more on Exchange and transport systems

Question 1

why is food broken down into smaller molecules during digestion?

Answer 1

large molecules are too big too cross cell membranes - can’t be absorbed
they are broken down by hydrolysis

Question 2

how are carbohydrates broken down?

Answer 2

they are broken down by amylase and membrane-bound disaccharides.
amylase is a digestive enzyme that data,yes the conversion of starch into the disaccharide maltose - this involves the hydrolysis of the glycosidic bonds
- it is produced by the salivary glands and also by the pancreas

Question 3

what are membrane bound disaccharides - disaccharidase?

Answer 3

they are enzymes that are attached to the cell membranes of epithelial cells lining the ilium - they help to break down disaccharides into monosaccharides

Question 4

what are lipids broken down by?

Answer 4

they are broken down by lipase and bile salts.
the lipase enzyme catalyses the break down of lipids into monoglyerides and fatty acids - this involves the hydrolysis of ester bonds.
it is made in the pancreases and works in the small intestine

Question 5

why are bile salts produce for the break down of Triglycerides

Answer 5

they are produced by the liver and they emulsify lipids - they cause the lipids to form small droplets - this increases the surface area of the for lipase hydrolysis. once the lipids have been broken down, the monoglyserides and the fatty acids form a droplet that has the hydrophilic heads facing outwards and the hydrophobic tails inwards

Question 6

hata re proteins brocken down by?

Answer 6

they are broken down by endopeptidase and Exopeptidase

Question 7

what is Endopeptidase?

Answer 7

it acts to hydrolyse the peptide bonds within a protein
Tyripsin and chymotrypsin are two examples of endopeptidase - they re synthesised in the pancreases and secreted in the small intestine
also pepsin which is released in the stomach lining

Question 8

what is Exopeptidase?

Answer 8

it acts to hydrolyse the peptide bonds at the end of molecules - they remove single amino acids from the chain
dipeptiase is one, it works specifically on the dipeptides

Question 9

how are monosaccharides absorbed across the cell membrane?

Answer 9

Glucose is absorbed by active transport with sodium ions via a co-transporter protein. Galactose is absorbed in the same way using the same co-transporter protein where as fructose is absorbed by facilitated diffusion across a different transporter protein - also a Na K pump is used to generate a concentration gradient

Question 10

how are monoglyserides and fatty acids absorbed?

Answer 10

micelles help to move the fatty acids and monoglycerides towards the epithelium. as micelles are always breaking apart and reforming they can break apart allowing the fatty acids and monoglyserides to diffuse across the cell surface membrane as they are non polar - they are lipid soluble
they are then transported to the endoplasmic reticulum where they are recombined to form triglycerides - they move to the golgi apparatus where associate with cholesterol and lipoproteins to form structures called chylomicrons.

Question 11

what is a chylomicron?

Answer 11

they are structures that are made up of triglycerides cholesterol and lipoproteins and are specially adapted to carry lipids.
they move out of the cells by exoctosis.

Question 12

how are amino acids absorbed?

Answer 12

tehy diffuse into cells via sodium-dependant transporter proteins in the epithelial membrane, they carry amino acids with them.

Question 13

how is oxygen carried round the body?

Answer 13

it is carried around by haemoglobin. haemoglobin is a large protein with a quaternary structure - made up of more than one polypeptide chain. - each of them has a heam group, contains an iron ion giving the haemoglobin a red colour. it has a high affinity for oxygen (each molecule can carry four oxygen) -forms oxyhemoglobin (reversible reaction.

Question 14

what does haemoglobin saturation depend on?

Answer 14

to depends on the partial pressure of oxygen. the greater the proportion of oxygen dissolved in the cells the greater the partial pressure.

Question 15

what doe the haemoglobin affinity for oxygen depend on?

Answer 15

the affinity varies depending on the partial pressure. when there is a high PP oxygen loads onto the haemoglobin and when the PP is lower it is easier to unload
blood. in the capillaries in the lungs the blood has a high PP so oxygen loads onto it and the opposite is true when cells respire.

Question 16

what do dissociation curves show?

Answer 16

they show how the affinity for oxygen changes.

Question 17

which directions does the dissociation curve move due to different affinities?

Answer 17

for a lower affinity where oxygen is more readily unloaded the cute moves to the right and when there is a higher affinity it moves to the right.

Question 18

why do mammals need a specialised transport system?

Answer 18

Multicellular organisms have a low surface area to volume ratio so they need a specialised transport system to carry raw materials from specialised exchange organs to their body cells

Question 19

how are arteries adapted for there specific function?

Answer 19

they carry blood from the heart to the rest of the body. they have thick muscular walls and elastic tissue to stretch and recoil as the heart beats helping to maintain the high pressure. the inner lining is folded (endothelium) allowing the artery to stretch also helping to maintain pressure.

Question 20

how are arterioles adapted for their specific function?

Answer 20

they are devisions from arteries. they form a network throughout the body. blood is directed to different areas of demand by the muscles inside the arterioles. they contract to restrict the blood flow and vice vera.

Question 21

how are veins adapted for their specific function?

Answer 21

veins take blood back to the heart under low pressure. they have a wider lumen, with very little elastic or muscle tissue. they contain valves to stop the blood flowing in the opposite direction. blood flow in the veins is helped by the contraction of muscle surrounding them

Question 22

how are the capillaries adapted for their specific function?

Answer 22

arterioles branch out into capillaries, they are the smallest of the blood vessels. substances are exchanged between the cells and the capillaries so they are adapted for efficient diffusion. they are found very near cells in exchange tissue so there is a short diffusion pathway - adding to this is the fact that their walls are only 1 cell thick. there is a large number of capillaries to increase the surface area for exchange. networks of capillaries are called capillary beds

Question 23

what is tissue fluid?

Answer 23

the fluid that surrounds cells in tissue. it is mad up of small molecule that leave the blood plasma. cells take in nutrients from the tissue fluid and release metabolic waste into it. this process of moving in and out is by pressure filtration.

Question 24

what is pressure filtration?

Answer 24

at the start o the capillary bed the hydrostatic pressure is greater than the inside the capillaries i greater than the hydrostatic pressure in the tissue.
this difference means that the overall outward pressure forces fluid out out o the capillaries and into the spaces between the cells, forming the tissue fluid.
as the fluid leaves the hydrostatic pressure reduces in the capillaries, so it is lower at the venule end of the capillary bed (the end that is nearest the veins)
the water potential at the venue end of the capillary bed is lower than the water potential in the tissue fluid meaning that some water re-enters the capillaries at the end via osmosis.