Cell Structure and Organelles

Cytoplasm is a semi-fluid matrix found in both prokaryotic and eukaryotic cells.
It is the site for many chemical reactions.

Organelles are membrane-bound structures found in eukaryotic cells.
Examples include the endoplasmic reticulum (ER), Golgi complex, lysosomes, mitochondria, microbodies, and vacuoles.
Prokaryotes lack membrane-bound organelles.

Mesosomes are membranous structures formed by extensions of the plasma membrane.
They are involved in cell wall formation, DNA replication, and distribution.
They also play a role in respiration, secretion, and increasing the surface area of the plasma membrane.

Chromatophores are membranous extensions in the cytoplasm of some prokaryotes like cyanobacteria.
They contain pigments.

Inclusion bodies are reserve materials found in the cytoplasm of prokaryotic cells.
They are not bound by a membrane.
Examples include phosphate granules, cyanophycean granules, and glycogen granules.
Gas vacuoles are found in blue green and purple and green photosynthetic bacteria.

Eukaryotes include protists, plants, animals, and fungi.
They have extensive compartmentalization of the cytoplasm, with membrane-bound organelles.

The ER is a network of membranous tubules and cisternae.
It is involved in the transport of substances, protein synthesis, lipoprotein synthesis, and glycogen synthesis.
There are two types of ER: rough (RER) and smooth (SER).
RER is studded with ribosomes, which are involved in protein synthesis.
SER is involved in the synthesis of lipids and steroids.

The Golgi complex is a membranous organelle composed of flattened sacs called cisternae.
It is involved in the packaging of materials for intracellular and extracellular transport.
The Golgi complex is closely associated with the ER.
It is the site of formation of glycoproteins and glycolipids.
The trans face of the Golgi complex is the mature face, while the cis face is the formation face.

Lysosomes are membrane-bound vesicles formed by the Golgi complex.
They contain hydrolytic enzymes that digest carbohydrates, proteins, lipids, and nucleic acids.
Their enzymes are optimally active at acidic pH.

The nucleus is enclosed by a double-membrane structure called the nuclear envelope.
The nuclear envelope has nuclear pores that allow RNA and protein molecules to move between the nucleus and the cytoplasm.
The nuclear matrix (nucleoplasm) contains nucleoli and chromatin.
Nucleoli are spherical structures where ribosomal RNA synthesis takes place.
Chromatin is a loose network of nucleoprotein fibres in the interphase nucleus.
The nucleus controls cell activities and plays a major role in heredity.

The endomembrane system includes the ER, Golgi complex, lysosomes, and vacuoles.
Centrosomes and centrioles form the basal body of cilia and flagella, which are involved in movement.
In animal cells, centrioles form the spindle apparatus during cell division.
Mitochondria are responsible for oxidative phosphorylation and the generation of adenosine triphosphate (ATP).
They are enclosed by a double membrane. The inner membrane folds into cristae.
Plastids are pigment-containing organelles that occur in plant cells only.
Chloroplasts contain chlorophyll and are responsible for capturing light energy for photosynthesis.
Grana within the plastid are the site of light reactions.
The stroma is the site of the dark reactions.
Other colored plastids are called chromoplasts and may contain pigments like carotene and xanthophyll.