B2.2 Flashcards
What does surface area to volume ratio compare?
Size of surface area vs volume of an organism.
How do you calculate volume?
Length × width × height.
How do you calculate surface area?
Length × width (for each face).
How is the surface area to volume ratio written?
a ratio in the smallest whole numbers.
Why does a large surface area to volume ratio matter?
Less need for specialised exchange/transport — diffusion alone is sufficient.
Why does a large surface area help diffusion?
More particles can pass through = faster rate.
How are lungs adapted for large surface area?
Spherical alveoli → ~75m² surface area. - large
How is the small intestine adapted for large surface area?
Lined with millions of villi. - increase surface area
Why are villi helpful?
Increase surface area → faster food absorption.
How do fish gills maximise surface area?
Contain lamellae.
How do leaves maximise surface area?
Flattened shape + internal air spaces.
Why is a thin membrane useful for exchange?
Short diffusion pathway = faster diffusion.
How are lungs adapted with thin membranes?
Alveoli and capillary walls are extremely thin.
How is the small intestine adapted with thin membranes?
Villi have a single layer of surface cells.
Why does blood supply/ventilation matter for diffusion?
Maintains steep concentration gradient.
How do lungs maintain a steep gradient?
Blood constantly receives oxygen and releases CO₂.
What is the effect of this constant exchange in lungs?
Gradient remains steep = faster diffusion.
How do fish maintain a steep gradient?
Water and blood flow in opposite directions.
Why does counterflow in fish gills help?
Oxygen in water always higher than in blood → diffusion continues.
What is the heart?
An organ in the circulatory system.
What does the circulatory system do?
Carries oxygen and nutrients to every cell and removes waste.
What kind of circulatory system do humans have?
Double circulatory system.
Why do mammals need a double system?
Their high metabolic rate needs faster oxygen/waste transport.
Describe system 1 of the double circulatory system.
Deoxygenated blood flows: right atrium → right ventricle → lungs.
Describe system 2 of the double circulatory system.
Oxygenated blood flows: left atrium → left ventricle → body.
What do muscular walls of the heart do?
Provide a strong heartbeat.
Why is the left ventricle wall thicker than the right?
It pumps blood around the whole body (not just to lungs).
How many chambers does the heart have?
4 — 2 atria (top), 2 ventricles (bottom).
What is the function of valves in the heart?
Stop blood flowing backwards.
What do coronary arteries do?
Cover the heart and supply it with oxygenated blood.
Step 1 of the process?
Blood enters right atrium (via vena cava) and left atrium (via pulmonary vein).
Step 2 of the process?
Atria contract → push blood into ventricles.
Step 3 of the process?
Ventricles contract →
Right ventricle → pulmonary artery → lungs
Left ventricle → aorta → body
Step 4 of the process?
Valves close → ensure blood doesn’t flow backwards.
What is the full circuit of blood through the body?
Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body
What do arteries do?
Carry blood away from the heart.
What makes artery walls strong?
Layers of muscle.
What do elastic fibres in arteries do?
Let arteries stretch → withstand high pressure.
What do veins do?
Carry blood towards the heart.
What is the lumen in a vein?
Wide channel for low pressure blood to flow.
Why do veins have valves?
ensure blood flows in the correct direction. - prevent back flow
What do capillaries allow?
Exchange of substances between blood and cells.
How are capillary walls adapted?
One cell thick → short diffusion pathway.
Why are capillary walls permeable?
So substances can move across them.
What do red blood cells contain?
Haemoglobin – binds to oxygen.
Why do red blood cells have no nucleus?
More space for haemoglobin.
Why are red blood cells biconcave?
Increases surface area for oxygen absorption.
Why are red blood cells flexible?
Helps them fit through narrow capillaries.
What is plasma?
The liquid that carries all components of blood.
What does plasma carry?
Blood cells, platelets, amino acids, urea, etc.
What is plasma mainly made of?
Water
Why are carbon dioxide, urea, and amino acids water-soluble?
So they can dissolve in plasma and be transported.
What is transpiration?
Loss of water vapour from the leaves and stems of a plant due to gaseous exchange.
Why does transpiration occur?
Stomata are open, allowing water to evaporate.
What causes a transpiration stream?
Water molecules move from high to low water potential → when some evaporate, others are pulled up the xylem.
What is the result of water being pulled up through the xylem?
More water is taken up from the soil → continuous transpiration stream.
What is the function of xylem?
Transports water and mineral ions from the roots to the leaves.
How is lignin involved in xylem function?
Lignin is deposited in xylem walls, causing cells to die and become hollow.
What structure do xylem cells form?
continuous tube for water and minerals to travel from the roots.
What bonding attracts water molecules in xylem?
Hydrogen bonding.
What does hydrogen bonding form in the xylem?
A continuous column of water up the plant.
How does evaporation drive the transpiration stream?
Water evaporates from the leaves, pulling water up.
How does lignin strengthen the plant?
helps the plant withstand the pressure of water movement.
What are bordered pits?
Holes in lignin that allow water and minerals to enter xylem vessels.
What do root hair cells do?
Absorb water from the soil via osmosis.
How are root hair cells adapted for their function?
They have a very large surface area.
What happens to water uptake when transpiration increases?
It also increases to replace lost water.
What is the function of guard cells?
Open and close the stomata.
What shape are guard cells and how are their walls structured?
Kidney-shaped with thin outer walls and thick inner walls.
What causes guard cells to open stomata?
They swell when lots of water is available → cells change shape.
What sensitivity do guard cells have?
They are light sensitive.
How do stomata help with gas exchange and water loss?
Open stomata = gases exchanged + water lost via evaporation.
Why are most stomata found on the bottom of the leaf?
To minimise water loss — lower surface is cooler and shaded.
What effect does increasing light intensity have?
More photosynthesis → more stomata open → transpiration rate increases.
What effect does increasing temperature have?
Faster evaporation and diffusion → higher transpiration and uptake.
What effect does increased air movement (wind) have?
Blows water vapour away → steeper concentration gradient → transpiration increases.
What effect does increased humidity have?
Decreases the concentration gradient → slower transpiration and uptake.
What does a potometer measure?
Water uptake as an estimate of transpiration rate.
Why is a potometer set up underwater?
To remove air bubbles and allow a continuous stream of water.
What does a faster-moving air bubble indicate in a potometer?
Greater water uptake = faster transpiration.
Why is one variable changed in potometer experiments?
To measure the effect of each factor on transpiration.
What is translocation?
Movement of food (sugars) made in leaves up or down the phloem.
Where are phloem tissues found?
In the roots, stems, and leaves.
What are sieve plates?
Holes in the end walls of phloem cells to allow sap movement.
Why are organelles removed in phloem cells?
To allow cell sap to flow through more easily.
What is the function of companion cells?
Contain many mitochondria to provide energy for transport.
In which direction does translocation move food?
Both up and down — to storage or for use.
