Cells, Membranes & Exchange — Chapter Practice, Grade 10

All cells contain a nucleus

Prokaryotic cells (like bacteria) have no nucleus, so 'all cells contain a nucleus' is false and is not part of cell theory.

Its resolution limit (~200 nm) is far larger than a ribosome, so it cannot separate that fine detail no matter how much it magnifies

Magnification and resolution are different. A light microscope's resolution stalls near 200 nm, so a 20 nm ribosome stays a blur; an electron microscope is needed.

400 ×

Total magnification = eyepiece × objective = 10 × 40 = 400×.

Cell theory's third tenet says cells only come from pre-existing cells. If life could arise spontaneously from non-living matter, that tenet would be false. Pasteur's swan-neck experiment showed sterile broth stayed lifeless until microbes reached it, confirming that cells come only from other cells.

Antonie van Leeuwenhoek

Leeuwenhoek's unusually powerful lenses let him observe living 'animalcules' in pond water in the 1670s.

About 50 μm if the printed image retains its stated scale.

Actual size=image size/magnification=25/500=0.05 mm.

Convert 0.05 mm to 50 μm.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

An instrument extends observation but conclusions still require evidence.

It allowed structures and cell division to be observed and compared across organisms.

State what the supplied observations or conditions establish, and separate that from any assumption.

No. Sampling, preparation, focus and resolution can limit detection; inspect appropriate fields and controls.

The original image may lack sufficient resolution; resizing cannot recover detail that was never resolved. Use an appropriate method or independent evidence.

Magnification is enlargement of an image. Resolution is the ability to distinguish nearby features as separate under the imaging conditions. A larger blurry spot can still hide two structures. Contrast, preparation, staining and artifacts also influence what can be seen. Light and electron imaging have different capacities and preparation requirements; neither one automatically shows every structure alive and unchanged. Before identifying an organelle, ask whether the feature is resolved, labeled with scale and supported by appropriate observations rather than a familiar-looking blob.

The original image may lack sufficient resolution; resizing cannot recover detail that was never resolved. Use an appropriate method or independent evidence.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

The estimate is 2.4×25 = 60 μm. A magnification label describes a particular display enlargement; resizing changes it, while an image and scale bar resized together preserve the specimen-length ratio.

The estimate is 2.4×25 = 60 μm. A magnification label describes a particular display enlargement; resizing changes it, while an image and scale bar resized together preserve the specimen-length ratio.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

A membrane-bound nucleus

Prokaryotes have DNA, ribosomes, and a cell membrane, but they lack a true membrane-bound nucleus — that is the defining eukaryotic feature.

Golgi apparatus

The Golgi apparatus is the cell's shipping department, tagging and packaging proteins into vesicles addressed to their destinations.

It is studded with ribosomes that build and process proteins

Ribosomes attached to its surface give the rough ER its bumpy look and its role in processing newly made proteins.

Mitochondria have their own circular DNA separate from the nucleus, they are wrapped in a double membrane, and they divide on their own schedule — all clues that they descend from free-living bacteria engulfed by an ancestral cell.

20 ×

40 ÷ 2 = 20 times wider, reflecting the much larger size of eukaryotic cells.

bacterial (prokaryotic) ribosomes differ enough from human (eukaryotic) ribosomes for the drug to target one and not the other

Prokaryotic ribosomes are structurally different from eukaryotic ones, so a drug can disable bacterial ribosomes while sparing our own — a key principle of selective antibiotics.

Ribosome→rough ER→Golgi→secretory vesicle→cell exterior, in a simplified pathway.

Ribosomes associated with rough ER synthesize the protein into the secretory pathway.

It passes through ER and Golgi processing and vesicles to the cell surface.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

Ribosomes alone do not distinguish these types.

Eukaryotic; these membrane-bound structures support that classification.

State what the supplied observations or conditions establish, and separate that from any assumption.

No. Chloroplast abundance depends on tissue and function; many root cells do not photosynthesize.

No. It handles selected cargo; many proteins remain in other compartments and use different targeting routes.

The endoplasmic reticulum, ER, is a membrane network; ribosomes attached to rough ER can make proteins entering the secretory pathway. The Golgi apparatus modifies and sorts selected products. A vesicle is a membrane-bounded transport compartment, and exocytosis releases contents when its membrane fuses with the plasma membrane. The nucleus supplies transcribed information rather than shipping a finished protein through the whole route. Not all proteins follow this pathway; cytosolic proteins and organelle-targeted proteins have other destinations and targeting mechanisms.

No. It handles selected cargo; many proteins remain in other compartments and use different targeting routes.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

Gene information is transcribed and used by ribosomes; selected secretory proteins enter the ER, undergo processing/sorting through Golgi and travel in vesicles to membrane fusion. A cytosolic enzyme generally follows a different localization pathway rather than compulsory secretion.

Gene information is transcribed and used by ribosomes; selected secretory proteins enter the ER, undergo processing/sorting through Golgi and travel in vesicles to membrane fusion. A cytosolic enzyme generally follows a different localization pathway rather than compulsory secretion.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

hydrophilic; hydrophobic

The phosphate head is water-loving (hydrophilic) and the fatty-acid tails are water-fearing (hydrophobic) — the split personality that lets a bilayer form.

The variety of proteins embedded throughout the membrane like tiles

'Mosaic' refers to the patchwork of many different proteins set into the fluid phospholipid sheet.

Oxygen (small, nonpolar)

Small nonpolar molecules like oxygen dissolve straight through the hydrophobic core; charged or large molecules need transport proteins.

Selective permeability means the membrane lets some substances cross while blocking or controlling others. It is essential because it lets the cell keep its internal chemistry different from the outside — taking in what it needs, removing wastes, and keeping harmful things out — which is the basis of homeostasis.

A receptor protein that detects the signal and relays it inward

Receptor proteins act as antennae: they bind the signal on the outside and trigger a response inside without the signal itself entering the cell.

Different chemical properties cause different permeabilities.

Oxygen is small and nonpolar.

A charged ion interacts poorly with the hydrophobic interior and generally needs a protein pathway.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

A membrane is neither an open sieve nor an absolute wall.

Its structure permits certain particles and not others; movement can still occur down an electrochemical gradient.

State what the supplied observations or conditions establish, and separate that from any assumption.

No. Channels and carriers can mediate passive transport; active transport requires an energy-coupled mechanism.

Size alone is insufficient; its charge makes passage through the lipid interior unfavorable, and suitable transport proteins may be required.

Selective permeability means passage depends on a substance and the membrane’s pathways. Small nonpolar molecules can often enter the lipid interior more readily than ions, whose charge and surrounding interactions create a barrier. Some water crosses lipid membranes, and aquaporin proteins greatly increase water permeability in many cells. A molecule being small does not automatically guarantee rapid passage. Channels and carriers have selectivity and regulation, so identify the relevant substance, concentration/electrical conditions and available protein before predicting transport.

Size alone is insufficient; its charge makes passage through the lipid interior unfavorable, and suitable transport proteins may be required.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

Charge and lipid-interior interactions limit the direct route; the selective channel changes the available pathway. Fluidity concerns component motion, not unrestricted permeability to every substance.

Charge and lipid-interior interactions limit the direct route; the selective channel changes the available pathway. Fluidity concerns component motion, not unrestricted permeability to every substance.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

water

Osmosis specifically refers to the movement of water across a selectively permeable membrane toward the side with more solute.

It requires energy (ATP) and can move substances against their concentration gradient

Active transport spends energy to move substances against the gradient; passive transport moves them down the gradient for free.

Water enters by osmosis and the cell swells and may burst

Pure water is hypotonic, so water rushes in by osmosis; with no wall to resist, the animal cell swells and can burst (lysis).

In endocytosis, the membrane wraps around material and pulls it into the cell inside a vesicle (bringing things in). In exocytosis, a vesicle fuses with the membrane and releases its contents outside the cell (sending things out). Both move large amounts of material and require energy.

1 charges

3 positive charges leave and 2 positive charges enter, so the net is 3 − 2 = 1 positive charge moved out.

So there is no net osmosis — the blood cells neither swell and burst nor shrivel

An isotonic fluid matches the solute concentration of blood, so water moves in and out equally and red blood cells keep their normal shape.

The cell initially loses water; the final behavior also depends on cell structure and pressure.

The external solution has the higher effective solute concentration.

Water moves out in the simple osmosis model.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

State permeability and effective solute conditions; not every solute is trapped.

The pump uses coupled energy; facilitated diffusion moves particles down their electrochemical gradient.

State what the supplied observations or conditions establish, and separate that from any assumption.

Its cell wall resists expansion, allowing turgor pressure to balance water entry.

No. Both can have limited protein capacity; gradient direction and energy coupling provide additional tests.

Facilitated diffusion uses a channel or carrier for down-gradient transport. Active transport couples energy transfer to movement against the relevant driving gradient, directly through ATP or indirectly through another gradient. Primary active transport uses a direct energy source; secondary transport can use a gradient maintained by other processes. A pump and a passive carrier can both become saturated as capacity is limited. Therefore, protein involvement or a plateau alone does not establish whether the step is active; use direction, gradients, coupling and controlled energy perturbations.

No. Both can have limited protein capacity; gradient direction and energy coupling provide additional tests.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

The change is −3/12×100 = −25%. Net water loss is consistent with a hypertonic external solution under the model. Comparable blotting, membrane integrity and limits on solute loss are needed before assigning all mass change to water.

The change is −3/12×100 = −25%. Net water loss is consistent with a hypertonic external solution under the model. Comparable blotting, membrane integrity and limits on solute loss are needed before assigning all mass change to water.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

2 mm⁻¹

6/3 = 2.

8 times larger

Volume depends on the cube of length.

Thinness shortens diffusion distance; folding increases exchange area.

The larger cube has half the area per unit volume.

At 1 mm, area=6 and volume=1, ratio=6 mm⁻¹.

At 2 mm, area=24 and volume=8, ratio=3 mm⁻¹.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

Both lengths use the same units.

54/27=2 inverse length units.

State what the supplied observations or conditions establish, and separate that from any assumption.

They increase membrane area available for transport relative to the volume served.

No. Area supports capacity, but driving conditions, permeability and supply/removal also determine rate.

A fold can increase exchange area within a compact region. A thin barrier reduces the distance across which a substance must move. Circulation maintains delivery and removal by bulk transport, affecting gradients at exchange surfaces. These mechanisms should not be collapsed into one vague explanation that every surface is “large.” Intestinal villi, respiratory surfaces and internal membranes use different combinations under their conditions. A structural observation supports a plausible function, but actual rates also need permeability, driving conditions and activity measurements.

No. Area supports capacity, but driving conditions, permeability and supply/removal also determine rate.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

At 2 mm: area 24 mm², volume 8 mm³, ratio 3 mm⁻¹. At 4 mm: area 96 mm², volume 64 mm³, ratio 1.5 mm⁻¹. Total surface increases while area per volume falls; actual exchange also depends on pathways and demand.

At 2 mm: area 24 mm², volume 8 mm³, ratio 3 mm⁻¹. At 4 mm: area 96 mm², volume 64 mm³, ratio 1.5 mm⁻¹. Total surface increases while area per volume falls; actual exchange also depends on pathways and demand.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.