B4.2. Organisation

What is a tissue?

A group of similar cells working together to carry out a particular function.

What is an organ?

A group of different tissues working together to perform a particular function.

What is an organ system?

A group of organs working together to perform a particular function.

What is the organisation of multicellular organisms?

Cells → tissues → organs → organ systems → organism.

What is the digestive system?

An organ system that breaks down large, insoluble food molecules into small, soluble molecules that can be absorbed.

What is digestion?

The breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed.

What are enzymes?

Biological catalysts that speed up chemical reactions without being used up.

What is a biological catalyst?

A substance that increases the rate of a chemical reaction without being used up.

What are enzymes made of?

Proteins.

What is the active site of an enzyme?

The part of an enzyme where the substrate binds and the reaction takes place.

What is a substrate?

The molecule that an enzyme acts on.

What is the lock-and-key model?

The idea that an enzyme's active site has a specific shape that is complementary to its substrate.

Why are enzymes specific?

Their active sites have specific shapes, so only substrates with complementary shapes can bind effectively.

What happens when an enzyme is denatured?

The shape of its active site changes, so the substrate can no longer bind effectively.

How does temperature affect enzyme activity?

As temperature increases, enzyme activity increases up to the optimum temperature. Above the optimum, the enzyme can denature and its activity decreases.

What is the optimum temperature?

The temperature at which an enzyme works at its fastest rate.

How does pH affect enzyme activity?

Each enzyme has an optimum pH. Moving too far from the optimum can change the shape of the active site and reduce enzyme activity.

What happens to enzyme activity at very high or low pH?

The enzyme can become denatured because the bonds holding its shape can be disrupted.

How does substrate concentration affect enzyme activity?

Increasing substrate concentration usually increases the rate until all available active sites are occupied.

What is a carbohydrase?

An enzyme that breaks carbohydrates down into smaller sugars.

What does amylase do?

It breaks starch down into sugars.

Where is amylase produced?

In the salivary glands, pancreas and small intestine.

What is a protease?

An enzyme that breaks proteins down into amino acids.

Where are proteases produced?

In the stomach, pancreas and small intestine.

What is a lipase?

An enzyme that breaks lipids down into fatty acids and glycerol.

Where are lipases produced?

In the pancreas and small intestine.

What are the products of carbohydrate digestion?

Simple sugars such as glucose.

What are the products of protein digestion?

Amino acids.

What are the products of lipid digestion?

Fatty acids and glycerol.

What is bile?

An alkaline substance produced by the liver and stored in the gall bladder.

Where is bile stored?

In the gall bladder.

What are the two main functions of bile?

It neutralises stomach acid and emulsifies fats.

Why does bile neutralise stomach acid?

It provides alkaline conditions for enzymes in the small intestine to work effectively.

What is emulsification?

The breaking up of large fat droplets into smaller droplets.

How does emulsification help lipase?

It increases the surface area of fat available for lipase to act on, increasing the rate of digestion.

Where is bile released?

Into the small intestine.

What is the role of the mouth in digestion?

Food is mechanically broken down by chewing and mixed with saliva, which contains amylase.

What is the role of the oesophagus?

It moves food from the mouth to the stomach by muscular contractions called peristalsis.

What is the role of the stomach?

It churns food and contains hydrochloric acid and protease enzymes.

What is the role of hydrochloric acid in the stomach?

It provides acidic conditions for stomach proteases to work effectively.

What is the role of the small intestine?

Digestion is completed and soluble products are absorbed into the blood.

What is the role of the large intestine?

It absorbs water from the remaining undigested food.

What is the role of the rectum?

It stores faeces before they are expelled.

What is the role of the anus?

It is where faeces leave the body.

What is the role of the pancreas in digestion?

It produces digestive enzymes that are released into the small intestine.

What is the role of the liver in digestion?

It produces bile.

What is absorption?

The movement of digested soluble food molecules from the digestive system into the blood.

How is the small intestine adapted for absorption?

It has villi and microvilli, giving it a large surface area, a thin surface and a good blood supply.

What are villi?

Finger-like projections in the lining of the small intestine that increase its surface area for absorption.

What is the function of microvilli?

They further increase the surface area available for absorption.

Why does the small intestine have a good blood supply?

It maintains concentration gradients, allowing digested food molecules to diffuse into the blood quickly.

What is the food test for starch?

Add iodine solution. A positive result is blue-black.

What is the food test for reducing sugars?

Add Benedict's solution and heat it. A positive result produces a colour change from blue towards green, yellow, orange or brick-red depending on concentration.

What is the food test for protein?

Add Biuret reagent. A positive result is lilac/purple.

What is the food test for lipids?

Add ethanol and shake, then add water. A positive result is a cloudy white emulsion.

How would you test a food sample for starch?

Add iodine solution and observe the colour change.

How would you test a food sample for reducing sugar?

Add Benedict's solution and heat the mixture in a water bath.

How would you test a food sample for protein?

Add Biuret reagent and observe the colour change.

How would you test a food sample for lipids?

Add ethanol, shake, then add water and look for a cloudy white emulsion.

Why is a water bath used when carrying out Benedict's test?

It provides controlled heating and reduces the risk associated with directly heating the test solution.

How can you investigate the effect of pH on amylase activity?

Mix amylase and starch with buffer solutions of different pH values, keep other variables controlled, and test at regular intervals for starch using iodine.

What happens when starch is no longer present in an amylase investigation?

Iodine remains orange-brown rather than turning blue-black.

How can you measure the rate of starch digestion by amylase?

Measure the time taken for the starch to disappear, then compare rates using rate = 1 ÷ time.

Why should temperature be controlled in an amylase investigation?

Temperature affects enzyme activity, so keeping it constant means pH is the main variable being investigated.

Why should the concentrations of amylase and starch be controlled?

Changing their concentrations would affect the rate of reaction and make it difficult to determine the effect of pH.

Why should an amylase investigation be repeated?

Repeats improve reliability and allow a mean to be calculated.

What is the circulatory system?

A transport system consisting of the heart, blood and blood vessels.

What type of circulatory system do humans have?

A double circulatory system.

What does a double circulatory system mean?

Blood passes through the heart twice during one complete circuit of the body.

What are the two circuits of the human circulatory system?

The pulmonary circuit carries blood between the heart and lungs, and the systemic circuit carries blood between the heart and the rest of the body.

What is the function of the heart?

It pumps blood around the body.

What are the four chambers of the heart?

Right atrium, right ventricle, left atrium and left ventricle.

What is the function of the right atrium?

It receives deoxygenated blood from the body through the vena cava.

What is the function of the right ventricle?

It pumps deoxygenated blood to the lungs through the pulmonary artery.

What is the function of the left atrium?

It receives oxygenated blood from the lungs through the pulmonary vein.

What is the function of the left ventricle?

It pumps oxygenated blood to the rest of the body through the aorta.

Why is the wall of the left ventricle thicker than the right ventricle?

It must pump blood around the whole body at higher pressure, whereas the right ventricle only pumps blood to the lungs.

What is the function of heart valves?

They prevent the backflow of blood and ensure blood flows in one direction.

What is the septum?

The muscular wall separating the left and right sides of the heart.

Why is the septum important?

It prevents oxygenated and deoxygenated blood from mixing.

What is a coronary artery?

A blood vessel that supplies the heart muscle with oxygenated blood.

What is an artery?

A blood vessel that carries blood away from the heart.

How are arteries adapted to their function?

They have thick muscular and elastic walls, a small lumen and carry blood at high pressure.

What is a vein?

A blood vessel that carries blood towards the heart.

How are veins adapted to their function?

They have thinner walls, a larger lumen and valves to prevent backflow.

What is a capillary?

A tiny blood vessel that connects arteries and veins and allows substances to move between blood and tissues.

How are capillaries adapted for exchange?

They have walls only one cell thick, giving a short diffusion distance.

Why do capillaries form networks around tissues?

They provide a large surface area for exchange and bring blood close to cells.

What is blood made of?

Plasma, red blood cells, white blood cells and platelets.

What is the function of plasma?

It transports dissolved substances such as glucose, amino acids, carbon dioxide, urea and hormones.

What is the function of red blood cells?

They transport oxygen around the body.

How are red blood cells adapted to carry oxygen?

They contain haemoglobin, have a biconcave shape giving a large surface area and have no nucleus, leaving more room for haemoglobin.

What is haemoglobin?

A protein in red blood cells that binds to oxygen.

What happens to haemoglobin in the lungs?

It combines with oxygen to form oxyhaemoglobin.

What happens to oxyhaemoglobin in body tissues?

It releases oxygen where it is needed for respiration.

What is the function of platelets?

They help the blood to clot.

Why is blood clotting important?

It prevents excessive blood loss and helps prevent microorganisms entering through wounds.

What are the three types of blood vessel?

Arteries, veins and capillaries.

What is the difference between arteries and veins?

Arteries carry blood away from the heart at high pressure and have thick walls. Veins carry blood towards the heart at lower pressure and have valves.

What is coronary heart disease?

A condition in which fatty material builds up in the coronary arteries, reducing blood flow to the heart muscle.