biology p and d

8/2/2019 biology p and d

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Blood

Just over half of the blood volume is made up of a pale yellow fluid called plasma. The rest of

the blood is made up of cells (red blood cells and white blood cells) and platelets.

Blood has several vital functions:

Transport - oxygen in the red blood cells, absorbed, digested food by the plasma, excretoryproducts by the plasma, hormones by the plasma etc.

Defence - by the white blood cells (a.k.a. leucocytes). Formation of lymph and tissue fluid. Homeostasis.

Red blood cells

Also known as erythrocytes. These contain a pigment, haemoglobin, which gives them their

colour.

Red blood cells are made in the bone marrow (the liver in a foetus) of many bones. They have a

life span of about 120 days and are about 7m in diameter (very small).

Being like a biconcave disc in shape, the surface area to volume ratio is very large. Oxygen cantherefore diffuse very quickly into the cell and because the cell is so small, quickly bind to a

haemoglobin molecule.

They lack organelles meaning that there is more room for haemoglobin. Their size and flexible

membrane also means that they can squeeze through capillaries and transport oxygen extremelyclose to cells.


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White blood cells

These cells all have a nucleus, most are much larger than red blood cells and are spherical or

irregular in shape.

There are two basic types of white blood cells; the granulocytes (they have granular cytoplasm

and lobed nuclei) and agranulocytes (the cytoplasm appears smooth and the nucleus is roundedor horseshoe in shape).

Made in: Function:

Agranulocytes:

MonocytesRed bone

marrowPhagocytic against bacteria and antibody-coated viruses

Lymphocytes

Spleen,

lymph

nodes

Produces antibodies

Granulocytes:

NeutrophilsRed bone

marrow

Phagocytic and contain lysosomes to break down ingested

bacteria

EosinophilsRed bone

marrowPhagocytic. Works against allergens by making antihistamines

BasophilsRed bone

marrow

Make antihistamines, make heparin (prevents unnecessary

blood clotting) and make serotonin (makes the capillaries

more leaky so that phagocytes can leave the blood and enter

the site of infection


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For more information, see the Learn It on Immunity.

Platelets

These are formed in the bone marrow and are fragments of larger cells. They have no nucleus but

reactions do take place in the cytoplasm.

They have a variety of role such as blood clotting and the production of prostaglandins that

regulate the degree of constriction or dilation in blood vessels.

Blood clotting: Platelets stick to damaged cells on the inner surface of blood vessels forming a

plug. Unless the damage is small, platelets are involved in a chain of reactions by releasing

particular chemicals. A soluble protein, fibrinogen (present in the plasma), becomes an insolubleprotein, fibrin, and this forms layers of fibres across the wound. The mesh that this creates trapsred blood cells and platelets and a scab is formed.

This has two useful effects:


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1. Blood does not leak out of the vessel.2. It is less likely that an infectious organism will enter from outside and cause harm.

Blood groups

The most commonly required blood-grouping system is the ABO system. It concerns twoantigens that can occur on the surface of red blood cells. The antigens are called agglutinogens

in this case and are: agglutinogen A and agglutinogen B.

Plasma also contains antigens, called agglutinins in this case, and they are agglutinin A and

agglutinin B.

We shall call agglutinogens A or B and the agglutinins a or b. If A and a come into contact, the

red cells will clump together. If B and b come into contact the red cells will clump together.

Therefore, in your blood you will not contain the agglutinogen and the agglutinin of the same

type.

Blood Group:Agglutinogen A:Agglutinin A:Agglutinogen B:Agglutinin B:

A

B


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AB

O

Blood transfusions

It is important to match blood correctly so that agglutinins in the recipient don't clump the red

blood cells of the donor.

In transfusions it is important to remember that the volume of blood donated is relatively small

compared to the volume of the recipients blood. The agglutinins in the plasma from the donor are

so diluted that no harm is done. However the aggluinogens on the red blood cells are not so

diluted so harm can be done. These are the possible transfusions (a is safe, a is not):

Recipient:

Donor:

A B AB O

A

B

AB

O

Oxygen carriage

Oxygen does dissolve in plasma but the solubility is low and decreases further if the temperature

increases. The amount that could be carried by the plasma therefore would be completely

insufficient to supply all cells.

There is a protein in the blood however that will carry 4 molecules of oxygen. The protein iscalled haemoglobin (Hb) and is made up of 4 polypeptide chains, each with a haem group. Each

haem group can pick up 1 molecule of O2. The protein, being fairly small, could pass out of the

blood during ultrafiltration in the kidneys so, to ensure that it is not lost, it is found within redblood cells.


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Note: During this topic you will come across the term ofpartial pressure of oxygen. It does not

mean the pressure of the blood itself. Essentially it is a measure of the concentration of oxygen.It is written in shorthand as pO2 and is measured in kilopascals (kPa).

Inhaled air in the alveoli has a pO2 = 14kPa. The pO2 of resting tissue = 5.3kPa (lower pO2 =

lower O2concentration due to respiration) and the pO2 of active tissues = 2.7kPa. In either case,blood arriving at the lungs has a lower pO2 than that in the lungs.

There is therefore a diffusion gradient and oxygen will move from the alveoli into the blood. The

O2 is then loaded onto the Hb until the blood is about 96% saturated with oxygen. The Hb is now

called oxyhaemoglobin (HbO2).

Hb + 4O2 HbO8

Dissociation curves

The blood is then taken to tissues where the cells are respiring all the time, using oxygen. ThepO2 will be low. As the red blood cell enters this region, the Hb will start to unload the O 2, which

will diffuse into the tissues and be used for further respiration. Since much of the Hb will haveunloaded the O2, a much lower percentage of the blood will be saturated with O2.

A graph of the percentage saturation of blood with O2, i.e. the amount of HbO2 as opposed to Hbat different pO2 is shown below. It is called an oxygen dissociation curve:

It is S-shaped because of the behaviour of the Hb in different pO2.

The first molecule of O2 combines with an Hb and slightly distorts it. The joining of the first isquite slow (the flatter part of the graph at the beginning) but after the Hb has changed shape a


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little, it becomes easier and easier for the second and third O2 to join. This is shown by the curve

becoming steeper. It flattens off at the top because joining the fourth O 2 is more difficult.

Overall, it shows that at the higher and lower end of the partial pressures, there isn't a great deal

of change in the saturation of the Hb, but in the middle range, a small change in the pO2 can

result in a large change in the percentage saturation of the blood.

The effect of pH - The Bohr effect

The amount of O2 carried and released by Hb depends not only on the pO2 but also on pH.

An acidic environment causes HbO2 to dissociate (unload) to release the O2 to the tissues. Just a

small decrease in the pH results in a large decrease in the percentage saturation of the blood withO2.

Acidity depends on the concentration of hydrogen ions.

H+

displaces O2 from the HbO2, thus increasing the O2 available to the respiring tissues.

H+

+ HbO2 HHb + O2

HHb is called haemoglobinic acid.

This means that the Hb mops up free H+. That way the Hb helps to maintain the almost neutral

pH of the blood. Hb acts as a buffer.

This release of O2 when the pH is low (even if the pO2 is relatively high) is called the Bohr

effect.

When does the pH decrease because of free H+

in the blood?

During respiration, CO2 is produced. This diffuses into the blood plasma and into the red bloodcells. Inside the red blood cells are many molecules of an enzyme called carbonic anhydrase. It

catalyses the reaction between CO2 and H2O. The resulting carbonic acid then dissociates into

HCO3 + H

+. (Both reactions are reversible.)

CO2 + H2O H2CO3

carbon dioxide Water carbonic acid

H2CO3 HCO3 + H+

Carbonic acid hydrogencarbonate ion hydrogen ion

Therefore, the more CO2, the more the dissociation curve shifts to the right:


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Carbon dioxide transport

About 85% of the CO2 produced by respiration diffuses into the red blood cells and forms

carbonic acid under the control of carbonic anhydrase.

The HCO3 diffuses out of the red blood cell into the plasma. This leaves a shortage of

negatively charged ions inside the red blood cells. To compensate for this, chloride ions move

from the plasma into the red blood cells. This restoration of the electrical charge inside the redblood cells is called the chloride shift.

About 5% of the CO2 produced simply dissolves in the blood plasma.

Some CO2 diffuses into the red blood cells but instead of forming carbonic acid, attaches directlyonto the haemoglobin molecules to form carbaminohaemoglobin. Since the CO2 doesn't bind to

the haem groups the Hb is still able to pick up O2 or H+.

Other effects

Carbon monoxide

If carbon monoxide is breathed in (for example from car exhaust fumes), it binds irreversiblywith haemoglobin to form carboxyhaemoglobin. This means that the Hb cannot load and carryO2.

To make matters worse, Hb combines with CO about 250 times more readily than it does with O 2so that, even if the CO concentration is fairly low, it can cause death due to lack of O2 to the

tissues.


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Cigarettes produce CO-containing smoke, which means that a small percentage of a smoker's

blood is unable to transport O2.

Foetal haemoglobin

A foetus developing in the uterus must be able to load O2 from its mother's blood. Due to therespiration occurring in the foetus' cells, the pO2 is lower in the foetus blood than in the mother'sblood. Some will unload from the mother's HbO2 and diffuse across to the foetus. However,

because of the relatively small concentration difference, not much O2 is passed across.

To maximise the amount of O2 that the foetus receives, it has different haemoglobin - foetal

haemoglobin. This has a higher affinity for O2 than adult Hb (it combines more readily with O2)

so the foetus picks up enough O2. The dissociation curve shifts to the left.

Myoglobin

Skeletal muscle contains a pigment called myoglobin. It is very similar to Hb but has a higher

affinity for O2.

It will load with O2 as Hb unloads and will store the O2 in the muscle until it is required. It only

releases the O2 when the pO2 is very low - when the Hb cannot supply O2 fast enough and the

demand is great. The dissociation curve shifts to the left.

Temperature

The higher the temperature, the less saturated the blood is with O 2, i.e. the more the HbO2unloads the O2.


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This situation might arise during exercise - heat is produced during metabolic activity and during

this time, the O2 supply will need to increase. The dissociation curve shifts to the right:

Environment

Animals living where there is a shortage of oxygen, animals living at high altitude need to be

able to pick up O2 when it is at a very low pO2. Their dissociation curves will look like those of

foetal haemoglobin and myoglobin - the curve shifts to the left.

If somebody were to climb quickly from sea level to high altitude, they are likely to suffer from

altitude sickness, which can be fatal. However if the body is given time to adapt, most people cancope well with high altitudes. Instead of taking up the normal 45% of blood volume, the red

blood cells can increase in numbers to take up

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Investigating the Effect of Temperature on Respiration in Maggots

120482 star_rating

Length: 1409 words (4 double-spaced pages)

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Investigating the Effect of Temperature on Respiration in Maggots

Aim: This is an experiment to investigate how temperature effects the

respiration rate in maggots.

The formula: The simple formula of respiration is:

[IMAGE]

[IMAGE]C6 H12O 6+ 6O26H 2O + 6CO2+ ENERGY

GLUCOSE + OXYGEN WATER + CARBON + ENERGY

========================================

DIOXIDE

[IMAGE]


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The Collins concise English dictionary explains thatrespirationis

'the processes by which a living organismtakes in oxygen, distributes

and utilizes it in oxidation, and gives off products, esp. carbon

dioxide'.

Background information:

Respiration is the chemical process of releasing energy from organic

compounds in living cells. The organic molecules are broken down

through a series of steps to act as fuel. The most common organic

compound for most cells is glucose however, some cells can break down

fatty acids, glycerol, and amino acids in respiration. The energy

gained from respiration is used to synthesise ATP (adenosine

triphosphate) which is required throughout the body, in order to

replenish ATP stores.

There are two types of respiration; anaerobic and aerobic. Aerobic

respiration occurs when oxygen is freely available, whilst anaerobic

respiration occurs when free oxygen is not present, and the process is

altered. We will investigate aerobic respiration.

There are four main stages of respiration (when breaking down

glucose), known as the glycolytic pathway. They are; glycolysis, the

link reaction, the Krebs cycle, and oxidative phosphorylation.

The first stage of respiration is Glycolysis, which takes place in the

cytoplasm of a cell.

Glycolysis:

Each step in the pathway is controlled by an enzyme. The product from

one enzyme controlled reaction becomes the substrate for the next.

The second and third stages occur in the matrix of the mitochondria of

a cell, and is the link reaction, and the Krebs cycle (also known as

the citric acid cycle, or TCA cycle.) (Tricarboxylic acid cycle)

Link reaction:

Krebs cycle:
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The last stage occurs in the cristae of the mitochondria and is known

as oxidative phosphorylation.

Oxidative phosphorylation:

The oxygen used in the equation for aerobic respiration is used as the

terminal acceptor in the electron transport chain for oxidative

phosphorylation.

So if the rate of respiration goes up, more oxygen should be consumed.

This can be used using a respirometer.

Enzymes play a vital role in the process of respiration, as is shown

in the diagrams of the different stages above. Enzymes are globular

protein molecules, with a tertiary structure found in all living

cells. They are organic catalysts that speed up the rate of reactions.

All enzymes contain an active site, a depression in the enzyme

molecule, where a specific substrate molecule can collide and fit

into, like a key fits a lock, to bind and form an enzyme-substrate

complex. (See diagram below:)

There are four factors that can effect the rate of an enzyme reaction:

v The pH

v The concentration of enzyme solution

v The concentration of substrate solution, and

v The temperature.

We will focus on theeffect of temperature.

If you increase the temperature, up to the optimum temperature, you

increase the amount of kinetic energy, increasing random movement,

allowing more collisions between the enzyme and substrate molecules to

take place. This will increase the chances of forming enzyme-substrate

complexes and speed up the rate of reaction. However if the

temperature increases past the optimum temperature, the enzymes will

denature and no products can be formed. The temperature coefficient

Q10 =2, meaning that for every ten degree rise in temperature, the
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rate of the reaction is doubled.

Prediction: I predictthat therespiration ratein maggots will

increase if the temperature increases. Respiration takes place through

a series of steps, requiring enzymes in each stage. If I increase the

temperature in the experiment, the amount of kinetic energy will

increase, causing the substrates and enzymes to collide more

frequently, improving the chance of being more enzyme-substrate

complexes, which speeding up the reaction.

This prediction could be quantitative. If I increase the temperature

by ten degrees, the rate of respiration should double, so the oxygen

consumption should double.

Variables:

My independent variable is the temperature, as I am manipulating

this factor. The different temperatures I will use are: 10C, 20C,

30C, 40C. I will not go any higher as maggots are living creatures

and it would not be ethical to test them at high temperatures.

My dependant variable is oxygen consumption, as this is what I am

measuring.

I will need to control all the variables other than the independent

variable to keep the experiment fair and accurate.

I will keep the time I equilibrate constant, 5 minutes each time,

using a stopwatch. The amount of time I measure for, will also remain

constant (10 minutes) using the stopwatch. However, the accuracy of

this method may be limited, as times will vary slightly as reaction

times may vary, even if the same person is used.

The volume of soda lime will also remain constant, by using the same

mass.

The mass of maggots will also remain constant.

The apparatus volume and size will remain constant by keeping the

same apparatus throughout the experiment.
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The water bath will remain the same temperature, using a pre-set,

pre-heated electronic water bath. The temperature of surrounding must

be kept constant whilst readings are taken because changes in

temperature and pressure, alter the volume of the air in the

apparatus.

Preliminary:

Our preliminary experiment was not very successful. We tested the

respiration rate of five and ten maggots in the respirometer, but

found that more maggots were required as to get a significant result.

We realised that twenty maggots would give a better result, but found

it difficult to find maggots the same size. Instead we have decided to

use the same mass of maggots. (5 grams)

Risk assessment: We will be working with living maggots so some

precautions should be made. Maggots usually feed on dead or rotten

flesh of meat, which carries a lot of bacteria. Therefore maggots may

be carrying germs and may be infected with diseases such as

salmonella, if the maggots had been into contact with infected chicken

meat. Equipment will be used to handle the maggots however, if one

maggot escapes, handling may be required. After the experiment all

hands, surfaces and equipment should be washed to destroy any

bacteria.

Lab safety also includes no running and removing all obstacles from

the floor, to avoid tripping up.

There were two sets of apparatus I could use to create a

respirometer. I could have used a capillary tube instead of a

manometer, by measuring with a ruler, (see below) but decided a

manometer would be easier to read, and restart again. My chosen method

and apparatus also allows me to use a control tube to compensate for

any environmental variables I cannot control, like atmospheric

pressure changes.

Apparatus:

Clamp

Stand


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Boss

Screw clip

5g live maggots

Test tube x2

Bung x2

Soda-lime

Stopwatch

Control tube

Glass beads

1 cm syringe

Three-way tap

Capillary U-tube containing manometer fluid and manometer

Gauze platform

Water bath set at 10C, 20C, 30C, and 40C.

I will use a stand, clamp and boss to hold the test tubes into place

and to keep them stable throughout the experiment. It will also keep

them at the same height, so the variables concerned are controlled,

(for example, the temperature, or amount of light at this level.) The

screw clip is left opened to allow for equilibration, and closed when

we start recording the respiration rates. 5 grams of maggots will be

used, as mass is more accurate than the number of maggots, as each

maggot varies in size/weight, so may not be the same. One test tube

will be the experimental tube, with the maggots, and the other will be

the control tube, with the beads. The same mass of soda lime will be

used. it is used to absorb the carbon dioxide, which is produced in

respiration. The stopwatch is fairly accurate, and will be used to


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tell us when to take the readings, to ensure that each reading is

taken at the same time. The same person will use the stopwatch to as

people have different reaction times. (This will eliminate this

variable). The glass beads are used as a control, so that any

environmental changes will be compensated for. The syringe is used to

'push' the liquid back to zero after each reading. The three-way

attaches the syringe to the bung. The capillary U-tube which will

contain the manometer fluid is what we use to measure the respiration

rate. The scale of the manometer allows us to do this easily. The

gauze platform keeps the maggots off the soda lime, but still allows

respiratory gases through. The water baths are used to investigate the

respiration rate at different temperatures. They are accurate and can

be kept at the same temperature for long periods of time.

Diagram of apparatus:

Method:

i. Set up apparatus as shown in diagram

ii. Weigh maggots (5 grams)

iii. Place maggots in test tube

iv. Place test tube into water bath (10C) for 5 minutes to allow time

to equilibrate. With the screw clip open. Use a stopwatch to measure

the time.

v. After the 5 minutes, set liquid to start (0), using syringe and

tighten the screw clip.

vi. Start stopwatch

vii. At 10 minutes observe how far the liquid has moved (mm), and

record data in a table.

viii. Repeat two more times at the same temperature

ix. Repeat at temperatures of 20C, 30 C, 40C, using electronic

water baths.


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References:

BOOKS

-----

Collins, W. (1978). Collins Concise English Dictionary. William

Collins Sons & Co. Ltd, Glasgow.

Jones, M et al. (2000) Biology 1. Cambridge: CUP (Cambridge

University Press)

ISBN 0 521 78719 x paperback

Jones, M. and Gregory, J. (2001) Biology 2. Cambridge University

Press, Cambridge. ISBN 0-521-79714-4

Simpkins J and Williams, J. (1987) Advanced Human Biology. Collins

educational.

WEBSITES

www.s-cool.co.uk AS & A2 Level Biology. Respiration: some basics

: glycolysis

: krebs cycle

:electron transport chain/ oxidative phosphorylation

How to Cite this Page

MLA Citation:

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