exchange and transport systems Flashcards
Why do smaller organisms have a higher surface area to volume ratio?
They have more surface area relative to their volume, which allows for faster exchange of substances via diffusion.
Why do larger organisms need exchange organs and mass transport systems?
They have a smaller surface area to volume ratio and a greater diffusion distance, so simple diffusion isn’t sufficient.
How do single-celled organisms exchange substances?
Substances diffuse directly across their cell membrane — short diffusion distance = fast rate.
Why can’t multicellular animals rely on simple diffusion?
Cells are deep within the body and have low SA:V ratios, so diffusion alone is too slow.
What are the key features of efficient gas exchange surfaces?
Large surface area
Thin for short diffusion distance
Steep concentration gradient
What structures increase surface area in fish gills?
Gill filaments with lamellae.
How is diffusion efficiency maximized in fish?
Lamellae have thin walls and capillaries
Counter-current flow keeps oxygen concentration gradient high across the entire gill
How do insects perform gas exchange?
Air enters via spiracles into tracheae, which branch into tracheoles that reach individual cells.
How is water loss reduced in insects?
Spiracles can close
Waterproof exoskeleton
Hairs around spiracles trap water
Where does gas exchange occur in dicotyledonous plants?
Mesophyll cells through stomata in the leaf epidermis.
How do plants control water loss?
Stomata close at night
Guard cells become flaccid when dehydrated, closing stomata
How do xerophytes reduce water loss?
Sunken stomata
Hairy leaves
Curled leaves
Fewer stomata
Thick waxy cuticle
What is the pathway of air through the respiratory system?
Trachea → bronchi → bronchioles → alveoli
What is ventilation?
Breathing in (inspiration) and out (expiration)
What happens during inspiration?
External intercostals and diaphragm contract
Volume increases, pressure decreases
Air flows in (active process)
What happens during expiration?
Muscles relax
Volume decreases, pressure increases
Air flows out (passive unless forced)
What adaptations do alveoli have for gas exchange?
Thin alveolar epithelium
Good blood supply
Large surface area
Short diffusion pathway
Steep concentration gradient
What is tidal volume?
Volume of air in and out during normal breathing (~0.4 dm³)
What is ventilation rate?
Breaths per minute (~15 at rest)
What is forced expiratory volume (FEV)?
Maximum air exhaled in a set time.
What is forced vital capacity (FVC)?
Maximum air exhaled after deep inhalation.
What does tuberculosis do to the lungs?
Forms tubercles → tissue damage → reduced gas exchange → fibrosis.
What is fibrosis?
Formation of thick, stiff scar tissue → reduces lung elasticity and volume.
What happens in asthma?
Airways inflamed, bronchioles contract, mucus produced → narrowed airways → reduced FEV.
What is emphysema?
Alveolar walls destroyed → reduced SA → less elastic recoil → harder to exhale.
Why is digestion necessary?
Large molecules must be hydrolysed to be absorbed across membranes.
What enzyme digests starch and where is it produced?
Amylase – produced in salivary glands and pancreas.
What does amylase produce?
Disaccharides like maltose
What enzymes break down disaccharides?
Membrane-bound disaccharidases:
Maltase → glucose + glucose
Sucrase → glucose + fructose
Lactase → glucose + galactose
How are lipids digested?
Lipase hydrolyses ester bonds → monoglycerides + fatty acids
Bile salts emulsify lipids → more SA
Products form micelles for absorption
What enzymes break down proteins?
Endopeptidases: break peptide bonds within proteins
Exopeptidases: remove terminal amino acids
Dipeptidases: hydrolyse dipeptides (membrane-bound)
How are monosaccharides absorbed?
Glucose/galactose: co-transport with Na⁺
Fructose: facilitated diffusion
How are fatty acids and monoglycerides absorbed?
From micelles, diffuse directly across epithelial membrane (lipid-soluble)
How are amino acids absorbed?
Co-transport with Na⁺ via sodium-dependent transporter proteins
What is haemoglobin?
A protein in red blood cells that carries oxygen — has 4 polypeptides, each with a haem group.
How many O₂ molecules can haemoglobin carry?
Four — forming oxyhaemoglobin
What is partial pressure (pO₂)?
A measure of O₂ concentration — affects haemoglobin’s affinity for oxygen.
Where does haemoglobin have high/low affinity for O₂?
High in lungs (high pO₂)
Low in tissues (low pO₂) — so O₂ is unloaded
What does the dissociation curve show?
The % saturation of haemoglobin at different pO₂ levels.
What is the Bohr effect?
Higher CO₂ → haemoglobin unloads O₂ more easily → curve shifts right
How does haemoglobin differ between organisms?
High O₂ environments → lower affinity (curve right)
Low O₂ environments → higher affinity (curve left)
What does the circulatory system transport?
Gases, nutrients, waste, and hormones.
Arteries:
Carry blood away from heart under high pressure — thick muscular walls, elastic tissue, small lumen.
Arterioles:
Smaller arteries — control blood flow to tissues via muscle contraction.
Veins:
Return blood to the heart under low pressure — valves, wider lumen, little muscle/elastic tissue.
Capillaries:
Thin (1 cell thick), close to cells, large surface area — ideal for exchange.
What is tissue fluid?
Fluid surrounding cells — formed from plasma.
What is pressure filtration?
High hydrostatic pressure at arterial end forces fluid out
Lower pressure and water potential at venous end → water re-enters by osmosis
Excess fluid returned via lymphatic system
Which side of the heart pumps oxygenated blood?
Left side — to the body
What causes valves to open and close?
Pressure differences between chambers
3 main phases of the cardiac cycle?
Atria contract → blood into ventricles
Ventricles contract → blood into arteries
Both relax → atria refill
What does xylem transport?
Water and mineral ions upward from roots.
What drives movement in xylem?
Transpiration pull
Cohesion & tension
What is transpiration?
Evaporation of water from leaf surfaces.
Factors that increase transpiration rate?
High light intensity
High temperature
Low humidity
Wind
What does phloem transport?
Organic solutes (mainly sucrose) — both up and down the plant.
What are sieve tube elements?
Living cells without a nucleus, supported by companion cells.
How does mass flow explain translocation?
Active loading at source lowers water potential
Water enters, creating pressure
Pressure gradient pushes solutes to sink
Evidence for mass flow?
Ringing experiments
Radioactive tracer
Aphid pressure experiments
ATP inhibitors stop translocation
Evidence against mass flow?
Sugar moves to multiple sinks
Sieve plates would resist flow
