Section 3: Gas Exchange + Digestion and Absorption Flashcards
What is the relationship between SA:V and metabolic rate?
- Rate of heat loss per unit mass increases as SA: V increases - smaller animals
- So they need a higher metabolic rate/ faster respiration
- To generate enough heat to maintain a constant body temp
What is the relationship between the size of the organism and its SA: V?
- Smaller organisms have a high SA:V
What are the adaptations of gas exchange across the body surface of a single-celled organism?
- Thin, flat shape
- Large SA: V
- Short diffusion pathway
- For rapid diffusion e.g oxygen/ carbon dioxide
How does gas exchange occur in an insect?
- Air moves through spiracles on the surface of the insect
- Air moves through tracheae
- Gas exchange at tracheoles directly to/from cells
- Oxygen diffuses down conc. gradient to respiring cells
- CO2 diffuses down conc gradient from respiring cells
What are the adaptations of the insect’s gas exchange system?
- Lots of thin, branched tracheoles - short diffusion pathway
- Large surface area - rapid diffusion
- Abdominal movements - increase the amount of O2 entering - maintains greater conc gradient for diffusion
How does gas exchange occur in a fish?
- Counter current flow
- Blood flows through lamellae and water flows over lamellae in opposite directions
- Always a higher conc of O2 near blood - hence a conc gradient is maintained along the whole length of lamellae
- Maximising diffusion of oxygen
What are the adaptations of the gas exchange of a fish?
- Each gill is made of lots of gill filaments which are covered in many lamellae - provide a large surface area
- Vast network of capillaries on lamellae - remove oxygen to maintain a conc gradient
- Thin/flattened epithelium - shorter diffusion pathway between water and blood
What is the process of gas exchange in plants?
- Co2/ oxygen diffuses through the stomata
- Stomata opened by guard cells
- CO2 / oxygen diffuse into mesophyll layer into air spaces
- CO2/ oxygen diffuses down conc gradient
What are the adaptations of the gas exchange system in plants?
- Lots of stomata that are close together
- Large SA for gas exchange
- Interconnecting air space in mesophyll layers
- Mesophyll cells have a large surface area
- Thin - short diffusion pathway
What are the adaptations in xerophytic plants?
- Thick waxy cuticle - increases diffusion distance
- Stomata in pits/grooves/ rolled leaves/ hairs - trap water vapour - WP gradient decreased - less evaporation
- Spindles/ needles - reduces SA:Vol
What is the order of passage in the gas exchange in humans?
- Mouth/ nose
- Trachea
- Bronchi
- Bronchioles
- Alveoli
How does gas exchange occur in the alveoli with oxygen?
- Oxygen diffuses from alveoli
- Down its concentration gradient
- Across the alveolar epithelium
- Across the capillary endothelium
- Into the blood
How does gas exchange occur in the alveoli with carbon dioxide?
- Carbon dioxide diffuses from capillary
- Down its concentration gradient
- Across the capillary endothelium
- Across the alveolar epithelium
- Into the alveoli
Why is ventilation needed?
- Maintains an oxygen gradient
- Brings in air containing higher concentration of oxygen
- Removes air with lower concentration of oxygen
What are the essential features of the alveolar epithelium which allows gas exchange to occur?
- Squamous epithelium - 1 cell thick
- Large surface area to volume ratio
- Permeable
- Good blood supply from network of capillaries - maintains conc gradient
- Elastic tissue - recoil
- Surfactant
How are the lungs adapted for efficient/ rapid gas exchange?
- Many alveoli/ capillaries
- Alveoli/ capillary walls are thin
- Ventilation/ circulation
What is the mechanism of breathing in?
- External intercostal muscles contract, internal intercostal muscles relax
- Ribcage moves up and out
- Diaphragm muscles contract - move down
- Increasing volume
- Decreasing pressure
- Atmospheric pressure higher than pressure in lungs
- Air moves down pressure gradient into lungs
What is the mechanism of Breathing out?
- Internal intercostal muscles contract, external intercostal muscles relax
- Moving rib cage down and in
- Diaphragm relaxes, move upwards
- Decreasing volume
- Increasing pressure
- Atmospheric pressure lower than pressure in lungs
- Air moves down pressure gradient out of lungs
What is tidal volume?
- Volume of air in each breath
What is Ventilation rate?
- Number of breaths per minute
What is Forced Expiratory volume (FEV)?
- Maximum volume of air that can be breathed out in 1 second
What is Forced Vital capacity (FVC)?
- Maximum volume of air possible to breathe forcefully out of lungs after a deep breath in
What is Fibrosis and what is its effect?
- Scar tissue in lungs - scar tissue is thicker and less elastic than normal
- Diffusion distance increased - rate of diffusion of decreased
- Lungs can expand and recoil less - can’t hold as much air - reduced tidal volume/ reduced forced vital capacity
What is asthma and what is its effect?
- Asthma - inflamed bronchi
- Asthma attack: smooth muscle lining bronchioles contracts
- Constriction of airways - narrow diameter - airflow in/ out of lungs reduced - FEV reduced
- Less oxygen enters alveoli/ blood
What happens when there is a reduced rate of gas exchange in the alveoli?
- Less oxygen diffuses into blood
- Cells receive less oxygen
- Rate of aerobic reduced
- Less energy released
- Fatigue/ weakness
Why are a large biological molecules hydrolysed into smaller molecules?
- Large biological molecules in food e.g starch/ proteins too big to be absorbed across cell membranes
- Digestion breaks them into smaller molecules e.g glucose/ amino acids - absorbed from the gut to the blood
How is starch hydrolysed?
- Amylase hydrolyses starch to maltose
- Amylase produced by salivary glands, released into mouth
- Amylase produced by pancreas, released into small intestine
- Membrane bound maltase hydrolyse maltose to glucose by hydrolyses glycosidic bond
How are disaccharides digested?
- Membrane bound disaccharides e.g maltose, sucrose, lactase hydrolyse a disaccharide into 2 monosaccharide
- Maltase - glucose + glucose
- Sucrase - fructose + glucose
- Lactase - galactose + glucose
- Hydrolyses a glycosidic bond
How are lipids digested in mammals?
- Bile salts produced by the liver
- Bile salts emulsify lipid to smaller lipid droplets - increasing surface area of lipids and speeds up action of lipases
- Lipase made in the pancreas, released to small intestine
- Lipase hydrolyses lipids - monoglycerides + fatty acids
- Breaking ester bond
- Monoglycerides, fatty acids and bile salts stick together to form micelles
How are lipids digested in mammals?
- Bile salts produced by the liver
- Bile salts emulsify lipid to smaller lipid droplets - increasing surface area of lipids and speeds up action of lipases
- Lipase made in the pancreas, released to small intestine
- Lipase hydrolyses lipids - monoglycerides + fatty acids
- Breaking ester bond
- Monoglycerides, fatty acids and bile salts stick together to form micelles
How are proteins digested in mammals?
- Endopeptidases -
- Hydrolyse peptide bonds within a protein/ between amino acids in the central region. 2 smaller peptides
- Exopeptidases -
- Hydrolyse peptide bonds at the ends of the protein molecules. Removing a single amino acid
- Dipeptidases -
- Often membrane bound to ileum. Hydrolyse peptide bond between dipeptide.
Exam Question: Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own (2)
- Endopeptidases hydrolyse internal peptide bonds OR exopeptidases remove amino acids/ hydrolyse bonds at ends
- More ends or increased surface area
How are glucose and amino acids absorbed?
- Sodium ions are actively transported out of the epithelial cells lining the ileum, into the blood by the sodium potassium pump
- This creates a concentration gradient (higher in the lumen than ileum)
- Sodium ions and glucose move by facilitated diffusion using a co-transporter protein
- This creates a concentration gradient of glucose - higher in epithelial than blood
- Glucose moves out of cell into blood by facilitated diffusion through a protein channel
Exam Question: The addition of a respiratory inhibitor stops the absorption of amino acids. Why?
- No/ less ATP produced
- Sodium ions not moved out of cell
- No diffusion gradient for sodium to move into cell with amino acid
How are lipids absorbed?
- Monoglycerides and fatty acids diffuse out of micelles into epithelial cell - because they are lipid soluble
- They recombine into triglycerides which aggregate into globules
- Globules coated with proteins to form chylomicrons
- Leave via exocytosis and enter lymphatic vessels
- Return to blood circulation
