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44 Cards in this Set
- Front
- Back
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What is Fick's law |
diffusion is directly proportional to (surface area x difference in concentration) ÷ length of diffusion path |
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What are 5 features of specialised exchange surfaces? |
•Large SA to V ratio to increase rate of exchange •Very thin so there is a short diffusion distance •Selectively permeable to allow selected materials to cross •Movement of the internal medium-e.g to maintain a diffusion gradient •A transport system to ensure movement of the internal medium |
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Why do small organisms not need specialised exchange surfaces? |
They have a large SA to V ratio so they can exchange substances efficiently across their body surface |
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What are tracheoles? |
A network of dead-end tubes, supported by strengthened rings to stop them collapsing, throughout the body of the insect |
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How does mass transport help air move in and out of the tracheoles? |
The contraction of muscles in the insect can squeeze the trachea, enabling mass movements of air in and out |
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In what three ways do gases move in and out of the tracheal system? |
•Along a diffusion gradient •Mass transport- by the contraction of muscles to squeeze the trachea to move air in and out •By the fluid filled ends of the trachea entering the cells by osmosis, drawing air further into them which means that during major activity the final diffusuion pathway is in a gas rather than a liquid so is more rapid. |
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How do the fluid-filled ends of the trachea help air move in and out? |
During periods of major activity, the muscle cells have to respire anaerobically which produces lactate, which is soluble so lowers the cell's water potential. This causes the water at the ends of the tracheoles to move in by osmosis and out of the tubes, drawing air further into the tracheoles |
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Why do insects have spiracles? |
They can either be open, to allow gas exchange, or during periods of rest they can be closed by the insect to prevent water vapour from evapourating from the insect |
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Why are insects small? |
As their tracheal system relies mostly on diffusion for gas exchange, they need to be small so the diffusion pathway is short |
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Why do fishes gills have lamellae? |
The gill lamellae are at right angles to the gill fillaments and increase surface area |
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Why do fish's gills use countercurrent exchange? |
It ensures that the maximum amount of oxygen can be absorbed- same direction flow only results in 50% of the oxygen being taken up. Countercurrent exhange ensures that blood always meets water with a higher concentration of oxygen in it than in the blood. |
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What are three adaptions leaves have for diffusion? |
•Many small pores called stomata, so no cell is far from a stomata and there is a short diffusion pathway •Numerous interconnecting air spaces throughout the mesophyll so gases can readily come in contact with mesophyll cells •Large SA of mesophyll cells for rapid diffusion |
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Why do plants have stomata? |
They allow gases to diffuse in and can be opened and closed depending on how much the plant needs to conserve water |
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What are three adaptions insects have to conserve water? |
•Small SA to V ratio- minimises the area over which water is lost •Waterproof coverings over their body surfaces- a rigid outer skeleton of chitin covered with a waterproof cuticle •Spiracles- which can be closed when the insect is at rest to prevent water loss |
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What are 5 adaptions of xerophytes to conserve water? |
•Thick cuticle-means less water can escape through the cuticle •Rolled leaves- as the stomata are mainly on the lower epidermis, rolling the leaf to protect the lower epidermis from the outside traps moist air outside the stomata, reducing the water potential gradient •Hairy leaves- also traps a layer of still, moist air to reduced water potential gradient •Stomata in pits or grooves-same again •Reduced SA to V ratio- needs to be balanced with the needs for a higher SA to V ratio for photosynthesis |
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Why do xerophytes sometimes have rolled leaves? |
The stomata of many plants are largely or entirely on the lower epidermis. Rolling the leaves helps trap a layer of still air within the rolled leaf. This becomes saturated with water vapour, reducing the water potential gradient between inside the leaf and outside. |
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Why are lungs located inside the body? |
•Air is not dense enough to support and protect them as they are very delicate •The body as a whole would otherwise lose a lot of water and dry out |
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What is the trachea? |
A flexible airway supported by rings of cartilage to keep it from collapsing when air pressure falls during inspiration. The tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells which produce mucus to trap dirt and move it towards the throat. |
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Why do the alveoli have elastic fibres between them? |
They allow the alveoli to stretch as they fill with air when breathing in. They then spring back when breathing out in order to expel the air |
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What are the bronchioles? |
A series a branching subdivisions of the trachea. Their walls are made of muscle, to allow them to constrict so they can control the flow of air in and out the alveoli, and epithelial cells. |
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Does the contraction of the internal intercostal muscles lead to inspiration or expiration? |
Expiration |
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Does the contraction of the external intercostal muscles lead to inspiration or expiration? |
Inspiration |
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What is the diaphragm? |
A sheet of muscle seperating the thorax from the abdomen. When it contracts in flattens, increasing the volume of the thorax. |
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What is the process for inspiration? |
•External intercostals contract, internals relax. This pulls the ribs up and out, increasing thorax volume •Diaphragm contracts, causing it to flatten, increasing thorax volume •This increased volume causes reduced air pressure inside the lungs, causing air to be forced in. |
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What is the process for expiration? |
•Internal intercostals contract, externals relax. This pulls the ribs down and inwards, reducing thorax volume •The diaphragm relaxes and is pushed up by the contents of the abdomen, reducing thorax volume further. •The decreased thorax volume increases the pressure in the lungs, causing the air to be forced out |
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What is the pancreas? |
A large gland situated below the stomach which produces a secretion called pancreatic juice. This secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch |
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What is physical digestion? |
The food is broken down into smaller pieces by the teeth and also through being churned by muscles in the stomach wall. This is to make it possible to ingest and to proivide a large SA for chemical digestion |
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How are lipids digested? |
First they are split up into tiny droplets called micelles by bile salts (this is called emulsification) which increases SA.Then their ester bond is hydrolysed by lipases to form fatty acids and monoglycerides. |
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What are endopeptidases? |
They hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules. |
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What are exopeptidases? |
They hydrolyse the peptide bond on the terminal amino acid of the peptide molecule formed by endopeptidases. They progressively release amino acids and dipeptidases. |
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What are dipeptidases? |
They hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound - they are part of the cell-surface membrane of the epithelial cells lining the ileum. |
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What does the reaction catalysed by sucrase produce? |
Glucose and fructose |
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What does the reaction catalysed by lactase produce? |
Glucose and galactose |
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What is the process for stach digestion? |
•Salivary amylase hydrolyses any starch to maltose. Saliva also contains mineral salts which help it to maintain a neutral pH, optimum for amylase •Food is swallowed to the stomach, where the acidity denatures the amylase. Then it is passed into the small intestine, where it mixes with pancreatic juice •This contains alkaline salts to make the pH neutral and pancreatic amylase which continues hydrolysing the starch to maltose •Muscles in the intestinal wall push the food along the ileum. Maltase is part of the cell-surface membranes of the epithelial cells and hydolyses the maltose into alpha-glucose. |
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What is produced in the reaction catalysed by maltase? |
alpha-glucose |
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What is produced in the reaction catalysed by amylase? |
Maltose |
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How do villi increase the efficiency of absorbtion? (5 ways) |
•Increase SA for diffusion •Thin walled, reducing diffusion pathway •They contain muscle and are able to move to mix the contents of the ileum, ensuring there is always a diffusion gradient •Well supplied with blood vessels so the blood can transport the products of digestion •They have microvilli that further increase SA |
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Why is diffusion of gases between the alveoli and the blood so rapid? (5 reasons) |
•The red blood cells travel very slowly through pulmonary capillaries as they are narrow, allowing more time for diffusion •Red blood cells are flattened against the capillary walls, reducing the distance gases have to diffuse •The walls of both alveoli and capillaries are very thin- reduces diffusion distance •Both alveoli and pulmonary capillaries have a very large SA •Blood flow through the capillaries and ventilation of the lungs ensures that a steep concentration gradient is maintained |
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What does the large intestine do? |
Absorbs water. Most of the water which is absorbed is water from the secretions of the many digestive glands |
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What is the role of the stomach? |
The stomach is a musclular sac with an inner layer that produces enzymes. Its role is to store and digest food, especially proteins. |
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What happens once the micelles come into contact with the epithelial cells lining the villi? |
They break down, releasing the monoglycerides and fatty acids. As they are non-polar they can then easily diffuse into the epithelial cells |
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What is a monoglyceride? |
A glycerol molecule with a single fatty acid molecule attatched |
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How are chylomicrons formed? |
The monoglycerides and fatty acids which have diffused into the epithelial cells are tranported to the ER where they are recombined to form triglycerides. Starting in the ER and combining in the golgi apparatus, these triglycerides associate with cholesterol and lipoproteins to form chylomicrons |
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How to chylomicrons transport lipids from epithelial cells to normal cells? |
They move out the epithelial cells by exocytosis and enter lympatic capillaries called lacteals found at the centre of each villus. They then pass via lymphatic vessels into the blood, where the triglycerides they contain are hydrolysed by an enzyme in the endothelial cells of blood capillaries, from where they diffuse into the cells |
