Chapter Summary and Practice

Problem
Differentiate the cell membrane and cell wall using permeability and structural role.

1. 1.The cell membrane is selectively permeable and controls movement into and out of the living cell.
2. 2.The cell wall is permeable to water and some dissolved substances.
3. 3.The membrane is thin and flexible; the wall is rigid.
4. 4.The membrane occurs in all cells; the wall occurs in plant, fungal and bacterial cells but not animal cells.
5. 5.The wall provides strength and shape, while the membrane maintains controlled exchange.

Problem
Differentiate rough and smooth endoplasmic reticulum by structure and function.

1. 1.RER has ribosomes attached to its surface and therefore appears rough.
2. 2.RER is associated mainly with protein synthesis and secretion.
3. 3.SER has no surface ribosomes and appears smooth.
4. 4.SER is associated with the synthesis and storage of fats and certain hormones.

Problem
Differentiate chloroplasts and chromoplasts by pigments and roles.

1. 1.Chloroplasts contain chlorophyll, which absorbs light for photosynthesis.
2. 2.Chromoplasts contain yellow, orange or red pigments.
3. 3.Chloroplasts support food synthesis.
4. 4.Chromoplasts colour flowers and fruits and can help attract pollinators or seed-dispersing animals.

Problem
Cell X is placed in pure water and swells. Cell Y is placed in concentrated salt solution and shrinks. Explain both observations.

1. 1.Pure water is hypotonic relative to Cell X, so water enters through the cell membrane by osmosis.
2. 2.Cell X swells because animal cells have no rigid cell wall.
3. 3.The concentrated salt solution is hypertonic relative to Cell Y.
4. 4.More water leaves Cell Y than enters it, so the cell shrinks.
5. 5.The observations are explained by water movement across selectively permeable membranes.

Problem
Two similar carrots are placed in plain water and concentrated salt solution. What hypothesis is being tested, and how can the setup be improved?

1. 1.The hypothesis is that surrounding solute concentration changes carrot firmness and mass through osmosis.
2. 2.Use carrots of equal initial mass, length and thickness.
3. 3.Use equal volumes of solution and the same treatment time and temperature.
4. 4.Measure initial and final mass rather than relying only on touch.
5. 5.Repeat the treatment with several carrot pieces and compare the results.
6. 6.The carrot in plain water remains stiff because water enters its cells; the carrot in concentrated solution becomes limp because water leaves.

Problem
Explain why water gathers in potato cups containing sugar or salt, but not in an empty cup or a cup made from boiled potato.

1. 1.Sugar or salt creates a concentrated solution inside the living potato cup.
2. 2.Water moves through selectively permeable cell membranes towards this concentrated region by osmosis.
3. 3.The empty cup acts as a control and provides no solute gradient drawing water inward.
4. 4.Boiling damages the cell membranes, so the selectively permeable living membrane system needed for the demonstration is lost.

Problem
A labelled cell diagram includes a rigid outer boundary, a thinner inner boundary, a large storage compartment, a nucleus, mitochondria, Golgi apparatus and chloroplasts. Match each structure with its function.

1. 1.Rigid outer boundary: cell wall — structural rigidity.
2. 2.Thinner inner boundary: cell membrane — separates contents and controls exchange.
3. 3.Large storage compartment: vacuole — storage and firmness.
4. 4.Nucleus — controls cellular activities through genetic information.
5. 5.Mitochondria — cellular respiration and energy release.
6. 6.Golgi apparatus — modification, sorting and packaging.
7. 7.Chloroplasts — photosynthesis.

Problem
One student says plastids occur in roots; another says roots have no plastids because they do not photosynthesise. Resolve the disagreement.

1. 1.Photosynthesis requires chloroplasts, but chloroplasts are only one type of plastid.
2. 2.Roots usually do not need chloroplasts because they receive little or no light.
3. 3.Root cells can contain colourless leucoplasts that store starch, oils or proteins.
4. 4.Therefore, the statement that plastids can occur in roots is correct.

Problem
Which major eukaryotic structures described in this chapter contain DNA?

1. 1.The nucleus contains chromosomes made of DNA and associated proteins.
2. 2.Mitochondria contain their own DNA.
3. 3.Chloroplasts, a type of plastid, contain their own DNA.
4. 4.Ribosomes, Golgi apparatus and lysosomes do not contain DNA in the chapter’s description.

Problem
The cell membrane contains proteins and lipids. Trace the organelles involved in making and delivering these materials.

1. 1.Ribosomes on RER synthesise membrane proteins.
2. 2.SER synthesises lipids.
3. 3.The ER transports newly made materials towards the Golgi apparatus.
4. 4.The Golgi apparatus modifies, sorts and packages them into vesicles.
5. 5.Vesicles deliver the proteins and lipids to the cell membrane.

Problem
Predict the outcome if all mitochondria are removed from a eukaryotic cell.

1. 1.Cellular respiration in mitochondria would no longer release the usual supply of usable energy.
2. 2.ATP available for most cellular activities would fall sharply.
3. 3.Energy-dependent transport, synthesis and maintenance would be disrupted.
4. 4.The cell would be unable to continue normal functioning and survival.

Problem
What would happen if gametes were formed through mitosis?

1. 1.Mitosis would maintain the parent chromosome number instead of halving it.
2. 2.Each gamete would carry a full chromosome set.
3. 3.Fusion of two such gametes would produce a fertilised cell with twice the expected chromosome number.
4. 4.The normal restoration of chromosome number at fertilisation would be disrupted.

Problem
Which phenomenon helps limit tumour formation in many animal tissues, and can plants show the same pattern?

1. 1.Contact inhibition stops many normal animal cells from dividing after they contact neighbouring cells.
2. 2.Loss of this control allows continued division and can contribute to tumour formation.
3. 3.Plant cells have rigid walls and follow a different growth pattern.
4. 4.They do not show contact inhibition in the same way as animal cells.

Problem
Explain how concentrated salt or sugar helps preserve fruit products.

1. 1.A high concentration of salt or sugar creates a hypertonic environment around many spoilage-causing microorganisms.
2. 2.Water moves out of their cells through selectively permeable membranes by osmosis.
3. 3.Loss of water interferes with their normal growth and multiplication.
4. 4.The method applies concentration and osmosis to reduce spoilage while converting surplus produce into storable food.