6-Exchange

Question 1

Tissue Fluid

Answer 1

The environment around cells in multicellular organisms.

Question 2

As surface area:volume ration increases

Answer 2

Rate of exchange increases

Question 3

Features of Specialised Exchange Surfaces

Answer 3

Large SA:V ration increases rate of exchange.
Very thin for short diffusion pathway.
Selectively permeable to allow specific materials across.
Movement of environment medium (air) to maintain diffusion gradient.
Transport system (blood) to ensure movement of internal medium to maintain diffusion gradient.

Question 4

Gas Exchange in Single-Celled Organisms

Answer 4

Have a large SA:V ration so oxygen is absorbed by diffusion across cell-surface membrane.

Question 5

Gas Exchange in Insects

Answer 5

Internal network of tracheae (tubes) supported by strengthened rings to prevent them from collapsing. Tracheae divides into tracheoles (smaller dead-end tubes). Tracheoles extend throughout body tissue of insect which results in a short diffusion pathway to body cells. Respiratory gases move in and out of tracheal system in 3 ways: ALONG DIFFUSION GRADIENT
MASS TRANSPORT
ENDS OF TRACHEOLES ARE FILLED WITH WATER

Question 6

Along diffusion gradient

Answer 6

When respiring O2 is used up so concentration at tracheole end decreases which causes a diffusion gradient so O2 goes towards the tracheoles. The same is applied to CO2 but in the opposite direction.

Question 7

Mass Transport

Answer 7

Muscles in insect contract which squeeze trachea, enabling mass movements of air in and out. This further speeds up exchange of respiratory gases.

Question 8

End of Tracheoles are filled with Water

Answer 8

When major activity is occurring muscle cells around tracheoles respire, carrying out anaerobic respiration which produces lactate.it’s soluble and lowers water potential of cells so water moves in by osmosis. This causes water at ends of tracheoles to decrease so more air is taken in and the diffusion pathway is a gas instead of liquid phase so diffusion is quicker.

Question 9

Gas Exchange in Fish: Structure of Gills

Answer 9

Behind the head
Made up of gill filaments which are stacked up in a pile.
Gill lamellae are at right angles to the gill filaments which increases surface area of gills.
Water is taken in through mouth and passes over gills.
Water and blood flow in opposite directions for Countercurrent Flow.

Question 10

Countercurrent Exchange Principle

Answer 10

Blood well loaded with O2 meets water with max conc of O2 so diffusion of O2 from water to blood takes place.
Blood with little O2 meets water with a lot and once again diffusion of O2 from water to blood takes place.
This maintains the O2 uptake across the entire width of the gill lamellae.

Question 11

Gas Exchange in Leaves of Plants

Answer 11

When photosynthesis takes place O2 is used by respiring cells but most of it diffuses out of the plant.
When photosynthesis isn’t taking place (in the dark) cells are respiring so CO2 is produced and diffuses out of the plant.

Question 12

Structure of Plant Lead and Gas Exchange

Answer 12

Many stomata (small pores) and no cell is far from stoma so diffusion pathway is short.
Numerous air spaces in spongy mesophyll so gases readily come in contact with mesophyll cells.
Large surface of mesophyll cells for rapid rate of diffusion.

Question 13

Limiting Water Loss in Insects

Answer 13

1) Small SA:V ratio to minimise area over which water is lost.
2) Waterproof coverings on body surface (waterproof cuticle covering rigid chitin outer skeleton of insect).
3) Spiracles (openings of trachea on body surface) which can be closed to reduce water loss but conflicts with need for oxygen so occurs when insect is at rest.

Question 14

Limiting Water Loss in Plants

Answer 14

1) Waterproof coverings

2) Ability to close stomata whenever necessary.

Question 15

Xerophytes

Answer 15

Plants that are adapted to living in areas where water is in short supply.

Question 16

Limiting Water Loss in Xerophytes

Answer 16

1) Thick waxy cuticle to stop water from escaping (holly).
2) Rolling up of leaves to trap a region of still air which becomes saturated with water vapour and has a very high water potential. Since there’s no water potential gradient no water is lost (Mariam grass).
3) Hairy leaves to trap still air near surface so a reduced water potential gradient is formed so less water is lost by evaporation (heather plant).
4) Stomata in pits/grooves to trap air and reduce water potential (pine trees).
5) Reduced SA:V ratio of leaves.

Question 17

Lungs

Answer 17

Pair of lobe-like structures made up of many bronchioles, ending with alveoli.

Question 18

Trachea

Answer 18

Flexible airway supported by rings of cartilage to prevent them from collapsing as air pressure falls when breathing in.
Tracheal walls made of muscle cells, lined with ciliates epithelial cells and goblet cells.

Question 19

Bronchi

Answer 19

2 divisions of the trachea, each leading to one lung. Similar in structure of trachea.

Question 20

Bronchioles

Answer 20

Series of branching sub-divisions of bronchi made of muscle and ciliates epithelial cells.
Muscle cells let them constrict so they can control the flow of air in/out of alveoli.

Question 21

Alveoli

Answer 21

Minute air sacs with a diameter of 100-300 micrometers at the end of bronchioles.
Has collagen and elastic fibres between them to stretch as they fill with air when breathing in.
Lined with epithelium.

Question 22

Ventilation (Mechanism of Breathing)

Answer 22

Inspiration (inhalation) and Expiration (exhalation)

Question 23

Inspiration

Answer 23

Active process
External intercostal muscles contract, internal relax.
Ribs pulled up and out, increasing thoracic volume.
Diaphragm muscle contracts, flattening it, increasing thoracic volume.
Increased thoracic volume decreases pressure in lungs.
Atmospheric pressure is now greater than pulmonary pressure so air is forced into lungs.

Question 24

Expiration

Answer 24

Passive process
Internal intercostal muscles contract, external relax.
Ribs move down and in, decreasing thoracic volume.
Diaphragm relaxes, decreasing thoracic volume.
Decreased thoracic volume increases pressure in lungs.
Pulmonary pressure is now greater than atmospheric pressure so air is forced out of the lungs.

Question 25

Diffusion of gases between alveoli and blood is rapid because…

Answer 25

1) Red blood cells are slowed as they pass through pulmonary capillaries, so there’s more time for diffusion.
2) Distance between alveolar air and red blood cells is reduced as red blood cells are flattened against capillary wall.
3) Both alveolar and capillary walls are thin so short diffusion pathway.
4) Alveoli and capillaries have large total surface area.
5) Blood flow through pulmonary capillaries maintains concentration gradient.

Question 26

Major parts of Digestive System

Answer 26

Oesophagus 
Stomach
Ileum
Large Intestine 
Rectum
Salivary Glands
Pancreas

Question 27

Oesophagus

Answer 27

Carries food from mouth to stomach

Question 28

Stomach

Answer 28

A muscular sac that produces enzymes to store an digest food, especially proteins.

Question 29

Ileum

Answer 29

Long muscular tube that further digests food due to enzymes produced from its walls/glands.

Question 30

Large Intestine

Answer 30

Absorbs water

Question 31

Rectum

Answer 31

Final section of the intestines where focus is stored before being removed by the anus by egestion.

Question 32

Salivary Glands

Answer 32

Situated in the mouth and contains amylase that hydrolysis starch into maltose.

Question 33

Pancreas

Answer 33

Large gland below the stomach which secretes pancreatic juice containing protease and lipase and amylase to hydrolyse proteins and lipids and starch.

Question 34

Physical Breakdown in Digestion

Answer 34

Food is broken down into smaller pieces by means of structures like teeth so they can be chemically digested. Food is also churned up by muscles in stomach wall.

Question 35

Chemical Digestion

Answer 35

Hydrolysis large insoluble molecules into smaller soluble ones. Carbohydrases hydrolyse carbohydrates. Lipases hydrolyse lipids. Proteases hydrolyse proteins.

Question 36

Carbohydrate Digestion

Answer 36

1) Saliva is mixed with food when chewing.
2) Salivary amylase in saliva hydrolysis starch in food to maltose.
3) Food is swallowed and amylase is denatured in acidic conditions of stomach.
4) Food passes through small intestine where it mixes with pancreatic juice secreted from pancreas.
5) Pancreatic amylase in pancreatic juice hydrolysis any remaining starch into maltose.
6) Muscles in intestinal wall push food along ileum. The epithelial lining produces the disaccharidase maltase which hydrolyses maltose into alpha-glucose.

Question 37

Lipid Digestion

Answer 37

1) Lipids are separated into tiny droplets called micelles by bile salts produced in the liver (process is called emulsification)
2) Lipases break down the micelles quicker due to an increase in surface area.

Question 38

Protein Digestion

Answer 38

Proteins are hydrolysed by peptidases (proteases), the main 3 being Endopeptidase, Exopeptidase, Dipeptidase.

Question 39

Endopeptidase

Answer 39

Hydrolyses the peptide bonds between amino acids in central region of protein, forming series of peptide molecules.

Question 40

Exopeptidase

Answer 40

Hydrolyses peptide bonds on terminal amino acids of peptide molecules formed by endopeptidases, releasing dipeptides and single amino acids.

Question 41

Dipeptidase

Answer 41

Hydrolyses bond between 2 amino acids of a dipeptide. They are membrane-bound, being part of the cell-surface membrane of epithelial cells lining the ileum.

Question 42

Structure of Ileum

Answer 42

Wall is folded and possesses villi which increases surface are of ileum so also increases rate of absorption.
Villi are situated at interface between lumen of intestines and blood/other tissues inside the body.

Question 43

How Ileum Increases Efficiency of Absorption

Answer 43

Increased surface area.
Thin wall so short diffusion pathway.
Contains muscle so are able to move which helps to maintain diffusion gradients.
Well supplied with blood vessels so blood can carry away absorbed molecules and hence maintain diffusion gradients.
Epithelial cells lining the villi posses microvilli that further increase rate of absorption.

Question 44

Absorption of Amino Acids and Monosaccharides

Answer 44

Amino acids and monosaccharides are produced from the digestion of proteins and carbohydrates. They are absorbed by by diffusion/co-transport.

Question 45

Absorption of Triglycerides

Answer 45

1) Micelles (4-7nm diameter) are formed from emulsification of lipid droplets.
2) Micelles come into contact with epithelial cells lining villi of ileum and are broken down, releasing monoglycerides and fatty acids.
3) They are non-polar so easily diffuse across cell-surface membrane.
4) Inside epithelial cells the monoglycerides and fatty acids are transported to Endoplasmic reticulum where they’re recombined into triglycerides.
5) In Golgi apparatus the triglycerides associate with cholesterol and lipoproteins to form chylomicrons (special particles adapted to for transport of lipids.
6) Chylomicrons move out of epithelial cells by exocytosis and enter lacteals (lymphatic capillaries) found at the centre of each villus.
7) Chylomicrons pass via lymphatic vessels into blood system.
8) Triglycerides in chylomicrons are hydrolysed by an enzyme in endothelial cells of blood capillaries where they diffuse into cells.