Question

Write long notes on the following :

1. Digestion in human beings

2. Photosynthesis

3. Plant hormones

4. Sieve of Erasthosthenes

5. Phloem tissue

6. Digestion and feeding in amoeba ​

Answer 1

$\textbf{Answer is in Attachment !}$

1. $\textbf{Alimentary Canal }$:

The digestive system from Oesophagus to the anus is called alimentary canal. It is about 9 metre long. It is also called food tube.

It constitutes the organs namely :

Buccal cavity, Oesophagus, Stomach, Small intestine, Large intestine, Rectum, Anus.

$\textbf{Role of mouth }$:

Humans take in food through the mouth. It is the uppermost part of alimentary canal which is bounded by lips and cheeks, and contains tongue and slaivary gland. The food taken in is chewed or groinded by teeth at the same time in the salivary glands, saliva starts to secrete which contains enzymes( $\textbf{Salivary Amylase }$ )that breaks search into sugar.

Now the tongue helps in mixing this saliva with food, it also gives taste of food also it helps in swallowing the food.

$\textbf{Role of oesophagus}$ :

It is tubular part of alimentary canal about 25cm long. It is also the narrowest part of alimentary canal. It is hollow which allows the passage of food from Buccal cavity to the stomach. During which food gets mixed with various digestive juices.

$\textbf{Role of Stomach }$

It is J-shaped bag like structure made of muscle. Here gastric glance are present which secret mucus, HCL and digestive enzymes. The function of mucus is to protect stomach lining from the action of enzymes and acid. HCL kills bacteria present in food, making the food acidic; so that enzymes can act on it. Here food stays for 4-5 hours.

$\textbf{Role of Small intestine }$:

It is located below the stomach and is coiled in appearance. This tube is abour 7.5 m long. It has three main divisons : duodenum, jejunum and ileum. Duodenum is the first part having two different ducts namely bile duct and pancreatic duct. In this tube digested food (partially) is mixed with pancreatic juice, bile juice anf other juices. Jejunum is the middle pary, found only in man. Ileum is the last part of Small intestine.

Total absorbtion takes place in the ileum. This ileum has villi on its surface. This villi increases surface area for absorbtion. The villi have blood vessels, digested food passes villi passes to there and enters the blood stream. Which then transfers to liver and then to the heart.

$\textbf{Role of Large intestine, Rectum and Anus}$:

It is about 1.5 m long organ Food from small intestine moves here. Here the most of water and salt be removed from the water by the absorbtion. This intestine allow the passage of faecal matter through the anus.

2. $\textbf{Photosynthesis}$:

6CO2 + 12H2O --chlorophyll,sunlight--> C6H1206 + 6O2 + 6H2O

It is the process by which green plants and some other organisms uses sunlight to synthesise nutrients from carbon dioxide and water. The main products forms here is glucose and by products are carbon dioxide and oxygen and water where which chlorophylls are the sites of photosynthesis.

Events occurring during Photosynthesis are as follows :

1. Absorption of light energy by chlorophyll.

2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.

3. Reduction of carbon dioxide to carbohydrates.

Stages of Photosynthesis are as follows :

1. $\textbf{Light Reaction }$:

It occurs in the Grana where photon are absorbed so as to excite electrons of chlorophyll to a higher energy level. These activated electrons are harnessed to form ATP from ADP and reduce NADP to NADPH. Water is also splitted during this and oxygen is released.

2. $\textbf{Dark Reactions }$:

Calvin cycle occurring in chlorophyll here carbon dioxide combined with 5-carbon sugar call ribulose biphosphate. This unstable compound breaks down into three carbon compounds (phosphoglyeric acid) this then forms glucose.

Answer 2

Digestion In Human Beings

Digestion is the longest syetem in the human body.It starts from the mouth.The mouth has the tongue and the teeth which help in the chewing of food.It has salivary glands which secrete salivary amylase.It breaks down little amount of carbhohydrates into simple sugars.Saliva also acts as an lubricant.Then the food passes through the oesophagus through peristaltic movement(wavy motion).Then the food enters the stomach which is a muscular bag present towards the left side of the body.The stomach secretes mainly 3 enzymes-HCl,pesin and

mucus.HCl kill the bacteria present in the food and activates pepsin,Pepsin converts proteins to proteyase and Mucus protects the lining of the stomach from theHCl acid.In the stomach only partial digestion takes place.The partiallydigested food enter the small intesine.The food is further digested and the nutrients are absorbed by the vili present in the small intestine.Then he foods goes to the large intestine where the water content present in the food is absorbed.The remaining waste is sent to the anus and that food comes out through it.

Hope this answer helped you.