members of her family including herself become obese and undergo hypertension; once her husband suddenly fell down and died.

a. Identify 2 suspected cardiovascular diseases associated with his death.

b. Demonstrate how one of those diseases develops.

8.11 Lymphatic system

Activity 8.11

Describe the structure and function of the lymphatic system.

8.11.1 Structure of a lymphatic system 

A lymphatic system is system composed of tissues and organs, including the bone marrow, spleen, thymus and lymph nodes that produce and store cells that fight infection and disease. The channels that carry lymph are also part of this system. So, the lymphatic system is part of the circulatory system and an important part of the immune system.

8.11.2 Functions of a lymphatic system

 iii. Drainage of fluid from blood stream into the tissues: The circulating blood through narrow vessels leads to leakage of fluid or plasma into the tissues carrying oxygen and nutrients to the tissues and taking waste materials from the tissues into the lymph channels. The leaked fluid drains into the lymph vessels.

 iv. Filtration of the lymph at the lymph nodes: The nodes contain white blood cells that can attack any bacteria or viruses they find in the lymph as it flows through the lymph nodes.

The cancer cells may also get trapped similarly at the lymph nodes and thus lymph nodes act as indicators of how far the cancer has already spread. 

v. Filtering blood: This is done by the spleen which filters out bacteria, viruses and other foreign particles. 

vi. Raises an immune reaction and fights infections: The lymphatic system especially the lymph nodes are over active in case of an infection; the lymph nodes or glands often swell up in case of a local infection.

8.11.3 Formation of tissue (interstitial) fluid 

 Fluids and proteins leak from the blood capillaries into the interstitial fluid that bathes the cells of tissues. This occurs due to the arterial end of capillary, where the blood pressure is greater than osmotic pressure so that fluid flows out of capillary into the interstitial fluid. This process is called pressure filtration or ultrafiltration.

Formation of lymph 

The lymph is the tissue fluid that moves within the lymphatic vessels. The lymphatic vessels recover some leaked fluid and proteins, and carry them to large veins at the base of the neck.

8.11.4 Comparison between lymphatic and circulatory systems 

Both cardiovascular and lymphatic systems are vascular networks carrying body fluids. 

Table 8.7. Differences between lymphatic and circulatory system

Application activity 8.11

Observe the figure below and respond to the following questions.

1. Identify the organs W, X, Y, Z shown on this figure 

2. Explain why the organs W, X, Y, Z are important to the body.

Skills lab 8

Aim: Acquire dissection skills and money.

Materials: Small capital, rabbit, breeding site of rabbits.

Procedure

1. Using your pocket money, buy two rabbit (male female).

2. Breed those rabbits and allow them to produce offspring.

3. Among the produced young ones, dissect one mature rabbit to investigate its circulatory system (heart, blood vessels and blood) structure.

4. Sell some of the young ones to get money.

Portfolio Report

i. Write your skills lab project implementation report focusing on how this skill lab has helped you to get much money and new biological skills, submit it to your teacher.

ii. Invite your classmate to visit your bleeding places at home

Note: Invent or discover other skill labs related to this unit.

End unit assessment 8

1. Blood returning to the mammalian heart in a pulmonary vein drains first into the:

a. Vena cava b. Left ventricle, c. Right ventricle, d.Left atrium

2. Pulse is a direct measure of:

a. Blood pressure, b. Breathing rate, c. cardiac output, d . Heart rate. e. stroke volume

3. Complete the following paragraph by filling in the blank spaces.

Blood is ………………in the lungs. The red pigment ………………has a high affinity for oxygen. The pumping action of the……………creates pressure which pushes the blood around the body. In the tissues the partial pressure of…………….is low. This causes the ………………of the oxyhaemoglobin. In the tissues, the oxygen is used in the process of……………………. Most of the carbon dioxide produced in this process enters the……………. cells. Here it is converted to carbonic acid by the action of the enzyme carbonic anhydrase. The carbon dioxide is transported as ………………. back to the lungs.

4. How many oxygen molecules can each haemoglobin molecule transport? 

5. Explain the function of fibrinogen.

6. Distinguish between plasma and serum.

7. a. Explain why haemoglobin is called conjugated protein.

 b) Describe the effect of high carbon dioxide concentrations on  the oxygen dissociation curve of haemoglobin.

8) a) By which process does fluid leave the blood and enter the  tissue fluid?

b) Which component of the blood does not enter the tissue fluid? 

9. The figure below shows a cross section through the human heart

a. Label the structure A-E

b. What are the functions of the structures A and B

10. The figure below shows pressure changes to the left side of the heart and the aorta during the cardiac cycle

a. State what is happening at point A-D on the graph. Explain your answer.

b. If the time taken for one complete cardiac cycle is 0.8 seconds, how many cardiac cycles are there in one minute?

11 Explain any two advantages of closed double circulatory system and 

two disadvantages of open circulatory system.

12 a) Where is the radial pulse taken?

 b) Suggest what will happen to the heart rate if the vagus nerve is cut off.

13 The diagram shows a vertical section through a human heart. The arrows represent the direction of movement of the electrical activity which starts muscle contraction

Carefully, observe the following and answer the questions that follow.

a. Name the structure denoted by the letter A

b. Explain why each of the following is important in then pumping of blood through the heart.

i. There is a slight delay in the passage of electrical activity that takes place at the point A

ii. The contraction of the ventricles starts at the base

c. Describe how stimulation of the cardiovascular centre in the medulla may result in an increase in heart rate.

14. Read the following passage and answer the questions that follow. 

The human heart is a double pump adapted to forcing blood, at the same rate but at different pressures, along the two systems of double circulation. High pressure in the systemic circulation has evolved with lower pressure in the pulmonary circulation and low pressure lymphatic circulation. Each heart beat is controlled by a wave of electrical excitation. In turn, the cardiac output of the heart adapts to meet the body needs and is influenced by nervous and hormonal control. 

a. Based on the statement: “The human heart is a double pump adapted to forcing blood, at the same rate but at different pressures, along the two systems of double circulation”. Explain how the mechanism that controls each heartbeat, and the structure of the heart, enable it to do this. 

b. Describe the role played by hormones and the nervous system in controlling heart rate. 

c. Describe the formation of how lymph fluid. 15. Draw this picture in your exercise book. It shows various internal parts of a leaf. These are marked us A, B, C, D, E and F. Identify and name these parts.