Exchange and Transport

Relationship between size of organism and surface area : volume ratio

When surface area and volume of organism increase so, surface area : volume ratio decreases

because volume increases more rapidly than surface area

What are the adaptations in large organisms to facilitate exchange?

Single-celled organisms = high SA: V ratio = allow exchange of substances via simple diffusion

Large surface area = max. absorption of nutrients and gases and secretion of toxic waste products.

Large multicellular animals and plants = have specialised tissues for exchange

Relationship between size of organism and surface area : volume ratio

When surface area and volume of organism increase so, surface area : volume ratio decreases

because volume increases more rapidly than surface area

What are the adaptations in large organisms to facilitate exchange?

Single-celled organisms = high SA: V ratio = allow exchange of substances via simple diffusion

Large surface area = max. absorption of nutrients and gases and secretion of toxic waste products.

Large multicellular animals and plants = have specialised tissues for exchange

Relationship between SA: V ratio and Metabolic rate

Metabolic rate = amount of energy used up by organism in given time.

Basal metabolic rate = metabolic rate of organism at rest

Greater mass of organism = higher metabolic rate

However, BMR higher in small animals = greater SA: V ratio = lose more heat = use more energy to maintain body temp.

Plants = lower metabolic rate = do not move around and don’t have to maintain body temp.

Human Gas Exchange System : Structure

Trachea: lined with mucus-secreting Goblet cells and cilia = sweep microorganisms and dust away from lungs

Bronchi

Left and right bronchi at bottom of trachea = similar in structure but narrower

Bronchiole

Narrow tubes { less than 1 mm} = carry air from bronchi to alveoli. So they are narrow, no supporting cartilage and can collapse.

Alveoli

Main site of gas exchange. Tiny sacs with many adaptations = thin walls and large SA: V ratio

Alveolar Epithelium

Air in alveoli contains high conc. of oxygen and oxygen diffuses from alveoli into epithelial cell lining of capillaries into red blood cells for aerobic respiration

High conc. of carbon dioxide in plasma of blood and carbon dioxide diffuses out of plasma into epithelial cell lining of alveoli and is exhaled

Features of Alveoli

• Large number of alveoli = increases surface area available for oxygen and carbon dioxide to diffuse across.

• Thin walls = only one cell thick = gases have very short diffusion distance = gas exchange quick and efficient.

• Extensive capillary network = wall of capillaries = one cell thick = diffusion distance short. Constant flow of blood = oxygenated blood away from alveoli and deoxygenated blood to alveoli. Maintains conc. gradient

How does ventilation in the lungs help?

There is always a higher concentration of oxygen in the alveoli than in the blood

Breathing in air through lungs

• External intercostal muscles contract

• Internal intercoastal muscle relaxes

• Ribcage moves up and out

• Diaphragm contracts and flattens

• Volume of thorax increases

• Pressure inside thorax decreases

• Air is drawn in

Breathing out through the lungs

• External intercostal muscles relax

• Internal intercostal muscles contract

• Ribcage moves down and in

• Diaphragm relaxes and becomes dome-shaped

• Volume of thorax decreases

• Pressure inside thorax increases

• Air is forced out

Factors affecting diffusion - Temperature

more kinetic energy = speed of particles increases

Moisture

presence of mucus

Increases in surface area to volume ratio

reduces diffusion distance

Concentration gradient

increases distance in concentration = gives faster diffusion

Short diffusion pathway

shorter distance = faster diffusion

Features of factors affecting rate of diffusion - Temperature

passing close to blood = because blood provides heat

Surface area to volume ratio

folding (long and thin) -small

Concentration gradient

good blood supply( plants = water)

Short diffusion pathway

1 cell thick, and close together

How does asthma affect the gas exchange?

Occurs in brochioles and asthma causes the muscle to contract. This narrows the lumen and also overproduction of mucus. Drugs help the muscle to relax

Insect gas exchange

Must prevent water loss and they have exoskeleton which is impermeable to water.

How are spiracles adapted?

• Spiracles can be closed

• Pitted stomata trap moisture - hairy

• Trapped water reduces concentration gradient

Adaptations of the insect tracheal network

• Oxygen goes directly to the muscle tissue

• Oxygen goes into muscle via diffusion. Concentration gradient is maintained as oxygen is used in the muscle for respiration

• Tracheoles inside much = short diffusion pathway

• Wall of tracheoles = 1 cell thick = short diffusion pathway

• Moisture - muscle respiring makes water

• Increase in SA:V ratio = long, thin and branched

Air sac - maintain/ create concentration gradient

• Ventilates tracheal system = decrease volume and increase pressure

• Pushes air to the muscles not diffusion

• As muscle contraction happens, spiracles close so air is not lost

• Finishes with low pressure in the air sac

  -air in the atmosphere higher pressure than inside

  -so air moves in from high pressure to low pressure

Lactic acid - creates concentration gradient

• Lactic acid produced because of oxygen debt through anaerobic respiration = this makes muscle become hypertonic = lower water potential

• So tracheole has higher water potential = so water will move from tacheole to muscle tissue by osmosis

• Air moves from high pressure area to low pressure area

Gas exchange in fish - Gill rakers

prevents stones from damaging gill filament to not decrease surface area

Gill filament

• Long and thin. Large surface area:volume ratio

• Good blood supply = maintains concentration gradient and 1 cell thick

Lamellae

Increases surface area:volume ratio

Very thin = short diffusion pathway

Concurrent flow

Blood and water move parallel in the same direction. Lose concentration gradient halfway along the lamellae

Counter current flow

• Always a concentration gradient, along the whole length of lamellae

• Diffusion all the way along

• Efficient