Unit 1, topic 1, Edexcel AS Biology

Transport in Simple organisms

Diffusion: Free movement of particles in a liquid or a gas down a concentration Gradient from an area of high concentration to an area of low concentration

For unicellular organisms, nutrients and oxygen can diffuse directly into the cell from its external environment;

• The membrane in contrast with the outside is very large relative to the volume of the inside of its cell. That is, its SURFACE TO VOLUME RATIO is large.

The bigger the organism gets, the smaller the surface area to volume ratio becomes.  The distance from outside the organism to the inside gets longer and there is less surface for substances to enter through. So it takes longer for substances to diffuse in.

Transport in Large Organisms

Internal transport systems which carries substances to every cell in the body, delivering oxygen and nutrients and taking away waste quickly so that cells can accru out their reactions efficiently.

Mass Transport system:

• In humans it is the heart and circluatory system and the blood which flows through it.
• substances are delivered over short distances to individual cells in the body by processes such as: Diffusion, Osmosis and Active Transport.

Features

A system of Vessels - usually tubes, sometimes following a very specific route, sometimes wide spread and branching

A way of making sure substances are moving in the right direction

A means of moving materials fast enough to supply the needs of the organism - (pumping of the heart/ active transport)

A suitable transport medium

Chemistry of water

Chemical formula: H2O - two atoms of hydrogen are joined to one atom of oxygen.

Each water molecule si slightly polarised: Oxygen > slightly negative, Hydrogen> slightly positive. The seperation of charges is called a Dipole.

Water molecules form Hydrogen Bonds, the negative oxygen atom will attract positive hydrogeb atoms of other water molecules in a weak Electrostatic Attraction.

Water has a high melting and boiling points  - it takes more energy to overcome the attractive forces of all the hydrogen bonds.

(Properties of water

1) it is an exellent solvent, ionic substances will disove in water because it has a dipole. Polar substances will disolve in water too. Water can also carry non-polar substances, it may form a colloids ( the solute particles are spread through the water but not seperated out).

2) It has one of the highest known surface tensions because water molecules form hydrogen bonds which tend to pull them down and together. There is no such attraction between the molecules of air and water, so the water layer holds together forming a thin skin of surface tention.

3) The water molecule is amphoteric. (act as an acid - it forms H+ ions and is a proton donor- and as a base - it forms OH- ions and is a proton acceptor). Therefore water acts as a Buffer, helping to prevent reactions form changing the PH as any excess H+ or OH- ions are 'mopped up'.

Components of Blood

Plasma: main component of the blood and consists largly of water. Contains a wide range of dissolved substances to be transported and also fibrinogen (for clotting of the bood).

Erythocytes (Red blood cells) : Contain haemoglobin (red pigment which carries oxygen). Formed in the red bone marrow or short bones (ribs).

Leucocytes ( White blood cells) : Much larger than red blood cells, but they can change their shape and go through tiny blood vessels. Contain a nucleus and have colourless cytoplasm. Formed in white bone marrow of long bones ( humerus in the arm). One type called lymphocytes are formed in the lymph glands and spleen, their main function is to defend the body.

Platelets : fragments of large cless called megakaryocytes, found in bone marrow. Involved in clotting of the blood.

The Plasma

Transports digested food products from the small intestine to all the parts of the body where they are needed either for immediate use or storage.

Transports food molecules from storage areas to the cells that need them.

Transports excretory products from cells to the organs such as the lungs or kidneys that excrete them from the body

Helps to maintain a steady body temperature by carrying heat around the system from deep-seated organs (the gut) or very active tissues (leg muscles)

Acts as a buffer to pH changes.

The Plasma

If a blood vessel is broken, the fibrinogen in the plasma , together with the platelets, clots the blood.

The clot seals the blood vessel and so prevents excessive blood loss.

If the broken blood vessel is on the surface of the skin, the clot also prevents the entry of disease-causing pathogens which could cause infection.

The clot dries to form a scab which protects the new skin growing beneath it and falls off once the damage is fully healed.

Red Blood cells

• transports oxygen from the lungs to all the cells.
• the biconcave disc shape means that they have a large surface area to volume ratio, so oxygen can diffuse into and out of them rapidly.
• Has no nucleus, so more space inside for haemoglobin molecules that carry the oxygen
• Haemoglobin also carries some of the carbon dioxide produced in respiration back to the lungs.

White blood cells

Defends against disease in two main ways

• 1) Some make antibodies which destroy pathogens, or antitoxins which neutralise the poisons made by pathogens. Once the body has encountered a pathogen, it can make antobodies to this pathogen very quickly if it invades again.
• 2) Some engulf and digest pathogens in a process known as phagocytosis

Oxygen

Oxygen moves from the lungs to the red blood cells by diffusion. The oxygen concentration in the lungs is much higher than that in the haemoglobin of the red blood cells. This maintains a steep concentration gradient from the air in the lungs to the red blood cells, so more and more oxygen diffuses in.

In body tissues oxygen levels are relatively low. Therefore oxygen diffuses into body tissues.

Carbon Dioxide 

When CO2 is dissolved in to the blood, it reacts with the water to form carbonic acid ( H2CO3). The carbonic acid separates to form the ions H+ and HCO3-.

5% of CO2 is carried by solution in the plasma. 10-20% combines with haemoglobin molecules to form carbaminohaemoglobin. Most of CO2 is transported in the cytoplasm of red blood cells as hydrogencarbonate ions.

The enzyme carbonic anhydrase controls the rate of the reaction between CO2 and H2O to form carbonic acid.

Carbonic anhydrase catalyses the reverse reaction and free C02 diffuses out of the blood and into the lungs.

Blood Clott

Seals up damaged blood vessels to minimise blood loss and prevent pathogens getting in.

Contact between the platelets and components of the issue (collagen fibres in the skin) causes the platelets to break open and release:

• Serotonin : causes the muscle of the blood vessel to contract, narrowing the blood vessel, cutting off the blood flow.
• Thromboplastin :enzyme with catalyses the conversion of a protein called prothrombin into the enzyme thrombin. The right concentration of calcium ions need to be present in order for the reaction to occur.

Thrombin converts fibrinogen into fibrin, forming a mesh of fibres.

Platelets and blood cells get trapped in this mesh, causing a clott.

The platelets in the mesh contract, making the clot tighter and tougher.

Circulation Systems

Single Circulation (e.g in Fish)

heart pumps deoxygenated blood to the gills, where the blood takes in oxygen from the outside water. The oxygenated blood then travels around the body and back to the heart.

Double Circulation (birds and mammals)

Involves two circulation systems which make sure that the oxygenates and deoxygenated blood cannot mix.

The Systemic Circulation : Carries oxygenated blood form heart to cells and carries deoxygenated blood back to the heart.

Pulmonary Circluation : Carries deoxygenated blood from the heart to the lungs to be oxygenated, and carries oxygenated blood back to the heart.

Arteries

Carrys Blood away from the heart to the cells of your body.

Most arteries carry oxygenated blood except:

• The pulmonary artery: carried deoxygenated blood from the heart to the lungs
• Umbilical cord artery: Carried deoxygenated blood from the fetus to the placenta.

major arteries close to  the heart contain elastic fibres so they can stretch to accommodate the greater volume of blood. between surges the elastic fibres return to the original lengh, squeezing the blood through.

Peripheral arteries: furthur away from the heart, contract and relax the lumen to controll blood flow.

Capillaries

Branch between cells. The diameter of each capillary is small so the blood flows slowly through it, giving more time for diffusion to occur.

They have :

• Thin walls which helps them fit between individual cells and allows diffusion of substances.
• The wall is only one cell thick, so oxygen and other molecules quickly diffuse into cells and carbon dioxide diffuses in.

Veins

Carry blood back towards the heart.

Can hold a large volume of blood, and blood pressure is relatively low, which is maintained in two ways:

• In the venous system (tiny veins which lead from the capillary network) there are semilunar valves which open to let blood flow through, but if the blood starts flowing backwards, the valves close.
• The veins situated between muscles are squashed when the muscles contract, helping to return the blood to the heart.

Structure of the Heart 1

Made up of Cardiac muscle which contracts with out rest.

• Inferior Vena Cava: collects blood from low part of body
• Superior Vena Cava: collects blood from head, neck, arms and chest.
• The blood from both of these are delivered to the right atrium.
• 

The Right Atrium:

• Receives blood from veins
• 
• it fills with blood and the pressure increases and opens up the tricuspid valve so the right ventricle fills with blood.When theh atrium is full, it contracts and forces the blood into the ventricle.
• Semilunar valves stop the backflow of bolld into the veins.

Structure of the Heart 2

Tricuspid valve:

• Made of three flaps
• 
• Known as an atrioventricular valve, as it seperates an atrium and a ventricle.
• Allows blood to pass from the atrium to the ventricle, but not the other direction.
• The tendinous cords make sure the valves are not turned inside out by the pressure of the contraction
• 

Right Ventricle:

• Produces the pressure needed for the blood to be forced out of the heart into the pulmonary arteries.

Structure of the Heart 3

• From the lungs the blood returns to the left atrium by the pulmonary veins.
• 

The Left Atrium:

• The left atrium has the same function as the right atrium:
• It contracts to force blood into the left ventricle.
• Backflow is prevented by the bicuspid valve
• As the left atrium contracts the left ventricle is filled with blood under high pressure, it then contracts to force the blood into the aorta.
• 

The aorta:

• Major artery of the body
• Carries blood away from the heart under hugh pressure
• Semilunar valves prevent backflow into the ventricle.

The Cardiac cycle

Systole:

•  contraction of the heart
• Atrial systole: when the atria contracts together forcing blood into the ventricles
• Ventricular systole: when the ventricles contract.
• 

Diastole: relaxion stage between contractions of the heart.

Controll of heart rate:

The cardiovascular centre in your brain responds to the variable levels of carbon dioxide in your blood.

Receptors send signals to the cardiovascular centre which sends signals to your heart.

This enables your heart too react to exercise or fear.

Normal blood pressure:

Friction between the blood and vessel walls, called peripheral resistance, which slows down the flow of blood.

Blood pressure falls as it travels through the capillaries as there is a greater surface area of vessel wall in contact wit the blood, so the peripheral resistance increases.

The nutrients you need

Macronutrients:

• Carbohydrates>provide energy
• Proteins > growth and repair of cells, broken down to amino acids
• Fats/ Lipids>provide energy, stored as body fat
• 

Micronutrients

• mineral salts> Sodium, muscular contractions and heartbeat
• vitamins> absorbed directly, lack of vit.C results in scurvy
• water> For body reactions
• fibre>hold water and provide bulk for the intestinal muscles to work on.

Carbohydrates

Made up of Carbon, Hydrogen and Oxygen

Monosaccharides-Simple Sugars

• General formula > (CH20)n
• Triose sugars: 3carbon atoms, important in mitochondria for respiration C3H6O3
• Pentose sugars: 5carbon atoms, important in nucleic acids DNA, C5H10O5
• Hexose sugars: 6carbon, glucose, galactose and fructose, C6H12O6
• 

Disaccharides- The double sugars

made up of two monosaccharides joined together

• Jion in a condensation reaction where H2O is removed
• 
• Link between a covalent bond known as a : glycosidic bond