STRUCTURAL ORGANISATION IN ANIMALS

 

Smooth muscle :

• The smooth muscle fibres tapers or pointed at both ends
• Do not show cross striation.
• Cell junctions hold them together.
• They are bundled together in a connective tissue sheath.
• Present in wall of blood vessels, stomach and intestine.
• They are involuntary in nature.

Cardiac muscles:

• Contractile muscular tissue present in heart.
• Cell junctions fuse the plasma membranes of cardiac muscles cells and make them stick together.
• Communication junction or intercalated discs at some fusion points allow the cells to contract as a unit.
• Muscle cells are branched and Uninucleated.

Neural tissues:

• Neural tissues exert greatest control over body’s response to changing condition.
• Neurons are the units of nervous tissues.
• Neuroglial cells non-conducting and protects and support neurons.
• Neuroglia makes up more than one-half the volume of neural tissue.
• Electrical impulse is conducted through the plasma membrane of neuron.

EARTHWORM :

Morphology :

• Earthworm has long cylindrical body.
• The body divided into more than 100 equal segments called metamere.
• Mid-dorsal dark line indicates the dorsal blood vessel.
• The ventral surface is distinguished by genital openings.
• Anterior end consists of the mouth and prostomium.
• The first segment is called peristomium, which contain the mouth.
• In matured worm, segments 14-16 are covered by dark band of glandular tissue called clitellum.
• Body divisible into:
  • Preclitellar.
  • Clitellar.
  • Postclitellar
  
  
• External apertures:
  • Four pairs of spermathecal aperture 5th – 9th segments.
  • A female genital aperture- 14th segment.
  • A pair of male genital apertures in 18th segment.
  • Numerous nephridial pores on the skin of each segment.
  
  
• There are row of S- shaped Setae in each segment except 1st and last segment.
• Setae have principal role in locomotion.

ANATOMY :

Body wall :

• Body wall externally covered by thin non-cellular cuticle.
• Body wall contains epidermis below cuticle.
• Epidermis is made of single layer of columnar epithelium with secretory glands.
• Two layers of muscles (circular and longitudinal).

Digestive system:

• Alimentary canal is a straight tube between 1st and last segment.
• Mouth present in the 1st segment.
• Mouth opens into buccal cavity 1-3 segments.
• Buccal cavity leads into muscular pharynx in 4th segment.
• Narrow oesophagus at 5-7 segments.
• Muscular gizzard in 8-9 segments helps in grinding of ingested food.
• Stomach extended from 9-14 segments.
• Calciferous gland present in the stomach, neutralize the acidic nature of humic acid present in the humus.
• Intestine starts from 15th segment and continues till last segment.
• A pair of Intestinal caecae present in the 26th segment.
• Presence of internal median fold of dorsal wall of intestine called typhlosole between 26-35 segments.
• Typhlosole increases the surface area for absorption.
• Intestine opens to outside by means of anus.

 

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
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