Exam map of the chapter

Knowledge questions with answers

1. ★★★ What is the main function that gives chloroplast its name “kitchen of the cell”?
   Food synthesis through photosynthesis.
2. ★★★ How many chloroplasts are generally found in a higher plant cell?
   Usually 10–40 chloroplasts.
3. ★★ What is the usual diameter of a disc-shaped chloroplast?
   About 3–5 μm.
4. ★★★ Which chloroplast structure contains the enzymes for sugar production and the C₃ or C₄ cycle?
   The stroma.
5. ★★★ What is a stack of thylakoids called?
   A granum; plural, grana.
6. ★★★ If a DNA template strand has the sequence ATTCGA, what RNA sequence is formed?
   UAAGCU.
7. ★★★ How many hydrogen bonds join G and C in DNA?
   Three hydrogen bonds.
8. ★★ What is the diameter of a DNA double helix?
   About 2 nm or 20 Å.
9. ★★★ What is the chromosome number of human somatic cells?
   2n = 46.
10. ★★★ How many haploid daughter cells are produced from one diploid cell by meiosis?
    Four haploid daughter cells.
11. ★★★ What is chromatin?
    Chromatin is the DNA–protein, mainly nucleoprotein, material forming the main substance of chromosomes.
12. ★★★ Define a chromosome.
    A chromosome is a thread-like nuclear structure containing genetic material that carries hereditary information and can replicate.
13. ★★★ What is a chromatid?
    A chromatid is either one of the two longitudinally separated, usually identical parts of a duplicated chromosome.
14. ★★★ What is a thylakoid?
    A thylakoid is a membrane-bound, flattened, disc-like sac present in the chloroplast stroma.
15. ★★★ What are stroma lamellae?
    Stroma lamellae are membrane channels that connect thylakoids of adjacent grana.
16. ★★★ State the complementary base-pairing rule in DNA.
    A pairs with T by two hydrogen bonds, while G pairs with C by three hydrogen bonds.
17. ★★★ What is transcription?
    Transcription is the process of producing RNA from a DNA template.
18. ★★★ What is translation?
    Translation is the process by which a ribosome uses mRNA information to synthesize a polypeptide or protein.
19. ★★★ Define a gene or cistron.
    A gene or cistron is a specific DNA segment that stores the information for a particular polypeptide chain or characteristic.
20. ★★★ What is meiosis, and why is it called reduction division?
    Meiosis is a division in which one mother cell produces four cells with half the maternal chromosome number; it is called reduction division because chromosome number is halved.

Admission-style MCQ with answers

1. ★★★ Why is the chloroplast called the kitchen of the cell?

   a) It stores genetic information	b) It synthesizes carbohydrate using light energy
   c) It controls cell division	d) It digests cellular waste

   ✔ b) It synthesizes carbohydrate using light energy — Chloroplasts synthesize food, especially carbohydrate, by photosynthesis.
2. ★★ The usual number of chloroplasts in a higher plant cell is approximately—

   a) 1–5	b) 10–40
   c) 50–100	d) 100–300

   ✔ b) 10–40 — The source states that higher plant cells generally contain 10–40 chloroplasts.
3. ★★★ Which pairing between an alga and its chloroplast shape is correct?

   a) Chlamydomonas—spiral	b) Spirogyra—spiral
   c) Oedogonium—cup-shaped	d) Zygnema—ribbon-shaped

   ✔ b) Spirogyra—spiral — Spirogyra has a characteristic spiral chloroplast.
4. ★★ The usual diameter of a cell-shaped chloroplast is—

   a) 0.5–1 μm	b) 3–5 μm
   c) 10–40 μm	d) 100–300 μm

   ✔ b) 3–5 μm — The source gives 3–5 micrometres as the usual diameter.
5. ★★★ In higher plants, new chloroplasts generally develop from—

   a) Mitochondria	b) Leucoplasts formed in darkness
   c) Proplastids	d) Ribosomes

   ✔ c) Proplastids — Higher plant chloroplasts originate from proplastids.
6. ★★★ In the presence of sunlight, a proplastid becomes a mature chloroplast mainly through the formation of—

   a) Vesicles, lamellae and grana	b) Centrioles, spindle fibres and asters
   c) Nucleosomes, chromatids and centromeres	d) Cristae, matrix and oxysomes

   ✔ a) Vesicles, lamellae and grana — The source describes vesicles forming lamellae and grana during chloroplast development.
7. ★★ A green plant part becomes colourless when chloroplasts develop into leucoplasts in the absence of—

   a) Carbon dioxide	b) Water
   c) Sunlight	d) Oxygen

   ✔ c) Sunlight — Without sunlight, chloroplasts may turn into leucoplasts and the green part becomes colourless.
8. ★★★ Which statement correctly distinguishes the chloroplast envelope?

   a) It is a single permeable membrane containing phospholipids only	b) It is a double semipermeable membrane containing glycolipids
   c) It is a double membrane made only of cellulose	d) It is a protein-free single membrane

   ✔ b) It is a double semipermeable membrane containing glycolipids — The chloroplast is enclosed by a double semipermeable membrane containing glycolipids.
9. ★★★ Which process occurs mainly in the chloroplast stroma according to the source?

   a) Carbon reduction and carbohydrate formation	b) Chromosome pairing
   c) Protein digestion	d) DNA translation into lipids

   ✔ a) Carbon reduction and carbohydrate formation — The C₃ or C₄ carbon-reduction cycle and sugar synthesis occur in the stroma.
10. ★★★ Which combination is found in chloroplast stroma?

    a) 70S ribosomes, DNA, RNA and enzymes	b) 80S ribosomes, centrioles and lysosomes
    c) Cellulose, chitin and peptidoglycan	d) Only chlorophyll and carotenoids

    ✔ a) 70S ribosomes, DNA, RNA and enzymes — The source lists 70S ribosomes, DNA, RNA and numerous enzymes in the stroma.
11. ★★★ A stack of thylakoids is called a—

    a) Lamella	b) Granum
    c) Stroma	d) Quantosome

    ✔ b) Granum — A granum is a stack of thylakoids.
12. ★★★ According to the source, a granum generally contains—

    a) 4–6 thylakoids	b) 10–100 thylakoids, commonly 40–60
    c) 100–300 thylakoids, commonly 200	d) 700–900 thylakoids

    ✔ b) 10–100 thylakoids, commonly 40–60 — The source gives 10–100 thylakoids per granum and commonly 40–60.
13. ★★ The width of a thylakoid membrane sac is approximately—

    a) 0.3–1.7 μm	b) 3–5 μm
    c) 100–300 Å	d) 20–40 nm

    ✔ c) 100–300 Å — The source states that thylakoids are 100–300 Å wide.
14. ★★★ The connecting channels between neighbouring grana are called—

    a) Cristae	b) Stroma lamellae
    c) Nucleosomes	d) Quantosomes

    ✔ b) Stroma lamellae — Stroma lamellae connect thylakoids of adjacent grana.
15. ★★ A photosynthetic unit contains chlorophyll-a, chlorophyll-b, carotene, xanthophyll and approximately—

    a) 3–4 molecules	b) 30–40 molecules
    c) 300–400 molecules	d) 3,000–4,000 molecules

    ✔ c) 300–400 molecules — The source states that each photosynthetic unit contains about 300–400 molecules.
16. ★★★ The primary role of ATP synthase particles in the thylakoid membrane is to—

    a) Synthesize ATP	b) Replicate chromosomes
    c) Produce DNA bases	d) Digest starch

    ✔ a) Synthesize ATP — ATP synthase contains the enzymes required for ATP formation.
17. ★★★ Chromosomes are best described as—

    a) Membrane-bound organelles that store starch	b) Thread-like nuclear structures containing hereditary material
    c) Enzymes that synthesize carbohydrates	d) Cytoplasmic vesicles containing chlorophyll

    ✔ b) Thread-like nuclear structures containing hereditary material — Chromosomes are thread-like hereditary structures mainly composed of DNA and nuclear proteins.
18. ★★ Who named the thread-like structures as chromatin in 1888?

    a) Karl Nagli	b) E. Strasburger
    c) Walter Flemming	d) W. Waldeyer

    ✔ c) Walter Flemming — Walter Flemming named the thread-like structures chromatin in 1888.
19. ★★★ The term chromosome was introduced by—

    a) W. Waldeyer	b) Sutton and Boveri
    c) Theophilus Painter	d) Maurice Wilkins

    ✔ a) W. Waldeyer — W. Waldeyer named them chromosomes in 1888.
20. ★★★ Which organism in the source has the highest reported chromosome number?

    a) Haplopappus gracilis	b) Ophioglossum reticulatum
    c) Aulacantha sp.	d) Poa littorosa

    ✔ c) Aulacantha sp. — Aulacantha sp. is listed with 2n = 1600, the highest value in the source.
21. ★★ If a human somatic cell has 46 chromosomes, its haploid gamete is expected to contain—

    a) 12	b) 23
    c) 46	d) 92

    ✔ b) 23 — A haploid cell contains half the diploid number, so 46 ÷ 2 = 23.
22. ★★ Which plant has 2n = 4 according to the source?

    a) Haplopappus gracilis	b) Poa littorosa
    c) Oryza sativa	d) Allium cepa

    ✔ a) Haplopappus gracilis — Haplopappus gracilis is listed with 2n = 4.
23. ★★★ Chromosomes are most distinctly visible as separate structures during—

    a) Interphase	b) Metaphase
    c) Cytokinesis only	d) The resting stage before DNA replication

    ✔ b) Metaphase — Chromosomes become condensed and separately visible during metaphase.
24. ★★★ Chromatin is chemically best represented as—

    a) DNA–protein complex	b) RNA–lipid complex
    c) Carbohydrate–protein complex	d) Phospholipid–DNA complex

    ✔ a) DNA–protein complex — The source identifies chromatin as a DNA–protein, or nucleoprotein, complex.
25. ★★★ Which statement correctly distinguishes heterochromatin from euchromatin?

    a) Heterochromatin is less coiled and actively synthesizes mRNA	b) Heterochromatin is more coiled and generally does not participate in mRNA synthesis
    c) Euchromatin is always permanently inactive	d) Both are identical in coiling and activity

    ✔ b) Heterochromatin is more coiled and generally does not participate in mRNA synthesis — Heterochromatin is highly coiled and generally inactive in mRNA synthesis.
26. ★★★ At metaphase, the two longitudinal parts of a duplicated chromosome are called—

    a) Homologous chromosomes	b) Sister chromatids
    c) Bivalents	d) Nucleosomes

    ✔ b) Sister chromatids — The two identical parts of a metaphase chromosome are sister chromatids.
27. ★★★ Which base pair is held together by three hydrogen bonds?

    a) A–T	b) T–A
    c) G–C	d) A–U

    ✔ c) G–C — Guanine and cytosine are joined by three hydrogen bonds.
28. ★★★ The two DNA strands are described as—

    a) Parallel and identical	b) Antiparallel and complementary
    c) Parallel and non-complementary	d) Single-stranded and complementary

    ✔ b) Antiparallel and complementary — The strands run in opposite directions and have complementary bases.
29. ★★★ A complete turn of the DNA double helix contains 10 base pairs and measures 3.4 nm. The distance between successive base pairs is—

    a) 0.034 nm	b) 0.34 nm
    c) 3.4 nm	d) 34 nm

    ✔ b) 0.34 nm — The rise per base pair is 3.4 nm ÷ 10 = 0.34 nm.
30. ★★★ Which statement best defines a chromosome according to the source?

    a) A thread-like nuclear structure made mainly of DNA and protein that carries hereditary information	b) A membrane-bound organelle that synthesizes ATP
    c) A cytoplasmic vesicle containing digestive enzymes	d) A carbohydrate polymer that stores genetic energy

    ✔ a) A thread-like nuclear structure made mainly of DNA and protein that carries hereditary information — Chromosomes are DNA–protein structures that carry hereditary information.
31. ★★ Which organism is stated to possess the highest diploid chromosome number in the source?

    a) Homo sapiens, 2n = 46	b) Ophioglossum reticulatum, 2n = 1260
    c) Aulacantha sp., 2n = 1600	d) Poa littorosa, 2n = 530

    ✔ c) Aulacantha sp., 2n = 1600 — The source gives Aulacantha sp. of Radiolaria the highest number, 2n = 1600.
32. ★★ A cell of Oryza sativa contains 24 chromosomes. If it undergoes meiosis, each resulting cell will normally contain—

    a) 6 chromosomes	b) 12 chromosomes
    c) 24 chromosomes	d) 48 chromosomes

    ✔ b) 12 chromosomes — Meiosis reduces the diploid number by half; 24 ÷ 2 = 12.
33. ★★ The average length of a human chromosome is given as—

    a) 0.5–2 μm	b) 3–5 μm
    c) 4–7 μm	d) 8–12 μm

    ✔ c) 4–7 μm — The source states that human chromosomes have an average length of 4–7 μm.
34. ★★★ Which type of chromatin is highly coiled during interphase and does not participate in mRNA synthesis?

    a) Euchromatin	b) Heterochromatin
    c) Nucleosome	d) Chromatid

    ✔ b) Heterochromatin — Heterochromatin remains highly condensed and is inactive in mRNA synthesis during interphase.
35. ★★★ A chromosomal region actively involved in mRNA synthesis is most likely—

    a) Heterochromatin	b) Euchromatin
    c) The centromere only	d) The chromosome terminal region only

    ✔ b) Euchromatin — Euchromatin is the relatively active chromatin region involved in mRNA synthesis.
36. ★★★ Which pairing is correct according to the Watson–Crick model?

    a) A–C with two hydrogen bonds	b) A–T with two hydrogen bonds
    c) G–T with three hydrogen bonds	d) G–A with three hydrogen bonds

    ✔ b) A–T with two hydrogen bonds — Adenine pairs with thymine through two hydrogen bonds.
37. ★★★ If one DNA strand has the sequence 5′-ATTCGA-3′, the complementary strand is—

    a) 5′-TAAGCT-3′	b) 3′-TAAGCT-5′
    c) 5′-UAAGCU-3′	d) 3′-UAAGCU-5′

    ✔ b) 3′-TAAGCT-5′ — DNA pairing gives TAAGCT, and the two strands are antiparallel.
38. ★★★ In the DNA double helix described in the source, the distance between two successive base-pair steps is—

    a) 0.034 nm	b) 0.34 nm
    c) 2.0 nm	d) 3.4 nm

    ✔ b) 0.34 nm — Each successive base-pair step is separated by 0.34 nm.
39. ★★ A complete turn of the DNA double helix contains approximately—

    a) 2 base pairs	b) 5 base pairs
    c) 10 base pairs	d) 20 base pairs

    ✔ c) 10 base pairs — The source states that one complete turn contains 10 base-pair steps.
40. ★★ The diameter of the DNA double helix is approximately—

    a) 0.34 nm	b) 2.0 nm
    c) 3.4 nm	d) 20 nm

    ✔ b) 2.0 nm — The source gives the diameter as 2.0 nm.
41. ★★★ Which arrangement correctly describes the DNA double helix?

    a) Two parallel strands with bases outside and phosphate inside	b) Two antiparallel strands with sugar-phosphate backbones outside and bases inside
    c) One strand with sugar and bases outside	d) Two identical strands joined by peptide bonds

    ✔ b) Two antiparallel strands with sugar-phosphate backbones outside and bases inside — DNA has antiparallel strands, external sugar-phosphate backbones and internal complementary bases.
42. ★★ In a DNA nucleotide, the nitrogenous base is attached to which carbon of deoxyribose?

    a) 1′ carbon	b) 2′ carbon
    c) 3′ carbon	d) 5′ carbon

    ✔ a) 1′ carbon — The source states that the nitrogenous base is attached to the 1′ carbon.
43. ★★ The phosphate group in DNA is associated with which carbons of deoxyribose?

    a) 1′ and 2′	b) 1′ and 3′
    c) 2′ and 4′	d) 3′ and 5′

    ✔ d) 3′ and 5′ — The source states that phosphate is linked with the 3′ and 5′ carbons.
44. ★★★ A DNA molecule contains 18% adenine. What percentage of its bases is guanine?

    a) 18%	b) 32%
    c) 41%	d) 64%

    ✔ b) 32% — Thymine is 18%, so G + C = 64%; therefore G = 32%.
45. ★★★ Which combination correctly distinguishes RNA from DNA according to the source?

    a) RNA contains deoxyribose and thymine	b) RNA is generally single-stranded and contains ribose and uracil
    c) RNA is always double-stranded and contains thymine	d) RNA contains no nitrogenous bases

    ✔ b) RNA is generally single-stranded and contains ribose and uracil — RNA is generally single-stranded and contains ribose, adenine, uracil, guanine and cytosine.
46. ★★★ A gene is best described as—

    a) Any protein present in a chromosome	b) A specific DNA segment at a chromosome locus that carries information for a particular characteristic
    c) The entire set of chromosomes of an organism	d) A ribosome-bound RNA molecule only

    ✔ b) A specific DNA segment at a chromosome locus that carries information for a particular characteristic — A gene is a specific DNA segment at a locus that controls a characteristic.
47. ★★ According to the source, the number of nucleotides in a gene may range approximately from—

    a) 7 to 80	b) 75 to 80,000
    c) 750 to 800	d) 75,000 to 800,000

    ✔ b) 75 to 80,000 — The source gives a range of 75 to 80,000 nucleotides per gene.
48. ★★★ The process by which RNA is synthesized using DNA as a template is called—

    a) Translation	b) Replication
    c) Transcription	d) Splicing

    ✔ c) Transcription — DNA-directed RNA synthesis is transcription.
49. ★★★ During RNA elongation, RNA polymerase moves along the DNA template strand in which direction?

    a) 3′ to 5′	b) 5′ to 3′
    c) 1′ to 5′	d) 5′ to 1′ only in RNA

    ✔ a) 3′ to 5′ — RNA polymerase reads the template strand in the 3′→5′ direction while synthesizing RNA.
50. ★★★ If the DNA template strand contains 5′-ATTCGA-3′, the RNA sequence produced is—

    a) 5′-UAAGCU-3′	b) 3′-UAAGCU-5′
    c) 5′-TAAGCT-3′	d) 3′-ATTCGA-5′

    ✔ a) 5′-UAAGCU-3′ — The RNA is complementary and antiparallel to the template, with uracil replacing thymine.

Short and explain questions with answers

1. ★★★ Explain why the chloroplast is called the kitchen of the cell.
   The chloroplast contains chlorophyll and is the main site of photosynthesis in green plant cells. It uses light energy to synthesize carbohydrate from carbon dioxide and water. The enzymes required for carbon reduction and sugar formation are present in the stroma. Therefore, the chloroplast acts like the kitchen or sugar-producing factory of the cell.

   • It contains chlorophyll and carries out photosynthesis.
   • It synthesizes carbohydrate using light energy.
   • Its stroma contains enzymes for carbon reduction and sugar formation.
2. ★★★ Describe the structure and functions of the chloroplast stroma.
   The stroma is the colloidal fluid matrix enclosed by the chloroplast envelope. It contains 70S ribosomes, DNA, RNA, numerous enzymes, starch grains and globules. Enzymes for sugar production are also present in it. The carbon-reduction reactions of photosynthesis, including the C₃ or C₄ cycle, occur in the stroma.

   • Stroma is the colloidal matrix inside the chloroplast envelope.
   • It contains 70S ribosomes, DNA, RNA and enzymes.
   • Carbon reduction and sugar synthesis occur in the stroma.
3. ★★ Explain how a proplastid develops into a complete chloroplast in sunlight.
   A proplastid is a spherical body of about 0.5 μm diameter with dense stroma and a double-layered envelope. In sunlight, vesicles arise from the inner membrane and become arranged parallel to one another in the stroma. The vesicles fuse to form lamellae, and some lamellae develop into grana. Chlorophyll formation along with this membrane development converts the proplastid into a mature chloroplast.

   • A proplastid has dense stroma and a double-layered envelope.
   • Vesicles form lamellae and some lamellae form grana.
   • Sunlight and chlorophyll formation help produce a mature chloroplast.
4. ★★★ Describe the organization of thylakoids, grana and stroma lamellae in a chloroplast.
   A thylakoid is a flattened, membrane-bound sac present in the stroma of a chloroplast. Several thylakoids are stacked one above another to form a granum; generally 10–100 thylakoids form one granum. The connecting channels between neighbouring grana are called stroma lamellae or intergranal lamellae. Thylakoid membranes contain chlorophyll and photosynthetic units, while lamellae contain some chlorophyll.

   • Stacked thylakoids form a granum.
   • Stroma lamellae connect neighbouring grana.
   • Thylakoid membranes contain chlorophyll and photosynthetic units.
5. ★★★ Explain how the structure of DNA is related to complementary base pairing.
   DNA consists of two antiparallel polynucleotide strands forming a double helix like a twisted ladder. The sugar-phosphate backbones remain outside, while the nitrogenous bases face inward. A pairs with T through two hydrogen bonds, and G pairs with C through three hydrogen bonds. Thus, a purine pairs with a pyrimidine and the two strands remain complementary rather than identical.

   • DNA has two antiparallel strands with external sugar-phosphate backbones.
   • A–T forms two and G–C forms three hydrogen bonds.
   • Complementary pairing maintains a constant distance and produces complementary strands.
6. ★★★ Describe the important measurements of the Watson–Crick DNA double helix.
   The diameter of the DNA helix is about 2 nm or 20 Å. The distance between successive base pairs is 0.34 nm or 3.4 Å. One complete turn of the helix measures 3.4 nm or 34 Å. There are about 10 base pairs in one complete turn, and major and minor grooves are formed.

   • The helix diameter is 2 nm.
   • Adjacent base pairs are 0.34 nm apart.
   • One turn is 3.4 nm and contains about 10 base pairs.
7. ★★★ Explain the differences between heterochromatin and euchromatin.
   Heterochromatin is the highly coiled part of chromatin, especially visible during interphase. It generally does not participate in mRNA synthesis and is relatively inactive. Euchromatin is the less condensed, lightly stained and genetically active part of chromatin. It participates in gene expression and mRNA synthesis.

   • Heterochromatin is highly coiled and generally transcriptionally inactive.
   • Euchromatin is less condensed and genetically active.
   • Euchromatin participates in mRNA synthesis, whereas heterochromatin generally does not.
8. ★★★ Describe transcription from initiation to termination.
   During transcription, RNA polymerase attaches to the promoter and begins RNA synthesis at the start site. It moves along the DNA template strand in the 3′ to 5′ direction and adds complementary ribonucleotides. For example, the template sequence ATTCGA produces UAAGCU in RNA because uracil replaces thymine. At the termination sequence, RNA synthesis stops and the RNA strand separates from the polymerase and DNA.

   • RNA polymerase begins at a promoter and start site.
   • It reads the template 3′ to 5′ and forms complementary RNA using U instead of T.
   • A specified termination sequence ends transcription.
9. ★★★ Explain why pre-mRNA requires processing before it can function as mature mRNA in a eukaryotic cell.
   The initial transcript formed by transcription is called pre-mRNA and contains both introns and exons. Introns do not code for the translated product, whereas exons are expressed sequences retained in the message. During splicing, introns are removed and adjacent exons are joined by the spliceosome. A 5′ modification and a 3′ poly-A tail are also added before mature mRNA leaves the nucleus for translation.

   • Pre-mRNA contains introns and exons.
   • Splicing removes introns and joins exons.
   • 5′ processing and a 3′ poly-A tail help produce mature mRNA.
10. ★★★ Explain the roles of mRNA and tRNA in translation.
    Translation is the synthesis of a polypeptide or protein using information carried by mRNA. mRNA acts as the template and carries the genetic message from DNA to the ribosome. tRNA carries specific amino acids to the ribosome and matches them with the appropriate mRNA codons. The ribosome joins the amino acids in the sequence specified by the mRNA.

    • mRNA carries genetic information and acts as the template.
    • tRNA transports amino acids to the ribosome.
    • The ribosome joins amino acids into a polypeptide according to the mRNA message.
11. ★★★ Explain the importance of meiosis in maintaining the continuity of a species.
    Meiosis produces four haploid cells from one diploid meiocyte, so the chromosome number is reduced by half. When male and female gametes fuse, the diploid chromosome number is restored in the zygote. Without this reduction, chromosome number would double in every generation after fertilization. Crossing over and gene exchange during meiosis also produce variation while preserving the characteristic chromosome number of the species.

    • Meiosis produces haploid gametes from a diploid mother cell.
    • Fertilization restores the diploid chromosome number and prevents doubling each generation.
    • Crossing over creates variation and contributes to species continuity.
12. ★★ Explain why monosaccharides are called reducing sugars and describe the Benedict’s test for them.
    Monosaccharides contain a free aldehyde group or ketone group, which can act as a reducing group. These groups reduce the alkaline copper hydroxide of Benedict’s solution. During the reaction, cupric ions are reduced and cuprous oxide, Cu₂O, is formed. The formation of a red precipitate indicates the presence of a reducing sugar.

    • A free –CHO or >C=O group gives monosaccharides reducing ability.
    • The sugar reduces alkaline Cu(OH)₂ in Benedict’s solution.
    • Red Cu₂O precipitate is formed as the positive test result.

Fill in the blanks and True/False

Fill in the blanks

1. Because it helps synthesize food, the chloroplast is called the ______ of the cell. [kitchen]
2. The ribosomes found in the chloroplast stroma are of the ______ type. [70S]
3. A thylakoid generally has a width of ______ Å. [100–300]
4. A stack of thylakoids is called a ______. [granum]
5. In DNA, adenine is joined to thymine by ______ hydrogen bonds. [two]
6. In DNA, guanine is joined to cytosine by ______ hydrogen bonds. [three]
7. The two strands of DNA are complementary and ______ to each other. [antiparallel]
8. The process by which RNA is synthesized from DNA is called ______. [transcription]
9. The process of synthesizing a polypeptide from mRNA is called ______. [translation]
10. Meiosis produces ______ haploid daughter cells from one diploid mother cell. [four]

True / False

1. In the absence of sunlight, a chloroplast may become a leucoplast. — True (Sunlight is associated with chlorophyll formation and chloroplast development.)
2. The chloroplast envelope contains phospholipids instead of glycolipids. — False (The source identifies glycolipids as the exceptional membrane component of the chloroplast envelope.)
3. Euchromatin is generally active in gene expression and participates in mRNA synthesis. — True (Euchromatin is described as genetically active and involved in mRNA synthesis.)
4. Heterochromatin is the less-coiled part of chromatin and actively participates in mRNA synthesis. — False (Heterochromatin is more coiled and does not participate in mRNA synthesis.)
5. The diploid chromosome number of humans is 46. — True (The source lists Homo sapiens as having 2n = 46.)
6. DNA contains uracil as one of its four nitrogenous bases. — False (DNA contains thymine; uracil is found in RNA instead.)
7. RNA is generally single-stranded and contains ribose sugar. — True (The source describes RNA as a single-stranded molecule containing ribose.)
8. A gene may contain between 75 and 80,000 nucleotides. — True (This range is stated in the source.)
9. During transcription, RNA polymerase moves along the template DNA strand in the 3′ to 5′ direction. — True (The source states that RNA polymerase advances along the template strand from 3′ to 5′.)
10. In meiosis, the nucleus divides once and the chromosomes divide twice. — False (In meiosis, the nucleus divides twice, whereas the chromosomes divide once.)

Quick facts to memorise

Chloroplast: Structure and Functions

Chromosome and DNA Essentials

RNA, Gene Expression and Meiosis

Exam strategy: shortcuts, traps and practice plan

Shortcuts and memory tricks

Common traps

Practice plan

1. First read the chapter once for the overall framework, marking the major sections: cell, chloroplast, chromosome, DNA, RNA, gene, transcription and translation.
2. Create one comparison sheet for chloroplast parts: envelope, stroma, thylakoid, granum, stroma lamella, photosynthetic unit and ATP synthase. Add each part's location and function.
3. Memorize the high-yield numerical facts separately: chloroplast diameter 3–5 μm, thylakoid width 100–300 Å, granum size 0.3–1.7 μm, DNA diameter 2 nm, base-pair spacing 0.34 nm and one-turn length 3.4 nm.
4. Practise chromosome and nucleic-acid comparisons using short tables: chromosome versus chromatin, DNA versus RNA, purine versus pyrimidine, transcription versus translation, and intron versus exon.
5. Solve sequence-application questions daily. Write a short DNA template sequence and derive its complementary DNA strand and RNA strand while checking antiparallel direction, A–T pairing and G–C pairing.
6. Attempt mixed timed practice covering definitions, discoveries, chromosome-number examples, chloroplast diagrams, DNA measurements and gene-expression steps. After each set, record why every wrong option is wrong.
7. Finish with a full admission-style mock test under strict time. Review only your error log afterward, especially numerical facts, terminology pairs and questions that require applying—not merely recalling—the source.

Last-minute revision

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Formulas

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