ALL GAS EXCHANGE P1

O2 and CO2 are referred to as

Respiratory Gases

Gaseous Exchange

uptake of molecule O2 from the external environment and the discharge of CO2 to the external environment across a respiratory surface

Cellular Respiration

• the oxidation of food to form energy, water and Co2

Respiratory Surface

• the surface across which gas exchange takes place

How does gas exchange take place

• by diffusion

Breathing

• process of inhaling and exhaling air - body systems exchange these gases between the body and outside environment

Respiratory Medium

• source of O2

Respiratory Medium - Air

• o2 is plentiful around 21%

• less dense and viscous then water so can be easily moved around in small passageways

• breathing doesnt need to be particularly efficient (Lots more O2 content than water)

Respiratory Medium - Water

• around 40x less O2 in water than in Air

  • warmer + saltier water holds less O2

• more energy demanding

why do respiratory organs tend to be large and thin

• rate of diffusion is proportional to surface area, and inversely proportional to the diffusion dist

  • maximizing surface area → large

  • decreasing dist diffusing gases must travel → thin

adaptations a respiratory surface must have

• moist → gases only diffuse in aq conditions

• Thin → shorter diffusion distance

• Large → to meet metabolic requirements

• Good Blood supply → efficient absorption of O2 and removal of Co2

• Good Ventilation → efficient delivery of O2 and discharge of CO2

• Permeable → for gases to pass through

challenges faced by;

1) Terrestrial organisms

2) Aquatic Organisms

1. desiccation

2. low o2 conc in water

briefly - how does gas exchange happen in vertebrates

• gas diffuses across AQ layer lining epithelial cells

• it is passive - driven only by conc/partial pressure diff

For dissolved gases we don’t use concentration but instead….

• Partial Pressure

Fick’s Law of Diffusion

R = D.A.p / d

• D → diffusion constant accounts for; size of molecule, membrane permeability and temperature

• _{rate of diffusion is directly proportional to the area over which diffusion occurs and the partial pressure difference of the gases, inversely proportional to the distance over which the gas must diffuse}

• respiratory systems evolved to optimize rate of diffusion by increasing A, conc diff or decreasing distance

how is diffusion maximized in flatworms

• increased surface area - every cell in the body is close enough to external env that diffusion can reach them

how is diffusion maximized in sponges and cnidaria

• flagella to beat water to the inner cavity - maintains a flow of water

• Cnidaria have low energy demands so slow diffusion rate is enough

Specialized Respiratory Organs/Surfaces

• Cutaneous Respiration

• Large, Thin Respiratory organs

• Specific Adaptations

Cutaneous Respiration

• respiratory surface is the skin

  • earthworms and some amphibians

• Dense network of blood capillaries just beneath the skin → exchange between circulatory system and the environment

• O2 which diffuses is rapidly taken up → large diffusion gradient

• Low O2 demand and High SA:V

• live in damp places → keep skin moist

since space was limited how did animals increase SA

• folded or branched respiratory systems

  • gills, tracheae and lungs

How do respiratory organs facilitate gas exchange and transport in animals?

• Respiratory organs (lungs, gills) bring air or water close to internal fluids.

• Gas exchange happens in bulk—O₂ is absorbed, CO₂ is released (Fick’s Law).

• Circulatory system transports gases:

  • Blood (closed system, vertebrates).

  • Hemolymph (open system, arthropods & mollusks).

Respiratory Organs in Invertebrates

• epithelium, tracheae and gills

Respiratory Organs in vertebrates

• gills, skin or lungs

How do small aquatic animals respire - eg cnidarians

• through their skin by diffusion, cilia move the water ensuring a continuous stream of water

  • maintains concentration gradient

3 major types of respiratory structures in vertebrates

• integumentary exchange areas, gills and lungs

internal vs external gills

• internal; protected, but require ventilation system

• external; axolotls, no protection but no ventilation is required to move gas medium in and out

Respiratory Pigment

protein that helps transport oxygen in the blood or body fluids of animals.

Haemoglobin

• protein composed of 4 polypeptide chains and haeme groups → contain 1 atom of Fe which binds to 1 molecule of oxygen

• this allows whole blood to carry more oxygen

• OXYGEN CARRIER AND RESPIRATORY PIGMENT!

• binds to oxygen coming from the alveoli forming oxyhaemoglobin, then eventually deoxyhaemoglobin once deoxygenated

Oxygen carriers in invertebrates

• haemocyanin

  • uses Cu as oxygen binding molecule

  • circulates in haemolymph of arthropods and some mollusks

Partial Pressure

• pressure of a single gas within a mixture of gases

Value of mmHg

760 - the atmosphere exerts a downward force equal to that of a column of mercury 760mm high

how to calculate partial pressure at sea level

conc of 760mmHg

21% () 760mmHg

.21 (760) = 159.1 mmgHG

Why does gas still diffuse if water is already at equilibrium with air

Even if water reaches equilibrium with air, blood is always moving and taking oxygen away. This keeps the oxygen level in the blood lower than in the air (or water), so oxygen keeps diffusing in.

Diffusion gradients of respiratory gases in mammals - how does this work (partial pressure wise)

• PO2 in the blood is lower than PO2 in the alveoli so O2 diffuses into the blood

• PCO2 however is higher in the blood than in the alveoli so diffuses across alveoli

• blood leaves pulmonary veins → po2 is raised, pco2 is lowered

• blood is then pumped around the body and diffuses through interstitial fluid O2 goes into cells and co2 moved into blood

what is plant gaseous exchange dominated by

• co2

• o2

• water vapor

two main processes plants do

• during the day photosynthesis which releases o2 and takes up co2 and water

• respiration is day and night - oxidizing carbohydrates to form food releases CO2 and water

• during the day photosynthetic rates are higher than respiration rates so O2 production is higher then Co2

ventilation in plants

• no ventilation systems

• require solely on diffusion for gas exchange

main site for gaseous exchange in plants

• the leaves

how do flowering plants exchange gases by diffusion

• lenticels → in cork or woody stems

• root hairs → take in oxygen dissolved in soil water

• stomata → leaves and green stems

adaptations of a leaf for diffusion

• increased surface area → many air spaces

• o2 and Co2 taken up quickly in photosynthesis/respiration → conc gradient

• mesophyll layers across which gas must diffuse are very thin

if u dont understand why increasing air spaces increases surface area

Imagine a sponge—it has lots of little holes inside, right? That means more of the sponge can touch water when you dip it in.

Now, think of a leaf like that sponge. Inside the leaf, there are tiny air spaces (like the holes in a sponge). These spaces help spread air around so that more cells inside the leaf can "breathe" (take in CO₂ for photosynthesis and release O₂).

Because the air can reach more cells, the leaf has more surface area for gas exchange, just like a sponge has more space to soak up water!

how do stomata function

• they are surrounded by two guard cells

• when flaccid they close the stomata

• when turgid they expand (longitudinally) and since theyre connected to each other it opens the stomata

• water enters in from the soil, moves into xylem vessel then into stem and leaves

what happens when stomata open

• free space between palisade and spongy layers comes into contact with atmosphere

• water moved across cellular membranes and evaporates into free space → diffuses out

• o2 produced during photosynthesis exits (High P in side)

• co2 moves into cell (low conc inside being used for photosynthesis)

during photosynthesis what happens (relate to gases and mitochondria etc)

• o2 produced by chloroplasts during photosynthesis is used by mitochondria in respiration

• co2 produced by mitochondria is used in photosynthesis by chloroplasts

how does gaseous exchange take place in root epidermal cells

• air spaces in soil stores o2

• this diffuses into root hair cell and taken ip for respiration

  • carbon dioxide is released by respiration goes out through root hair cell

why is overwatering plants bad?

• no space for air in soil

• no o2 means anaerobic respiration which causes a build up of lactic acid

• this is toxic to the cell and can only be broken down in the presence of oxygen which the plant cant get

adaptation of root cell

• root hairs increase surface area and contact with the air spaces containing oxygen

• root hairs are very thin allowing efficient diffusion of water and gases to xylem vessels which are close to root epidermis

• gases are taken up very quickly due to tension within xylem bcs of transpiration→ steep conc gradient

Tracheal System consists of

tracheae → small branched cuticle lined air ducts

Explain the full tracheal system of insects (Spiracles and all)

• spiracles - found in the 2nd and 3rd thoracic region in first 8 abdominal segments lead to air filled sacs

• can be opened or closed by valves for water loss

• spiracles branch into trachea which are supported by thin layers of chitinous material

• branch into tracheoles - lack a chitinous lining

  • direct contact with individual cells - allow o2 to diffuse directly into tissues

what is the purpose of air filled sacs - spiracles lead to these air filled sacs

• to fly away quickly they need lots of air, this air comes from the air sac

spiracles contain what

• hair

  • prevents water loss and entry of foreign bodies

how can larger insects meet energy demands

• ventilating in and out - compress and expand air tubes

  • regulated by a valve mechanism at the spiracles

aperture size of spiracles

• adjusted based on co2 levels inside

  • chemoreceptors detect this - trigger spiracle opening

describe briefly ventilation in insects

• expiration of air; contracting and flattening of muscles which decreases volume of air

• inspiration happens passively when elastic segments in the trachea return to their og shape

• air flow is one directional → enters from thorax, expired through abdomen

describe what happens to insects during flight

• insects during flight consume 10-200 times more o2

• at resting, hypotonic solution surrounds the cell and moves into tracheole

• during flight - respiration and production of lactic acid makes the solution hypertonic

• so the fluid in the tracheoles moves out of the cell, making more space for oxygen and come closer contact with tissues

simple gills ex

• papulae of echinoderms

complex gills

• highly convoluted gills of fish

external gills

• not enclosed within the body

• epithelium is damaged

• organism must constantly be moving to ensure a continuous flow of fresh water

• resistance to movement

internal gills of mollusks - explain how they work - IGNOREE

• mantle cavity contains gills and opens to outside

• muscular contractions pulls water inside over the inhalant siphon

• o2 diffuses into blood

• water is pushed out by exhalent siphon

Internal gills of crustaceans in branchial chambers - explain how it works IGNORE

• branchial chamber opens beneath a limb

• the constant movement of a limb pulls water into the branchial chamber

• water passes over gills and o2 diffuses

• water then exists chamber

where are gills of bony fish located

• between buccal and opercular cavity

how do the buccal and opercular cavity act as pumps

• oral valve in mouth is opened, jaw is depressed, pulls water into buccal cavity

• opercular cavity expands once oral valve closes

• operculum is opened drawing water into gills to outside

bony vs cartilagenous fish

• bony fish have an operculum while cartilaginous fish dont

• cartilaginous fish have their gills exposed

functions of operculum

• protects gills

• causes movement of water in and out of opercular cavity like a valve

ram ventilation - ignore

• fish have immobile opercula

• swim with mouth partially open forcing water over their gills

  • eg tuna

remoras - ignore

• use ram ventilation when shark is swimming

• when shark stops swimming uses its opercula

inspiration of water

• buccal cavity is open, pressure decreases so water moves inside

• pressure of water pushes on posterior operculum preventing water from entering

• muscle in the operculum contract - enlarging opercular cavity, decreasing pressure hence water moves into opercular cavity (lower pressure)

• gas exchange takes places as water is pushed through the opercular cavity

expiration of water

• mouth and entrance to esophagus close, floor of buccal cavity is raised (higher pressure ) therefore, moving water into the opercular cavity

• gill filaments overlap at their tips slowing water down, allowing for more gaseous exchange

• increased pressure forces posterior end of operculum to open and water exits

structure of gills in bony fish - how many pairs of gills are present

4-5 covered by an operculum.

Tissue between gill slits - branchial/gill arches

contain v-shaped gill filaments

each gill filament are divided into evenly spaced folds known as lamella - increase SA

gill arch

between mouth cavity and opercular flaps

contains two rows of gill filaments - primary lamellae

and each primary lamellae (gill filament) has a secondary lamella which is a thin membranous sheet

(capillaries are present in the lamellae)

water flows past lamellae in one direction only

adaptations of gills

• countercurrent flow to maintain a constant gradient

• gill arches are lined with gill filaments and lamellae which increase SA

• dense network of blood capillaries near lamellae

• lamellae contain flattened epithelial cells - diffusion distance is shorter

  • lamellae and capillaries are lined with squamous epithelia which is thin and flat

countercurrent flow vs concurrent flow

• countercurrent flow allows o2 saturation to reach 85% while concurrent flow only 50% - inefficient

• at first concurrent flow has a higher gradient but then eventually reaches equilibrium

where is concurrent flow present + define it

• when blood in the gill plates flows in the same direction as the water

  • cartilaginous fish

Countercurrent flow + define

• when blood in the gill plates moves parallel to the flow of water

• Maximizes oxygenation as blood is constantly meeting water of a higher o2 content so maintain a diffusion gradient

• by Fick’s law it increases change P (concgradient)

• while a smaller gradient then concurrent flow it is more efficient

• hence, fish gills are the most efficient respiratory organ