T6 Flashcards
How are lipids digested and then absorbed?
The digestion of lipids occurs as follows:
Bile salts emulsify lipids into tiny droplets called micelles, increasing the surface area of the lipids.
Pancreatic lipase breaks down micelles into fatty acids and monoglycerides.
How triglycerides are absorbed into the blood:
Micelles are broken down to release fatty acids and monoglycerides.
As they are both non-polar, fatty acids and monoglycerides can diffuse into the epithelial cells that line the ileum.
Triglycerides reform inside the cells’ endoplasmic reticulum.
Triglycerides are packaged into chylomicrons for transport.
Chylomicrons are released from the epithelial cells by exocytosis into lacteals, which are lymphatic vessels in the villi.
Chylomicrons are transported via lymph vessels in the lymphatic system to the blood.
Describe the mass flow hypothesis in plants
It is hypothesised to occur as follows:
At the source, solutes like sucrose are actively loaded into sieve tube elements from companion cells.
This decreases the water potential in sieve tube elements.
Water enters the sieve tube elements from the xylem and companion cells by osmosis.
This increases hydrostatic pressure in the sieve tube elements at the source.
At the sink, solutes are actively removed from the sieve tube elements.
This increases the water potential in sieve tube elements at the sink.
Water leaves the phloem by osmosis, decreasing the hydrostatic pressure at the sink.
This creates a pressure gradient, pushing solutes from the source to areas of lower pressure at the sink.
At the sink, solutes are actively unloaded from the sieve tube element into companion cells. They can then move into sink cells where the solutes can be used, for example in respiration, or stored.
What is translocation?
Features of translocation:
It requires energy.
It transports substances from sources (where they are made, like the leaves) to sinks (where they are used, like the roots).
The substances are transported through the phloem.
Water provides the medium in which these substance dissolve for transport in the phloem.
It maintains a concentration gradient using enzymes.
Describe how tissue fluid is formed
At the arteriole end of capillaries:
A high hydrostatic pressure, exerted by the force of the heart pumping, forces fluid out of capillaries.
This forms tissue fluid surrounding body cells.
At the venule end of capillaries:
The hydrostatic pressure is lower.
Proteins in blood exert a high oncotic pressure, a type of osmotic pressure, in capillaries.
The water potential is lower in capillaries than in tissue fluid due to fluid loss.
Some tissue fluid moves back into capillaries by osmosis.
