Biology Booklet 3 Flashcards
Structure and function of arterioles
Structure - thick muscle layer, which contracts and relaxes
Function - reduces/ controls blood pressure and flow into the capillaries
Structure and function of an artery
Structure- thick elastic layer which stretches and recoils and narrows the lumen
Function - maintains a high blood pressure created by heart contraction
Structure- thick walls
Function - prevents damage caused by high pressure
Structure and function of veins
Muscle layer is thin as their constriction and dilation cannot control blood flow
Elastic layer is thin as pressure is low
Wall thickness is small as the pressure is low
Valves present to prevent back-flow
Structure and function of capillaries
Fick’s law
Rate of diffusion ( oxygen, carbon dioxide and glucose) is increased
Numerous and branched so surface area is large
Thin endothelium so diffusion pathway is short
Constant circulation of blood maintains a steep concentration gradient
Rd blood cell is approx same size as capillary lumen so passage of blood is slow … Allows more time for diffusion to occur
Formation, reabsorption and drainage of tissue fluid (6)
High hydrostatic pressure at the arteriole end of the capillary
Forces water out through the thin capillary wall into tissues.
Plasma proteins are too late to pass through the capillary wall
So they become mo concentrated in the blood. This makes the water potential inside the capillary more negative
Compared to the less negative tissues. Water moves back into the capillary by osmosis
Along a water potential gradient. The high hydrostatic force outside the capillary also helps to use water back in.
Where is the excess tissue fluid drained?
The body makes more tissue fluid over a day than it can reabsorb. The excess is drained by the lymph vessels. Accumulation of fluid may lead to tissue swelling (oedema).
Why a person experiencing high blood pressure may get swelling?
Hydrostatic pressure of blood is high so more water is forced out of the arteriole end of the capillary, some tissue fluid accumulates as not all of it can be reabsorbed.
Why a starving person may get swelling
Fewer plasma proteins in the blood so concentration gradient is not as steep and inside the capillary is less negative, therefore less water can be reabsorbed into the capillary by osmosis.
Where may tissue fluid accumulate and why?
Gravity pulls tissue fluid down So it tends to accumulate in ankles and feet
What do you need to remember about tissue fluid For example lymph vessels
Feet have any few lymph vessels
Blockages of lymph vessels can result from some bacterial infections and this would also lead to excess tissue fluid & swelling
There are some metabolic diseases which lead to low levels of plasma proteins
Contraction of body muscles surrounding the lymph vessels squeeze the lymph back to the chest where it can be drained and eventually excreted.
Explain how active transport of mineral ions into xylem vessels result in water entering and being moved up the tissues
The water potential in the xylem is made more negative
By the active transport of ions into the xylem
This establishes a water potential gradient
So water moves from an area with a less negative water potential to an area with a more negative water potential
By osmosis
This increases pressure in the xylem
Use cohesion-tension theory to explain why the presence of an air bubble in a xylem vessel blocks the movement of water
The presence of air bubbles break the continuous column of water and prevents cohesion of water molecules. Water in the xylem is under tension due to transpiration from leaves. The air bubble inhibits this tension.
Using Fick’s law explain how the structural adaptations of xerophytes reduce the rate of water diffusion
Fick’s law states that the rate of diffusion s proportional to the surface area times the concentration gradient divided by the the length of diffusion pathway.
Xerophytes have reduced numbers if stomata this decreases the surface area. These plants also have a waxy cuticle this increases the length of diffusion pathway. These features means that the water potential gradient is reduced so less water is lost to the atmosphere.
Explain how evaporation of water from leaves causes the water to move upwards
The water potential in the mesophyll becomes more negative. Water moves out of the xylem by osmosis and is evaporated from the open stomata. This creates a transpiration pull caused by cohesion of the water molecules to each other and adhesion to the xylem wall.
Explain how root pressure and cohesion-tension are responsible for the movement of water in the xylem vessels.
Salts are actively transported into the xylem. This causes the xylem to have more negative water potential. Water enters the xylem by osmosis. Evaporation of water from the stomata causes transpiration pull. This lowers the water potential of the mesophyll. Water molecules cohere de to the hydrogen bonding and adhere to xylem walls. This pulls water up the xylem.
