Transport in humans

Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration.

Temperature, concentration gradient, surface area, volume

At higher temperatures, molecules have more kinetic energy and so move faster. Therefore diffusion occurs faster

If there is a very large difference in concentration between two areas, molecules will diffuse from the higher to the lower concentration quickly

A large surface area speeds up the rate of diffusion, as there is more space for the molecules to move

diffusion takes longer if it has to fill a large volume, as molecules have further to move

Both surface area and volume increase, volume increases much faster, less diffusion

To transport substances around the body; oxygen and nutrients are transported from exchange surfaces to all the cells and waste products from cells to the lungs and kidneys.

• A liquid to transport substances in – the blood • A pump to move the liquid – the heart • A series of pipes to direct the liquid and move it efficiently – the blood vessels

Humans have a double circulation. The heart pumps blood twice, sending it through two different circulatory circuits.

Blood returning from the body (deoxygenated) is pumped to the lungs, where oxygen is gained and carbon dioxide is lost, and then returned to the heart

Heart to the aorta, then hepatic artery to the hepatic vein and hepatic portal vein, then the renal artery to the renal vein, all body veins lead to vena cava, which goes to pulmonary artery in lungs, then through pulmonary vein to heart and cycle repeats

Animals with high metabolic rates like mammals and birbos

plasma, white blood cells, platelets, red blood cells

Plasma is a straw coloured liquid; mainly water, it contains a wide range of dissolved and suspended molecules. As well as transporting the blood cells, plasma carries: dissolved nutrients such as glucose and amino acids; dissolved waste products including urea and carbon dioxide;

Red blood cells (erythrocytes) are highly specialised cells, which are made in the bone marrow and only live for around 100 days before being destroyed by the liver or spleen. Their function is to transport oxygen.

Red blood cells contain haemoglobin. This is an iron-containing protein which combines with oxygen to form oxyhaemoglobin. Red blood cells are biconcave (discs with a dip in the middle); this increases their surface area: volume ratio and decreases the distance to the centre of the cell. They have no nucleus, meaning that more haemoglobin can be packed into each cell and so more oxygen can be transported.

Platelets are small cell fragments which help to form clots, preventing blood loss and infection.

White blood cells destroy pathogens which infect our bodies – they are an essential part of the immune system.

The function of the heart is to pump blood around the body, through the blood vessels.

The alveolus, The oxygen diffuses into the blood because the blood is mainly deoxygenated, and therefore has a lower concentration of oxygen.

Water-diffusion, movement of free water particles from an area of high concentration to an area of low concentration over a semi-permeable membrane

They attach to the sugar, less free water molecules

‘Water potential’ is a measure of the concentration of free water molecules in a solution. Pure water has a water potential of zero. As a solute is added, water potential falls as there will be a lower concentration of free water molecules.