Exchange Flashcards
(28 cards)
What surface area to volume ratio do larger organisms have?
Smaller ratio
How does gas exchange work in unicellular organisms?
They are constantly respiring (using up oxygen) so the concentration of oxygen inside the cell will always be low compared with outside the cell,
Oxygen then diffuses through the cell-surface membrane and carbon dioxide diffuses out,
Because they have a high surface area to volume ratio the rate at which gases are exchanged is enough to supply the cells need so it doesn’t have any adaptations to help,
There is also a very short diffusion pathway,
How do insects exoskeleton help them breath?
The exoskeleton is made of chitin and covered in a cuticle which is impermeable to water so helps the insects conserve water,
There are small openings in the cuticle called spiracles, they are connected to the inner organs by tracheae,
The system has a very large surface area but in protected inside the body so avoids water loss.
Gas exchange happens in the ends of the tracheae- called the tracheoles, diffusion pathways are very short,
Very active insects have muscles that pump air in and out of the tracheae.
How does gas exchange work in fish?
They obtain their oxygen from it being dissolved in the water,
Water is passed over the gills (their gas exchange surface),
Inside the gills are projections called secondary lamellae which provide a large surface area,
The diffusion path is short because there is only a very thin layer of cells between the lamellae and the blood,
What is a counter current system?
Oxygen is not very soluble in water so fish struggle to obtain enough oxygen from it, they have evolved a system where the water and blood flow in opposite directions which increases the efficiency of gas exchange because;
- The water that has just entered the gills is saturated with dissolved oxygen so there is a large diffusion gradient
- The water keeps moving and although much of the oxygen has already diffused it then encounters the blood that has just entered the gills and so has a lower concentration of oxygen so more diffuses down the concentration gradient
How does gas exchange work in plants?
They have a much more branching shape than animals which increases their surface area to volume ratio,
Gases diffuse through the stomata the diffuse through the intercellular spaces in the mesophyll, because the leaves are thin the diffusion pathway is short,
Loss of water vapor can be avoided by guard cells around the stoma that can close or open the stoma to allow more of less gas to leave,
What is the structure of the human gas exchange system?
The traches, a tube with cartilage reinforced wall, runs from the mouth and nose down into the thorax,
It then branches into two bronchi which then divide into multiple bronchioles- these branch again into millions of tiny sacks called alveoli,
How does gas exchange work in humans?
Epithelial cells, that make up the walls of the alveoli, contain lots of capillaries, this rich blood supply is essential to carry oxygen away and bring carbon dioxide in,
The oxygen rich blood is quickly taken away creating a steep concentration gradient so oxygen continues to diffuse in,
Alveolar walls are very thin so there is a short diffusion pathway
The walls of the alveoli are permeable which allows oxygen to pass into the cells and water pass out- the exchange surface is always moist so the cells don’t dry out and die,
What is ventilation?
The movement of air in and out of the lungs, it is a tidal process because air passes in both directions,
What happens during inspiration?
It is an active process,
The diaphragm contracts and flattens,
The external intercostal muscle contracts which pulls the rib cage up and out,
Both of these actions increase the thoracic volume which reduces the pressure inside the thorax- which creates a pressure gradient and air flows into the lungs (down the concentration gradient)
What happens during expiration?
It is a passive process,
The diaphragm muscles relax and curve,
The external intercostal muscle relaxes so the lungs and chest return to normal volume which increases the pressure and air flows out of the lungs (down the pressure gradient)
What is a spirometer
A piece of apparatus that measures the gas exchange in the lungs by measuring the volume of air breathed in an out
What is tidal volume
The volume of air in a normal breath
What is vital capacity
The total volume of the lungs (max amount of air that can be breathed out after breathing in as much air as possible)
What is breathing rate
How many breaths in one minute
What is ventilation rate
Volume of air breathed in/out in 1 minute
What are some lung diseases
Tuberculosis, Fibrosis, Asthma, Emphysema, Lung cancer
What are some risk factors for lung diseases
Smoking, radiation exposure
What is the definition of digestion
The process which large, insoluble molecules are broken down into small, soluble molecules
How are carbohydrates digested
They are broken down into maltose by amylase from the salivary glans in the mouth,
The stomach then neutralises the amylase enzyme using bile,
Pancreatic amylase breaks down any remaining starch into maltose,
The lining of the small intestine contains an enzyme called maltase which breaks down maltose into glucose,
The glucose is then absorbed into the bloodstream,
Disaccharides pass through the stomach to the small intestine, hydrolysed by enzymes located in the wall of the small intestine
Sucrose is digested by sucrase, lactose is digested by lactase
How are proteins digested
Exopeptidase hydrolyses the peptide bonds within protein molecules (pepsin, trypsin) then the endopeptidase hydrolyse the peptide bonds at the end of protein molecules, releasing amino acids,
Dipeptidases only work on dipeptides to separate two amino acids, they are found on the cell membrane of the small intestine endothelium,
How are Lipids digested
Lipids are insoluble in water so remain clumped together when they mix with watery liquids in the alimentary canal,
Bile produces by the liver flows into the small intestine, bile contains bile salts which are molecules with hydrophobic and hydrophilic regions,
These break down the lipid molecules as they can interact with the complimentary polar region,
They form tiny droplets called micelles which increase the surface area for lipase action, the mixture o micelles and water is called an emulsion
Once the lipid droplets have dispersed in this way, lipase enzymes are able to make contact with the individual lipid molecules in the micelles,
Lipase is in pancreatic juices which are in the small intestine
How is the small intestine adapted for efficient absorption
The lining of the small intestine is folded,
Its surface is covered in villi,
Th epithelial cells on the surface of the villi have a folded cell membrane, forming microvilli,
What is absorption
Once food molecules have been digested they need to pass into the body by passing through the epithelial cells of the small intestine, which involves crossing the cell membranes twice
