CBSE Class 10 Science Advanced Biology Nutrition Long Answer Questions Set 01

Long Answer Type

Question 1. Explain the process of nutrition in Amoeba.
Answer:
Amoeba is a single-celled animal living in water. Its nutrition is holozoic, and it takes in food by phagocytosis (cell eating). All the steps take place inside the one cell:

1. Ingestion: Amoeba surrounds a food particle by putting out finger-like pseudopodia, and the particle is enclosed with a little water in a bag called the food vacuole, the temporary stomach.
2. Digestion: digestive enzymes from the cytoplasm enter the food vacuole and break the food into small, soluble molecules.
3. Absorption: the digested food diffuses from the vacuole into the cytoplasm, and the vacuole disappears.
4. Assimilation: the absorbed food gives energy by respiration, and is used for growth and reproduction.
5. Egestion: the undigested food is thrown out of the cell through the surface.
In simple words: Amoeba engulfs food with pseudopodia, digests it in a food vacuole, absorbs it by diffusion and throws out the waste.

Teacher's Note:
1. Draw the five stages as in the figure and label the food vacuole.
2. Name the steps in the proper order for full marks.

Question 2. Describe the alimentary canal of man
Answer:
The human alimentary canal is a long, hollow tube running from the mouth to the anus, together with the digestive glands.

1. Mouth and buccal cavity: food enters through the mouth. The cavity has the palate (roof), the tongue (taste, chewing, swallowing) and teeth (incisors cut, canines tear, premolars and molars grind). Salivary glands open into it.
2. Oesophagus: a muscular food pipe that pushes the food into the stomach by peristalsis. No digestion occurs here.
3. Stomach: a J-shaped bag on the left side of the abdomen. Its glands secrete gastric juice (HCl, pepsin, mucus), and protein digestion begins here.
4. Small intestine: the longest part (about 6.5 m), with the duodenum, jejunum and ileum. Bile and pancreatic juice enter the duodenum, intestinal juice acts in the ileum, and villi absorb the digested food.
5. Large intestine: the caecum, colon and rectum. It absorbs water from the undigested food, and the faeces leave through the anus.
In simple words: The canal is a tube made of the mouth, oesophagus, stomach, small intestine and large intestine, with glands that pour juices into it.

Teacher's Note:
1. Draw the figure first and then describe each part in a line or two.
2. Do not forget the pharynx between the mouth and the oesophagus.

Question 3. Explain the mechanism of photosynthesis.
Answer:
Photosynthesis is the making of glucose from CO₂ and water by the green cells of plants in the presence of sunlight and chlorophyll: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. It takes place in the chloroplast in two stages.
A. Light reaction (photochemical reaction, Hill's reaction): site, the grana; raw materials, light and water; products, ATP, NADPH₂ and O₂. It has three steps:
1. Photo-excitation of chlorophyll: chlorophyll absorbs photons and an electron is raised to a higher energy level and leaves the molecule.

2. Photolysis of water (in the presence of Mn²⁺ and Cl⁻ ions): 4H₂O → 4H⁺ + O₂ + 4e⁻ + 2H₂O. Oxygen is released, and H⁺ reduces NADP: 2NADP + 4H⁺ → 2NADPH₂.
3. Photophosphorylation: ATP is formed from ADP and inorganic phosphate (ADP + iP → ATP) in the quantasomes.
B. Dark reaction (Calvin–Benson cycle): site, the stroma; it needs CO₂, ATP, NADPH₂ and enzymes, and the product is glucose. The steps are: 1. carboxylation (CO₂ is taken up by RuBP in C₃ plants or PEP in C₄ plants with the help of RuBisCO or PEPCase), 2. synthesis of glucose from the fixed carbon, and 3. regeneration of RuBP.
In simple words: Photosynthesis has a light reaction in the grana, which makes ATP and NADPH₂ and releases oxygen, and a dark reaction in the stroma, which makes glucose.

Teacher's Note:
1. Write the site, raw materials and products of each stage; it is the easiest way to organise this answer.
2. Remember that the oxygen comes from water.

Question 4. Explain the three pathways of breakdown of food in living organisms.
Answer:
This topic is not covered in the Nutrition text of the book; the answer below is the standard one. The food that the cells use as fuel is mainly glucose, which is broken down in three ways to release energy:
1. Aerobic respiration (in the presence of oxygen): glucose is broken down to pyruvate in the cytoplasm, and the pyruvate is completely oxidised to CO₂ and water in the mitochondria. It gives the most energy (38 ATP).
2. Anaerobic respiration in yeast (without oxygen): the pyruvate is changed into ethanol and CO₂. Little energy is released (2 ATP). This is called fermentation.
3. Anaerobic respiration in muscle cells (when oxygen is short): the pyruvate is changed into lactic acid, which causes cramps. Little energy is released.
In all three pathways the first step, the breakdown of glucose to pyruvate (glycolysis), occurs in the cytoplasm.
In simple words: Glucose is broken down with oxygen into CO₂ and water, or without oxygen into alcohol and CO₂ in yeast, or into lactic acid in muscles.

Teacher's Note:
1. This question belongs to the chapter on respiration, so learn it from there too.
2. Give the end products and the place for each pathway.

Question 5. (a) Draw diagram of human alimentary canal and label the following
(i) Part in which starch digestion starts (ii) Part in which bile is stored
(iii) Part in which nutrients are absorbed (iv) Part in which water is absorbed
(b) Mention the role of hydrochloric acid in the stomach.
(c) What function is served by the following:
(i) Gastric sphincter (ii) Anal sphincter [CBSE 10TH BOARD: 2013]
Answer:
(a)

In the diagram: (i) starch digestion starts in the mouth (buccal cavity); (ii) bile is stored in the gall bladder; (iii) nutrients are absorbed in the small intestine (ileum and jejunum); (iv) water is absorbed in the large intestine (colon).
(b) HCl makes the medium of the stomach acidic, which is needed by pepsin; it changes the inactive pepsinogen into active pepsin; and it kills the bacteria that come in with the food.
(c) (i) The gastric sphincter is a ring of muscle at the opening of the stomach. It controls the passage of food, and the one at the exit lets the food go into the small intestine in small amounts. (ii) The anal sphincter is a ring of muscle at the anus that controls the removal of faeces from the body.
In simple words: The diagram shows the canal; HCl activates pepsin and kills germs; sphincters are rings of muscle that control the passage.

Teacher's Note:
1. Draw a neat diagram and show the four parts with leader lines.
2. Sphincter muscles act like gates.

Question 6. (a) Draw diagram to show the nutrition in amoeba and label the part used for this purpose. Mention any other purpose served by this part other than nutrition.
(b) Name the glands associated with digestion of starch in human digestive tract and mention their role.
(c) How is required pH maintained in the stomach and small intestine. [CBSE 10TH BOARD: 2016]
Answer:
(a) The part used for taking in food is the pseudopodium (see the figure, stage a). Other than nutrition, the pseudopodia are used for movement (locomotion) of the amoeba.

(b) Salivary glands secrete saliva with salivary amylase, which changes starch into maltose in the mouth. The pancreas secretes pancreatic juice with amylase, which changes the remaining starch into maltose in the small intestine. The intestinal glands secrete enzymes that turn maltose into glucose.
(c) In the stomach the HCl of the gastric juice keeps the medium acidic (pH about 1.5 to 3), and its mucus protects the wall. In the small intestine the alkaline bile and pancreatic juice neutralise the acid that comes with the food and make the medium alkaline (pH about 8), which the pancreatic and intestinal enzymes need.
In simple words: Pseudopodia catch food and also help amoeba move; salivary, pancreatic and intestinal glands digest starch; acid in the stomach and alkali in the intestine set the pH.

Teacher's Note:
1. Give the second function of the pseudopodia, which is movement.
2. Remember: acid in the stomach, alkaline in the duodenum.

Question 7. Describe the structure and role of chloroplast along with a well labelled diagram ?
Answer:

Structure: the chloroplast is a green plastid with a double membrane (outer and inner membrane) with a fluid-filled space between them. Inside it are two parts:
1. Grana: stacks of flattened sacs called thylakoids (40–60 grana per chloroplast, 50 or more thylakoids per granum). Chlorophyll lies in the thylakoid membranes. The grana are joined to one another by stroma lamellae (Fret's channels).
2. Stroma: the colourless, protein-rich matrix in which the grana lie. It contains the enzymes of the dark reaction, ribosomes, a loop of DNA, starch grains and lipid globules.
Role: the chloroplast is the site of photosynthesis. The light reaction takes place in the grana (trapping of light, making ATP, NADPH₂ and oxygen), and the dark reaction takes place in the stroma (making glucose from CO₂).
In simple words: The chloroplast has grana for the light reaction and stroma for the dark reaction.

Teacher's Note:
1. Label at least: outer membrane, inner membrane, stroma, granum, thylakoid and lamella.
2. Chloroplasts are called the kitchens of the cell.

Question 8. Describe the mechanism of photosynthesis ?
Answer:
Photosynthesis is the making of glucose from CO₂ and water by the green cells of plants in the presence of sunlight and chlorophyll: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. It takes place in the chloroplast in two stages.
A. Light reaction (photochemical reaction, Hill's reaction): site, the grana; raw materials, light and water; products, ATP, NADPH₂ and O₂. It has three steps:
1. Photo-excitation of chlorophyll: chlorophyll absorbs photons and an electron is raised to a higher energy level and leaves the molecule.

2. Photolysis of water (in the presence of Mn²⁺ and Cl⁻ ions): 4H₂O → 4H⁺ + O₂ + 4e⁻ + 2H₂O. Oxygen is released, and H⁺ reduces NADP: 2NADP + 4H⁺ → 2NADPH₂.
3. Photophosphorylation: ATP is formed from ADP and inorganic phosphate (ADP + iP → ATP) in the quantasomes.
B. Dark reaction (Calvin–Benson cycle): site, the stroma; it needs CO₂, ATP, NADPH₂ and enzymes, and the product is glucose. The steps are: 1. carboxylation (CO₂ is taken up by RuBP in C₃ plants or PEP in C₄ plants with the help of RuBisCO or PEPCase), 2. synthesis of glucose from the fixed carbon, and 3. regeneration of RuBP.
In simple words: Light reaction in the grana makes ATP and NADPH₂; dark reaction in the stroma uses them to make glucose.

Teacher's Note:
1. This question comes again in the Board-level exercise; the answer is the same in outline.
2. A flow chart of the two stages is a good addition.

Question 9. Explain the process of 'Photosynthesis' in plants. List four factors which influence this process and describe how each of them, affects the rate of the photosynthesis.
Answer:
Process: green plants make glucose from CO₂ and water by using sunlight energy trapped by chlorophyll in the chloroplast; oxygen is released: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. In the light reaction (in the grana) light energy is changed into the chemical energy of ATP and NADPH₂, and water is split to release oxygen; in the dark reaction (in the stroma) CO₂ is turned into glucose by using this ATP and NADPH₂.
Factors that affect its rate:
1. Light: the rate is highest in red light and lowest in green light; it rises with intensity, but a very high intensity damages (denatures) chlorophyll and lowers the rate.
2. Temperature: the best range is 25 °C to 30 °C; outside this range the enzymes of the dark reaction work more slowly or are damaged.
3. Carbon dioxide: it is the first limiting factor, as the air has only 0.03–0.1% of it; more CO₂ increases the rate up to a limit.
4. Chlorophyll: the rate is directly proportional to the chlorophyll content; there is no photosynthesis in etiolated cells or in the white patches of variegated leaves. (Oxygen is another factor: a high concentration of O₂ lowers the rate.)
In simple words: Photosynthesis makes glucose from CO₂ and water in light; light, temperature, CO₂ and chlorophyll control its rate.

Teacher's Note:
1. Write the equation and two lines for each factor.
2. Name the limiting factor idea: the factor in shortest supply sets the rate.

Question 10. (i) Explain why the rate of photosynthesis in plants is low both at lower and higher temperatures ?
(ii) Is green light most or least useful in photosynthesis and why ?
(iii) Describe an activity to show that chlorophyll is necessary for photosynthesis in plants.
Answer:
(i) The dark reaction is controlled by enzymes. At low temperature the enzymes work very slowly, and at high temperature they are denatured (and the stomata may close), so the rate is low at both ends. It is highest between 25 °C and 30 °C.
(ii) Green light is the least useful, because the green parts of the plant reflect the green light instead of absorbing it. Chlorophyll absorbs mostly red and blue light.
(iii) Activity: take a potted plant with variegated leaves (such as croton), whose leaves are partly green and partly white (no chlorophyll).
1. Keep the plant in the dark for three days to destarch the leaves, and then keep it in bright sunlight for three to four days.
2. Pluck a leaf, boil it in water, and then boil it in alcohol to remove the chlorophyll. Wash it with hot water.
3. Pour iodine solution on it. The part that was green turns blue-black (starch present) but the part that was white does not (no starch).
Conclusion: photosynthesis to make starch does not take place without chlorophyll.
In simple words: Enzymes fail at low and high temperatures; green light is reflected; the variegated-leaf starch test shows that chlorophyll is needed.

Teacher's Note:
1. For the activity write the aim, the steps, the observation and the conclusion.
2. Always destarch the plant first.

Question 11. Draw a well labelled diagram of human alimentary canal. Mention the functions of liver in digestion.
Answer:

Functions of the liver in digestion:
1. The liver, the largest gland, makes bile, which is stored in the gall bladder and passed into the duodenum.
2. Bile makes the acidic food from the stomach alkaline, so that the pancreatic enzymes can act.
3. Bile salts break large fat globules into tiny droplets (emulsification), which helps lipase to digest the fat and helps its absorption.
4. The liver also stores the extra glucose as glycogen, after absorption.
In simple words: The liver makes bile, which makes the food alkaline and emulsifies fat.

Teacher's Note:
1. Draw the diagram with the liver, gall bladder and pancreas clearly marked.
2. Bile has no enzymes.

Teacher's Note:
1. Use the table form: gland, secretion and function.
2. The pancreas is both an exocrine and an endocrine gland.