Answers to Hands on Pg 72

Section B

3a)

(a) Waxed cuticle

• Reduces loss of water through transpiration.

Upper epidermis

• Transparent thin layer of cells which allows sunlight to reach the mesophyll layer.

Palisade mesophyll cells

• Elongated cells perpendicular to the surface.
• They are densely packed and rich in chloroplasts to allow maximum absorption of sunlight.

Spongy mesophyll cells

• Irregular in shape, loosely arranged and contain chloroplasts.
• Large air spaces between cells allow gaseous exchange between the cells and the surrounding air.

Stoma

• Regulate the passage of oxygen, carbon dioxide and water vapour across the surface of the leaf.

Guard cells

• Contain chloroplasts.
• Control the closing and opening of the stoma.

Vascular bundle

• Xylem is used for the transport of water and mineral salt.
• Phloem is used for the transport of soluble food materials from the leaf to other parts of the plant.

b) Photosynthesis involves light reaction and dark reaction.

Light reaction

• Chlorophyll absorbs light energy.
• Light energy causes the chloropyhll to emit electrons.
• Light energy also splits the water molecules, into H⁺ ions and OH^- ions.
• OH^- ions combine to produce water and oxygen.

24OH^- - 24e --->12H₂O + 6O₂

• H⁺ ions accepts an electron to form a hydrogen atom which is used in the dark reaction.

Dark reaction

• Hydrogen atom reduces CO₂ to form CH₂O
• 6 units of CH₂O combine to form 1 unit of glucose, C₆H₁₂O_6.

4. a)

Bread is a carbohydrate which consists of starch.

Starch is digested into glucose.

Half-boiled egg contains proteins which are digested into amino acids.

Glucose and amino acids are absorbed into the villi of the ileum.

Glucose and amino acids enter the blood capillaries of the villi and are transported by the

hepatic portal vein to the liver.

From liver, glucose and amino acids are transported to body cells.

Glucose is oxidised to release energy.

Excess glucose is converted to glycogen and stored in the liver.

Amino acids are used for synthesis of new protoplasm in the body cells.

Amino acids are used for synthesis of hormones, enzymes and plasma proteins.

Excess amino acids are converted to urea and excreted through the kidneys.

Margarine contains lipids.

Lipids are digested into fatty acids and glycerol.

Fatty acids and glycerol are absorbed into lacteals in the villi.

Glycerol and fatty acids are transported in the lymphatic system before entering the blood circulatory system.

Glycerol and fatty acids recombine to form lipids.

Lipids are used as components of the plasma membranes.

Excess lipids are stored as fat in the adipose tissue.

b)

Rice is starch.

Starch is a complex molecule which consists of polysaccharide chains.

The size of starch molecule is too big to move across the intestinal wall.

Starch needs to be broken down into smaller and simpler units.

These smaller units (monosaccharides) are able to move across the intestinal wall into the blood stream.

Salt, which is also known as sodium chloride, dissolves in water to form sodium ions and chloride ions.

Sodium ions and chloride ions are small enough to pass through the intestinal wall to be absorbed into the blood stream.

Therefore, salt does not need to be digested.