3B Exchange and Transport

AQA A Level Biology

digestion

the process in which large insoluble molecules are hydrolysed into smaller soluble molecules which can be absorbed and used by the body

mechanical digestion

food is physically broken down into smaller pieces by the teeth or muscle contraction to increase the total surface area, enabling rapid chemical digestion

amylase

carbohydrase produced by salivary glands and pancreas that hydrolyses alternate glycosidic bonds to produce maltose in the mouth and small intestine

maltase

carbohydrase produced by the small intestine that hydrolyses maltose into alpha glucose in the small intestine

lipase

enzyme produced by the pancreas that hydrolyses ester bonds in triglycerides to produce fatty acids and a monoglyceride in the small intestine

endopeptidase

enzyme produced in the stomach and pancreas that hydrolyses internal peptide bonds in a protein in the stomach and small intestine

exopeptidase

enzyme produced in the pancreas that hydrolyses peptide bonds in terminal amino acids to produce dipeptides in the small intestine

dipeptidase

enzyme produced in the small intestine that hydrolyses peptide bonds in dipeptides to produce single amino acids in the small intestine

adaptations of ileum cells

microvilli increase surface area, many mitochondria, many carrier and channel proteins for facilitated diffusion, many carrier proteins for active transport

transport of amino acids into ileum cells

1. amino acids are co-transported with sodium ions down sodium concentration gradient into cell

2. sodium is actively transported out of the cell via sodium pump

3. amino acids diffuse into bloodstream down their concentration gradient

bile function

emulsifies fats into smaller droplets to increase the total surface area → more enzyme-substrate complexes, neutralises stomach acid to prevent ionic and hydrogen bonds in tertiary structure being broken → stops enzymes denaturing

micelle

a temporary compound formed from monoglycerides and fatty acids associated with phospholipids and bile salts

process of fat absorption in ileum cells

1. micelle releases fatty acids and monoglycerides which diffuse across cell membrane

2. triglycerides are reformed in the SER

3. Golgi produces chylomicrons from triglycerides and lipoproteins by forming a vesicle

4. chylomicrons leave cell by exocytosis

5. chylomicrons are absorbed into the lacteals in the capillaries

tissue fluid

solution of water and small soluble molecules from the blood that diffuses out of capillaries into gaps between cells

ultrafiltration

process in which small soluble molecules are forced out of capillaries due to hydrostatic pressure to form tissue fluid

movement of tissue fluid at arterial end of capillary

high hydrostatic pressure causes molecules to diffuse out of capillary

movement of tissue fluid at venous end of capillary

proteins remain in capillary which causes a low water potential which causes water to diffuse back into the capillary by osmosis down a water potential gradient

substances found in tissue fluid

fatty acids, hormones, minerals

substances that can’t pass into tissue fluid

red blood cells, platelets, white blood cells, proteins

oedema

swelling caused by an accumulation of tissue fluid

causes of oedema

increased blood pressure, damaged capillaries - increased tissue protein concentration, malnutrition - decreased blood protein concentration, obstruction of lymph vessels

coronary arteries

network of blood vessels that supply the cardiac muscle with oxygenated blood

why left side of heart is thicker

thicker cardiac muscle wall in order to contract more forcefully to produce a higher pressure needed to pump blood around the whole body

capillaries

site of exchange of substances between blood and tissues

septum

tissue between left and right side of heart that prevents deoxygenated and oxygenated blood from mixing

atrioventricular valve

valve between atria and ventricles that prevents backflow of blood by opening when pressure behind them is greater than infront

semi-lunar valve

valve between arteries and ventricles that prevents backflow of blood

features of arteries

thick muscle layer to generate force for a high pressure, elastic layer that recoils to withstand pressure changes, narrow lumen to maintain high pressure, smooth endothelium which reduces friction so no blood gathers to prevent blood clots, thick collagen wall for structural support

features of veins

wide lumen to lower resistance of blood, smooth endothelium to reduce friction so less blood clots, thin muscle layer to control blood flow, valves to prevent backflow of blood

features of capillaries

small lumen and thin walls to provide short diffusion distance, smooth endothelium to reduce friction for less blood clots, spaces between lining so white blood cells can leave, narrow lumen maximises diffusion as cells pass through slowly, highly branched to maximise surface area

myogenic heart tissue

it beats by itself as it generates its own electrical impulses

diastole

relaxation of heart

systole

contraction of heart

diastole process

atria and ventricles are relaxed so atria fill with blood

atrial systole process

atria contract so atrial pressure increases, atrioventricular valves open and blood flows into the ventricles

ventricular systole process

ventricles contract so ventricular pressure increases, atrioventricular valves close and semi-lunar valves open and blood flows into the arteries

cardiac output

volume of blood leaving the heart per minute

cardiac output equation

stroke volume x heart rate

stroke volume

volume of blood pumped out of the left ventricle per beat

heart rate

number of heart beats per minute

red blood cell adaptations

biconcave shape so larger surface area, no organelles to carry more haemoglobin, flexible so can fit through narrow capillaries

oxyhaemoglobin

haemoglobin bound to oxygen/ saturated

haemoglobin

haemoglobin not bound to oxygen/ unsaturated

structure of haemoglobin

globular protein, alpha helix secondary structure, tertiary structure caused by hydrogen and ionic bonds between R groups in amino acids, quaternary structure of 4 polypeptide chains each including a haem group contains a ferrous ion

partial pressure

pressure exerted by a specific gas within a mixture of gases

1st oxygen associating with haemoglobin

difficult because all haem groups are in the middle of the molecule so harder to reach

2nd and 3rd oxygen associating with haemoglobin

haemoglobin changes shape causing haem groups to be more exposed making it easier for oxygen to bind to

4th oxygen associating with haemoglobin

harder because there is only 1 remaining haem group to bind to so less chance of collision

transpiration

evaporation of water through aerial parts of a plant

transpiration stream

movement of water through a plant

factors affecting transpiration

light - more stomata open, temperature - particles have more energy so more evaporation, wind - maintains a high water potential gradient, humidity, maintains a low water potential gradient

xylem formation

xylem vessel elements join together and waterproof themselves with lignin causing them to die, the endplates die and this process moves up the vessel to form a continuous tube with no end walls between cells

features of xylem vessel

thick walls stiffened with lignin, no end walls between cells, one-way only, negative tension forces water up, lignin prevents top collapsing

movement of water up xylem

moves in 1 continuous column held together by hydrogen bonds forming cohesion because of negative tension created by xylem

features of phloem

transports assimilates, made of sieve tube elements with perforated sieve plates between them, supported by companion cells that help with loading and unloading, movement of sap is mediated by hydrostatic pressure from xylem

sink

part of a plant that removes assimilates (actively growing)

features of a sieve tube element

no/few organelles, very little cytoplasm and hollow with a large vacuole to make space for assimilates to diffuse across, thick walls to resist pressure

features of a companion cell

lots of mitochondria for active transport

plasmodesmata

gap between cells

loading of sucrose into phloem process

1. sucrose is made in the source and diffuses down the concentration gradient via facilitated diffusion into the companion cells

2. H+ ions are actively transported from the companion cells into spaces within the cell walls

3. H+ ions diffuse through carrier proteins into the sieve tube elements

4. sucrose molecules are co-transported with the H+ ions into the sieve tube elements

mass flow of sucrose through phloem process

1. sucrose moves into sieve tube elements, decreasing their water potential

2. water moves into the sieve tube elements from the xylem via osmosis which increases the hydrostatic pressure inside the sieve tube

3. at the sink sucrose is used for respiration and sucrose is actively transported from the sieve tube element to replace it which lowers the water potential in the sink

4. water moves into the sink from sieve tube via osmosis which decreases hydrostatic pressure in sieve tube element

5. this creates a pressure gradient causing water to move from source to sink taking sucrose with it

effect of negative tension on trunk diameter

as negative tension increases, diameter decreases due to adhesion between water molecules and xylem walls as fewer water molecules are present

how to use a potometer

1. cut shoot at a slant under water to increase SA and stop air entering xylem

2. check apparatus is full of water and air bubble free

3. insert shoot into apparatus underwater

4. dry leaves of shoot

5. leave for shoot to acclimatise

6. record time taken for bubble to move a certain distance and calculate rate

7. repeat and calculate a mean

8. keep environmental conditions constant

volume of water uptake

area of tube cross section x distance moved

arteriole during exercise

smooth muscle relaxes and vasodilation occurs allowing more blood to flow to muscles

what happens to pyruvate when oxygen is available?

it’s transported to the mitochondrial matrix via active transport and is oxidised to form NADH and H+