Gas exchange [humans]

Ventilation is the process of air entering and leaving the lungs.

After air passes through the nose, it passes through the trachea, which is lined with cartilage for support. After, it moves through the two bronchii. These bronchii extend into smaller bronchioles which end in tiny, microscopic air sacs called alveoli. These are single celled and situated close to blood capillaries. The trachea and bronchi are lined with cilia and mucus which prevent dust and dirt from entering the lungs and causing infection.

The thorax is the name given to the whole respiratory system containing the lungs, trachea, bronchi, alveoli, intercostal muscles, diaphragm, bronchioles, ribs and pleural membranes.

The diaphragm is a muscular, fibrous dome-shaped tissue that separates the contents of the thorax from the rest of the abdomen.

When a person breathes in, the diaphragm contracts and the external intercostal muscles contract allowing the rib cage to expand outwards and upwards. The volume of the lungs therefore increases as well as the pressure inside decreasing. As a result, the air is drawn into the lungs. The pleural membranes prevent the friction between the lungs and other organs.

The opposite happens when a person exhales. The internal intercostal muscles contract whilst the diaphragm expands. The volume of the lungs decreases and the pressure increases. As a result, air is pushed out of the lungs.

The alveoli are adapted for gas exchange in four main ways:

1. Their walls are thin, making the diffusion of gases more efficient and occur at a greater rate.
2. Their walls are one cell thick and are situated close to blood capillaries which are also one cell thick. Therefore the diffusion distance is very small hence gas exchange can occur at a greater rate.
3. The alveoli have moist linings which allows gases to dissolve into.
4. Combined, the walls of the alveoli have a massive surface surface area. This allows gases to diffuse in and out at a great rate.

Smoking

Smoking is very destructive for the body. It primarily affects the circulatory system and respiratory system. There are a vast number of ways it can inhibit the function of various organs:

1. The carbon monoxide from the smoke binds irreversibly to haemoglobin thus preventing oxygen from being transported around the body.
2. Smoking destroys the cilia that lines the trachea and bronchi. This makes dust and dirt more prevalent in the lungs, making one more prone to infection.
3. It can cause excess mucus production. This inhibits the air that can be inhaled and taken into the lungs.
4. Tobacco smoke causes bad cholesterol to build up in veins and arteries. This decreases the space for blood to travel through as it narrows the lumen therefore increasing the blood pressure. High blood pressure means there is a greater chance of narrower blood vessels bursting.
5. Angina is the pain in the chest resulting from lack of oxygen. When carbon monoxide binds to haemoglobin it reduces the amount of oxygen in the blood. A lack of oxygen means cells respire anaerobically. This produces lactic acid. When the lactic acid is not removed and the 'oxygen debt' has not been paid, pain is caused.

An experiment investigating the effect of exercise on the breathing rate:

Count how many breaths a person takes when stationary for a minute.
Then make them run at 5mph for one minute.
As soon as they stop, count how many breaths they take for a minute.
Make them run at 5mph for two minutes.
Count how many breaths they take for a minute.
The increase in rate should be linear.

Respiration

Respiration is the release of energy from glucose [in living organisms].

Aerobic respiration is the release of energy by use of oxygen.

Anaerobic respiration is the release of energy without oxygen. It results in less energy being released. In plants, carbon dioxide and ethanol are produced whereas in animals, lactic acid is produced. The ethanol contains stored chemical energy that releases heat energy when burned.

When muscle cells respire anaerobically, they produce lactic acid. This poisons the muscle cells, often making them feel heavier. In order to get rid of the lactic acid, one has to respire aerobically and pay off the 'oxygen debt'. Oxygen oxidises lactic acid, therefore getting rid of it. 

When yeast respire anaerobically they release an enzyme called zymase. This catalyses the reaction of glucose into ethanol. This is used in fermentation. Yeast also release carbon dioxide which is beneficial in making bread rise.

The equation for aerobic respiration in plants and animals.

C6H12O6 + 6O2 = 6H2O + 6CO2

An experiment to investigate the release of carbon dioxide from seeds:

Bubble the gas emitted from the respiring seeds into limewater and see if it turns cloudy.

Place the seeds in cotton wool along with a thermometer and measure the increase in temperature.

The movement of substances into and out of cells

Substances can move into and out of substances by three processes:

1. Active transport
2. Diffusion
3. Osmosis

1. Active transport is the movement of substances across cell membranes against the concentration gradient. This is done by using the energy released through the process of respiration. It occurs most commonly in the roots of a plant. The mineral ions in the soil are pumped into the roots of the plant by active transport.

2. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. An experiment to see this uses food colouring and a beaker of water. Drop the food colouring in and watch as the water slowly becomes the same colour.

3. Osmosis is the movement of water from a high water potential to a low water potential. An experiment to investigate osmosis involves two potatoes.

Weigh them using a mass balance.
 Place one in a distilled water beaker and the other in a salt-water beaker.
After a certain time, take them out at the same time and weigh them again.
The potato in the salt-water beaker should weigh less due to more water moving out. This is a result of the greater concentration gradient i.e. there was a small water potential with the salt. The salt was highly concentrated.
The potato in the distilled water beaker should have gained weight due to more water moving in. This potato had a lower water potential to begin with, in comparison to the water beaker. It was less dense and as a result, the water moved in.

The rate of movement into and out of cells is influenced by three main characteristics/ processes:

1. Surface area to volume ratio. A greater surface area means there is more surface by which the molecules can diffuse through.

2.  Temperature. A higher temperature would increase the kinetic energy of the molecules. Therefore they are more likely to collide with the membrane hence they will more likely diffuse out.

3. Concentration gradient. The steeper the concentration gradient, the more molecules will diffuse out of the cell.

Turgid cells as a means of support.

Turgid cells are a means of support because they are filled with water hence the pressure they exert on their surroundings is greater. This means the cells are stronger and push against each other, enabling the plant to grow upwards.

Cell structure

Plant cells differ from animal cells.

Only they contain:

1. Cell walls
2. Chloroplasts
3. Vacuole

They both contain:

1. Cytoplasm
2. Cell membrane [that is selectively permeable]
3. Nucleus

1. Cell walls keep a cell turgid. They provide a means of support which give plants their shape.

2. Chloroplasts are the site of photosynthesis. They absorb the light energy and convert it into chemical energy by form of glucose.

3. Vacuoles store minerals, nutrients and other dissolved solutes.

4. Cytoplasm is the site of many chemical reactions.

5. Nuclei contain the genetic information for a cell.

6. Cell membranes control what enters and leaves the cells. They are selectively permeable meaning not all substances can enter.

Characteristics of a living organism

Tissue: A group of cells that perform a common function.

Organ: A group of tissues that perform a common function.

Organ System: A group of organs that perform a common function.

Organism: A complete living thing.

1. M-ovement

2. R-espiration

3. S-ensitivity

4. H-omeostatis

5. R-eproduction

6. E-xcretion

7. N-utrition

8. G-rowth

MR SHRENG = The characteristics of a living thing.