Further Biology
ACTIVE TRANSPORT
There are times when cells need to move chemicals across the cell membrane against the concentration gradient (i.e. from a low concentration to a high concentration). This requires energy, as the chemicals need to be pumped across the cell membrane. The cells of the small intestine absorb some food particles by active transport. The cells lining the kidney nephrons (see kidney) absorb vital chemicals like glucose from a filtrate, which would otherwise be lost in urine. Cells, which use active transport a great deal, will have large quantities of mitochondria to supply them with energy. Obviously there needs to be a good supply of oxygen and glucose so that energy can be released by respiration.
Substances are selectively transported. The cell can choose which chemicals are pumped into or out of the cell. For example, nerve cells actively pump potassium inside the cell while pumping sodium out of the cell.
Root hair cells absorb mineral ions via active transport.
EXCHANGE OF GASES IN THE LUNGS
The alveoli are the tiny air sacs at the ends of the bronchioles and the site of gaseous exchange. It is here that oxygen is absorbed into the blood while carbon dioxide is put in to the air
Deoxygenated blood arrives at the alveoli in tiny blood capillaries. These have very thin walls, as does the alveoli itself. This makes it easier for the gases to pass from the air into the blood or vice versa. The deoxygenated blood has red blood cells low in oxygen and blood plasma high in carbon dioxide. The carbon dioxide diffuses from the blood plasma into the air. The oxygen diffuses from the air into the red blood cells. Blood constantly moves through the capillaries picking up O
2
and giving up its CO
2
.
EXCHANGE IN DIGESTION (ABSORPTION OF FOOD)
As food is digested the products are absorbed into the blood. There are a number of adaptations which increases the surface area for absorption. Without these adaptations digested food may not be absorbed before it is egested through the anus.
1.
The ileum is long and narrow which produces a larger surface area than a short broad tube.
2.
The ileum is folded which increases the surface area.
3.
The surface is covered with tiny (about 1mm long) fingerlike projections called villi.
4.
The cells on the surface of the villi have tiny fingerlike projections on their cell membrane called
micro-villi.

General Principles for Efficient Gas Exchange
Different organisms have different mechanisms for obtaining the gases they require.
Diffusion is required to supply all organisms with oxygen.
The efficiency of diffusion is increased if there is:
1.
A large surface area over which exchange can take place.
2.
A concentration gradient without which nothing will diffuse.
3.
A thin surface across which gases diffuse.
The larger the area and difference in concentration and the thinner the surface, the quicker the rate.
Unicellular organisms
Unicellular Organisms do not have specialised gas exchange surfaces. Instead gases diffuse in through the cell membrane.
The smaller something is, the smaller the surface area is but, more importantly, the bigger the surface area is compared to its volume.
Multicellular Organisms are bigger than Unicellular organisms. This makes efficient diffusion of gases more difficult.
However, if they are small, or large but very thin (like the flatworms, Platyhelminths), the outer surface of the body is sufficient as an exchange surface because the surface area to volume ratio is still high.
Gas Exchange in Plants
Plants obtain the gases they need through their leaves. They require oxygen for respiration and carbon
dioxide for photosynthesis.
The gases diffuse into the intercellular spaces of the leaf through pores, which are normally on the underside of the leaf - stomata. From these spaces they will diffuse into the cells that require them.

Gas Exchange in Insects
Insects have no transport system so gases need to be transported directly to the respiring tissues.
There are tiny holes called spiracles along the side of the insect.
The spiracles are openings of small tubes running into the insect's body, the larger ones being called
tracheae and the smaller ones being called tracheoles.
The ends of these tubes, which are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles.
Ventilation movements of the body during exercise may help this diffusion.
The spiracles can be closed by valves and may be surrounded by tiny hairs. These help keep humidity around the opening, ensure there is a lower concentration gradient of water vapour, and so less is lost from the insect by evaporation.
Gas Exchange in Fish
Fish use gills for gas exchange. Gills have numerous folds that give them a very large surface area.
The rows of gill filaments have many protrusions called gill lamellae. The folds are kept supported and moist by the water that is continually pumped through the mouth and over the gills.
Both the intercostal muscles (in between the ribs) and the diaphragm receive impulses from the respiratory centre. Stretch receptors in the lungs send impulses to the respiratory centre in the brain giving information about the state of the lungs.
TRANSPIRATION
The transpiration stream is the flow of water from the roots to the leaves of a plant.
Transpiration is the loss of water from the leaves of a plant.
Water goes through xylem tissue, to travel from the roots to the leaves.
A plant uses the transpiration stream to:
Evaporate the water to keep the plant cool.
Keep the plant cells turgid to support the weight of the plant.
Provide the necessary water for photosynthesis.
Transpiration works fastest in warm, dry, sunny, windy conditions.
Water is evaporated through the stomata, as well as taking in carbon dioxide and emitting oxygen.
Stomata are found on the underside of leaves, and control the rate of transpiration by opening and closing the guard cells.

THE CIRCULATORY SYSTEM
The function of the circulatory system is to transport materials around the body. There are many materials that need transporting. These include oxygen, carbon dioxide, nutrients (such as glucose and amino acids), hormones and waste chemicals such as urea. These substances are transported in a medium called blood through the body through tubes called blood vessels. The blood is forced around these vessels by a pump - the heart.
There are different types of blood vessels.



Arteries - take blood away from the heart.
Veins - take blood towards the heart.
Capillaries - small vessels connecting arteries & veins.
The blood travels around the circulatory system in a series of parallel circuits so that the blood travels from the heart, through an organ before returning to the heart. If the blood went through each organ in turn the organs near the end of the chain would not receive as many nutrients as the organs first in line. This is because the first organs would take out the nutrients leaving fewer for the organs that follow.
There is one exception to this. The blood leaving the stomach & intestines first goes through the liver. The
Liver receives its own blood supply, but this second supply gives the liver a chance to absorb any extra nutrients the body needs to store as well as neutralising any toxins that have been absorbed before they can wreak havoc throughout the body.

The heart is really two pumps stuck together. There are two chambers to each side of the heart. The first chamber is called the atrium (atria - plural) and is the smaller of the two chambers. The larger one is called the ventricle. This chamber is the more powerful of the two as it forces blood out of the heart.
The left-hand side receives deoxygenated blood from the body. The job of the left-hand side of the heart is to pump blood to the lungs to pick up oxygen and get rid of carbon dioxide. As the lungs are close by the pump does not need to be very strong.
The right-hand side receives the newly oxygenated blood from the lungs and has to pump it around the rest of the body. As the distances are greater and in the case of the upper body, blood flow is against gravity, the right-hand side needs to be more powerful.
The two chambers of the heart are separated by valves that prevent the blood going the wrong way through the heart.
TRANSPORT IN BLOOD
Blood travels via arteries until it reaches smaller vessels called capillaries. It is here that materials are exchanged between blood and the tissue cells.

1.
The blood enters a capillary bed. These vessels are very leaky and are only wide enough for one cell at a time to pass through. The capillary walls are only 1 cell thick!
2.
The blood pressure forces some of the blood plasma to leak out of the capillary. This fluid is high in nutrients and oxygen (from the red blood cells). Large objects like red blood cells and protein molecules cannot pass through the walls of the capillary. The fluid that is surrounding the tissue cells is called tissue fluid. It is from this fluid that materials will diffuse into the cells.
3.
White blood cells are the only cells, which can leave the blood, so they can hunt down pathogens.
4.
Waste materials like carbon dioxide and urea diffuse from the cells into the tissue fluid. This fluid is drawn back into the blood capillary by an osmotic pressure supplied by the large proteins in the blood.
5.
Not all the tissue fluid flows back into the blood. If it did not return the tissues would swell with fluid. Sets of vessels, called lymph vessels, drain this tissue fluid and carry it away from the tissues. Eventually the fluid (called lymph) drains back into the blood.
6.
The blood leaves the capillary beds and travels back to the heart via veins.
7.
Red blood cells are bioconcave discs (for a large surface area) They are packed with haemoglobin which can absorb oxygen
8.
Plasma transports urea, carbon dioxide and dissolved food around the body
THE EFFECTS OF EXERCISE ON THE BODY
The effects of exercise on the circulatory system.
Short term effects
During exercise the heart rate increases rapidly.
This provides the muscles with the necessary oxygen and nutrients to provide the muscles with energy.
During exercise, cardiac output is increased.
Cardiac output = stroke volume x heart rate.
During exercise stroke volume increases because:


 more blood is sent back to the heart due to the muscles squeezing blood in the veins. as the heart fills up, it stretches. as the muscle fibres stretch, they contract more strongly, pumping out more blood.
Long term effects
The heart muscle will grow and strengthen.
The heart muscle will become more efficient in heart rate and stroke volume.
Note: Stroke volume is the amount of blood leaving each ventricle on each beat.
The effects of exercise on the respiratory system
Short term effects

During exercise, the body needs a supply of oxygen to release energy in the muscles.
Respiration increases to provide that oxygen and remove carbon dioxide.
This is done by:
 increasing breathing rate by about three times the normal rate.
 increasing tidal volume by five times the normal rate.
 increasing blood supply to and through the lungs.
 increasing oxygen up take.
Note: Tidal Volume is the amount of air taken in or out with each breathe.
Long term effects
The body becomes more efficient at using oxygen.
This is known as VO2 max and is a significant indicator of an athlete's physical fitness.
VO2 max can be accurately tested.
The effects of exercise on the digestive system
Short term effects
Blood is diverted to the heart, lungs and working muscles, away from parts of the digestive system.
It is best to rest for up to two hours after a meal before exercising.
The effects of exercise on the body.
Short term effects
During intense exercise the body's temperature rises.
Messages are sent from the brain to the skin to make it sweat. Sweat is formed by sweat glands under the skin.
Losing heat through sweating is caused by the evaporation of sweat from the skins surface.
Blood is diverted to the capillaries just below the skin. This causes the skin to redden.
Long term effects
Exercise improves the general health and well being of the body.
It is kept toned and helps to prevent heart disease in later life.
It provides positive mental and social contributions to a persons life as well as positive physical contributions.
ANAEROBIC RESPIRATION
There are occasions when the cells undergoing respiration cannot get enough oxygen to perform aerobic respiration. For example when exercising vigorously the amount of oxygen getting to the muscles may be insufficient for aerobic respiration. If the cells still require energy then they need to respire without oxygen. This is anaerobic respiration.
Without oxygen the breakdown of the food is incomplete. This means less energy is released. There are two types of anaerobic respiration depending whether it takes place in an animal or a plant / fungi.
Anaerobic Respiration in Animals
In animals, anaerobic respiration produces lactic acid as the glucose is not fully broken down.
Glucose
Lactic acid + energy
If the lactic acid builds up it can stop the muscles from working, causing cramp. This lactic acid needs to be broken down. This requires oxygen. Respiring in this way builds up an oxygen debt which must be repaid in order to get rid of the lactic acid. As a result, animals cannot respire for very long without oxygen.

Anaerobic Respiration in Plants / Fungi
When plants or fungi respire they produce ethanol (alcohol) and carbon dioxide.
Glucose
Carbon Dioxide + Ethanol + energy
A build up of ethanol can be toxic. Some organisms, such as yeast, respire in this way all the time. Yeast is used to make alcoholic drinks. The process is called fermentation.
Yeast is also used in bread making as it gives of carbon dioxide gas which makes the bread rise, giving it a light and fluffy texture.
THE HUMAN KIDNEY
There are two kidneys. The outer part of the kidney, called the capsule, is an outer skin, holding the kidney together. Underneath this is the cortex. It is here that the capillary knots and Bowman's capsule can be found. This is where the blood is filtered. The process is called ultrafiltration.
The medulla lies under the cortex. This area helps with the reabsorption of water. It is here that the loop of
Henle, part of the kidney tubule, can be found. The pyramids are formed from the collecting ducts which bring urine from the kidney tubule. These lead into the pelvis, which leads into the ureter, carrying urine to the bladder to be stored.
The kidney performs a vital role in keeping the water, salt and pH levels of the body constant. It also rids the body of many unwanted and toxic chemicals. If the kidney stops functioning correctly the person may die.
There are a number of problems, which could occur with the kidney. An infection could cause bleeding and the kidney may not be able to reabsorb nutrients, as it should. It may also mean that the urine may also contain things that should not be there, like blood & protein.
If kidney failure occurs there will be no functioning of the kidney and the levels of urea & salt will soon become lethal unless treatment like dialysis is given.

The urine of patients is often tested for the presence of certain chemicals so as to help with diagnosis of the disease. For example the presence of protein in the urine can indicate a kidney infection or kidney failure, as can the presence of blood in the urine. Glucose in the blood may mean kidney problems, but may also mean the patient is a diabetic, as sufferers of this disorder often have very high blood glucose levels, making it impossible for the kidney to reabsorb all the glucose from the glomerular filtrate.
A patient with kidney failure will soon die unless there is a way to rid the body of the urea and excess salt.
A kidney dialysis machine provides an artificial kidney for the sufferers of kidney failure.
Blood is drawn from a vein in the body and enters the dialysis machine. The blood flows through a dialysis membrane, which is semi-permeable. It has in it pores which will allow small particles to pass through, like water, urea, salt, glucose and amino acids but not large particles like protein or cells.
Surrounding the membrane is dialysis fluid. This contains chemicals, which should be in the blood plasma
(glucose, amino acids & salts), in the correct concentrations.
The urea moves from the blood to the dialysis fluid by diffusion. Other small particles diffuse from the blood to the dialysis fluid too. As glucose diffuses out of the blood, glucose also diffuses into the blood from the dialysis fluid. This keeps the concentration of important chemicals in the blood constant.
Excess salt diffuses out of the blood, keeping it at the right levels. Osmoregulation occurs in much the same way. If there is too much water in the blood it will enter the dialysis fluid by osmosis. The reverse occurs if the blood is too concentrated.
The blood is kept at the correct temperature while it passes through the machine. The blood then returns to the body.
The patient needs to be on the machine for around 12 hours and the treatment needs to be repeated three times a week. The patient needs to be careful what they eat & drink. Too much salt & protein between dialysis treatments can cause problems. Also the amount of fluid which may be taken is very restricted, as the body has no way of getting rid of it. Obviously the kidney dialysis machine is not as good as a real kidney. A kidney can be transplanted to take over the role of the damaged kidneys. This is preferable but kidneys are hard to come by, as someone has to die to supply them.
Kidney machines are more readily available than transplants but they are restrictive in that you are tied down to them and diet must be controlled. Kidney transplants enable you to lead a normal life, but the kidney needs to be a correct tissue match (to avoid rejection) and there needs to be a donor.