Exchange and Transport Flashcards
Diffusion equation
diffusion= (SA x diff. in concentration)/ length of diffusion path
Methods of transportation
Passively (no energy)- diffusion and osmosis Actively (energy)- active transport
Gas exchange in single celled organisms
Their small SA:Volume ratio means that oxygen is absorbed by diffusion across the cell-surface membrane. If it has a cell wall this is permeable and so not a barrier to gas diffusion.
Respiratory system in insects
Spiracle -> trachea -> tracheoles -> muscle fibre
How gases diffuse in insects
Diffusion gradient- oxygen is used up by respiring cells at the end of the tracheoles, reducing its concentration. This creates a diffusion gradient from along the trachea. It works in the opposite direction for carbon dioxide. In water this occurs more quickly as diffusion is more rapid than in air. Ventilation- Muscle movements can create movements of air which speeds up respiratory exchange.
Describe spiracles and their limitations
Tiny pores on the body surface, which can be opened/closed by a valve. When open water can evaporate, so they are mostly kept closed. Limits the size an insect can achieve as the diffusion pathway must stay short.
Gill structure
Countercurrent flow and parallel flow
Gas exchange in a leaf
Stomata structure
Features of transport systems
- A medium to carry materials eg/ blood
- A form of mass transport in which the transport medium is moved aorund in bulk over large distances
- A closed system containing the transport medium
- A mechanism for moving the transport medium within vessels, which requires a pressure difference eg/ muscle contractions or water evaporation
- Mechanism to keep flow in one direction eg/ valves
- Means of controlling flow
Mammalian transport system
Types of blood vessel
- Arteries carry blood away from the heart and into arterioles
- Arterioles are smaller arteries that control blood flow from arteries to capillaries
- Capillaries are tiny vessels which link arterioles to venules
- Veins and venules carry blood from the capillaries back to the heart
Basic structure of arteries and veins
Tough outer layer resists internal and external pressure changes
Muscle layer can contract to control blood flow
Elastic layer maintans blood pressure by stretching and springing back
Thin innner lining (endothelium) is smooth to prevent friction and thin for diffusion
Lumen is the cavity the blood flows through
Artery structural function
- Thick muscle means smaller veins can be constricted and dilated to control the volume of blood passing through them.
- Thick elastic layer because pressure has to be kept high for blood to reach extremities. Stretches at systole and springs back at diastole. This maintains high pressure and smooths the pressure surges created by the heart beating.
- Overall wall thickness resists the vessel bursting under pressure
- No valves as the high pressure means the blood doesn’t flow backwards
Arteriole structural function
Thicker muscle layer than arteries to control blood movement into capillaries
Thinner elastic layer because the pressure is lower
Vein structural function
Thin muscle layer as it is not needed to control blood flow to tissues
Thin elastic layer due to low pressure. Pressure is too low to create a recoil action
Overall wall is thin because there is no risk of bursting. They can then also be flattened easily to aid blood flow.
Valves throughout to ensure blood doesn’t flow backwards. When muscles contract and veins are compressed, the valves ensure the pressurised blood only flows one way.
Capillary structural function
Walls only consist of lining layer giving a short diffusion distance for rapid diffusion.
Numerous and highly branched for a large diffusion surface area.
Narrow diameter to permeate tissues so no cell is far from a capillary.
Narrow lumen means RBC are squeezed flat against the side reducing diffusion distance and increasing SA.
Spaces between endothelial cells allow WBC to escape to deal with infections in tissues.
What is tissue fluid?
Watery liquid containing glucose, amino acids, fatty acids, salts and oxygen. It supplies tissues with these substances and receives carbon dioxide and other waste. It bathes all the cells of the body abd is the exchange fluid between blood and cells. It is formed from blood plasma.
Tissue fluid formation
Blood being pumped into the capillaries creates hydrostatic pressure at the arterial end. This forces tissue fluid out of the blood plasma. This outward pressure is opposed by two other forces:
- Hydrostatic pressure of tissue fluid outside the capillaries
- Lower water potential of blood due to plasma proteins pulls water back into the blood within the capillaries
Only small molecules leave the capillaries leaving cells and proteins in the blood. This is called ultrafiltration.
Tissue fluid returns to the circulatory system
Most tissue fluid returns to the blood plasma directly vie the capillaries. At the venous end, hydrostatic pressure in the capillaries is less than the tissue fluid so the tissue fluid is orced back into the capillaries. Also, osmotic forces due to water potentialpull water back into the capillaries.
Lymphatic system carries the remainder tissue fluid back to two ducts that join veins near the heart. The contents of the lymphatic system are moved by hydrostatic pressure and muscle contractions that squeeze the vessels (valves for same purpose as veins).
Root hair diagram
Water enters root hair cells
Large SA and thin surface layer which materials can move across easily. The soild has a high water potential as it is mostly water, while the root hair cells have a much lower water potential due to suagars, amino acids, and minerals dissolved in them. As a result, water moves by osmosis into the root hair cells down the water potential gradient.
Apoplastic and symplastic pathway
Passage of water into the xylem
When water reaches the endodermis by the apoplastic pathway it is forced into the protoplast of the cell to join the water that arrived by the symplastic pathway. This is due tue the waterproof Casparian strip.
Endodermal cells actively transport salts into the xylem, lowering the water potential. Water can then enter by osmosis. The pressure caused by these salts is called root pressure.
What is the main force that pulls water up the stem of a plant?
Transpiration
Water movement out of the stomata
If the stomata are open, water vapour molecules diffuse into the surrounding air. The water lost is replaced by water evaporating from the cell walls of the surrounding mesophyll cells.
Water movement across a leaf
Water moves down a water potential gradient out of the leaf from the xylem, through the mesophyll to air through the stomata.
Evidence supporting cohesion-tension theory
- Diameter of tree trunks changes according to the rate of transpiration. In they day the tree diameter is smaller than at night
- A broken xylem vessel means a plant can no longer draw up water because the continous column o water is broken so the water molecules can no longer stick together
- When a xylem is broke water doesn’t leak out, but air is drawn in, showing it is under tension and not pressure
Energy needed for transpiration
As a [assive process it doesn’t directly need metabolic energy. However, energy in the form of heat from the sun is necessary to draw the water up.
Factors affecting transpiration
- Light. Photosynthesis only occurs in the light, and so stomata are mostly open in the light for gas exchange. Water leaves via the stomata, and so light increases rate of transpiration.
- Temperature. This affects the water potential of air, as well as the speed at which water molecules move. An increase in temperature increases kinetic energy meaning water eaporates more readily from the leaf. It also decreases humidity i.e. water potential.
- Humidity. This affects the diffusion gradient from the air in the leaf and the air outside the leaf. Less humid= more transpiration.
- Air movement. Wind moves water from the leaves more easily by reducing the layer of moist air, increasing transpiration rate.
Potometer
Adaptations of xerophytic plants
- Thick cuticle (waterproof barrier)
- Rolled leaves traps a region of still air within the leaf, making a very small water potential gradient
- Hairy leaves trap moist air next to the leaf surface, reducing the water potential gradient
- Stomata in pits/grooves traps moist air
- Reduced SA:Volume ratio of leaves to reduce water loss, but must be balanced with are for photosynthesis
