Topic 3

How to work outSurface area to volume ratio and how does an organisms size affect it?

* The surface area of an organism divided by its volume
* the larger the organism, the smaller the ratio

Factors affecting gas exchange:

* diffusion distance
* surface area
* concentration gradient
* temperature

What is Ventilation?

* Inhaling and exhaling in humans
* controlled by diaphragm and antagonistic interaction of internal and external intercostal muscles

What is Inspiration?

* External intercostal muscles contract and internal relax
* pushing ribs up and out diaphragm contracts and flattens
* air pressure in lungs drops below atmospheric pressure as lung volume increases
* air moves in down pressure gradient

What is Expiration?

* External intercostal muscles relax and internal contract
* pulling ribs down and in
* diaphragm relaxes and domes
* air pressure in lungs increases above atmospheric pressure as lung volume decreases
* air forced out down pressure gradient

Describe the Passage of gas exchange:

* Mouth / nose → trachea → bronchi → bronchioles → alveoli
* crosses alveolar epithelium into capillary endothelium

Describe Alveoli’s structure:

* Tiny air sacs
* highly abundant in each lung - 300 million
* surrounded by the capillary network
* epithelium 1 cell thick

Why do large organisms need specialised exchange surface?

* They have a small surface area to volume ratio
* higher metabolic rate - demands efficient gas exchange
* specialised organs e.g. lungs / gills designed for exchange

Describe the Fish gill anatomy:

* Fish gills are stacks of gill filaments
* each filament is covered with gill lamellae at right angles

How does fish gas exchange surface provide a large surface area?

* Many gill filaments covered in many gill lamellae are positioned at right angles
* creates a large surface area for efficient diffusion

Describe the Countercurrent flow:

* When water flows over gills in opposite direction to flow of blood in capillaries
* equilibrium not reached
* diffusion gradient maintained across entire length of gill lamellae

Name the three structures in the tracheal system:

Involves trachea, tracheoles, spiracles

How does the tracheal system provide a large surface area?

* Highly branched tracheoles
* large number of tracheoles
* filled in ends of tracheoles moves into tissues during exercise
* so larger surface area for gas exchange

What is the purpose of Fluid-filled tracheole ends?

* Adaptation to increase movement of gases
* when insect flies and muscles respire anaerobically - lactate produced
* water potential of cells lowered, so water moves from tracholes to cells by osmosis
* gases diffuse faster in air

How do insects limit water loss?

* Small surface area to volume ratio
* waterproof exoskeleton
* spiracles can open and close to reduce water loss
* thick waxy cuticle - increases diffusion distance so less evaporation

What are the Dicotyledonous plants leaf tissues?

Key structures involved are mesophyll layers
(palisade and spongy mesophyll)
stomata created by guard cells

Describe the Gas exchange in plants?

* Palisade mesophyll is site of photosynthesis
* oxygen produced and carbon dioxide used creates a concentration gradient
* oxygen diffuses through air space in spongy mesophyll and diffuse out stomata

What is the Role of guard cells?

* swell - open stomata
* shrink - closed stomata
* at night they shrink, reducing water loss by evaporation

What are Xerophytic plants?

* Plants adapted to survive in dry environments with limited water (e.g. marram grass/cacti)
* structural features for efficient gas exchange but limiting water loss

What are the Adaptations of xerophyte?

* Adaptations to trap moisture to increase humidity -> lowers water potential inside plant so less water lost via osmosis
* sunken stomata
* curled leaves
* hairs
* thick cuticle reduces loss by evaporation
* longer root network

What is Digestion?

* Process where large insoluble biological molecules are hydrolysed into smaller soluble molecules
* so they can be absorbed across cell membranes

What are the Locations of carbohydrate digestion?

Mouth → duodenum → ileum

What are the Locations of protein digestion?

Stomach → duodenum → ileum

What is the role of Endopeptidases?

* Break peptide bonds between amino acids in the middle of the chain
* creates more ends for exopeptidases for efficient hydrolysis

What is the role of Exopeptidases?

Break peptide bonds between amino acids at the ends of polymer chain

What is the role of Membrane- bound dipeptidases?

Break peptide bond between two amino acids

Describe the Digestion of lipids:

* Digestion by lipase (chemical)
* emulsified by bile salts (physical)
* lipase produced in pancreas
* bile salts produced in liver and stored in gall bladder

What is the use of Lipase and where is it produced?

* Produced in pancreas
* Breaks ester bonds in triglycerides to form :
* monoglycerides
* glycerol
* fatty acids

What is the Role of bile salts?

* Emulsify lipids to form tiny droplets and micelles
* increases surface area for lipase action - faster hydrolysis

What are Micelles?

Water soluble vesicles formed from fatty acids, glycerol, monoglycerides and bile salts

Describe the process of Lipid absorption:

* Micelles deliver fatty acids, glycerol and monoglycerides to epithelial cells of ileum for absorption
* cross via simple diffusion as lipid-soluble and non-polar

What is Lipid modification?

* Smooth ER reforms monoglycerides / fatty acids into tryglycerides
* golgi apparatus combines tryglycerides with proteins to form vesicles called chylomicrons

How do lipids enter blood after modification?

* Chylomicrons move out of cell via exocytosis and enter lacteal
* lymphatic vessels carry chylomicrons and deposit them in bloodstream

How are glucose and amino acids absorbed?

Via co-transport in the ileum

Describe the structure of Haemoglobin (Hb) and its role:

* Quaternary structure protein
* 2 alpha chains
* 2 beta chains
* 4 associated haem groups in each chain containing Fe2+
* transports oxygen

Affinity of haemoglobin

The ability of haemoglobin to attract / bind to oxygen

Saturation of haemoglobin

When haemoglobin is holding the maximum amount of oxygen it can hold

Loading / unloading of haemoglobin

* Binding/detachment of oxygen to haemoglobin
* also known as association and disassociation

Oxyhaemoglobin dissociation curve

* oxygen is loaded in regions with high partial pressures (alveoli)
* unloaded in regions of low partial pressure (respiring tissue)

Oxyhaemoglobin dissociation curve shifting left

Hb would have a higher affinity for oxygen
load more at the same partial pressure
becomes more saturated adaptation in low-oxygen environments
e.g. llamas/ in foetuses

Cooperative binding

* Hb's affinity for oxygen increases as more oxygen molecules are associated with it
* when one binds, Hb changes shape meaning others bind more easily
* explaining S shape of curve

How carbon dioxide affects haemoglobin

* When carbon dioxide dissolves in liquid, carbonic acid forms
* decreases pH causing Hb to change shape
* affinity decreases at respiring tissues
* more oxygen is unloaded

Bohr effect

* High carbon dioxide partial pressure
* causes oxyhaemoglobin curve to shift to the right

Oxyhaemoglobin dissociation curve shifting right

* Hb has lower affinity for oxygen
* unloads more at the same partial pressures
* less saturated
* present in animals with faster metabolisms that need more oxygen for respiration
* e.g. birds/rodents

Closed circulatory
system

Blood remains within blood vessels

Name different types of blood vessels

Arteries, arterioles, capillaries, venules and veins

Structure of arteries

* Thick muscular layer
* thick elastic layer
* thick outer layer
* small luman
* no valves

Capillary endothelium

* Extremely thin
* one cell thick
* contains small gaps for small molecules to pass through (e.g. glucose, oxygen)

Capillaries

* Form capillary beds
* narrow diameter (1 cell thick) to slow blood flow
* red blood cells squashed against walls shortens diffusion pathway
* small gaps for liquid / small molecules to be forced out

Arterioles

* Branch off arteries
* thickest muscle layer to restrict blood flow
* thinner elastic layer and outer layer than arteries as pressure lower

Tissue fluid

* Liquid bathing all cells
* contains water, glucose, amino acids, fatty acids, ions and oxygen
* enables delivery of useful molecules to cells and removal of waste

Tissue fluid formation

* At arteriole end, the smaller diameter results in high hydrostatic pressure
* small molecules forced out (ultrafiltration)
* red blood cells / large proteins too big to fit through capillary gaps so remain

Reabsorption of tissue fluid

* Large molecules remaining in capillary lower its water potential
* towards venule end there is lower hydrostatic pressure due to loss of liquid
* water reabsorbed back into capillaries by osmosis

Role of the lymph in tissue fluid reabsorption

* Not all liquid will be reabsorbed by osmosis as equilibrium will be reached
* excess tissue fluid (lymph) is absorbed into lymphatic system and drains back into bloodstream and deposited near heart

Cardiac muscle

* Walls of heart having thick muscular layer
* unique because it is:
* myogenic - can contract and relax without nervous or hormonal stimulation
* never fatigues so long as adequate oxygen supply

Coronary arteries

* Blood vessels supplying cardiac muscle with oxygenated blood
* branch off from aorta
* if blocked, cardiac muscle will not be able to respire, leading to myocardial infarction (heart attack)

Structure of the heart

Adaptation of left ventricle

* Has a thick muscular wall in comparison to right ventricle
* enables larger contractions of muscle to create higher pressure
* ensures blood reaches all body cells

Veins connect to the heart

* Vena cava - carries deoxygenated blood from body to right atrium
* Pulmonary vein - carries oxygenated blood from lungs to left atrium

Arteries connected to the heart

* Pulmonary artery - carries deoxygenated blood from right ventricle to lungs
* Aorta - carries oxygenated blood from left ventricle to rest of the body

Valves within the heart

* Ensure unidirectional blood flow
* semilunar valves are located in aorta and pulmonary artery near the ventricles
* atrioventricular valves between atria and ventricles

Opening and closing of valves

* Valves open if the pressure is higher behind them compared to in front of them.
* AV valves open when pressure in atria > pressure in ventricles
* SL valves open when pressure in ventricles > pressure in arteries

The Septum

* Muscle that runs down the middle of the heart
* separates oxygenated and deoxygenated blood
* maintains high concentration of oxygen in oxygenated blood
* maintaining concentration gradient to enable diffusion to respiring cells

Cardiac output

* Volume of blood which leaves one ventricle in one minute.
* heart rate = beats per minute
* Cardiac output = heart rate\* stroke volume

Stroke volume

* Volume of blood that leaves the heart each beat
* measured in dm^3

Cardiac cycle

Consists of diastole, atrial systole and ventricular systole

Diastole

* Atria and ventricular muscles are relaxed
* when blood enters atria via vena cava and pulmonary vein
* increasing pressure in atria

Atrial systole

* Atria muscular walls contract, increasing pressure further.
* pressure atria > pressure ventricles
* atrioventricular valves open and blood flows into ventricles
* ventricular muscle relaxed

Ventricular systole

* After a short delay (so ventricles fill), ventricular muscular walls contract
* pressure ventricle > atria pressure and artery pressure
* atrioventricular valves close and semi-lunar valves open
* blood pushed into artery

Transpiration

* Loss of water vapour from stomata by evaporation
* affected by:
* light intensity
* temperature
* humidity
* wind
* can be measured in a lab using a potometer

How light intensity affects transpiration

* As light intensity increases, rate of transpiration increases
* more light means more stomata open
* larger surface area for evaporation

How temperature affects transpiration

* As temperature increases, rate of transpiration increases
* the more heat there is, the more kinetic energy molecules have
* faster moving molecules increases evaporation

How humidity affects transpiration

* As humidity increases, transpiration decreases
* the more water vapour in the air, the greater the water potential outside the leaf
* reduces water potential gradient and evaporation

How wind affects transpiration

* As wind increases, rate of transpiration increases
* the more air movement, the more humid areas are blown away
* maintains water potential gradient, increasing evaporation

Cohesion in plant transport

* Because of the dipolar nature of water, hydrogen bonds can form - cohesion
* water can travel up xylem as a continuous column

Adhesion in plant transport

* Water can stick to other molecules (xylem walls) by forming H-bonds
* helps hold water column up against gravity

Root pressure in plant transport

* As water moves into roots by osmosis, the volume of liquid inside the root increases
* therefore the pressure inside the root increases
* this forces water upwards

Cohesion- tension theory

* As water evaporates out the stomata, this lowers pressure
* water is pulled up xylem (due to negative pressure)
* cohesive water molecules creates a column of water
* water molecules adhere to walls of xylem pulling it upwards
* this column creates tension, pulling xylem inwards

Translocation

* Occurs in phloem
* explained by mass flow hypothesis
* transport of organic substances through plant

Sieve tube elements

* Living cells
* contain no nucleus
* few organelles
* this makes cell hollow
* allowing reduced resistance to flow of sugars

Companion cell

* Provide ATP required for active transport of organic substances
* contains many mitochondria

Mass flow hypothesis

* Organic substances, sucrose, move in solution from leaves (after photosynthesis) to respiring cells
* source -> sink direction

How is pressure generated for translocation

* Photosynthesising cells produce glucose which diffuses into companion cell
* companion cell actively transports glucose into phloem
* this lowers water potential of phloem so water moves in from xylem via osmosis
* hydrostatic pressure gradient generated

What happens to sucrose after translocation?

* Used in respiration at the sink
* stored as insoluble starch

Investigating translocation

* Can be investigated using tracer and ringing experiments
* proves phloem transports sugars not xylem

Tracing

* Involves radioactively labelling carbon - used in photosynthesis
* create sugars with this carbon
* thin slices from stems are cut and placed on X-ray film which turns black when exposed to radioactive material
* stems will turn black as that is where phloem are

Ringing experiments

* Ring of bark (and phloem) is peeled and removed off a trunk
* consequently, the trunk swells above the removed section
* analysis will show it contains sugar
* when phloem removed, sugar cannot be transported

How do small organisms exchange gases

* Simple diffusion
* across their surface

Why don't small organisms need breathing systems

* They have a large surface area to volume ratio
* no cells far from the surface

How alveoli structure relates to its function

* Round shape & large number in - large surface area for gas exchange (diffusion)
* epithelial cells are flat and very thin to minimise diffusion distance
* capillary network maintains concentration gradient

How fish gas exchange surface provides a short diffusion distance

* Thin lamellae epithelium means short distance between water and blood
* capillary network in every lamella

How fish gas exchange surface maintains diffusion gradient

* Counter-current flow mechanism
* circulation replaces blood saturated with oxygen
* Ventilation replaces water with oxygen removed

Name of gas exchange system in terrestrial insects

Tracheal system

Describe structure of spiracles

* Round, valve-like openings
* running along the length of the abdomen

Describe trachea & tracheoles structure

* Network of internal tubes
* have rings of cartilage adding strength and keeping them open
* trachea branch into smaller tubes - tracheoles
* tracheoles extend through all tissues delivering oxygen

How tracheal system provides short diffusion distance

Tracheoles have thin walls so short diffusion distance to cells

How tracheal system maintains concentration gradient

* Body can be moved by muscles to move air - ventilation
* Use of oxygen in respiration and production of CO2 sets up steep concentration gradients

Amylase

* Produced in pancreas & salivary gland
* hydrolyses starch into maltose

Membrane-bound disaccharidases

* Maltase / sucrase / lactase
* hydrolyse disaccharides into monosaccharides

Enzymes involved in protein digestion

* endopeptidases
* exopeptidases
* membrane-bound dipeptidases