Cell Classification and Types

Questions and Answers

What is the name of the process that allows each daughter nucleus to receive one copy of each chromosome during nuclear division?

Mitosis

What are the two types of generations involved in sexual reproduction in most eukaryotes?

Haploid and diploid generations

What is the process of nuclear fusion called?

Syngamy

How are cells organized in multicellular organisms?

Cells associate to form tissues, tissues form organs, and organs make up the whole organism. Signup and view all the answers

What is the relationship between surface area to volume ratio and metabolic rate in eukaryotes compared to prokaryotes?

Eukaryotes have a smaller surface area to volume ratio than prokaryotes, resulting in lower metabolic rates and longer generation times. Signup and view all the answers

How do cells specialized for metabolism in multicellular organisms compensate for their lower surface area to volume ratio?

They have enlarged surface area, such as intestinal villi. Signup and view all the answers

What is the primary function of mitosis?

To produce two daughter cells that are genetically identical to the parent cell. Signup and view all the answers

What is the primary function of meiosis?

To produce gametes (sex cells) that have half the number of chromosomes as the parent cell. Signup and view all the answers

What are the two main differences between prokaryotes and eukaryotes?

Prokaryotes lack a nucleus and membrane-bound organelles, while eukaryotes have both. Signup and view all the answers

Describe the relationship between cell division and nuclear division.

Cell division is typically coordinated with nuclear division, ensuring that each daughter cell receives a complete set of chromosomes. Signup and view all the answers

Study Notes

Organisms Classification

Organisms with one cell in their body are called unicellular organisms (bacteria, blue-green algae, some algae, Protozoa, etc.).
Organisms with many cells in their body are called multicellular organisms (fungi, most plants and animals).

Prokaryotic Cells

Prokaryote means "before nucleus" in Greek.
Prokaryotes include all cells that lack a nucleus and other membrane-bound organelles.
Examples of prokaryotes include Mycoplasma, viruses, bacteria, and cyanobacteria or blue-green algae.
Most prokaryotes range between 1 µm to 10 µm in size, but they can vary in size from 0.2 µm to 750 µm (Thiomargarita namibiensis).
Prokaryotes belong to two taxonomic domains: bacteria and archaea.
Most prokaryotes are unicellular, with exceptions being myxobacteria which have multicellular stages in their life cycles.

Prokaryotic Cell Structure

Prokaryotes lack cell organelles but have internal structures such as cytoskeletons and ribosomes.
Membranous organelles are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties (e.g., photosynthesis or chemolithotrophy).
Some species also contain protein-enclosed microcompartments, which have distinct physiological roles (carboxysomes or gas vacuoles).

Gram Staining

Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids.
Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins.

Cell Components

Cell membrane: surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.
Cytoplasm: a fluid in nature that fills the cell and is composed mainly of 80% water that also contains enzymes, salts, cell organelles, and various organic molecules.
Ribosomes: organelles responsible for protein synthesis.
Nucleoid Region: the area of the cytoplasm that contains the bacterial DNA molecule.

Plasmids and Pili

Plasmid: a DNA molecule (mostly in bacteria) that is separate from and can replicate independently of the chromosomal DNA.
Pili: hair-like structures on the surface of the cell that help attach to other bacterial cells.
Types of pili include conjugative pili (allow the transfer of DNA between bacteria) and type IV pili (generate motile forces).

Morphology of Prokaryotic Cells

Prokaryotic cells have various shapes, including cocci (spherical), bacilli (rod-shaped), spirochaete (spiral-shaped), and vibrio (comma-shaped).

Prokaryote Environments and Sociability

Prokaryotes live in nearly all environments on Earth, including extreme conditions (thermophiles or halophiles).
Some archaea and bacteria thrive in extreme conditions.
Prokaryotes can form stable aggregated communities in a stabilizing polymer matrix called "biofilms".
Cells in biofilms often show distinct patterns of gene expression (phenotypic differentiation) in time and space.

Colony of Bacteria

A colony of bacteria is a group of individual organisms of the same species living closely together in mutualism.
The shape of the colony can be circular and irregular.
Bacterial colonies are frequently shiny and smooth in appearance.

Reproduction

Bacteria and archaea reproduce through asexual reproduction known as binary fission.
Binary fission is an asexual mode of reproduction in which the genomic DNA undergoes replication and the original cell is divided into two identical cells.