All Free Biology MCQs with Answers

• A. Mutation
• B. Controlled cell division
• C. Regulated mitosis
• D. Haploid division

Explanation: Cancer is caused by changes (mutations) to the DNA within cells. The DNA inside a cell is packaged into a large number of individual genes, each of which contains a set of instructions telling the cell what functions to perform, as well as how to grow and divide.Cancer arises from genetic mutations that disrupt a cell's normal growth and division, leading to uncontrolled proliferation and potential spread. These mutations can occur in proto-oncogenes, turning them into oncogenes that drive growth, or in tumor suppressor genes that lose their ability to slow or stop cell growth. DNA repair genes can also be affected, preventing the correction of other mutations, which accumulate over time.

• A. Segregation
• B. Independent assortment
• C. Crossing over
• D. Mutation

Explanation: During prophase I, non-sister chromatids of homologous chromosomes undergo crossing over and exchange of genetic material takes place. This exchange leads towards genetic variations.

• A. G1
• B. G2
• C. S
• D. G0

Explanation: The S phase of a cell cycle occurs during interphase, before mitosis or meiosis, and is responsible for the synthesis or replication of DNA. In this way, the genetic material of a cell is doubled before it enters mitosis or meiosis, allowing there to be enough DNA to be split into daughter cells

• A. Prophase
• B. Metaphase
• C. Anaphase
• D. Telophase

Explanation: During cell division, most sensitive phase is that in which spindle fibers contract and chromosomes move away from one another to opposite poles of the spindle. Anaphase ensures the equal distribution of genetic material in next generation.

• A. Prophase I
• B. Telophase I
• C. Metaphase I
• D. Anaphase I

Explanation: Meiosis consists of two divisions, both of which follow the same stages as mitosis (prophase, metaphase, anaphase, telophase). Meiosis is preceded by interphase, in which DNA is replicated to produce chromosomes consisting of two sister chromatids. A second growth phase called interkinesis may occur between meiosis I and II, however no DNA replication occurs in this stage:Prophase I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs.Crossing over occurs in Prophase I when homologous chromosomes pair up, forming a tetrad, and then non-sister chromatids exchange genetic material at points called chiasmata. This genetic exchange, known as recombination, shuffles alleles and creates new combinations of genes on the chromosomes. The process involves enzymes breaking DNA at similar locations on each chromosome and then reattaching the broken ends in a criss-cross pattern, resulting in genetically unique gametes. Metaphase I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell.Anaphase I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell.Telophase I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells.

• A. Chromosome number is duplicated
• B. The chromosomes are left with only one chromatid
• C. Energy is stored for chromosome movement and mitotic specific proteins (Tubulin) are produced
• D. Specific enzymes are synthesized and DNA base units are accumulated

Explanation: Option A occurs during the S phase, where DNA is replicated.Option B occurs after the M phase, when the cell has divided.Option C is 'G2', which occurs right before mitosis. Steps are taken to prepare the cell for cell division, and they include storing energy for chromosome movement and production of tubulin proteins, which are microtubule subunits that will be used in the formation of spindle fibers in the M phase. The G2 phase, or Gap 2 phase, is the third and final subphase of interphase in the cell cycle, following DNA replication (S phase) and preceding mitosis (M phase). During this phase, the cell continues to grow, synthesizes necessary proteins and organelles like spindle fibers, and ensures all components are prepared for cell division. The G2 phase includes a crucial checkpoint that verifies DNA integrity, preventing cells with damaged DNA from entering mitosis and potentially causing further problems. Option D is G1 phase, where the cell prepares for DNA replication so, enzymes, such as DNA polymerase, are synthesized along with nucleotides that will be used to form new DNA.

• A. G1
• B. M
• C. G2
• D. S

Explanation: Microtubule subunits are tubulin proteins, which are formed prior to the initiation of mitosis. They are formed during the G2 phase, hence option C is the correct answer. During the G2 phase, the necessary microtubule subunits, which are α- and β-tubulin proteins, are synthesized and then assembled into microtubules to prepare for cell division. The cell increases its mass and produces molecules, including microtubule components, needed for the upcoming mitosis. These newly formed microtubules are then organized into specialized structures like the preprophase band in plant cells or contribute to the growing spindle apparatus that will separate chromosomes during the M phase. G1 phase, involves normal growth and protein synthesis of the cell, leading up to the DNA replication phase (S).M is mitosis in which nuclear division occurs and it consists of prophase, metaphase, anaphase, and telophase. Prophase involves the assembly of microtubules into the spindle fibers, but the subunits of the microtubules, which are tubulin proteins, are formed prior to this stage, i.e. G2.S phase involves DNA replication.

• A. Period of growth
• B. Replication of DNA
• C. Followed by cell division
• D. Followed by nuclear mitosis

Explanation: The cell undergoes a sequence of changes, which involves period of growth, replication of DNA, followed by cell division. This sequence of changes of called cell cycle

• A. Inter
• B. Mitotic
• C. Meiotic
• D. Post mitotic

Explanation: It comprises two phases viz., interphase which is the period of non-apparent division and the period of division also known as mitotic phase. Each phase is further subdivided into different subphases.

• A. Interphase
• B. Mitotic phase
• C. Meiotic phase
• D. Post mitotic phase

Explanation: The period of life cycle of cell (cell cycle) between two consecutive divisions is termed as the interphase or misleadingly called resting phase. It is the period of great biochemical activity and can further be divided into G1-phase, Sphase and G2-phase