Exchange

Question 1

what is tissue fluid?

Answer 1

the environment around the cells of multicellular

Question 2

what are the attributes of surface area to volume ratio?

Answer 2

for the exchange within an organism to be effective the exchange surfaces must be larger than the volume.
a small organism have a surface area that is large enough, compared to their volume allowing efficient exchange across their body surface.

Question 3

what have organisms evolved to have to maximise exchange?

Answer 3

either a flattened shape to ensure that no cell is ever far from the surface
or specialised exchange surfaces with large areas to increase the SA:vol ratio

Question 4

what are the features of specialised exchange surfaces?

Answer 4

a large sa:vol ratio which will increase the rate of exchange
they are very thin to provide a short diffusion pathway meaning that materials cross the exchange surface rapidly
they are selectively permeable to allow select materials across.
movement of the environmental medium to maintain a concentration gradient
a transport system to ensure the movement of the internal medium in order to maintain a diffusion gradient.

Question 5

what is gas exchange in single cell organisms like?

Answer 5

the y have a large sa:vol ratio. oxygen is absorbed across their body surface via diffusion, the surface is only covers by a cell membrane.

Question 6

what is gas exchange like in insects?

Answer 6

they have evolved an internal network of tubes called tracheae which are supported by rings to support them rom collapsing. these than split into smaller tubes called tracheoles oxygen i therefore brought directly to respiring tissue which has a short diffusion pathway.

Question 7

what are the three ways that gases move in and out of the tracheal system?

Answer 7

along a diffusion gradient - when cells are respiring the oxygen is used up at the end of the tracheoles, this forces oxygen to diffuse from the atmosphere along the tracheae and the tracheoles into the cells. As diffusion of gases are much quicker in air than in water this method is used.
mass transport - the contraction of muscles will squeeze the tracheae enabling the mass movement of air in and out.
the ends o the tracheoles are filled with water

Question 8

why are the ends of the tracheoles filled with water?

Answer 8

during periods of major activity the cells may respire anarobiclaly, this will produce lactate and therefore reduce the water potential of the cell. water therefore moves into the cells from the tracheoles via osmosis therefore decreasing the volume in the tracheoles and so air from the atmosphere is the drawn in. this means that the final diffusion pathway is in air weather than liquid and so the exchange is more rapid.

Question 9

how do gases enter and leave the trachea in insects?

Answer 9

through the spiracles on the body surface (the majority of the time they are closed to prevent water loss)

Question 10

what are the limitations of the exchange system in insects?

Answer 10

it relies on diffusion and so for diffusion to be effective a small diffusion pathway is required which is why insects are small in size.

Question 11

what is meant by the metabolic rate?

Answer 11

the speed that chemical reactions take place in the body

Question 12

describe the structure of the gills

Answer 12

the gills are made up of gill filaments. along the gill filaments at right angles to them are the gill lamellae which increase the surface area of the gills. the gill filaments are located on the gill arch and on the other side of this are the gill rakers to stop food from going into the gills.

Question 13

what is countercurrent flow?

Answer 13

the opposite flow of blood through the gill lamellae and the flow of water over the gills.

Question 14

what is the countercurrent exchange principle?

Answer 14

water and blood flow in opposite directions. this means that the blood that is well loaded with oxygen meets water with the maximum concentration of oxygen in it. this means that diffusion will take place. it also means that blood that has little oxygen in it will meet water that has had most but not all of its water removed, this ensures that diffusion will take place. this means that a diffusion gradient will be maintained across the entire lamellae.

Question 15

how is the structure of a plant adapted for gas exchange?

Answer 15

no living cell is far from the external air
diffusion takes place in the gas phase
overall, there is a short diffusion pathway in addition the air spaces within the leaf have a very large surface area compared with the volume of the living tissue. there is no specific transport system.
there are many small stomata - no cell is far away from a stomata
there are numerous interconnecting air-spaces that occur throughout the mesophyll layer
a large surface area of mesophyll cells for rapid diffusion.

Question 16

what are the stomata?

Answer 16

minute pores that are primarily found on the underside of a leaf. each stomata is surrounded by a pair of guard cells. they are important as terrestrial organisms lose water via evaporation and so plants have adapted t balance the needs of gas exchange and water loss.

Question 17

how is water loss limited in insects?

Answer 17

they have a small surface area to volume ratio to minimise the area over which water is lost
waterproof coverings in the form of a rigid outer skeleton of chitin that is covered with a water proof cuticle.
spiracles can be closed to reduce water loss

Question 18

how is water loss limited in plants?

Answer 18

plants cannot have a small surface to volume ratio as they carry out photosynthesis which requires a large area
to reduce water loss terrestrial plants have water proof coverings, stomata.

Question 19

what are the adaptations of xerophytes?

Answer 19

a thick outer cuticle means that less water can escape
rolling up of leaves protects the lower epidermis from the outside helps to trap a still region of air. this region becomes saturated with water vapour and so therefore has a very high water potential. there is n water potential gradient between the outside and the inside and so now water is lost.
hairy leves - still moist air is trapped next to the leaf. the water potential gradient is therefore reduced and therefore less water is lost.
stomata in pits or grooves traps still moist air
a reduced surface area to volume ratio

Question 20

why are the volumes of oxygen absorbed and the volumes of CO2 produced so high in mammals?

Answer 20

they are large organisms with a high volume of living cells

they have to maintain a high body temperature which is related to them having high metabolic and respiratory rates.

Question 21

why are the lungs located inside the body?

Answer 21

air is not dense enough to support and protect these structures
the body would lose a great deal of water and dry out.

Question 22

what are the main parts of the human gas exchange system?

Answer 22

the trachea - a flexible airway that is supported by rings of cartilage which prevents it from collapsing due to the negative pressure created. the walls are lined with ciliated and goblet cells
the bronchi - two devisions of the trachea, also produce mucus and have cartilage rings. the amount of this is reduced as they get smaller
the bronchioles - branching subdivisions of the bronchi. Their walls are made out of muscle lined with epithelial cells. this muscle can constrict so they can control the amount of air going to the alveoli
the alveoli - minute air sacs with a small diameter between 100-300 micrometers. between the alveoli there are some collagen and elastic fibres. they are lined with epithelium

Question 23

what three sets of muscles bring about pressure changes within the lungs?

Answer 23

the diaphragm, a sheet of muscle that separates the thorax from the abdomen
the intercostal muscles, which lie in-between the ribs. there are two sets of intercostal muscles
- the internal intercostal muscles whose contraction leads to expiration and the external whose contraction leads to inspiration

Question 24

describe the process of inspiration

Answer 24

the external intercostal muscle contracts, while the internal relaxes.
the ribs are pulled up and outwards increasing the volume of the thorax
the diaphragm muscles contract causing it to flatter which also increases the volume of the thorax. this results in a increase in volume and so an increase in pressure
atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs.

Question 25

describe the process of expiration

Answer 25

the internal intercostal muscles contract forcing the ribs down and inwards decreasing the volume of the thorax
the diaphragm relaxes further decreasing the volume of the thorax. decrease in volume means an increase un pressure in the lungs. the pulmonary pressure is therefore greater than the atmospheric pressure and so air is forced out of the lungs.

Question 26

what is the role of alveoli in gas exchange?

Answer 26

there are about 300 million alveoli in the lungs which amount to around 70m squared or surface area.around each alveolus is a network of capillaries. they are so thin that the red blood cells have to be flattened against the cell wall in order for them to pass through. the diffusion of gases will be very quick because:
RBCs are slowed as they pass through the capillary allowing more time for diffusion
short diffusion pathway
alveoli and capillaries have a very high surface area
a steep concentration gradient is always maintained

Question 27

what are the major parts of the digestive system?

Answer 27

the salary glands are located near the mouth - produce amylase which hydrolyses maltose
the oesophagus carries food from the mouth to the stomach
the stomach is a muscular sac with an inner lining that produces enzymes - has smooth muscles for mechanical digestion
the ilium is a long muscular tube. food further digested here by enzymes. the inner walls are folded into villi giving it a larger surface area - further increased by microvilli on the epithelial cells of each villus
the large intestine absorbed water
the rectum is for storage and compaction - then removal through the anus is called egestion
the pancreas produces pancreatic enzymes

Question 28

what is physical digestion?

Answer 28

the breakdown of foods by structures such as the teeth. not only makes it possible to ingest the food but also increases its surface area for chemical digestion

Question 29

what is chemical digestion?

Answer 29

hydrolysis of large insoluble molecules into smaller soluble ones - carried out by enzymes. there are different types of enzyme that are involved in chemical digestion the three that are particularly important are:
Carbohydrases, Lipases, proteases

Question 30

describe the process of carbohydrate digestion

Answer 30

1) saliva enters mouth from salivary glands
2) contains salivary amylase which starts hydrolysing any starch into malts (glycosidic bonds), it also contains mineral salts helping to maintain the pH
3) the food is then swallowed (acidic conditions) denatures amylase
4) food passes into the SI were it mixes with pancreatic juices - pancreatic amylase hydrolyses any remaining starch
5) muscles in the intestine wall push the food song the ilium, its epithelial lining produces the disaccharidase maltase - refers to as a membrane bound disaccharide

Question 31

describe the process of lipid digestion

Answer 31

hydrolysed by enzymes called lipase - produced by the pancreas they hydrolyses the ester bond to break down triglycerides to form ftty acids and a monoglyceride.
lipids are first split up into tiny droplets called micelles by bile salts, this process is called emulsification and increases the sucrose area of he lipids

Question 32

describe the process of protein digestion

Answer 32

proteins are broken down by a number of different peptidases:
endopeptidase hydrolyses the peptide bond between amino acids in the central region of a protein molecule
exopeptides hydrolyse the peptide bonds on the terminal amino acids. in this way they progressively release dipeptides into single amino acids
dipepeptides hydrolyse the bond between two amino acids of a dipeptide - they are membrane bound being part of the cell-surface membrane of the epithelial cells lining the ilium.

Question 33

how does the properties of the villi increase the efficiency of absorption?

Answer 33

they increase the surface area for diffusion
tehy have a short diffusion pathway
they contain muscles so are able to move. this helps to maintain diffusion gradients because there movement mixes up the contents of the ilium
they are well supplied with blood vessels so that blood can carry away absorbed molecules and maintain a diffusion gradient
contain microvilli

Question 34

how are amino acids and monosaccharides absorbed?

Answer 34

via diffusion and co-transport

Question 35

how are triglycerides absorbed?

Answer 35

micelles come into contact with epithelial cells lining the villi due to the movement of material within the lumen of the ilium. here the micelles break down, releasing monoglyerides and fatty acids. these are non-polar molecules so easily diffuse across the cell-surface membrane into the epithelial cells.
once inside the epithelial cells the monoglycerides and fatty acids are transported to the endoplasmic reticulum where they are reformed to form triglycerides. starting in the ER and then moving onto the golgi apparatus the Triglycerides are associated with cholesterol and lipoproteins to from structures called chylomicrons.
they move out of the cell by exocytosis. they enter lymphatic capillaries calls lacteals that are found at the centre of each villus. from here they pass into the blood stream.

Question 36

what are chylomicrons?

Answer 36

special particles that are adapted for the transport of lipids