Mock Revision Topic 3 Flashcards
Exchange, Digestion + Mass Transport
What is the relationship between the size of an organism/structure and its SA:VOL?
As size increases, the surface area to volume ratio
decreases
How could a single celled organism be adapted to increase its ability to exchange gases? (3)
- Flat
- Long
- Cell membrane projections
Name the structures in the tracheal system of an insect (3)
- Spiracles
- Trachea
- Tracheoles
Explain the counter current principle in fish gills (5)
- Blood flows in the opposite direction to water
- Water always has a higher concentration of oxygen than blood
- Equilibrium never reached
- Diffusion gradient maintained along the whole length of the gill lamella
- Diffusion can happen all along the whole length of the
gill lamella
Describe the path of an oxygen molecule from a chloroplast to the air (6)
- Thylakoid
- Stroma
- Cytoplasm
- Cell wall
- Air space
- Stomata
Terrestrial insects and xerophytic plants have to balance which 2 opposing needs and so make structural and functional compromises?
Gas exchange vs Water retention
Name the structures of the human gas exchange system (9)
- Trachea
- Lung
- Bronchus
- Bronchiole
- Alveolus
- Diaphragm
- Rib cage
- External intercostal muscles
- Internal intercostal muscles
Describe the essential features of the alveolar epithelium as a surface for gas exchange (2)
- A single layer of flattened epithelial cells – the alveolar wall
- A single layer of endothelial cells – the capillary wall
Describe the mechanism of breathing in and how this affects volume/pressure in the thoracic cavity (5)
Inspiration
1. External intercostal muscles contract pulling the ribs upwards and outwards
2. While the internal intercostal muscles relax
3. The diaphragm muscle contracts pulling the diaphragm down so it flattens
4. Both these actions increase the volume of the thoracic cavity.
5. The pressure inside the lungs decreases below atmospheric pressure and air enters the lungs along a pressure gradient.
Describe the mechanism of breathing outand how this affects volume/pressure in the thoracic cavity (6)
Expiration
1. External intercostal muscles relax
2. Internal intercostal muscles contract pulling the ribcage downwards and inwards
3. Diaphragm muscles relax and the diaphragm moves upwards to its dome shape
4. These actions decrease the volume of the thorax
5. The pressure inside the thorax increases above atmospheric and air is forced out of the lungs
6. Elastic recoil of the lung tissue helps to force air out of the lungs during expiration
What is the formula for calculating pulmonary
ventilation rate?
Pulmonary Ventilation = Tidal volume x Ventilation rate
Define digestion (3)
- The process in which large molecules are hydrolysed
- By enzymes to produce smaller molecules
- That can be absorbed and assimilated
For amylase, name the substrate, product and where it is found (2)
Starch into maltose
Salivary glands and pancreas
For maltase , name the substrate, product and where it is found (2)
Maltose into glucose
Ileum epithelium
For membrane-bound dissacharidases, name the substrate, product and where it is found (2)
Dissacharides into glucose
Ileum epithelium
For lipase, name the substrate, product and where it is found (2)
Triglycerides into glycerol, fatty acids and monoglycerides Pancreas
For bile salts, name the process and where it is found (2)
Emulsification
Liver/gall bladder
For endopeptidases, name the substrate, product and where it is found (2)
Large polypeptides into smaller polypeptides and peptides
Stomach
For exopeptidases , name the substrate, product and where it is found (2)
Smaller polypeptides into dipeptides and amino acids Pancreas
For membrane-bound dipeptidases, name the substrate, product and where it is found (2)
Dipeptides into amino acids
Ileum epithelium
Describe the process of co-transport of amino acids or monosaccharides (8)
- Sodium ions move into the epithelial cells down a concentration gradient
- Therefore, when sodium ions enter the epithelial cells
they are actively transported out of these cells and into the blood capillaries - This occurs via specific carrier proteins (sodium-potassium pump) with potassium ions moving in the opposite direction to sodium ions
- Sodium ions will now continue to diffuse into the
epithelial cells from the lumen of the intestines - Through a carrier protein in the cell- surface membrane
- Glucose moves through with the sodium ions, hence the term ‘co-transport’ via a glucose-sodium co transporter
- The glucose then passes into the blood capillary by
facilitated diffusion - Through another specific channel or carrier protein
Describe the role of micelles in the absorption
of lipids (2)
- Micelles transport the poorly soluble monoglycerides
and fatty acids to the surface of the epithelial cell - Where they can be absorbed by diffusing through the
phospholipid bilayer of the epithelial cell surface
membrane
Describe haemoglobin (3)
- Haemoglobin is an iron containing pigment
- Which loosely and reversibly combines with
oxygen to form oxyhaemoglobin - Each haemoglobin molecule consists of four haem units and four polypeptide chains
Name 3 different types of haemoglobin and where they are found
- Adult haemoglobin: red blood cells
- Fetal haemoglobin: red blood cells of fetus
- Myoglobin: muscle
Describe the oxyhaemoglobin dissociation curve when it shifts to the left (2)
- Haemoglobin has a higher affinity for oxygen at a given partial pressure oxygen
- It quickly loads (associates with) oxygen in the lungs where the partial pressure of oxygen is high.
Describe the oxyhaemoglobin dissociation curve when it shifts to the right (4)
- Haemoglobin has a lower affinity for oxygen at a given partial pressure of oxygen
- Bohr shift
- Haemoglobin unloads (dissociates) some of its O2 to the rapidly respiring cells.
- The release of oxygen is increased due to the higher concentration of carbon dioxide in the tissues.
Explain what is meant by the ‘cooperative nature of oxygen binding’ (2)
- The binding of the first oxygen molecule changes the
tertiary/quaternary structures of haemoglobin - This uncovers the binding site of the next haem unit allowing the next oxygen molecule to bind
What is the Bohr effect? (5)
- The Bohr effect is due to the decrease in pH produced as carbon dioxide dissolves in the blood plasma
- To form an acid which increases the concentration of hydrogen ions
- It depresses the O2 dissociation curve (i.e. it moves to
the right) - And haemoglobin has a lower affinity for oxygen and dissociates more readily at the same partial pressure of oxygen
- More oxygen released to respiring tissues.
Describe the location of the coronary arteries
Flows into the heart muscle
Name and describe the location of the blood vessels entering the heart (6)
- Vena carva
- Deoxygenated blood from the body (except lungs)
- Flows into the right atrium
- Pulmonary vein
- Oxygenated blood from the lungs
- Flows into the left atrium
Name and describe the location of the blood vessels leaving the heart (6)
- Pulmonary artery
- Blood flows into the right ventricle
- Which contracts to move deoxygenated blood into the pulmonary artery leading to the lungs
- Aorta
- Blood flows into the left ventricle
- Which contracts to move oxygenated blood into
the aorta leading to the rest of the body / organ systems
Name and describe the location of the blood vessels related to the kidneys (4)
- Renal artery
- Into kidneys
- Renal vein
- From kidneys
Name and describe the location of the blood vessels related to the liver (4)
- Hepatic artery
- Into liver
- Hepatic vein
- From liver
Describe the pressure, volume and associated valve movements during a cardiac cycle to maintain unidirectional flow of blood (13)
- Contraction of the atria
- Pressure becomes higher in the atria then the ventricles
- Atrioventricular valves open
- Blood moves from atria to ventricles
- Contraction of ventricles and atria relax
- Pressure higher in the ventricles than the atria.
- Atrioventricular valves close
- Pressure higher than the pulmonary artery and aorta
- Semilunar valves open and blood leaves the heart
- Ventricles relax
- Pressure in aorta / pulmonary artery higher than ventricles
- Semi lunar valves close
- Blood stops leaving the heart
How does the structure of arteries relate to its function? (5)
- Have a thicker wall and a smaller lumen than
veins - And contain more elastic fibres and smooth muscle fibres
- Do not possess valves except for the aorta and
pulmonary artery - Transport blood at a higher pressure than veins
- Carry oxygenated blood (except for the pulmonary artery)
How does the structure of veins relate to its function? (6)
- Carry blood under low pressure towards the
heart - The walls of veins are thinner than arteries
- And contain less elastic fibres and smooth muscle
- The lumen is larger than in arteries so that even at low pressure, blood flows back to the heart at the same rate
that it leaves along the arteries - Contracting muscles in the legs and body press on the
veins and squeeze the blood along. - Veins have semi-lunar valves at intervals, preventing back-flow ensuring blood travels in one direction
towards the heart
How does the structure of arterioles relate to its function? (2)
- Have a higher proportion of muscle tissue
compared to elastic tissue - Muscles can contract to control blood flow by reducing the size of the lumen
How does the structure of capillaries relate to its function? (11)
- The walls are one endothelial cell thick
- Giving a very short diffusion pathway for the exchange of substances with the tissues
- Gaps between the endothelial cells increase the
permeability of the capillary - Very large numbers of capillaries and they are highly branched
- Giving a large surface area for exchange with the tissues
- The total cross-sectional area of capillaries is very
high - Producing a large frictional resistance, reducing the rate of blood flow
- Allowing more time for the exchange of substances
- No cells are very far from a capillary, giving short
diffusion pathways - Have a very small diameter and red blood cells are squeezed flat against the capillary wall
- Reducing the distance for diffusion of oxygen
What is the function of xylem vessels? How does their structure enable this function? (6)
- Transport of water and ions
- The xylem tissue is dead, there are no cell contents
- This leaves hollow tubes so that there is minimal resistance to the flow of water and ions
- The cell wall has been strengthened by lignin providing support and is impermeable to water
- The cross-walls have broken down completely to allow free flow
- They have pits that allow water and solutes to move
out laterally
Describe the cohesion-tension theory of water transport (9)
- Solar heat energy causes the evaporation or
transpiration of water from leaves - Water evaporates from the mesophyll cells and diffuses
out through the stomata - The water potential of these mesophyll cells is reduced
compared to inner mesophyll cells - Water moves from inner to outer mesophyll cells by
osmosis down a water potential gradient - This water potential gradient extends across the leaf
mesophyll cells to the xylem vessels - Water is drawn from the xylem creating a tension in the
xylem vessels - The water column is maintained in the xylem by cohesive forces and adhesive forces
- Cohesion refers to the attraction of the water molecules to each other by hydrogen bonding
- Adhesion refers to the attraction of the water molecules to the xylem walls
What is the function of phloem vessels? How
does their structure enable this function? (6)
- Transport of photosynthetic products is known as
translocation - Sieve elements are joined end to end to form sieve tubes
- The end walls of sieve elements are known as sieve
plates as they possess pores - Mature sieve elements do not possess a nucleus
- And the cytoplasm which is around the edge of the cell contains few organelles
- Next to each sieve element is a companion cell with
dense cytoplasm and many mitochondria.
Describe the mass flow hypothesis for the mechanism of translocation in plants (9)
- Photosynthetic products are produced in the mesophyll cells in the leaves, known as the source
- These sugars are converted into sucrose
- Sucrose is actively transported into the sieve tubes by
companion cells - This lowers the water potential of the sieve tubes
causing water to enter from xylem by osmosis - This creates a high hydrostatic or turgor pressure in the
sieve tubes in the leaf - Sucrose and other photosythetic products (e.g. amino
acids) are moved from the source to the sink down a
pressure gradient by mass flow - At the sink sucrose is actively transported from the sieve tube into the sink, for growth or storage as insoluble starch.
- This will increase the water potential
- Water moves out of the sieve cells into the xylem which
decreases the hydrostatic pressure
Explain how ringing experiments provided evidence for mass flow (6)
- Ringing involves removing a complete ring of phloem
around part of a plant (usually the stem) - Preventing transport through the phloem at this point
- The first experiments using ringing involved the removal of a complete ring of phloem from
the trunk of a tree during the summer - A few months after ringing a tree trunk, a slight swelling develops above the ring
- This swelling was linked to the build-up of
photosynthetic products from the leaves - Which were prevented from being transported past the ring due to the removal of the phloem
Explain ringing experiments and tracers provided evidence for mass flow (8)
- Using radioactive isotope 14C as a tracer has
enabled more sophisticated experiments using ringing - Obtain two plants of the same species at similar
stages of growth - The stem of plant A is ringed, whereas the other plant B (the control) is left intact
- A leaf below the ring in plant A, and at a similar position in plant B, is supplied with radioactive 14CO2
- The plants are left for a few hours in sunlight
- The transport of the radioactively labelled photosynthetic products can be detected using autoradiography
- Autoradiography involves placing each plant between
X-ray (or photographic) film - The film is then exposed by the radioactively labelled
compounds showing their location
