Cell Theory and Cell Types Questions and Answers

Answer: C

Correct answer: division of labour among specialised cells

Once cells need not each do everything, they can specialise, and a nerve cell, a muscle cell and a secretory cell can each be built for one job and be far better at it than any general-purpose cell could be. Multicellularity also allows an organism to exceed the size a single cell can reach, but the specialisation is what makes the size worth having.

Answer: D

Both are true and the reason gives the constraint that forces the arrangement: since exchange is limited by surface area, growth is achieved by adding cells rather than by enlarging them, which brings specialisation as a further benefit.

Answer: A

The theory rests entirely on observations that only a microscope could supply, and it followed Hooke's and Leeuwenhoek's work by more than a century and a half. Instrument and idea are inseparable here, since nobody can theorise about what nobody has seen.

Answer: B

Correct answer: terminally differentiated

A terminally differentiated cell has left the cell cycle permanently and devotes itself to its specialised function - a neuron, a cardiac muscle cell, a mature red blood cell. It is neither damaged nor dying, which distinguishes it from a genome failure and from apoptosis, and it is the opposite end of the scale from the totipotent cell that has differentiated into nothing at all.

Answer: C

Almost every organism reads the same codons as the same amino acids, which would be an extraordinary coincidence had life arisen more than once independently. Size, walls and water content are far weaker evidence, since each varies widely among cells.

Answer: A

The order is nuclei, mitochondria, microsomes, and ribosomes.

In differential centrifugation, larger and denser particles sediment at lower forces. Nuclei, the largest organelles, pellet first at about 600 to 1000 g. Mitochondria (and lysosomes, peroxisomes) come down next at roughly 10,000 to 20,000 g. Microsomes, the vesicles formed from the endoplasmic reticulum, need around 100,000 g, and free ribosomes and large macromolecules need the highest forces, about 150,000 to 300,000 g.

The other orders put small particles such as ribosomes or microsomes ahead of the much larger nuclei or mitochondria, which reverses the dependence of sedimentation on size.

Answer: C

The organelle enclosed by a single membrane is the endoplasmic reticulum.

The ER is a network of tubules and sacs bounded by a single lipid bilayer, continuous with the outer membrane of the nuclear envelope. Lysosomes, the Golgi apparatus, vacuoles and peroxisomes are other single-membrane organelles.

Mitochondria have two membranes, an outer one and a folded inner one forming cristae. Ribosomes and the centrosome have no membrane at all: ribosomes are RNA-protein particles and the centrosome is built of centrioles and protein.

Answer: A

The main parts of a cell are the plasma membrane, cytoplasm and nucleus.

Every typical cell has a plasma membrane that encloses it and controls what enters and leaves, cytoplasm in which the organelles lie and most metabolism takes place, and a nucleus that holds the genetic material and directs the cell's activities.

A cell wall and chloroplasts are found in plant cells but not in animal cells, so they cannot be main parts of every cell. Mitochondria, ribosomes, the Golgi apparatus and lysosomes are organelles inside the cytoplasm, not the cell's main divisions.

Answer: B

Cytology is the study of cells.

The word comes from the Greek kytos, a vessel or cell, and logos, study. Cytology deals with the structure, function and chemistry of cells; when applied to diagnosis, it becomes cytopathology.

The study of disease is pathology. The study of tissues is histology, from the Greek histos, tissue. The study of bones is osteology, from osteon, bone.

Answer: B

Cells can supercool to only about \(-40\)°C.

Pure water does not freeze at 0°C unless ice can nucleate; small volumes free of nucleating particles stay liquid well below that. The limit is homogeneous nucleation, which happens spontaneously at about \(-40\)°C, so cell water, held in small compartments, can supercool down to roughly that temperature and no further. In cold-hardy trees this sets the lower limit of deep supercooling, which is why their northern range ends near the \(-40\)°C isotherm.

0°C is the normal freezing point, not a supercooling limit; \(-20\)°C stops short of the limit, and \(-80\)°C lies beyond it.