Biology 103 - Main points/Questions

1. How do your lungs work?

2. How do gasses get to your cells?

3. What gasses do plant cells need to

transport?

Remember Circulation …• Plants and animals push extracellular fluids

– Plants generate flow w/o muscle tissue

– Animals generate flow with pumping muscles

• Fungi move intracellular fluids

– Use cytoplasmic streaming

– Proteins in the cell “stir” the cytoplasm moving nutrients etc. to rapidly growing hyphae.

• Protists use diffusion & streaming

Why exchange gases?

Cellular respiration - summarized as:• Glucose + oxygen carbon dioxide + water

• Look! This consumes oxygen and gives off CO2

• And, of course, produces ATP!

• So - Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide

Gas Exchange• All the complex multicellular critters use

oxygen to produce ATP in mitochondria

– So all cells need gas exchange for this

• Many plant cells also need a supply of carbon dioxide for photosynthesis

• We look at animals first

Gas exchange occurs between an organism and the environment, often in specialized respiratory organs.

In vertebrates gases are transferred via the circulatory system!

Ultimately exchange happens between cells and the interstitial fluid that surrounds them!

Types of Respiratory Systems

• The simplest animals obtain oxygen directly from their environments through diffusion

1.5 mm

Cnidarians

Exchange

Exchange

Mouth

Gastrovascularcavity

Diffusion works well as long as distances are small and surfaces are permeable

But as organisms become more complex they need specialized exchange organs

1.5 mm

Cnidarians

Exchange

Exchange

Mouth

Gastrovascularcavity

Diffusion works well as long as distances are small and surfaces are permeable

All organisms use diffusion at the cellular level but…

Types of Respiratory Systems

• As organisms get more complex they need specialized organs to exchange gases with the environment

• different phyla have different organs:

– Gills in fish, some arthropods, mollusks,

– Tracheae in insects,

– and lungs mostly in terrestrial chordates

Why do gases move?

Gases diffuse down pressure gradients in the lungs and other organs

In the lungs and tissues, O2 and CO2 diffuse from where their concentrations are higher to where they are lower

Remember diffusion• Movement from high concentration to low

– Doesn’t require any energy expenditure to make happen

– Works very quickly over short distances

– Important transport mechanism of cellular material

Factors controlling diffusion rate:

• Can you remember what some are?

Factors controlling diffusion rate:

• Temperature

• Size of molecule:

• Concentration gradient:

• Surface area:

• Distance:

• Medium

• set by organism

• set

• constantly maintained

• Increased as much as possible

• Decrease as much as possible

• Gas as often as possible

Respiratory Medium

• Animals can use air or water as a source of O2, or respiratory medium

• In a given volume, there is less O2 available in water than in air

• Obtaining O2 from water requires greater efficiency than air breathing

Respiration in Aquatic Vertebrates• Water moves past a fish’s gills in one direction

– this permits countercurrent flow

Respiration in Aquatic Vertebrates• Countercurrent flow

– extremely efficient way of extracting oxygen

– blood flows through a gill filament in an opposite direction to the movement of water

– the blood always encounters water with a higher oxygen concentration (constant gradient for diffusion)

Figure 30.3 Countercurrent flow

Because the two fluids flow in opposite directions blood can continue to pick up oxygen well past the 50% mark.

Figure 30.3 Countercurrent flow

If blood flowed in the same direction as water the system could exchange at most 50% of the gas dissolved.

Terrestrial gas exchange• For organisms on the land gas exchange

poses a new problem• The exchange must happen on living

cells bathed in fluid – but fluid loss can be a huge problem so…

• Gas exchange organs are moved into the body & adaptations to prevent water loss are common.

Tracheal Systems in Insects• The tracheal system of insects consists

of tiny branching tubes that penetrate the body

• The tracheal tubes supply O2 directly to body cells

Fig. 30.1.c

Lungs• Lungs - an infolding of the body surface

• The circulatory system transports gases between the lungs and the body

• The size and complexity of lungs correlate with an animal’s metabolic rate

In humans:• A system of branching ducts conveys air

to the lungs• Air inhaled through the nostrils passes

through the pharynx via the larynx, trachea, bronchi, bronchioles, and alveoli, where gas exchange occurs

• Exhaled air passes over the vocal cords and can create sounds

Fig. 30.6

Fig. 30.4.c

How a Mammal Breathes

• Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs

• Lung volume increases as the rib muscles and diaphragm contract

Figure 30.7 How breathing works

• Blood arriving in the lungs has a low amount of O2 and a high concentration of CO2 relative to air in the alveoli

• In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air

• In tissue capillaries, gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood

Alveolus

PO2 = 100 mm Hg

PO2 = 40

PO2 = 100

PO2 = 100PO2

= 40

Circulatorysystem

Body tissue

PO2 ≤ 40 mm Hg PCO2

≥ 46 mm Hg

Body tissue

PCO2 = 46 PCO2

= 40

PCO2 = 40PCO2

= 46

Circulatorysystem

PCO2 = 40 mm Hg

(b) Carbon dioxide(a) Oxygen

• Blood arriving in the lungs has a low O2 and a high CO2 relative to air in the alveoli

• When it leaves this has reversed

• Then in body tissue the situation is the opposite

Alveolus

PO2 = 100PO2

= 40

Circulatorysystem

Body tissue

PO2 ≤ 40 mm Hg PCO2

≥ 46 mm Hg

Body tissue

PCO2 = 46 PCO2

= 40

Circulatorysystem

• In tissue capillaries, O2 moves out of the blood and CO2 moves into the blood… why?

• To move more gas they are carried in several ways

Figure 30.8 The hemoglobin molecule

• hemoglobin molecules contain iron - oxygen binds in a reversible way

hemoglobin acts like little sponges for oxygen

• at high O2 levels (like in the lungs), most hemoglobin carry a full load of O2

• in the tissues, the O2 levels are much lower and hemoglobin gives up its bound oxygen

• The vast majority (> 90%) of oxygen you use was carried to your cells on hemoglobin

• CO2 must also be transported by the blood

– about 8% simply dissolves in the plasma

– 20% is bound to hemoglobin

– rest is carried as HCO3- in blood cells & plasma

• This is highlighted on figure from your book…

Figure 30.9 How respiratory gas exchange works

H2O

H2Oand minerals

CO2 O2

O2

CO2

Sugar

Light• What about

plants? Do they transport gasses in circulatory system?

• No! – they rely only on diffusion

• specialized anatomy makes this work…

Leaf cross section shows…

• Cells packed in top layer - photosynthesis

• Open “spongy” layer below for exchange

• But cuticle blocks gas exchange…

Plant leaf anatomy:

• Lots of open spaces inside but…

• Must open stomata (pores) to get gasses in

Opened Closed

This causes leaf to lose water so…

• plants need to balance water loss and gas exchange

• Guard cells control opening/closing

• How…?

• changes in the water pressure of guard cells

• When the guard cells are plump and swollen with water, they are said to be turgid and the stoma is open

• When the guard cells lose water, the stoma closes

Figure 23.20 - guard cells open and close stomata

Controlling stomata opening:

• Most plants keep closed at night open during the day. Why?

• Some specially adapted plants keep closed during day & open at night… Why would you do that?

• Hint: ➔