Life at the Molecular and Cellular Level

What is the primary function of enzymes in biological processes?

• To provide energy for reactions

• To speed up chemical reactions

• To store genetic information

• To transport molecules across cell membranes

Answer explanation

The primary function of enzymes is to speed up chemical reactions in biological processes by lowering the activation energy required, making reactions occur more efficiently.

Which of the following is a key component of the cell membrane?

• Nucleic acids

• Phospholipids

• Ribosomes

• Mitochondria

Answer explanation

Phospholipids are a key component of the cell membrane, forming a bilayer that provides structure and regulates the movement of substances in and out of the cell. The other options do not play a direct role in membrane structure.

What is the relationship between cellular respiration and photosynthesis?

• Both processes release oxygen as a byproduct

• Photosynthesis converts glucose into energy, while cellular respiration converts energy into glucose

• Photosynthesis stores energy in glucose, while cellular respiration releases energy from glucose

• Both processes occur in the mitochondria

Answer explanation

Photosynthesis captures energy from sunlight to convert carbon dioxide and water into glucose, storing energy. Cellular respiration then breaks down glucose to release that stored energy, making this choice correct.

Tags

NGSS.HS-LS2-5

Which phase of the cell cycle involves the replication of DNA?

• G1 phase

• S phase

• G2 phase

• M phase

Answer explanation

The S phase of the cell cycle is where DNA replication occurs, ensuring that each daughter cell receives an identical set of chromosomes. The G1 and G2 phases involve growth and preparation, while the M phase is for mitosis.

How do enzymes affect the activation energy of a chemical reaction?

• They increase the activation energy

• They decrease the activation energy

• They have no effect on the activation energy

• They eliminate the need for activation energy

Answer explanation

Enzymes act as catalysts that lower the activation energy required for a chemical reaction to occur. By decreasing this energy barrier, enzymes increase the rate of the reaction, making it easier for the reaction to proceed.

Which property of water is most important for maintaining homeostasis in organisms?

• High surface tension

• Low density as a solid

• High specific heat capacity

• Ability to dissolve nonpolar substances

Answer explanation

High specific heat capacity allows water to absorb and retain heat, stabilizing temperatures in organisms and their environments, which is crucial for maintaining homeostasis.

What is the role of ribosomes in a cell?

• To synthesize proteins

• To replicate DNA

• To store energy

• To transport substances

Answer explanation

Ribosomes are essential cellular structures that synthesize proteins by translating messenger RNA (mRNA) into amino acid sequences, making them crucial for cell function and growth.

Which of the following best describes the structure of DNA?

• A single-stranded helix

• A double-stranded helix

• A triple-stranded helix

• A quadruple-stranded helix

Answer explanation

DNA is best described as a double-stranded helix, consisting of two strands that twist around each other, forming a structure that is essential for its function in genetic information storage.

What is the primary function of the cell membrane?

• To provide structural support

• To control the movement of substances in and out of the cell

• To produce energy

• To store genetic information

Answer explanation

The primary function of the cell membrane is to control the movement of substances in and out of the cell, maintaining homeostasis and allowing selective permeability.

Which of the following is a characteristic of multicellular organisms?

• They consist of a single cell

• They have specialized cells for different functions

• They do not require energy

• They reproduce asexually only

Answer explanation

Multicellular organisms are characterized by having specialized cells that perform different functions, allowing for greater complexity and efficiency. The other options do not accurately describe multicellular organisms.

Tags

NGSS.MS-LS1-1

NGSS.MS-LS1-3