More Exchange And Transport Systems

Front 1

Digestive enzymes

Back 1

Digestive enzymes break biological molecules in food.

Digestive enzymes are produced by specialised cells in the digestive system of mammals which are then released to mix with food.

Different digestive enzymes catalyse the breakdown of different food molecules as enzymes work with specific substrates.

Front 2

The digestion of carbohydrates

Back 2

Amylase

Amylase is a digestive enzyme that catalyses the breakdown of starch.

Amylase works by catalysing the hydrolysis reactions that break the glycosidic bonds in starch to produce maltose.

Amylase is produced by the salivary gland which release amylase into the mouth.

Amylase is also produced by the pancreas which release amylase into the small intestine.

Membrane - Bound disacharidases

Membrane - Bound disaccharidases are enzymes that are attached to the cell membrane of epithelial cell lining the ileum.

They help break down disaccharides into monosaccharides which involves the hydrolysis of glycosidic bonds.

Front 3

The Digestion of lipids

Back 3

Lipase enzymes catalyse the break down of lipids into monoglycerides and fatty acids which involve the hydrolysis of ester bonds in lipids.

Lipase enzymes are mainly made in the pancreas and are then secreted into the small intestine where they act.

Bile salts are produced by the liver and emulsify lipids (cause lipids to form small droplets).

Bile salts are not enzymes but they are important in the process of lipid digestion.

Several small lipid droplets have a large SA than one single large droplet. So the formation of small droplets greatly increases the SA of lipid that’s available for lipase’s to works on.

Once the lipid is broken down by lipase, the monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles.

Micelles help the product of lipid digestion to be absorbed.

Front 4

The digestion of proteins

Back 4

Proteins are broken down by a combination of different peptidases which are enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.

There are endopeptidases, exopeptidase and dipeptidases.

Endopeptidases act to hydrolyse peptide bonds within a protein.

Exopeptidase act to hydrolyse peptide bonds at the end of a protein molecule. They remove single amino acids from proteins.

Dipeptidases are exopeptidase that work specifically on dipeptides. They act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bonds between them.

Front 5

Absorption of the products of digestion

Back 5

The products of digestion are absorbed across the ileum epithelium into the bloodstream.

Front 6

How are monosaccharides absorbed?

Back 6

Glucose is absorbed by active transport with sodium ion VIA a co-transporter protein. Galactose is absorbed in the same way.

Fructose is absorbed VIA facilitated diffusion though a different transporter protein.

Front 7

How are amino acids absorbed?

Back 7

Amino acids are absorbed in a similar way to glucose and galactose.

Sodium ions are actively transported out of the epithelial cells into the ileum. They then diffuse back into the cells through sodium - dependent transporter proteins in the epithelial cell membranes and carry amino acids with them.

Front 8

How are monoglycerides and fatty acids absorbed?

Back 8

Micelles help to move monoglycerides and fatty acids towards the epithelium.

As micelles constantly break up and reform they can ‘release’ monoglycerides and fatty acids, allowing them to be absorbed.

Monoglycerides and fatty acids are lipid soluble so they can diffuse directly across the epithelial cell membrane.

Front 9

The role of haemoglobin (Hb)

Back 9

Hb is an important part of the circulatory system. It is found in red blood cells.

It’s role is to carry oxygen around the body.

Front 10

Haemoglobin and Oxyhemoglobin

Back 10

Hb is a large protein with a quaternary made up of four polypeptide chains.

Each chain has a haem group which contains an iron ion and give Hb it’s red colour. Each molecule of Hb can carry four oxygen molecules.

In the lungs oxygen joins to Hb in red blood cells to form oxyhemoglobin. This is referred to as loading or association. This is a reversible reaction. Near the body cells, oxygen leaves oxyhemoglobin and turns back into Hb. This is referred to as unloading + dissociation.

Front 11

Affinity for oxygen and pO2

Back 11

The affinity for oxygen means the tendency a molecule has to bind with oxygen.

The Hb’s affinity for oxygen varies depending on the condition it’s in. One of the condition that affects it is the partial pressure of oxygen (pO2).

The pO2 is a measure of oxygen concentration.

The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.

As the pO2 increases, the Hb’s affinity for oxygen also increases:

Oxygen loads onto Hb to form oxyhemoglobin where there’s a high pO2.

Oxyhemoglobin unloads it’s oxygen where there’s a low pO2.

Oxygen enters the blood capillaries at the alveoli in the lungs.

Alveoli have a high pO2, so oxygen loads onto Hb to form oxyhemoglobin (HbO8).

When cells respite they use up oxygen which lowers the pO2.

Red blood cells deliver oxyhemoglobin to respiring cells where it unloads it’s oxygen. The Hb then returns to the lungs to pick up more oxygen.

Alveoli in the lungs have:

High oxygen concentration.

High pO2.

High affinity.

Oxygen loads.

Respiring tissues have:

Low oxygen concentration.

Low pO2.

Low affinity.

Oxygen unloads.

Front 12

Dissociation curves

Back 12

Dissociation curves show how saturated the Hb is with oxygen at any given partial pressure.

Where pO2 is high, the Hb has a high affinity for oxygen, so it has a high saturation of oxygen.

Where pO2 is low, the Hb has a low affinity for oxygen, so it has a low saturation of oxygen.

Front 13

The carbon dioxide concentration

Back 13

The carbon dioxide concentration affects oxygen unloading.

The partial pressure of carbon dioxide (pCo2) is a measure of carbon dioxide concentration in a cell.

Hb gives up it’s oxygen more readily at a higher pCo2.

When cells respire the produce carbon dioxide. Which raises the pCo2. This increases the rate of oxygen unloading. The dissociation curves shifts to the right.

Front 14

The Bohr effect

Back 14

The saturation of blood with oxygen is lower for a given partial pressure of oxygen, meaning oxygen is being released. This is called the Bohr effects.

Front 15

Different types of haemoglobin

Back 15

Different organisms have different types of Hb with different oxygen transporting capacities. It depends on things like where they live, how active they are and their size.

Having a particular type of Hb is an adaptation that helps the organism to survive in a particular environment.

Front 16

Low oxygen environments

Back 16

Organisms living in environments with a low concentration of oxygen have Hb with a higher affinity for oxygen than human Hb.

This is because there isn’t enough oxygen available, so the Hb has to be very good at loading any available oxygen.

So the dissociation curve is to the left of ours.

Front 17

High activity levels

Back 17

Organisms that are very active and have a high oxygen demand have Hb with a lower affinity for oxygen than human haemoglobin.

This is because they need their Hb to easily unload oxygen, so that it is available for them to use.

The dissociation curve is to the right of the human one.

Front 18

Size

Back 18

Small mammals have a high SA: Volume ratio than larger mammals. This means they lose heat quickly, so they have a high metabolic rate to help them keep warm which means they have a high oxygen demand.

Small mammals have Hb with a lower affinity for oxygen than human Hb.

This is because they need their Hb to easily unload oxygen to meet the high oxygen demand.

The dissociation curve is to the right.

Front 19

The structure of the heart

Back 19

Right side pumps deoxygenated blood to the lungs.

Left side pumps oxygenated blood to the whole body.

Front 20

Left ventricle

Back 20

The left ventricle has thicker and more muscular walls than the right ventricle. This allows it to contract more powerfully and pump blood all the way around the body.

The right ventricle is less muscular so it’s contractions are only powerful enough to pump blood to the nearby lungs.

Front 21

Ventricles

Back 21

The ventricles have thicker walls than the atria, therefore they can push blood out of the heart, whereas the atria just need to push blood a short distance into the ventricles.

Front 22

The atrioventricular (AV) valves

Back 22

The AV link the atria to the ventricles and stop the blood flowing back into the atria when the ventricles contract.

Front 23

The semi lunar (SL) valves

Back 23

The SL valves link the ventricles to the pulmonary artery and the aorta and stop the blood flowing back into the heart after the ventricles contract.

Front 24

Cords

Back 24

The cords attach the AV valves to the ventricles to stop them being forced up into the atria when the ventricles contract.

Front 25

Heart valves

Back 25

The heart valves only open one way.

The opening and closing of the heart valves depend on the relative pressure of the heart chambers.

If there is a higher pressure behind the valve, the valve is forced open.

If there is higher pressure in front of the valve, the valve is forced shut.

This means the blood flows through the heart in one direction.

Front 26

What is the function of the circulatory system?

Back 26

The multicellular organisms e.g. mammals have a low SA:Volume ratio. This means they need a specialised mass transport system such as the circulatory system to carry raw materials from specialised exchange organs to their body cells.

Front 27

The structure of the circulatory system

Back 27

The circulatory system is made up of the heart and blood vessels. The heart pumps blood through the blood vessels to reach different parts of the body.

Front 28

Blood vessels

Back 28

Arteries

Arterioles

Veins

Capillaries

Front 29

What does blood transport round the body?

Back 29

Respiratory gases

products of digestion

metabolic waste

hormones

There are two circuits.

One circuit takes blood from the heart to the lungs, then back to the heart.

The other loop carries the blood around to the rest of the body. This means the blood has to go through the heart twice to complete one full circuit of the body.

The heart has its own blood supply, the left and right coronary arteries.

Front 30

Arteries

Back 30

The arteries carry blood from the heart to the rest of the body.

The walls of the arteries are thick and muscular and have an elastic tissue to stretch and recoil as the heart beats. This helps maintain high pressure.

The inner lining, the endothelium is folded, allowing the artery to stretch. This also maintains high pressure.

All arteries carry oxygenated blood except for the pulmonary arteries which take deoxygenated blood to the lungs.

Front 31

Arterioles

Back 31

The arteries divide into small blood vessels called arterioles.

The arterioles form a network throughout the body.

Blood is directed to different areas of demand in the body by muscles in the arterioles.

The muscles contract to restrict blood flow and the muscles relax to allow full blood flow.

Front 32

Veins

Back 32

Veins carry blood back into the heart under low pressure.

Veins have a wider lumen than the arteries with very little elastic or muscle tissue.

Veins contain valves to stop the blood flowing backwards.

Blood flow through the veins is helped by the contraction of the body muscles surrounding them.

All veins carry deoxygenated blood as oxygen has been used up by body cells excepts for the pulmonary veins which carry oxygenated blood to the heart from the lungs.

Front 33

Capillaries

Back 33

Arterioles branch into smaller blood vessels called capillaries.

Substances such as glucose and oxygen are exchanges between the cells and the capillaries, so they are adapted for efficient diffusion.

Capillaries are found near cells in the exchange tissue e.g alveoli in the lungs, so there is a short diffusion pathway. Also their walls are only one cell thick, which also shortens the diffusion pathway.

There are a large number of capillaries to increase the SA for exchange.

Network of capillaries in the tissues are called the capillary bed.

Front 34

The tissue fluid

Back 34

The tissue fluid is the fluid that surrounds cells in tissue.

The tissue fluid is made from small molecules that leave the blood plasma such water, oxygen and nutrients.

In a capillary bed, substances move out of the capillaries into the tissue fluid, by pressure filtration:

1. At the start of the capillary pressure, near the arteries, the hydrostatic pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid.

2. The difference in hydrostatic pressure means an overall outward pressure forces the fluid out of the capillaries and into the spaces around the cells, forming the tissue fluid.

3. As the fluid leaves, the hydrostatic pressure in the capillaries reduces, so the hydrostatic pressure is much lower at the venule end of the capillary bed.

4. Due to the fluid loss and an increasing concentration of plasma proteins, the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid.

5. This means that some water re - enters the capillaries from the tissue fluid at the venule end by osmosis.

Any excess tissue is drained into the lymphatic system which transports this excess fluid from the tissues and puts it back into the circulatory system.

Front 35

What is the cardiac cycle?

Back 35

The cardiac cycle is an ongoing sequence of contractions and relaxations of the atria and ventricles that keeps the blood circulating round the body.

The volume of the atria and ventricles changes as they contract and relax.

The pressure also changes due the changes in chamber volume.

Front 36

What happens when the ventricles relax and the atria contract?

Back 36

The ventricles relax and the atria contract;

Decreasing the volume of the chambers and increasing the pressure inside the chambers.

This pushes the blood into the ventricles.

There is a slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria.

Front 37

What happens when the ventricles contract and the atria relax?

Back 37

The ventricles contract and the atria relax;

Decreasing the volume of the chambers and increasing the pressure inside the chambers.

The pressure becomes higher in the ventricles than the atria, which forces the AV valves to shut to prevent back flow.

The pressure is also higher in the ventricles than the aorta and pulmonary artery, which forces open the SL valves and bloods is forced out into these arteries.

Front 38

What happens when the ventricles and atria both relax?

Back 38

The atria and ventricles both relax;

The higher pressure in the pulmonary artery and aorta close the SL valves to prevent back flow into the ventricles.

Blood returns to the heart and atria fill again due to the higher pressure in the vena cava and pulmonary vein. This starts to increase the pressure of the atria.

As the ventricles continue to relax their pressure falls below the pressure of atria and the AV valves open. This allows blood to flow passively into the ventricles from the atria.

So the atria contract and whole process begins again.

Front 39

Calculating cardiac output

Back 39

Cardiac output is the volume of blood pumped by the heart per minute measured in cm3 min-1.

Cardiac output = stroke volume x heart rate

Heart rate; the number of beats per minute (bpm).

Stroke volume; the volume of blood pumped during each heartbeat, measure in cm3.

Front 40

What is cardiovascular disease?

Back 40

Cardiovascular diseases are diseases associated with the heart and blood vessels.

Cardiovascular disease includes:

Aneurysms

Thrombosis

Myocardial infarction

Most cardiovascular disease starts with atheroma formation.

Coronary heart disease (CHD) is a type of cardiovascular disease. It occurs when the coronary arteries have a lot of atheroma in them, which restricts blood flow to the heart muscle. This can lead to myocardial infarction.

Front 41

Atheroma formation

Back 41

The wall of the artery is made up of several layers.

The endothelium is usually smooth and unbroken.

If damage occurs to the endothelium by high blood pressure, the white blood cells and the lipids in the blood clump together under the lining to form fatty streaks.

Over time, more white blood cells, lipids and connective tissue build up and harden to form a fibrous plaque called Atheroma. This plaque partially blocks the lumen of the artery and restricts blood flow which causes blood pressure to increase.

Front 42

What is Aneurysm?

Back 42

An aneurysm is a balloon - like swelling of the artery. It starts with the formation of atheromas. Atheroma plaque damage and weaken arteries. They also narrow arteries increasing blood pressure.

When blood travels through a weakened artery at high pressure, it may push the inner layers of the artery through the outer elastic layer to form an aneurysm.

This aneurysm may burst, causing a haemorrhage.

Front 43

What is a thrombosis?

Back 43

A thrombosis is the formation of a blood clot. It also starts with the formation of atheromas. An atheroma plaque can rupture the endothelium of an artery. This damages the wall of the artery and leaves a rough surface. Platelets and fibrin stay at the site of damage and form a blood clot (thrombus).

This blood clot can cause a complete blockage of the artery or it can become dislodged and block a blood vessel else where in the body.

Debris from the rupture can cause another blood clot to form further down the artery.

Front 44

What is myocardial infarction?

Back 44

The heart muscle is supplied with blood by the coronary arteries. This blood contains oxygen needed by heart muscle cells to carry out respiration.

If the coronary artery become completely blocked by a blood clot an area of the heart muscle will be totally cut of from its blood supply, receiving no oxygen. This causes myocardial infarction known as a heart attack.

A heart attack can cause damage or death to the heart muscle.

Symptoms include:

Pains in the chest and upper body

Shortness of breath

Sweating

If large areas of the heart muscle are affected complete heart failure can occur which is often fatal.

Front 45

What is a risk factor?

Back 45

A risk factor is something that increases your chance of developing a disease.

Front 46

What few things increase your risk of getting atheromas in your arteries?

Back 46

Smoking or too much salt in your diet.

Front 47

What risk factors can lead to the development of myocardial infarction?

Back 47

High blood pressure

High blood cholesterol and poor diet

Cigarette smoking

Front 48

How does high blood pressure lead to the development of myocardial infarction?

Back 48

HBP increase the risk of damage to the artery walls. Damage to the wall have an increased risk of atheroma formation causing a further increase in blood pressure.

Atheroma can also cause blood clots to form. A blood clot could block flow of blood to the heart muscle, resulting in myocardial infarction.

So anything that increases blood pressure also increases the risk of cardiovascular disease.

Front 49

How does high blood cholesterol level lead to development of myocardial infarction?

Back 49

If the blood cholesterol level is high, then the risk of cardiovascular disease is increased. This is because cholesterol is one of the main constituents of the fatty acids that form atheromas.

Atheromas can lead to increased blood pressure and blood clots which could cause a myocardial infarction.

A diet high in saturated fat is associated with high blood cholesterol levels.

A diet high in salt also increases the risk of cardiovascular diseases because it increases the risk of HBP.

Front 50

How does cigarette smoking lead to the development of myocardial infarction?

Back 50

Both nicotine and carbon monoxide are found in cigarette smoke and increase the risk of cardiovascular disease and myocardial infarction.

Carbon monoxide combines with Hb and reduces the amount of oxygen transported in the blood and so it reduces the amount of oxygen available for tissues. If the heart muscle doesn’t receive enough oxygen it can lead to a heart attack.

Smoking decrease the amount of antioxidants in the blood which are important for protecting cells from damage.

Fewer antioxidants means cell damage in the coronary artery walls is more likely and this can lead to atheroma formation.

Front 51

What are the roles xylem and phloem?

Back 51

Xylem tissue transports water and mineral ions in solution.

Phloem tissue transport organic substances both up and down the plant.

Xylem and phloem tissue are both mass transport systems and can move substances over large distances.

Front 52

Structure of the xylem

Back 52

Xylem vessels are part of the xylem tissue that actually transport water and ions.

Xylem vessels are very long tube like structures form from dead cells joined end to end. There are no end walls on these cells making an uninterrupted tube that allows water to pass up through the middle easily.

Front 53

Water movement up a plant

Back 53

Water moves up a plant against the force of gravity, from roots to leaves.

Cohesion and tension:

1. Water evaporates from the leaves at the top of the xylem. This process is called transpiration.

2. This creates tension which pull more water into the leaf.

3. Water molecules are cohesive so when some water molecules are pulled in to the lead other follow. This means the whole column of water in the xylem move from the leaves down to the roots move upwards.

4. Water then enters the stem through the roots.

Front 54

What is transpiration?

Back 54

Transpiration is the evaporation of water from a plants surface, especially the leaves.

Water evaporates from moist cells walls and stays in spaces between the cells in the leaf. When the stomata opens water moves out of the leaf down the water potential gradient.

Front 55

Factors affecting transpiration rate

Back 55

Light intensity

The lighter it is the faster the transpiration rate.

This is because the stomata opens when it gets light to let in carbon dioxide for photosynthesis.

Temperature ☀️😄

The higher the temperature the faster the transpiration rate.

Warmer water molecules have more energy so they can evaporate from the cells inside the leaf faster. This increase the water potential gradient between the inside and outside of the leaf, making water diffuse out of the leaf faster.

Humidity

The lower the humidity the faster the transpiration rate.

If the air around the plant is dry, the water potential gradient is increased between the leaf and air, which increases the transpiration rate.

Wind 💨

The winder it is, the faster the transpiration rate.

Lots of air movement blows away water molecules from around the stomata. This increases the water potential gradient which increases the transpiration rate.

Front 56

The structure of the phloem

Back 56

The phloem tissue transports organic solutes round plants.

Phloem cells are formed from cells arranged in tubes. Sieve tube elements and companion cells are important cell types in the phloem tissue.

Sieve tube element are living cells that form the tube for transporting solutes. They have no nucleus and a few organelles so there is a companion cell for each sieve tube element. They carry out the living functions for sieve cells.

Front 57

What is translocation?

Back 57

Translocation is the movement of solutes to where they needed in a plant.

Solutes are called assimilates which is an energy requiring process that happens in the phloem.

Translocation moves the solutes from sources to sinks.

The source is where assimilates are produced (at high concentration).

The sink is where assimilates are used up (at low concentration).

Enzymes maintain the concentration gradient from the source to the sink by changing the solutes at the sink e.g by breaking them down or changing them into something else. This makes sure there’s always a Lower concentration at the sink than at the source.

Front 58

The mass flow hypothesis

Back 58

1. At the source end:

Active transport is used to actively load solutes from companion cells into the sieve tubes of the phloem at the source.

This lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells.

This creates a higher pressure inside the sieve tubes at the source end of the phloem.

2. At the sink end:

The solutes from the phloem are removed to be used up.

This increases the water potential gradient so water moves out of the tubes by osmosis.

This lowers the pressure inside the sieve tubes.

3. Flow

The result is a pressure gradient from the source end to the sink end. This gradient pushes the solutes along the sieve tubes towards the sink.

When they reach the sink, the solutes will be used/stored.

The higher the concentration of sucrose at the source, the higher the rate of translocation.

Front 59

Supporting evidence for mass flow hypothesis

Back 59

1. If a ring of a bark is removed from a woody stem, a bulge forms above the ring. The fluid from the bulge has a higher concentration of sugars than the fluid from below the ring. This is evidence that there’s a downward flow of sugars.

2. A radioactive tracer for example radioactive carbon or carbon -14 can be used to track the movement of organic substances in a plant.

3. Pressure in the phloem can be investigated using aphids. The sap flows out quicker near the leaves than further down the stem. This is evidence that there is a pressure gradient.

4. If a metabolic inhibitor is put into the phloem, then translocation stops. This evidence that active transport is involved.

Front 60

Evidence against mass flow

Back 60

1. Sugar travels to many different sinks not just to the one with the highest water potential, as the model would suggest.

2. The sieve plates would create a barrier to mass flow. A lot of pressure would be needed for the solutes to get through at a reasonable rate.