Explain the number of red blood cells per altitude, how skin prevents micro-organisms, and name the cells that destroy micro-organisms in skin. Also, determine the genotype of parents in a 3:1 green t

4. (continued)

iv) Account for the number of red blood cells per altitude.

• As the altitude increases, the atmospheric pressure and partial pressure of oxygen decrease. To compensate for the lower oxygen availability at higher altitudes, the human body produces more red blood cells to increase the oxygen-carrying capacity of the blood, ensuring sufficient oxygen supply to tissues.

v) How does the skin prevent entry of micro-organisms into the body?

• The skin acts as a physical barrier due to its tough, keratinized outer layer (epidermis). It also produces sebum and sweat, which create an acidic environment and contain antimicrobial substances that inhibit the growth of microorganisms.

vi) Name the type of cells that destroy micro-organisms in the human skin.

• Phagocytes (e.g., macrophages, neutrophils) and Langerhans cells (a type of dendritic cell) are present in the skin and destroy or help to eliminate microorganisms.

5. When the offspring of pea plant having green pods and pea plant having yellow pods were crossed, they produced green pods and yellow pods in the ratio 3:1. Using letter G to represent the gene for green pods (a) State genotype of:

a) i) Parents

• Based on the 3:1 ratio in the offspring, the parents of this cross must have been heterozygous. These heterozygous parents (Gg) are the F1 generation from an initial cross of pure-line green (GG) and pure-line yellow (gg) plants.
  • Parents: GG and gg

a) ii) F1 generation

• The F1 generation results from crossing the pure-line parents (GG $\times$ gg).
  • F1 generation: Gg

b) Work out the cross between plants in the F1 generation.

• Cross: Gg $\times$ Gg
• Gametes: G, g from each parent
• Punnett Square: $$\begin{array}{|c|c|c|} \hline & \text{G} & \text{g} \\ \hline \text{G} & \text{GG} & \text{Gg} \\ \hline \text{g} & \text{Gg} & \text{gg} \\ \hline \end{array}$$
• Genotypic ratio: 1 GG : 2 Gg : 1 gg
• Phenotypic ratio: 3 Green pods : 1 Yellow pod

c) Account for the colour of the pods in plants of the F1 generation.

• The F1 generation plants all have green pods because the gene for green pods (G) is dominant over the gene for yellow pods (g). Therefore, even in the heterozygous state (Gg), the dominant green phenotype is expressed.

SET 4 SECTION A (40 MARKS)
1. The diagrams below show beaks of various birds. Study the diagrams and answer the questions that follow.

a) Name the:

i) The type of evolution represented by the diagrams

• The type of evolution represented is adaptive radiation (or divergent evolution).