Topic 3B - More Exchange and Transport Systems

Question 1

How are carbohydrates digested? (2)

Answer 1

1. Amylase — Amylase catalyses the breakdown of starch. It works by catalysing hydrolysis reactions that break the glycosidic bonds in starch to produce maltose.
2. Membrane-bound disaccharidases — These are enzymes which help breakdown disaccharides into monosaccharides. This is done by catalysing the hydrolysis of glycosidic bonds.

Question 2

Where is amylase produced? (2)

Answer 2

1. The salivary glands — this releases amylase into the mouth.
2. The pancreas — this releases amylase into the small intestine.

Question 3

Where are membrane-bound disaccharidases found?

Answer 3

Attached to the cell membranes of epithelial cells lining the ileum.

Question 4

What makes up sucrose?

Answer 4

Glucose + Fructose

Question 5

What makes up maltose?

Answer 5

Glucose + Glucose

Question 6

What makes up lactose?

Answer 6

Glucose + Galactose

Question 7

What is the disaccharidase of sucrose?

Answer 7

Sucrase

Question 8

What is the disaccharidase of maltose?

Answer 8

Maltase

Question 9

What is the disaccharidase of lactose?

Answer 9

Lactase

Question 10

How are lipids digested? (2)

Answer 10

1. Lipase enzymes — They catalyse the breakdown of lipids into monoglycerides and fatty acids. This is done by catalysing the hydrolysis of the ester bonds in lipids.
2. Bile salts — These emulsify lipids (form small droplets), which are then easier to be hydrolysed by lipases as they’ll have a greater surface area.

Question 11

Where are lipases produced?

Answer 11

The pancreas — they are then secreted into the small intestine.

Question 12

Where are bile salts produced?

Answer 12

The liver

Question 13

How are proteins digested? (3)

Answer 13

1. Endopeptidases — They act to hydrolyse peptide bonds within a protein.
2. Exopeptidases — They hydrolyse peptide bonds at the end of protein molecules. They remove single amino acids from proteins.
3. Dipeptidases — They are exopeptidases that work specifically on dipeptides. They act to separate the two amino acids that make up dipeptides by hydrolysing the peptide bond between them.

Question 14

Where are endopeptidases produced? (2)

Answer 14

1. Some endopeptidases (Trypsin & Chymotrypsin) are produced in the pancreas — they are secreted into the small intestine.
2. Another endopeptidase (Pepsin) is produced in the cells lining the stomach — it is then secreted directly into the stomach.

Question 15

How are monosaccharides absorbed into the bloodstream? (3)

Answer 15

Glucose is absorbed by active transport with sodium ions via a co-transporter protein.

Galactose is absorbed in the same way by the same co-transporter protein.

Fructose is absorbed via facilitated diffusion through a different transporter protein.

Question 16

How are monoglycerides and fatty acids absorbed into the bloodstream?

Answer 16

Micelles help to move monoglycerides and fatty acids towards the epithelium. As micelles constantly break up and reform they can ‘release’ monoglycerides and fatty acids, allowing them to be absorbed. Monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane.

Question 17

How are amino acids absorbed into the bloodstream?

Answer 17

Sodium ions are actively transported out of the epithelial cells into the ileum itself. They then diffuse back into the cells through sodium-dependent transporter proteins in the epithelial cell membranes, carrying the amino acids with them.

Question 18

What is the role of haemoglobin?

Answer 18

To carry oxygen around the body.

Question 19

Describe the structure of haemoglobin.

Answer 19

Haemoglobin is a protein with a quaternary structure, made up of four polypeptide chains. Each chain has a haem group which contains an iron ion and gives haemoglobin its red colour. Each haemoglobin molecule can carry four oxygen molecules.

Question 20

How many oxygen molecules can each haemoglobin molecule carry?

Answer 20

Four

Question 21

How is oxyhaemoglobin formed?

Answer 21

When oxygen associates/loads onto haemoglobin in the lung.

Question 22

How is haemoglobin reformed?

Answer 22

When oxygen disassociates/unloads from oxyhaemoglobin in respiring tissue.

Question 23

What does affinity for oxygen mean?

Answer 23

The tendency a molecule has to bind with oxygen.

Question 24

What is partial pressure of oxygen?

Answer 24

A measure of oxygen concentration.

Question 25

A high partial pressure of oxygen means a _____ concentration of oxygen.

Answer 25

High

Question 26

A low partial pressure of oxygen means a ____ concentration on oxygen.

Answer 26

Low

Question 27

When does oxygen load onto haemoglobin?

Answer 27

When there’s a high partial pressure of oxygen (in the lungs).

Question 28

When does oxygen unload from oxyhaemoglobin?

Answer 28

When there’s a low partial pressure of oxygen (in respiring tissue).

Question 29

What are the conditions in the lungs? (4)

Answer 29

• High oxygen concentration
• High partial pressure of oxygen
• There is a high affinity for oxygen
• Oxygen loads onto haemoglobin

Question 30

What are the conditions in respiring tissue? (4)

Answer 30

• Low oxygen concentration
• Low partial pressure of oxygen
• There is a low affinity for oxygen
• Oxygen unloads from oxyhaemoglobin……

Question 31

What does a dissociation curve show us?

Answer 31

How saturated the haemoglobin is with oxygen at any given partial pressure

Question 32

What does 100% saturation of haemoglobin with oxygen mean?

Answer 32

Every haemoglobin molecule is carrying the maximum of 4 molecules of oxygen.

Question 33

What does 0% saturation of haemoglobin with oxygen mean?

Answer 33

None of the haemoglobin molecules are carrying any oxygen.

Question 34

Describe and explain the appearance of a dissociation curve.

Answer 34

It has the appearance of an s-shape and not a straight line as the saturation of haemoglobin can also affect the affinity.
When haemoglobin combines with the first oxygen molecule, it’s shape alters in a way that makes it easier for the other oxygen molecules to join too. But as the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join.
This means there is a shallow area at the start and end where it is hard for oxygen to bind and a steep area in the middle where it is easier for oxygen to bind.

Question 35

When there is a high partial pressure of oxygen, haemoglobin has a _________________ so it also has a _______________________.

Answer 35

High affinity for oxygen

High saturation of oxygen

Question 36

When there is a low partial pressure of oxygen, haemoglobin has a _________________, so it has a _____________________.

Answer 36

Low affinity for oxygen

Low saturation of oxygen

Question 37

What is the partial pressure of carbon dioxide?

Answer 37

A measure of the concentration of carbon dioxide in a cell.

Question 38

How does pCO2 affect oxygen loading and unloading?

Answer 38

Oxyhaemoglobin unloads it’s oxygen more readily in higher pCO2.
Haemoglobin loads oxygen more readily in a lower pCO2.

Question 39

What is the Bohr effect?

Answer 39

The Bohr effect describes the observation that increases in the partial pressure of carbon dioxide results in a lower affinity for oxygen.

Question 40

What does it mean when the dissociation curve shifts?

Answer 40

The further the curve is to the left, the higher the haemoglobin’s affinity for oxygen is.
The further the curve is to the right, the lower the haemoglobin’s affinity for oxygen is.

Question 41

What are the different types of haemoglobin that exist in different environments? (3)…

Answer 41

1. Low oxygen environments — they have haemoglobin with a higher affinity for oxygen than human haemoglobin. This is because there isn’t much oxygen available, so the haemoglobin has to be very good at loading any available oxygen.

Question 42

What does a dissociation curve for an organism living in a low oxygen environment look like? Why does it look like this?

Answer 42

Further to the left than the dissociation curve for human haemoglobin. They have a higher affinity for oxygen as they have less oxygen available so they they have to be good at loading whatever oxygen they can.

Question 43

What does a dissociation curve for an organism smaller than a human look like?

Answer 43

Further to the right than the dissociation curve for human haemoglobin. This is because they respire more (to maintain their heat) than humans so they need their haemoglobin to be able to unload easily at respiring tissue.

Question 44

What does a dissociation curve for an organism with higher activity levels than humans look like?

Answer 44

Further to the right than the dissociation curve for human haemoglobin. This is because they have a high oxygen demand as they respire a lot to provide ATP for their muscles. So oxygen needs to be able to unload easily at the respiring muscles.