Active transport

• Sometimes substances need to be absorbed against a concentration gradient i.e. from a lower to a higher concentration. This process is referred to as active transport
• Root hairs take in minerals and water
• Each branch of a root will be covered in millions of these microscopic hairs

  
• The hairs on the cells give the plant a large surface area for absorbing water and mineral ions from the soil

  
• The concentration of minerals is usually higher in the root hair cells than in the soil around them

  
• Water is taken into root hair cells by osmosis
• Root hairs take in minerals using active transport
• Minerals should move out of the root hairs if they followed the rules of diffusion. The cells must use another method to draw them in
• Active transport allows the plant to absorb minerals from a very dilute solution, against a concentration gradient. This is essential for its growth. But active transport needs energy from respiration to make it work
• Active transport also happens in humans, e.g. in taking glucose from the gut and from the kidney tubules
• Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood
• When there's a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood. But sometimes there's a lower concentration of nutrients in the gut than there is in the blood

  
• Active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient in the wrong way. This means that glucose can be taken into the bloodstream when its concentration is the blood is already higher than in the gut. It can be transported to cells, where it's used for respiration