B3 gas exchange

Organisms with ____ can rely on diffusion directly for gas exchange

high SA-V

Usually unicellular, like yeast, bacteria

What are 3 gas exchange surfaces

• Alveoli in lungs of mammals, birds, reptiles

• Gills in fish

• Tracheal system in insects

Properties of gas exchange surfaces (5)

• Thin (often 1 cell) → short diffusion distances

• Moist → helps dissolve gases before they diffuse across the exchange surface (ex. Alveolar fluid)

• Large SA → maximize diffusion as there is more membrane surface available

• Permeable → must have pores allowing gases to be exchanged across the surface (ex. stomata)

Concentration gradient → diffusion involves difference in [ ] of the two gases

Describe how concentration gradients are used for gas exchange in gills and lungs

• Gills

  • 2 fluids involved: water passing over the gills, blood inside gill capillary

    • More O2 must be in water vs. blood → for diffusion into the blood

  • Animals

    • Concentration of O2 in lung capillaries is lower than air inspired into lungs

    • Concentration of CO2 in lung capillaries is higher than in air

    • Thus, diffusion gradients take a place

Adaptations at exchange surfaces to maintain steep concentration gradients? (3)

• Ventilation → ensures the air or water rich in the gas is moved across exchange surface

  • Water (air) must be continuously passed over gills/ventilated in lungs

• Continuous blood flow → ensuring that substances are immediately transported away when entering the blood 

  • Ensures a low [ ] of that substance in the blood supply in relation to exchange surface

Dense network of blood vessels → many opportunities for substances to be exchanged between surface and blood

What is purpose of alveolar fluid/surfactant

• Secreted by type II pneumocytes

• Moistens the alveoli surface, allowing gases to dissolve before diffusing into the blood

• Made of lipids + proteins

• Reduces surface tension of moist inner surface and prevents alveolus from collapsing each time air is expired

What is the structure of bronchiole, why is it important

• Each bronchiole branches into alveoli

• Increases the SA for gas exchange = boosts the rate

• Ensures air is distributed properly

• Small diameter of bronchioles (compared to trachaea/bronchi) slows down rate of airflow → increases efficiency of gas exchange

What is the main purpose of capillary beds being around alveoli?

• short diffusion distance

What are the main structures involved in lung ventilation

• Diaphragm = sheet of muscle below ribs

• Intercostal muscles = group of muscles between/anchored to ribs (internal and external, they are antagonistic)

• Abdominal muscles 

• Tissue that makes up lungs is passive and not muscular (cannot purposefully move)

Breathing is based on _____ law

Boyle’s

An increase in V = decrease in pressure

Describe inspiration processes, 5 step

• 1. Diaphragm contracts to move downwards

• 2. External intercostal muscles and one set of abdominal muscles contract to raise rib cage, causing rib cage to move up

• 3. Since thoracic cavity has inc in V, pressure inside thoracic cavity decreases

• 4. Lung tissue responds to lower pressure by increasing its volume

• 5. Leads to a decrease in pressure inside the lungs (partial vacuum). Air comes in to counter this and fills alveoli

Describe the parts in lung volume

• Measured using a spirometer

• 1. Tidal volume (air breathed in/out in one cycle/normal breath)

• 2. Inspiratory reserve volume (max volume of air that a person can breathe in)

• 3. Expiratory reserve volume (max volume of air that a person can breahte out)

• 4. Vital capacity (sum of inspiratory + tidal + expiratory)

• *residual volume is the air in lungs that cannot be further exhaled, preventing lungs from collapsing

Leaf adaptations for efficient gas exchange (5)

• 1. Waxy cuticle (covers cells of upper epidermis, hydrophobic, prevents water loss and dehydration)

• 2. Epidermis (regulates exchange of gases between leaf and air using stomata)

  • Stomata: numerous microscopic openings on the lower surface of leaves. Each stoma = 2 guard cells, which can open or close.

    • When open = permit CO2 to enter, and H2O and O2 to exit (diffusion) → rate of gas exchange increases

    • Location on lower surface limits water loss due to transpiration

    • Stomata are also unprotected against physical factors (rain)

• 3. Palisade mesophyll: densely packed cylindrical cells in upper portion of leaf. Has many chloroplasts and located to get maximum sunlight for photosynthesis

• 4. Spongy mesophyll: loosely packed cells below palisade layer. Few chloroplasts and many air spaces → large SA for gas exchange

5. Thin and flat → large SA for gas diffusion and sunlight absorption

Define transpiration, how does it work, its function

• Definition: the evaporation/loss of water through open stomata

• Since there is more [ ] H2O in the leaf than outside, this water vapour diffuses out through stomata

  • Diffusion results in negative pressure (pulls on H2O in xylem due to capillary action, which is cohesive + adhesive properties of water)

• A result of a leaf’s function to accomplish photosynthesis

• Transpiration not only allows a plant to absorb water/nutrients from soil and transport it throughout

  • Also regulates temperature

Factors affecting transpiration (4)

Environmental factor	explanation
Light intensity	When higher, guard cells cause stomata to open wider (for CO2 to enter for photosynthesis) More water evaporates from plant
Temperature	More kinetic energy will be gained by H2O, so they can diffuse out of stomata Also increases saturation point of the atmospheric air, so it can hold more H2O vapour
Wind intensity	The higher it is, the faster H2O are moved away from the leaf after transpiration Results in increased [ ] gradient between stomata and air, increasing rate of diffusion of H2O
Humidity	Increased humidity, more H2O vapour in the air Lower [ ] gradient between leaf and surrounding air, slowing rate of diffusion of H2O

Purpose of measuring stomata density

• More stomata = higher rate of transpiration → indicate how efficiently a plant uses water

• Changes in density in different environments understand effect of climate on plates

• Similarities and differences indicate phylogenetic relationships

• Density of past fossils indicate past environmental conditions

Describe haemologbin and its purpose

• Haemoglobin = protein molecule in erythrocytes responsible for carrying most of oxygen

  • Purpose: transport O2 from lungs to tissues, transport CO2 from respiring tissues to lungs

  • Can reversibly bind to CO2 or O2

  • Composed of 4 polypeptides with a quaternary structure

    • Each polypeptide has a haem group with an iron atom

  • When binding to O2, it’s the iron that does it

  • Can bind to 4 O2 (saturated)

Describe structure and adaptations of foetal haemoglobin

• Quaternary, 2 alpha + 2 gamma polypeptide chains, each has a haem group

• Presence of gamma allows it to higher affinity for O2 (compared to mother haemoglobin)

  • Increases efficiency in which foetus gets O2 from mother blood across placenta

  • Important since O2 [ ] in foetal blood is lower than in the mother

Describe structure of adult haemoglobin

• quaternary structure, 2 alpha + 2 beta polypeptide chains, each has a prosthetic group (haem) containing an iron

• Has lower affinity to O2 than foetal

  • Since it has a higher affinity for (2,3 BPG) (organic phosphate) which competes with O2 for binding

What is myoglobin

*another type of haemoglobin is myoglobin, found in muscle tissue. Consists of 1 polypeptide chain and has much higher affinity for O2 than HbF or HbA

What is cooperative binding?

• Any O2 bonded to haemoglobin subunit increases its affinity for more O2 (conformational change)

  • Called cooperative binding since oxygen molecules interact with each other to increase its affinity

haemoglobin with ____ O2 has the greatest affinity for O2

3

Describe shape of oxygen dissociation curve

• Y axis = % of haemoglobin saturation with O2

• X axis = partial pressure (concentration) of oxygen

  • This varies depending on where the blood is

• Cooperative binding of haemoglobin to O2 results in a sigmoidal shape (otherwise would be linear)

  • Rate of O2 intake by haemoglobin increases rapidly

  • However, it eventually levels off as it becomes fully saturated with o2 in areas of higher O2 partial pressure (ex. lungs)

Define partial pressure

• Definition = the pressure exerted by a single gas within a mixture of gases

• This partial pressure of O2 decreases in the body and blood as it’s used for aerobic cellular respiration

How is CO2 transported in body?

Most is dissolved in plasma (carbonic acid, low pH), small amount binds to haemoglobin

What molecule can undergo allosteric binding to haemoglobin? describe. Why is this important?

• CO2 binds to allosteric region of haemoglobin (polypeptide regions) whereas O2 binds to haem group 

• Allostery → when binding of CO2 to polypeptide chains of haemoglobin results in a conformational change, decreasing haemoglobin's affinity for O2

  • Important to ensure that haemoglobin unloads O2 in areas of low partial pressure of O2 (respiring tissues)

Define bohr shift, why is it important

• Definition: shifting the oxygen dissociation curve to the right with higher partial pressures of O2 in the blood

  • The change in affinity of haemoglobin for O2 in the presence of CO2

    • Essentially, when CO2 is present, haemoglobin has a greater tendency to give up O2

• why important: Due to decreased affinity for O2, haemoglobin releases more O2 into tissues with higher partial pressures of CO2 (respiring muscles) → important while exercising

Describe the 2 types of alveolar cells

Type I pneumocytes	Type II pneumocytes
Cover 95% alveolar surface	Cover 5% alveolar surface, found between type I
Function: allow gas exchange between alveoli and capillaries	Function: produce pulmonary surfactant (Reduces surface tension to prevent alveoli from collapsing and sticking while breathing)
Adaptations Thin, squamous and flat (increase SA, minimize diffusion distance) Shared basement membrane with lining of lung capillaries (minimizes diffusion distance) Tightly joined to another (no fluid can enter from capillaries)	Adaptions Cube shape (larger cytoplasmic area to contain organelles producing surfactant) Microvilli orientated towards alveolar sac (increase SA for more surfactant secretion) Cytoplasm has many organelles (like secretory vesicles/lamellar bodies) Can transform to type I

Capillary structure

• small, thin walled blood vessels for material exchange  between blood and itnernal/external environment

  • Highly branched (more SA-V, and slows flow of blood for more time exchanging materials)

  • Wall is 1 cell thick (endothelial cells) → short diffusion distance

  • Has a basement membrane (thin layer of ECM providing structural support to endothelium to regulate material exchange)

2 types of capillaries

• Most capillaries are continuous (complete endothelial lining)

  • Allows selective exchange of small molecules/ions

• Other capillaries are fenestrated

  • Definition = gaps in endothelial cells allow for more rapid exchange of materials

  • Found in organs with high metabolic demands (kidney, small intestine)

Capillary adaptations

• Small inside diameter

• Thin walled

• Permeable

• Large SA

• Fenestrations

Describe capillary beds and their functions

All chemical exchanges in lungs and body tissues occurs in capillary beds

• Structure

  • Capillaries receive blood from arterioles (smallest artery)

    • Arteriole branches into capillary bed within body tissues (network of capillaries receiving blood from same arteriole)

    • Capillary bed drains blood into venules (smallest veins)

• Some metabolically active tissues in the body have more capillary beds (highly vascular tissue) 

• Some tissues have capillary beds that are more permeable to substances (fenestrated)

  • Small slits allowing large molecules to pass, and faster movement

  • Examples: capillaries in kidneys and intestine

• When blood enters a capillary bed → much of pressure and velocity is lost

  • Blood cells line in a single file because the lumen of capillary is small

  • Capillary bed is extensively branched leading to large SA, so it can reach body cells

What is the artery’s purpose and adaptations

• Transports high pressure blood away from the heart

• Main one is the aorta → branches into smaller arteries → branches into arterioles → connects to capillaries for substance exchange

• Adaptations

  • Wall is made of smooth muscle

    • Regulates diameter of artery/blood flow by contracting or relaxing based on signals (ex. Hormones, blood pressure)

    • Can contract → diameter of lumen decreases (vasoconstriction) to increase blood pressure

    • Can relax → diameter of lumen increases (vasodilation), decreasing blood pressure

    • Controlled by autonomic nervous system (ANS) → unconscious

  • Walls contain proteins (elastin and collagen) 

    • Reduces fluctuations in blood pressure (prevents damage to smaller blood vessels)

    • When blood is pumped in → these fibres are stretched and allow blood vessel to accommodate more pressure

    • Once blood passed, the fibres recoil and provide pressure to propel the blood forwards

    • Thus, blood in arteries maintains high pressure during pumping

  • Muscle + elastic tissues permit withstanding of high pressure (ensure blood is moving)

  • small lumen

Describe veins and their adaptations

• Return low pressure blood to the heart

• Also has 3 layers (same as artery)

• Blood vessels that return blood to heart after passing through a capillary bed

• Adaptations

  • To account for the loss of pressure and velocity in blood in capillary beds

  • Thin walls → easily compressed by muscles to make blood pushed along

    • Ex. in the limbs during vigorous exercise

  • Large lumen (more blood flows at lower pressure)

  • Has one way valves → unidirectional flow to the heart → prevents backflow

    • Important in lower parts of body, like feet, when force of gravity is difficult for blood to flow back

Describe process of transpiration and its purpose

• To transport water and minerals unidirectionally against gravity using xylem

• Rely on tension force

• From roots → other plant parts

• Possible due to transpiration (loss of water from plants through stomata)

  • When water evaporates through stomata, a negative pressure potential is created/tension is created (lower water potential outside stomata vs. inside of leaf) at upper end of xylem tube

• Results in water moving up xylem → entire water column due to cohesion moves up

• Cohesion-tension theory

Describe structure of xylem

• Structure: thin, continuous columns running from the roots through the stems

• Formed from specialized cells (which lose their cell contents and membrane as they mature and die) 

• Dead → leave behind the cell wall

  • Have lignin for strength → binds to cellulose → provides strength and rigidity to withstand tension (due to tension in transpiration)

  • Also waterproofs the xylem

• Even the end walls (where cells were joined to each other in the time) → degenerate

  • partial/total lack of these allows unobstructed water to flow upwards

• The specialized cells that make up xylem walls contain pit areas

  • Where cell wall is thinner, no lignin

  • Allow water to move between adjacent cells

Describe the 5 main parts of stems and roots

• Stem

Tissue	Function
epidermis	Prevents water loss, protection from microorganisms
cortex	Unspecialized cell layer, can store food
xylem	Transport tubes that bring up water from roots
Vascular bundle	Contains vessels of xylem and phloem
phloem	Transports carbohydrates, usually leaves to other parts of the plant

• Root

Tissue	Function
Epidermis	Grows root hairs that increase SA for water uptake
cortex	Unspecialized cell layer that stores food reserves
xylem	Transport tubes for water and minerals, starting in roots
Phloem	Transport tubes that receive sugars from leaves
Vascular bundle	Center of root, contains xylem and phloem

What is tissue fluid?

• Tissue fluid = made from blood plasma that is pushed through capillary walls into surrounding tissues

  • Contains water and small solutes (ions, hormones)

  • It bathes cells and facilitates exchange of substances between blood and cells

How is tissue fluid created

• Amount of fluid/solutes pushed out of capillary wall is due to the hydrostatic pressure of blood on the wall

  • Arteriole end → hydrostatic pressure is high (fluid is pushed out of wall into tissue) due to ultrafiltration (pressure filtration)

    • This pressure is high enough to open gaps between cells making up capillary walls

  • Venule end → fluid has already been lost inside capillary, decreasing hydrostatic pressure → majority of tissue fluid draws back into capillaries (some amount doesn’t and enters lymph ducts)

Exchange between cells and tissue fluid can occur in 2 ways

Can occur through diffusion or active transport

What can leave capillaries and enter tissue fluid? What can’t?

• RBC and large proteins don’t leave capillaries (remain in blood) since they are too large

• Some WBC can squeeze through capillaries into tissue fluid (fight infection)

How much tissue fluid reenters venous side of capillary bed vs. entering lymphatic capillaries?

90% vs 10%

What is lymph? Lymph vessels? Lymph nodes?

• Lymph = the fluid that enters lymphatic capillaries

  • Prevents fluid build up around body cells

  • Helps transport immune cells and remove toxins from body

• Lymph vessels 

  • Low pressure → relies on contracting muscles to squeeze liquid

  • Valves 

  • Join into larger lymph ducts

• *Fluid entering lymphatic vessels is routed through lymph nodes before returning to a vein

• Lymph nodes = filter bacteria, viruses, cancer cells = part of immune system

What is single circulation

• Single (to complete 1 circulation, blood passes through heart once)

  • Bony fish

  • 2 chambered heart (one receives blood, another pumps out)

  • When pumped out, sent to gills for gas exchange

  • Reoxygenated blood collected from gills and sent to capillary beds in body tissues

  • Deoxygenated blood returns to heart

  • Limitation: loss of blood pressure when blood is in gill capillaries

What is double circulation, give some benefits

• Double (to complete 1 circulation, blood passes through heart twice through 2 types of circulation)

  • Mammals

  • Heart has 4 chambers

    • One side pumps to capillaries in lungs (pulmonary circulation)

      • Heart → lungs → heart

    • Blood returns to other side of heart to pump to body tissue capillaries (systemic circulation)

      • Heart → rest of organism → heart

  • Benefits

    • Physical separation of oxygenated + deoxygenated blood helps maintain high [ ] gradients (efficient gas exchange)

    • This additional trip to the heart restores blood pressure

Describe left and right side of the heart, and adaptations (Structural features)

• Right side

  • Sends blood to and from lung capillaries (pulmonary circulation)

• Left side

  • Sends blood to and from body tissues (systemic circulation)

• Advantage of this 2 compartments → both lung and body capillaries receive blood (allows pressure filtration to occur in all capillaries)

• Adaptations for efficient blood flow

  • Heart is a double sided pump

  • Cardiac muscle

    • Highly vascular

    • Thick in the ventricles (left is thickest)

  • Pacemaker

    • Also called SA (sinoatrial mode) → an area of specialized cells in right atrium create a spontaneous electrical impulse to start a heartbeat

  • Atria

    • Thin muscular chambers

    • Receive low pressure blood through veins

    • Sends blood to ventricles

  • Ventricles

    • Thick muscular chambers

    • Pump pressurized blood

  • Atrioventricular valves

    • Between atria + ventricles

    • Closes each heart cycle to prevent backflow of blood into atria

  • Semilunar valves

    • Close after blood enters aorta to prevent backflow of blood into ventricles

  • Septum

    • Wall of muscular/fibrous tissue

    • Separates right from left side of heart

  • Coronary vessels

    • Blood vessels providing oxygenated blood to heart muscle

*heart valves open/close due to different blood pressure on either side

most water transport in plants is due to ____ but it can also occur using ____

transpiration (negative pressure pulling water through xylem using capillary action)

Root pressure

Define root pressure and how it works

• Generated by active transport of mineral ions (K+, Mg2+) from soil → root hair

• This reduces water potential inside root hair

• Water moves through osmosis from soil → root

• Movement of water → xylem generates hydrostatic pressure that pushes it upwards

Define purpose of phloem and the direction of movement

• Phloem = the vascular tissue in plants that transports organic molecules from 1 location to another (called sap, basically sugar)

• Direction of movement based on = movement from a source to a sink

  • Source = plant organ that is a net producer of sugar (photosynthesis or hydrolysis of starch) → like leaves

  • Sink = plant organ that uses or stores sugar (buds, stems, seeds) → parts actively growing or metabolically active

  • However, some sources are sources and sinks 

    • Roots can store sugar or hydrolyze starch to provide it depending on the season

How are carbon compounds transported in phloem? what is the name of this process? give a 5 step method

• source —> sink

• called translocation (movement of sap within sieve tube elements)

• requires active transport

• nslocation: the movement of sap within sieve tube elements

  • 1. Occurs as sugars/carbon compounds are actively transported into phloem (sieve tube elements) (from companion cells through plasmodesmata) at the source → decreases water potential

  • 2. Water is drawn into phloem from xylem due to osmosis

  • 3. Increases hydrostatic pressure exerted on sap 

  • 4. Creates a pushing effect, moving sap through sieve plates to the sink (mass flow) (where there is lowest pressure)

  • 5. At the sink, solutes are unloaded (passively, active transport) → decreases solute concentration, causing water to return to xylem by osmosis to lower hydrostatic pressure

Describe phloem structure (2 cell types)

• both living

• Phloem sieve tubes

  • Connected to each other by porous sieve plates to form sieve tube elements

  • Cannot remain alive without companion cells (providing metabolic activities)

  • No nucleus/organelles since they must be empty to carry fluid as their function

• Companion cells

  • Contain many mitochondria → produces ATP for active transport and loading nutrients into phloem at the source

  • Can also unload nutrients from phloem at the sink

• Both have connections called plasmodesmata (pores)

• For transporting nutrients + communication between cells

• Sap doesn’t travel through cytoplasm of these cells, but the tube like area of sieve tube elements

  • Which has reduced plasma membrane and cytoplasm