2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH

If the pH is too far from the ideal, optimum pH, the enzymes can de-nature, as a change in pH can cause the bonds that hold the structure in place to break :( This would mean that the substrate no longer fits in the active site. 

Different enzymes will work at different pH values. Eg the enzymes in your stomach will work best at a more acidic pH than those in your small intestine.

Figure 1: A graph showing the relationship between rate of enzyme activity
and pH

2.31 Describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine

These are tiny little hair-like things that line the wall of the small intestine and are responsible for the absorption of nutrients. (they are not actually hairs, just to make it clear)

• Lined with microvilli → increased surface area → quicker diffusion
• Blood capillaries → concentration gradient constant → nutrients (glucose & amino acids) quickly absorbed into bloodstream 
• Walls one cell thick → quick diffusion → molecules can pass easily
• Lacteal → central vessel in villi → responsible for absorption of fats

Figure 1: Structure of a villus

2.30 understand that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids

Basically...

• Bile is produced by the liver
• It is used to neutralise the food after it has left the stomach, as it is highly acidic.
• It emulsifies lipids, as they are not soluble in water: instead of one big oily blob, it is broken down into various tiny little blobs.
• It is a gross shade of vomit green (but you don't need to know that)

Figure 1
(If you're a bit squeamish like I am, may I suggest that you do not look up "bile" on google images)

2.29 Understand the role of digestive enzymes, to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases.

Enzymes, as mentioned before, are biological catalysts. They help break down the food that moves through our digestive system. Different enzymes do different tasks, and break down very specific components of food:

amylase and maltase break down starch into glucose

protease breaks down proteins into amino acids

lipase breaks down lipids into fatty acids and glycerol 

Figure 1: The structure of lipids

2.28 Explain how and why food is moved through the gut by peristalsis

Food moves down the oesophagus through a process known as peristalsis. This is when the two sets of muscles in the gut contract, creating a squeezing action that moves the food down. 

This is necessary because food needs to be mechanically moved to get through the digestive system. 

Source: BBC BitesizeFigure 1: Peristalsis 

2.27 Understand the processes of ingestion, digestion, absorption, assimilation and egestion

Ingestion: the act of taking food into the body; eating

Digestion: the process by which food is broken down and nutrients are absorbed into the bloodstream. Large, insoluble molecules are broken down into smaller, soluble ones.

Absorption: the process by which the soluble molecules are taken from the gut (typically in the small intestine) and transported into the bloodstream for use in the body.

Assimilation: the act of absorbing molecules through the cells in tissues

Egestion: To get rid of as a waste product (undigested food. Not to be confused with excretion)

Figure 1: Part of the digestive system

2.26 Describe the structures of the human alimentary canal and describe the functions of the mouth, oesophagus, stomach, small intestine, large intestine and pancreas

I hope you like reading :)

Food goes from… the mouth → oesophagus (gullet) → stomach → small intestine → large intestine → anything that is not digested goes out the body through the anus

The mouth mechanically breaks up the food into physically smaller bits. This is then moved down the oesophagus through a movement known as peristalsis. From there, it goes through the stomach. The sphincter between the end of the oesophagus and the stomach opens as the food goes through. The (very strong) acid in the stomach further breaks down the food chemically. From there, it goes into the duodenum where pancreatic juices (from the pancreas) are added to the food and digestive enzymes are also secreted by the pancreas, which speed up the breaking down of the food. Bile is added to neutralise the “mixture”, as it was highly acidic after leaving the stomach. The nutrients from the food are absorbed in the small intestine thanks to the hundreds of thousands of villi that line the small intestine walls, whose large surface area helps the nutrients dissolve quickly into the blood stream. From here, any remaining food goes through the large intestine, where the water is absorbed. Any undigested substances are excreted.

Figure 1: Human digestive system