digestion and absorption and gas exvhange Flashcards
Define digestion
The hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes.
Which enzymes are involved in carbohydrate digestion? Where are they found?
● Amylase in mouth
● Maltase, sucrase, lactase in membrane of small intestine
What are the substrates and products of the carbohydrate digestive enzymes?
● Amylase → starch into smaller polysaccharides
● Maltase → maltose into 2 x glucose
● Sucrase → sucrose into glucose and fructose
● Lactase → lactose into glucose and galactose
Where are lipids digested?
The small intestine.
What needs to happen before lipids can be digested?
They must be emulsified by bile salts produced by the liver. This breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area.
How are lipids digested?
Lipase hydrolyses the ester bond between the monoglycerides and fatty acids.
Which enzymes are involved in protein digestion? What are their roles?
● Endopeptidases= break between specific amino acids in the middle of a polypeptide.
● Exopeptidases= break between specific amino acids at the end of a polypeptide.
● Dipeptidases= break dipeptides into amino acids.
How are certain molecules absorbed into the ileum despite a negative concentration gradient?
Through co-transport.
Which molecules require co-transport?
Amino acids and monosaccharides.
Explain how sodium ions are involved in co-transport.
Sodium ions (Na+) are actively transported out of the cell into the lumen, creating a diffusion gradient. Nutrients are then taken up into the cells along with Na+ ions.
Why do fatty acids and monoglycerides not require co-transport?
The molecules are nonpolar, meaning they can easily diffuse across the membrane of the epithelial cells.
How does an organism’s size relate to their surface area to volume ratio?
The larger the organism, the lower the surface area to volume ratio.
How does an organism’s surface area to volume ratio relate to their metabolic rate?
The lower the surface area to volume ratio, the lower the metabolic rate.
How might a large organism adapt to compensate for its small surface area to volume ratio?
Changes that increase surface area e.g. folding; body parts become larger e.g. elephant’s ears; elongating shape; developing a specialised gas exchange surface.
Why do multicellular organisms require specialised gas exchange surfaces?
Their smaller surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism.
Name three features of an efficient gas exchange surface.
- Large surface area, e.g. folded membranes in mitochondria.
- Thin/short distance, e.g. wall of capillaries.
- Steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli.
Why can’t insects use their bodies as an exchange surface?
They have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water.
Name and describe the three main features of an insect’s gas transport system.
● Spiracles= holes on the body’s surface which may be opened or closed by a valve for gas or water exchange.
● Tracheae= large tubes extending through all body tissues, supported by rings to prevent collapse.
● Tracheoles= smaller branches dividing off the tracheae
Explain the process of gas exchange in insects.
● Gases move in and out of the tracheae through the spiracles.
● A diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.
● Contraction of muscles in the tracheae allows mass movement of air in and out.
Why can’t fish use their bodies as an exchange surface?
They have a waterproof, impermeable outer membrane and a small surface area to volume ratio.
Name and describe the two main features of a fish’s gas transport system.
Gills= located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles.
Lamellae= at right angles to the gill filaments, give an increased surface area. Blood and water flow across them in opposite directions (countercurrent exchange system).
Explain the process of gas exchange in fish.
● The fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure.
● The water passes over the lamellae, and the oxygen diffuses into the bloodstream.
● Waste carbon dioxide diffuses into the water and flows back out of the gills.
How does the countercurrent exchange system maximise oxygen absorbed by the fish?
Maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant along whole length of gill enabling 80% of available oxygen to be absorbed.
Name and describe three adaptations of a leaf that allow efficient gas exchange.
- Thin and flat to provide short diffusion pathway and large surface area to volume ratio.
- Many minute pores in the underside of the leaf (stomata) allow gases to easily enter.
- Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis.
