A2.2 Cell Structure

Comprehensive practice flashcards covering cell theory, microscopy techniques, prokaryotic and eukaryotic structures, atypical cell structures, and endosymbiosis based on IB Biology A2.2 lecture notes.

What are the three core principles of the cell theory?

1. Cells are the smallest unit of life. 2. All organisms are made of one or more cells. 3. Cells arise from pre-existing cells.

What term did Robert Hooke coin in 1655 after observing cork under a microscope?

He coined the term 'cell' because the tiny blocks reminded him of a monk's cell in a monastery.

What did Anton von Leeuwenhoek discover when observing pond water under his microscope?

He discovered single-celled organisms and termed them 'animalcules'.

Why are phospholipid molecules in the plasma membrane considered amphipathic?

They possess both a hydrophilic (water-attracting) head composed of glycerol and phosphate, and hydrophobic (water-repelling) tails composed of fatty acid chains.

How do prokaryotic and eukaryotic ribosomes differ in size?

Prokaryotes contain $70\text{S}$ ribosomes, while eukaryotes contain larger $80\text{S}$ ribosomes.

What is the primary structural component of a bacterial cell wall?

Peptidoglycan.

What structural differences determine whether a bacterium is Gram-positive or Gram-negative?

The thickness of the peptidoglycan cell wall layer and the presence or absence of an outer lipid membrane.

How do the cell wall compositions of plant cells and fungal cells differ?

Plant cell walls are made of cellulose, whereas fungal cell walls are made of chitin.

What feature shown on this fungal cell surface indicates how many times the cell has divided?

A budding scar, which is a crater-like ring of tissue that forms when a daughter cell buds from a parent cell.

Why are skeletal muscle fibers considered an atypical cell structure?

They are very long (approximately $30\,\text{mm}$) and contain multiple nuclei (multinucleated) because they are formed by the fusion of many smaller cells.

Why are mature human red blood cells anucleate?

Lacking a nucleus increases their internal hemoglobin capacity, allowing them to transport more oxygen.

What structural feature of phloem sieve tube elements allows for low resistance to transport?

They are anucleate and contain very little cytoplasm and few organelles.

What formula is used to calculate magnification in microscopy?

$\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}$ where image size is measured directly with a ruler.

What is the equivalent measurement of $1\,\mu\text{m}$ in meters?

$1\,\mu\text{m} = 10^{-6}\,\text{m}$ (or $0.000001\,\text{m}$).

How do Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM) differ in how they create images?

TEM passes electrons through a specimen to produce a 2D cross-sectional view, while SEM scatters electrons across the surface to produce a 3D surface map.

What is freeze fracture electron microscopy used for?

It involves freezing a sample and breaking it along lines of weakness to visualize internal cellular structures that are otherwise hidden, such as the interior of the plasma membrane.

What are the primary advantages of Cryogenic Electron Microscopy (Cryo-EM)?

Freezing samples to cryogenic temperatures stabilizes molecules, enhances image resolution, and reduces structural damage caused by the electron beam.

What structural evidence supports the endosymbiotic origin of mitochondria and chloroplasts?

Both organelles contain double membranes, circular naked DNA, $70\text{S}$ ribosomes, divide by binary fission, are susceptible to antibiotics, and are similar in size to bacteria.

What is the cellular basis of differentiation in multicellular organisms?

Differentiation is driven by selective gene expression, where specific genes required for a specialized cell type are turned on while unneeded genes are turned off.

What are emergent properties in complex biological systems?

Emergent properties are characteristics or functions that arise from the interaction of smaller individual components, which single isolated cells cannot perform on their own.

How do Paramecium and Chlamydomonas differ in how they carry out nutrition?

Paramecium feeds heterotrophically by ingesting smaller organisms via endocytosis, while Chlamydomonas is an autotroph that produces food through photosynthesis using a chloroplast.

What functions do pili serve in prokaryotic cells?

Pili allow bacteria to adhere to surfaces (attachment pili) or facilitate bacterial conjugation and horizontal gene transfer (sex pili).

What technique uses dye-conjugated antibodies to identify specific cellular target molecules?

Immunofluorescence staining.

What book published by Robert Hooke led to him being considered the father of modern microscopy?

Micrographia.

What are the four kingdoms within the domain Eukarya?

Protista, Fungi, Plantae, and Animalia.

How do plant, animal, and fungal cells store carbohydrate energy?

Plant cells store carbohydrates as starch, whereas animal cells and fungal cells store carbohydrates as glycogen.