GCSE Biology unit 3 (AQA)

Diffusion - the movement of particles from an area of high concentration to an area of low concentration. Moves down the concentration gradient and is free (no energy cost). Example - plants getting CO2.

Osmosis - The diffusion of water through a semi permeable membrane. Moves down the concentration gradient and is free (no energy cost). Example - homeostatis, plant roots absorbing water.

Active transport - The movement of substances against a concentration gradient and/or across a cell membrance using energy. Low to high concentration. These cells usually have a lot of mitochondria to provide energy.

Rate of diffusion (amount of ocygen transferred) = (surface area x concentration difference) / length of diffusion pathway. 

The rate of diffusion in the lungs is increased by increasing the surface area (lots of alveolie) and concentration difference. It is also increased by decreasing the length of diffusion pathway. This is done as the layer of cells between the air in the lungs and the blood is very thin, meaning the distance is as short as possible. 

3 parts; cortex, medula and pelvis. The cortex is filled with blood and the waste goes down the ureter. 

Urea is formed in the liver when the excess amino acids are broken down. It has to be removed as it is poisonous. The kidneys filter it out of your blood and into your urine. All of the important stuff such as glucose and proteins are also filtered through to start with but is then reabsorbed into the blood. 

Too little water in blood - Hypothalamus detects it so sends nervous impulse. The impulse goes to the pituatory which releases more ADH. There is too little water but now more ADH . More ADH enters kidney so more water is reabsorbed, so there is less urine which is more concentrated. You wee less.

Too much water in blood - Hypothalamus detects it so sends message. The pituatory recieves message and releases less ADH. There is too much water but now less ADH. Less ADH enters kidney so less water is reabsorbed, so theres more urine which is more dilute. You wee more.

Kidney transplant:

Advantages - 1) They have a better quality of life and may feel physically fitter. 2) Longer life. 3)Dont have to be hooked to a machine. 4) Get normal life back. 5)Long term success rate is higher. 

Disadvantages - 1) shortage of organ donators so may have to wait a long time. 2) kidney may be rejected. 3) lots of risks such as infection. 4) need to find matching organ. 5) side effects from medicines 6) on medication for life.

Kidney dialysis:

Advantages - 1) keeps you alive, before donor is found. 2) No complications that are involved with surgery. 3) Dont have to wait like you would with transplant. 

Disadvantages - 1) Takes a lot of time. 2) Hard to pack up and carry. 3) Have to be tied to a machine or hospital. 4) need to be careful with diet.

Anaerobic respiration is used when the muscles do so much exercise that in increase in heart reate and breathing rate does not supply enough oxygen. So, respiration without oxygen is done.

Anaerobic = glucose ---> lactic acid (+energy)

aerobic = glucose + oxygen ---> Co2 +H2O + lots of energy.

Oxygen debt = the amount of oxygen required to break down the lactic acid in the body after exercise. (only during anaerobic respiration).

Breathing in - intercostal muscles and diaphragm contract. The thorax volume increases. This decreases the pressure and lets air in.

Breathing out - Intercostal muscles and diaphragm relax. The thorax volum decreases so the pressure increases and air is forced out.

Exercise increases the heart rate - the muscles use oxygen to release energy from glucose (respiration), which is used to contract the muscles. An increase in muscle activity requires more glucose and ocygen. Extra carbon dioxide has to be removed from the muscle cells. For this to happen the blood has to flow faster. The arteries dilate to supply the blood to the muscles.

Physical activity increases your breathing rate to meet the demand for extra oxygen. It increases the speed at which the heart pumps, also causing the arteries to dilate.

Blood is made up of white blood cells, red blood cells, plasma and platelets. The white blood cells fight infection. The red blood cells carry oxygen. They dont have a nucleus which allows for a large surface area to carry more oxygen. The plasma is the liquid part of the blood. It carries all the blood cells as well as urea CO2 and nutrients etc. The platelets help blood to clot at the womb.

The arteries carry blood away from the heart to the organs in the body.  This is oxygenated blood. They have thick walls and a thick layer of muscle. Have a small lumen.

The veins carry blood towards the heart. This is deoxygenated blood. They contain valves to prevent a backflow of blood. Have thin walls and a large lumen.

Capillaries are found in the junctions betweeb the arteries and veins. The walls are a single celled thick so substances can easily diffuse out of the blood and into the body.

Growing microbes - Nutrients microbes need to grow are contained in agar. You pour hot agar into a petri dish. Then, you leave it to cool and set before adding microorganisms. As well as the nutrients in the agar, it also need to be provided with warmth and oxygen.

Food production - Yeast is a single celled organism that can be very useful. Each cell has a nucleus, cytoplasm and a membrane surrounded by a cell wall. Yeast reproduces by asexual budding (splitting in 2 to form new yeast cells). Once yeast is given oxygen, it respires aerobically, breaking down sugar to provide energy for the cells and producing water and CO2.

It can also be respired anaerobically which is known as fermentation. When yeast cells break down sugar without oxygen, ethanol and CO2 is produced. Aerobic respiration is better as it provides more energy which allows them to grow and reproduce quicker.

Gas exchange in plants:

The leaves of plants have small holes on the underside called stomata. These can be controlled by guard cells which can open and close to change the size of the stomata.

It is through the stomata that the plants lose water through transpiration. This is when carbon dioxide enters the plant and water vapour and CO2 diffuse out.