B2 Topic 3 - Organ Systems

Question 1

How does the pentadactyl limb provide evidence for evolution?

Answer 1

A pentadactyl limb is a limb with five digits and many species have them, including mammals, amphibians and reptiles. In every example of a pentadactyl limb, the bone structures of different species is very similar. This suggests that all of these organisms evolved from the same common ancestor that also had this similar bone structure. If all of these animals evolved from different ancestors, it is very unlikely that they all evolve to have pentadactyl limbs.

Question 2

What are the three ways in which you can measure the growth of an organism?

Answer 2

Size - weight, height, width or circumference
Wet mass - the mass of an organism including all the water in its body, this can vary from day to day
Dry mass - the mass of an organism with no water in it, this can only be measured after the organism is dead. It is dried out and left in a hot oven, what is left is weighed

Question 3

What are the three methods of growth in plants and animals?

Answer 3

Cell differentiation - when a cell becomes specialised for a certain job
Cell division - when cells divide through mitosis
Cell elongation - (only in plants) where the plant cell gets longer, it does this by absorbing more water into its vacuole

Question 4

What is the main difference in the growth between animals and plants?

Answer 4

Animals do most of their growing at an early age through cell division. Later in life, cell division is used mostly for repair rather than growth. This also means that they lose their ability to differentiate quite early on.

Plants grow continuously throughout their lives, mainly through cell elongation, division only really occurs in the tips of roots and shoots.

Question 5

Define tissue.

Answer 5

A tissue is a group of similar cells working together to carry out a particular function. E.g. Muscle tissue

Question 6

Define organ.

Answer 6

An organ is a group of different tissues that work together for a particular function. E.g. Stomach

Question 7

Define organ system.

Answer 7

An organ system is a group of organs working together for a particular function. E.g. Circulatory system.

Question 8

Describe how blood travels through each part of the heart, starting with the right atrium.

Answer 8

1. The right atrium of the heart receives deoxygenated blood from the body through the vena cava.
2. The blood travels past the tricuspid valves, which prevent the back flow of blood, and into the right ventricle.
3. The ventricle then pumps the deoxygenated blood past the semi-lunar valves to the lungs again through the pulmonary artery.
4. Oxygenated blood moves into the left atrium from the lungs through the pulmonary vein.
5. The blood passes the bicuspid valves and into the left ventricle.
6. The left side of the heart then pumps the blood past the semi-lunar valves to the aorta, which sends the blood around the body.

The left wall of the heart is thicker than the right as it needs to pump blood around the body, while the right side only pumps blood to the lungs.

Question 9

What are the four main components of blood?

Answer 9

Red blood cells
White blood cells
Platelets
Plasma

Question 10

How do fossils provide evidence for evolution?

Answer 10

Fossils show how an organisms looked like, so by comparing the fossils of the same species from different time periods, scientists can see how an organism has evolved.

Unfortunately, fossil records are largely incomplete because very few dead organisms form fossils, soft tissues decaying soon after death and that there are many fossils yet to be discovered.

Question 11

What is the purpose of a white blood cell?

Answer 11

White blood cells fight foreign microorganisms in the body that can cause harm to it. They do this by eating pathogens, producing antibodies which fight microorganisms or by producing antitoxins to neutralise any damaging chemicals produced by any pathogens.

There are two main types of white blood cells: phagocytes and lymphocytes.

Phagocytes go to sites of infection and either absorb pathogens and toxins or release enzymes that destroy them. They can also release chemical messages to lymphocytes that helps them identify the pathogen.

Lymphocytes identify chemicals on pathogens called antigens that are unique for every microorganism. Once the antigen is identified, lymphocytes create a opposite copy of the antigen, called an antibody. Once it has been made, the lymphocytes multiply very quickly so that many of these antibodies are created. Antibodies bind to pathogens, clumping them together so that they become immobilised and easier to engulf for phagocytes. Antibodies also release chemicals to attract more phagocytes and sometimes even damage the pathogens by releasing chemicals of their own.

After a pathogen has been fought off, memory lymphocytes ‘remember’ how to make the antibodies for those particular antigens, in case of another attack. This way, the response to the pathogen is much faster and they can be neutralised quicker. The body now is said to be immune to that pathogen.

Question 12

What is the purpose of platelets in the blood?

Answer 12

Platelets travel around the body in the blood and if a blood vessel tears, they clot at the wound so that it can repair. The do this by turning fibrinogen into fibrin, which forms a net over the damaged area. Blood cells then get stuck to this mesh and prevent any more blood from escaping.

Question 13

What is the purpose of a red blood cell?

Answer 13

Red blood cells carry oxygen from the lungs to cells in the body in haemoglobin, which contains a lot of iron. The oxygen binds to haemoglobin to form oxyhaemoglobin. Red blood cells don’t have a nucleus so that there is more room for haemoglobin. They also have large surface areas to carry more oxygen.

Question 14

What is the purpose of plasma in the blood?

Answer 14

Plasma is a pale yellow liquid that transports everything in the blood, including:
Red and white blood cells
Platelets
Nutrients like glucose and amino acids
Carbon dioxide and water vapour from respiration
Urea
Hormones
Antibodies and antitoxins made by white blood cells

Question 15

What are the three types of blood vessels? Explain their differences.

Answer 15

Arteries - carry blood away from the heart, strong and elastic walls, thick walls of muscle to make them strong

Capillaries - carry blood to cells, one cell thick for quicker diffusion, have permeable walls, supply food and oxygen to cells, take away waste products

Veins - take blood towards the heart, lower pressure so walls aren’t as thick, bigger lumen to help blood flow, have valves to prevent back flow of blood

Question 16

What are the three main types of enzymes involved in digestion? Give an example and explain what they do.

Answer 16

Carbohydrases - digest starch into sugar e.g. Amylase
Proteases - digest proteins into amino acids e.g. Pepsin
Lipase - digests fats into fatty acids and glycerol

Question 17

What does the mouth do in digestion?

Answer 17

Food is moistened with saliva from salivary glands
Amylase in saliva breaks down starch
Food is chewed to form a ball of food before being swallowed

Question 18

What does the oesophagus do in digestion?

Answer 18

Tube that takes food from mouth down into the stomach

Lined with muscles to help move food down through peristalsis

Question 19

What does the stomach do in digestion?

Answer 19

Mixes and disturbs food with muscular walls
Produces pepsin to digest proteins
Produces hydrochloric acid to kill bacteria and provide the optimum pH for pepsin (pH 2)

Question 20

What does the liver do in digestion?

Answer 20

Produces bile to neutralise stomach acid and emulsify fats

Question 21

What does the gall bladder do in digestion?

Answer 21

Where bile is stored before being released into the small intestine

Question 22

What does the pancreas do in digestion?

Answer 22

Produces lipase, amylase and protease which are then released into the small intestine

Question 23

What does the small intestine do in digestion?

Answer 23

Also produces lipase, amylase and protease to complete digestion
Absorbs all the nutrients and minerals from food straight into the blood stream

Question 24

What does the large intestine do in digestion?

Answer 24

Any remaining water is absorbed from the food into the body

Question 25

How can visking tubing be used to model the gut?

Answer 25

Visking tubing is semi-permeable so it only lets small molecules pass through, like a gut. On the other hand, it doesn’t have a large surface area.

1. Add equal volumes of starch suspension and 0.25% amylase solution to the visking tubing and then wash the outside of the tubing.
2. Place the tubing in a boiling tube filled with distilled water.
3. Test a drop of water from the test tube with an iodine solution, record the colour change, if any.
4. Test 5 drops with Benedict’s reagent, record the colour changes, if any.
5. Repeat steps 3 and 4 every 15 minutes.
6. Repeat steps 1-5 with 0.5% and 1% amylase solutions.

The orangey-brown colour of the iodine shows that no starch is present in the test tube as large molecules can t pass through the tubing.

The colour change of Benedict’s reagent shows that sugar is present. This is because the amylase breaks down the large starch molecules into smaller sugar molecules which can pass through the visking tubing.

Question 26

How does peristalsis work in the digestive system?

Answer 26

Longitudinal muscles that run down the length of the gut contract just ahead of the food to keep it in a ball.

Circular muscles that run in circles around the gut contract behind the food to push it down the gut.

They contract in waves to move food down the gut.

Question 27

What is the purpose of bile?

Answer 27

Neutralises stomach acids:
pH of stomach acid is too high for the enzymes in the small intestine so bile, which is a strong alkali, neutralises the acid and makes the conditions of the small intestine alkaline, which is best for the enzymes there.

Emulsifies fats:
Breaks fats done into small drops, increases its surface area for the enzyme lipase to work on, which increases the speed of digestion.

Question 28

How do villi help in digestion?

Answer 28

The small intestine is covered in villi and micro villi which increase its overall surface area. This means that more nutrients can be absorbed at a time. Villi are also only one cell thick to decrease the diffusion distance to the good supply of capillaries inside them. This way, nutrients don’t have to diffuse very far to get into the bloodstream.

Question 29

What are probiotics?

Answer 29

Probiotics are live bacteria that are “good” for your stomach. They are similar to those already in the stomach, help keep the digestive system healthy and help strengthen the immune system.

They can be found in foods such as yoghurt, soya milk and dietary supplements.

Examples include Bifidobacteria and Lactobacillus (a lactic acid bacterium)

Question 30

What are prebiotics?

Answer 30

Prebiotics are carbohydrates that the body can’t digest that are a good food supply for stomach bacteria. It is thought that eating prebiotics can promote the growth of these bacteria which can improve the health of the digestive system and immune system.

They can be found in leeks, onions and oats but there are not enough in a normal diet to affect you very much.

Examples include oligosaccharides.

Question 31

What are plant stanol esters?

Answer 31

Stanols are chemicals that lower blood cholesterol and help reduce the risk of heart disease. They can be found naturally in plants but only in very small amounts. Many manufacturers use bacteria to produce stanols in commercial quantities from sterols, which are types of fats in plants like soya beans.