Question 1

Which of the following best explains the outcome of Pasteur's experiment using a swan-necked flask, as shown in the image?

Accepted Answer

No cells appeared in the broth because preexisting cells were trapped in the neck, supporting the 'all-cells-from-cells' hypothesis.

Question 2

According to the central dogma illustrated, what is the correct sequence for the flow of genetic information in a cell?

Accepted Answer

DNA \rightarrow RNA \rightarrow Protein

Question 3

A carbon atom has 6 protons, 7 neutrons, and 6 electrons. What is its atomic number and mass number?

Accepted Answer

Atomic number: 6, Mass number: 13

Question 4

Which statement best describes the formation of a covalent bond between two hydrogen atoms?

Accepted Answer

A covalent bond forms when two hydrogen atoms share a pair of electrons, filling their valence shells.

Question 5

Which of the following molecules contains a polar covalent bond?

Accepted Answer

Water ($$H_2O)$$

Question 6

Why is water considered a polar molecule, and how does this polarity contribute to hydrogen bonding?

Accepted Answer

Water is polar because electrons are pulled toward oxygen, creating partial charges that allow hydrogen bonds to form between water molecules.

Question 7

Which part of the amino acid structure is responsible for the diversity of amino acids and their chemical properties?

Accepted Answer

The R-group (side chain)

Question 8

What type of interaction stabilizes the secondary structure of proteins, such as the α-helix and β-pleated sheet?

Accepted Answer

Hydrogen bonds between backbone groups

Question 9

Which of the following is NOT a type of R-group interaction that contributes to the tertiary structure of proteins?

Accepted Answer

Peptide bonding

Question 10

Why do carbohydrates store more energy than carbon dioxide, as shown in the image?

Accepted Answer

Carbohydrates have more C–H and C–C bonds, which have higher potential energy than C==O bonds.

Question 11

Which structural feature of fatty acids determines whether a lipid is solid or liquid at room temperature?

Accepted Answer

The presence of double bonds (especially cis double bonds) in the hydrocarbon chain

Question 12

What is the primary difference between fats and phospholipids, as shown in the image?

Accepted Answer

Fats are composed of three fatty acids linked to glycerol, while phospholipids have two fatty acids and a phosphate-containing hydrophilic head.

Question 13

Which structure forms spontaneously in water due to the amphipathic nature of lipids?

Accepted Answer

Micelles and lipid bilayers

Question 14

According to the permeability scale shown, which type of molecule crosses a phospholipid bilayer most easily?

Accepted Answer

Small, nonpolar molecules

Question 15

How does cholesterol affect membrane permeability and fluidity at different temperatures?

Accepted Answer

Cholesterol decreases membrane permeability and increases packing density; at high temperatures, it reduces fluidity, and at low temperatures, it prevents rigidity.

Question 16

Which model of membrane structure is currently accepted and why?

Accepted Answer

The fluid-mosaic model, because proteins are embedded within the phospholipid bilayer and the membrane is dynamic.

Question 17

Which cytoskeletal filament is responsible for moving chromosomes during cell division?

Accepted Answer

Microtubules

Question 18

During cellular respiration, what is the main purpose of the electron transport chain?

Accepted Answer

To transfer electrons and create a proton gradient for ATP synthesis

Question 19

What is the role of fermentation in cells when oxygen is absent?

Accepted Answer

Fermentation regenerates $$NAD^+ so $$glycolysis can continue to produce ATP.

Question 20

Which enzyme is responsible for carbon fixation in the Calvin cycle during photosynthesis?

Accepted Answer

Rubisco (Ribulose-1,5 biphosphate carboxylase/oxygenase)

Essential Concepts in Biology: Cells, Chemistry, Biomolecules, and Cellular Processes

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