Maintaining a BalancePart 2

Maintaining a Balance

Contextual Outline

Multicellular organisms have specialised organ systems that are adapted for the uptake and transport of essential nutrients from the environment, the utilisation or production of energy and the removal of waste products arising from cellular activities.

The basis of healthy body-functioning in all organisms is the health of their cells. The physical and chemical factors of the environment surrounding these cells must remain within narrow limits for cells to survive. These narrow limits need to be maintained and any deviation from these limits must be quickly corrected. A breakdown in the maintenance of this balance causes problems for the organism.

The nervous and endocrine systems in animals and the hormone system in plants bring about the coordinated functioning of these organ systems. They are able to monitor and provide the feedback necessary to maintain a constant internal environment. Enzyme action is a prime example of the need for this balance. Enzymes control all of the chemical reactions that constitute the body’s metabolism. As enzymes normally function only within a narrow temperature range, even a small rise in body temperature can result in the failure of many of the reactions of metabolism that are essential to life.

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Say What

Maintaining a Balance

Part 2

Plants and animals transport dissolved nutrients and gases in a fluid medium

Background: Blood is the transport medium of mammals. It maintains the internal environment of all organs as it supplies material to every cell in the body and removes the unwanted substances that cannot be allowed to accumulate in cells. Blood consists of 55% plasma, a straw-coloured liquid of which 90% is water. The other components of the blood are red and white blood cells and platelets.

Red blood cells are unique in that they do not contain a nucleus and have a biconcave shape. They are much smaller than white blood cells and more numerous. They contain the protein haemoglobin, a complex protein molecule consisting of four polypeptides, each containing an iron atom. The iron atom has an affinity for oxygen molecules. When haemoglobin is combined with an oxygen molecule, it is called oxyhaemoglobin.

Plants carry dissolved mineral nutrients in the xylem vessels and carry food (mostly glucose) in phloem tubes.

identify the form(s) in which each of the following is carried in mammalian blood:– carbon dioxide– oxygen– water– salts– lipids– nitrogenous waste– other products of digestion

Carbon DioxideMost carbon dioxide enters the red blood cells and is combined with water to form bicarbonate ions (HCO3

-). Some is attached to haemoglobin molecules in red blood cells and a small percentage is transported in plasma as dissolved CO2.

It is produced as a waste product of respiration in body cells.

After entering the bloodstream it may:

Be converted into carbonic acid which is then changed into hydrogen

carbonate ions. This change from carbon dioxide to carbonate ions

happens on the red blood cells. Then they are just transported in the

plasma.

Binds to haemoglobin in erythrocytes forming carbaminohaemoglobin

Be dissolved directly in the plasma.

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Carbon dioxide + water → carbonic acid → hydrogen ions + hydrogen carbonate ions

CO2 + H2O → H2CO3 → H+ + HCO3-1

Oxygen attaches itself to haemoglobin in the red blood cells, becoming a complex called oxyhaemoglobin (HbO2).   Liquid water is the solvent making up 90% of the plasma.   Salts are carried as dissolved ions in the plasma.   Lipids are carried with phospholipids and cholesterol in a protein coated package called a chylomicron.  The nitrogenous wastes (urea, uric acid and creatinine) are dissolved in blood plasma.   Other products of digestion, such as sugars, amino acids and various vitamins, are transported in the plasma.

explain the adaptive advantage of haemoglobin

Oxygen is not very soluble in water and so cannot be carried efficiently dissolved in the blood plasma. Most of the oxygen is carried by haemoglobin in the red blood cells. Thus, the presence of haemoglobin in red blood cells in blood increases the blood's capacity to carry oxygen. Organisms with blood (containing haemoglobin) are able to deliver oxygen to cells more efficiently than other organisms with blood that has no haemoglobin. The net effect is that these organisms are more effective operators in a given environment than their competitors.   At high altitudes, blood is not able to absorb as much oxygen as at sea level. The human body adapts to what is effectively oxygen deprivation by initially increasing heart rate, breathing rate, then the number of red blood cells (more haemoglobin), and the density of capillaries.

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Structure of haemoglobin:

Globule-shaped protein containing four polypeptide sub-units

Each polypeptide encloses an IRON-containing structure, called

the HAEM group (4 HAEM groups altogether)

The haem groups combine with the oxygen.

Oxygen fuses with haemoglobin where the concentration of oxygen in the

blood is low; that is, in the lungs.

It makes an unstable compound – oxyhaemoglobin

One haemoglobin molecule can carry four molecules of oxygen

Hb + 4O2 = Hb(O2)4

Where oxygen is needed, the oxygen bond easily breaks and the oxygen is used.

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Adaptive Advantage:

Mammalian cells need a lot of energy and therefore must have a

continual supply of OXYGEN for RESPIRATION

Oxygen is not very soluble in water

Blood is a WATERY liquid; if oxygen was carried only by being

dissolved in blood plasma, 100 ml of water would only be able to

carry 0.2 ml of oxygen

The presence of haemoglobin increases the oxygen carrying capacity

of blood by 100 times. Now 100 ml of blood can carry 20 ml of

oxygen.

Dissolved only ----> 0.2 ml O2 / 100 ml blood

Haemoglobin ----> 20 ml O2 / 100 ml blood

This ability of blood to carry large quantities of oxygen gives

mammals a considerable survival advantage

It allows mammals to be active, as well as grow large.

1ml of blood contains 5-6 million red blood cells.

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compare the structure of arteries, capillaries and veins in relation to their function

ARTERIES:

Carry blood away from heart (high blood pressure)

The pressure created by the heart’s pumping creates great stress and high pressure in the arteries

This is why the arteries are thick walled, elastic and muscular.

They have thick, but elastic walls, made up of three tissue layers: endothelium as a lining, smooth muscle to contract the vessel and connective tissue to allow for expansion. Arteries do not pump blood.

The arteries are not motionless; they have muscle fibres in them which can

contract and relax.

This contracting maintains the pressure on the blood, so that the blood travels

in spurts towards the body tissues (the contracting and relaxing also creates

the pulse on your wrist or neck).

The muscle fibres of the arteries also maintain the rate of the flow of blood.

Arteries usually carry oxygenated blood

Arteries lead to arterioles (small arteries).

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CAPILLARIES:

Capillaries are an extension of the inner layers of the arteries and veins

They join arterioles and venules (small veins).

Capillaries are only one cell thick, and are so narrow, that only one red blood

cell can pass at a time.

Capillaries surround all tissue cells.

Thus, they provide a very large surface area over which exchange of materials

between blood and body can occur.

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VEINS:

Veins carry blood back to the heartThe capillaries join to form venules, which join to form veins

Veins are not under a lot of stress - blood pressure is low

This is why they have thinner walls than arteries, less muscle and a wider

diameter.

Since there are no thick muscular walls to keep the blood pulsing along, the

veins have a series of valves which prevent the blood from back-flowing on its

way back up to the heart.

The veins also run through muscles, such as your leg muscles, and as you use

these muscles, they press on the veins, pushing blood through the veins.

Veins have the same three layers as the arteries: endothelium, smooth muscle and connective tissue. However, the layers are not as thick.

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describe the main changes in the chemical composition of the blood as it moves around the body and identify tissues in which these changes occur

PULMONARY CIRCUIT:

Blood flows from heart to lungs and then back to the heart.

Blood is under lower pressure than in the systemic circuit.

However, the rate of blood flow is faster.

The blood, having just returned from the body, contains high CO2

levels and low oxygen levels

In the lungs, blood loses CO2 and collects oxygen

SYSTEMIC CIRCUIT:

Blood flows from the heart to the body (except the lungs) and

returns back to the heart.

Blood is under high pressure due to contractions of the left

ventricle of the heart, but pressure gradually lessens.

Blood pressure forces some fluid out of blood to become body fluid.

In the tissues:

1. Blood gives up oxygen and other ions and nutrients

2. Waste products, eg urea, CO2, enter the blood

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KIDNEYS:

Blood loses urea to the kidney and the kidney controls the level of water and salts.

INTESTINES:Blood collects the products of digestion

Levels of glucose, lipids, and amino acids rise

LIVER:

Regulates the level of glucose in blood

Excess glucose is converted to glycogen and is stored

Converts excess amino acids to urea

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outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is essential

All living cells need oxygen for respiration.

As a result of respiration, carbon dioxide is produced

When carbon dioxide dissolves in water, it makes carbonic acid.

This means that if a lot of carbon dioxide is produced, the body cells (and the

blood and lymph) will become acidic

As studied before, enzymes can only function within a specific pH range

So an increase in carbon dioxide will result in a lowering of pH, which will affect

the overall metabolism of the body.

describe current theories about processes responsible for the movement of materials through plants in xylem and phloem tissue

XYLEM:

Transport of water is passive and depends on transpiration and the physical

properties of water:

1. Transpiration: Evaporation of water from the leaf cells through the

stomates initiates the pull of the TRANSPIRATON STREAM. Water is

then drawn up the xylem tubes to replace this loss

2. Cohesion: Water molecules tend to bind together, forming a continuous

column in the xylem, which replaces any loss

3. Adhesion: Water molecules stick to the sides of the xylem tubes (cellulose

walls).

The movement of water through narrow tubes is called CAPILLARITY (Capillary action)

It is caused by the two forces of COHESION and ADHESION

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PHLOEM:

Movement of organic molecules, eg sugars, amino acids and hormones, in the

phloem is called translocation.

Materials are transported both up and down the stem. Materials are distributed

especially to the growing points and reproductive structures, including

developing fruits and seeds

Flow of materials in the phloem is an active process that requires energy.

It is thought to occur by a mechanism called the source-path-sink system and

is driven by a gradient generated osmotically.

Theory 1: The source-path-sink system

1. Sugars and other mineral nutrients are ‘loaded’ into phloem sieve tubes of

the leaves:

SYMPLASTIC LOADING: Sugars and nutrients move in the

cytoplasm from the mesophyll cells to the sieve elements through

plasmodesmata. Plasmodesmata (singular: plasmodesma) are

microscopic channels which traverse the cell walls of plant cells and

some algal cells, enabling transport and communication between them.

(NOTE: Plasmodesmata have not been found in all plants)

APOPLASTIC LOADING: Sugar and nutrients move along the cell

walls to the sieve tube. Then they cross the cell membrane by active

transport.

2. As sugars enter the phloem the concentration of phloem sap increases and

the water decreases. This causes the entry of water by osmosis from the

surrounding cells. This resulting pressure causes water and dissolved

solutes to flow towards a SINK.

A sink is a region of the plant where sugars and other nutrients are actively

being removed from the phloem. As sugars move out of the phloem, water

flows out with them. This reduces the pressure in the sieve cells at the sink

region.

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This mechanism is called pressure flow.

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Theory 2: Sugars are moved through the phloem by CYTOPLASMIC

STREAMING which is the movement of the fluid substance

(cytoplasm) within a plant or animal cell. The motion transports

nutrients, proteins, and organelles within cells and ACTIVE

DIFFUSION within the sieve tubes.

perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water

perform a first-hand investigation using the light microscope and prepared slides to gather information to estimate the size of red and white blood cells and draw scaled diagrams of each

analyse information from secondary sources to identify current technologies that allow measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and explain the conditions under which these technologies are used

Arterial Blood Gas (ABG) Analysis

Analysis takes blood samples from an artery, and the sample is tested for the concentration of oxygen and carbon dioxide, and for pH.

This procedure is invasive, and delays can occur between sampling and result processing.

The information obtained is vital for critically ill patients, in determining their situation, as many illnesses present with similar symptoms.

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Pulse Oximetry

This uses two wavelengths of light to measure the absorption of light as it passes through a patient’s finger. The amount of light absorbed by haemoglobin is dependent on how saturated it is with oxygen.

Mathematical calculations work out the proportion of oxygenated haemoglobin present.

This is useful as it is non- invasive, and allows for the constant monitoring of arterial blood.

analyse information from secondary sources to identify the products extracted from donated blood and discuss the uses of these products

Red Blood Cells

Used to treat people with Anaemia, as red blood cells increase the amount of oxygen that can be carried to body tissues, and consequently increase the amount of iron.

Given to people whose bone marrow doesn’t make enough RBCs.

Used for treatment of trauma patients and surgery patients, e.g. Open Heart Surgery.

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White Blood Cells

Infection fighting components of blood

Used to treat life-threatening illnesses or infections when the white blood cell count is low.

Plasma

Contains blood clotting factors and immunoglobins.

Used for treatment of patients with clotting disorders such as haemophilia.

Used to adjust the osmotic pressure of blood, to pull fluids out of tissues.

IMMUNOGLOBINS: Also called gamma globulins, immune serum, or

antibodies, these are also infection fighting parts of the blood plasma. Given

to people who have difficulty fighting infections, eg AIDS sufferers.

Platelets

Essential for blood clotting.

Platelets are given to patients suffering from leukaemia or lymphoma, who do not produce enough platelets.

analyse and present information from secondary sources to report on progress in the production of artificial blood and use available evidence to propose reasons why such research is needed

The problems of using real blood:

Shortage of real blood

It has to be ‘cross-matched’. This is because, if you receive the

wrong type of blood, it can be fatal. This is a great disadvantage in

emergency situations.

It has to be free of infectious agents. Only blood that is free of

bacteria and infectious agents (such as HIV) can be used. Testing

the blood is costly.

It has a short shelf-life. Because red blood cells only survive for 3

months, the blood has a short life span (blood can only survive for 3-

4 weeks).

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Some proposed replacements for blood: Perflurochemicals:

Synthetic and inert

Cheap to produce

Can dissolve 50 times more oxygen

Free of biological materials, therefore no risk of infections

BUT - must be combined with other materials to mix

in with the bloodstream (eg lecithin).

Haemoglobin Based Oxygen Carriers (HBOCs):

Made from haemoglobin extracted from red blood cells

Haemoglobin is not contained in membrane - cross matching unnecessary

Can be stored for a long time

BUT - haemoglobin tends to oxidise to a different form,

break down, and can no longer carry oxygen.

Dextrose Solution:

Made of 4% glucose solution in a fluid with equal salinity to blood

Only used to restore blood pressure after accidents.

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choose equipment or resources to perform a first-hand investigation to gather first-hand data to draw transverse and longitudinal sections of phloem and xylem tissue

Transverse section of Phloem and Xylem

Longitudinal Sections

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