Nutrition And Digestion In Amoeba

Nutrition In Amoeba . Amoeba is an omnivorous i.e. it feeds on smaller animals , plants  micro organisms and Fragments of larger organisms. It is microscopic single celled organism found in pond water, Amoeba has a cell membrane , a rounded Dense nucleus and many small bubble like vacuoles in its cytoplasm.

 In amoeba nutrition is holozoic. Ingestion can take at any place on the surface since regular mouth is absent. Ingestion occurs through pseudopodium. The engulfed food particles come to lie inside a food vacuole. the latter is surrounded by a membrane
                        Digestive juices are secreted into the food vacuole They act on the food and break down into simpler substance. Gradually the digested food is absorbed . The absorbed food are used for growth maintenance and multiplication.    the undigested residue of food is expelled outside by the vacuole

Posted By Gaurav Thakur21:47

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Human Eye - Principal, Construction And Working

Human eye is the most remarkable and most delicate optical instrument.

Principal. Its principal is simmilar to a photographic camera , it is far most delicate and perfect than the finest camera ever designed by human being ingenuity
Structure of human eye. The human eye consist of nearly spherical ball of about 2.5cm diameter.
Its outermost coating is made of a  tough and opaque white substance known as SCLEROTIC. Sclerotic prevents the shape of eye and protect it against external injury .
              Front portion of the sclerotic is transparent and slightly bulged outward and known as CORNEA . There is a layer of black tissue below the sclerotic and is called CHOROID. It serves to absorb any stray light and thus avoid blurring of image by reflecting from the eye ball.
        In front of the eye , Choroid emerges into a colorful  diaphragm known as IRIS  with a hole in the middle called PUPIL. When we refer to the color of the eye we refer to the color of iris of the person. By means of involuntary muscles control, it regulates the amount of light entering the eye. In strong light, the pupil  contracts so as to admit less light whereas in dim light it expends so as to admit as much      light as required.
         Behind iris is a crystalline lens with a jelly like layer. The layer is held in position with the help of  CILIARY MUSCLES. The lens devides the eye ball into two chambers - the front chamber is called anterior chamber and the other between lens and retina called posterior chamber. Anterior chamber is filled with a fluid called AQUEOUS HUMOUR while the posterior chamber is filled with VITREOUS HUMOUR. 
          The innermost coating of eye , convering the rear of inner surface , is a very delicate membrane  called the RETINA . It is richly supplied with blood vessels and nerve fiver  and serves as a light - sensitive screen to receive the image  . The sensation of vision in the retina  is carried to the brain by a nerve called OPTIC NERVE. The most sensitive part of retina is known as yellow spot. It is a slightly raised portion with a slight depression known as the forvea centralis . The portion where the optic nerve enters the eye is totally insensitive to light and is known as blind spot
EYELIDS  are provided to control the amount the light fallin on the eye Lids also protect the eye from dust.
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Posted By Gaurav Thakur18:04

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Human Alimentary Canal With diagram

Mammalian (Human) alimentary Canal comprises mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine(duodenum, jejunum and ileum), Large intestine (caecum, Colon and rectum) and anus

Human Alimentary Canal

Mouth is bounded by Two Lips open into oral cavity.
Buccal cavity contains teeth and tounge, and receives saliva from 3 pairs of salivary gland (parotid, submaxilary, sublingual, )
Teeth are meant for cutting and mastication of food

Buccal cavity of a men. The mouth is a slit- like aperature bounded by two lips. It leads to buccal cavity. its roof is formed of hard plate, and hangs as uvula. the side of buccal cavity is formed of cheeks. At the floor is present a  musculo-sensory organ called tounge.
Pharynx. It is a vertical tube. It is a cross passage for both air and food. It has uvula and epiglottis which closes the internal nares and glottis respectively during swallowing of food to ensure the passage of food into oesophagus (food pipe)

 Oesophagus. It is 25cm long narrow muscular straight tube. It runs downward through the chest behind heart and passes through diaphragm into the abdomen here, it opens into stomach oesophagus propels the swallowed food into stomach.

Stomach of man. It is a sac like structure situated in the upper part of abdominal cavity below the diaphragm. Large part of this sac is situated left of the median line.

Small intestine. It is the longest part of alimentary canal. It is thin walled and highly coiled tubular structure. It is about 3 to 3.5m long and occupies most part of abdominal cavity. It is coiled upon itself. It is diffrentiated into 3 regions, viz., duodenum, jejunum and ileum.
Duodenum is 25cm long C- shaped. It recieves the opening of bile pancreatic duct. It also recieves the opening of stomach.
Jejunum is 90cm long. It lies above and left beyond duodenum.
Ileum is 180cm long its inner linning is thrown into numerous villi.
Large intestine. The large intestine is about 1.5m long. It is divided into following parts i.e,the vermiform appendix, the colon and the rectum. Caecum is blind tube and represented by vermiform appendix(5-8cm) and is present below the junction of small and large intestine. Rectum is the last part and opens to outside by anus gaurded by anal sphincter.


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