CBSE Class 11 – Biology Question Paper 2023  

SECTION – A

Q1. Respiratory process is regulated by certain specialized centers in the brain. One of the following centres can reduce the inspiratory duration upon stimulation:

a- Medullary inspiratory centre

b- Pneumotaxic centre (Correct Answer)

c- Apneustic centre

d- Chemosensitive centre 

Q2. Which of the following suffixes used for units of classification in plants indicates a taxonomic category of family?

a- Ales

b- Onae

c- Aceae (Correct Answer)

d- Ae  

Q3. Identify the different types of placentations shown in figure and select the correct option:

a- Axile, Marginal, Free central, Parietal, Basal

b- Marginal, Basal, Axile, Free central, Parietal

c- Marginal, Axile, Parietal, Free central, Basal

d- Marginal, Parietal, Axile, Basal, Free-central (Correct Answer)  

Q4. Arrangement of microtubule in a flagellum and a centriole is respectively

a- 9+2 and 9+1

b- 9+0 and 9+2

c- 9+1 and 9+0

d- 9+2 and 9+0 (Correct Answer)

Q5. Zygotene of prophase-I is characterized by

a- Chromosomes

b- Synaptonemal complex (Correct Answer)

c- Crossing over

d- Terminalization of chiasmata

Q6. Enzyme catalyze the biochemical reactions by

a- Lowering the activation energy (Correct Answer)

b- Increasing the activation energy

c- Unaltering the activation energy

d- Either a or b

Q4. Arrangement of microtubule in a flagellum and a centriole is respectively

a- 9+2 and 9+1

b- 9+0 and 9+2

c- 9+1 and 9+0

d- 9+2 and 9+0 (Correct Answer)

Q5. Zygotene of prophase-I is characterized by

a- Chromosomes

b- Synaptonemal complex (Correct Answer)

c- Crossing over

d- Terminalization of chiasmata

Q6. Enzyme catalyze the biochemical reactions by

a- Lowering the activation energy (Correct Answer)

b- Increasing the activation energy

c- Unaltering the activation energy

d- Either a or b

Q7. Adenosine, guanosine, thymidine, uridine, cytidine, are all ______ but adenylic acid, uridylic acid, Cytidylic acid are ______

a- Nucleotides, nucleosides

b- Nucleosides, nucleotides (Correct Answer)

c- Nucleotides, nucleic acids

d- Nucleosides, nucleic acids

Q8. The phase in which active synthesis of DNA takes place, is

a- G₁ phase

b- G₂ phase

c- S phase (Correct Answer)

d- G₀ phase

Q9. Alternate name of Kreb’s cycle is

a- TCA cycle

b- Citric acid cycle

c- Both a and b (Correct Answer)

d- None of these

Q10. Which of the following structure is found in diencephalon?

a- Pons

b- Basal ganglia

c- Corpora quadrigemina (Correct Answer)

d- Hypothalamus

Q11. Select the mismatched pair

a- Insulin- gluconeogenesis

b- Glucagon-glycogenolysis

c- Oxytocin-contraction of uterine muscles

d- Prolactin-milk production in mammary glands (Correct Answer)

Q12. Basic functional unit of human kidney is

a- Nephridia

b- Henle’s loop

c- Pyramid

d- Nephron (Correct Answer)

Question no 13 to 16 consist of two statements-Assertion(A) and Reason (R). Answer these questions by selecting the appropriate option given below

(A) Both A and B are true, and R is the correct explanation of A

(B) Both A and R are true, and R is not the correct explanation of A

(C) A is true but R is false

(D) A is false but R is true.  

Q13. Assertion: Cell wall of chrysophytes are indestructible Reason: Cell wall of chrysophytes have layer of magnesium pectate embedded in it

Answer: (C) A is true but R is false

Q14. Assertion: Small disc shaped structures at the surface of the centromeres are called kinetochores Reason: Kinetochores serve as the sites of attachment of spindle fibers to the centromere  

Answer: (A) Both A and B are true, and R is the correct explanation of A

Q15. Assertion: Decapitation is widely used in tea plantation and hedge making Reason: Removal of shoot tips usually results in the growth of lateral buds.  

Answer: (A) Both A and B are true, and R is the correct explanation of A

Q16. Assertion: Sino- atrial node (SAN) is called the pacemaker Reason: SAN generates the maximum number of action potentials and is responsible for initiating and maintaining the rhythmic contractions of the heart  

Answer: (A) Both A and B are true, and R is the correct explanation of A

 SECTION – B

Q17. In classification of animals, cats and dogs are kept in separate families. Name family and genus of following animals:

a- Cats

• Family: Felidae
• Genus: Felis

b- Dogs

• Family: Canidae
• Genus: Canis

Q18. Differentiate between dicot stem and monocot stem. 

Dicot Stem vs. Monocot Stem

Mesosome in Prokaryotic Cell:

• Definition: Mesosomes are invaginations of the plasma membrane in prokaryotic cells, forming internal vesicles, tubules, and lamellar structures.
• Functions:
  • Increase surface area: Provides a larger surface area for cellular processes like respiration and photosynthesis.
  • Cell wall synthesis: Involved in the synthesis of cell wall components.
  • DNA replication and segregation: May play a role in DNA replication and segregation during cell division.
  • Secretion: May be involved in the secretion of extracellular enzymes.

Q19. Mention two functions of centrioles.

• Organization of Microtubules: Centrioles are involved in organizing microtubules, which form the mitotic spindle during cell division.
• Formation of Cilia and Flagella: Centrioles give rise to basal bodies, which act as the organizing centers for the assembly of cilia and flagella.

Q20. Differentiate between cyclic and non-cyclic photophosphorylation.

Electrocardiogram (ECG):

• Definition: An ECG is a graphical representation of the electrical activity of the heart over time. It records the electrical signals generated by the heart as it beats.

• Components:

  • P wave: Represents the atrial depolarization (contraction).
  • QRS complex: Represents the ventricular depolarization (contraction).
  • T wave: Represents the ventricular repolarization (relaxation).

• Uses:

  • Diagnose heart conditions such as arrhythmias, heart attacks, and heart enlargement.
  • Monitor the effectiveness of heart medications.
  • Assess the overall health of the heart.

 SECTION – C

Q22. Name the phylum having the largest number of animals. Name the major category of animals it has. Write any two special morphological features of this phylum.

• Phylum: Arthropoda
• Major Category: Insects
• Two Special Morphological Features:
  • Exoskeleton: Arthropods have a hard, external skeleton made of chitin, providing protection and support.
  • Jointed Appendages: They possess jointed appendages that allow for a wide range of movement and adaptation to different environments.

Q23. Write the name of plant growth regulator for the following:

a- Bolt a rosette plant
b- Quickly ripen a fruit
c- Induce rooting in a twig

• a- Bolt a rosette plant: Gibberellin
• b- Quickly ripen a fruit: Ethylene
• c- Induce rooting in a twig: Auxin

Q24. Write the name of family with the help of following floral formula: ⊕ ⚥ K(5) C(5) A₅ G(2)

• Family: Solanaceae (Nightshade Family)

Two Characteristic Features of Solanaceae:

1. Flowers: They typically have five sepals (K₅), five petals (C₅), five stamens (A₅), and a bicarpellary syncarpous gynoecium (G(2)).
2. Fruits: The fruits are usually berries or capsules.

Q25. Write any three economic importance of algae.

1. Food Source: Algae are a source of food for humans (seaweed), livestock, and fish.
2. Biofuel Production: Algae can be used to produce biofuels like biodiesel.
3. Pharmaceutical Uses: Many algae produce compounds with medicinal properties, such as antivirals and antimicrobials.

OR

What is heterospory? Briefly comment on its significance. Give two examples.

• Heterospory: Heterospory is the production of two different types of spores: microspores (male) and megaspores (female).

• Significance: Heterospory is a significant evolutionary step as it leads to the development of seeds, which are more resistant to desiccation and can survive for longer periods.

• Examples:

  • Selaginella
  • Marsilea

Q26. Draw the structure of amino acid: Alanine, glycine, serine

• Unfortunately, I cannot draw images directly. However, I can describe the general structure of an amino acid and then specify the side chains for Alanine, glycine, and serine.

General Structure of an Amino Acid:

An amino acid consists of a central carbon atom (α-carbon) bonded to: – An amino group (-NH₂) – A carboxyl group (-COOH) – A hydrogen atom (H) – A side chain (R group) which varies between different amino acids.

• Alanine: R group = -CH₃
• Glycine: R group = -H
• Serine: R group = -CH₂OH

Q27. Explain oxygen dissociation curve. Write any reason for its sigmoidal pattern.

• Oxygen Dissociation Curve: This curve illustrates the relationship between the partial pressure of oxygen (pO₂) in the blood and the percentage of oxygen saturation of hemoglobin (Hb).

• Sigmoidal Pattern: The sigmoidal shape of the curve is due to the cooperative binding of oxygen to hemoglobin. Hemoglobin has four subunits, each with a heme group that can bind one oxygen molecule. The binding of the first oxygen molecule to one subunit increases the affinity of the other subunits for oxygen, leading to a higher oxygen saturation at higher pO₂. This cooperative binding results in the sigmoidal shape of the curve.

Q28. Give a brief account of the counter current mechanism in nephron.

• Counter Current Mechanism: This mechanism in the nephron helps to concentrate urine. It involves the countercurrent flow of filtrate in the loop of Henle and the interstitial fluid in the medulla of the kidney.

• Process:

  • The descending limb of the loop of Henle is permeable to water but impermeable to salts. As the filtrate flows down, water is reabsorbed into the interstitial fluid, increasing the salt concentration of the filtrate.
  • The ascending limb of the loop of Henle is impermeable to water but permeable to salts. As the filtrate ascends, salts are actively transported out of the limb, creating a high salt concentration in the interstitial fluid of the medulla.
  • This countercurrent flow of filtrate and the increasing salt concentration in the medulla allow for the reabsorption of more water from the collecting ducts, leading to the formation of concentrated urine.

 SECTION – D

Q29.

a) Write any two differences between Phycomycetes and Ascomycetes.

Phycomycetes

• Mycelium: Aseptate, coenocytic (multinucleate)
• Sexual Reproduction: Mostly oogamous (female gametangium is oogonium)

Ascomycetes

• Mycelium: Septate (divided into cells)
• Sexual Reproduction: Ascogenous hyphae produce asci, which contain ascospores.

b) What do the terms phycobiont and mycobiont signify?

• Phycobiont: The photosynthetic component of a lichen. It is usually an alga or cyanobacterium that provides food for the lichen.
• Mycobiont: The fungal component of a lichen. It provides structure and protection for the phycobiont and absorbs water and minerals.

c) What is the nature of cell wall in diatoms?

• Diatoms have a unique cell wall composed of silica. This silicaceous cell wall forms a hard and intricate shell called a frustule, which provides protection and structural support.

Or

a) Give a comparative account of the nature of cell wall and the characteristics of flagella among three classes of algae.

b) Differentiate between thallophytes and bryophytes.

Q30. Explain various stages of Meiosis-I with the help of well-labelled diagram.

Unfortunately, I cannot draw diagrams directly. However, I can describe the stages of Meiosis-I:

1. Prophase I:

   • Leptotene: Chromosomes start to condense.
   • Zygotene: Homologous chromosomes pair up (synapsis) to form bivalents.
   • Pachytene: Crossing over occurs between homologous chromosomes.
   • Diplotene: Synaptonemal complex breaks down, but homologous chromosomes remain attached at chiasmata.
   • Diakinesis: Chromosomes further condense, and nuclear envelope breaks down.

2. Metaphase I: Bivalents align at the metaphase plate.

3. Anaphase I: Homologous chromosomes separate and move towards opposite poles.

4. Telophase I: Nuclear envelope reforms around each set of chromosomes, and cytokinesis occurs, resulting in two haploid daughter cells.

OR

A) Both lysosomes and vacuoles are membraneous structures, yet they differ in terms of their functions.

• Lysosomes: Membrane-bound organelles containing digestive enzymes. They break down cellular waste products, debris, and foreign material.
• Vacuoles: Membrane-bound organelles that store water, nutrients, and waste products. They also maintain cell turgor pressure.

B) Draw the diagram of cilia and flagella.

• I cannot draw diagrams directly. However, both cilia and flagella are hair-like structures that extend from the cell surface.
• Cilia are typically shorter and more numerous, while flagella are usually longer and fewer in number.

C) Who discovered ribosome and give its function.

• Discovered by: George Palade
• Function: Ribosomes are the site of protein synthesis in the cell. They read the genetic code from mRNA and translate it into the amino acid sequence of a protein.

Q31.

a) In old age people suffer from stiffness and inflammation in joints. What is this condition called? What is the cause of osteoporosis?

• Condition: Osteoarthritis
• Cause of Osteoporosis: Osteoporosis is caused by a decrease in bone density, making bones more fragile and prone to fractures. This can be due to various factors such as age, hormonal imbalances, and insufficient calcium intake.

b) Explain the sliding theory of the mechanism of muscle contraction.

• The sliding filament theory proposes that muscle contraction occurs due to the sliding of actin filaments over myosin filaments within the sarcomere (the basic unit of muscle contraction).

OR

a) Myelinated and non-myelinated neuron

b) Dendrites and axon

• Dendrites: Short, branched extensions that receive signals from other neurons.
• Axon: A long, single extension that transmits signals away from the cell body.

c) Rods and cones

• Rods: Photoreceptor cells in the retina responsible for vision in dim light (black and white vision).
• Cones: Photoreceptor cells in the retina responsible for color vision and visual acuity.

d) Thalamus and hypothalamus

• Thalamus: Acts as a relay center for sensory information, directing it to the appropriate areas of the cerebral cortex.
• Hypothalamus: Controls many vital functions, including body temperature, hunger, thirst, and hormone secretion.

e) Cerebrum and cerebellum

• Cerebrum: The largest part of the brain, responsible for higher functions such as thought, perception, and voluntary movement.
• Cerebellum: Involved in coordination, balance, and motor learning.