3.3 and 3.4 Flashcards
Explain what happens in digestion:
Large (insoluble) molecules hydrolysed to smaller (soluble) molecules that are small enough to be absorbed across cell membranes into blood
Describe the digestion of starch in mammals:
Amylase produced by salivary glands hydrolyses starch to maltose
Membrane bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
Hydrolysis of glycosidic bond
Describe the digestion of disaccharides:
Membrane bound disaccharidases hydrolyse disaccharides to 2 monosaccharides
Hydrolysis of glycosidic bond
Describe the digestion of lipids in mammals, including action of bile salts
Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
This increases surface area of lipids for increased/faster lipase activity
Lipase (made in pancreas) hydrolyses lipids to monoglycerides and fatty acids
Hydrolysis of ester bond
Describe the digestion of proteins by a mammal:
Endopeptidases- hydrolyse internal bonds within a polypeptide- smaller peptides
Exopeptidases- hydrolyse terminal peptide bonds at ends of polypeptide- single amino acids
Membrane-bound dipeptidases- 2 amino acids
Hydrolysis of peptide bond
Why are membrane bound enzymes important in digestion?
Membrane bound enzymes are located on cell membranes of epithelial cells lining ileum
By hydrolysing molecules at the site of absorbtion they maintain conc. gradients for absorption
Describe the pathway for absorption of products of digestion in mammals:
Lumen of ileum
Cells lining ileum
Blood
Describe the absorption of glucose/amino acids in mammals:
Na+ actively transported from epithelial cells lining ileum to blood by Na+/K+ pump
Establishes conc. gradient of Na+
Na+ enters epithelial cells down its conc. gradient with glucose/amino acid against its conc. gradient
Via a co-transporter protein
Glucose/amino acid moves down conc. gradient into blood via facilitated diffusion
Describe the absorption of lipids by a mammal including the role of micelles:
Micelles contain bile salts, monoglycerides and fatty acids
-Make monoglycerides and fatty acids more soluble in water
-Carry release fatty acids and monoglycerides to cell/lining of ileum
-Maintain high conc of fatty acids to cell/lining
Monoglycerides/fatty acids absorbed into epithelial cell by diffusion
Triglycerides reformed in epithelial cells and aggregate into globules
Globules coated with proteins forming chylomicrons which are then packaged into vesicles
Vesicles move to cell membrane and leave via exocytosis
Enter lymphatic vessels and eventually return to blood circulation
Describe the role of red blood cells and haemoglobin
RBC contain lots of Hb, and have no nucleus, biconcave shape, high SA:V and short diffusion pathways
Hb associates with O2 at gas exchange surfaces where pO2 is high
This forms oxyhaemoglobin which transports O2
Hb dissociates from/unloads O2 near cells/tissues where pO2 is low
Describe the stucture of Hb
Protein with quarternary structure
Made of 4 polypeptide chains
Each chain contains a haem group containing an iron ion
Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve
Areas with low pO2:
Hb has low affinity for O2
So O2 readily dissociates with Hb
So % saturation is low
Areas with high pO2:
Hb has a high affinity for O2
So O2 readily loads/associates with Hb
So % saturation is high
Explain how the cooperative nature of O2 binding results in an s-shaped curve:
Binding of first oxygen changes tertiary/quarternary structure of haemoglobin
This uncover haem group binding sites making further binding of O2 easier
Describe evidence for the cooperative nature of oxygen binding:
At low pO2 as oxygen increases there is little/slow increase in % saturation of Hb with oxygen
At higher pO2 as oxygen increases there is a big/rapid increase in % saturation of Hb with oxygen
What is the Bohr effect?
Effect of CO2 conc. on dissociation of oxyhaemoglobin- curve shifts to the right
Explain the effect of CO2 concentration on the dissociation of oxyhaemoglobin:
Increasing blood CO2 (e.g due to increased rate of respiration
Lowers blood pH (more acidic)
Reducing Hbs affinity for oxygen as shape/tertiary/quarternary structure changes slightly
So more/faster unloading of oxygen to respiring cells at a given pO2
Explain the advantage of the Bohr effect:
More dissociation of oxygen so faster aerobic respiration/less anaerobic respiration so more ATP produced
Explain why different types of haemoglobin can have different oxygen transport properties
Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
Results in different tertiary/quarternary structures/shape so different affinities for oxygen
Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties:
Curve shifts left so Hb has higher affinity for O2:
-More O2 associates with Hb more readily
-At gas exchange surfaces where pO2 is lower
-E.g organisms in low O2 environments (high altitudes/underground/foetuses)
Curve shifts right so Hb has lowere affinity for O2:
-More O2 dissociates more readily
-At respiring tissues where O2 is more needed
-E.g organisms with high rates of respiration/metabolic rate (may be small or active)
Define closed double circulatory system:
Blood passes through heart twice for every circuit around the body
Describe the general pattern of blood circulation in a mammal:
Deoxygenated blood in right side of heart pumped to lungs, oxygenated returns to left side
Oxygenated blood in left side of heart pumped to rest of body, deoxygenated returns to right
Suggest the importance of a double circulatory system:
Prevents mixing of oxygenated/deoxygenated blood so blood pumped to body is fully saturated for aerobic respiration
Blood can be pumped to body at a higher pressure so substances taken to/removed from body cells quicker/more efficiently
Name the blood vessels entering and leaving the heart and lungs:
Vena cava- transports deoxygenated blood from respiring body tissues to heart
Pulmonary artery- transports deoxygenated blood from heart to lungs
Pulmonary vein- transports oxygenated blood from lungs to heart
Aorta- transports oxygenated blood from heart to respiring body tissues
Name the blood vessels entering and leaving the kidneys
Renal arteries- oxygenated blood to kidneys
Renal veins- deoxygenated blood from kidneys to vena cava
Name the blood vessels that carry oxygenated blood to the heart muscle
Coronary arteries- located on surface of heart branching from aorta
Suggest why the wall of the left ventricle is thicker than that of the right:
Thicker muscle to contract with greater force
To generate higher pressure to pump blood around entire body
Explain the pressure and volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional blood flow
Atrial systole:
Atria contract- volume decreases, pressure increases
Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
Semilunar valves remain shut as pressure in arteries exceeds pressure in ventricles
So blood pushed into ventricles
Ventricular systole:
Ventricles contract- volume decreases, pressure increases
Atrioventricular valves shut when pressure in ventricles exceeds pressure in atria
Semilunar valves open when pressure in ventricles exceeds pressure in arteries
So blood pushed out of heart through arteries
Diastole:
Atria and ventricles relax- volume increases, pressure decreases
Semilunar valves shut when pressure in arteries exceeds pressure in ventricles
Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
So blood fills atria via veins and flows passively to ventricles
What is the equation for cardiac output?
Cardiac output = stroke volume x heart rate
How can heart rate be calculated from cardiac cycle data?
Heart rate= = 60 ÷ length of one cardiac cycle
Explain how the structure of arteries relates to their function:
Thick smooth elastic tissue- can contract and control/maintain blood flow/pressure
Thick elastic tissue- can stretch as ventricles contract and recoil as ventricles relax to reduce pressure surges/even out blood pressure/maintain high pressure
Thick wall- withstand high pressure/ stop bursting
Smooth/folded endothelium- reduces friction/can stretch
Narrow lumen- increases/ maintains high pressure
What is the function of arterioles?
Direct blood flow to different capillaries/tissue
Explain how the structure of arterioles relates to their function:
Thicker smooth muscle layer than arteries:
Contracts to narrow lumen (vasoconstriction) and reduce blood flow to capillaries
Relaxes to woden lumen (vasodilation) and increases blood flow to capillaries
Thinner elastic layer- pressure surges are lower (as further from heart)
Explain how the structure of veins relates to their function:
Wider lumen than arteries- less resistance to blood flow
Very little elastic and muscle tissue- blood pressure lower
Valves- prevent backflow of blood
What is the function of capillaries?
Allows efficient exchange of substances between blood and tissue fluid
Explain how the structure of capillaries relates to their function:
Wall is a thin layer of endothelial cells to reduce diffusion distance
Capillary bed is a large network of branched capillaries to increase SA for diffusion
Small diameter/narrow lumen- reduces blood flow rate so more time for diffusion
Pores in walls between cells- alllow larger substances through
Explain the formation of tissue fluid:
At arteriole end of capillaries:
Higher blood/hydrostatic pressure inside capillaries (due to contraction of ventricles) than tissue fluid
Forces water (and dissolved substances out of capillaries
Large plasma proteins remain in capillary
Explain the return of tissue fluid to the circulatory system
At venule end of capillaries
Hydrostatic pressure reduces as fluid leaves capillary
Increasing conc. of plasma proteins lowers water potential of capillary below that of tissue fluid
Water enters capillaries from tissue fluid by osmosis down a water potential gradient
Excess water taken up by lymph capillaries and returned to circulatory system through veins
Suggest and explain causes of excess tissue fluid accumulation:
Low conc. of protein in blood plasma:
Water potential in capillary not as low so water potential gradient reduced
So more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis
High BP- high hydrostatic pressure:
Increased outward pressure from arterial end, and reduced inward pressure at venule end
So more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis
Lymph system may not be able to drain excess fast enough
What is a risk factor?
An aspect of a person’s lifestyle or substance in a person’s body/environment
That have been shown to be linked to an increased rate of disease
Describe the function of xylem tissue
Transports water (and mineral ions) through the stem, up the plant to leaves of plants
Suggest how xylem tissue is adapted for its function:
Cells joined with no end walls to form a long continuous tube- water flows down as a continuous column
Cells contain no cytoplasm/nucleus so easier water flow/no obstructions
Thick cells walls with lignin- provides support/withstand tension/prevents water loss
Pits in walls- allow lateral water movement
Explain the cohesion tension theory:
Water lost from leaf by transpiration- water evaporates from mesophyll cells into air spaces and water vapour diffuses through open stomata
Reducing water potential of mesophyll cells
So water drawn out of xylem down a water potential gradient
Creating tension in xylem
Hydrogen bonds result in cohesion between water molecules so water pulled up as one continuous column
Water also adheres to walls of xylem
Water enters roots by osmosis
How does light intensity affect transpiration rate?
Increases rate of transpiration
Stomata open in light to let in CO2 for photosynthesis
allowing water to evaporate faster
Stomata close when its dark so there is a low transpiration rate
How does temperature affect transpiration rate?
Water molecules gain kinetic energy as temperature increases so water evaporates faster
How does wind intensity affect transpiration rate?
Wind blows away water molecules from around stomata, decreasing water potential of air around stomata
Increases water potential gradient so water evaporates faster
How does humidity affect transpiration rate?
More water in air so it has a higher water potential
Decreases water potential gradient from leaf to air so water evaporates slower
Describe the function of the phloem tissue
Transports organic substances in plants
Suggest how the phloem tissue is adapted for its function
Sieve tube elements
-no nucleus/few organelles to maximise space for/easier flow of organic substances
-End walls between cells perforated
Companion cells
-many mitochondria so high rate of respiration to make ATP for active transport of solutes
What is translocation?
Movement of assimilates/solutes such as sucrose
From source cells to sink cells by mass flow
Explain the mass flow hypothesis for translocation in plants:
At source end, sucrose is actively transported into phloem sieve tubes/cells by companion cells
This lowers water potential in sieve tubes so water enters by osmosis
This increases hydrostatic pressure in sieve tubes/ creates a hydrostatic pressure gradient
So mass flow occurs- movement of source to sink
At sink, sucrose is removed by active transport to be used by respiring cells or stored in storage organs
Describe the use of tracer experiments to investigate transport in plants:
Leaf supplied with radioactive tracer e.g CO2 containing radioactive isotope 14C
Radioactive carbon incorporated into organic substances during photosynthesis
These move around plant by translocation
Movement tracked using autoradiography or a Geiger counter
Describe the use of ringing experiment to investigate transport in plants:
Remove/kill phloem e.g remove a ring of bark
Bulge forms on source side of ring
Fluid from bulge has higher conc. of sugars than below- shows sugar is transported in phloem
Tissues below ring die as cannot get organic substances
