lysosome
lysosomes
A Vesicle
The small spherical structure you are referring to is a lysosome. Lysosomes contain enzymes that break down waste materials and cellular debris in a process called digestion or autophagy.
The structure of the plasma membrane consists of the phospholipid bilayer, which gives it a fluid structure, and not rigid, allowing the materials ease to pass through. Next, there are also integral proteins which can be thought of as 'tunnels', allowing the materials to come in and out. Then, there are peripheral proteins which also aid in getting the materials inside an out. On the cell membrane, there are receptors which recognize outside materials, and if they are really big, the cell engulfs these molecules through endocytosis [pinocytosis, and phagocytosis, which are basically for liquid molecules, and solid molecules]. This takes us back to the fluidity of the cell membrane. That's roughly how the cell membrane allows for the entering and exiting materials.
A semipermeable membrane
Osmosis.
A vesicle is a small, spherical sac surrounded by a lipid bilayer membrane. Its function is to transport and store cellular materials, such as proteins and neurotransmitters, within a cell. Vesicles are involved in processes like exocytosis (release of materials from the cell) and endocytosis (uptake of materials into the cell).
Vesicles transport materials in the cell. A vesicle is a small membrane enclosed sack that can have specialized functions depending on what materials they contain.
cell membrane, large vacuole, small vacuoles, cytoplasm, nucleus
endocytosis
ileocecal valve
Materials that can cross the cell membrane include small non-polar molecules like oxygen and carbon dioxide, as well as small polar molecules like water. These molecules can freely pass through the lipid bilayer of the membrane due to their small size and compatibility with the hydrophobic environment of the lipid tails. However, larger molecules and charged ions require specific protein channels or transporters to cross the membrane.