Module 3 - OCR A Level Biology

3.1.1 EXCHANGE SURFACES

3.1.1 EXCHANGE SURFACES

Why do multicellular organisms need specialised exchange surfaces but single celled organisms don't?

single celled organisms can exchange materials across their CSM to meet requirements

• metabolic activity low → O2 needs low + CO2 produced is low

• large SA:V ratio

Multicellular organisms are the opposite

• high metabolic rate (active + maintain temp)

• small SA:V ratio

3 main features of an efficient exchange surface

• increased surface area • thin layer • good blood supply/ventilation to maintain gradient

how to calculate surface area to volume ration using a sphere

• calculate SA with 4π²

• calculate volume with 4/3πr³

• ratio = surface area/volume

can see as radius gets bigger the SA:V ration decreases

How does increased SA aid diffusion?

larger SA:V ratio

bigger area for exchange

e.g root hair cells, villi

How do thin layers aid diffusion?

reduces diffusion distance

e.g in alveoli

How does a good blood supply aid diffusion?

Increases concentration gradient

substances constantly delivered and removed

e.g alveoli, gills, villi

human gaseous exchange system diagram

Nasal cavity features

• large SA with good blood supply

• goblet cells secrete mucus to trap dust + bacteria

• moist surface so gases dissolve helping them to pass across the gas exchange surface

trachea structure

• supported by incomplete rings of strong flexible cartilage

• lined with ciliated epithelium which uses synchronised movement to move bacteria out of lungs to throat

• also lined with goblet cells which produce mucus to trap bacteria

• smooth muscle and elastic fibres

Bronchiole structure

• smooth muscle - contracts to constrict airways to control air flow

• elastic fibres

• ciliated epithelium

• goblet cells

alveoli structure

• layer of thin flattened epithelial cells → short diffusion pathway

• elastin + collagen → stretch and recoil

• large surface area

• surrounded by capillaries → good blood supply

• covered in surfactant which speeds up transport of gases + reduces the surface tension of fluid in alveoli

• good ventilation

what happens in the alveoli?

main gas exchange surfaces

what is the purpose of cartilage in the trachea?

prevents it collapsing on itself

diagrams comparing bronchiole and trachea

describe route taken by air as it is inhaled

• through the mouth

• down trachea

• into bronchi

• into bronchioles

• alveoli

What is ventilation?

movement of air into and out of the lungs

what happens during inspiration?

• diaphragm contracts, flattens + lowers

• external intercostal muscles contract so rib cage moves upwards and outwards

• volume of thorax increases so pressure in thorax decreased

• pressure in thorax lower than than atmospheric pressure so air is drawn into lungs

what happens during expiration?

• diaphragm relaxes, moves up into dome shape

• external intercostal muscles relax so rib cage moves downwards and inwards

• volume of thorax decreases so pressure in thorax increased

• pressure in thorax higher than than atmospheric pressure so air moves out of lungs

Is inspiration active or passive?

Active

Is expiration active or passive?

Passive

What does a spirometer measure?

record volumes of air inspired and expired over time

produces a spirograph

spirograph

Tidal volume (TV)

volume of air breathed in, in one breath at rest

around 500cm3

Expiratory reserve volume (ERV)

volume of air that you can force out after a normal tidal expiration

Inspiratory reserve volume (IRV)

volume of air that can be inspired over and above a tidal inspiration

vital capacity (VC)

greatest volume of air you can move into lungs in one breath

VC = IRV + ERV + TV

what is vital capacity affected by

age, sex, exercise, posture

residual volume (RV)

volume of air left in lungs when you have exhaled as hard as possible

keeps alveoli partly inflated

Total lung capacity

vital capacity + residual volume

What is the formula for ventilation rate?

Tidal volume x breathing rate

units = dm3min-1

(breathing rate = breaths per minute)

how to calculate breathing rate

(no. of breaths x 60) ÷ no. of seconds

spirometer trace

calculate gradient (using P and Q on graph)

amount of oxygen consumed/number of seconds

this gives the rate of oxygen consumption measured in dm3 per second

What does air enter and leave an insect through?

Spiracles along insect abdomen

what happens to air after it passes through spiracles?

enters trachea and then tracheoles so O2 is directly delivered to tissues

How is air drawn into trachea?

• insect pumps thorax and abdomen

• these movements change volume of body and pressure in trachea

• air drawn into the trachea or forced out as pressure changes

what does the trachea in insects contain

chitin to strengthen it

What is at the end of the tracheoles in insects?

tracheal fluid

oxygen diffuses faster in air than it does in water so tracheal fluid is a barrier to oxygen diffusion

when insect is active more SA of muscle is exposed so more O2 can diffuse

structure of gills

gills composed of thousands of filaments.

each filament is covered in lamallae

lamallae are thin so diffusion pathway of O2 from water into blood is short and they increase SA

large SA, good blood supply

operculum (bony flap) protects gills

What do fish need to maintain for efficient gas exchange?

Continuous flow of water over the gills

explain process of ventilation in fish

water is constantly pushed over gill filaments for constant supply of O2:

• fish mouth opens, buccal cavity lowered, increases volume of buccal cavity

• pressure now lower in buccal cavity than outside pressure so water flows in

• fish mouth closes, buccal cavity raised, increased pressure pushes water into gill cavity (has lower pressure)

• pressure builds up in gill cavity which forces open the operculum and water is pushed out

*when buccal cavity is lowered has effect of forcing operculum shut

What is counter current flow in fish

• water flowing over gills and blood in gill filaments flow in different directions

• it ensures that all the way across the gill filament, blood constantly meets water with higher O2 conc than it has, maintains diffusion gradient

How do fish slow the movement of water to allow more time for gas exchange?

Tips of adjacent gill filaments overlap

How does a countercurrent exchange system help fish with gas exchange?

Maintains steep concentration gradient

3.1.1 EXCHANGE SURFACES

3.1.1 EXCHANGE SURFACES

3.1.2 TRANSPORT IN ANIMALS

3.1.2 TRANSPORT IN ANIMALS

purpose of transport systems

• supply nutrients + oxygen

• remove waste products

• hormone circulation

• temp maintenance

• immune responses

Why do multi-cellular animals need transport systems?

• metabolic demands high → greater demand for oxygen + waste removal

• SA:V ratio smaller as animals get bigger so diffusion distances bigger

• diffusion pathway increases as size of animal increases → need short diff. pathway to supply cells efficiently

if relied on diffusion would be too slow

Which circulatory system is found in insects?

Open

• pumped straight from heart into body cavity

How it works:

• open body cavity = haemocoel

• insect blood = haemolymph → transports waste + food

• haemocoel = low pressure

• haemocoel has direct contact with tissues + cells → where exchange take place between haemolymph + cells

• haemolymph then returns to the heart

• don't rely on circulatory system to transport O2/CO2

what is a closed circulatory system?

blood confined to blood vessels and has no direct contact with cells

distribution of blood to diff tissues can be adjusted

Which circulatory system is found in fish?

single closed

how it works:

• blood travels only once through the heart for each complete circulation of the body

• O2 poor blood pumped from atrium to ventricle

• O2 poor transported to gill capillaries to get oxidised

• O2 rich blood transported to body capillaries and O2 gets used up

• back to heart (2 chambers)

How can fish so active with an inefficient single closed system?

usually blood returns to heart slowly which limits exchange process → less active

but fish have have countercurrent gaseous system that means they can take up lots of O2

also don't maintain body temp

reduces metabolic demand

Which circulatory system is found in mammals?

double closed

how it works:

• blood is pumped from the right side of heart to the lungs to pick up O2 + unload CO2

• blood flows back through left side of the heart and pumped out to be transported to body tissues

• returns to heart

extra:

• blood travels x2

• 4 chambered heart

Why do blood vessels contain elastin?

• stretch and recoil

• Flexibility

Why do blood vessels contain smooth muscle?

can contract and relax to change lumen size

Why do blood vessels contain collagen?

Structural support for shape

where do arteries take blood?

where do veins take blood?

arteries take oxygenated blood away from the heart

veins take deoxygenated blood to heart

a = away

structure of artery

• endothelium (single layer of squamous epithelium) reduces friction

• elastic fibres + smooth enable them to withstand + maintain high pressure and stretch and recoil

• layer of collagen prevent over-stretching and damage

• small lumen

• no valves

structure of veins

• endothelium (single layer of squamous epithelium) reduces friction

• thin layer of smooth muscle and elastic tissue as no need for stretch and recoil bc low pressure

• thin layer of collagen for strength

• overall thinner walls

• large lumen to reduce resistance to flow

• valves to prevent back-flow

how muscles support blood flow in veins in arms and legs?

when muscles contract they squeeze the veins and force blood up

then the muscles relax and blood is sucked upwards

structure of capillaries

• capillary wall is one cell thick and has gaps (one layer of squamous endothelium)

• this allows for rapid diffusion between blood and tissues bc short diffusion pathway

• small lumen which gives time for exchange

• provide large SA

which vein does NOT carry deoxygenated blood?

Pulmonary vein

(still takes blood into the heart)

Which artery does NOT carry oxygenated blood (apart from umbilical artery)?

Pulmonary artery

(still blood away)

How many red blood cells can fit through a capillary side by side?

1

explain the difference between plasma, tissue fluid and lymph

plasma leaks out of capillaries and becomes tissue fluid

tissue fluid is fluid surrounding cells

fluid in lymphatic system is lymph

not much difference in terms of what consist of

what does plasma contain ?

glucose, amino acids, mineral ions, hormones, plasma proteins (albumin, fibrinogen, globullin)

plasma also transports red blood cells, white blood cells and platelets

functions of blood

it transports:

• O2 to and CO2 from respiring cells

• nitrogenous waste from cells

• hormones

• antibodies + WBCs for immune response

acts as buffer

how does tissue fluid form from plasma?

• as blood flows through the capillaries some plasma passes out (via capillary fenestrations)

• this is tissue fluid

• tissue fluid similar to plasma but doesn't contain large plasma protein molecules

• tissue fluid supplies cells with glucose, aa's etc

• fluid then returns to blood in capillaries with waste products OR into lymph vessels

what is osmotic pressure

tendency of water to move into blood by osmosis

diagram to help envision structure of capillary network

what happens at the arterial end of a capillary

• hydrostatic pressure of blood is high which encourages filtration of fluid through fenestrations

• bc blood has low Ψ water moves into the capillary from tissue fluid due to osmosis

• hydrostatic pressure encouraging fluid out of capillary is higher than osmotic pressure encouraging water into the capillary

• net result is plasma moves out of the blood and into tissue fluid

what happens at the venule end of a capillary

• hydrostatic pressure of blood lower due lots of fluid being lost

• hydrostatic pressure still encourages filtration of fluid out of blood into tissue fluid but force has been reduced

• blood now has very low Ψ as it consists of mainly red blood cells + plasma proteins with little fluid content

• water moves by osmosis into the capillary

• osmotic pressure encouraging water back into capillary greater than hydrostatic pressure encouraging it out

• net result of fluid re-entering the capillary

what is lymph

after plasma becomes tissue fluid, the tissue fluid either re-enters capillaries and becomes plasma again or does not return and drains into lymph capillaries

lymph has less oxygen and nutrients and contains fatty acids

why does lymph have fatty acids?

aborbs fat from villi of the small intestine

where are lymph nodes?

what builds up in them?

lymph nodes are along the lymph vessels

lymphocytes build up in the lymph node when necessary and produce antibodies which are passed into blood

swollen nymph nodes = fighting infection

do lymph vessels have valves?

yes to prevent backflow of lymph

how is lymph transported?

similar to blood in veins

• muscles squeeze lymph nodes which forces liquid to move

• one direction flow (tissues to heart)

• most lymph re-enters blood at subclavian veins

how many oxygen molecules can bind to one haemoglobin

4

one red blood cell contains millions of haemoglobin molecules

what is the reaction of haemoglobin forming oxyhaemoglobin?

Hb + 4O₂ ⇌ Hb(O₂)₄

why does O2 move into erythrocytes in lungs?

• low O2 in lung capillaries when erythrocytes enter

• steep conc gradient between inside erythrocyte and air in alveoli

• O2 moves into erythrocytes and binds with Hb until saturated

why does O2 move out of the erythrocytes in respiring tissues?

• conc of oxygen in cytoplasm of body cells = low

-O2 moves out of erythrocyte down its conc gradient

what is partial pressure of O2 (pO2)?

concentration of O2

What does a typical oxygen dissociation curve look like?

shows the affinity of Hb for oxygen

s-shape

How does an increase in partial pressure of carbon dioxide affect the haemoglobin?

They give up oxygen more easily

what is the effect on increasing carbon dioxide concentration on the oxygen dissociation graph?

Bohr shift occurs

if CO2 concs increase the oxygen dissociation curve moves downwards and to the right

curve starts and finishes at the same point

why is the bohr shift important?

• in repiring tissues with high partial pressure of CO2, Hb gives up O2 more readily

• In lungs where partial pressure of CO2 is relatively low, O2 binds to the Hb molecules easily

Which type of haemoglobin has the highest affinity for oxygen?

Foetal haemoglobin

• foetus dependent on mother for O2

• Oxygenated blood from mother runs close to deoxygenated blood of foetus

• if foetus blood had same affinity for O2 as mother, little O2 would be transferred to foetus

• so foetal Hb has higher affinity for O2 than adult Hb

• O2 is removed from maternal blood

Process: The mothers Hb:

• blood arrives in placenta and the p(O2) is 2-4 KPa

• mothers Hb has low affinity for O2

• Hb releases O2 to placenta readily

The foetal Hb:

• p(O2) in placenta 2-4 KPa

• at this point, foetal Hb still has a high affinity for O2

• foetal Hb will bind to O2 released by mothers Hb across placenta

In humans why does foetal Hb change to adult Hb after birth

if the foetus becomes a mother, O2 would not be able to taken up by their foetus as their affinity for Hb would be the same

What happens to most of the carbon dioxide that diffuses into the blood?

Converted into hydrogen carbonate ions (HCO₃⁻)

what happens to rest of CO2 in blood

• dissolved in plasma

• combined with Hb (carbaminohaemoglobin)

what happens when the HCO₃⁻ ions from CO2 react with water

forms carbonic acid

needs the enzyme carbonic anhydrase (in red blood cells)

How does Hb act as a buffer?

Some of the carbonic acid dissociates and releases H+ ions

Hb is able to bind H+, removing it from solution to keep pH constant

H+ and Hb = haemoglobinic acid

When hydrogen carbonate ions leave erythrocytes, what occurs?

hydrogen carbonate ions leave erythrocytes down conc gradient

Cl- ions move in = chloride shift

Why do erythrocytes need to remove the CO2?

• by converting it to HCO₃⁻ ions the erythrocytes maintain a steep conc gradient for CO2 to diffuse from tissues into erythrocytes

What happens when blood reaches lungs and lung tissue has a low conc of CO2?

• carbonic anhydrase catalyses reverse reaction, turning carbonic acid into CO2 + water

• HCO₃⁻ ions diffuse back into the erythrocytes to form more carbonic acid

• when all the carbonic acid is broken down it releases free CO2

• free CO2 diffuses out of blood into lungs

• Cl- ions diffuse out of erythrocytes

What's the term for the inner dividing wall of the heart?

Septum

internal heart diagram

mitral valve = bicuspid valve

external heart diagram

Why does the left ventricle have a thicker wall?

because it pumps blood at a higher pressure and to the whole body

also right side of the heart only has to pump short distance to lungs

what supplies the heart with oxygenated blood

coronary arteries