Cellular Components and Transport Mechanisms

Cytoplasm

The cytoplasm is located just after the plasma membrane. Its components are mostly water, which acts as a solvent, and proteins that function as enzymes.

Chloroplasts

Chloroplasts produce nutrients from the sun's radiant energy through photosynthesis. They have two membranes: an outer and an inner smooth one. The inner membrane has folds called lamellae, which are located in the grana.

Mitochondria

Mitochondria oxidize food through cellular respiration and store the released energy. They are surrounded by two membranes: a smooth external surface and internal folds or ridges.

Endoplasmic Reticulum

The endoplasmic reticulum has a membrane structure that connects easily with the membrane of the nucleus and has compartments called cisterns. The complex comprises a rough endoplasmic reticulum and a smooth one. Its function is the synthesis of proteins.

Golgi Apparatus

The Golgi apparatus is located near the nucleus. Its function is to receive vesicles from the smooth endoplasmic reticulum and package products such as enzymes and membranes. Here, we find secretory vesicles, vesicles from the RER, and Golgi saccules.

Lysosomes

Lysosomes, very abundant in animal cells, have many digestive enzymes that degrade food ingested by the cell. They generate cellular digestion and attack and degrade bacteria.

Vacuoles

Vacuoles are specific to plant cells. These large saccules are structured separately from the cytosol of cells in a membrane called the tonoplast. There are three types:

• Digestive vacuoles
• Reserve vacuoles
• Contractile vacuoles

Cellular Transport

Cellular transport is the passage of substances from inside to outside the cell or vice versa, with or without energy expenditure.

Passive Cellular Transport

Passive cellular transport is the passage of substances into the cell that requires no expenditure of energy. Within passive transport, we find diffusion, osmosis, and dialysis:

Diffusion

Diffusion is the spontaneous movement of molecules from an area of higher concentration to an area of lower concentration.

Osmosis

Osmosis is a type of passive transport where molecules move from a less concentrated solution to an area of greater concentration.

Types of Solutions in Osmosis

• Isotonic: A solution whose solute concentration is equal to the concentration of the solvent, which means there is a hydric balance.
• Hypertonic solution: A solution where the solute concentration is greater than the concentration of the solvent, which causes plasmolysis around a cell.
• Hypotonic solution: A solution where the solute concentration is lower than the concentration of the solvent. When a hypotonic solution surrounds a cell, the phenomenon of turgidity occurs.

Dialysis

Dialysis is a type of passive transport in which solute molecules move from a less concentrated area to a greater concentration through a semi-permeable membrane.

Active Cellular Transport

Active cellular transport is a type of transport that requires the expenditure of cellular energy to move molecules into and out of the cell.