MASS TRANSPORT Flashcards
explain how the heart muscle and heart valves maintain a one way flow of blood from the left atrium to the aorta (5)
1.Atrium has higher pressure than ventricle due to filling / contraction. This causes the
atrioventricular valves to open;
2.Ventricle now has higher pressure than atrium (due to filling /
contraction). This causes atrioventricular valves to close;
3.Ventricle has higher pressure than aorta causing semilunar valve to
open;
4.This leads to a higher pressure in the aorta than the ventricle (as heart
relaxes) causing semilunar valve to close;
5.(Muscle / atrial / ventricular) contraction causes increase in pressure;
describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue (4)
1.Permeable capillary membrane;
2.Single cell thick walls - reduces diffusion distance;
3.Flattened (endothelial) cells - reduces diffusion distance;
4.Fenestrations - allows large molecules through;
5.Small diameter/ narrow - gives a large surface area to volume / short
diffusion distance;
6.Narrow lumen - reduces flow rate giving more time for diffusion;
7.Red blood cells in contact with wall / pass singly - gives short diffusion
distance / more time for diffusion
explain how tissue fluid is formed and how it may be returned to the circulatory system (6)
1.Hydrostatic pressure of blood is high at arterial end;
2.Fluid & soluble molecules pass out;
3.Proteins & large molecules remain behind;
4.This lowers the water potential;
5.Water moves back into venous end of capillary by osmosis;
6.Lymph system collects any excess tissue fluid which returns to blood and
returns this tissue fluid to the veins;
explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water (6)
filaments / lamellae - large surface area
gill plates/ secondary lamellae
large number of capillaries - the remove oxygena nd maintain a gradient
thin epithelium - short diffusion pathway
pressure changes - to bring in more water and maintain gradient
countercurrent flow - exchange occurs along the whole length as a concentration gradient is maintained and an equilibrium is not achieved
describe and explain how fish maintain a flow of water over their gills (5)
- mouth opens, operculum / opercular valve shuts;
- floor of mouth lowered;
- water enters due to decreased pressure / increased volume;
- mouth closes, operculum / opercular valve opens;
- floor raised results in increased pressure / decreased volume;
- high / increased pressure forces / pushes water over gills;
describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood (6)
- Alveoli provide a large surface area;
- Walls of alveoli thin to provide a short diffusion pathway;
- Walls of capillary are thin between the alveoli so provides a short diffusion pathway;
- Walls of capillaries/alveoli have flattened cells;
- Cell membrane permeable to gases;
- Many blood capillaries provide a large surface area;
- Intercostal muscles & diaphragm muscles used to ventilate lungs to maintain a
diffusion gradient; - Wide trachea & branching of bronchi/bronchioles for efficient flow of air;
- Cartilage rings used to keep airways open
describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them (5)
1.Many alveoli / alveoliwallsfolded provide a large surface area;
2.Many capillaries provide a large surface area;
3.(So) fastdiffusion;
4.Alveoli or capillary walls / epithelium / lining are thin / short distance
between alveoli and blood;
5.Flattened / squamous epithelium;
6.(So) shortdiffusiondistance / pathway;
7.(So) fastdiffusion;
8. Ventilation / circulation;
9. Maintains a diffusion / concentration gradient;
10. (So) fastdiffusion;
describe the gross structure of the human gas exchange system and how we breathe in and out (6)
- trachea, bronchi , bronchioles , alveoli
- breathing in - diaphragm contracts and external intercostal muscles relax
- causes volume increase and pressure decreasing in thoracic cavity to below atmospheric, so air moves in
OPPOSITE FOR EXHALATION
from the root, water is transported upwards through the stem. explain how evaporation from the leaves can cause the water to move upwards (4)
- Water potential in leaf cells decreases / becomes more negative;
- Therefore water moves out of xylem (into surrounding tissues)
- by osmosis; this creates a tension on the water in xylem;
- which is in a continuous column as water molecules are cohesive;
- The cohesion is due to H bonding;
- The column of water doesn’t break because of adhesion with xylem walls;
describe the processes involved in the transport of sugars in plant stems (5)
- At source sucrose is actively transported into the phloem/sieve tube;
- By companion cells;
- Lowers water potential in phloem/sieve element/tube
and water enters by osmosis; - This produces a high hydrostatic pressure;
- Mass flow/transport towards sink/roots/storage tissue
- At sink/roots sugars are removed/unloaded;
use your knowledge of the cohesion-tension theory of water movement through a plant to explain why the diameter of the trunk is smallest during midday (6)
1.Diameter of trunk is minimal at warmest/brightest time of day;
2.Stomata are open in light → so more water loss;
3.Water evaporates more when warm as there is more heat energy for
water evaporation;
4.Hydrogen-bonding between water molecules causes cohesion between
water molecules;
5.Adhesion occurs between water molecules and walls of the xylem
vessels;
6.The xylem is pulled inwards by faster flow of water/tension;
describe and explain three ways in which the leaves of the xerophytic plants may be adapted to reduce water loss (3)
thick cuticle/ wax layer - waterproof / impermeable
sunken stomata - saturated layer of still air outside
hairy - saturated layer of still air outside
small leaves / spines / needles - less surface area for water loss
reduced number of stomata -reduced surface area for water loss
