Topic 3 - Organisms Exchange Substances Flashcards
How does gas exchange occur in the lungs
Oxygen diffuses into the alveoli through the bilayer. It then diffuses across the alveolar walls and capillary endothelium into the blood.
How is the alveolar endothelium adapted for gas exchange
-Large surface area
-Short diffusion pathway as they have thin walls
-Good blood supply
Why is diffusion from the alveolar into the blood rapid
-Red blood cells are slowed as they pass through pulmonary capillaries due to friction so oxygen can bind to them
-Distance between alveolar and red blood cells is reduced as the red blood cells are flattened against the capillary
-Breathing and blood movement ensure a steep concentration gradient is maintained
-Capillaries are touching the alveoli so O2 doesn’t have to go through tissue fluid
Outline how ventilation works when breathing in
-Volume of the thorax increases so pressure decreases and air enters the lungs
-Rigs move up and out
-External intercostals contract
-Diaphragm muscle contracts and moves down
Outline how ventilation works when breathing out
-Volume of thorax decreases, so pressure increases and air is forced out
-Ribs move in and down
-Internal intercostal muscles relax
-Diaphragm muscles relax and move up
Outline the structure of the human gas exchange structure
-Trachea leads into the bronchi which leads into smaller bronchioles which lead to alveoli
-Lungs are supported by the ribcage
Outline gills in fish for gas exchange
-Fish have 4 pairs of gills located in the pharynx
-Gills are composed of thousands of filaments covered in feathery lamallae which are at a right angle
-Gills have a rich blood supply
Why is fish using water as a gas exchange medium a problem
- Water contains less oxygen than air (30 times less - 0.7% compared to 21%)
- Diffusion takes longer as there is a smaller concentration gradient
- Water is more dense and harder to move
Outline the countercurrent exchange principle
-The blood and water flow over the fill lamellae in opposite directions so the oxygen concentration gradients is maintained across the whole membrane
-The water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood
Why do smaller fish tend to use parallel flow
-They don’t need as much oxygen so tend to use parallel flow as it’s less efficient
-Faster fish need more oxygen for energy so use counter current flow so oxygen exchange is very efficient
Why is fish having a one-way flow of water over its gills an advantage
-Less energy is needed
-Continuous flow of O2 or H2O
Outline gas exchange in a plant leaf
-No living cell is far from the external air and therefore a source of O2 and CO2
-Diffusion takes place in air so it is more rapid than if it’s in water
How are leaves adapted for gas exchange
-Short diffusion pathway
-Air spaces inside the leaf have large surface area. Compared to volume of living tissue.
-Small pores (stomata) so no cell is far from a stoma therefore the diffusion pathway is short
-Large surface area of mesophyll cells
How do insects balance the opposing needs of gas exchange with reducing water loss
-Waterproof coverings over their body surfaces. This is a rigid outer skeleton that is covered with a water proof cuticle.
-Small surface area: volume ratio to minimise which water is lost
How do gases move in and out of the tracheal system by ventilation
The movement of muscles in insects creates mass move of air in and out of the tracheae. This speeds up has exchange and is known as abdominal pumping and is a feature of larger insects during activity such as flight.
How do gases move in and out of the tracheal system along a diffusion gradient
O2 is higher in the air than in the trachea and tracheoles as the insect is continually using up O2 in respiration
How do spiracles work on insects
Gas enters and leaves tracheae through tiny pores called spiracles on the surface. They are opened and closed by a valve. When open, water can evaporate and so insects keep them closed apart from when they periodically open to allow gas exchange.
How do insects adapt when moving in order to exchange gas
-At rest tracheoles contain a large volume of water fluid
-Diffusion of O2 in H2O is about 300,000 times slower than in air, so the presence of his fluid slows the uptake of O2
-During activity water is withdrawn from the ends of the tracheoles so that the gases can diffuse more quickly
What is digestion
Large biological molecules (e.g. starch and proteins) in food are too big to cross cell membranes so they can’t be absorbed from the gut into the blood. During digestion they are broken into smaller molecules which can cross the cell membrane so they can be absorbed from the gut into the blood to be transported around the body for use by the body cells.
What are digestive enzymes
Used to break down biological molecules in food. A variety of different digestive enzymes are produced by specialised cells in the digestive systems. The enzymes are released to mix with food. Since enzymes only work with specific substrates different enzymes are needed to catalyse the breakdown of different food molecules.
Outline how amylase breaks down food molecules
It is a digestive enzymes that catalysed the breakdown of starch which is a mixture of two polysaccharides, each made from long chains of alpha-glucose molecules. Amylase works by catalysing hydrolysis reactions that break the glycosidic bonds in starch to produce maltose.
Where is amylase produced
-The salivary glands, which release amylase into the mouth
-The pancreas which releases amylase into the small intestine
Outline membrane-bound disaccharides
Enzymes that are attached to the cell membranes of epithelial cells lining the ileum (end of small intestine) and they break down disaccharides into monosaccharides which involves the hydrolysis of glycosidic bonds.
What happens to the monosaccharides after carbohydrate digestion
They can be transported across the epithelial cell membranes in the ileum via specific transporter proteins
What is the process of digestion lipids
- Lipase enzymes catalyse the breakdown of lipids into monoglycerides and fatty acids. This involves the hydrolysis of the ester bonds in lipids. Lipases are mainly made in the pancreas - they’re then secreted into the small intestine where they act.
- Bile salts are produced in the liver and emulsify lipids. Several small lipid droplets have a higher SA than a single large droplet so this increases SA of lipid for lipases.
- The monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles which help the products of lipid digestion to be absorbed
Outline bile salts
-Produced by the liver and emulsify lipids
-Not enzymes but are important in lipid digestion process
-Bile is alkaline and neutralises the acidity of the food coming from the stomach ensuring lipase cane function at its optimum pH
What is endopeptidase
Breaks down proteins in the middle into smaller pieces
What is exopeptidase
Breaks down proteins at the end of the chain
Outline the digestion of proteins
-Broken down by a combination of different peptidases. These are enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.
-Endopeptidases hydrolyse peptide bonds within a protein
-Exopeptidase act to hydrolyse peptide bonds at the ends of protein molecules. They remove single amino acids from proteins.
Outline dipeptidases
Exopeptidases that work specifically on dipeptides. They act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them. Dipeptidases are often located in the cell-surface membrane of epithelial cells in the small intestine
How are monosaccharides absorbed after digestion
-Glucose is absorbed by active transport with sodium ions via a co-transporter protein.
-Galactose is absorbed in the dame way using the same co-transporter protein.
-Fructose is absorbed via facilitated diffusion through a different transporter protein
How are monoglycerides and fatty acids absorbed after digestion
Micelles help to move them towards the epithelium. As micelles constantly break up and reform they can release the products allowing them to be absorbed. Whole micelles are not taken up across the epithelium. Monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane.
How are amino acids absorbed by digestion
They are absorbed in a similar way to glucose and galactose. Sodium ions are actively transported out of the epithelial cells into the ileum itself. They then diffuse back into the cells through sodium dependent transport proteins in the epithelial cell membranes, carrying the amino acids with them.
What is the role of haemoglobin
It’s found in red blood cells and it carries oxygen around the body
Outline haemoglobin transporting oxygen
-Oxygen is carried around the body in red blood cells
-Red blood cells contain the molecule haemoglobin which joins with oxygen to make oxyhemoglobin in the lungs (loading) , this is a reversible reaction - near the body cells oxygen leaves and turn back to haemoglobin (unloading)
What is the reversible reaction for unloading/loading between haemoglobin and oxygen
Hb + 4O2 > HbO8
Haemoglobin + oxygen > oxyhaemoglobin
Outline the haemoglobin structure
-Large globular protein made up of four polypeptide chains, each chain contains one haem group. A haem group contains an iron ion and gives haemoglobin its red colour. Each molecule of human haemoglobin can carry four oxygen molecules.
Outline haemoglobin’s protein structure
Primary - 4 polypeptide chain
Secondary - Polypeptide chains coil into alpha helix chains
Tertiary - Each chain is folded into a precise shape which is an important factor in its ability to carry oxygen
Quaternary - 4 polypeptide chains are linked together to form an almost spherical molecule.
What is high affinity haemoglobin
Readily binds with oxygen
What is low affinity haemoglobin
Bind with oxygen less readily
What is oxygen saturation
-The amount of oxygen bound to the haemoglobin in our blood
-Units are SaO2%
-Blood leaving the lungs normally has a saturation of 95-99%
Outline how oxygen loading and unloading takes place
-CO2 at gas exchange is removed increasing the pH, changing haemoglobin structure so has higher affinity for oxygen.
-In tissues CO2 is produced by reprising cells so pH of tissue blood is low which makes haemoglobin has lower affinity for oxygen, so oxygen releases oxygen into respiring tissues.
-If tissue with low respiratory rate it’ll only release 1 oxygen molecule returning to the lungs 75% saturated
-If tissue is active haemoglobin will unload 3 oxygen molecules and become 25% saturated.
