GCSE Biology Digestive System, Nutrition and Excretion

GCSE Biology Digestive System, Nutrition and Excretion GCSE Biology Syllabus At A Glance ChaptersGlossary of   Terms for GCSE BiologyNutritionDietDigestionEgestionMaking Biology GCSE Fun: Some Interesting FactsUseful LinksA very large proportion of the GCSE Biology course is focused on the human body, teaching you about the structure and functions that help us to survive day in, day out.This particular area of Biology, related to the digestive system, nutrition, and excretion, covers a wide spectrum of subtopics, however, the two subject matters that are the most directly linked with humans are those linked to diet and digestion. As such, this is what I will focus on in this educational blog aimed at GCSE level students.To help you to follow the biological parts, processes and functions described below, we have provided a glossary of terms, put together by the experts at BBC Bitesize, which can be referred to whilst you read this text, or can be saved for future reference. Go to their website for tonnes more guides, tests and other useful references during your course.No te: Having a list of key terminology can be very useful when you come to revise for your exam, as this topic is likely to come up in at least one question on your paper.Labelled Digestive SystemTake a look at this labelled digestive system. Image sourced from http://freeencyclopedia.wikia.com/wiki/File:Digestive-system-diagram.jpgWhere Is Bile Produced?After being in the stomach, food makes its way to the small intestine where food molecules get into the blood through the wall of the intestine. This is called absorption. Enzymes work best in alkaline conditions, so bile is produced by the liver, stored in the gallbladder  and then released into the small intestine to help to emulsify fats and help the lipases to work more effectively.Digestion and EnzymesAs we've seen, enzymes play an important role in the chemical breakdown of food during digestion. But what exactly are these molecules and how do they do their job?We already know that enzymes work at their best when at their optimu m pH, so they rely heavily on the right conditions being set up for them in the stomach or gut.There are three principal types of enzymes: Protease, Carbohydrase, and Lypase.AbsorptionProtease enzymes are found in the stomach, small intestine and pancreas and their task is to digest proteins. Pepsin is a common type of protease and helps to break down the long chains of amino acid molecules found in proteins into smaller links called peptides and then into individual amino acids which are easier absorbed in the small intestine. You may be required to know the equation for this process which is:proteins -protease- amino acidsCarbohydrase enzymes, as you might expect, break down long starch molecules. They are secreted by the mouth, pancreas and small intestine. One type, named amylase, is found in our saliva and starts doing its work as we chew our food.The first step is to break down the complex starch molecules into maltose molecules (taking them from polysaccharide to disaccharide ) and then it gets broken down again into glucose.The equation is as follows:starch -amylase- maltose -maltase- glucoseLastly, Lipase is found in the pancreas and the walls of the small intestine. Complex fats, called lipids, get broken down into soluble fatty acid and glycerol molecules as indicated in the word equation:lipids -lipse- fatty acids + glycerolA Summary of The Principal Enzymes And Their FunctionsBelow are the main enzymes found in the human digestive system and what they do.Digestive enzyme nameWhere in the body it is producedWhat reaction is catalysedProteaseStomach, small intestine and pancreasTurns protein into amino acidsCarbohydraseSaliva, pancreas and small intestineTurns starch into glucoseLipasePancreas and small intestineTurns fats into fatty acid and glycerolDid you know that the longest part of the small intestine would measure  between 2-4 metres long if laid down flat? The large surface area means that absorption happens quickly, helped by finger-like vil li which further increase the area.What Does The Large Intestine Do In The Digestive System?Different things happen to digested and undigested foods once they have passed through the gut; digested food molecules provide energy and build new proteins in a process called assimilation while indigestible substances reach the colon, the first part of the large intestine.EgestionWhat Does The Rectum Do?Once all of the remaining water has been absorbed, the bacteria and cells (undigested food) that are left become waste, also known as faeces. This semi-solid material is stored in the rectum, which makes up the final part of the large intestine and then gets passed out of the anus in a process called egestion.The rectum provides temporary storage, and it is as the rectal walls expand due to collecting faeces that cause you to feel the need to go to the toilet, or defecate. Peristaltic waves then push the waste out of the rectum.The anus then takes over and controls the expulsion of the faec es, in particular by the anal sphincter muscle. The internal and external muscles relax, allowing the waste to be passed and then by pulling the anus up over the exiting feaces.Egestion, i.e. the process of passing semi-solid waste when you go to the toilet, is not be confused with excretion.Excretion  is the removal of waste products from the body via other organs, like the skin.During your course, you will also learn more about  urine and how this leaves the body in both males and females.Making Biology GCSE Fun: Some Interesting FactsIf all of the above feels a bit scientific and has left your mind a bit frazzled, take a look at the following fun facts and look at the digestive system in more relatable terms.We humans are said to eat about 500 kilograms of food a yearOur bodies produce around 1.7 litres of saliva in just a dayThe standard oesophagus measures around 25 centimetres longEven if you did a handstand, your body would still move the food you ingest down the oesophagus a s the muscles contract like waves to push it in the right directionAn ordinary adult's stomach can hold around 1.5 litres of food and drinkOut of the, roughly, 11.5 litres of food and water you take in in a day, only 100 millilitres is lost in your faeces. You'll learn more about excretion in your classes.Food that enters your mouth is both warmed and cooled to make it the optimum temperature for digestion. So, if you eat food, your mouth will cool it down and if you eat chilled materials, it will bring the temperature up.It's fascinating what our bodies can do and how much work they put in just to keep us alive and well. It is no wonder we need to rest at night! But even while we sleep, our bodies continue to carry out their numerous and momentous tasks...To learn even more than you would do in your classroom or using self-study methods, why not look out for biology a level tutors.Useful LinksAs part of your revision for Biology GCSE, you may wish to brush up on the following topic s:GCSE Biology Syllabus: Topics At A Glance GCSE Biology Revision: Reproduction In Humans GCSE Biology Evolution GCSE Biology Revision: Living Organisms GCSE Biology Revision: Inheritance and Genetics