Describe the mechanism of inhalation in man. Using photosynthesis theory explain the mechanics of opening of stomata.

a) The process of fertilization in flowering plants:

1. After pollination, a pollen grain lands on the stigma and germinates, forming a pollen tube.
2. The pollen tube grows down through the style towards the ovule, guided by chemical signals.
3. Two male gametes travel down the pollen tube.
4. Upon reaching the ovule, one male gamete fuses with the egg cell to form a zygote.
5. The other male gamete fuses with the central cell (polar nuclei) to form the endosperm, which provides nourishment to the embryo. This entire process is known as double fertilization.

b) Changes that take place in a flower after fertilization:

• The ovary develops into the fruit.
• The ovules inside the ovary develop into seeds.
• The zygote develops into the embryo within the seed.
• The central cell develops into the endosperm, which stores food for the embryo.
• Parts like petals, sepals, stamens, style, and stigma wither and fall off.

a) The mechanism of inhalation in man:

1. The diaphragm contracts and flattens, moving downwards.
2. The external intercostal muscles contract, pulling the rib cage upwards and outwards.
3. These actions increase the volume of the thoracic cavity.
4. The increase in volume leads to a decrease in pressure inside the lungs, making it lower than the atmospheric pressure.
5. Air then rushes into the lungs from the higher atmospheric pressure to the lower pressure in the lungs until the pressures equalize.

b) Using photosynthesis theory to explain the mechanics of opening of stomata:

1. During the day, guard cells contain chloroplasts and perform photosynthesis.
2. Photosynthesis produces glucose, which increases the solute concentration within the guard cells.
3. This increase in solute concentration lowers the water potential inside the guard cells.
4. Water then moves from adjacent epidermal cells into the guard cells by osmosis.
5. The influx of water makes the guard cells turgid. Due to their unevenly thickened walls, they bow outwards, causing the stoma to open.