Cell Surface Membrane: The cell surface membrane, also known as the plasma membrane, is a selectively permeable barrier that encloses the cell. It is primarily composed of a phospholipid bilayer with embedded proteins. The phospholipid bilayer creates a barrier, regulating the passage of substances into and out of the cell. Proteins within the membrane perform various functions, including transport, signaling, and cell recognition. Its selective permeability is crucial for maintaining cellular homeostasis.

Nucleus: The nucleus is the control center of the cell, housing the cell's genetic material (DNA) in the form of chromatin. It is surrounded by the nuclear envelope.

Nuclear Envelope: The nuclear envelope is a double membrane that surrounds the nucleus, separating the nuclear contents from the cytoplasm. It contains nuclear pores, which regulate the movement of molecules between the nucleus and the cytoplasm. The nuclear envelope also plays a role in DNA replication and transcription.

Nucleolus: The nucleolus is a dense structure within the nucleus responsible for ribosome biogenesis. It is the site where ribosomal RNA (rRNA) is transcribed and ribosomal subunits are assembled. These subunits are then exported to the cytoplasm to participate in protein synthesis.

Contribution to Cellular Function: These structures work together to maintain cellular integrity, control gene expression, and regulate cellular processes. The membrane controls what enters and exits, the nucleus houses the genetic blueprint, the nuclear envelope protects the DNA, and the nucleolus ensures the availability of ribosomes for protein synthesis. This coordinated function is essential for the cell's survival and proper operation.

Both plant and animal cells are eukaryotic cells, meaning they have a membrane-bound nucleus and other organelles. However, significant structural differences exist reflecting their distinct functions. Plant cells are characterized by the presence of a cell wall, chloroplasts, and a large central vacuole, while animal cells lack these features.

Cell Wall: A rigid cell wall provides structural support and protection to plant cells. It is composed primarily of cellulose. Animal cells do not have a cell wall, allowing for greater flexibility and movement.

Chloroplasts: Chloroplasts are the sites of photosynthesis, converting light energy into chemical energy (glucose). This process is essential for plant survival. Animal cells do not perform photosynthesis and therefore lack chloroplasts.

Central Vacuole: A large central vacuole in plant cells stores water, nutrients, and waste products. It also helps maintain cell turgor pressure, which is crucial for rigidity. Animal cells may have smaller vacuoles, but they are not typically central or as large as in plant cells.

Other Organelles: Both cell types share many organelles, including the nucleus (containing DNA), mitochondria (for energy production), ribosomes (for protein synthesis), endoplasmic reticulum (for protein and lipid synthesis), Golgi apparatus (for protein processing and packaging), and lysosomes (for waste disposal). However, the relative abundance and specific functions of these organelles can differ between plant and animal cells.

Table Summary:

Mitochondria: Mitochondria are often referred to as the "powerhouses of the cell." Their primary function is to generate ATP (adenosine triphosphate), the cell's main energy currency, through cellular respiration. The structure of mitochondria is directly related to this function. They have a double membrane: an outer membrane and a highly folded inner membrane (cristae). The folds increase the surface area available for the chemical reactions involved in ATP production. The matrix within the inner membrane contains enzymes and molecules necessary for the Krebs cycle and electron transport chain.

Endoplasmic Reticulum (ER): The ER is a network of interconnected membranes that extends throughout the cytoplasm. There are two types: rough ER (studded with ribosomes) and smooth ER (lacks ribosomes). The structure of the ER reflects its diverse functions. Rough ER is involved in protein synthesis; ribosomes on the surface translate mRNA into proteins, which are then folded and modified within the ER lumen. Smooth ER is involved in lipid synthesis, detoxification, and calcium storage. The extensive network of membranes provides a large surface area for these processes.

Golgi Apparatus: The Golgi apparatus receives proteins and lipids from the ER, further processes and modifies them, and then packages them into vesicles for transport to other destinations within or outside the cell. The structure of the Golgi apparatus – a stack of flattened, membrane-bound sacs called cisternae – is crucial to its function. Each cisterna has distinct regions (cis and trans faces) where modifications occur. Proteins are glycosylated (sugars are added), sorted, and packaged into vesicles at the trans face. The vesicles then bud off from the trans face and deliver their contents to the appropriate locations.