Cell structure

What is the basic structural and functional unit of all living organisms?

Cell

Which group of organisms consists of prokaryotic cells?

Bacteria and Archaea

What does the Greek root "pro-karyon" (prokaryotic) mean?

Before nucleus

Where is the DNA located in a prokaryotic cell?

Free in the cytoplasm (nucleoid region)

What is the shape of DNA in prokaryotic cells?

Circular and naked (without histone proteins)

What size of ribosomes is found in prokaryotic cells?

70S

What is the typical diameter of a prokaryotic cell?

1 – 5 µm (less than 10 µm)

How do prokaryotic cells divide?

Binary fission

What are small, circular, independently replicating DNA molecules in bacteria called?

Plasmids

Which substance makes up the cell wall of bacteria (prokaryotes)?

Peptidoglycan

Which structures are present in BOTH prokaryotic and eukaryotic cells?

Plasma membrane, cytoplasm, DNA, ribosomes

What is the main advantage of internal compartmentalization in eukaryotic cells?

It separates incompatible chemical reactions and increases efficiency

Which structures are found in plant cells but NOT in animal cells?

Cell wall, chloroplasts, large permanent central vacuole

How do plant and animal cells store carbohydrates differently?

Plants store starch; animals store glycogen

What is the main component of a plant cell wall?

Cellulose

What is the main component of a fungal cell wall?

Chitin

What is the partially permeable membrane surrounding the large central vacuole in plant cells called?

Tonoplast

What are the microscopic channels through plant cell walls that connect the cytoplasm of neighboring cells?

Plasmodesmata

What is the permeability difference between a plant cell wall and a cell surface membrane?

Cell wall is freely permeable; cell membrane is partially (selectively) permeable

Instead of a cell wall, what do animal cells secrete on their exterior for support and cell-to-cell interaction?

Extracellular matrix (ECM) made of collagen and glycoproteins

What are the three main types of cell junctions found in animal tissues?

Tight junctions, desmosomes, and gap junctions

What is the liquid portion of the cytoplasm surrounding the organelles called?

Cytosol

Which is the largest organelle in a typical eukaryotic cell that controls cellular activities?

Nucleus

What is the structure that encloses the eukaryotic nucleus?

A double membrane called the nuclear envelope

What is the function of nuclear pores?

Regulate the exchange of materials (like mRNA and proteins) between the nucleus and cytoplasm

What is chromatin composed of?

Linear DNA wrapped around proteins (histones) and some RNA

What is the main function of the nucleolus inside the nucleus?

Manufacture of ribosomes (ribosomal subunits)

Which human eukaryotic cell lacks a nucleus at maturity to specialize in gas transport?

Red blood cell

What is the primary function of ribosomes?

Protein synthesis

What is the size and diameter of eukaryotic cytoplasmic ribosomes?

80S (about 25 nm)

With which structure is the outer membrane of the nuclear envelope continuous?

Endoplasmic reticulum (ER)

How does Rough Endoplasmic Reticulum (RER) differ from Smooth ER (SER)?

RER is covered with ribosomes and synthesizes proteins; SER lacks ribosomes and synthesizes lipids

What is the main function of the Golgi apparatus?

Store, chemically modify, and package proteins (e.g., into glycoproteins) into vesicles for secretion

Which organelle acts as the "garbage disposal" of the cell, containing hydrolytic enzymes to digest debris and worn-out parts?

Lysosome

What is the process by which a cell digests its own damaged organelles using lysosomes?

Autophagy

Which organelle produces hydrogen peroxide (H₂O₂) as a by-product and then converts it to water using peroxidases?

Peroxisome

Why are mitochondria known as the "powerhouses" of the cell?

They carry out aerobic respiration to produce ATP

What are the infoldings of the inner mitochondrial membrane that increase surface area for oxidative phosphorylation called?

Cristae

Where do the Link Reaction and the Krebs cycle (citric acid cycle) take place in the mitochondrion?

Matrix

What evidence supports the Endosymbiont Theory that mitochondria and chloroplasts evolved from ancient bacteria?

They contain their own circular DNA and 70S ribosomes

Which organelle is bounded by a double membrane, contains stacks of membranes called grana, and carries out photosynthesis?

Chloroplast

Which organelles are surrounded by a DOUBLE membrane (envelope)?

Nucleus, Mitochondrion, Chloroplast

Which cell structures are NON-MEMBRANOUS (have no membrane)?

Ribosomes, Centrioles, and Microtubules

What is the function of centrioles (found in the centrosome of animal cells, absent in higher plants)?

Organize spindle microtubules during cell division and form cilia/flagella

What is the internal microtubule arrangement of eukaryotic cilia and flagella?

"9 + 2" arrangement

What is the accepted model of the cell surface membrane structure (approx. 7 nm thick)?

Fluid Mosaic Model

Why are phospholipids described as "amphipathic" molecules?

They have a hydrophilic (water-loving) phosphate head and hydrophobic (water-fearing) fatty acid tails

What is the role of cholesterol in the animal cell membrane?

Stabilizes the membrane, regulates fluidity, and makes it less permeable to water-soluble substances

Why are viruses NOT considered to have a cellular structure?

They lack a plasma membrane, cytoplasm, and organelles; they only consist of DNA or RNA, a protein coat, and sometimes an outer envelope

Why does an electron microscope achieve much higher resolution than a light microscope?

Electrons have a very short wavelength