Exchange

Question 1

What are characteristics of specialised exchange surfaces?

Answer 1

• A large surface area relative to the volume of the organism which increases the rate of exchange
• Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly.
• Selectively permeable to allow selected materials to cross
• Movement of the environmental medium to maintain a diffusion gradient.
• A transport system to ensure the movement of the internal medium in order to maintain a diffusion gradient.

Question 2

What is the equation for diffusion?

Answer 2

diffusion = (surface area x difference in concentration) / distance

Question 3

Why are specialised exchange surfaces often located inside an organism?

Answer 3

• Being thin, specialised exchange surfaces are easily damaged and dehydrated.

Question 4

How do single-celled organisms undergo gas exchange?

Answer 4

• Have small metabolic requirements and have a small surface area : volume ratio so gases move by diffusion

Question 5

Describe the respiratory system of an insect

Answer 5

• Insects have an internal network of tubes called tracheae, supported by strengthened rings to prevent them from collapsing.
• The trachea divide into smaller dead-end tubes called tracheoles, which extend throughout all the body tissues of the insect.
• They have tiny pores called spiracles on their sides where gas enters and leaves

Question 6

How are respiratory gases moved in and out of the tracheal system?

Answer 6

• ALONG A DIFFUSION GRADIENT -> when cells are respiring oxygen is used up and carbon dioxide is produced which creates a diffusion gradient that causes oxygen to diffuse into the cells and carbon dioxide to diffuse out of the cells.
• MASS TRANSPORT -> the contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases.
• THE ENDS OF THE TRACHEOLES ARE FILLED WITH WATER -> During periods of activity where muscle cells respire anaerobically and release lactic acid, the water potential of the cell decreases. As a result water in the tracheoles moves into the cell by osmosis. The water in the ends of the tracheoles decreases in volume and in doing so draws air further into them. This means the final diffusion pathway is in a gas rather than a liquid and therefore diffusion is more rapid. This increase the rate at which air is moved in the tracheoles but leads to greater water evaporation.

Question 7

How are insects adapted for gas exchange?

Answer 7

• Water filled tracheole ends
• Muscles contract to decrease the volume of trachea to push air out and then relax to move air pack in.
• Spiracles can be opened and closed by a valve.
• Tracheoles extend throughout the body tissue of insect. This means there is a short diffusion distance from a tracheole to any body cell.

Question 8

How are insects adapted to have minimal water loss?

Answer 8

• Small surface area : volume ratio to minimise the area over which water is lost.
• Waterproof coverings over their body surfaces. In the case of insects this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle
• Spiracles are the openings of the tracheae and can be closed to reduce water loss. This conflicts with the need for oxygen and so occurs largely when the insect is at rest.

Question 9

Describe the structure of the gills

Answer 9

• The gills are located behind the head of the fish.
• They are made up of gill filaments which are stacked up in a pile.
• At right angle to these are the gill lamellae, which increase the surface area of the gills.

Question 10

Describe the movement of water in fish

Answer 10

• Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body.
• The flow of water over the gill lamellae and the flow of blood within are in opposite directions which is called Countercurrent flow.

Question 11

Countercurrent exchange principle explanation

Answer 11

• Counterflow is when the direction of flow of blood is the opposite direction of the flow of water.
• It means that there is always a higher concentration of oxygen in the water than in the blood throughout the length of the lamellae and so there is always a concentration gradient throughout the length of the lamellae.
• This means that oxygen is always moving into the blood by diffusion.
• As a result 80% of oxygen in blood in absorbed

Question 12

What is physical digestion?

Answer 12

• The break down of large food into smaller pieces by means of structures such as teeth.
• It also provides a larger surface area for chemical digestion.

Question 12

Explain the human digestive system briefly.

Answer 12

• Oral cavity where teeth mechanically digest food and where salivary glands release amylase which chemically digest starch into maltose
• The oesophagus carries food to the stomach via peristalsis
• The stomach is a muscular sac with an inner layer that produces enzymes. Its role is to store and digest food, especially proteins.
• The small intestine is made up of three parts: the duodenum, jejunum and ileum.
• The ileum is a long muscular tube, which has walls and glands which produce and release enzymes. The inner walls of the ileum are folded into villi, with a larger surface area.
• The large intestine absorbs water.
• The rectum is where faeces is stored before being removed via the anus.
• The pancreas is a large gland below the stomach which produced pancreatic juice containing enzymes.

Question 12

What enzymes are involved in carbohydrate digestion? (in order)

Answer 12

• Amylase is produced in the mouth and the pancreas. It is released by salivary glands into the mouth and released into the small intestine from the pancreas. Amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose. It also contains mineral salts that help to maintain the ph at around neutral.
• Maltase is produced by the epithelial cells in the lining of the ileum and released there. It is referred to as membrane-bound disaccharidase. It hydrolyses maltose into alpha glucose.
• Sucrase and lactase are also enzymes which are involved in the hydrolysation reaction with the complimentary substrate.

Question 13

What is emulsification?

Answer 13

• Lipids are split into tiny droplets called micelles by bile salts, which are produced by the liver. It increases the surface area of the lipids to increase the rate of enzyme action.
• One end of the bile salt molecule is soluble in fat (lipophilic) but not in water (hydrophobic). The other end is soluble in water (hydrophilic) but not in fat (lipophobic).
• Bile salt molecules therefore arrange themselves with their lipophilic ends in fat droplets, leaving their lipophobic ends sticking out.
• In this way they prevent fat droplets from sticking to each other to form large droplets, leaving only tiny ones.

Question 13

What enzymes are involved in lipid digestion? (in order)

Answer 13

• Lipids hydrolysed by enzymes called lipases.
• Lipases are produced in the pancreas and hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides.

Question 14

What is chemical digestion?

Answer 14

• Chemical digestion hydrolyses large, insoluble molecules into smaller soluble ones.
• It is carried out by enzymes.

Question 14

How are triglycerides absorbed ?

Answer 14

• Monoglycerides and fatty acids remain in association with the bile salts and the structures formed are called micelles.
• The micelles come into contact with the epithelial cells.
• Here the micelles break down, releasing the monoglycerides and fatty acids which diffuse across the cell-surface membrane into the epithelial cells as they are non-polar.
• They are transported to the endoplasmic reticulum where they are recombined to form triglycerides.
• The move into the Golgi apparatus, and associate with cholesterol and lipoproteins to form structures known as chylomicrons, special particles adapted for transport of lipids.
• The chylomicrons move out of the epithelial cells by exocytosis. They enter lymphatic capillaries called lacteals that are found at the centre of each villus and then pass into the blood stream.
• The triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries from where they diffuse into cells.

Question 14

What enzymes are involved in protein digestion? (in order)

Answer 14

• Proteins are hydrolysed by a group of enzymes called peptidases.
• Endopeptidase hydrolyse the peptide bonds between amino acids in the central region of a protein molecule, forming a series of peptide molecules.
• Exopeptidases hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they progressively release dipeptides and single amino acids.
• Dipeptidases hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane- bound, being part of the cell-surface membrane of the epithelial cells lining the ileum.

Question 15

How do all plants limit water loss?

Answer 15

• They have waterproof covering (waxy cuticle)
• They have stomata which can open and close

Question 16

What are some adaptations to limit water loss in xerophytes?

Answer 16

• A thick cuticle -> increases diffusion distance so slower rate of diffusion
• Rolling up of leaves -> Most stomata are located on the lower epidermis. Rolled leaves traps a region of air within the rolled leaf which becomes saturated with water vapour. Hence there is a high water potential so there is a higher water potential outside the cell than inside it, meaning that water doesn’t move out of the leaf.
• Hairy leaves -> Hair traps still moist air next to the surface of the leaf, reducing the water potential gradient between the outside and inside of the leaf so less water is lost by evaporation.
• Stomata in pits or grooves (sunken stomata) -> This traps still, moist air next to the leaf and reduces the water potential gradient.
• a reduced area to volume ratio of the leaves which reduces surface area for water loss.
• Lower stomata density -> less water is lost due to fewer pores

Question 17

Describe the structure of the lungs

Answer 17

• Lungs area a pair of lobed structures made up of a series of highly branched tubules, called bronchioles, which end in a tiny air sac called alveoli
• The trachea is a flexible airway that is supported by rings of cartilage. The tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells.
• The bronchi are two divisions of the trachea, each leading to one lung. They are a similar structure to the trachea. Also produce mucus and cilia to move dirt-laden mucus towards the throat.
• The bronchioles are a series of branching subdivisions of the bronchi. Their walls are made of muscle lined with epithelial cells. This muscle allows them to constrict so that they can control the flow of air in and out of the alveoli.
• The alveoli are air sacs at the end of the bronchioles. Between alveoli there are some collagen and elastic fibres. The alveoli are lined with epithelium. The elastic fibres allow the alveoli to stretch.

Question 18

Describe inspiration

Answer 18

• The external intercostal muscles contract, while the internal intercostal muscles relax.
• The ribs are pulled upwards and outwards, increasing the volume of the thorax.
• The diaphragm muscles contract causing it to flatten which also increases the volume of the thorax.
• The increased volume of the thorax results in a lower pressure in the lungs.
• There is a pressure gradient so that there is a higher pressure outside than inside the lungs so air moves in.

Question 19

Describe expiration

Answer 19

• The external intercostal muscles relax, while the internal intercostal muscles contract.
• The ribs downwards and inwards, decreasing the volume of the thorax.
• The diaphragm muscles relaxes causing it to dome which also decreases the volume of the thorax.
• The decreased volume of the thorax results in a higher pressure in the lungs.
• There is a pressure gradient so that there is a lower pressure outside than inside the lungs so air moves out.

Question 20

What are some adaptions of the alveoli which make it more suitable for gas exchange?

Answer 20

• red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
• the distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls.
• the walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very short.
• alveoli and pulmonary capillaries have a very large total surface area
• breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of the gases to be exchanged is maintained.
• blood flow through the pulmonary capillaries maintains a concentration gradient.

Question 21

What enzymes are involved in protein digestion?

Answer 21

• Endopeptidase hydrolyses the peptide bonds in the central region of the proteins
• Exopeptidase hydrolyses the peptide bonds in the protein in its terminal ends
• Dipeptidase hydrolyses the dipeptide bond between two amino acids to form singular amino acids.

Question 22

What is COPD?

Answer 22

• COPD stands for chronic obstructive pulmonary disease and is essentially lung disease.
• Examples include emphysema and chronic bronchitis.

Question 23

What factors increase the risk of developing COPD ?

Answer 23

• Smoking -> 90% of people suffering from COPD are, or have been, heavy smokers
• Air pollution -> Pollutant particles and gases like sulfur dioxide can increase the likelihood of COPD
• Genetic make-up -> Some people are genetically to develop COPD.
• Infections -> People who frequently get chest infections have a higher incidence of COPD.
• Occupation -> People working with harmful chemicals, gases and dusts that can be inhaled have a higher incidence of COPD