Biology AS Cells Exchange And Transport Module 2 Exchange And Transport

OCR Biology AS

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Side ASide B
Define Exchange Surface
An exchange surface is a specialised area that is adapted to make it easier for molecules to cross from one side of the surface to the other.
What substances do living cells need? (6)
- oxygen for aerobic respiration- glucose as a source of energy - proteins for growth and repair- fats to make membranes and to be a store of energy- water- minerals to maintain their...
What features do good exchange surfaces have in common?
- large surface area to provide more space for molecules to pass through- thin barrier to reduce diffusion distance- fresh supply of molecules on one side to keep the concentration...
List 4 exchange surfaces in living organisms
1) small intestine (where nutrients are absorbed)2) liver (where levels of sugars in the blood are adjusted)3) root hairs of plants (where water and minerals are absorbed)4) hyphae...
Define Gaseous exchange
Gaseous exchange is the movement of gases by diffusion between an organism and its environment across a barrier such as the alveolus wall.
How does gaseous exchange occur in the lungs?
Gases pass both ways through the thin walls of the alveoli. Oxygen passes from the air in the alveoli to the blood in the capillaries. Carbon dioxide passes from the blood to the air...
Why do the lungs have a large surface area?
The large surface area provides more space for molecules to pass through.
Why do the lungs have a barrier permeable to oxygen and carbon dioxide?
The plasma membranes that surround the thin cytoplasm of the cells form the barrier to exchange. These readily allow the diffusion of oxygen and carbon dioxide.
Why do the lungs have a thin barrier to reduce diffusion distance?
- the alveolus wall is one cell thick- the capillary wall is one cell thick- both walls consist of squamous cells- the capillaries are in close contact with the alveolus walls- the...
Why must the lungs produce surfacant?
To reduce the cohesive forces between the water molecules. Without the surfacant, the alveolus would collapse due to the cohesive forces between the water molecules lining...
Why is a steep diffusion gradient needed in the lungs?
For diffusion to be rapid.
What is meant by a steep diffusion gradient?
This means having a high concentration of molecules on the supply side of the exchange surface and a low concentration on the demand side.
How is a steep duffusion gradient maintained?
A fresh supply of molecules on one side is needed to keep the concentation there high, and a way of removing the molecules from the other side is needed to keep the concentration there...
How is a diffusion gradient maintained in the lungs?
This is achieved by the action of the blood transport system and the ventilation movements. The blood brings carbon dioxide from the tissues to the lungs. This ensures that...
Outline inspiration (inhaling)
- Diaphragm contacts to become flatter and pushes digestive organs down - External intercostal muscles contract to raise ribs- Volume of chest cavity increases- Pressure in chest cavity...
Outline expiration (exhaling)
- Diaphragm relaxes and is pushed up by displaced organs underneath- External intercostal muscles relax and ribs fall- Volume of chest cavity decreases- Pressure in lungs increases...
What 5 requirements must the airways meet?
1) larger airways must be large enough to allow sufficient air to flow without obstruciton2) they must divide into smaller airways to deliver air to all the alveoli3) the airways must...
What is the difference between the trachea and bronchi?
The bronchi are narrower
List the 4 features of the trachea and bronchi
1) Much of the wall consists of cartilage2) The cartilage is in the form of incomplete rings in the trachea, but is less regular in the bronchi3) On the inside surface of the cartilage...
Describe the bronchioles
They are much narrower than the bronchi.Larger bronchioles may have some cartilage.The wall is made mostly of smooth muscle and elastic fibres.Very small bronchioles have clusters of...
What is the role of cartilage?
Cartilage plays a structural role. It supports the trachea and bronchi, holding them open.
What is the role of smooth muscle?
The smooth muscle can contract. When it contracts it constricts the airway and makes the lumen of the airway narrower. Constricting the lumen can restrict the flow of air to and from...
What is the role of elastic fibres?
When smooth muscle contacts, it reduces the diameter of the lumen of the airway. The smooth muscle cannot reverse this effect. When the airway constricts, it deforms the elastic fibres...
What is the role of goblet cells and glandular tissue?
Goblet cells and glandular tissue secrete mucus. Mucus traps tiny particles from the air. These particles may include pollen and bacteria. Removing the bacteria will reduce the risk...
What is the role of ciliated epithelium?
This consists of ciliated cells. The cilia on these cells (hair like projections) move in a synchronised pattern to waft mucus up the airway to the back of the throat. The mucus can...
What is tidal volume?
Tidal volume is the volume of air moved in and out of the lungs with each breath when you are at rest. Normally 0.5dm3
What is vital capacity?
Vital capacity i sthe largest volume of air that can be moved into and out of the lungs in any one breath. Normal 5dm3
What is residual volume?
Residual volume is the volume of air that always remains in the lungs, even after the biggest possible exhalation. Normally 1.5dm3
What is dead space?
Is the air in the bronchioles, bronchi and trachea.
What is inspiratory reserve volume?
Inspiratory reserve volume is how much more air can be breathed in over and above the normal tidal volume when you take in a big breath. You call on this reserve when exercising.
What is expiratory reserve volume?
Expiratory reserve volume is how much more air can be breathed out over and above the amount that is breathed in a tidal volume breath.
How does a spirometer work?
A spirometer consists of a chamber filled with oxygen that floats on a tank of water. A person breathes in from a disposable mouthpiece attached to a tube connected to the chamber...
Why is soda lime used in measuring oxygen uptake?
Soda lime is used to absorb the carbon dioxide that is exhaled. This causes the volume of gas in the spirometer to go down.
Look at spirometer trace
Define transport
Transport is the movement of oxygen, nutrients, hormones, waste and heat around the body.
What three factors affect the need for a transport system?
- size- surface area to volume ratio - level of activity
What 5 things will and effecient/effective transport system include?
- a fluid or medium to carry nutrients and oxygen around the body (blood)- a pump to create pressure that will push the fluid around the body (heart)- exchange surfaces that enable...
What sort of circulatory system to fish have?
Single circulatory system
How does a single circulatory system work in fish?
The blood flows from the heart to the gills and then on to the body before returning to the heart.
What sort of circulatory system do mammals have?
A double circulatory system
How does the double circulatory system work?
One circuit carries blood to the lungs to pick up oxygen. This is the pulmonary circulation. The other circuit carries the oxygen and nutrients around the body to the tissues. This...
What happens in the single circulatory system of fish?
- the blood pressure is reduced as blood passes through the tiny capillaries of the gills- this means it will not flow very quickly to the rest of the body - this limits the rate at...
What happens in the double circulatory system of mammals?
- the heart can increase the pressure of the blood after it has passed through the lungs, so blood flows more quickly to the body tissues - the systemic circulation can carry blood...
Define the heart
The heart is a muscular pump that creates pressure to propel blood through the arteries and around the body.
What does the right side of the heart do?
Pumps deoxygenated blood to the lungs to be oxygenated.
What does the left side of the heart do?
Pumps oxygenated blood to the rest of the body.
What forces blood along the arteries?
The heart squeezes the blood, putting it under pressure. The pressure forces the blood along the arteries.
Look at diagram of heart
What do the coronary arteries do?
They carry oxygenated blood to the heart muscle itself.
What do the atria do?
These recoeve blood from the major veins.
Where does deoxygenated blood from the body flow?
From the vena cava into the atrium.
Where does oxygenated blood from the lungs flow?
From the pulmonary vein into the left atrium.
Where does blood flow from the atria?
Blood flows down through the atrioventricular valves into the ventricles.
What happens when the ventricles contract?
The valves fill with blood and remain closed. This ensures that the blood flows upwards into the major arteries and not back into the atria.
What is the septum and what does it do?
A wall of muscle that seperates the ventricles from each other. This ensures that the oxygenated blood in the left side of the heart and the deoxygenated blood in the right side are...
What do the semilunar valves do?
They are at the base of the major arteries and prevent blood returning to the heart as the ventricles relax.
Why is the muscle of the atria very thin?
Because these chambers do not need to create much pressure. Their function is to push the blood into the ventricles.
Why are the walls of the right venticle thicker than the walls of the atria?
This enables the right ventricle to pump blood out of the heart.
Why are the walls of the right ventricle thinner than those of the left?
The right ventricle pumps deoxygenated blood to the lungs. The lungs are in the chest cavity beside the heart, so the blood does not need to travel very far. Also, the lungs contain...
Why are the walls of the left venrticle much thicker than the right?
The blood from the left ventricle is pumped out through the aorta and needs sufficient pressure to overcome the resistance of the systemic circulation.
Define cardiac cycle
The cardiac cycle is the sequence of events in one heartbeat.
Describe the filling phase (1)
While both the atria and the ventricles are relaxing, the internal volume increases and blood flows into the heart from the major veins. The blood flows into the atria, then through...
Describe atrial contraction (2)
The heart beat starts when the atria contract. Both right and left atria contract together. The small increase in pressure created by this contraction helps to push blood into the ventricles....
Describe ventricular contraction (3)
Now there is a short period when all four heart valves are closed. The walls of the ventricles contract. This is called ventricular systole. This raises the pressure in the ventricles...
How do the atrioventricular valves work?
When the venticle walls relax and recoil after contracting, the pressure in the ventricles drops below the pressure in the atria. This causes the atrioventricular valves to open. Blood...
How do the semilunar valves work?
When the ventricles start to contract, the pressure in the major arteries is higher than the pressure in the ventricles. This means that the semilunar valves are closed. As the ventricles...
What is the sound of the heart?
The sound of the heart is made by the valves closing. - the first sound (lub) is made by the atrioventricular valves closing as the ventricles start to contract. - the second sound...
Define sionatrial node
The SAN is the heart's pacemaker. It is a small patch of tissue that sends out waves of electrical excitation at regular intervals to initiate contactions.
Define Purkyne tissue
Purkyne tissue is specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles.
Why is heart muscle described as myogenic?
Because it can initiate its own contraction.
How does the heartbeat start? (1)
At the top of the right atrium, near the point where the vena cava empties blood into the atrium, is the SAN. There is a small patch of tissue that generates electrical activity. The...
Desctibe how contaction of the atria works (2)
The wave of excitation quickly spreads over the walls of both atria. It travels along the membranes of the muscle tissue. As the wave of excitation passes, it causes the cardiac...
Descirbe how contraction of the ventricles works (3)
After this delay, the wave of excitation is carried away from the AVN and down specialised conducting tissue. This is Purkyne tissue and it runs down the inter-ventricular septum. At...
What are electrocardiograms and how do they work?
ECG's are used to measure the activity heart. Sensors are attached to the skin. Some of the electrical activity generated by the heart spreads through the tissues next to the heart...
What is this?
A normal ECG - P shows excitation of the atria - QRS indicates excitation of the ventricles - T shows diastole
Define open circulatory system.
In an open circulatory system the blood is not always in vessels.
Define closed circulatory system.
In a closed circulatory system the blood always remains within vessels.
Why don't all animals have an open system?
Open systems work for insects as they are small and they don't rely on the blood to transport oxygen and carbon dioxide. Larger organisms rely on blood to transport oxygen and carbon...
What happens in closed circulatory systems?
The blood stays entirely inside vessels. Tissue fluid bathes cells and tissues. This means blood can be pumped at a higher pressure and flow quickly. It means oxgyen and nutrients can...
Describe arteries.
Arteries carry blood away from the heart. The blood is at high pressure so the wll must be able to withstand that pressure. - The lumen is relatively small to withstand that pressue. -...
Describe veins.
Veins carry blood back to the heart. The blood is at low pressure and the walls do not need to be thick. - The lumen is relatively large to ease the flow of blood. - The walls have...
Describe capillaries.
Capillaries have very thin walls. They allow exchange of materials between the blood and cells of tissues via the tissue fluid. - The walls consist of a single layer of endothelial...
Define blood
Blood is held in the heart and blood vessels.
Define tissue fluid
Tissue fluid bathes the cells of induvidual tissues.
Define lymph
Lymph is help within the lymphatic system.
Describe blood.
Blood consists of blood cells in a watery liquid called plasma. The plasma contains many dissolved substances. The cells include red and white blood cells as well as platelets.
Describe tissue fluid and its role
Tissue fluid is similar to blood but does not contain plasma proteins or as many cells. The role of tissue fluid is to transport oxygen and nutrients from the blood to the cells, and...
Explain how tissue fluid is formed
The fluid that leaves the capillary is known as tissue fluid. This fluid surrounds the body cells, so exchange of gases and nutirents can occur across the cell surface membranes. This...
Explain how the fluid returns to the blood.
The tissue fluid itself has some hydrostatic pressure and this pushes the fluid back into the capillaries. Both the blood and tissue fluid contain solutes which give them a negative...
Describe the formation of lymph.
Lymph is similar to tissue fluid and contians the same solutes.
What is haemoglobin?
Haemoglobin is a complex protein with 4 subunits. Each subunit consists of a polypeptide chain and a haem group. The heam group has a high affinity for oxygen.
How does haemoglobin take up oxygen?
Oxygen molecules diffuse into the blood plasma and enter the red blood cells. Here they are taken up by haemoglobin. This takes the oxygen molecules out of solution and so maintains...
How is oxygen released by heamoglobin?
Cells need oxygen for aerobic respiration. Oxyhaemoglobin must be able to release the oxygen. This is called dissociation.
Describe and explain haemoglobin and oxygen transport
The ability of haemoglobin to take up and release oxygen depends on the amount of oxygen in the surrounding tissues. This is called partial pressure (oxygen tension). Haemoglobin...
What is fetal heamoglobin?
Has a higher affinity for oxygen than adult haemoglobin. It must be able to absorb oxygen from the fluid in the mother's blood. This reduces oxygen tension within the blood fluid which...
How is carbon dioxide transported?
5% dissolved directly into plasma10% combined with haemoglobin to form carbaminohaemoglobin85% is transported in the form of hydrogencarbonate ions.
How are hydrogencarbonate ions formed?
CO2 enters the red blood cell and is combined with water to form carbonic acid. The enxyme carbonic anhydrase ensures that this occurs. The carbonic acid dissociates to hydrogen ions...
Describe the Bohr effect
The Bohr effect results in oxygen being more readily released where more carbon dioxide is produced from respiration.
Define xylem
Xylem transports water up the plant
Define phloem
Phloem transports sugars and other assimilates up and down the plant
Why do plants need transport systems?
So that all of the cells can recieve enough water and nutrients in order to survive.
What substances do plants need to move?
- water and soluble minerals (these travel upwards in xylem tissue) - sugars (these travel up and down in phloem tissue)
What are the vascular tissues?
xylem and phloem
What is the vascular bundle?
The xylem and phloem are found together in vascular bundles. These bundles often contain other types of tissue that give the bundle some strenght and help to support the plant.
Describe xylem and phloem in the stem.
The vascular bundles are found near the outer edge of the stem. The xylem is found towards the inside of each vascular bundle. The phloem is found towards the outside of the bundle....
Describe xylem and phloem in the leaf
The vascular bundles form the midrib and veins of a leaf. A dicotyledon leaf has a branching network of veins that get smaller as they spread away from the midrib. Within each vein,...
Describe the structure of xylem
Xylem tissue consitsts of tubes to carry the water and dissolved minerals, fibres, to help support the plant and living parenchyma cells.
What are xylem vessels?
These are long cells with thick walls that have been inpregnated by lignin. - The lignin waterproofs the walls of the cells. As a result the cells die, this leaves a long column of...
How is xylem adapted to its function?
- It is made from dead cells aligned end-to-end to form a continuous column - The tubes are narrow so the water column does not break easily and capillary action can be effective -...
Describe the structure of phloem
Phloem tissue consists of two types of cell: - sieve tube elements - companion cells
What are sieve tubes?
Sieve tubes are not true cells as they contain little cytoplasm and no nucleus. They are lined up end to end to create a tube. The tube contains cross walls at intervals. These cross...
What are companion cells?
In between the sieve tubes are small cells which have a large nucleus and dense cytoplasm. They have numerous mitochondria to produce the ATP for active processes. The companion cells...
Define water potential
Water potential is the total potential energy of the water molecules in a system. It is a measure of how likely it is that water will be lost from the system by diffusion down its water...
How does water move between cells?
When plant cells are touching each other, water molecules can pass from one cell to another. The water molecules will move from the cell with the higher water potential to the cell...
Describe the apoplast pathway
The cellulose cell walls have many water-filled spaces between the cellulose molecules. Water can move through these spaces and between the cells. In this pathway - the apoplast pathway...
Describe the symplast pathway
Water enters the cell cytoplasm through the plasma membrane. It can then pass through the plasmodesmata from one cell to the next. The plasmodesmata are gaps in the cell wall that contain...
Describe the vacuolar pathway
This is similar to the symplast pathway, but the water is not confined to the cytoplasm of the cells. It is able to pass through the vacuoles as well.
Define plasmodesma
A plasmodesma is a fine strand of cytoplasm that links the contents of adjacent cells.
How is water taken up from the soil?
How does water move across a root?
What is the role of the Casparian strip?
What three processes help to move water up the stem?
Describe and explain root pressure
Describe and explain transpiration pull.
Describe and explain capillary action
Describe and explain how water leave the leaf
Define transpiration
What three processes does transpiration involve?
What is the transpiration stream?
In what ways is movement of water up the stem useful to the plant?
How can we measure the rate of transpiration?
What features affect th rate of water loss and how do they affect water loss?
What happens if the plant loses too much water?
Define xerophyte
Why is the loss of water via transpiration unavoidable?
Most plants can reduce water loss by strucutal and behavioural adaptations. List 4 examples.
List adaptations of xerophytes.
Define translocation.
Define source.
Define sink.
How does sucrose enter the phloem?
How does sucrose move along the phloem at the source?
Sucrose is used in all cells surrounding the phloem. The sucrose may be converted to starch for storage, or may be used in metabloic processes such as respiration. This reduces the...
How does sucrose move along the phloem at the sink?
Water entering the phloem at the source, moving down the hydrostatic pressure gradient and leaving the phloem at the sink, produces a flow of water along the phloem. This flow carries...
Where are the sources and sinks?
Sources: leaf, roots,
What is meant by active loading?
Active loading means using ATP (energy) to transport sugars in the phloem.

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