Nutrition

 Chapter # 12

NUTRITION
BOTANY PART

Q.1: What is nutrition and what are different types of nutrition?

Ans:
The process by which living organisms obtain energy to perform all their functions of life to make important materials and to maintain their structure is called nutrition.

Types Of Nutrition:
There are two types of nutrition:

Autotrophic Nutrition:
When the living organisms can manufacture their own food material, it is called autotrophic nutrition, and the living organisms are known as autotrophs. There are two types of autotrophic nutrition.

• Phototrophic Nutrition:
  In this nutrition, the living organisms manufacture their food in the presence of sunlight. This type of nutrition is found in plants and bacteria.
• Chemotrophic Nutrition:
  This type of nutrition is also common in bacteria. In this nutrition, light is not used, but certain inorganic substances are involved to produce energy by oxidation process. The bacteria use inorganic compounds as source of carbon and get energy by oxidation and reduction process. They oxidize the compounds like nitrate, sulphur, ammonia, ferrous iron, hydrogen sulphide etc.

Heterotrophic Nutrition:
When the living organisms cannot manufacture their own food and they depend upon other organisms for their food, it is called heterotrophic nutrition and the living organisms are known as heterotrophs. Heterotrophs may be parasites or saprophytes.

Q.2: What is the role of Nitrogen in plants?

Ans:
The plants absorb nitrogen in the form of nitrates and ammonium salts. It is present in the structure of protein molecules, nucleic acids, and chlorophyll.

Deficiency Symptoms:

• Chlorosis: Due to the loss of chlorophyll yellowing of leaves develops, called chlorosis.
• Process of cell division and cell elongation is stopped

Q.3: What is the role of Phosphorus in plants?

Ans:
The plants absorb phosphorus in the form of soluble phosphates such as $H_2PO_4$ and $HPO_4$. It is present in sufficient amount in the growing and storage organs such as fruits and seeds. In the body of plants, phosphorus is present in the nucleic acids, phospholipids, ATP, NAD, and NADP compounds. Phosphorus promotes healthy growth of plants and fruit ripening. The coenzymes NAD and NADP contain phosphorus. These are important in oxidation-reduction processes. These are involved in many processes like photosynthesis, respiration, nitrogen metabolism, and fatty acid synthesis.

Deficiency Symptoms:

• Dead necrotic regions: The deficiency causes dead necrotic regions on the leaves, petioles, and fruits.
• Premature leaf fall occurs.
• Cambium activity is affected.
• Dormancy is prolonged.
• Accumulation of carbohydrates occurs.
• In some plants, the leaves show dark to blue-green coloration, such as dark green in Pisum (Gram).
• Sometimes purple or red anthocyanin pigmentation takes place in leaves.

Q.4: What is the role of Potassium in plants?

Ans:
Potassium is also an important mineral. It is present in growing regions of plants. It is used in the processes of respiration, photosynthesis, chlorophyll formation, and nucleic acid synthesis. It is involved in the opening of stomata. It is also used in enzyme action required in carbohydrate metabolism and formation of peptide bonds.

Deficiency symptoms:

• Dull Or Bluish Green Leaves:
  The deficiency of Potassium causes dull or bluish-green leaves.
• Irregular Chlorosis:
  Irregular chlorosis occurs near the tips and margins of leaves.
• Stunted Growth:
  Plant is stunted in growth with short internodes.
• Tips of leaves turn downward.

Q.5: What is the role of Magnesium in plants?

Ans:
Magnesium is required by the plant for the formation of chlorophyll. Without chlorophyll, photosynthesis cannot occur. It is also an activator of certain enzymes. It acts as a phosphorus carrier in the plant. It takes part in seed formation having high oil contents. It is also required in the preparation of fats and carbohydrate metabolism.

Deficiency Symptoms:

• Chlorosis or yellowing: Chlorosis or yellowing occurs first in older leaves and then in younger leaves.
• Hard stem: Stem becomes hard and woody and yellowish green.
• Fall of leaves: Affected leaves wither and fall earlier.
• Necrotic spots are developed on leaves.

Q.6: What are the heterotrophic plants?

Ans:
Some plants are not able to manufacture their own food material due to the lack of chlorophyll or some other reason, so they completely or partially depend upon other organisms. These are called heterotrophic plants, and the nutrition is known as heterotrophic nutrition.

There are two types of heterotrophic plants:

• Parasitic Plants:
  They obtain their food from living organisms.
• Saprophytic Plants:
  They obtain their food from non-living organisms.
• Carnivorous Plants:
  These plants obtain nitrogenous compounds from insects or other small animals.

Q.7: Write a note on parasitic plants?

Ans:
Parasitic Plants:
These plants obtain their food from other living organisms. These plants are two types:

• Obligate Parasites:
  These plants entirely depend upon other living organisms for their food. They are also called total parasites.
• Partially Parasites:
  These plants partially depend upon other organisms for their food. They are also called partially parasites. The parasitic plants produce special root-like structures, called haustoria. These haustoria penetrate into the host plant body and absorb food material.

The parasitic angiospermic plants are as follows:

• Partial stem parasite
• Total stem parasite
• Partial root parasite
• Total root parasite

Partial Stem Parasite: These plants grow upon other host plants, they can manufacture some of their food due to the presence of chlorophyll, and they partially depend upon the host plant. They absorb nutrients and water from the host plant by the help of haustoria.

Examples:

• Loranthus has thick green leaves, woody stem, and haustoria. It grows up mango, Bauhinia plant, rosaceous trees, and many shrubs.
• Viscum
• Cassytha filiformis.

Total Stem Parasite: These plants completely depend upon host plants for their food. They produce haustoria into the body of the host plant and absorb food material. Ultimately the host plant may die.

Example:
Cuscuta plant (Amar bail).

Partial Root Parasite: These plants get their food partially from the roots of other plants. For example, Sandalwood tree. Its seedling does not grow independently. Its roots absorb nourishment from the roots of other plants.

Total Root Parasite: These plants obtain their food completely from the roots of neighboring plants. These plants usually attack the plants of the family Cruciferae and Solanaceae. For example, Orobanche, Cistanche, Striga. Cistanche parasites on the roots of Calotropis plant. Striga is a parasite on the roots of sugarcane, Sorghum, or Jawar.

Q.8: What are the saprophytic plants?

Ans: SAPROPHYTIC PLANTS: These are special plants, which grow upon dead organic matter. These plants do not contain chlorophyll. Their roots are without root hairs and cannot absorb nourishment from the soil. They decompose dead organic food into simpler compounds and use them for their growth and development. For example, Neothia (bird’s nest or orchid), Monotropa. Roots of these plants form an association with fungi, which helps in the absorption of food from dead bodies.

Q.9: What are Carnivorous plants? Name some carnivorous plants?

Ans: CARNIVOROUS PLANTS: Some plants use insects, so they are called carnivorous or insectivorous plants. These plants show certain modifications to capture insects. These plants contain chlorophyll and manufacture their own food, but cannot prepare nitrogenous compounds and proteins, so to get these compounds, the plants use insects. These plants usually grow in those regions where nitrogen is not sufficiently available, so they depend upon insects for nitrogen and proteins.

Some insectivorous plants are as follows:

• Pitcher plant
• Sundew plant
• Utricularia or Bladder wort
• Venus fly trap plant
• Water fly trap plant.

Q.10: Write a note on Pitcher Plant?

Ans: PITCHER PLANT:

• In this plant, leaves are modified into flask-shaped structures, called leaf pitcher. These pitchers are used to capture insects.
• The pitcher also has a lid to close its mouth.
• When insects come on its mouth, they are slipped into the pitcher.
• From the inner surface of the pitcher, digestive enzymes are secreted, which help in the digestion of insects.

Q.11: What are Sundew insectivorous plants?

Ans: SUNDEW PLANT: (DROSERA INTERMEDIA)

• It is a small herb plant with about half a dozen leaves.
• Each leaf is covered on the upper surface with many glandular hairs, called tentacles.
• The glands secrete a fluid, which glitters in the sunlight like dew, so the plant is called Sundew plant.
• The insects are attracted to the plant due to smell, these insects are captured by the tentacles, then they are digested by enzymes.

Q.12: Describe Venus fly trap plant?

Ans: VENUS FLY TRAP PLANT:

• It is a herb plant, grows in moist places.
• The leaves of the plant consist of two halves with a midrib in the centre.

Q.13: Describe Utricularia? (Bladderwort)

Ans: UTRICULARIA: (BLADDER WORT)

• It is a water-living plant, in which leaves are modified into small cup-shaped structures, called bladders.
• The bladders are used to capture the insects.
• Each bladder has a small opening, which acts as a trap-door.
• The insects enter the bladder through the trap-door. From the inner region of the bladder, enzymes are produced for the digestion of insects.

Q.14: Describe water fly trap plant?

Ans: WATER FLY TRAP PLANT: (ALDROVANDA)

• It is a water-living free-floating plant. It is rootless with whorls of leaves.
• The leaves are modified to capture the water flies. Each leaf has two lobes.
• Along the margin of leaf, teeth-like structures are present. It also has jointed hairs and stalked glands on the surface.
• When flies are captured, enzymes are secreted from glands which take part in digestion of insects.

Q.15: What is Heterotrophic nutrition in Animals?

Ans: HETEROTROPHIC NUTRITION IN ANIMALS: In heterotrophic nutrition, living organisms are not able to manufacture their own food, but they depend upon other organisms. All animals, fungi, and many bacteria are included in heterotrophic organisms. These are called heterotrophs.

In animals, there are different types of heterotrophic nutrition:

• Holozoic Nutrition: In this nutrition, the animals take solid organic food, it is digested by the action of enzymes, then it is assimilated to release energy by oxidation process.
• Saprozonic Nutrition: When the organisms take their food from dead organic substances, it is called saprozoic nutrition.
• Parasitic Nutrition: In this nutrition, the organisms obtain their food from the body of host and cause great damage to their body.

Q.16: What are different types of animals on food basis?

Ans: TYPES OF ANIMALS ON THE BASIS OF FOOD: On the basis of feeding system, the animals are of the following types.

• Detritivores: These animals take their food from organic debris (detritus). When the organic debris is decomposed, they use them as their food e.g. Earthworm.
• Predators: These animals attack other animals, kill them, and then use them as their food e.g. Lion.
• Herbivores: These animals use plants as their food e.g. Cow, Rabbit, Horse etc.
• Carnivores: These animals obtain their food from other animals e.g. Cats, Dogs.
• Omnivores: These animals use both plants and animals as their food i.e. eat meat and vegetable matter. e.g. Man, Crow, Rat etc.
• Filter feeders: These are water-living animals, in their body food enters along with water. Food particles are used by the body, water is filtered out. e.g. Sponges.

• Fluid Feeders:
  These animals take their food from other animals in the form of fluid. e.g. Mosquitoes suck blood from man.

  Microphagus Feeders:
  These animals take food in the form of small pieces.

  Macrophagus Feeders:
  These animals take food in the form of large pieces.

Q.17: What is Holozoic Nutrition?

Ans: HOLOZOIC NUTRITION:
When complex food substances are taken in, these are converted into simpler diffusible form by enzymes, absorbed by the body, and used to provide energy. This process is called holozoic nutrition.

The holozoic nutrition consists of five steps:

1. Ingestion: When complex food molecules are taken inside the body with the help of certain organs, it is called ingestion.
2. Digestion: When complex food molecules are converted into simpler and diffusible form by the action of enzymes, it is called digestion.
3. Absorption: When digested diffusible food substances diffuse into blood or body cells across the membrane of the digestive part, it is called absorption.
4. Assimilation: When the products of digestion are used to produce energy in the body, it is called assimilation.
5. Egestion: When undigested food substances are expelled out of the body, it is called egestion.

Q.18: What are extracellular and intracellular digestion?

Ans:
There are two types of digestion:

• Extracellular Digestion: When the digestion takes place outside the cells in the digestive tract, it is called extracellular digestion.
• Intracellular Digestion: When the digestion occurs inside the cells, it is called intracellular digestion.

Intracellular Digestion:
When digestion takes place inside the cells, it is called intracellular digestion.

Q.19: Describe the process of nutrition in Amoeba?

Ans: NUTRITION IN AMOEBA:
Amoeba is a unicellular freshwater organism. It is a microphagus feeder, meaning it uses small organisms as its food, such as minute food particles, bacteria, flagellates, and ciliate animals and plants.

Ingestion:
Amoeba captures food particles with the help of pseudopodia. It produces two pseudopodia at the same time, forming a cup-like structure around the food. Then the food is taken in through the surface of the body. The food is surrounded by a drop of water, which forms a food vacuole. This process is known as ingestion.

Process of Digestion:
In the digestion of food, lysosomes are involved. Some lysosomes are attached to the membrane of the food vacuole. They secrete certain enzymes like proteases, amylases, and lipases into the food vacuole. The food vacuole decreases in size as a result of water loss. Due to the enzyme activity, the food is completely digested.

Absorption of Food:
After digestion, fine canals are produced from the digestive vacuole. Along these canals, the soluble products of food pass into the surrounding cytoplasm. These food products are absorbed into the cytoplasm, where the absorbed food circulates throughout the cytoplasm.

Assimilation:
After absorption, the food is assimilated to form new cytoplasm and to produce energy.

Egestion:
Insoluble or undigested food particles are expelled out of the body by exocytosis. In Amoeba, digestion of food occurs inside the cell, so it is called intracellular digestion.

Q.20: Describe the process of nutrition in Hydra?

Ans: NUTRITION IN HYDRA:
Hydra is a water-living animal. It is a macrophagus feeder, meaning it takes large pieces of food. Hydra has an elongated tube-like body. At its upper end, the mouth is present, surrounded by finger-like projections called tentacles, which are used to capture prey.

Hydra is a diploblastic animal, meaning it consists of two layers: the outer layer is called ectoderm, and the inner is known as endoderm. Between these layers is a non-cellular sheet called mesogloea. The mouth of Hydra opens into a cavity called gastrocoel or enteron, which is closed at the lower side. Endodermal cells lie close to the enteron.

The endoderm layer contains two types of cells: glandular cells (with glands) and flagellated cells (with flagella). When food enters the enteron through the mouth, the glandular cells secrete proteolytic enzymes to digest the food. Flagellated cells and contractions of the body wall also aid in digestion, which occurs extracellularly in the enteron. After partial digestion, some of the digested food is absorbed by endodermal cells, where intracellular digestion also takes place. This dual digestion process is both extracellular and intracellular in nature. The digested food is absorbed by endodermal cells and diffused to other body regions, while undigested particles are expelled through the mouth.

Q.21: Describe the process of nutrition in Planaria?

Ans: NUTRITION IN PLANARIA:
In Planaria, an alimentary canal is present, consisting of three parts: mouth, pharynx, and intestine. The mouth is in the middle of the lower body region. When Planaria takes food from outside, it passes through the pharynx into the intestine, which divides into three branches—one central branch extending forward and two lateral branches extending backward. These branches divide into numerous branches, forming a branching system responsible for digestion, absorption, and distribution of food. This system is known as the gastrovascular system, differing from that of other animals.

The food of Planaria consists of dead aquatic animals. The food is taken in through the mouth, which opens into the pharynx and then the intestine. The enzymes act upon the food in the intestine. The digested food is absorbed by the branches of the intestine, which is distributed throughout the body by diffusion. In Planaria, the digestion is both intracellular and extracellular. The branching system of the intestine mainly helps in the supply of food throughout the body; otherwise, simple diffusion does not help in this process. This system is like the circulatory system of higher animals. The undigested food is expelled out of the body through the mouth, as the anus is absent.

Q.22: Describe the process of nutrition in Cockroach?

Ans: NUTRITION IN COCKROACH:
Cockroach is an insect; it is omnivorous, meaning it takes any kind of organic matter. It uses its antennae in the search of food. The digestive system of the cockroach consists of a tube-like alimentary canal, which extends from the mouth to the anus. The alimentary canal consists of three parts:

• Fore gut or stomodaeum
• Mid gut or mesenteron
• Hind gut or proctodaeum

Fore Gut or Stomodaeum:
It is the upper region of the alimentary canal. It consists of the mouth, buccal cavity (preoral cavity), pharynx, oesophagus, crop, and gizzard. The mouth opens into the pre-oral cavity (buccal cavity). The food is mixed with saliva, secreted by salivary glands. The saliva contains amylase enzyme, which digests carbohydrates. The mouth opens into the pharynx. It is tube-like, present up to the end of the head, then it opens into the oesophagus. The oesophagus is thin-walled and tube-like. It passes through the neck, enters the thorax, and opens into the crop. The crop is a pear-shaped sac-like large part, present in the thorax. It stores food material and leads into the gizzard. The gizzard is a small, thick-walled structure, present at the lower region of the crop. Its internal lining is raised into six teeth-like structures, which are used for the grinding of food, so the food is converted into a fine state.

Mid Gut or Mesenteron:
It is the middle part of the alimentary canal. It is a thin-walled, narrow, tube-like structure. From the upper outer surface of the mesenteron, six to eight club-shaped structures are produced, called hepatic caecae. These secrete digestive enzymes, which help in the digestion of proteins and fats. After digestion, the food is also absorbed in the mid-gut.

Hind Gut or Proctodaeum:
It is the lower region of the alimentary canal. It consists of three parts: ileum, colon, and rectum. The ileum is the upper part of the hind gut. It is thin-walled, tube-like. The mesenteron opens into the ileum. From the outer region of the ileum, fine hair-like structures are developed, called Malpighian tubules. These are excretory organs. The ileum opens into the colon. The colon is long...

Q.23: Name the different parts of alimentary canal of man?

Ans: PARTS OF ALIMENTARY CANAL:
The alimentary canal of man consists of the following parts:

• Mouth and buccal cavity
• Pharynx
• Oesophagus
• Stomach
• Small intestine: This part is further divided into (i) Duodenum, (ii) Jejunum, (iii) Ileum.
• Large intestine: This part is further divided into three portions: (i) Colon, (ii) Caecum, (iii) Rectum.

Q.24: What are the glands of digestion in man?

Ans: GLANDS:
In the body of man, three types of glands are present, which secrete digestive enzymes. These are as follows:

• Salivary glands
• Liver
• Pancreas

Q.25: Write a note on teeth of man & write down the dental formula?

Ans:
There are different types of teeth in man: incisors, canines, premolars, and molars. Incisors and canines are the anterior teeth, while premolars and molars are the posterior ones. They change the food into small particles. Man has two sets of teeth; it is called diphyodont. One set is of milk teeth, deciduous, and these are replaced by another set, permanent teeth. The teeth are of different shapes and sizes; it is called heterodont. These teeth are embedded in the gums; it is called thecodont. Man has 8 incisors, 4 canines, 8 premolars, and 12 molars. The human dental formula is
$\left(\frac{2}{2}, \frac{1}{1}, \frac{2}{2}, \frac{3}{3}\right) \times 2 = 32$

Q.26: Write a note on plaque and dental diseases of man?

Ans: PLAQUE AND DENTAL DISEASES:
When salivary material and bacteria are mixed together, it is called plaque. Many diseases and abnormalities can occur by plaque.

• Periodontal Disease:
  When plaque is accumulated, bacteria cause inflammation of the gums. By this continuous process, inflammation spreads to the roots of teeth and destroys their peridental layer, due to which the teeth become loose and fall off. It is called periodontal disease.

• Calculus:
  When plaque combines with certain chemicals in the saliva, it becomes hard and calcified. It is deposited on the teeth and cannot be removed easily; it is called calculus.

  Dental Caries:
  When the enamel part of the teeth is destroyed and dentine and pulp are attacked by bacteria, converting sugar into acid, it causes toothache and loss of teeth, which is called dental caries.

  There are many factors of dental caries:

  • Sugary foodstuffs are used, and teeth are not cleaned properly.
  • Saliva composition may be disturbed or changed.
  • Lack of oral hygiene.
  • Low level of fluoride in drinking water.
  
  

  Q.27: Describe the salivary glands of man?

  Ans: SALIVARY GLANDS AND SALIVA
  The teeth change the food into small particles. In this process, the tongue also helps. It is also used for sucking and testing the food. During this process, salivary glands are stimulated and secrete saliva, which is mixed with food.

  There are three pairs of salivary glands in the oral cavity:

  • Parotid Glands: Present below the ear pinnae.
  • Sub Lingual Glands: Present under the tongue.
  • Sub Mandibular Glands: Present at the base of jaws.

  Saliva is an alkaline fluid. It contains water and mucus, which moisten and soften the food and help in lubrication, making it easier to swallow. Saliva contains two enzymes, amylase and lysozyme. Amylase of saliva digests starch and converts it into polysaccharides, then into disaccharides. Lysozyme enzyme destroys pathogenic bacteria.

  Q.28: What are peristalsis and antiperistalsis?

  Ans: PERISTALSIS & ANTIPERISTALSIS:
  In the gut wall, contraction and expansion occur in an alternate manner. This propulsive movement is called peristalsis. For the swallowing of food and water, peristaltic movements are required.

When there is great stretching and irritation in the gastrointestinal wall, it is called antiperistalsis. It occurs at the time of vomiting. When there is contraction in the abdominal muscles and the stomach is squeezed, the gastric contents move upward through the oesophagus in the form of vomiting. In antiperistalsis, the movements are reversed. It usually occurs due to overeating or any other reason.

Q.29: Describe the process of digestion in the stomach of man?

Ans:
The stomach is a muscular sac-like part, present on the left side of the abdominal cavity below the diaphragm. The stomach performs three functions:

• Storage of food
• Mechanical digestion of food
• Chemical digestion of food by enzymes

The stomach has three regions. Its upper region is called the cardiac end. This end contains a valve called the cardiac sphincter. The middle region of the stomach is the fundus. It is the main part containing gastric glands. These glands have three types of cells:

• Mucus secreting cells
• Zymogen cells, which secrete pepsinogen enzyme
• Oxyntic cells, which secrete dilute HCl

The lower part of the stomach is called the pyloric region. It opens into the duodenum; at this region, a valve is present, called the pyloric sphincter. When food comes into the stomach, the gastric glands secrete gastric juice which is mixed with the food.

Gastric Juice contains the following compounds:

• Mucus: It protects the inner lining of the stomach from the action of enzymes.
• Water: It moistens and softens the food.

HCl:

• It stops the action of saliva and kills bacteria. It also provides an acidic medium.

Enzymes: In the gastric juice, the following enzymes are present:

• Pepsin: By the action of HCl, the pepsinogen enzyme is changed into pepsin, which converts proteins into peptones and proteoses.
• Rennin: It changes the milk into curd in young ones. In adults, this process takes place by HCl.
• Gastrin: A hormone produced in the stomach. It activates gastric glands to produce gastric juice.

The partly digested food is in the form of a paste-like substance called chyme. It comes into the duodenum.

Q.30: Describe the process of digestion in the small intestine of man?

Ans: SMALL INTESTINE: The stomach leads into the small intestine. It is about 6 meters long and 2.5 cm wide. It consists of three parts:

• Duodenum
• Jejunum
• Ileum

Duodenum: The stomach directly opens into the duodenum, which is about 30 cm long. It receives a common bile duct and a pancreatic duct through a common opening. When food comes into the duodenum, it mixes with the bile, which is secreted by the liver. Bile contains water, bile salts, and bile pigments.

Bile:

• It neutralizes the acid in the food and makes it alkaline.
• It acts upon fats and converts them into a milky suspension, i.e., emulsification takes place.

There are two bile pigments: red pigment (bilirubin) and green pigment (biliverdin). These are produced by the breakdown of hemoglobin from ruptured RBCs in the liver. Bile pigments are excretory products.

Pancreatic Juice: It is secreted by the pancreas and produced by the activity of a hormone called secretin, which is produced by the duodenum. Secretin enzyme is also produced due to HCl, which comes from the stomach along with food.

Pancreatic juice contains the following enzymes:

• Trypsin (Protease): It is an active enzyme, but it is converted into an active enzyme from the inactive enzyme trypsinogen by the activity of enterokinase enzyme. Trypsin acts upon proteins and converts them into polypeptides.
• Chymotrypsin: It converts milk protein casein into amino acids.
• Amylase: It converts starch into maltose.
• Lipase: It converts fats into fatty acids and glycerol.

Digestion In Jejunum: The duodenum opens into the jejunum, which is about 2.4 meters long. It secretes the following enzymes:

• Peptidase (Erepsin): It acts on proteoses and peptides and converts them into amino acids. These are diffusible substances.
• Maltase: It converts maltose into glucose.
• Sucrase: It converts sucrose into glucose and fructose.
• Lactase: It converts milk sugar into glucose and galactose.

In this way, starch is changed into simple sugars.

Q.31: Describe the absorption of food in man?

Ans: ABSORPTION OF FOOD: Absorption of food takes place in the ileum, which is about 3.6 meters long. It receives much diluted food, called chyle. The inner surface of the ileum has numerous finger-like projections, called villi. The villi contain smooth muscles and are supplied by blood capillaries and lacteals (lymph vessels).

As a result of digestion, carbohydrates are changed into simple sugars, and proteins are converted into amino acids. These are absorbed by the mucous membrane of the villi. The absorption of food occurs through diffusion or active transport. The simple sugars and amino acids are carried to the liver by the hepatic portal vein. Fatty acids and glycerols are absorbed by the lacteals.

epithelial cells of villi. In these cells, they are changed into simple fats, called triglycerides. The simple fats are diffused into lymph vessels, lacteals.

Some glucose is added to the blood and supplied to different parts of the body. It is used as energy. The extra amount of glucose is converted into glycogen and stored in the liver. It is used again by the body at the time of need. The amino acids cannot stay in the liver. Their large amount is diffused into the blood and used by the body. The additional amount of amino acids is either changed into glucose or into a substance called urea, which is removed from the body by the excretory system.

The fatty acids and glycerols are diffused into the lymph vessels called lacteals, where they are changed into small droplets. The lymph vessels distribute them to all cells of the body, where assimilation takes place. The short-chain fatty acids and glycerine are water-soluble; they are absorbed by the blood capillaries. The extra fats are stored in the body and are used when the body requires energy.

Q.32: Describe the large intestine of man?

Ans: THE LARGE INTESTINE: The large intestine consists of three parts:

• Colon
• Caecum
• Rectum

Colon: It consists of three portions, an ascending, a transverse, and a descending portion. It reabsorbs water and salts from the undigested food and returns them to the circulatory system. They are again used by the body. If this reabsorption of water and salts does not occur, diarrhea causes excessive loss of water and salts, which can lead to dehydration, which is very dangerous to the body.

Caecum: The part of the colon which lies below the T-like junction with the small intestine is called the caecum. It contains bacteria that take part in the digestion of cellulose. The caecum has a small finger-like projection, called the appendix. Sometimes, some food substances are diffused into the appendix and cause disturbance and infection, called appendicitis. Due to extreme pain, the appendix is removed from the body.

Rectum: It is the last part of the large intestine. It opens to the outside by the anus. When the undigested food enters the colon, it reabsorbs water and salts from it. The remaining undigested food comes into the rectum and is then discharged out of the body through the anus.

Q.33: Describe the functions of the liver?

Ans: FUNCTIONS OF LIVER:

• It produces a secretion called bile. The bile combines with the food and neutralizes its acidity. It also acts as an antiseptic. It works upon fats and changes them into a milky substance, after which the enzymes take part in further digestion of fats.
• The liver performs a metabolic function. From the ileum, the digested food is transferred to the liver by the hepatic portal vein. The liver keeps the food substances in balance.
• The liver converts an extra amount of glucose into glycogen, which is stored in the body and can be used again.
• The liver changes the amino acids into carbohydrates by removing the nitrogen. These carbohydrates are used as energy, while the nitrogenous substances are removed from the body in the form of urine.
• The liver acts upon fatty acids and stores them in the form of fats. They are again used as nutrients by the body.
• The liver converts poisonous materials into non-poisonous and harmless substances.
• It stores vitamins.
• It produces special materials to help in the clotting of blood.
• It maintains the chemical composition of blood.
• It takes part in the removal of bile particles such as biliverdin, bilirubin, and other unnecessary substances.

Q.34: Describe the functions of the pancreas?

Ans: PANCREAS: The pancreas is an important gland. It is located behind the stomach. It is an exocrine gland because it secretes pancreatic juice, which contains important enzymes for the digestion of food. The pancreas also acts as an endocrine gland by secreting a hormone called insulin. This hormone converts extra sugar into glycogen. It also secretes another hormone, glucagon, which again converts glycogen into glucose for the production of energy.

Q.35: Name the disorders of the gastrovascular tract?

Ans: DISORDERS OF THE GASTRO-INTESTINAL TRACT: In the digestive cavity of human beings, many disorders or diseases can develop. These are as follows:

• Diarrhoea
• Dysentery
• Constipation
• Piles
• Dyspepsia
• Peptic ulcer
• Food poisoning

Q.36: Write a note on Diarrhoea?

Ans: DIARRHOEA: When the undigested matter is discharged rapidly through the large intestine, it is called loose motions or diarrhoea.

There are many reasons for diarrhoea:

• Enteritis: It is an infection caused by a virus or bacteria. By their activity, the mucosa lining of the intestine is affected, causing diarrhoea.
• Cholera: It is caused by bacteria. The inner layer of the intestine is damaged, due to which water and minerals (bicarbonate ions and sodium ions) are rapidly discharged out of the body, leading to dehydration. In severe cases, death may occur.
• Psychogenic Diarrhoea: Due to certain nervous tensions, a disorder occurs in the intestine, causing diarrhoea. It is called psychogenic diarrhoea.

Q.37: Write a note on Dysentery?

Ans: DYSENTERY: When there is inflammation in the large intestine and blood and mucosa are discharged along with undigested material, it is called dysentery. Dysentery is caused by the infection of bacteria or entamoeba. The internal lining of the large intestine is damaged, resulting in the secretion of blood and mucus.

Q.38: What is Constipation?

Ans: CONSTIPATION: When the undigested matter is passed very slowly through the intestine and includes hard and dry parts, it is called constipation. It is due to the accumulation of undigested food in the large intestine for a long time, where its water is reabsorbed by the wall of the colon, causing it to become dry and hard. Another reason for constipation is habitual in certain individuals. In such conditions, the inner part of the intestine develops a tendency to prevent normal and regular discharge of undigested matter.

Q.39: What is Piles (Haemorrhoids)?

Ans: PILES (HAEMORRHOIDS): When the veins close to the anus are dilated, it is called piles or haemorrhoids. These dilated veins sometimes start bleeding at the time of discharge of undigested matter, so the patient feels a great difficulty and pain. The haemorrhoids may be just outside the anus or inside the anal opening. The main cause of piles is constipation. When the pressure is exerted for the discharge of undigested matter, it results in the dilation of veins.

There are certain methods to avoid piles:

• Constipation should be controlled.
• Hygienic conditions should be maintained.
• Soft food or laxatives may be used.
• Fiber diet should be used, because fibers help for the easier passage of undigested matter.

Q.40: What is Dyspepsia?

Ans: DYSPEPSIA: Dyspepsia is the incomplete or imperfect digestion. It may be due to peptic ulcer, more acidity in the stomach, abnormal function of stomach or intestine. In dyspepsia, there may be heartburn, flatulence, nausea (feeling of vomiting), and vomiting. Sometimes dyspepsia occurs without any proper reason. It may be due to certain disturbances in the alimentary canal.

Q.41: What is Peptic ulcer?

Ans: PEPTIC ULCER: When the mucous layer of the alimentary canal is damaged by the digestive enzymes, it is called a peptic ulcer. The ulcer may occur in the stomach, in the upper region of the duodenum, or sometimes in the lower region of the oesophagus. In severe cases of ulcers, small holes and wounds are developed by the action of acid and pepsin enzyme. The reasons for ulcers may be hereditary character, psychogenic reasons, or anxiety, i.e., uneasiness and depression.

Q.42: What is Food poisoning?

Ans: FOOD POISONING: The indigestion of food containing toxic substances causes food poisoning. Its main reasons are bacteria, viruses, protozoa, or some allergy. In human beings, it is caused by the use of contaminated food or milk. Its main symptoms are diarrhoea, vomiting, and pain in the digestive tract. Food poisoning is caused by Salmonella bacteria, which are usually present in uncooked chicken or eggs. Food poisoning mostly appears within 48 hours after using the contaminated food.

Malnutrition:

• Defined as the deficiency or excess of nutrients in the body.
• Under-nutrition is common in poorer countries due to lack of access to food, while over-nutrition is more common in developed countries, leading to obesity and other health issues.

Overweight and Obesity:

• Excessive body fat due to over-eating and low energy expenditure.
• It may have genetic links and can lead to severe health consequences, even death.

Anorexia Nervosa:

• A condition characterized by a loss of appetite, often found in young women due to psychological reasons.
• Fear of gaining weight leads to food refusal, dangerous weight loss, and potential vomiting, requiring psychiatric treatment.

Bulimia Nervosa:

• Involves binge eating followed by attempts to avoid weight gain, often through vomiting.
• Linked to nutrient deficiency and prolonged treatment.

Endoparasites of Humans:

• Viruses: Cause diseases like influenza, polio, smallpox, rabies, measles, and yellow fever.
• Bacteria: Responsible for diseases like tuberculosis, typhoid, cholera, plaque, tetanus, and leprosy.

Fungi:

• Dermatophyte fungi cause skin-related diseases in humans, such as:
• Skin diseases
• Athlete’s foot
• Ringworm disease

Protozoans:

• Protozoans are responsible for various diseases, including:
• Malaria (caused by Plasmodium)
• Amoebic dysentery (Amoebiasis, caused by Entamoeba)
• Sleeping sickness (caused by Trypanosoma, leading to Trypanosomiasis)
• Leishmaniasis (caused by Leishmania)

Helminths (Parasitic Worms):

• Flatworms and roundworms cause several diseases in humans, such as:
  • Taeniasis (caused by Taenia saginata)
  • Hookworm disease (caused by Ancylostoma)
  • Intestinal worm disease in children (caused by roundworms, specifically Ascaris)
  • Filariasis (caused by Filaria)

BIOENERGETICS

 BIOENERGETICS

Q.1: What is Photosynthesis?

Ans: Photosynthesis is a process in which plants manufacture their food in the presence of chlorophyll and sunlight by the combination of carbon dioxide and water to form simple carbohydrates. In this process, oxygen is liberated. It is important to note that the amount of carbon dioxide consumed in this process is equal to the amount of oxygen liberated.

In photosynthesis, not only simple carbohydrates are formed but also a considerable amount of energy, which is initially obtained from sunlight as radiant energy, is transferred by green cells into chemical energy.

$$6CO_2 + 12H_2O \xrightarrow{\text{Light, Chlorophyll}} C_6H_{12}O_6 + 6H_2O + 6O_2 \uparrow$$

In terms of energy, photosynthesis can be defined as the metabolic process during which light energy is converted into chemical or food energy in the presence of chlorophyll and electron carriers.

Q.2: What are the reactants and products of Photosynthesis?

Ans: Reactants: In photosynthesis, $CO_2$ and water are the raw materials. The water is absorbed from the soil by the help of roots, and $CO_2$ enters the body through stomata of leaf from the atmosphere. In aquatic plants, the dissolved $CO_2$ enters the plant along with water.

Photosynthetic products: In photosynthesis, simple carbohydrate glucose is formed by the combination of $CO_2$ and hydrogen of water. Oxygen is produced by the hydrolysis of water, which is released out as a byproduct. The important product, simple sugar, forms other complex compounds like starch and cellulose. A part of sugar is changed into oil and another part produces nitrogen, sulfur, and phosphorus, which help to form proteins and other compounds.

Q.3: What is the role of Chlorophyll and other Pigments in Photosynthesis?

Ans: Role of Chlorophyll and Other Pigments:
Chloroplasts are the chlorophyll-containing organelles. Each photosynthetic cell of leaf has about 20-100 chloroplasts. Each chloroplast consists of three parts:

• A surrounding double membrane.
• A liquid called stroma that is surrounded by a double membrane. It has important enzymes required for the formation of carbohydrates.
• Thylakoids:
  These are sets of flattened sac-like structures, which are embedded in the stroma. The thylakoid membrane contains an inner fluid-filled cavity or lumen. This cavity (lumen) is separated from the stroma by the thylakoid membrane. The columns of thylakoid are called grana.

Chlorophyll and other photosynthetic pigments are present in the thylakoid membranes and show the green color of plants. Electron acceptors of photosynthesis are also found in these membranes, so thylakoid membranes are involved in the formation of ATP compounds.

Chlorophyll and other pigments absorb sunlight.
This light energy is converted into chemical energy of ATP and NADPH. These are used to prepare glucose in the stroma region of the chloroplast. The pigments of plants are Carotenes (orange), Phaeophytin (grey), Xanthophyll (yellow), Chlorophyll-a (blue-green), and Chlorophyll-b (yellow-green). Chlorophylls are of different types, a, b, c, d.

The formula of chlorophyll a and b is given below:
Chlorophyll a - $C_{55}H_{72}O_5N_4Mg$
Chlorophyll b - $C_{55}H_{70}O_6N_4Mg$

Q.4: What is the Photosystem in Plants?

Ans: Photosynthesis takes place by the help of sunlight energy, which is absorbed by photosynthetic pigments. The photosynthetic pigments are present in groups, called photosystems. The photosystem consists of two parts: a light-gathering part called the antenna complex and a reaction center. The antenna complex part contains many molecules of chlorophyll-a, chlorophyll-b, and carotenoid molecules.

When light is received, the light energy is transferred from one pigment molecule to another pigment molecule until it reaches the reaction center, where chemical reactions of the photosystem occur, and light energy is converted into chemical energy.

Types of Photosystem or Pigment System:
There are two types of photosystems or pigment systems.

• Pigment System I or Photosystem I
• Pigment System II or Photosystem II

Pigment System I or Photosystem I (PS-I)
It consists of chlorophyll-a molecules which absorb maximum light of 700 nm, called $P_{700}$. FRS (Ferredoxin reducing substance), ferredoxin molecule. PS-I controls the process of reducing NADP into NADPH + H.

Pigment System II or Photosystem II (PS-II)
It consists of chlorophyll-b ($P_{680}$) a primary electron acceptor $Q$, a plastoquinone, cytochrome-$b_{559}$, cytochrome-$b_6$, plastocyanin, Mn molecules bound with protein and chloride.

PS-II is concerned with the formation of oxidant and reductant with the release of oxygen.

Q.5: What is the role of light in Photosynthesis?

Ans:
Role of Light:
The light comes in packets, called quanta. A single quantum of light is known as a photon. The light travels in waves which have different lengths. The light of longer wavelengths has less energy, and light of short wavelengths contains more energy. The human eye can only see the light of a certain wavelength. The visible light has a wavelength between 400 nm (violet) and 700 nm (red). The light is composed of seven different colors: violet, blue, green, yellow, orange, and red.

The molecules that absorb light are called pigments. Chlorophyll a and b absorb violet, blue, and red regions of light, while yellow and orange light is absorbed very slightly. Green light is reflected, so plants are shown green in color. When light is captured in the antenna complex, it is rapidly transferred to the chlorophyll molecules present in the photosynthetic reaction center. The energy of light photons results in the activation of an electron from the ground state to an excited state. This energy is used to start chemical reactions and all other steps of photosynthesis.

Q.6: What is the role of water and $CO_2$ in Photosynthesis?

Ans:
Role of Water:
Water has a very important role in photosynthesis. Photosynthesis is a redox (reduction-oxidation) process. It needs $H^+$ and electrons. For this purpose, photolysis of water takes place. $H_2O$ splits into oxygen and hydrogen. Hydrogen ions ($H^+$) are used in dark reactions to produce sugar by the combination of $CO_2$. The oxygen is released from the body of the plant.

Role of $CO_2$:
$CO_2$ plays a basic role in photosynthesis. In the dark reaction, it takes part in chemical processes and involves in the formation of simple carbohydrates. The rate of photosynthesis is increased by the increase of $CO_2$ in the atmosphere.

Q.7: Describe the light reaction of Photosynthesis?

Ans:
The light reaction consists of two steps.

• Electron transport
• Phosphorylation (Formation of ATP)

Electron Transport:
The light reaction of photosynthesis is started from the reaction center of PS-II ($P_{680}$). The steps of this process are as follows:

• The Chlorophyll b of Pigment System II (P.S.II) absorbs sunlight and becomes activated. It releases an electron. The electron becomes excited to a high energy level. The excited electron produced within P is transferred to the primary electron acceptor Phaeophytin.
• From primary electron acceptor (Phaeophytin), it is transferred to the plastoquinone (PQ), which is associated with Fe ions.
• From the plastoquinone, the electron is passed to the cytochrome complex.
• The chlorophyll $P_{680}$ gets electron from water by its splitting into two hydrogen ions and an oxygen. This process is called photolysis of water.
• From cytochrome complex, the electron is moved to the plastocyanin (PC). Plastocyanin is reduced, it is present in the lumen. Plastocyanin is a copper-containing protein.

(Diagram titled "Non-cyclic electron flow during the light reaction generates ATP and NADPH (Z-Scheme)")    

• The plastocyanin (PS) moves along the membrane to PS-I, where the chlorophyll-a ($P_{700}$) accepts the electron. This chlorophyll also absorbs light energy.
• From the chlorophyll-a $P_{700}$, the electron is transferred to Ferredoxin reducing substrate (FRS). It is the primary acceptor of Photosystem-I.
• From Ferredoxin reducing substrate (FRS), the electron is transferred to the Ferredoxin (Fd).
• From Ferredoxin, the electron is transferred to NADP. The NADP is reduced to NADP + $H^+$.

Photophosphorylation (Formation of ATP): (Non-cyclic)
During the electron transport, when the electron moves through the chain, its energy is used by thylakoid membrane to produce ATP; this is called photophosphorylation. The electron does not come back to its original position, but it takes part in the reduction of NADP to form NADPH + $H^+$. In this way, a cycle is not completed, so this process is called non-cyclic photo-phosphorylation.

Q.8: Describe the light-independent reaction (Dark reaction) of Photosynthesis?

Ans:
Light Independent Reaction: (Dark Reaction)
(Calvin-Benson Cycle)
The dark reaction does not require light and may take place both in light and dark during the night.

In the dark reaction, the hydrogen separated from water combines with Carbon of $CO_2$ and forms simple carbohydrates with the help of the energy-rich compound ATP. Melvin Calvin worked on the pathway of carbon to carbohydrates. The cycle of chemical reactions in the dark reaction is known as Calvin-Benson cycle. It is also called $C_3$ Photosynthetic carbon reaction cycle.

(Diagram of Benson Calvin Cycle showing Carbon-Fixation Phase-I, Reduction Phase-II, and Regeneration of Ribulose biphosphate (RuBP) in Phase-III)

The Calvin cycle actually consists of 13 main reactions which are catalyzed by 11 enzymes, but it can be divided into three distinct phases:

1. Carboxylation:
   In which $CO_2$ combines with organic molecules, it is also called carbon fixation.

2. Reduction:
   In which organic molecules are reduced, and phosphoglyceraldehyde (PGAI) compound is formed.

3. Regeneration:
   In which reduced carbon is used to regenerate the carbon acceptor molecules or used for metabolism.

Q.9: Describe $C_4$ Photosynthesis mechanism in plants?

Ans:
$C_4$ Photosynthesis:
It is also called Hatch and Stack cycle or dicarboxylic acid cycle. In this cycle, the $CO_2$ acceptor molecule is Phosphoenol pyruvic acid (PEP).

The steps of $C_4$-Photosynthesis are as follows:

• In the chloroplasts of mesophyll cells, $CO_2$ is accepted by phosphoenol pyruvate to form oxaloacetate. It is a 4-carbon compound, so the process is called $C_4$ mechanism.
• Oxaloacetate is converted into malate. Malate is transferred to the chloroplasts of bundle sheath cells.
• Malate combines with NADP to produce pyruvate and $CO_2$. $CO_2$ is used in the Calvin cycle to form sugar. This process is common in sugar-cane, maize of grass family.

(Diagram showing $C_4$-Photosynthesis cycle)

Q.10: Describe the CAM Cycle of Photosynthesis in Plants?

Ans:
CAM Cycle (Crassulacean Acid Cycle):
This process of Photosynthesis occurs in Cacti plants, Pineapple, and many other plants. In such plants, stomata are closed during the day and remain open during the night, so the loss of water is prevented. These plants take up $CO_2$ and use them to produce organic acids, so the process is called crassulacean acid cycle (CAM). These organic acids are stored in their vacuoles. During the day, by the help of ATP and NADPH + H, $CO_2$ is released from organic acids and takes part in the Calvin cycle to form sugar molecules.

Step to CAM Cycle:

• In the night $CO_2$ is accepted by phosphoenol pyruvate to form oxaloacetate.
• Oxaloacetate is converted into malate (Malic acid organic acid).
• In daytime malate is converted into pyruvate and $CO_2$.
• $CO_2$ enters the Calvin cycle to take part in the formation of sugars.

(Diagram showing CAM Cycle of Photosynthesis)

Q.11: What is oxidative phosphorylation?

Ans: Oxidative Phosphorylation:
Respiration is an oxidation-reduction or redox process, in which electrons are donated or accepted in different reactions. The glucose loses hydrogen atoms when it is converted into $CO_2$, and when molecular oxygen is converted into water, it gains hydrogen atoms. Each hydrogen atom contains one electron and one proton, so the transfer of hydrogen atoms is the transfer of electrons and protons.

In respiration, oxidation of glucose takes place with the loss of electrons, and reduction of oxygen occurs by the gain of electrons. During redox reaction, the energy of electrons is used in the formation of ATP from ADP and inorganic phosphate (Pi). The synthesis of ATP is known as oxidative phosphorylation.

Q.12: What is aerobic respiration?

Ans: Aerobic Respiration:
This type of respiration occurs in the presence of $O_2$. The glucose is converted into $CO_2$ and $H_2O$. In this process, a sufficient amount of energy is released. Most organisms show aerobic respiration; such organisms are called aerobes.

Q.13: What is anaerobic respiration?

Ans: Anaerobic Respiration:
This type of respiration takes place in the absence of oxygen. In this process, glucose is converted into $CO_2$ and ethyl alcohol or lactic acid. In this mechanism, very little energy is released.

The organisms which show anaerobic respiration are called anaerobes. These are bacteria, yeast, some species of annelids which live in mud containing less oxygen, parasites in the intestine such as Tapeworms, roots of plants growing in water-logging conditions.

$$C_6H_{12}O_6 \rightarrow C_2H_5OH + CO_2 + 28 \text{ K. cal energy}$$

There are two types of anaerobes:

• Obligate Anaerobes: These organisms show respiration without oxygen, i.e., they never need oxygen.
• Facultative Anaerobes: These organisms show aerobic respiration in the presence of oxygen, but in the absence of oxygen, they start anaerobic respiration.

Q.14: What is Fermentation?

Ans: Fermentation:
Anaerobic respiration (without $O_2$) is also called fermentation. When ethyl alcohol is formed in this process, it is called anaerobic respiration. When lactic acid is formed in the process, it is called lactic acid fermentation.

Economic Importance Of Fermentation:
The economic importance of fermentation is as follows:

• By this process many chemical products are prepared, such as ethyl alcohol, lactic acid, propionic acid, and butanol.
• It is used in the brewing industry.
• It is used in the dairy industry, in the formation of curd, cheese, butter, etc.
• It is used in the preparation of wines and beers. Wines are produced from fruits like grapes. Beers are produced from malted cereals, e.g., Barley.
• Yeast is used in bakeries to prepare many items, such as bread.
• Lactic acid is used to produce flavor for yogurt and cheese. Lactic acid prevents the spoilage of dairy products.
• Lactic acid is also used to produce flavor in pickles.
• Fermentation is also used in the preparation of acetone and other industrial solvents.

Q.15: Describe briefly the process of glycolysis in plants?

Ans: Glycolysis:
The initial stage of respiration is called glycolysis in which $O_2$ is not used. It is common both in aerobic and anaerobic respiration. In this process, carbohydrates are changed into a 3-carbon compound, pyruvic acid. The reactions of glycolysis are as follows:

1. Glycolysis starts with glucose. The glucose is converted into glucose-6-phosphate by the utilization of an ATP compound (an energy-rich compound).
2. Glucose-6-phosphate is changed into fructose 1-6 biphosphate by the arrangement of carbon atoms.
3. Fructose-6-phosphate is converted into fructose 1-6 biphosphate by the use of an ATP compound.
4. Fructose 1-6 diphosphate is divided into two 3-carbon compounds, 3-phosphoglycer-aldehyde and bihydroxy acetone-phosphate.
5. 3-Phospho-glycer-aldehyde is changed into 1-3-biphospho glyceric acid.
6. 1-3-diphospho glyceric acid is converted into 3-phospho-glyceric acid. It reacts with ADP (adenosine diphosphate), which forms ATP (adenosine-triphosphate).
7. 3-phosphoglyceric acid is changed into 2-phospho-glyceric acid.
8. 2-phospho-glyceric acid is changed into phosphoenol pyruvate, which finally produces pyruvate (end product).

Q.16: Describe briefly the Kreb Cycle (Tricarboxylic Cycle)?

Ans: In the presence of sufficient amount of oxygen, the pyruvic acid is oxidized. In the presence of coenzyme A, it releases $CO_2$ and changes into acetyl coenzyme A. In this process, two hydrogens are also removed which are accepted by NAD molecules to form $NADH_2$. The acetyl coenzyme A enters the Krebs cycle or Tricarboxylic acid cycle or citric acid cycle.

Steps Of Krebs Cycle:

• In the first reaction of Krebs cycle, the acetyl-CoA combines with oxalo-acetic acid, a 4-carbon compound, and changes into citric acid. In this reaction, coenzyme A is released, and one molecule of water is used.
• Citric acid is converted into cis-aconitic acid in the presence of enzyme by dehydration in which a water molecule is released.
• Cis-aconitic acid is converted into isocitric acid. In this reaction, a molecule of water is used.
• Isocitric acid produces oxalo-succinic acid by the liberation of hydrogen. It combines with NAD to form $NADH_2$.

Q.17: What is electron transport chain?

Ans: ELECTRON TRANSPORT CHAIN:
The last stage of aerobic respiration is the electron transport chain. In glycolysis and Krebs cycle, hydrogen is transferred to different carriers such as NAD, NADP, and FAD. These compounds are then oxidized through the electron transport system, and the energy released in this process is used in the formation of ATP.

The electron transport system takes place in the mitochondria where hydrogen acceptors are arranged in an order. The system is controlled by enzymes. The series of carriers is called the electron transport chain. The hydrogen atoms are removed in pairs at various stages during glycolysis and Krebs cycle. A pair of hydrogen atoms is separated into a pair of electrons and a pair of protons.

Reaction:
$2H \rightarrow 2H^+ + 2e^-$

The electrons are accepted by NAD and FAD. They are passed along a series of electron carriers, such as cytochrome "b," cytochrome "c," cytochrome "a," and cytochrome "a3." In the electron transport system, a pair of electrons forms 3 ATP. One ATP is produced when NAD transfers its electron to FAD. One ATP is formed when one electron is migrated from cyt.b to cyt.c. The third ATP is produced when electron is transferred from cyto.a to cyto.a3. The formation of ATP is called oxidative phosphorylation.

Q.18: What are the trophic levels?

Ans: TROPHIC LEVELS:
Food is very important for all living organisms because it provides energy. In an ecosystem, the flow of energy occurs through a chain, for example, plants are eaten by herbivores and the herbivores are eaten by carnivores, thus the food manufactured by plants travel from producers to primary consumers, i.e., herbivores and then to secondary consumers, i.e., carnivores. "This stepwise process through which food energy moves, with repeated stages of eating and being eaten, is known as the food chain."
e.g.,
Grass → Sheep → Man

Food chain represents various levels of nourishment. These levels are called trophic levels. The green plants occupy the first trophic level. It is the primary producer level. The herbivores form the second level or primary consumer level.

These trophic levels are arranged in a systematic manner:
Plants → Primary consumers → Secondary consumers → Tertiary consumers → Bacteria (decomposers).
In each step, the number and mass of organisms is limited by the amount of energy available. Because some energy is lost in the form of heat, thus the steps become progressively smaller near the top. These trophic levels are shown graphically by means of pyramids, called ecological pyramids. In the pyramid, the producer level constitutes the base of the pyramid and tertiary consumers or decomposers level make the apex.

Q.19: What is the Pyramid of Energy?

Ans: PYRAMID OF ENERGY:
This pyramid shows the rate of energy flow or productivity at successive trophic levels. This pyramid is always upright and it gives the best picture of the overall nature of the ecosystem. It indicates the amount of energy available for successively higher trophic levels. In most cases, there is always a gradual decrease in the energy content at successive trophic levels from the producers to various consumers.

Q.20: What is Productivity (Energy Flow)?

Ans: PRODUCTIVITY (ENERGY FLOW):

• The most approximate rate of product obtained from photosynthesis during one year in an ecosystem is known as productivity.
• The productivity cannot be estimated from the crop of a field, because they obtain productivity is different. In an ecosystem, the productivity depends upon the sunlight...

Q.21: Distinguish between the following:

Respiration & Photosynthesis:

Respiration	Photosynthesis
It is a catabolic process, i.e., compounds are broken down.	It is an anabolic process, i.e., compounds are formed in this process.
In this process, carbohydrates are broken down into simpler compounds.	In this process, carbohydrates are manufactured.
This process starts with carbohydrates (glucose) and O₂.	This process starts with CO₂ and H₂O.
The end-products of this process are CO₂ and H₂O.	The end-products of this process are simple carbohydrates.
In respiration, O₂ enters the plant body and CO₂ is released.	In photosynthesis, CO₂ enters the plant and O₂ is given out.
It occurs during both day and night. Light is not necessary for this process.	It occurs during the daytime only. Light is necessary for this process.
It takes place inside mitochondria (Krebs cycle) and cytoplasm (glycolysis).	It takes place within mitochondria.
In respiration, energy is released from food material.	It is an energy-consuming process, but energy is stored in the form of food material.

 In this process, the dry weight of the plant body decreases.

In this process, dry weight of plant body increases.

During the breakdown of one glucose molecule, 38 ATP molecules are formed.
During the formation of one glucose molecule, 18 ATP molecules are utilized.

Light Dependent and Independent Phase of Photosynthesis:

Light Dependent Phase of Photosynthesis (Light Reaction)	Light Independent Phase of Photosynthesis (Dark Reaction)
This phase requires light.	This phase does not require light.
In this system, light is used in the photolysis of water. The water splits into Hydrogen & Oxygen.	In this system there is no photolysis of water.
In this phase, Hydrogen is attached with NADP compound, called reduction of NADP.	In this phase, Hydrogen of NADP takes part in the chemical process to form glucose.
In this process, CO₂ does not play any role.	In this phase, CO₂ enters the process and helps in the formation of glucose.
Glucose is not produced in this phase.	Glucose is produced in this phase.
In this phase, chlorophyll absorbs sunlight.	In this phase, there is no role of chlorophyll.
In this phase, Pigment System I (P.S.I) and Pigment System II (P.S.II) are involved.	P.S.I and P.S.II are not involved in this phase.

PS-I and PS-II (Pigment System I and Pigment System II)

PS-I (Pigment System I)	PS-II (Pigment System II)
Pigment System I (P.S-I) contains chlorophyll a, which can absorb maximum light of 700 nm, called P₇₀₀.	Pigment System II (P.S-II) consists of chlorophyll b which can absorb maximum light of 680 nm, called P₆₈₀.
It contains Ferredoxin reducing substrate (FRS) and Ferridoxin.	It contains plastoquinone, plastocyanin, and cytochromes.
In this system, Mn and chloride are not involved.	In this system, Mn and chloride are also involved.
In this system, reduction of NADP with Hydrogen takes place.	In this system, there is no reduction of NADP compound.

Photophosphorylation & Oxidative Phosphorylation:

Photophosphorylation	Oxidative Phosphorylation
In this process, formation of ATP compounds takes place in the presence of sunlight.	In this process, ATP compounds are not produced in the presence of sunlight. It is by the process of oxidation.
It occurs during the light reaction of photosynthesis.	It occurs in the process of respiration.
In this process, chlorophyll is necessary to absorb sunlight.	In this process, there is no role of chlorophyll.
In this process, light energy is used in the electron transport.	In this process, energy of glucose is used by oxidation in the electron transport.

Aerobic Respiration & Anaerobic Respiration:

Aerobic Respiration	Anaerobic Respiration
In this process O₂ is required.	In this process O₂ is not required.
In this process glucose is converted into CO₂ and H₂O.	In this process glucose is converted into CO₂ and Ethyl alcohol (or Lactic acid in animals).
In this process huge amount of energy from glucose molecule (673 k cal) is released.	In this process very less amount of energy is produced i.e. 28 k cal.
It occurs in all higher plants and animals.	It occurs in Bacteria and fungi, mostly which are decomposers.