Page 24 - Q & A STPM 2022 Biology

Biology STPM Chapter 3 Membrane Structure and Transport
– In phagocytosis, the cell membrane encloses a particle such as a
bacterium to engulf it into the cell.
– In pinocytosis, the cell surface membrane invaginates inwards
in order for the droplets containing materials to flow inside. The
membrane then pinches off to form pinocytic vesicles.
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– In receptor-mediated endocytosis, ligands such as cholesterol
molecules bind to receptors in coated pits on the cell membrane
which then form coated vesicles by endocytosis.
Semester
1 (b) – Carbohydrates in the membrane exist as short sugar chains
(oligosaccharides)
– These carbohytrates are attached to the proteins and phospholipids
to form glycoproteins and glycolipids respectively.
– Glycoproteins and glycolipids act as antigens, that are identify
markers.
– These molecules enable cells to identify and differentiate themselves
from others.
– This is known as cell to cell recognition.
– Glycoproteins and glycolipids can act as receptors for chemical
signals such as hormones.
– In addition, these molecules are involved in holding the cells together
to form tissues.

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