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

Short Answer Type

Question 1. What are various steps of holozoic mode of nutrition ?
Answer:
Holozoic nutrition has five steps:
1. Ingestion: taking in of food.
2. Digestion: breakdown of large, complex food molecules into smaller, soluble ones with the help of enzymes.
3. Absorption: the digested food passes into the blood or body fluid (or into the cytoplasm in a single cell).
4. Assimilation: the absorbed food is taken up by the body cells and used for energy, growth and repair.
5. Egestion: removal of the undigested food from the body.
In simple words: Holozoic nutrition goes through ingestion, digestion, absorption, assimilation and egestion.

Teacher's Note:
1. Learn the steps as I-D-A-A-E.
2. These steps are the same in amoeba and in humans.

Teacher's Note:
1. Give one example on each side.
2. The name sanguivore comes from the Latin word for blood.

Question 3. If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring ? Justify your answer
Answer:
No, it does not mean that photosynthesis has stopped.
Respiration goes on all the time and releases CO₂. Photosynthesis uses CO₂ and gives O₂ only in the presence of light.
When the light is weak (for example, early morning or evening, or on a very cloudy day) the rate of respiration is higher than the rate of photosynthesis. The CO₂ produced in respiration is more than that used in photosynthesis, so the net result is that CO₂ is released and O₂ is taken in. Photosynthesis is still going on, but at a slower rate.
In simple words: Photosynthesis may still be occurring but respiration is faster in weak light, so the net gas exchange is the reverse.

Teacher's Note:
1. Mention the compensation point.
2. Net exchange depends on which of the two processes is faster.

Teacher's Note:
1. Always give examples in a table of differences.
2. Four points make a good 2-mark table.

Question 5. Write one feature which is common to each of the following pairs of terms: [CBSE 10TH BOARD: 2013]
(i) Glycogen and starch
(ii) Chlorophyll and haemoglobin
Answer:
(i) Glycogen and starch are both polysaccharides made of glucose units; both are stored forms of carbohydrate (starch in plants, glycogen in animals).
(ii) Chlorophyll and haemoglobin are both coloured pigments with a metal atom at the centre of a ring-shaped (porphyrin) structure: magnesium in chlorophyll and iron in haemoglobin.
In simple words: Both polysaccharides store glucose; both pigments have a metal atom at the centre of a ring.

Teacher's Note:
1. Any one correct common feature for each pair is acceptable.
2. Colour is the simplest answer for the pigment pair.

Question 6. What are villi ? What is their function ? [CBSE 10TH BOARD : 2014]
Answer:
Villi are the numerous tiny, finger-like projections present on the inner wall of the small intestine.
Function: they greatly increase the surface area for the absorption of digested food. Each villus has a network of blood capillaries (to take up glucose and amino acids) and a lacteal (to take up fats), and its wall is only one cell thick.
In simple words: Villi are finger-like folds of the small intestine that increase its surface for absorption.

Teacher's Note:
1. Say 'increase the surface area' to earn the mark.
2. Microvilli on the villus cells increase the area even more.

Question 7. Explain why : [CBSE 10TH BOARD : 2015]
(a) Digestion of food is a decomposition reaction.
(b) All decomposition reactions are endothermic reactions.
(c) A popping sound is produced when a burning candle is brought near mouth of a test tube used in electrolysis of water.
Answer:
(a) In digestion, large complex molecules of food (starch, proteins, fats) are broken down into simpler, smaller molecules (glucose, amino acids, fatty acids and glycerol) by the action of enzymes. One substance breaking into simpler substances is a decomposition reaction.
(b) To break a compound into simpler substances, energy (heat, light or electricity) has to be supplied to break the chemical bonds. Energy is absorbed, so such reactions are endothermic. (This is true of most decomposition reactions, but not all: a few, such as the decomposition of hydrogen peroxide, give out heat.)
(c) Electrolysis of water gives hydrogen at the negative electrode and oxygen at the positive one. Hydrogen gas burns with a popping sound when a burning candle is brought near it.
In simple words: Digestion splits big molecules into small ones; breaking bonds needs energy; hydrogen burns with a pop.

Teacher's Note:
1. Part (b) is a general statement; the answer says that most, but not every, decomposition is endothermic.
2. In electrolysis the hydrogen is collected in twice the volume of the oxygen.

Teacher's Note:
1. Draw the table: it shows the classification at a glance.
2. Lichens (alga and fungus) are a classic symbiotic example.

Question 9. What is the importance of the following process occurring during photosynthesis in plants ?
(i) Emission of electrons from chlorophyll
(ii) Photolysis of water
Answer:
(i) Emission of electrons: when chlorophyll absorbs a photon, it becomes excited and loses an electron. This electron starts a flow of electrons that supplies the energy for making ATP (photophosphorylation) and for reducing NADP.
(ii) Photolysis of water: water is split as 4H₂O → 4H⁺ + O₂ + 4e⁻ + 2H₂O. The electrons given by water fill the gap left in chlorophyll, the H⁺ ions are used to reduce NADP to NADPH₂ (needed in the dark reaction), and oxygen is released into the air.
In simple words: The lost electron drives ATP and NADPH formation; water splitting replaces the electron, gives hydrogen and releases oxygen.

Teacher's Note:
1. Link (i) and (ii): water is the source that refills the chlorophyll.
2. Oxygen is a by-product of photolysis.

Question 10. Explain how water and temperature influence the rate of photosynthesis ?
Answer:
Water: water is a raw material, and it keeps the cells turgid and the stomata open. When there is a shortage of water, the guard cells lose water and the stomata close, so less CO₂ enters the leaf and the rate of photosynthesis falls. Severe loss of water makes the leaves wilt and stops the process.
Temperature: the dark reaction is controlled by enzymes. The rate rises with temperature and is highest at the optimum of 25 °C to 30 °C. At lower temperatures the enzymes work slowly; at higher temperatures they are damaged (denatured), and the rate falls.
In simple words: Too little water closes stomata; temperature must be near 25–30 °C for the enzymes to work well.

Teacher's Note:
1. A graph shape with a peak is a good way to remember the effect of temperature.
2. Both water and temperature act through the stomata and enzymes.

Question 11. Explain the following aspects of photosynthesis in plants:
(i) The role of chlorophyll
(ii) Calvin – Benson Cycle / Dark reaction
Answer:
(i) Role of chlorophyll: chlorophyll, the green pigment in the grana of the chloroplast, traps the energy of sunlight (mostly blue and red light) as photons. Its excited electrons start the light reaction, which makes ATP and NADPH₂. Without chlorophyll, as in the white parts of a variegated leaf, no starch is made.
(ii) Calvin–Benson cycle: this is the dark (thermochemical) reaction discovered by Melvin Calvin and Benson. It takes place in the stroma, and needs CO₂, ATP, NADPH₂ and enzymes. It has three steps: 1. Carboxylation (CO₂ is joined to RuBP in C₃ plants, with the help of the enzyme RuBisCO), 2. synthesis of glucose from the fixed CO₂, and 3. regeneration of RuBP. The product is glucose.
In simple words: Chlorophyll traps light; the Calvin cycle in the stroma uses ATP and NADPH₂ to turn CO₂ into glucose.

Teacher's Note:
1. Write the three steps of the dark reaction by name.
2. The dark reaction does not need light directly, but it needs the products of the light reaction.

Question 12. Describe the digestion process of carbohydrate in humans.
Answer:
1. Mouth: salivary amylase (ptyalin) in the saliva converts a part of the starch into maltose. Food stays only a short time in the mouth, so this digestion is incomplete.
2. Stomach: no carbohydrate digestion occurs here.
3. Small intestine: in the duodenum the pancreatic amylase changes the remaining starch into maltose. In the ileum the enzymes of the intestinal juice change maltose into glucose (sucrose and lactose are also changed into simple sugars).
4. The glucose is absorbed into the blood through the villi, and the extra glucose is stored in the liver as glycogen.
In simple words: Starch turns to maltose in the mouth and duodenum, and the intestinal juice turns the maltose into glucose.

Teacher's Note:
1. Write the word equation: starch to maltose to glucose.
2. Note that digestion of starch begins in the mouth and ends in the small intestine.

Question 13. What is meant by assimilation of food ? Name the digestive glands of human.
Answer:
Assimilation is the process in which the digested and absorbed food is carried by the blood to all the cells and is taken up by them, to become a part of the cell. The cells use it for energy, growth and repair. The unused glucose is stored in the liver as glycogen.
Digestive glands: salivary glands, gastric glands, liver, pancreas and intestinal glands.
In simple words: Assimilation is the use of absorbed food by the cells.

Teacher's Note:
1. Absorption puts food in the blood; assimilation puts it in the cells.
2. The five glands are in the same order as the food passes.

Question 14. When a person puts food in his mouth, then teeth cut it into small pieces, chew and grind it. The glands A in the mouth secrete a substance B which is mixed with the food by tongue. The substance B contains an enzyme C which starts the digestion of food in the mouth. The slightly digested food from the mouth goes down a tube D. The special type of movements E in the walls of tube D push the food into stomach for further digestion. The stomach wall secretes gastric juice containing three substance F, G and H. One of the functions of F is to kill bacteria which may enter the stomach with food. The substance G protects the inside layer of stomach from the damaging effect of substance F whereas substance H is an enzyme for digestion. The partially digested food then enters into small intestine for further digestion.
(A) What is (i) gland A (ii) substance B, and (iii) enzyme C ?
(B) Name the tube D
(C) What is the movement E known as ?
(D) What are (i) F (ii) G, and (iii) H ?
Answer:
(A) (i) Gland A: salivary glands; (ii) substance B: saliva; (iii) enzyme C: salivary amylase (ptyalin), which digests starch.
(B) Tube D: the oesophagus (food pipe).
(C) Movement E: peristalsis (waves of contraction and relaxation of the muscular wall).
(D) (i) F: hydrochloric acid; (ii) G: mucus; (iii) H: pepsin.
In simple words: The passage describes saliva, the oesophagus, peristalsis and the three parts of gastric juice.

Teacher's Note:
1. Solve it by following the food: mouth, oesophagus, stomach.
2. The three contents of gastric juice are HCl, pepsin and mucus.

Question 15. A unicellular animal P having no fixed shape ingests a food particle by forming temporary finger-like projections Q. The food particle is engulfed with a little surrounding water to form a temporary stomach R inside it. The chemicals S from surrounding cytoplasm enter into R and break down food into small and soluble molecules by chemical reactions. The digested food is absorbed directly into cytoplasm by the process T. The undigested food is thrown out of the body by the rupture of a cell organelle U in a process called V.
(A) Name the unicellular animal ?
(B) What are (i) Q, and (ii) R ?
(C) Name (i) chemical S, and (ii) process T.
(D) Name (i) organelle U, and (ii) process V.
Answer:
(A) The unicellular animal P is Amoeba.
(B) (i) Q: pseudopodia; (ii) R: food vacuole.
(C) (i) S: digestive enzymes; (ii) T: diffusion.
(D) (i) U: the food vacuole (now holding only the undigested residue); (ii) V: egestion (also called exocytosis).
In simple words: The passage describes nutrition in amoeba: pseudopodia, food vacuole, enzymes, diffusion and egestion.

Teacher's Note:
1. The temporary stomach of amoeba is the food vacuole.
2. Amoeba has no fixed mouth or anus; waste leaves at any point on the surface.