Free Cell Structure and Function MCQs with Answers

11. A human somatic cell contains how many chromosomes?

• A. 23
• B. 44
• C. 46
• D. 92

Explanation: Human body cells are diploid with 46 chromosomes, which is 23 homologous pairs made up of 22 pairs of autosomes and one pair of sex chromosomes. Gametes are haploid and carry 23. The count of 92 would only appear briefly after replication if chromatids were miscounted as separate chromosomes, which they are not.

12. The region of a chromosome where the two sister chromatids are joined and to which spindle fibres attach is the

• A. telomere
• B. centromere
• C. centriole
• D. chromomere

Explanation: The centromere holds sister chromatids together and carries the kinetochore, the protein structure the spindle microtubules attach to during division. Telomeres are the protective caps at the chromosome ends that shorten with each replication. Centrioles are separate cytoplasmic structures that organise the spindle rather than part of the chromosome.

13. In a eukaryotic chromosome, DNA is packaged by winding around proteins called

• A. histones
• B. collagens
• C. tubulins
• D. keratins

Explanation: Histones are small positively charged proteins that bind the negatively charged phosphate backbone of DNA, forming nucleosomes that condense roughly two metres of DNA into a nucleus a few micrometres across. Tubulin builds microtubules, collagen is a structural protein of connective tissue, and keratin is found in hair and nails.

14. In a chloroplast, the light dependent reactions take place in the

• A. stroma
• B. thylakoid membranes of the grana
• C. outer membrane
• D. intermembrane space

Explanation: Chlorophyll and the electron carriers are embedded in the thylakoid membranes, which are stacked into grana to give the largest possible area for absorbing light. The stroma is the surrounding fluid, and it is where the light independent reactions fix carbon dioxide using the ATP and reduced NADP made in the membranes. Dividing the organelle this way keeps the two stages physically separate.

15. The statement that all cells arise from pre-existing cells was added to the cell theory by

• A. Robert Hooke
• B. Schleiden and Schwann
• C. Rudolf Virchow
• D. Anton van Leeuwenhoek

Explanation: Schleiden and Schwann established that plants and animals are made of cells, but it was Virchow who added in 1855 that every cell comes from the division of another, which ruled out spontaneous generation. Hooke first used the word cell after looking at cork, and Leeuwenhoek first saw living microorganisms. The three statements together form the modern cell theory.

16. The large central vacuole of a mature plant cell is bounded by a membrane called the

• A. tonoplast
• B. plasmalemma
• C. nuclear envelope
• D. cell wall

Explanation: The tonoplast controls what enters and leaves the cell sap, and the vacuole's contents create the osmotic pressure that keeps the cell turgid and so supports the non woody parts of a plant. It also stores sugars, salts, pigments and waste products. The plasmalemma is the plasma membrane at the cell surface, and the cell wall outside it is not a membrane at all.

17. Proteins made on the rough endoplasmic reticulum are modified, sorted and packaged for export by the

• A. lysosome
• B. nucleolus
• C. peroxisome
• D. Golgi apparatus

Explanation: Vesicles carry newly made protein from the endoplasmic reticulum to the Golgi, where sugars are added, the product is sorted and it is packed into vesicles for secretion or for use inside the cell. Cells that secrete heavily, such as those of the pancreas, have a large and active Golgi. Lysosomes are one of the products of the Golgi rather than an alternative to it.

18. The nucleolus is the site of

• A. DNA replication
• B. synthesis of ribosomal RNA and assembly of ribosomal subunits
• C. protein synthesis for export
• D. storage of the cell's lipid reserve

Explanation: The nucleolus is a dense region of the nucleus with no membrane around it, and it transcribes ribosomal RNA and combines it with proteins to form the subunits that are then exported through the nuclear pores. Cells making large quantities of protein have prominent nucleoli, which is a useful clue under the microscope. Protein synthesis itself takes place on the ribosomes in the cytoplasm.

19. The nuclear envelope differs from the plasma membrane in that it

• A. is made of protein only
• B. has no pores of any kind
• C. consists of two membranes perforated by pores
• D. is freely permeable to all molecules

Explanation: Two membranes enclose the nucleus, and the pores that pierce them at intervals let mRNA and ribosomal subunits out and let nucleotides, enzymes and regulatory proteins in, while keeping the chromosomes separate from the cytoplasm. The outer membrane is continuous with the rough endoplasmic reticulum. Free permeability would defeat the whole purpose of enclosing the genetic material.

20. Which structure is normally absent from the cells of higher plants?

• A. Centrioles
• B. Mitochondria
• C. Golgi apparatus
• D. Ribosomes

Explanation: Higher plant cells organise their spindle without centrioles, which is why the presence of a pair of centrioles beside the nucleus is taken as an animal cell feature in a diagram question. Centrioles are present in animal cells and in the motile cells of lower plants. Mitochondria, Golgi and ribosomes are common to both kingdoms.