IGCSE Biology Paper-4: Specimen Questions with Answers 244 - 245 of 279
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Passage
The diagram shows a section through a leaf.
Question 244 (6 of 6 Based on Passage)
Write in Short
Short Answer▾Most photosynthesis in plants happens in leaves.
(i) Name the two raw materials needed for photosynthesis.
Explanation
Photosynthesis is the process by which plants and other organisms, such as algae and some bacteria synthesize their own food in presence of light. So, they are called autotrophs. Green plants capture energy from sun and convert it into chemical energy (food) with the help of taken from atmosphere, water from soil and releases oxygen.
Photosynthesis is important due to two reasons:
- It is the primary source of all food on earth.
- It is also responsible for the release of oxygen into the atmosphere by green plants.
The simplest equation for photosynthesis in higher plants and algae is given below:
Question 245
Describe in Detail
Essay▾Explain the roles of chewing and of enzymes in the process of digestion.
Explanation
The physical process of chewing food in our mouth helps to break down larger particles of food into smaller particles. This helps to reduce stress on the oesophagus and helps the stomach metabolize and breakdown your food. Saliva also contains digestive enzymes, which are released when chewing and assist in digestion. As our mouth releases these enzymes, which then pass into the throat and stomach, further improve the digestive process.
| Gland | Enzyme | pH | Site of action | Substrate | Product | |||
| Carbohydrate | Fat | Protein | Nucleic acid | |||||
| Salivary glands (Saliva) | Ptyalin (Amylase) | 6.7 | Buccal cavity, Oesophagus & part of stomach | Starch. Glycogen | – | – | – | Limit dextrin՚s, Maltoe, Isomaltose |
| Gastric glands (Gastric juice) | (i) Prorennin ⇾ Rennin (Calf) (ii) Pepsinogen ⇾ Pepsin (iii) Gastric lipase (Infants) | 2.0 – 3.7 2.0 – 3.7 2.0 – 3.7 | Stomach Stomach Stomach | – – – | – – Milk Fat | Casein (a) Protein (b) Calcium Paracaseinate | – – – | Calcium Paracaseinate Peptones Fatty acid & glycerol |
| Liver (Bile) | No digestive enzymes | Makes food alkaline, emulsifies fat and helps in its absorption. | ||||||
| Pancreas (Pancreatic juice) | (i) Chymotrypsinogen ⇾ Chymotrypsin (ii) Trypsinogen Trypsin (iii) Procarboxy peptidases ⇾ Carboxypeptidases (iv) Pancreatic Lipase (v) Pancreatic amylase (vi) DNA-ase (vii) RNA ase | 7.5 – 8.5 7.5 – 8.5 7.5 – 8.5 7.5 – 8.5 7.5 – 8.5 7.5 – 8.5 7.5 – 8.5 | Small intestine Small intestine Small intestine Small intestine Small intestine Small intestine Small intestine | – – – – Starch, Glycogen, Dextrins – – | – – – Fat – – – | Casein (a) Protein (b) Calcium Paracaseinate Larger Peptides – – – – | – – – – – DNA RNA | Calcium Paracaseinate Peptones & Peptides Smaller peptides Fatty acids, Monoglycerides, Glycerol Limit dextrins maltose, Isomaltose, Deoxyribonucleo-tides Ribonucleotides |
| Small intestine (Succus entericus) | (i) Aminopeptidases (ii) Dipeptidases (iii) Nucleotidases (iv) Nucleosidases (v) Intestinal Lipase (vi) Isomaltase (vii) Maltase (viii) Lactase (ix) Sucrase (Invertase) | 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 7.0 – 7.5 | Small intestine Small intestine Small intestine Small intestine Small intestine Small intestine Small intestine Small intestine Small intestine | – – – – – Limit dextrins, Isomaltose Maltose Lactose Sucrose | – – – – Fat – – – – | Peptides Dipeptides – – – – – – – | – – Nucleotides Nucleotides – – – – – | Amino acids and smaller peptides Amino acids Nucleosides, Phosphates Nitrogen bases, Pentose sugars Fatty acids, glycerol, Monoglycerides Glucose Glucose Glucose, Galactose Glucose, Furctose |