B3 extended response Flashcards
(13 cards)
Q1. Describe the role of the enzymes of the digestive system in the complete breakdown of
starch.
amylase
starch to maltose
maltase
maltose to glucose
hydrolysis of glycosidic bond
Q2. Describe the processes involved in the absorption of the products of starch digestion.
- Glucose moves in with sodium
- Via carrier protein
- Sodium removed by active transport / sodium- potassium pump;
- Into blood;
- maintaining sodium concentration gradient
- Glucose moves into blood;
- By facilitated diffusion;
Q3. Describe how proteins are digested in the human gut.
- Hydrolysis of peptide bonds;
- Endopeptidases break polypeptides into smaller peptide chains;
- Exopeptidases remove terminal amino acids;
- Dipeptidases hydrolyse dipeptides into amino acids.
Q4. The epithelial cells that line the small intestine are adapted for the absorption of glucose.
Explain how.
- Microvilli provide a large surface area;
- Many mitochondria produce ATP to provide energy for active transport;
- Carrier proteins for active transport;
- channel / carrier proteins for facilitated diffusion;
- Co-transport of sodium ions and glucose
- Membrane-bound enzymes digest disaccharides to produce glucose;
Q5. 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.
- permeable capillary wall
- thin walls, reduces diffusion distance;
- flattened endothelial cells, reduces diffusion distance;
- fenestrations, allows large molecules through;
- small diameter / narrow, gives a large
surface area to volume and short diffusion distance; - narrow lumen, reduces flow rate giving more time for diffusion;
- red blood cells in contact with wall / pass singly, gives short diffusion distance and more time for diffusion;
Q6. Explain how tissue fluid is formed and how it may be returned to the circulatory system.
- high hydrostatic pressure of blood at arteriole end;
- small soluble molecules leave ;
- proteins and large molecules remain;
- this lowers the water potential
- water moves back into venule end of capillary by osmosis;
- lymph system collects any excess tissue fluid which returns to blood
Q7. Explain how the heart muscle and the heart valves maintain a one-way flow of blood
from the left atrium to the aorta.
- AV valves close; Ventricle has higher pressure than atrium, due to muscle contraction
- SL valve open; Ventricle has higher pressure than aorta
- SL valve closes; Higher pressure in aorta than ventricle as heart relaxes
- AV valves open ; Atrium has higher pressure than ventricle, due to muscle contraction
Q8. 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.
- Many alveoli and alveoli walls folded provide a large surface area;
- Many capillaries provide a large surface area; So fast diffusion;
- Alveoli and capillary walls are thin so short distance between alveoli and blood;
- Flattened epithelium; So short diffusion distance so fast diffusion;
- Ventilation / circulation maintains a diffusion gradient so fast diffusion;
Q9. Describe the gross structure of the human gas exchange system and how we breathe in
and out.
- trachea, bronchi, bronchioles, alveoli;
- Breathing in - diaphragm contracts and external intercostal muscles contract;
- Causes volume increase and pressure decrease in thoracic cavity to below atmospheric, resulting in air moving in;
- Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
- Causes volume decrease and pressure increase in thoracic cavity to above atmospheric, resulting in air moving out;
Q10. Describe the processes involved in the transport of sugars in plant stems.
- At source sucrose is actively loaded into the sieve element in the phloem;
- By companion cells;
- This involves active transport and co transport;
- This lowers water potential in phloem and water enters by osmosis;
- Produces high hydrostatic pressure creating a pressure gradient;
- Mass flow towards sink;
- At sink sugars are unloaded and used in respiration or stored;
Q11. Describe the cohesion-tension theory of water transport in the xylem.
- Water lost from leaf due to transpiration;
- (Which is) the evaporation of water from mesophyll cells and diffusion out of the stomata;
- Lowers water potential of mesophyll cells;
- Water pulled up xylem creating tension;
- Water molecules ‘stick’ together by hydrogen bonds due to cohesion;
- Forming continuous water column;
- Adhesion of water molecules to walls of xylem;
describe and explain the cardiac cycle
- Atrial systole
- ventricles relaxed and atria contract, - decreases their volume so increases the pressure
- forces AV valves to open ,
- blood is pushed into the ventricles
- (Ventricular pressure increases slightly as they fill with blood.) - Ventricular systole
- The atria relax,
- the ventricles contract
- decreases volume
- increases pressure
- forces the AV valves close.
- When pressure increases enough the SL valves are forced open and blood is pumped out through the arteries. - Diastole
- Both atria and ventricles relax.
- pressure in arteries higher than ventricles
- so the SL valves shut.
- Blood enter the atria from the veins.
- starts to increase the pressure of the atria
- eventually pressure exceeds the ventricle pressure,
- the AV valves open slightly, and blood begins to passively flow into the ventricles
Then the cycle restarts.
cardiac cycle condensed
- atrial systole
- atria contract
- increased pressure
- pushing blood into ventricles
> AV valves open & SL closed - ventricular systole
- ventricles contract
- increasing pressure
- AV valves shut
pushing blood out of heart - diastole
- all chambers relax
- pressure in ventricles less than arteries
- SL valves close
- blood flows into heart
