3.3 Exchange and Transport

Question 1

What is digestion?

Answer 1

Larger biological molecules hydrolysed to smaller molecules that can be absorbed across cell membranes

Question 2

How are carbohydrates digested?

Answer 2

•pancreatic and salivary gland amylase will hydrolyse starch into maltose
•membrane bound disaccharidases in ileum epithelial cells hydrolyse maltose into glucose (co-transport with Na+)

Question 3

How are proteins digested?

Answer 3

•endopeptidases: hydrolyse peptide bonds between aa in middle of polypeptide chain (smaller peptide chains)
•exopeptidases: hydrolyse peptide bonds between aa at the end of a polypeptide chain (remove terminal aa)
•membrane bound dipeptidases: hydrolyse peptide bonds between 2 aa (dipeptides to aa)

Question 4

How are lipids digested?

Answer 4

•bile salts emulsify lipids into smaller droplets- increase SA for faster hydrolysis action by lipase
•micelles form from bile salts, monoglycerides, glycerol=make them more soluble and they are absorbed by diffusion.

•inside cell: modified back into triglycerides by Golgi body and ER
•vesicle moves to cell surface membrane to be released by exocytosis

Question 5

What is a chylomicron?

Answer 5

In the Golgi body, (modified) protein is added to the lipids and it is packed in a vesicle and released by exocytosis

Question 6

Why are micelles important?

Answer 6

•micelles form from bile salts, monoglycerides, glycerol and fatty acids
•micelles make fatty acids more water soluble
•micelles carry fatty acids to epithelial cells of ileum
=fatty acids released from micelles are absorbed into cell by simple diffusion

Question 7

What do very small organisms use for gas exchange compared to larger organism?

Answer 7

•small: have a very large SA:V + small distances so can do simple diffusion
•large: smaller SA:V + larger distances + higher metabolic rates so gas exchange systems

Question 8

What is a consequence of a larger SA:V for small organism?

Answer 8

Lose heat more quickly so to compensate they have a higher metabolic rate. More Respiration so more heat energy to maintain temp.

Question 9

How do terrestrial insects have an efficient gas exchange system?

Answer 9

1. Large no. of tracheoles branching to each cell (large SA for rapid diffusion and short diffusion distance)
   2.thin tracheal walls (short diffusion distance)
   3.use of O2 and making of CO2 sets up steep conc. gradient

Question 10

How do terrestrial insects minimise water loss?

Answer 10

1.have small SA:V less surfaces for evaporation
2.waterproof exoskeleton so less evaporation
3.spiracle valves close

Question 11

What are the methods of gas exchange in terrestrial insects?

Answer 11

1. Diffusion: conc. gradient when respiring

2.mass transport: abdominal muscles relax and contract to move gases on mass, so more air/O2 enters to maintain conc. gradient

3.anaerobic respiration: lactic acid lowers water potential of muscle cells so they gain water by osmosis from tracheoles=
•tracheole volume decreases so more air drawn in
•gases move faster in air than H2O
•greater SA exposed to air

Question 12

How are insects able to obtain oxygen?

Answer 12

1.air enters through spiracles
2.travels down tracheae
3.diffusion gradient in tracheae as oxygen is used in respiration
4.tracheae associated with all cells (branching)
5.O2 diffuses into cells
6.ventilation replaces air in tracheae

Question 13

What makes gas exchange in fish efficient?

Answer 13

•large SA:V=lots of gill filaments with lots of gill lamellae
•short diffusion distance=capillary network in every lamellae + very thin lamellae
•maintain conc. gradient=countercurrent flow, ventilation (fresh water), capillaries (good blood circulation)

Question 14

What is the countercurrent flow in fish?

Answer 14

1.blood + water flow in opposite directions (blood always meets H20 with a higher O2 conc.)

2.equilibrium is not reached

3.diffusion gradient is maintained across the entire length of gill lamellae

Question 15

What are the steps in inspiration?

Answer 15

1.external intercostal muscle contract
2. Diaphragm muscle contracts and flattens
3.Ribcage moves upwards + outwards
4. Volume of thoracic cavity increases
5.Pressure in thoracic cavity decreases
6.air moves into the lungs, down the pressure gradient

Question 16

What are the steps in expiration?

Answer 16

1.internal intercostal muscles contract
2.Diaphragm muscle relaxes and domes
3. Ribcage moves downwards + inwards
4.Volume of thoracic cavity decreases
5. Pressure of thoracic cavity increases
6. Air is drawn out of the lungs, down pressure gradient

Question 17

What features of the alveolar epithelium make it an efficient exchange surface? (+lungs?)

Answer 17

•single layer of cells - short diffusion distance
•each surrounded by a network of capillaries - steep conc. gradient
•many- large SA for rapid diffusion
•permeable- allows diffusion of O2/CO2

Lungs:
•ventilation brings in air with higher O2 conc. and removed air with lower O2 conc. (conc. gradient of O2 maintained)
•good circulation of blood

Question 18

What is the pathway taken by O2 from air to blood?

Answer 18

1. Trachea, bronchi, bronchioles
2. Down pressure gradient
3. Down diffusion gradient
4. Across alveolar epithelium
5. Across capillary endothelium

Question 19

How is pulmonary ventilation calculated?

Answer 19

PV= tidal volume * ventilation rate
Tidal volume:vol of air enters+leaves at normal resting breath (0.5dm3)
Ventilation rate:breaths per minute

Question 20

What are adaptations of xerophytic plants to reduce water loss?

Answer 20

•sunken stoma with hairs traps water vapor and increases humidity to lower water potential gradient
•curled leaves to protect from wind
•reduced no. of open stomata
•thick waxy cuticle to reduce evaporation

Question 21

How are plants adapted for efficient gas exchange?

Answer 21

•short diffusion distance: thin leaves
•steep diffusion gradient: palisade use up CO2 for photosynthesis
•large SA: spongy mesophyll has lots of air space

Question 22

How could you find the surface area of a leaf?

Answer 22

1.draw around leaf on graph paper
2.count squares
3.multiply by 2 (2 sided)

Question 23

Why might the rate of H2O uptake not be the same as the rate of transpiration by a plant?

Answer 23

Water used in photosynthesis , hydrolysis, for turgid, made in respiration

Question 24

What is the structure of haemoglobin?

Answer 24

•quaternary protein= 4 polypeptide chains (more than 1)
•each chain has haem group (Fe2+) which binds to O2 to become oxyhaemoglobin

Question 25

Explain a oxyheamoglobin dissociation curve

Answer 25

•Low PO2 = low affinity = O2 unloaded for respiration •High PO2 = high affinity = O2 loaded in e.g alveoli

Question 26

What is cooperative binding?

Answer 26

When 1st O2 binds, haemoglobin changes shape (changes quaternary structure of hb) and it is easier for further O2 to bind as it uncovers more haem group binding sites.

Question 27

What is the Bohr effect?

Answer 27

•High PCO2 will decrease affinity for O2 as acidic CO2 (Ph) will change the shape of haemoglobin so more oxygen is unloaded. •High PCO2 will shift oxyhaemoglobin curve to the right Right= release Left= load

Question 28

When will oxyhaemoglobin curve shift to the left? (E.g)

Answer 28

•higher affinity for O2 E.g •high altitudes + underground have lower PO2 so higher affinity of O2 needed to load more o2

Question 29

When will oxyhaemoglobin curve shift to the right? (E.g)

Answer 29

•lower affinity for O2 E.g •faster metabolism so need more O2 for more respiration so more ATP/heat energy for more muscle contraction or to maintain body temp. So have lower O2 affinity to unload more O2 in respiring cells

Question 30

What do the coronary arteries do?

Answer 30

Supply oxygenated blood and glucose to cardiac muscles to respire and release ATP energy for contractions

Question 31

What is the pathway of blood circulation?

Answer 31

Vena cava, right atrium/ventricle, pulmonary artery to lungs, pulmonary vein, left atrium/ventricle, aorta to body

Question 32

What are valves and what types are there?

Answer 32

Valves prevent back flow of blood as they only open when pressure is higher behind. •atrioventricular valves between atrium and ventricles •semi lunar valves between ventricle and aorta/pulmonary artery

Question 33

What is a septum and why is it helpful?

Answer 33

It separates oxygenated and deoxygenated blood which will maintain a high concentration gradient of oxygen

Question 34

Why is a double circulatory system useful?

Answer 34

•blood flows to the *lungs* at a lower pressure to prevent damage to capillaries in alveoli + reduces speed of blood flow to give time for gas exchange •blood flows to *body* at higher pressure to ensure it reaches all respiring cells

Question 35

What are the blood vessels in lungs and kidneys?

Answer 35

Lungs: pulmonary artery/vein Kidney: renal vein (out)/ renal artery (in)

Question 36

Why are arterioles different to arteries?

Answer 36

•thicker muscle layer to help restrict blood flow into capillaries •thinner elastic layer as lower pressures •muscle contracts + relaxes and lumen narrows to reduce blood flow into capillary

Question 37

What is the structure of the artery and why?

Answer 37

•thicker muscle layer to allow constriction/dilation to control blood volume •thicker elastic muscle layer to maintain blood pressure. The walls can stretch and recoil in response to a heart beat •thicker wall to prevent it bursting at high pressure

Question 38

What is the structure of the vein and why?

Answer 38

•thin muscle/elastic layer as pressures are much lower, so low risks of bursting •valves to prevent back-flow of blood

Question 39

What is the structure and function of capillaries?

Answer 39

•form capillary beds as exchange surfaces= narrow diameter to slow blood flow and maximise diffusion of O2 from RBC •one cell thick= short diffusion distances

Question 40

How is tissue fluid formed?

Answer 40

1.blood enters capillaries from arterioles. As is enters a small diameter, there is high hydrostatic pressure which is higher than osmotic effect (increase in outward pressure) due to contraction from left ventricle so H2O and small molecules forced 2.large plasma proteins too big to leave capillary and lower the water potential + hydrostatic pressure at venule end (in the blood) is very low so water re-enters capillary by osmosis

Question 41

What happens to excess tissue fluid and why?

Answer 41

•Not all liquids can be reabsorbed by osmosis as equilibrium is reached •rest of the tissue fluid is absorbed into the lymphatic vessel/capillaries and will drain back into the bloodstream near the heart

Question 42

How is one way blood flow maintained in the heart? (Route)

Answer 42

1. Diastole: atria and ventricular muscles relax so blood enters the atria (pressure increases) 2.atrial systole: atria muscle walls contract (++pressure), so AV valve opens and blood flows into ventricles (ventricular diastole) 3. Ventricular systole: after short delay, ventricle muscle walls *contract* and its pressure is higher that in atria so AV valve closed and semi lunar valves will open to allow blood to be pushed out of ventricles to arteries 4.semi lunar valves will close when the pressure in the arteries is higher than in the ventricles

Question 43

How is a heartbeat initiated and coordinated?

Answer 43

1.sino atrial node (SAN) will send wave of electrical excitation across atria, atrial contraction happens 2.layer of non-conducting tissue prevents immediate contraction of ventricles , as impulse doesn’t reach it 3.atrioventricular node (AVN) delays impulses whilst blood leaves atria 4. AVN sends wave of electrical excitation down Bundle of His (into purkyne fibres) 5.this causes ventricles to contract from base up

Question 44

Why is there a short delay of electrical activity after SAN?

Answer 44

It allows atria to be fully empty of blood and the ventricles fully full before the ventricles contract

Question 45

Why are electrical impulses passed to the base of the ventricles?

Answer 45

So that ventricles contract from base upwards, which makes sure all the blood can be pushed out of the ventricles and into the arteries (aorta or pulmonary artery)

Question 46

How is cardiac output measured?

Answer 46

Stroke volume x heart rate (dm3) (bpm) Cardiac output (dm3/min) amount of blood pumped by the left ventricle in one minute

Question 47

What is the structure of the xylem?

Answer 47

•waterproof lignin to withstand tension •no organelles to allow easy flow of water •no end walls to allow continuous water columns •pits in walls to allow lateral movement

Question 48

Describe the cohesion-tension theory of transpiration

Answer 48

1.water evaporates in the leaf via stomata 2.water potential gradient across cells of the leaf produced 3.this causes water to be drawn out of the xylem and creates tension in the xylem 4.hydrogen bonds cause a cohesive force between molecules so water gets pulled up the xylem as a continuous column

Question 49

Why are there larger fluctuations in blood pressure in the aorta that the small arteries?

Answer 49

1.aorta is close to the heart 2.it has elastic tissue 3.it has stretch/recoil

Question 50

How is directional flow of blood maintained?

Answer 50

1.valves stop backflow of blood 2.pressure gradient/moves from high to low pressure

Question 51

What affects rate of transpiration?

Answer 51

1.light intensity as + so more stomata open 2.humidity as + water potential gradient reduced 3.wind as + water potential gradient maintained 3.temperature as + more evaporation

Question 52

What is the structure of the phloem?

Answer 52

•cellulose cell wall-resist high pressure in sieve tubes •sieve plates-provide structural strength but pores allow flow of sap •plasmodesmata-connects sieve tube elements and companion cells •companion cells-provide metabolic support •few organelles-hollow to let sap through

Question 53

What is the mass flow hypothesis? (Translocation)

Answer 53

1.in source cell, companion cells use active transport to load sucrose into the sieve tube elements 2.water potential of sieve tube is reduced 3.water moves into the tubes from the xylem by osmosis, causing a high hydrostatic pressure 4.in the sink cell, sucrose is unloaded from the sieve tubes using active transport 5.water potential is increased in the tubes 6.water moves back into the xylem by osmosis, reducing the hydrostatic pressure (Sucrose will move down its pressure gradient from source to sink) *sugars used/converted in root for respiration/storage

Question 54

Why does diameter decrease when transpiration increases?

Answer 54

Increase in transpiration produces a higher tension in the xylem. There is adhesive forces between xylem and water and this will pull the walls inward

Question 55

How can we prove that the phloem is the site of translocation?

Answer 55

•radioactively labelling carbon which can traced to show that sugars are transported in the phloem in the stem •ringing- ring of phloem removed and it swells above due to sugar build up (test it) as no phloem to transport it •aphids will penetrate into phloem, we cut its stylet and test the sap flowing out

Question 56

What is the advantage of giving data as %?

Answer 56

•allows comparison •as different initial no. /value

Question 57

Why does uptake of CO2 fall to zero when light is turned off?

Answer 57

1.no use of CO2 in photosynthesis when no light 2.no diffusion gradient for CO2 into the leaf

Question 58

Why are veins weak/damaged often in legs/feets?

Answer 58

1. Far from the heart 2. Blood must travel against gravity to reach the heart 3.weak valves means blood travels backwards/accumulates in veins

Question 59

Why is sucrose transported rather than glucose?

Answer 59

•sucrose can enter and exit via transport proteins •sucrose is less likely to be used in respiration