Biology Unit 3

Osmosis- is the movement of water, from a high concentration to a low concentration across a selectively permeable membrane. 

A selectively permeable membrane allows small, soluble molecules to pass through it, but prevents large insoluble molecules from passing through.

This is also going from a dilute solution to a more concentrated one. 

Animal cells are surrounded only by the membrane and no cell wall, therefore may swell up and burst if too much water enters through osmosis. Plant cells have a strong cell wall outside the membrane and this wall prevents them from swelling up too much. They become stiff and hard like a well-inflated football. The cell is turgid.

Animals cells will also become flaccid when they lose water via osmosis.

Active transport is the process by which dissolved molecules move across a semi-permeable membrane from a low concentration to a high concentration. In active transport, particles move against the concentration gradient, therefore require an input of energy from the cell.

Carrier proteins pick up specific molecules and take them through the cell membrane against the concentration gradient.

Active transports requires energy which is released during respiration

Diffusion and osmosis do not need energy.

In humans, active transport takes place during the digestion of food in the small intestine. Carbohydrates are broken down into simple sugars such as glucose. The glucose is absorbed by active transport into the villi, to be passed into the bloodstream and taken around the body.

After exercising you become hot and you produce sweat in order to cool down, sweat contains water and minerals ions. If you sweat a lot your body cells may become dehydrated. so you need to replace the ions that you have lost during sweating. Sports drinks are a solution of sugar and mineral ions, the drinks are designed to balance the concentration of body fluids and the concentration within the cells. An isotonic drink is one that matches the bodies fluids. 

If water and ions are not replaced, the ion/water balance of the body is disturbed and the cells do not work as efficiently

Large organisms need exchange surfaces:

• They have large surface area (Highly folded)
• Monocellular for a short diffusion pathway
• Large capillary network to maintain a steep concentration gradient 

The alveoli have all these adaptations to keep them efficient for gaseous exchange

Breath in:

• The intercostal muscles contract
• The ribcage move up and out and the diaphragm flattens
• The volume in the thorax increases 
• The pressure in the thorax decreases and air is drawn in 

Breathe out:

• The intercostal muscles relax and the diaphragm relaxes
• The ribcage move down and in and the diaphragm becomes domed
• The pressure increases inside the thorax and air is forced out.

Reasons for Artificial Breathing

• The alveoli  surface area is damaged 
• The tubes are narrowed 
• The person is paralysed 

The iron lung is for people who were paralysed. The person would lay in a sealed metal cylinder. when the air was drawn out the pressure made the chest move up and down to make them breathe in and out. 

• The vacuum which was formed in the cylinder would create negative pressure  

• breathing aids which force air into the lungs create positive pressure,  positive pressure is usually smaller and easier to use

The food we eat is digested in the gut into small, soluble molecules. In the small intestines, these solutes are absorbed into the blood. The villi line the inner surface of the intestine. 

• They have great surface area 
• The walls are mono-cellular, so have a short diffusion pathway
• The capillaries are close to the wall, short diffusion pathway
• Large capillary network maintains a concentration gradient
• The products can be absorbed  through diffusion or active transport

Gases diffuse in and out of the leaves through tiny holes called the stomata, the size of the stomata is controlled by the guard cells. Plants also lose water through the stomata.

Water and minerals are taken up by the roots. Root hair cells increases the surface area of the roots and the surface area of leaves is increased by the flattened shape and internal air spaces

If the plant is losing more water than it can replace the stomata can close. 

Plants have stomata to obtain carbon dioxide from the atmosphere and to remove oxygen produced in respiration.

If plants lose water faster than it is replaced by the roots, the stomata can close to prevent wilting.

Plants use the energy from photosynthesis and respiration in order to take up mineral ions against a concentration gradient from the soil through active transport.

Plants take up water through the roots. the water passes through the stem of the plant to the leaves. In the leaves, the water evaporates from the surfaces of leaf cells and the water vapour diffuses through the stomata. 

The movement of the water through the plant is called transpiration stream.

Water rises through the xylem because:

Adhesion

Water rises in the narrow vessels partly because water molecules are attracted to the walls of the vessels.

Cohesion

Water molecules are attracted to each other, and as water evaporates from the leaves columns of water are drawn up through the xylem vessels

It carries water for photosynthesis to the palisade cells in the leaves

The water carries essential mineral salts in solution

Evaporation from the leaves has a cooling effect

The heart is a double pump – Arteries take blood away from the heart while veins take blood to the heart. The right (left as you look at the diagram, right in real life) takes deoxygenated blood to the heart, while the left takes oxygenated blood around the body.

Arteries carry blood at high pressure, arteries also have fluctuations

As a rule arteries carry oxygenated blood while veins carry deoxygenated blood. However, the pulmonary vein and artery break this rule and carry the opposite type of blood.

The arteries split off into thousands of tiny capillaries and take blood to every cell

The veins transport the deoxygenated blood at low pressure back to the heart

Arteries

• Carry blood away from the heart (always oxygenated apart from the pulmonary artery which goes to the lungs)
• Have thick muscular walls
• Contain blood under high pressure

Veins

• Carry blood to the heart (always de-oxygenated apart from the pulmonary vein which goes from the lungs to the heart)
• Have thin walls and a large lumen
• Contain blood under low pressure
• Have valves to prevent blood flowing backwards

Capillaries

• Monocellular
• Very low blood pressure
• Where gas exchange takes place. Oxygen passes through the capillary wall and into the tissues, carbon dioxide passes from the tissues into the blood
• Small lumen and thin walls

Plasma

• Fluid part of blood
• Carries carbon dioxide, hormones and waste

Red blood cells

• Contain haemoglobin which carries oxygen, forms a temporary bond with oxygen to form oxyhaemoglobin
• Made in the bone marrow.

White blood cells

• An important part of the immune system, they produce antibodies and destroy harmful microorganisms
• Made in the bone marrow

Platelets

• Clump together to form clots, clump in a mesh
• Protect the body by stopping bleeding

Blood enters the atria of the heart. The atria contract and force blood into the ventricles. The ventricles contract and force blood out of the heart. Valves in the heart ensure that blood flows in the correct direction. Blood flows from the heart to the organs through arteries and returns through veins. There are two separate circulation systems, one for the lungs and one for all other organs of the body.

The heart has four chambers. The two atria collect the blood. The two ventricles pump the blood out of the heart.

Valves prevent the blood from flowing backwards.

The septum separates the two sides of the heart.

The right side of the heart pumps de-oxygenated blood to the lungs to pick up oxygen. The left side of the heart pumps the oxygenated blood from the lungs around the rest of the body.

Stents help keep coronary arteries open and reduce the chance of a heart attack. A stent is inserted into the clogged artery with a balloon catheter. The balloon is inflated and the stent expands and locks in place. This holds the artery open and allows blood to flow more freely.

Advantages

• They allow the person to live, without they would die
• They extend the persons life time

Disadvantages

• Damage red blood cells as they pass through the open valves
• Require the patient to take anti-blood clotting drugs for the rest of their life
• Some people say they can hear the valves opening and closing
• They have to carry around a battery to keep the heart charged
• They can become worn down over long periods of time

Carbon dioxide, produced by respiration and removed via the lungs when we breathe out

Urea, produced in the liver by the breakdown of amino acids and removed by the kidneys in the urine, which is temporarily stored in the bladder.

Healthy kidney produces urine by:

• first filtering the blood
• reabsorbing all the sugar
• reabsorbing the dissolved ions needed by the body
• reabsorbing as much water as the body needs
• releasing urea, excess ions and water as urine.

People who suffer from kidney failure may be treated either by using a kidney dialysis machine or by having a healthy kidney transplanted.

Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels and has to be carried out at regular intervals.

In a dialysis machine a person’s blood flows between  partially permeable membranes. The dialysis fluid contains the same concentration of useful substances as the blood. This ensures that glucose and useful mineral ions are not lost. Urea passes out from the blood into the dialysis fluid.

In kidney transplants a diseased kidney is replaced with a healthy one from a donor. However, the donor kidney may be rejected by the immune system unless precautions are taken.

The recipient’s antibodies may attack the antigens on the donor organ as they do not recognise them as part of the recipient’s body.

To prevent rejection of the transplanted kidney:

• a donor kidney with a ‘tissue-type’ similar to that of the recipient is used
• the recipient is treated with drugs that suppress the immune system.

The blood glucose concentration of the body is monitored and controlled by the pancreas. The pancreas produces the hormone insulin, which allows the glucose to move from the blood into the cells.

A second hormone, glucagon, is produced in the pancreas when blood glucose levels fall. This causes glycogen to be converted into glucose and be released into the blood.

 Type 1 diabetes is a disease in which a person’s blood glucose concentration may rise to a high level because the pancreas does not produce enough of the hormone insulin.

Type 1 diabetes may be controlled by careful attention to diet, exercise, and by injecting insulin.

If the core body temperature is too high:

• blood vessels supplying the skin capillaries dilate so that more blood flows through the capillaries and more heat is lost
• sweat glands release more sweat which cools the body as it evaporates.

If the core body temperature is too low:

• blood vessels supplying the skin capillaries constrict to reduce the flow of blood through the capillaries
• muscles may ‘shiver’ – (skeletal muscle) this is their contraction needs respiration, which releases some energy to warm the body, as 70% of energy produced during respiration is heat energy

Body temperature is monitored and controlled by the thermoregulatory centre in the brain. This centre has receptors sensitive to the temperature of the blood flowing through the brain.

Also, temperature receptors in the skin send impulses to the thermoregulatory centre, giving information about skin temperature.

A blood substitute is a substance used to mimic and fulfil some functions of biological blood. It aims to provide an alternative to blood transfusion

Advantages

• Can be used in emergencies in order to keep the person the alive
• Can be carried in large amounts
• Can be created in large amounts
• No risk of causing an infection due to the blood not coming from another person

Disadvantages

• Only short term alternative
• Can cause vasoconstriction — a tightening and narrowing of the blood vessel walls