2. Eukaryotes and Prokaryotes

Eukaryotic Cell

cell parts
Parts of a typical animal cell: (1) nucleolus, (2) nucleus, (3) ribosomes, (4) vesicle, (5) rough endoplasmic reticulum, (6) Golgi apparatus, (7) cytoskeleton, (8) smooth endoplasmic reticulum, (9) mitochondrion, (10) vacuole, (11) cytosol, i.e. the fluid that contains organelles, comprising the cytoplasm, (12) lysosome, (13) centrosome, (14) cell membrane.
Plant cell schematic diagram
A eukaryotic plant cell possesses various cell structures, such as nucleus, chloroplasts, mitochondria, a central vacuole, Golgi apparatus, and endoplasmic reticulum. They are surrounded by a cell membrane and further enveloped by a plant cell wall.

The cell of a eukaryote has several membrane-bound structures dispersed in the cytoplasm. They are called organelles. Organelles typically found inside a eukaryotic cell are the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondrion, and plastid. Other cytoplasmic structures are cytoskeleton, inclusions, and biomolecules. These subcellular structures have their distinct functions and involved in various metabolic activities that regulate homeostasis.

The cells of eukaryotes divide by mitosis and meiosis. While mitosis gives rise to two daughter cells meiosis gives rise to four daughter cells. The cells from meiosis will be haploid after two consecutive divisions. In males, the haploid cell will grow into a spermatozoon (sperm cell) whereas, in females, it could develop into an ovum (egg cell). These two gametes could come together in a union via fertilization and give rise to a diploid zygote. In multicellular eukaryotes, the zygote divides by series of mitoses to give rise to stem cells that can develop and differentiate later into specialized cells that carry out a particular function and assemble into tissues, organs, and biological systems. In humans, there are several cell types: myocytes, adipocytes, blood cells, neurons, hepatocytes, osteocytes, macrophages, etc.

Some eukaryotes are single-celled. The cell is an entire organism capable of performing all the fundamental functions (e.g. ingestion, respiration, excretion, osmoregulation, homeostasis, etc.) that different systems do in a multicellular organism. These single-celled organisms are exemplified by protists.

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