exchange Flashcards
Why do single celled organisms have no specialised exchange system?
Large SA:V, thin surface and short diffusion pathway
Describe the structure of gills:
Lots of thin filaments (increases SA), covered in lots of tiny lamellae (further increases SA), lots of capillaries and thin surface layer of cells so short diffusion distance.
Describe the counter current system:
Water and blood flow in opposite directions. Blood always flows next to water with a slightly higher conc. of oxygen which maintains concentration gradient, so diffusion occurs down entire length of gill
How are plants adapted for gas exchange?
Mesophyll cells are the main gas exchange surface of leaves. Lots of air pockets so large SA.
Stomata are pores in the leaves, they are opened and closed by guard cells
What are trachae, spiracles and tracheoles?
Trachae: air filled pipes
Spiracles: pores on surface of insects
Tracheoles: small tubes with thin permeable walls that go to individual cells
Describe the gas exchange system in insects:
Air moves into trachae through spiracles
Oxygen moves down concentration gradient towards cells
Trachae branch off into smaller tracheoles so oxygen diffuses directly into cells (not transported by the circulatory system)
Carbon dioxide moves down concentration gradient towards spiracles and is released into atmosphere
Insects use rhythmic abdominal movements to move air in/out spiracles
How do insects control water loss?
Insects close spiracles and have thick waxy cuticles all over their body, as well as tiny hairs around spiracles.
How do plants control water loss?
If plant gets dehydrated. Water is lost by guard cells which become flaccid, closing the pore
What is a xerophyte?
Adapted to live in warm, dry or windy habitats
How do xerophytes control water lost?
Stomata sunk into pits to trap water vapour (reducing conc. gradient)
Layers of hair on epidermis
Curled leaves with stomata inside, protecting them from wind
Reduced number of stomata (fewer places for water to escape)
Thicker, waxy, waterproof cuticle on leaves and stem
These all reduce evaporation
Describe the gross structure of the gas exchange system:
Trachea, bronchi, brochioles, alveoli
Describe inspiration:
External intercostal muscles and diaphragm contract, pushing ribs upwards and outwards.
Volume of throacic cavity increases so pressure decreases below atmospheric pressure
Air flows into lungs down pressure gradient
Describe expiration:
External intercostal muscles and diaphragm relax, internal intercostal muscles contract, pulling ribs down and inwards.
Volume of thoracic cavity decreases so pressure increases above atmospheric pressure
Air moves out of lungs, down pressure gradient
How are alveoli adapted to their role?
Wall made of a single layer of cells (alveolar epithelium)
Walls of alveoli contain elastin to recoil to their normal shape after inhaling/exhaling
Have thin exchange surface so short diffusion pathway and large surface are as millions of alveoli
Define:
tidal volume
ventilation rate
forced expiratory volume
forced vital capacity
Tidal volume: volume of air in each breath
Ventilation rate: number of breaths per minute
Forced expiratory volume₁ (FEV₁): max. volume of air that can be breathed out in one second
Forced vital capacity: max. volume of air to forcefully breathe out after 1 deep breath
What is tuberculosis, and what are the common symptoms?
Caused by bacteria. immune cells build wall around bacteria in lungs forming small hard lumps (tubercles). Infected tissue dies and gas exchange surface is damaged so tidal volume decreases. Also causes fibrosis. reduced tidal volume therefore increased ventilation rate
Common symptoms: persistent cough, blood when coughing, mucus, chest pain and shortness of breath
What is fibrosis, and what are the common symptoms?
Formation of scar tissue in lungs caused by infection or substances like asbestos/dust. Scar tissue is thicker and less elastic than lung tissue so less able to expand and tidal volume and FVC reduced. Reduction in the rate of gaseous exchange (bigger diffusion distance). Faster ventilation rate
Common symptoms: shortness of breath, dry cough, chest pain, fatigue and weakness
What is asthma, and what are the common symptoms?
Typically an allergic reaction, causing airways to become irritated and inflamed. Smooth muscle in bronchioles contracts and mucus produced, constricting airways, so difficult to breathe. Reduced air flow in and out of lungs so less oxygen moves into the blood. FEV₁ severely reduced. Asthma treated by drugs in inhalers which relax the bronchiole muscles
Common symptoms: wheezing, tight chest and shortness of breath
What is emphysema, and what are the common symptoms?
Caused by smoking/air pollution- foreign particles become trapped in alveoli. Inflammation attracts phagocytes to area. Phagocytes produce enzyme which breaks down elastin. Alveoli can’t recoil and expel air as well. Also leads to destruction of alveoli walls, reducing surface area so rate decreases. Increased ventilation rate
Common symptoms: shortness of breath, wheezing
What does each enzyme hydrolyse:
amylase
membrane bound disaccharidases
endopeptidase
exopeptidase
dipeptidase
lipase ?
Amylase: hydrolyses glycosidic bonds in starch
Membrane-bound disaccharidases: breaks down disaccharides into monosaccharides
Endopeptidase: hydrolyse peptide bonds within a protein
Exopeptidase: hydrolyse peptide bonds at the end of protein
Dipeptidase: hydrolyse peptide bonds in a dipeptide
Lipase: hydrolyse ester bonds between glycerol and fatty acids
How are carbohydrates digested and absorbed?
Amylase produced by pancreas and salivary glands, and works in mouth and small intestine. Membrane bound disaccharidases attached to cell membrane of epithelial cells lining the ileum. Monosaccharides are absorbed by active transport with Na+ via contransporter. Fructosoe is absorbed via facilitated diffusion
How are proteins digested and absorbed?
Proteins broken down into amino acids by peptidases. Amino acids are absorbed by contransport with Na+
How are lipids digested and absorbed?
Bile salts are produced by liver and emulsify lipids (form small droplets). Formation of droplets increases surface area of lipid available for lipase to work on. Once lipid has been broken down, monoglyceride and fatty acid stick with bile salts to form micelles. Micelles make monoglycerides more soluble in water. Carry monoglycerides to cell membrane and maintain high conc. gradient of monoglycerides to cells lining ileum. Monoglycerides diffuse into cell. Triglycerides reformed, modified and processed by golgi. Combined with protein to form chylomicron. Golgi vesicle transports chylomicron to opposite side of cell to be released by exocytosis.
What is haemoglobin?
Quarternary structure protein, made of 4 chains where each chain has a haem group attached (iron ion)
Define loading, unloading, affinty and pO2:
Loading: oxygen jons Hb
Unloading: oxygen leaves Hb
Affinity: tendency to bind with oxygen
pO2: measure of oxygen concentration
How does pO2 affect Hb’s affinity?
As pO2 increases, haemoglobin’s affinity increases.
Hb loads at high pO2 and unloads at low pO2
Oxygen loads at alveoli in the lungs (high pO2) and unloads at the respiring tissue (low pO2)
What does the dissociation curve show?
Shows how saturated the Hb is with oxygen at any giving pO2.
Where pO2 is high, Hb has a high affinity so has a high saturation, but where pO2 is low, Hb has a low affinity and saturation
Why is the dissociation curve ‘s’ shaped?
Its difficult for the first oxygen molecule to bind to Hb. When it does, the shape of Hb changes slightly, exposing more oxygen binding sites. This makes it easier for more oxygen molecules to bind, causing the s shape
What is the Bohr effect?
pCO2 affects oxygen unloading. Carbon dioxide increases the acidity of blood, changing the tertiary structure of haemoglobin. This causes oxygen to unload at a faster rate. The dissociation curve shifts to the right (lower affinity)
What position is the curve for organisms in low oxygen environments?
Hb has higher affinity than human Hb so curve to the left
What position is the curve for organisms with high activity levels?
Higher oxygen demand (respire more), lower affinity than human Hb (unloads more easily) so curve to the right
What possition is the curve for small animals?
Have high metabolic rate so high oxygen demand. Lower affinity than human Hb so curve to the right.
Describe the role and structure of arteries:
Carry blood away from the heart. Thick muscular walls with elastic tissue to stretch and recoil as the heart beats. Helps maintain high blood pressure. Folded inner lining allows artery to stretch. All carry oxygenated blood except pulmonary artery.
Describe the role of arterioles:
Divided off from arteries. Blood directed to different areas of the body by muscles in the arterioles, which contract to restrict the blood flow or relax to allow full blood flow
Describe the role and structure of veins:
Take blood back to the heart at low pressure. Wider lumen than arteries with very little elastic or muscle. Contain valves to stop backflow of blood. Blood flow helped by constriction of body muscles surrounding them. Carry deoxygenated blood except for the pulmonary vein.
Describe the role and structure of capillaries:
Smallest of blood vessels. Exchange substances with cells. Always found very near cells in exchange tissues, so theres a short diffusion pathway. Large number of capillaries to increase surface area. Networks of capillaries are called capillary beds
Describe how tissue fluid is formed:
At arteriole end of capillary there is a high hydrostatic pressure. This forces any dissolved substances out of capillary and into tissues. Proteins are too large to leave capillaries so the water potential of capillaries decreases. Water enters capillary from tissue by osmosis. Any excess fluid is drained by the lymphatic system, which returns this back to the circulatory system
Define:
Cardiac output
Heart rate
Stroke volume
Cardiac output: volume of blood pumped out by the heart each minute
Heart rate: number of beats per minute
Stroke volume: volume of blood pumped during each heart beat
Describe the structure of the ventricles:
Left has thicker, more muscular walls than the right in order to contract more powerfully. Both have thicker walls than the atria to push blood out the heart
Describe the role of heart valves:
AV valves link the atria to the ventricles to stop backflow into the atria when the ventricles contract
SL valves link ventricles to the pulmonary artery and aorta to stop blood flowing back into the heart when the ventricles contract
Explain the cardiac cycle:
Stage 1: ventricles relaxed, atria contract, decreasing volume of chambers and increasing pressure. AV valves are open so blood pushed into ventricles. Slight increase in ventricular pressure and chamber volume
Stage 2: atria relax, ventricles contract, increasing pressure above atria so AV valves forced shut. Pressure higher in ventricles than aorta and pulmonary arteries so SL valves open and blood forced into these arteries.
Stage 3: ventricles and atria relax, higher pressure in aorta and pulmonary artery so SL valves close. Blood returns to the heart and atria fill again due to higher pressure in vena cava and pulmonary vein. AV valves open. Cycle starts again
What is the role of cords in the heart?
Attach AV valves to ventricles to prevent them being forced into atria when the ventricles contract
How do you calculate cardiac output?
Stroke volume x heart rate
What is an atheroma?
When damage occurs to the epithelial lining of arteries, WBC and lipids from the blood clump together to form fatty streaks. Over time, more WBC, lipids and connective tissue build up and harden to form an atheroma. Partially blocks lumen, restricting blood flow so BP increases
What is an aneurysm?
Balloon like swelling of the artery, caused by atheroma plaque. Damages and weakens arteries and causes BP to increase. When blood travels through at high pressure, it may push the layers of artery through outer elastic layer to form an aneurysm. Can cause a haemorrhage if burst
What is thrombosis?
Atheroma plaque can burst through the endothelium. Damages artery wall and leaves rough surface. Platelets and fibrin accumulate at site of damage and form a blood clot. Can cause complete blockage of artery, or can become dislodged and block a vessel elsewhere. Debris can cause another blood clot further down
What is a myocardial infarction?
If a coronary artery becomes completely blocked, an area of the heart muscle will be totally cut off from its blood supply, receiving no O2, causing a heart attack. Can cause damage and death of heart muscle. If large areas of the heart are affected then complete heart failure can occur.
What are the risk factors for cadiovascular disease?
High BP
High cholesterol
Cigarette smoking
What does the xylem transport?
Water and mineral ions in solution from roots to leaves
What does the phloem transport?
Organic substances both up and down the plant
Outline the cohesion tension theory:
Water evaporates from leaves at ‘top’ of xylem by transpiration
This decreases the water potential of mesophyll, creating tension which pulls more water up to the leaf.
Water molecules are cohesive due to hydrogen bonding so move up xylem in continuous column
Water molecules adhere to xylem walls
What factors affect transpiration?
Light intensity- more light means more stomata open so more area to evaporate from
Temp- higher temperature means more evaporation
Humidity- low humidity means grater concentration gradient between leaf cells and air so increased transpiration rate
Wind- the windier it is, the faster the transpiration rate
Outline the mass flow hypothesis:
At source end, solutes are actively transported from companion cells into sieve tubes.
Water potential decreases inside sieve tubes and water enters sieve tubes by osmosis from xylem
This creates a high pressure at source end of sieve tube
Mass movement of solutes down pressure gradient towards sink end of sieve tube
Solutes are then either used or stored at sink, and water returns to xylem
