B3.1 Gas exchange

Describe how ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.

Ventilation is the process of breathing in and out

• Fresh air is draw induring ventilation

• Oxygen at higher concentration in air sacs than in blood

  • diffuses out of the alveoli into blood capillaries

  • the level of oxygen inside them gradually falls and the level of carbon dioxide rises

  • Carbon dioxide higher in concentration in blood than airs sacs

  • Carbon dioxide moves into air sacs down concentration gradient

  • Concentration gradients maintained when stale air with high levels of carbon dioxide and low levels of oxygen is expelled

Outline how muscle contractions achieve ventilation including pressure changes.

Breathing happens because of two sets of intercostal muscles between the ribs, and by the diaphragm, the sheet of muscle separating the thorax from the abdomen

• External and internal intercostal muscles are an example of antagonistic muscles

• The work of external intercostals produces an opposite effect to the contraction of the internal intercostals

• Pressure increases in the lungs during exhalation

• Pressure decreases in the lungs during inhalation;

Describe how different muscles are required for inspiration and expiration because muscles only do work when they contract.

Muscles work in antagonistic pairs;

What is tidal volume?

The volume of air breathed in and out during normal ventilation/breathing.

Define Antagonistic muscles

a muscle that opposes the action of another.

Name the two main branches of the trachea that go into the lungs; this then further divides into the bronchioles and alveoli.

Bronchi

Define Bronchioles

any of the fine, thin-walled, tubular extensions of a bronchus.

Describe the Diaphragm

a dome-shaped muscular partition separating the thorax from the abdomen. It plays a major role in breathing as its contraction increases the volume of the thorax and so inflates the lungs.

Define Emphysema

a chronic respiratory disease where there is over-inflation of the air sacs (alveoli) in the lungs causing a decrease in lung function and often breathlessness.

Define Expiration

when the muscles of the thorax contract to cause the volume to decrease, this increases the pressure in the lungs and air moves from the higher pressure inside the lungs to the lower pressure outside the body.

Define Inspiration

when the air moves from a higher pressure (outside the body) to the lower pressure (inside the lungs).

Name the muscles found between the ribs. They are mainly involved in the mechanical aspect of breathing.

Intercostal muscles

Name an instrument for measuring the volume of air entering and leaving the lungs.

Spirometer

Name the substance composed of lipoprotein that is secreted by the alveolar cells of the lung and serves to maintain the stability of pulmonary tissue by reducing the surface tension of fluids that coat the lung.

Surfactant

Define Tidal volume

the volume of air inspired or expired in a single breath during regular breathing.

Why do larger organisms face greater challenges in exchanging gases with their environment?

Because their surface area-to-volume ratio decreases, reducing the efficiency of diffusion; the distance from the centre of an organism to its exterior increases;

Define vital capacity.

The maximum amount of air a person can exhale after a maximum inhalation, representing the total volume of air exchanged during deep breathing.

Define inspiratory reserve volume

The additional volume of air that can be inhaled forcefully after a normal inhalation.

Define expiratory reserve volume

The additional volume of air that can be exhaled forcefully after a normal exhalation.

What is the role of the waxy cuticle in leaves?

The waxy cuticle reduces water loss by minimizing evaporation while still allowing light penetration for photosynthesis.

Outline the role of air spaces in the spongy mesophyll in gas exchange.

They create a large surface area for gas diffusion; provide pathways for the movement of CO₂ and O₂ between cells and the atmosphere;

Explain how guard cells open and close to control gas exchange in leaves.

They swell with water due to osmotic changes, opening the stomata; shrink when water is lost, closing the stomata;

How does stomatal density and distribution vary in response to environmental humidity?

Stomatal density is higher in environments with high humidity and lower in dry conditions to minimize water loss;

How does stomatal density affect the rate of transpiration?

Higher stomatal density increases transpiration rates by providing more openings for water vapor to escape;

List the key factors affecting transpiration rate.

Light intensity; temperature; humidity; wind;

Explain how light intensity affects the rate of transpiration.

Light triggers stomatal opening to allow CO₂ uptake for photosynthesis. Open stomata also allow more water vapor to escape, increasing transpiration.

Explain how temperature affects the rate of transpiration.

Higher temperatures increase the kinetic energy of water molecules; speeding up evaporation from the leaf surface; and diffusion of water vapor through the stomata;

Explain how humidity affects the rate of transpiration.

High humidity outside the leaf reduces the water vapour concentration gradient between the leaf interior and the surrounding air, slowing down the diffusion of water vapour;

Explain how wind affects the rate of transpiration.

It removes the humid air around the leaf, maintaining a steep water vapour concentration gradient, which promotes faster diffusion of water vapor from the leaf;

How do stomata balance the need for gas exchange with water conservation?

Stomata open during the day for photosynthesis when CO₂ is needed and close at night or during water stress to conserve water;

Why is the upper epidermis free of chloroplasts while the palisade mesophyll is rich in them?

The upper epidermis is transparent to allow light to reach the palisade mesophyll, which is packed with chloroplasts for maximum photosynthesis;

How can stomatal density be measured using a leaf peel or cast?

By applying nail polish or clear tape to the leaf surface, peeling it off, and examining it under a microscope to count stomata per unit area.

Contrast stomata in xerophytic plants with mesophytic plants.

Xerophytes have fewer stomata to minimize water loss in arid environments, balancing water conservation with gas exchange;

Explain how the distribution of tissues in a dicotyledonous leaf supports its function.

The upper palisade mesophyll maximizes light capture for photosynthesis, the spongy mesophyll facilitates gas diffusion, and veins transport water and nutrients efficiently;