Do humans have the enzyme for starch intracellular digestion? Also, do plants have the ability to digest Glycogen? Intra or extracellular, or both?
The problem with your question is that, right now, you have three different questions:
- Is the starch/glycogen digestion intra or extracellular?
- Do humans have the enzyme for intracellular digestion of starch?
- Do plants have the ability to digest glycogen?
Unfortunately, that goes against Bio SE rules: you have to pick one question, otherwise your post will be closed as too broad ("Avoid asking multiple distinct questions at once.").
That being said, I'll address only this question:
Do humans have the enzyme for intracellular digestion of starch?
The answer is yes. Intracellular digestion in humans (as in any animal) is performed by lysosomes, organelles that contain hydrolytic enzymes.
Lysosomes can digest proteins, lipids, carbohydrates, nucleic acids etc. Regarding digestion of carbohydrates, this is a short list of enzymes (the complete list is way bigger) found in human lysosomes:
- alpha-L-Fucosidase beta-Galactosidase-1
- beta-Glucuronidase Chitinase
- Chondroitin B Lyase/Chondroitinase B
- Cytosolic beta-Glucosidase
- Lysosomal alpha-Glucosidase
Among the enzymes listed above, this is the one that answers your question: Lysosomal alpha-Glucosidase.
That enzyme, which is a α-1,4-glucosidase, breaks down starch (and glycogen) to glucose.
DIGESTION IN THE MOUTH:
Starch digesting enzymes are extracellular in human beings.All starches and some glycogen are hydrolysed in the mouth by the time the food is swallowed due to the effect of ptyalin(alpha amylase)enzyme in our saliva.
DIGESTION IN THE DUODENUM OF SMALL INTESTINE:
Pancreatic juice containing pancreatic amylase promotes extracellular starch digestion.And almost all the starch in food is completely hydrolysed to maltose, limit dextrin and isomaltose in its effect.
The same enzyme pancreatic amylase also causes the total extracellular digestion of glycogen in the duodenum and forms maltose and other products like limit dextrin, isomaltose.
DIGESTION IN THE UPPER JEJUNUM OF SMALL INTESTINE:
Products like limit dextrin and isomaltose is digested extacellularly in the small intestine by the enzyme isomaltase and maltose by maltase in intestinal saccus entericus to form glucose.
NATUREOF INTERCONVERSION OF GLYCOGEN AND GLUCOSE IN HUMAN:
The principal glycogen storing organ in human is the liver and glycogen formation or hydrolysis in the organ is 'intracellular'.
NATURE OF INTERCONVERSION OF STARCH AND GLUCOSE IN PLANTS:
Similarly in starch storing organs in plants the hydrolysis or formation is 'intracellular'.