NCERT Solutions for Class 11 Biology Chapter 7: Structural Organisation in Animals

(i) Give the common name of Periplaneta americana.

Answer: The common name for Periplaneta americana is the American cockroach.

(Note: This question is a remnant from the older syllabus but may still be asked as a general knowledge question. The detailed anatomy is no longer in the curriculum).

(ii) How many spermathecae are found in an earthworm?

Answer: Four pairs of spermathecae are found in an earthworm, located in segments 6 to 9 (one pair in each segment).

(Note: Similar to the above, this is from the older syllabus. The focus is now on animal tissues.)

(iii) What is the position of ovaries in the cockroach?

Answer: In a cockroach, the ovaries are located laterally in the 2nd to 6th abdominal segments.

(iv) How many segments are present in the abdomen of a cockroach?

Answer: The abdomen of a cockroach consists of 10 segments.

(v) Where do you find malpighian tubules?

Answer: Malpighian tubules are excretory structures found at the junction of the midgut and hindgut in insects, including cockroaches.

(a) Chondrocytes

• What they are: Chondrocytes are the cells that make up cartilage. They are mature cartilage cells.
• Where they are found: They are found enclosed in small cavities called lacunae within the matrix of the cartilage. Cartilage itself is found in various places like the tip of the nose, outer ear joints, between vertebrae, and in the limbs and hands of adults.

(b) Axons

• What they are: An axon is a long, slender, cylindrical projection of a nerve cell, or neuron.
• Where they are found: It is part of the neural system. The axon carries nerve impulses away from the neuron's cell body (cyton) to other neurons, muscles, or glands. They are found throughout the body, forming nerves in the peripheral nervous system and pathways in the brain and spinal cord.

(c) Ciliated epithelium

• What it is: Ciliated epithelium is a type of epithelial tissue where the cells (usually cuboidal or columnar) on the free surface bear cilia. Cilia are fine, hair-like outgrowths.
• Where it is found: Its function is to move particles or mucus in a specific direction. It is found in the inner surface of hollow organs like bronchioles (small airways in the lungs) and fallopian tubes (oviducts).

Epithelial tissues are classified into two main types: Simple Epithelium and Compound Epithelium.

1. Simple Epithelium: Composed of a single layer of cells.

• (a) Squamous Epithelium: Made of a single thin layer of flattened cells with irregular boundaries.
  • Function: Forms a diffusion boundary.
  • Location: Walls of blood vessels, air sacs of lungs.
  • [*Image: A neat, labelled diagram of Simple Squamous Epithelium*]
• (b) Cuboidal Epithelium: Composed of a single layer of cube-like cells.
  • Function: Secretion and absorption.
  • Location: Ducts of glands, tubular parts of nephrons in kidneys.
  • [*Image: A neat, labelled diagram of Simple Cuboidal Epithelium*]
• (c) Columnar Epithelium: Composed of a single layer of tall, slender cells with nuclei located at the base.
  • Function: Secretion and absorption.
  • Location: Lining of the stomach and intestine.
  • Modification: If these cells have cilia, they are called ciliated columnar epithelium (found in bronchioles).
  • [*Image: A neat, labelled diagram of Simple Columnar Epithelium*]

2. Compound Epithelium: Composed of more than one layer (multi-layered) of cells.

• Structure: Multiple layers of cells, with the deepest layer resting on the basement membrane.
• Function: Its main function is to provide protection against chemical and mechanical stresses. It has a limited role in secretion and absorption.
• Location: The dry surface of the skin, the moist surface of the buccal cavity (mouth), pharynx, and inner lining of ducts of salivary glands.
• [*Image: A neat, labelled diagram of Compound Epithelium (Stratified Squamous)*]

(a) Simple epithelium and compound epithelium

(b) Cardiac and skeletal muscle

(c) Dense regular and Dense irregular connective tissue

(d) Adipose and blood tissue

(e) Simple gland and compound gland

(a) Areolar tissue; blood; neuron; tendon
Answer: Neuron.
Reason: Areolar tissue, blood, and tendon are all types of connective tissue. A neuron is a cell of the neural tissue.

(b) RBC; WBC; platelets; cartilage
Answer: Cartilage.
Reason: RBC, WBC, and platelets are components of blood (a fluid connective tissue). Cartilage is a type of specialized skeletal connective tissue.

(c) Exocrine; endocrine; salivary gland; ligament
Answer: Ligament.
Reason: Exocrine, endocrine, and salivary gland are all related to glands and secretion. A ligament is a type of dense regular connective tissue.

(d) Maxilla; mandible; labrum; antennae
Answer: Antennae.
Reason: Maxilla, mandible, and labrum are mouthparts of a cockroach. Antennae are sensory appendages but not mouthparts.

(e) Protonema; mesothorax; metathorax; coxa
Answer: Protonema.
Reason: Mesothorax, metathorax, and coxa are all parts of a cockroach's body (thorax and leg segments). Protonema is a stage in the life cycle of a moss (plant kingdom).

Muscular tissue is responsible for movement in our body. It is made of long, cylindrical fibres arranged in parallel arrays, which are composed of fine fibrils called myofibrils. When stimulated, muscle cells contract (shorten) and then relax to their original length, causing movement.

Muscular tissue is of three types:

1. Skeletal Muscle:
   • It is attached to the bones, hence the name skeletal.
   • It is under voluntary control.
   • The muscle fibres are bundled together, unbranched, and show alternate light and dark bands, so they are called striated muscles.
   • They are responsible for locomotion and body movements.
2. Smooth Muscle:
   • The fibres are spindle-shaped (tapering at both ends) and do not show striations, hence they are 'smooth' or non-striated.
   • They are involuntary in function.
   • They are found in the walls of internal organs such as the stomach, intestine, and blood vessels.
3. Cardiac Muscle:
   • It is the muscle of the heart wall only.
   • It is involuntary in nature.
   • The muscle fibres are branched and striated.
   • A unique feature is the presence of intercalated discs, which are communication junctions that allow the cells to contract as a single unit.

Ligaments are dense regular connective tissues that connect bone to bone. If ligaments were absent, our joints would become highly unstable and dislocate easily. There would be no structure to hold the bones together in their correct alignment, leading to a complete loss of joint function and mobility.

1. Epithelial Tissue: Function - Protection, secretion, absorption.
2. Connective Tissue: Function - Support, binding, transport.
3. Muscular Tissue: Function - Movement and locomotion.
4. Neural Tissue: Function - Control and communication.

Location: Areolar tissue is found beneath the skin, around nerves and blood vessels, and between muscles.

Functions:

1. It acts as a support framework for epithelium.
2. It helps in the repair of tissues after an injury and combats foreign toxins.

[*Image: A neat, labelled diagram of a neuron showing the cell body (cyton), dendrites, nucleus, axon, myelin sheath, and axon terminal.*]

Labels should include:

• Dendrites
• Cell body (Cyton)
• Nucleus
• Axon
• Myelin Sheath (if applicable)
• Node of Ranvier
• Axon terminal

Connective tissue is broadly classified into three types:

1. Loose Connective Tissue (e.g., Areolar, Adipose)
2. Dense Connective Tissue (e.g., Dense regular, Dense irregular)
3. Specialized Connective Tissue (e.g., Cartilage, Bone, Blood)

Loose Connective Tissue:

In this type of tissue, the cells (fibroblasts, macrophages, mast cells) and fibres are loosely arranged in a semi-fluid ground substance.

(a) Areolar Tissue:

• Structure: It has all three types of fibres (collagen, elastin, reticular) and various cells loosely scattered in its matrix.
• Location: It is the most widely distributed connective tissue, found beneath the skin, supporting epithelium.
• Function: It serves as a support framework for epithelium and acts as a reservoir of water and salts. It is the main site of inflammatory reactions.

(b) Adipose Tissue:

• Structure: It is another type of loose connective tissue located mainly beneath the skin. The cells of this tissue, called adipocytes, are specialized to store fats.
• Location: Found in the subcutaneous layer, around the heart, kidneys, and in yellow bone marrow.
• Function: The excess of nutrients which are not used immediately are converted into fats and are stored in this tissue. It acts as an insulator (reduces heat loss) and a shock absorber.

A gland consists of one or more cells that make and secrete a particular product. Glands are formed from epithelial tissue. Based on the mode of pouring out their secretions, glands are divided into two categories: exocrine and endocrine.

Based on the above information, answer the following questions:

1. (a) Identify the tissue. (1 Mark)
   The tissue is Skeletal Muscle Tissue. The description (long, cylindrical, unbranched, striated, multinucleated) perfectly matches it.
2. (b) Why is this tissue called 'voluntary'? (1 Mark)
   It is called 'voluntary' because its contraction is under the conscious control of the brain. We can decide when to move the muscles attached to our bones, like when waving a hand.
3. (c) What do the 'light and dark bands' signify? (1 Mark)
   The light and dark bands signify the striated appearance of the muscle, which is due to the specific arrangement of contractile proteins (actin and myosin).
4. (d) Where else in the body can you find this tissue? (1 Mark)
   This tissue is found attached to all the bones of the skeleton, such as in the limbs (arms and legs), trunk, and head.