13 Exchange and transport

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  • Created by: Naana
  • Created on: 28-03-15 22:06
How does the size of an organism relate to its surface area to volume ratio?
Small organisms have a large surface area to volume ratio whereas large organisms have a small surface area to volume ratio (because volume increases at a faster rate than their surface area)
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What must the surface area to volume ratio be, in order for efficient exchange?
The surface area of a organism must be large compared with its volume- allow efficient exchange across their body surface
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How do larger organisms increase their surface area to volume ratio?
Specialised exchange surfaces with large areas to increase the surface area to volume ratio e.g. lungs in mammals, gills in fish. A flattened shape so that no cell is ever far from the from the surface
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How are surfaces specially adapted to facilitate exchange?
Large surface area to volume ratio- increased rate of exchange, thin so that diffusion pathway is short- exchange rapid, partially permeable to allow selected materials through easily, movement of the environmental medium (air) and the internal mediu
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What is the relationship between the size of an organism and heat loss?
If an organism is large (small SA:V) it is hard to loss heat from its body, whereas if an organism is small (large SA:V) then heat is lost easily
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How do single celled organisms exchange gases?
By diffusion. Single celled organisms are small therefore have large SA:V ratio, body surface is covered by only a cell surface membrane
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How do terrestrial (live on land) organisms reduce their water loss?
Waterproof covering- insects have an exoskeleton that is covered with a waterproof cuticle. They have a small surface area to volume ratio to miminise the area over which water is lost. (Insects) close their spiracles if they are losing too much wate
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How do insects exchange gases? Outline the process
They used the tracheal system. 1) Air moves in the tracheae through tiny pores called spiracles 2) Oxygen travels by diffusion down concentration gradient in the tracheae and is brought to respiring tissues 3) in the opposite direction co2 from cells
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How does ventilation speed up the exchange of respiratory gases?
The abdominal pumping (movement of muscles) in insects can create mass movements of air in and out of the trachea
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Why is the diffusion pathway in the tracheae system short?
Because every cell of an insect is only a very short distance from one of the tracheae or tracheoles
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What is the structure of gills?
Each gill is made up of lots of thin plates called gill filaments which have a big surface area for exchange of gases. The gill filaments are covered in tiny structures called gill lamellae which increases the surface area. Gill lamellae have lots o
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How are gases exchanged in a fish?
The counter current flow. In the gills of a fish, blood flows through the gill lamellae in one direction and water flows over the gill lamellae in the opposite direction. This means that water with a high o2 conc always flows next to blood with a low
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What is the different between parallel flow and countercurrent flow?
Parallel flow- water and blood are flowing in the same direction. As a result the concentration gradient is only maintained across part way of the gill lamellae (50% diffusion) Whereas countercurrent flow- water and blood are flowing in opposite dire
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How do plants exchange gases?
During respiration (dark) o2 moves in co2 moves out.During photosynthesis (light) Co2 moves in and o2 moves out of the mesophyll cells through special pores in the epidermis called stomata. The stomata can open to allow gas exchange and close to prev
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How is a leaf adapted for efficient gas exchange?
It has a thin, flat shape that provides large surface area, many stomata's, numerous interconnecting air spaces within the mesophyll.
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How are xerophyte plants adapted for life in warm, dry and windy habitats where water loss from transpiration is a problem?
They have sunken stomata (in pits or grooves) which trap moist air and reduce evaporation, rolled leaves with the stomata inside protecting them from wind, epidermal hairs which traps moist air round the stomata reducing the water potential gradient,
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Why do large organisms e.g mammals need a specialised transport system?
Large organisms have a small surface area to volume ratio so a specialised exchange surface is needed to absorbs nutrients and respiratory gases needed by body cells and removing excretory products
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What are the features of transport systems?
A suitable medium to carry materials e.g blood, a form of mass transport to move the transport medium around in a bulk over large distances, a closed system that contains the transport medium and distributes it to all parts, a mechanism for moving th
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How is blood circulated in mammals?
Mammals have a double circulatory system. This refers to the fact that blood passes twice through the heart for each complete circuit of the body. In one circuit blood is pumped from the heart to the lungs and then back to the heart. This increases t
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What is the basic layered structure of the arteries, arterioles and veins (from outside inwards)?
Tough outer layer- resists pressure changes from both within and outside, muscle layer- contracts to control flow of blood, elastic layer- helps to maintain blood pressure by stretching and springing back, thin inner lining (endothelium)- smooth to p
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How is the structure of the artery related to its function?
The arteries transport blood rapidly from the heart to the tissues under high pressure. Muscle layer is thicker than veins- can contract and relax to control the volume of blood passing through. Elastic layer thicker than veins- stretching and recoil
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What are the functions of the different blood vessels (arteries, arterioles, capillaries and veins)?
Arteries carry blood from the heart and into the arterioles. Arterioles are smaller arteries that control blood flow from arteries to capillaries. Capillaries are vessels that link arterioles to veins. Veins carry blood from capillaries back to the
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How is the structure of the arterioles related to its function?
Arterioles carry blood from arteries to capillaries under high pressure (lower than arteries). Muscle layer is thicker than arteries-contraction allows the arteriole's lumen to constrict which restricts the flow of blood. This controls the movement o
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How is the structure of the veins related to its function?
Veins transport blood slowly from the tissues to the heart under low pressure. Muscle layer is thinner than arteries- as contraction and relaxing cant control the flow of blood to the tissues, elastic layer is thinner than arteries and thin walls- lo
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How is the structure of the capillary related to its function?
The capillary exchanges materials such as o2,co2 and glucose between blood and body cells. Thin walls (one cell thick)- short pathway to diffusion, numerous and highly branched- large surface area for diffusion, capillaries are very close to cells in
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What is tissue fluid?
Tissue fluid is the means by which materials are exchanged between blood and body cells. Tissue fluid is the watery liquid (fluid) that surrounds cells in tissues. Tissue fluid contains glucose, oxygen, amino acids, fatty acids and salts which it sup
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How is tissue fluid formed?
A hydrostatic pressure is created when blood pumped by the heart passes along arteries, then narrower arterioles and then even narrower capillaries. At the arterial end of the capillary bed (end nearest the arteries), the hydrostatic pressure created
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How does tissue fluid return to the circulatory system once it has exchanged materials?
When the tissue fluid is lost from the capillaries it reduces the hydrostatic pressure inside the capillaries. As a result by the time blood has reached the venous end of the capillary bed, its hydrostatic pressure is lower than the hydrostatic pres
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Why does some water re-enter from the tissue fluid at the venous end of the capillary bed ?
When the tissue fluid is force out of the capillaries, this causes the water potential at the venous end of the capillary bed to be lower than the water potential in the tissue fluid, so water moves in by osmosis.
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What happens to the excess tissue fluid that can't return to the capillaries?
They are collected into the lymphatic system. The contents of the lymphatic system which are called lymph, are moved by the hydrostatic pressure of the tissue fluid that has been left by the capillaries, and the contraction of body muscles that squee
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What ensures that the lymph moves in the right direction?
The valves in the lymph vessel ensure that the lymph moves away from tissues and moves in the direction of the circulatory system
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How is water taken up by the root hair cells?
The soil has a high water potential as the soil solution is mostly water, whereas the root hair cell has a much lower water potential as it has sugars, amino acids and mineral ions dissolved inside them. As a result water moves from the soil into th
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What is the apoplastic pathway?
When water moves through cell walls by osmosis , as the walls are very absorbent and water can simply diffuse through them
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What happens when the water in the apoplast pathway reaches the endodermis cells?
The path of the water is blocked by the Casparian strip in the cell walls which is made of a waxy waterproof substance. Now the water has to take the symplast pathway
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What is the symplast pathway?
When water moves through the cytoplasm and plasmodesmata (fine strands of cytoplasm that extend through pores in cell walls and connect cytoplasm of neighbouring cells) by osmosis
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How does the cohesion and tension help water move up plants, from roots to leaves?
Water evaporates from the leaves at the top of the xylem. This creates tension which pulls more water into the leaf. Water molecules are cohesive (they stick together due to hydrogen bonds) so this means the whole column of water in the xylem moves
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How is root pressure created? How does root pressure help water to move up plants?
The active transport of mineral ions e.g salts into the xylem by the endodermal cells create a lower water potential in the xylem. Water now moves into the xylem by osmosis. The water potential gradient created creates a force called root pressure.
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What is transpiration?
The evaporation of water from the leaves
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How does water move through the leaf?
Water is lost by the mesophyll cells by evaporation from their surfaces to the air spaces of the leaf. As the mesophyll cells now have a lower water potential ,water moves in from neighbouring cells by osmosis. The loss of water from the neighbouri
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How does water move up the xylem?
Water evaporates from leaves as a result of transpiration. Due to water being cohesive, water forms a continuous unbroken pathway across the mesophyll cells and down the xylem. As water evaporates from the mesophyll cells into the air spaces, more wa
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How does the time of the day affect the diameter of tree trunks?
During the day, transpiration is at its greatest so there is more tension in the xylem, which causes the tree trunk to shrink in diameter. Whereas, in the night, transpiration is at its lowest, so there is less tension in the xylem and so the tree tr
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What happens when a xylem vessel breaks?
When a xylem vessel is broken, air enters in and the tree can no longer draw up water, because the continuous column of water is broken- water molecules are no longer cohesive
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Why does transpiration occur?
Because without transpiration, water would not be so plentiful and the transport of materials (such as mineral ions, sugars and hormones) would not be as rapid
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How does light increase the rate of transpiration?
The stomata opens when it is light, so water is able to move out of the leaf- greater transpiration
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How does a rise in temperature increase the rate of transpiration?
The rise in temperature increase the kinetic energy of the water molecules . So the water molecules can move at a greater speed, which increases the rate of evaporation- transpiration. It also decreases the humidity of the air outside the leaf
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How does low humidity increase the rate of transpiration?
Humidity is a measure of the number of water molecules in the air. If the air around the plant is dry, the water potential gradient between the leaf and the air will be increased- so faster rate of transpiration
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How does an increase in air movement (wind) increase the rate of transpiration?
As water diffuses through the stomata, water molecules accumulate as vapour around the stomata. So increased air movement will blow away water molecules from around the stomata and this would increase the water potential gradient- increased transpira
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