Biology Unit 3 (Higher tier)

Biology revision

HideShow resource information

Gas and Solute Exchange

Substances move by diffusion, osmosis and active transport

Dissolved subastances move by diffusion. Diffusion is from an area of HIGH CONCENTRATION to an area of LOW CONCENTARTION.

Glucose + oxygen --> Carbon dioxide + water + energy

Substances can sometimes be absorbed against a concentration gradient. This requiers the use of energy from respiration.

This process is called ACTIVE TRANSPORT and it enables cells to absorb ions from very dilute solutions.

(Other substances, such as sugar and ions, can also pass through the cell membranes)

1 of 23

Gas and Solute exchange II

Osmosis is a "special kind of diffusion"

It is when water diffuses from a concentrated area to a less concentrated area through a semi-permeable membrane.

The structure of leaves lets gases diffuse in and out of cells.

Carbon dioxide diffuses into air spaces and then into the cells where photosynthesis happens. Underside of leaf covered in little holes called stomata. Water vapour and oxygen also diffuse out of the stomata.

Flattened shape increases surface area of exchange surface (Underside of leaves) so it is more effective. Air spaces inside the leaf increase the area of cell walls and so there is more chance of carbon dioxide getting into the cells.

2 of 23

Organ Systems

Many organ systems are specialised for exchanging materials

In humans the gas exchange in the lungs is increased due to alveoli:

1) They have enormous surface area

2) They have a moist lining for dissolving gases

3) Very thin walls

4) A thick blood supply

3 of 23

Organ Systems

Humans also have villi to provide a really really big surface area meaning that digested food is absorbed much more quickly into the blood.

They have:

1) A single layer of surface cells making it easier for the digested food to pass through

2) A very good blood supply to assist quick absorption

4 of 23

The breathing system

The Lungs

Air breathed in goes through the trachea. This then splits up into two tubes called "bronchi" (One going to each lung). The bronchi then split into progressively smaller tubes called bronchioles. The brioncholes finally end up at small bags called alveoli where gas exchange takes place.

Breathing In:

Diaphragm contracts, thorax volume increases, this decreases the pressure, drawing air in.

Breathing Out:

Diaphragm relaxes, thorax volume decreases, air is forced out.

5 of 23


Plants lose water vapour from the surface of their leaves.

This loss of water is called Transpiration

Transpiration is more rapid in hot, dry and windy conditions and so plants that  live in these conditions usuallu have a thick waxy layer on the outside of the leaf.

Most of trtanspiration is through the stomata which is controlled by the guard cells.

If plants lose water faster than the roots replace it, the stomata can then close to prevent wilting.

6 of 23

Transportation and the circulation system

Sybastances are transported around the body by the circulation system

The right side of the heart pumps deoxygenated blood to the lungs to collect oxygen and get rid of carbon dioxide. The left side of the heart pumps oxygenated blood around the body.

Blood flows from the heart to the organs through arteries and returns through veins.

When it reaches the organs, the arteries split into capillaries.

Capillaries use diffusion to deliver food and oxygen direct to body tissues and take carbon dioxide and other waste materials away.

7 of 23


Blood is made up of four main parts:

1) White blood cells - they destroy invading microbes

2) Red blood cells - Carry oxgen from the lungs to the cells. Doghnut shape to give a large surface area. They have no nucleus so they can carry more oxygen. Contain haemoglobin which combines with oxygen in the lungs to become oxyhaemoglobin. In body tissues the reverse happens to release oxygen to the cells.

3) Plasma - Liquid that carries everything in the blood. Red and white blood cells, platelets, nutrients like glucose and amino acids, carbon dioxide from the organs to the lungs, urea, hormones, antibodies and antitoxins produced by the white blood cells.

4)  Platelets - These are small fragments of cells which help blood to clot at a wound.

8 of 23


The human body needs to react to the increases demand for energy during exercise.

Energy released during respiration used to enable muscles to contract.

During exercise:

1) Heart rate increases

2) Rate and depth of breath increases

3) Arteries supplying the mucles dilate

These changes increase the blood flow to the muscles. This in turn increases the supply of sugar and oxygen

9 of 23

Exercise II

Glycogen is stored in the muscles. During vigarous exercise the muscles use glucose rapidly, and have to draw on their glycogen stores. When the glycogen stores run low, the muscles dont get enough energy to keep contracting and so they get tired.

Anaerobic respiration in the incomplete breakdown of glucose.

glucose --> energy + lactic acid

Lactic acid is poisonous if it does not leave the body - it causes cramp.

As the breakdown of glucose is incomplete, much less energy is released.

Anaerobic respiration results in OXYGEN DEBT

While high levels of CO2 and lactic acid are detected in the blood, the pulse and breathing rate stay high to try and sort out the situation.

10 of 23


A helthy kidney produces urine by:

1) First filtering the blood

2) Reabsorbing all the sugar

3) Reabsorbing all the dissolved ions needed by the body

4) Reabsorbing as much water as the body needs

5) Releasing urea, excess ions and water as urine

11 of 23

How a kidney really works

1) A high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the bowmans capsule.

2) The membranes between the blood vessels and the bowmans capsule act like filters, so big molecules like proteins and blood cells are not squeezed out. They stay in the blood

3) As the liquid flows along the nephron, useful subastances are reabsorbed back into the blood. These substances include sugar (with the help of active transport), sufficient ions (again with the help of active transport), and sufficient water.

4) The remaining subastances continue out of the nephron, into the ureter and down into the bladder as urine.

12 of 23


In a dialysis machine, a persons blood flows between a semi permeable membrane.

The dialysis fluid contains the same concentration of useful substances as the blood ensuring that glucose and useful mineral ions are not lost.

The fluid however does not contain any urea meaning that the urea from the blood passes out into the machine. Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels and has to be carried out at regualr intervals.

Advantages - If the patient has a haemodialysis machine it can be carried out at home. Quite a long life can be expected

Disadvantages - Takes a huge amount of time. Risk of infection. Causes nausea, vomiting, muscle cramps, and depression.

13 of 23


A Kidney transplant enables a diseased kidney to be replaced with a healthy one from a donor. However, the donor kidney may be rejected by the the body unless precautions are taken:

1) A donor kidney with a tissue type similar to that of the recipient is used

2) The recipient is treated with drugs that suppress the immune system (although then they cant fight any diseases that may come along and so it has to be done in a totally sterile condition)

3) The patients bone marrow is zapped with radiation to stop white blood cells being produced so they wont attack the transplanted kidney.

Advantages - You feel better physically. Once transplant is done, no more worrying like with dialysis

Disadvantages - Risk of rejection. Have to take anti rejection drugs for whole life

14 of 23


The theory of biogenesis has been developed over the years. People used to think that life could spontaneously generate from non living material. Evidence showed that this could not be the case. The evidence supported the theory that living thigs are created from other living organisms - this is the THEORY OF BIOGENESIS

Before 1765 they thought food went off because food was changed into microbes. Lazzaro Spallanzani boiled two sets of broth to kill the microbes. He sealed one flask and left the other one open - only the open one went off. This showed that microbes got into the food from the air.

In 1859 Louis Pasteur carried out more conclusive experiements. He heated broth in two flasks, both which were left open to the air. However, one flask had a curved neck so that bacteria from the air would settle in the loop, and not get through to the broth. The broth in the flask with the curved neck stayed fresh. This proved that it was the microbes and not the air causing it to go off.

15 of 23

Cheese and Yoghurt

Most cheese is made using bacteria.

1) A  culture of bacteria is added to milk which then produces solid curds in the milk.

2) The curds are seperated from the liquid whey and left to ripen into cheese!

Yoghurt is made using bacteria too:

1) Milk heated to kill off any bacteria. Then a starter culture of bacteria is added. This ferments the lactose sugar to lactic acid.

2) The acid causes the milk to clot and solidify into yoghurt. You can then add fruit and flavours.

16 of 23


Yeast can respire with or without oxygen, producing carbon dioxide and ethanol.

This is called FERMENTATION

In the presence of oxygen, yeast carries our aerobic respiration. This produces carbon dioxide and water, Aerobic respiration provides more energy. It is also necessary for the yeast to grow and reproduce.

Making beer:

Starch in barley grains is broken down into a sugary solution by enzymes in the germinating grains in a process called MALTING. The sugary solution is extracted and then fermented. Hops are then added to give the beer flavour.

17 of 23

Microorganisms in industry

Microorganisms are used on a large scale to make many useful substances:

1) Antibiotics such as penicillin

2) Foods such as mycoprotein ( used to make meat substances for vegetarian meals e.g Quorn)

3) Fuels such as biogas and ethanol

Fermenters are used to grow these microorgansims.

Fermentation is when bacteria or yeast break sugars down by anaerobic respiration.

18 of 23


Fermenters ususally have these things:

1) Air supply - to provide oxygen for respiration of the microorganisms

2) Stirrer - to keep microorganisms in suspension and maintain an even temperature.

3) Water cooled jacket - to remove heat produced by respiring microorganisms

4) Instruments - to monitor factors such as pH and temperature

19 of 23

Fuels from microorganisms

Ethanol is made by anaerobic fermentation of sugar

Glucose --> Ethanol + carbon dioxide + energy

ethanol is ditilled to seperate it from the yeast and remaining glucose before its used

Biogas is usually about 70% methane and 30% carbon dioxide

Microorgansisms ferment plant and animal waste, which contains carbohydrates. It is made in a simple fermenter called a generator or digester. They need to be kept at a constant temperature to keep the microorganisms respiring.

Fuel production can happen on a large or small scale.

20 of 23

Fuels from microorganisms

Batch generators make biogas in small batches.

Continuous generators make biogas all the time

Four factors to consider when designing a generator:

1) Cost - Continuous are more expensive than batch because it is all done mechanically.

2) Convenience - Batch are less convenient as they have to be continually loaded, emptied and cleaned.

3) Efficiency - Gas produced quickest at 35C. The generator shouldnt have any leaks or gas will be lost.

4) Position - Waste will smell during deliveryso generators should be moved away from homes.

21 of 23


Usung biofuels has economic and environmental effects.

They are "Greener" - they dont release CO2 and dont produce much Sulfur dioxide.

The raw material is cheap and readily available

 The digested material is far better fertiliser than undigested dung.

Biogas generators act as a waste disposal unit,  getting rid of human and animal waste that would otherwise stay around and cause disease and pollute water supplies.

22 of 23

Using microorganisms safely

Microorganisms are grown on agar jelly in a petri dish:

They are grown in a culture medium. They need carbohydrtaes as an energy source, plus mineral ions  and sometimes supplementry proteins and vitamins.

Equipment is sterilised to prevent contamination

Inoculating loops are sterilised by passing them through a flame. The petri dish must have a lid to stop any microorganisms in the air contaminating the culture. The lid should be taped on.

The temperature must be kept fairly low in school labs

 In the school lab, cultures of microorganisms are kept at about 25C. Harmful pathogens arent likely to grow at this temperature.

In industrial conditions, cultures are incubated at higher temperatures so that they can grow a lot faster

23 of 23




This is really good thanks - do you also have your bio exam tomoz?

Similar Biology resources:

See all Biology resources »