Cell Biology and Structure

Animal cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular.

 The rod-shaped structures in the nucleus of a cell are chromosomes. They carry genetic material in a 'rod' of DNA that is bonded to various proteins in the cell nucleus.

The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose and pectin.

Cytoplasm is the jelly-like, water-based substance that fills the cell and surrounds organelles. It provides the medium for metabolic reactions and organelle movement.

Plant cells differ from animal cells in the presence of a large central vacuole.

The nucleoid is the nuclear region in prokaryotic cells where the genetic material (DNA) is located, but it is not surrounded by a nuclear membrane. Nucleolus is found within eukaryotic nuclei, while vesicles and cisternae are membrane-bound structures in eukaryotes.

The nucleus contains the cell's genetic material (DNA) and controls all cellular activities, including growth, development, and protein synthesis, thereby determining how the cell develops and what form it takes. Vacuoles store materials, mitochondria produce energy, and plastids (in plants) have specific functions like photosynthesis or storage.

Chloroplasts are organelles found exclusively in plant cells and some algae, where they conduct photosynthesis. Ribosomes, nuclei, and plasma membranes are universal features found in both plant and animal cells.

The endoplasmic reticulum (ER) is a complex network of membrane-bound tubules and sheets that extends throughout the cytoplasm. It provides a large surface area for cellular activities like protein synthesis and lipid metabolism. Vacuoles are storage sacs, chloroplasts are for photosynthesis, and mitochondria produce energy.

Plastid is absent in an animal cell. The plastid is a major double-membrane organelle, found among others, in the cells of plants and algae.

Lysosomes are membrane-bound sacs containing digestive enzymes but lack DNA. Plastids (including chloroplasts) and mitochondria have their own DNA from their evolutionary origin as independent prokaryotes. The nucleus contains the main cellular DNA.

Mitochondria are called the powerhouse of the cell because they generate ATP through cellular respiration, releasing energy from organic compounds. Lysosomes digest waste, plastids (in plants) handle photosynthesis, and vacuoles are storage compartments.

Cytoplasm is the gel-like, jelly-like fluid that fills the cell and suspends organelles. It provides the medium where cellular processes occur and organelles are embedded or suspended. The nucleus is the control center, lysosomes digest waste, and vacuoles store materials.

Mitochondria are membrane-bound organelles found only in eukaryotic cells, absent in prokaryotes. Prokaryotes do have cell membranes, cytoplasm, and ribosomes (70S type). The lack of mitochondria is a key distinguishing feature of prokaryotic cells.

Both prokaryotic and eukaryotic cells contain chromosomes carrying genetic material, though they differ in structure (circular vs linear) and location (nucleoid vs nucleus). Prokaryotes lack a nuclear membrane and have circular chromosomes. Respiratory enzymes on the cell membrane are a prokaryotic feature, not shared by eukaryotes.