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.

Vascular Bundle

Question 244 (6 of 6 Based on Passage)

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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

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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.

Explain the Roles of Chewing and of Enzymes in the Process of Digestion
GlandEnzymepHSite of actionSubstrateProduct
CarbohydrateFatProteinNucleic acid
Salivary glands (Saliva)Ptyalin (Amylase)6.7Buccal cavity, Oesophagus & part of stomachStarch.

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 enzymesMakes 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

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