1. A hypothesis should be:

A. A definitive statement of fact based on existing knowledge.
B. A testable prediction based on observations and reasoning.
C. A broad question without any specific direction or focus.
D. A personal belief or opinion not requiring further investigation.

Correct answer: B

Rationale: Hypotheses guide scientific exploration by providing a framework for testing potential explanations.

2. The rigid structure that provides shape and support to plant cells is called the:

A. Cell wall
B. Plasma membrane
C. Nucleus
D. Cytoplasm

Correct answer: A

Rationale: The correct answer is A: Cell wall. The cell wall is a rigid structure found in plant cells, providing support and shape to the cell. It is composed mainly of cellulose, a tough and fibrous substance that helps plants maintain their structure. The plasma membrane, option B, is a semi-permeable membrane that surrounds the cell and regulates the passage of substances in and out of the cell. The nucleus, option C, is the control center of the cell that contains genetic material. Cytoplasm, option D, is the jelly-like substance that fills the cell and houses organelles. In this context, the function of providing shape and support points specifically to the cell wall, making it the correct choice.

3. The author's attitude towards history seems to be

A. indifferent and neutral, presenting it as an objective field of study.
B. critical and dismissive, questioning its practical applicability in the present.
C. enthusiastic and optimistic, highlighting its potential to guide the future.
D. pessimistic and cautious, emphasizing the risk of repeating past mistakes.

Correct answer: C

Rationale: The passage's overall tone highlights the value and utility of history, showcasing its potential to inspire and guide us, suggesting an optimistic and encouraging view.

4. Deuterium, a stable isotope of hydrogen, has a nucleus containing:

A. A single proton
B. A proton and a neutron
C. Two protons and an electron
D. Two neutrons

Correct answer: B

Rationale: The correct answer is B: 'A proton and a neutron.' Deuterium is an isotope of hydrogen with an atomic number of 1, meaning it has 1 proton in its nucleus. However, deuterium also has a neutron in its nucleus, making it different from regular hydrogen which only has a proton in its nucleus. Therefore, deuterium has a nucleus containing both a proton and a neutron, making option B the correct choice.

5. What is the purpose of the spindle apparatus in cell division?

A. To separate sister chromatids
B. To move chromosomes to opposite poles of the cell
C. To form a new nuclear envelope around each daughter cell
D. To synthesize new DNA

Correct answer: B

Rationale: Rationale: The spindle apparatus is a structure composed of microtubules that plays a crucial role in cell division (mitosis and meiosis). Its main purpose is to ensure the proper separation and distribution of chromosomes to opposite poles of the cell during cell division. This process is essential for the formation of two genetically identical daughter cells in mitosis or four haploid daughter cells in meiosis. Option A is incorrect because the separation of sister chromatids specifically refers to the role of the kinetochore fibers within the spindle apparatus. Option C is incorrect because the formation of a new nuclear envelope occurs after the chromosomes have been properly segregated. Option D is incorrect because DNA synthesis does not occur within the spindle apparatus; it takes place during the S phase of the cell cycle.