B3.1 – Gas Exchange B3.2 – Transport B3.3 – Muscle and Motility

Define gas exchange

The diffusion of gases (e.g. oxygen and carbon dioxide) across membranes

State where gas exchange occurs in humans

Across the alveolar surface in the lungs.

List four properties of effective gas exchange surfaces

Thin tissue

Explain why thin tissue is important for gas exchange

It reduces the diffusion distance

Define Type I pneumocyte

A flat alveolar cell specialized for gas exchange.

Define Type II pneumocyte

A cuboidal cell that secretes surfactant to reduce surface tension in alveoli.

Outline the role of surfactant in alveoli

Reduces surface tension

Explain the role of ventilation in maintaining concentration gradients

Replaces oxygen-poor air with oxygen-rich air in alveoli

Describe the pathway of air into the lungs

Mouth → trachea → bronchi → bronchioles → alveoli.

Outline the changes in pressure and volume during inhalation

Diaphragm and external intercostals contract → thoracic volume increases → pressure decreases → air enters lungs.

List components measured in lung volume assessment

Ventilation rate

Compare the methods of measuring lung volume

Spirometer uses digital tracking

State the direction of gas movement in leaves

CO₂ enters

Identify adaptations in leaves for gas exchange

Stomata

Define transpiration

The loss of water vapor through stomata in leaves.

Explain how stomata regulate transpiration

Guard cells swell or shrink to open or close stomata based on water availability and environmental cues.

Calculate stomatal density from micrographs or leaf casts

Count stomata per given area (e.g. per mm²).

Discuss how gas exchange surfaces are adapted to both plants and mammals

Include comparisons of leaf stomata to alveoli; both maximize surface area and maintain concentration gradients.

Describe how capillaries are adapted for exchange

Thin walls

Compare the structure of arteries and veins

Arteries have thick walls

Define pulse

The rhythmic expansion and recoil of an artery during a heartbeat.

State how pulse rate is measured

By palpation (neck/wrist) or using a digital pulse reader

Explain how veins overcome low pressure to return blood to the heart

Skeletal muscle contractions and valves prevent backflow.

Outline the consequences of coronary artery occlusion

Reduced oxygen to heart muscle → myocardial infarction (heart attack).

List risk factors for coronary heart disease

Smoking

State the function of xylem

Transports water and minerals from roots to shoots.

Explain transpiration pull

Evaporation at stomata creates tension

Define cohesion and adhesion in the context of xylem transport

Cohesion: water to water; Adhesion: water to xylem wall.

Describe adaptations of xylem vessels

Dead hollow cells

Draw and label a transverse section of a dicot stem

Xylem (inner)

Draw and label a transverse section of a dicot root

Xylem in X-shape

Compare xylem and phloem

Xylem = dead cells

Discuss how plant and animal transport systems use pressure differences

Plant: tension and osmotic gradients in xylem/phloem; Animal: blood pressure from heart contractions.

State the two types of movement

Internal movement (e.g.

List an example each of motile and sessile organisms

Octopus (motile)

Outline the relationship between muscle fibers

myofibrils

Annotate a diagram of a sarcomere

Z-line

Explain the sliding filament model

Myosin heads form cross-bridges with actin

Describe the role of ATP in muscle contraction

ATP hydrolyzes to power the myosin head pivot and detaches the cross-bridge for reattachment.

Define titin

A giant elastic protein that connects myosin to Z-lines and stores potential energy during stretch.

Explain the role of titin in muscle relaxation and contraction

Titin stretches when the sarcomere relaxes and recoils to assist contraction.

Define motor unit

One motor neuron and all the muscle fibers it innervates.

Explain how motor units coordinate contraction

One motor neuron stimulates multiple fibers for synchronized contraction.

Define neuromuscular junction

The synapse between a motor neuron and a muscle fiber.

State the role of acetylcholine

Neurotransmitter that triggers depolarization and contraction in the muscle fiber.

Compare endoskeletons and exoskeletons

Endoskeleton: internal

Define lever and its biological components

Bone = lever arm

Describe how synovial joints function

Bones meet at joints; synovial fluid lubricates

Label a generalized synovial joint diagram

Femur

Compare the range of motion in hinge vs ball-and-socket joints

Hinge: flex/extend only (knee); Ball-and-socket: multi-directional (hip

Measure joint angles using a goniometer

Use the goniometer arms aligned with bones and read the angle of flexion or rotation.

State the roles of external and internal intercostals

External: contract during inhalation; Internal: contract during exhalation.

Explain how antagonistic intercostal muscles aid ventilation

When one contracts the other relaxes

List reasons for animal locomotion

Foraging

Outline adaptations of marine mammals for swimming

Streamlined bodies

Discuss how the sliding filament model exemplifies form and function in biological systems

Structure of actin/myosin